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Note. This monograph about IPRS Băneasa is the extended standalone online version of the
Chapter 3 about IPRS Băneasa which will be included in the book „The Romanian School of
Micro- and Nanoelectronics”, intended to be published by Editura Academiei
IPRS Băneasa
Silicon Technology: Industrial Research and Development
Authors, in alphabetical order:
Viorel Banu, Radu Coteț, Petru Dan, Tudor Dunca, Virgil Gheorghiu, Eugen Popa,
Adrian Veron, Andreas Wild
Memento. The authors want to pay tribute to all
their colleagues who passed away. This
presentation is also meant as a memorial to
their contribution
Contents
List of Abbreviations for Romanian Institutions and Forums .................................................... 4
1. Introduction ............................................................................................................................ 6
1.1 The Decision ..................................................................................................................... 6
1.2 Setup and Milestones ........................................................................................................ 7
2. From Production to Science ................................................................................................... 9
3. Section 2300: The Power Semiconductor Devices Factory ................................................. 12
3.1. Introduction ................................................................................................................... 12
3.2. Historical Perspective .................................................................................................... 12
3.3. Challenges in Power Semiconductors ........................................................................... 14
3.3.1 The Mesa Concept ................................................................................................... 15
3.3.2. The “Core Compromise” ........................................................................................ 16
3.3.3. The Guard Rings ..................................................................................................... 16
3.4. Technologies and Products ............................................................................................ 17
3.4.1. Low and medium power diodes, thyristors and triacs ............................................ 17
3.4.2. High Power Diodes and Thyristors ......................................................................... 18
3.4.3. Specialty Technologies ........................................................................................... 18
3.5. People and their areas of responsibility ......................................................................... 19
3.5.1. Management ............................................................................................................ 19
3.5.2. Product Families ..................................................................................................... 19
3.5.3. Wafer and Chips Processing ................................................................................... 20
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3.5.4. Assembly and Chemical Protection ........................................................................ 21
3.5.5. Rectifier Bridges and Modules with Diodes and Thyristors ................................... 22
3.5.6. Test, Quality and Reliability Assessment ............................................................... 22
3.6. Partners ...................................................................................................................... 23
3.7. Scientific Contributions ................................................................................................. 24
3.8. Epilogue ......................................................................................................................... 24
3.9. Acknowledgements and Notes About the Authors ........................................................ 25
4. Section 2400 - The Integrated Circuits Factory ................................................................... 26
4.1. Introduction: Integrated Circuits in the 1960s ............................................................... 26
4.2. Starting Integrated Circuits in Romania ........................................................................ 28
4.2.1. Acquiring a License ................................................................................................ 28
4.2.2. Building the Facility ............................................................................................... 29
4.2.3. People ...................................................................................................................... 30
4.2.4. Functioning in the IPRS Framework ...................................................................... 31
4.2.5. Partners ................................................................................................................... 32
4.3. Advancing Silicon Processing Technology (Front End Manufacturing) ...................... 32
4.3.1. Wafer size ............................................................................................................... 33
4.3.2. Mask Making .......................................................................................................... 33
4.3.3. Photolithography ..................................................................................................... 33
4.3.4. Diffusion and Ion Implantation ............................................................................... 34
4.3.5. Metallization ........................................................................................................... 35
4.3.6. Passivation .............................................................................................................. 35
4.3.7. Wafer Probe ............................................................................................................ 35
4.4. Assembly and Test Technology (Back End Manufacturing) ........................................ 35
4.4.1. Assembly ................................................................................................................. 36
4.4.2. Electric Test ............................................................................................................ 37
4.4.3 Reliability and Quality Assurance ........................................................................... 37
4.5. Product Portfolio Expansion .......................................................................................... 37
4.5.1. Digital Integrated Circuits ....................................................................................... 38
4.5.2. General Purpose and Industrial Linear ICs ............................................................. 41
4.5.3. Radio and TV ICs ................................................................................................... 43
4.5.4. Products summary ................................................................................................... 45
4.6. Conclusions and Evolution after 1989 ........................................................................... 45
4.7. Acknowledgements and Notes About the Authors ........................................................ 45
5. Section 2500: The Silicon Transistors and Small-Signal Diodes Factory ........................... 47
5.1. Introduction ................................................................................................................... 47
5.1.1. A brief history ......................................................................................................... 47
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5.1.2. People ...................................................................................................................... 49
5.2. Technology .................................................................................................................... 51
5.2.1 Wafers ...................................................................................................................... 51
5.2.2 Epitaxy ..................................................................................................................... 51
5.2.3 Thermal oxidation .................................................................................................... 51
5.2.4 Diffusion .................................................................................................................. 52
5.2.5 Ion implantation ....................................................................................................... 53
5.2.6 Photolithography and etching .................................................................................. 53
2.5.7 Chemical vapor deposition....................................................................................... 54
5.2.8 Passivation ............................................................................................................... 55
5.2.9. Gettering ................................................................................................................. 55
5.2.10. Wafer thinning and metallization .......................................................................... 56
5.2.11. Process characterization ........................................................................................ 57
5.2.12. Wafer probe and dicing ......................................................................................... 58
5.2.13. Packaging and final testing ................................................................................... 59
5.3. Product Development .................................................................................................... 61
5.3.1 Diodes ...................................................................................................................... 61
5.3.2 Small and Medium Power Transistors ..................................................................... 63
5.3.3 Power and high voltage transistors .......................................................................... 65
5.3.4 Optoelectronic Devices ............................................................................................ 67
5.3.6 Integrated Circuits .................................................................................................... 68
5.4. Acknowledgments and Notes About the Authors ......................................................... 69
6. Confessions of a Former IPRS Băneasa General Manager .................................................. 70
7. The Twilight of IPRS Băneasa ............................................................................................. 71
7.1. December 1989 .............................................................................................................. 71
7.2. Băneasa SA .................................................................................................................... 71
7.3. The Brain Drain ............................................................................................................. 73
7.4. The Aborted Privatization ............................................................................................. 73
7.5. A Survivor ..................................................................................................................... 74
8. What Happened Since .......................................................................................................... 74
9. References: Published Works Authored or Co-authored by People from IPRS Băneasa .... 77
Figures ...................................................................................................................................... 86
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List of Abbreviations for Romanian Institutions and Forums
CAS
Conferința anuală de semiconductoare, organizată de ICCE
Annual Semiconductor Conference, organized by ICCE
CCPCE
Centrul de cercetareși proiectare pentru componente electronice, ulterior ICCE
Centre for Research and Design of Electronic Components, later renamed ICCE
DCE
(Catedra de) dispozitive și circuite electronice din Facultatea de electronică și telecomunicații
din IPB, devenită mai târziu Catedra de tehnologie electronică și microelectronică
(Chair for) Electronic Devices and Circuits, in the Faculty of Electronics and
Telecommunications of IPB, which later became Chair of Electronics Technology and
Microelectronics
DCAE
(Catedra de) dispozitive, circuite și arhitecturi electronice din Facultatea de electronică și
telecomunicații și tehnologia informației, din UPB
(Chair for) Electronic Devices, Circuits and Architectures, in the Faculty of Electronics,
Telecommunications and Information Technology of UPB
ICCE
Institutul de cercetări pentru componente electronice, București, anterior CCPCE
Research Institute for Electronic Components, Bucharest, formerly named CCPCE
ICPE
Institutul de cercctare și proiectare pentru electrotehnică, București
Research and Design Institute for Electrotechnics of Bucharest
ICPMS
Institutul de cercetare și producție pentru materiale semiconductoare, București
Institute for Research and Production of Semiconductor Materials, Bucharest
ICRET
Întreprinderea de construcții și reparații pentru echipamente de telecomunicații, București
Enterprise for Construction and Repairs of Telecommunications Equipment of Bucharest
IFA
Institutul de fizică atomică București
Institute of Atomic Physics of Bucharest
IFIN
Institutul pentru fizică și inginerie nucleară, București
Institute for Nuclear Physics and Engineering of Bucharest
IFTAR
Institutul pentru fizica și tehnologia aparatelor cu radiații, București
Institute for Physics and Technology of Radiation Appliances of Bucharest
IMT
Institutul național de microtehnologie, București
National R&D Institute for Microtechnology of Bucharest
IPB
Institutul politehnic București, ulterior UPB
Polytechnic Institute of Bucharest, later UPB
IPEE
Întreprinderea de produse electronice Electroargeș, Curtea de Argeș
Enterprise for Passive Electronic Components of Curtea de Argeș
IPRS Băneasa
Întreprinderea de piese radio și semiconductoare Băneasa, București
Enterprise for Radio Components and Semiconductors Băneasa, Bucharest
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OSIM
Oficiul de stat pentru invenții și mărci
State Office for Inventions and Trademarks of Romania
UPB
Universitatea POLITEHNICA București, anterior IPB
University POLITEHNICA of Bucharest, formerly named UPB
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IPRS Băneasa
Silicon Technology: Industrial Research and Development
1. Introduction (Andreas Wild, Petru Dan)
The micro- and nanoelectronics emerged and progressed to a large extent through industrial
research. Essential discoveries and inventions happened in industrial laboratories: this is the
case for the transistors (Bell Telephone Laboratories), the thyristor (RCA), the integrated circuit
(Fairchild Semiconductor, Texas Instruments), the microprocessor (Intel), the dynamic random
access memory (IBM) etc. Moore’s Law was formulated by an industrial manager (Intel), and
the scaling theory that opened the way towards the nanoelectronics era was developed in an
industrial company (IBM). Many of these ideas have been considered scientific contributions
recognized with the Nobel Prize. Naturally, Romanian industrial research, in particular the
activity within the company IPRS Băneasa over about 45 years, was an essential element of
progress.
1.1 The Decision
Up to the end of 1989, the communist State in Romania had a monopoly on entrepreneurship:
companies were started only by decisions of the Council of Ministers; the only source for
investments was the State budget; only State Committees could decide upon the manufacturing
volume and the price for every single product; and roadmaps had to be derived from the five-
year plans issued by the Communist Party. The overall objective of the centralized planned
economy of Romania was to make the country self-sufficient by the autarchic development of
the industries.1 In a closed non-competitive market it was not the profitable growth that
mattered, but growth alone, the industry was striving to make quality products available from
domestic suppliers, and sometimes also... taking pride in achieving world class technical
performances. Hampered by a non-convertible currency under tight governmental control,
financing imports was always an uphill battle and import avoidance was an overarching priority.
Communist Romania invested in an electronic industry that by 1989 had 33 units, both R&D
institutes and industrial companies, supported by five University centres and vocational
education. Each company was assigned a market segment, without overlapping: there was no
need for competition in a planned economy.2 Some prominent personalities of those times
recognized the need for a domestic supply of electronic components and actively contributed
to establishing this capability: first and foremost Acad. Prof. Mihai Drăgănescu, the founder
of the Romanian school of microelectronics, Prof. Stere Roman active both in the University
and in the industry, as well as the open minded communist minister Gaston Marin.
The Enterprise for Radio Components and Semiconductors of Bucharest, known as IPRS
Băneasa, was established by the Decision of the Council of Ministers (HCM) Nr. 438 from 12
Mai 1962 intended to create a domestic supply of components for the Romanian electronic
industry, so it could avoid imports. IPRS Băneasa became the main manufacturer of electronic
components in Romania, a major supplier for all industries: consumer electronics, computers,
1 Lucian Boia – „România țara de frontieră a Europei” („Romania the Frontier Country of Europe”), Editura
Humanitas, ediția a 6-a (2016)
2 Andreas Wild – „Rise and Fall of the Romanian State-owned Micro/nanoelectronics”, The 45th ICOHTEC
Symposium, Saint-Étienne, France, 17 – 21 July 2018
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automation, electrotechnics, electric machines and drives, communications, automotive,
constructions, chemical industry, metallurgy, oil drilling, railway and naval transportation,
agriculture, health etc. This overextended spectrum resulted in an ineffective spreading of
resources, diluting the economic efficiency. The need for imported materials specific for
semiconductor technologies permanently forced the specialists to lower consumption through
novel design ideas, technological innovations, and yield improvements, while using scarce
resources to compete, in a sort of remote race, with performances achieved by the best world-
wide producers. IPRS successfully exported up to 25% of its production; this justified in front
of the State committees its permanent requests for convertible currency.
1.2 Setup and Milestones
In June 1962 began the getting started phase: the enterprise ELECTRONICA seeded the new
company by transferring some of its production lines, enabling IPRS Băneasa to start with two
departments: Section 2200 (Semiconductor Germanium Devices – diodes and transistors,
produced under a license from the French company THOMSON-CSF) and Section 2700
(Passive Components – capacitors, resistors, printed circuit boards). IPRS Băneasa added
technical support functions: Chief Mechanical Workshop, Technical Office, Investment
Department, and Quality Control Department. R&D activities started in 1965. Two years later,
Section 2100 started building in-house tools and equipment items, and in 1969 an internal
Tooling Department was created, and a Psychology Laboratory was added.
A growth phase followed. In the next five years development was explosive. A “Centre for
Research and Design of Electronic Components” (Romanian abbreviation: CCPCE) was
established to perform in-house R&D (1969). Three new sections have been started: Section
2300 on a license from SILEC SEMICONDUCTEURS, France, for silicon diodes and
thyristors (1969); Section 2400 on a license from THOMSON-CSF, France, for bipolar
integrated circuits (1970); and Section 2500 on a license from ITT-INTERMETAL, Germany,
for silicon diodes and transistors (1972). The activities have been focussed on silicon
technology, Section 2700 has been spun off as a new entity, the enterprise specialized in passive
electronic components IPEE Curtea de Argeș manufacturing resistors, capacitors, and
thermistors; later, the printed circuit boards (PCB) production has been moved to another
company, while the germanium products have been discontinued.
In 1975, CCPCE was separated from IPRS Băneasa as an independent “Research Institute for
Electronic Components” (Romanian abbreviation: ICCE), but IPRS Băneasa continued
performing R&D, generating a continuous, sustained flux of innovation, thanks to a surprisingly
modern concept introduced in 1972: „The Integrated Section for Design, Research,
Development, Investments and Production”, a structure anticipating the modern lab-fabs.3,4
IPRS Băneasa was much more vertically integrated that it is customary today. It produced fluids
(hydrogen, oxygen, nitrogen); pumped water from deep wells and deionized it; pulled and
purified first germanium ingots, then silicon 38 mm ingots, then sliced and polished raw wafers
out of them; and it built in-house tools and machinery.
3 Anton Vătășescu – „IPRS Băneasa – 25 de ani de activitate” („IPRS Băneasa – 25 Years of Activity”),
Electrotehnica, Electronica și Automatica EEA, vol. 31 (1987).
4 Doina Didiv – „A Life Devoted to the Electronic Components Branded IPRS Băneasa”, interview published in „Școala românească de micro- și nanoelectronică” („The Romanian School of Micro- and Nanoelectronics”),
Editura Academei Române, București, 2018, p. 59
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The talent supply has been strengthened after two turning points. First, a specialised section for
“Electronic Components and Devices” was created at the Polytechnic Institute Bucharest
(Romanian abbreviation IPB, as will be referred to from now on), later renamed University
POLITEHNICA of Bucharest (abbreviated UPB). As of 1969 the section curricula were
changed from nuclear engineering to microelectronics. Second, in 1974 a Government decision
forbade graduates to join Universities or R&D institutions. For several years, this put IPRS
Băneasa, a company offering high-tech jobs, in the privileged position to be able to recruit the
best graduates, with appropriate specialized education, and keep them for at least three years,
becoming a top-notch community of professionals.
The context of the planned economy controlled by State Committees and Ministries made
unnecessary a Go-To-Market strategy at the company level. IPRS Băneasa used almost
exclusively the so called “Zero-level Channel” approach, in which the producer delivers
directly to the customer (note that in the planned economy, with non-overlapping specialisation
of the companies, it was not uncomment that there was only one customer for a family of
components). On the positive side, the technologists were directly exposed to customer
demands and could rely on first-hand requirements when engaging in R&D programmes.
Although on a closed market, IPRS Băneasa strived to make its products and capabilities widely
known and increase demand. It printed several Catalogues between 1976 and 1989; published
the technical bulletin “BETA” that had 19 issues between 1979 and 1989 containing more than
110 technical papers and application notes; it even helped the “Alexandru Sahia” Studios
produce two documentaries intended for the public at large entitled “The Transistor” and “The
Integrated Circuit”.5
IPRS Băneasa could not engage in CMOS technology that was reserved for a different factory,
MICROELECTRONICA, established in the 1980s. The structure comprising three fairly
autonomous integrated sections (2300, 2400, and 2500), each one responsible for a product line,
relying on corporate support functions - was operational until 1989, when the world entered a
new era. After 1989 started the last phase of IPRS Băneasa: the twilight.
The general managers of IPRS Băneasa in the three main phases of its existence have been:
- Phase 1: Getting started (1962-1968)
Mihai Alexe (for a couple of months in the beginning)
Mihai Oncescu
Grigore Danciu
Ion Chicoș
Lazăr Șandra
Nicolae Cocoș (for about one year)
- Phase 2: Growth and Maturity (1969-1989)
Lazăr Șandra, an engineer coming from the defence industry: a severe, goal oriented but fair general manager. Deputy technical manager: engineer Anton Vătășescu, till 08
Dec. 1979 (Fig. 1).
Anton Vătășescu, (from Dec. 1979 till April 1989), an open minded, highly cultivated, „Western-style” character, a bright professional, excellent manager and great leader.
5 Script by Prof. M. Bodea (IPB) and Andreas Wild (S2400), directed by Alexandru Sîrbu (Sahia Studios)
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Deputy technical manager: physicist Doina Didiv (former manager of Section 2300).
Deputy commercial manager: engineer Mihai Petrescu (Fig. 2). Anton Vătășescu was
demoted to Section manager because the communist party leaders did not accept
anymore his too liberal behaviour.
Doina Didiv (between 1989 and 1992), a very empathic and supportive leader, always confident that entrusting challenging responsibilities to professionals will be paid off by
their spectacular results. Deputy technical manager: engineer Gheorghe Florea
(formerly acting as manager of Section 2300). Doina Didiv retired in 1992.
- Phase 3: Twilight
Gheorghe Florea (between 1992 and 1999) having three successive technical deputies: Radu Râpeanu, Marian Niculae and Adrian Oanea
Vlad Ciulei and Eugen Popa (co-managers between February 1999 and November 1999)
Gheorghe Florea (November 1999 – March 2002)
Eugen Popa (since 2002 till 2008)
Mihai Stan (for a few months in 2004)
Eugen Popa (till 2008)
Gheorghe Lifu, with Eugen Popa as technical deputy.
2. From Production to Science (Andreas Wild, Petru Dan)
IPRS Băneasa demonstrated over the years of its existence a breadth and depth of technical
achievement unparalleled in the Romanian industry.
IPRS Băneasa collaborated closely with the specialty Chairs in the Faculty of Electronics,
Telecommunications and Information Technology of IPB/UPB, first DCE, then Chair of
Electronic Technology and Microelectronics, now DCAE..
Teaching: the cursus “Theory and Design of Semiconductor Devices and Integrated Circuit” was delivered, from 1973 to 1980, by Constantin Bulucea, the head of ICCE (linear
ICs), and Anton Vătășescu, Technical Manager of IPRS Băneasa (digital ICs); Petru Dan of
IPRS was an invited lecturer for twenty years. There were delegated Diploma thesis co-advisors
(from IPRS Băneasa, Virgil Gheorghiu, Alexandru Hartular, Nicolae Marinescu, Andreas
Wild, Sorin Negru etc) and assistant professors (Andrei Vais and Horia Profeta of ICCE,
Andreas Wild and Rodica Savin from IPRS Băneasa etc.). IPRS Băneasa specialists helped
translating in Romanian reference books and co-authored up-to-date textbooks for the students.
Reciprocally, IPRS Băneasa technologists could pursue a PhD degree while keeping their
regular responsibilities; by 1987, there were four PhD and 12 doctoral students.
Researching: numerous examples will become visible in the description of the work done in all Sections (see following paragraphs). IPRS Băneasa technologists co-authored with
University professors, besides a considerable number of papers and patents, ten volumes
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published by the Technical Printing House and the Romanian Academy Printing House6
[References 1-7, Books].
The research activities in the sections benefitted from the merging of manufacturing and
research in the „lab-fab” setup; this was one of the main recipes for success: most technical
staff had a double duty, being in charge both of overseeing a workstation in manufacturing and
of developing new products. While managing operators, debugging equipment and fixing
process flaws detracted time from doing research, it also gave access to a solid experimental
infrastructure and eliminated the lengthy and risky technology/product transfer from a research
to an industrial environment. Often, technologists were allowed to take initiatives and launch
R&D programmes. This freedom and the professional passion to obtain significant results was
a real incentive (not a pecuniary one).
A memory of Petru Dan, a co-author. Immediately after joining IPRS, he was presented with
the challenging task to develop a TV scanning device using hybrid integration of a fast thyristor
and a diode. Encouraged to strive for the utmost performance, he proudly presented the results,
only to be told by the customer that, although technically superior, the product was
economically not sustainable. The management did not blame him but was rather appreciative
of the learning effect for the organization. This was typical for the stimulating atmosphere in
IPRS! The young engineer learned the lesson and strived throughout his career for products
both competitive and profitable, as well as for a truly professional working atmosphere,
stimulating the creativity and commitment of the team.
All sections engaged in a rather close cooperation with external research organizations. Besides
DCAE in Academia, numerous collaborative efforts have taken place with research institutes
in semiconductors and related fields, including first and foremost CCPCE/ICCE, but also the
Institute of Atomic Physics (IFA), the Institute for Nuclear Physics and Engineering (IFIN), the
Institute for Research and Production of Semiconductor Materials (ICPMS), the Research and
Design Institute for Electrotechnics (ICPE) and other entities. After 1989, the National R&D
Institute for Microtechnology (IMT) became a major collaboration partner of IPRS Băneasa.
IPRS Băneasa organised a few editions of its own Scientific Session, but the management also
supported publications and participations in conferences such as the Annual Semiconductor
Conference CAS organized by ICCE (international conferences were hardly accessible, given
the severe travel limitations). Articles with authors or co-authors from IPRS have been accepted
6 6.1 Vătășescu, M. Ciobanu, T. Cârcu, I. Rateș, V. Gheorghiu – „Dispozitive semiconductoare – manual de
utilizare” („Semiconductor Devices – Application Handbook”), Editura Tehnică, București, 1975; 6.2 M. Bodea., A. Vătășescu, (Ed.) – „Circuite integrate liniare. Manual de utilizare” („Linear Integrated Circuits.
Application Handbook”) Vol.1 (1979), Vol. 2 (1980), vol. 3 (1984), Vol. 4 (1985), Editura Tehnică, București;
6.3 R. Râpeanu, L. Sârbu – „30 de aplicații ale circuitului integrat βU 1011” („30 Applications of the Integrated
Circuit βU 1011”), Editura Tehnică, București, 1985;
6.4 N. Marinescu – „Radioreceptoare cu circuite integrate” („Radioreceivers with Integrated Circuits”), Editura
Tehnică, București, 1985;
6.5 Dan Dascălu, Gheorghe Brezeanu, Petru Al. Dan – „Contactul metal-semiconductor în microelectronică” („The
Metal-Semiconductor Contact in Microelectronics”), Editura Academiei RSR, 1985;
6.6 Mircea Bodea, Petru Al. Dan, Nicolae Iosif, Andrei Silard, Gheorghe Brezeanu, Eugen Popa, Marian Udrea-
Spenea – „Diode și tiristoare - 1. Performanțe” („Diodes and Tyristors - 1. Performances”), Editura Tehnică,
București, 1989;
6.7 Mircea Bodea, Ioan Teodorescu, Radu Dragomir, Andrei Silard, Sorin Negru, Eugen Popa, Petru Al. Dan,
Marian Udrea-Spenea – „Diode și tiristoare - 2. Aplicații” („Diodes and Tyristors - 2. Applications”), Editura
Tehnică, București, 1990.
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by prestigious publications, both national like Revue Roumaine de Physique, Revue Roumaine
des Sciences Techniques, Electrotehnica-Electronica-Automatica (EEA), Automatica-
Management-Computers (AMC) and international ones like IEEE Transaction on Electron
Devices, IEEE Journal of Solid-State Circuits, Electron Device Letters, Solid-State Electronics,
Applied Physics Letters, Journal of Electrochemical Society, Microelectronics and Reliability.
The company paid the fees for those who became members of IEEE technical societies. To stay
current with the newest development in the world, Section 2500 reimbursed to cost of mail
orders placed with the library of the Institute of Atomic Physics for western publications
(exceedingly difficult to get in Romania).
It is not surprising that, over time, IPRS employees generated a considerable amount of
innovative solutions. By 1987, IPRS had submitted more than 100 patent proposals to the State
Office for Inventions and Trademarks (OSIM), out of which more than 50 were already issued.
Production, research and education cohabited in IPRS Băneasa. The site located in a forest
was nicknamed, with modesty and also pride, the „Silicon Forest of Băneasa”. The Sections
enjoyed a lot of autonomy, but everybody was working to ensure the success of IPRS Băneasa.
Without commercial competitors, collaboration prevailed. It was normal that a section would
help another one „cross border” (or „over-the-fence”) to execute its projects, would share its
technological infrastructure and even its know-how and specialists, to overcome budgetary
shortages and resource scarcity7. This spirit was present in the collaboration with the University
and the external entities: ideas circulated freely, numerous publications and even patents had
authors from different organizations, anticipating in a way the modern “open innovation”
concept.
It was a living, self-standing eco-system that is pertinent even today. Scaled up to the national
level, it underpins contemporary efforts to define in Romania a strategy for the future re-
engagement in micro/nanoelectronics, an essential element in the broader concept of Cyber
Physical Systems.8,9
7 R. Râpeanu, N. Marinescu, S. Negru, S. Puchianu, P. A. Dan, F. Țurțudău, G. Mânduțeanu, T. Dunca, S.
Georgescu, D. Sdrulla – CAS Proceedings, 12 (1989). Re. feasibility of unitary silicon processing workflow.
8 Dan Dascălu – „Transformarea digitală – o regândire a perspectivei” („Digital Transformation – Rethinking the
Perspective”), Market Watch, April 2020
9 Andreas Wild – „Sistemele ciber-fizice – o oportunitate pentru România („Cyber-physical Systems – an
Opportunity for Romania”), Academica, April 2020
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3. Section 2300: The Power Semiconductor Devices Factory (Petru Dan, Eugen Popa, Viorel Banu)
3.1. Introduction
This is a brief retrospective review of the history, profile, people, growth and fall of the Section
2300 (Silicon Diodes and Thyristors), which later became the Factory for Power Semiconductor
Devices. It is an overview, sometimes from a personal angle, about the unit which in 1969
opened the adventure of silicon microelectronics in IPRS Băneasa, then grew and became an
outstanding success story, finally survived the longest during the sad decline of the enterprise
renamed in 1990 Băneasa SA, and eventually originated the only surviving entity, SC Băneasa
Silicon SRL, one of the top Small and Medium-Sized Enterprises in Romania today.
3.2. Historical Perspective
The power semiconductors evolved from a few seminal inventions. The first semiconductor
diode with germanium was created in 1952 by R. N. Hall of General Electrics, and its
counterpart in silicon was invented by R. Ohl at Bell Laboratories. The p-n-p-n structure, known
as Silicon Controlled Rectifier (SCR) or Thyristor, was proposed by W. Shockley in 1950 as
he was at the Bell Laboratories, was theoretical described by J. L. Moll of General Electrics in
195610, demonstrated experimentally in 1957 and proposed commercially as promoted by F.W.
Gutzwiller of General Electrics in 1958. The “Gate Turn Off” (GTO) thyristor was created by
F.W. Gutzwiller in 1963.
In the world, the established manufacturers of power semiconductor devices were often
vertically integrated electrotechnics companies or were located close to the electrotechnics
industry that was their main market; this is the case of General Electric and Westinghouse in
U.S.A., AEG and Siemens in Germany, Brown-Boveri in Switzerland, but also the case of the
Eastern Block manufacturers like CKD in Czechoslovakia or the factories in the Soviet Union.
In 1970, on the IPRS Băneasa campus, next to the manufacturing lines for passive components
(Building “A”) and germanium transistors (Building “B”), a new facility was erected: Building
“C”, with a new architecture, without any windows. It had four big rooms: one intended for the
newly established CCPCE, one for an assembly line for small signal silicon transistors and two
for a new section to manufacture silicon diodes (later on, the product lines included rectifier
and controlled avalanche diodes, thyristors, triacs, rectifier bridges and modules). It was rather
unusual at that point in time to co-locate power devices with the small signal ones, as it was the
case in IPRS.
Section 2300 was started in 1970 with a French license form SILEC SEMICONDUCTEURS
for manufacturing low and medium power diodes in mesa technology, soldered on metal cases
or connectors and passivated with organic materials. This was followed by the development of
high power diodes in mesa technology, consisting of sandwiches of silicon diode structures
attached to aluminium on molybdenum disks (to improve rigidity, the latter material exhibiting
almost the same thermal expansion coefficient as silicon); they were passivated with an organic
resin, then soldered on a copper base and copper connector. The Section manager, the physicist
Mrs Doina Didiv and her deputy the engineer Nicolae Iosif (Fig. 2 and 3), who led the project
for establishing the section, as well as for acquiring and implementing the license, have been
trained at the facilities of SILEC SEMICONDUCTEURS as part of the license agreement.
10 Moll, J.; Tanenbaum, M.; Goldey, J.; Holonyak, N. – "P-N-P-N Transistor Switches". Proceedings of the IRE.
44 (9) (September 1956), pp: 1174–1182.
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The first years were dedicated to learning and accumulating experience, but in 1974 the Diodes
and Thyristors Section was already the fast growing „blue chip” of IPRS, so that when the
influx of top-notch graduates, following the Government new regulation, came into IPRS, the
lion‘s share was assigned to the Section 2300. Four graduates from the Electronic Components
and Devices specialty started their careers here: engineers George Mânduțeanu, Marian
Niculae, Eugen Popa and Petru Dan (the valedictorian) were assigned to develop the lines of
low, medium and high power devices. Two graduates from the Applied Electronics specialty,
Adrian Niculiu and Alexandru Zamfirescu, were chartered to design and build electronic test
equipment, as well as perform electronic maintenance. A seventh newcomer was physicist
Florian Țurțudău, graduated from the Physics Department of the Imperial College in London.
Their roles and contributions will be shown in the next paragraphs.
A memory of Petru Dan, a co-author of this chapter. In the beginning of our activity in IPRS,
in September 1974, we were first introduced to the management team of IPRS by engineer Anton
Vătășescu, the technical manager of IPRS at that time. When joining the Section 2300, we had
the great chance to meet there a team of remarkable specialists with various backgrounds and
benefitting of a solid experience accumulated since working in IPRS. We were welcomed by the
Section manager, the physicist Mrs Doina Didiv and her deputy the engineer Nicolae Iosif.
Both were excellent specialists in the field of silicon mesa diodes. They were the ones who
guided us throughout the field of power silicon devices as well as through the „mystery” of
managing related production processes and leading teams of graduates and operators.
The period 1975-1980 is considered as definitory for the personality developed by Section
2300. The staff doubled, the output tripled, and the products started being exported.
Considerable investments brought the equipment set up-to-date, and by 1980 the in-house
research produced a spectacular growth of the product portfolio reaching 19 families of diodes
(normal and fast, Zener, controlled avalanche and suppressor types), 6 families of thyristor and
triacs and a broad range of rectifier bridges. Section 2300 was leading the company in the
number of issued patents.
In 1980, the product range was enhanced with high power diodes and thyristors, in normal and
fast versions, with pressed contacts and flat base, under a German license from AEG, which
won the licensing offers competition with Silec Semiconducteurs (France), Westcode (United
Kingdom), Brown-Bovery (Switzerland). The manufacturing license was granted only for four
thyristor types (two normal and two fast) in four package (housing) versions. This sparked
another creativity explosion, generating a large range of new high-power products developed
in-house, introducing very high-power diodes, thyristors and gate turn-off thyristors (GTO),
entering the markets for railway and machinery driving applications. The power devices were
packaged in flat base and in stud base packages, as well as in disc packages for double side
cooling both in ceramic and plastic housing. The plastic housing for double side cooling
responded to the customers requirement for low-cost products used in common applications.
Finally, power modules including two devices with insulated bases have simplified a lot the
new customers applications.
In order to increase the economic efficiency at customers, as well as to enable the optimal sizing
and correct assembling for the required practical purpose, Section 2300 started manufacturing
some new products with high added value, based on high-power rectifiers and thyristors. A
specialized application workshop was created to ensure both the mounting of power devices on
suitable heat sinks (according to their nominal power) and building up rectifier assemblies or
high-power modules. In addition, the option was offered to include the control circuits on
request. These prototypes workshop was later moved from Section 2300 to Section 2200 that
was transformed into an applications and prototypes section assisting the users of IPRS Băneasa
components.
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The portfolio diversification of high-power semiconductor devices was almost immediately
followed by a national increase in high-power product demand. Imports of high-power
semiconductors from COMECON countries (Czechoslovakia, Poland, USSR) were soon
abandoned. The pressure on the high-power division was huge, given the limited production
capacity of the manufacturing line delivered under the AEG license. There was no legal
limitation in expanding the AEG technology to other similar products, but the license was only
for the domestic market.
Unfortunately, the Romanian state policy almost completely banned new imports of machinery
and equipment, which were necessary to increase the capacity. The only chance was to utilize
the local expertise and production resources. In this respect the collaboration with other
enterprises or research institutes became essential. It was a tremendous effort made by a small
team which, apart from the current production tasks, had to ensure the assimilation of materials,
technologies and new equipment aimed to increase not only the production capacity but also
the product quality. For instance, shortly after production began, a laser machine was needed
to cut dice from the silicon wafers. Because it was forbidden to acquire imported lasers, a
research team from the Lasers department of IFTAR was identified and accepted to collaborate
in the design and construction of a YAG:Nd laser for this purpose. This was the first laser built
in Romania for the circular cutting of silicon wafers in industrial regime, which enabled to
extend the diameter range of silicon wafers up to 3 inches. It has also been applied to cutting
ceramic tiles used as internal electrical insulators for power modules.
The maximum production capacity reached over 250,000 high-power devices per year, more
than three times the licensed capacity.
A crucial point for increasing the economic efficiency was the spare parts recovery and
materials saving. Metals such as gold, silver, molybdenum, copper or even ceramic housings
were the main target of this policy. The two electron beam devices that were built in cooperation
with a section of Romanian Academy in Cluj-Napoca allowed Section 2300 to completely
replace the use of gold for pellet fabrication and to recover the molybdenum discs from the
failed devices. It is worth mentioning that the gold-plated molybdenum disc was one of the
most expensive parts in the fabrication of the pellet devices (diodes or thyristors).
A memory from Eugen Popa, a co-author of this chapter. The last major development phase of
Section 2300 took place in 1980-1981 when the license for high power diodes and thyristors
from AEG Germany was acquired and put into operation. I was part of this project and …it
was also the moment when my career took a different turn. I should have been part of the license
implementation team but, as I did not have a “clean” political file from the viewpoint of the
communist rulers, I was not eligible. So I embarked into the new task as head of the team for
the design and manufacturing of the rectifier bridges for Oltcit cars: new challenges and
opportunities that helped heal the wound of not being sent to the training stage in Germany.
The level achieved by Section 2300 in the early eighties allowed it to navigate the much more
challenging period that followed, when the political priorities resulted in massive reductions
both in the capital investments and in the access to imported materials and piece parts.
3.3. Challenges in Power Semiconductors
The power semiconductors have a few essential characteristics that differentiate them from the
rest of the industry. Among them:
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- While many products strive for miniaturization, the power devices are getting bigger and bigger, to be able to handle increasing amounts of energy.
- The electronic stress, in terms of levels of injection in the conductive state, respectively size of the depleted regions and the electric field intensity across them in the blocking
state impose unparalleled levels of purity for the silicon crystal that must be free of
defects and maintain its quality throughout all manufacturing steps.
- The intense thermal and mechanical stress they must sustain in silicon, in the package and in the whole built of the application system is without comparison.
- The unit cost and therefore the product price are determined primarily by the high material costs in manufacturing that cannot be eroded as for miniaturized electron
devices.
It is useful to start with a brief overview of the basics of the technologies used for power silicon
devices in Section 2300.
The manufactured devices covered a large range of power values: forward currents between 1-
5000 A, reverse blocking voltages up to 4000 V (the most performant being a diode of 5000 A
/ 200 V for welding resistive steel pipes and a diode of 4000 A / 5000 V for a special order, in
the biggest case used in IPRS at that point in time, T70). It is important to note that the
designations high-, respectively low-power are context dependent: the technologies and
products at the lower range of currents and voltages shown above are referred in this chapter as
„low power”, but they actually can operate at levels one or more orders of magnitude higher
that the integrated circuits or small signal devices designated as „high power”.
3.3.1 The Mesa Concept
The mesa structure is the specific common feature of the products manufactured in Section
2300. The shape of the silicon dice remembers the mesa flat-topped hills bounded from all sides
by steep slopes, normally slightly bevelled.
A rectifier device is supposed to work in two basic modes: (1) allowing a current flow through
it when directly biased, and (2) blocking the current flow when reversely biased, up to certain
voltage values. The pn junctions exhibit a low barrier for the direct current flow, and a high
barrier in the opposite direction, sustaining the reverse voltage across a space charge region
depleted of mobile charge carriers. But the reverse voltage must remain below the value at
which the electric field it generates across the depletion layer will cause a breakdown, i.e. an
uncontrolled current flow. The volume breakdown depends on the doping values and profile.
The breakdown may also be provoked by crystal imperfections (defects). It occurs differently
at the device borders and worsens at the surface of the bevel.
If the lateral bevel intersects the junction at a positive angle (i.e., when the junction area is
decreasing from the heavier to the lighter doped side), the depletion region bends towards the
bevel, its thickness increases, the electric field intensity underneath the bevel is diminished and
the breakdown voltage here becomes higher than in the volume. Obviously, a negative angle
will have the opposite effect, diminishing the breakdown voltage. The bevel surface is actually
protected by a passivation layer; it creates a complex bevel interface between the silicon crystal
and the passivation coating material, that must exhibit very good and stable dielectric properties
as well as a strong chemical compatibility with and adherence to the semiconductor. Local non-
ideal behaviour like lateral current leakage or even lateral spot breakdown may occur,
depending on the dielectric properties of the coating as well as on the electric charges
accumulated at the semiconductor surface. The mesa profile of the edge secures a high reverse
voltage, closer to but always different than in the volume.
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A memory of Viorel Banu, a co-author of this chapter. In October 1978, when I was hired, the
800 V thyristor was considered a great success although it exhibited uneven blocking voltages
because of the asymmetrically bevelling of the anode and cathode junctions: if one angle was
positive, the other one had to be negative. I came up with a new, rather simple, high-
productivity bevelling procedure that produced positive angles for both junctions. Once, when
the Section and IPRS technical management were abroad to negotiate licenses, being “home
alone”, I decided to apply the “double positive bevel angle” procedure to all thyristors families.
Upon their return, the management was surprised to see perfectly symmetrical characteristics
sustaining regularly 1600, 1800 and even 2000V, never attained before. It was like a mini
revolution.
3.3.2. The “Core Compromise”
When speaking about power devices (such as rectifying diodes, thyristors, triacs), in order to
ensure a maximum power for a given device size, a careful optimization, which can be named
the core compromise, is necessary to achieve simultaneously the specified values for the
forward current (crossing the whole volume between the top and bottom of the silicon
structure), the reverse blocking voltage (sustained by the deep pn junctions), the maximum
allowed temperature, the desired reliability under thermal cycling, the surge current and
voltage values, and the switching speed.
The lower the doping and the thicker the silicon wafer, the higher the sustainable reverse
blocking voltage (of course, taking also into account the edge effects). On the other hand, a
lower doping and a thicker silicon wafer result in a higher electrical resistance and a higher
power dissipation, hence limiting the forward current the structure can lead without exceeding
the maximum allowable temperature. Good electrical and thermal contacts to the metal parts of
the case may substantially improve the situation by effectively removing heat, so that a higher
power dissipation would be tolerable, enabling higher maximum forward currents. Next,
structural defects in the semiconductor and at its edge may impose limitations on the
withstandable surge currents and voltages. The monocrystal quality is therefore especially
important, the careful limitation of monocrystal damaging during high-temperature treatments,
as well as the accuracy of the mesa etching and passivation are crucial. For fast switching
devices, the lifetime of the charge carriers has to be lowered, which in turn results in a higher
semiconductor resistivity, hence a lower withstandable forward current; this can be mitigated
by thinning the wafer. Finally, larger area devices are subject to substantial expansion and
contraction during thermal cycling, which may cause microstructural damages of the silicon if
it is tightly attached (e.g. soldered) to other materials like copper piece parts of the case, which
exhibit very different thermal expansion coefficients. A molybdenum interlayer between silicon
and copper is used to attenuate the mismatch of the thermal coefficients, while pressure contacts
give silicon the flexibility to expand/contract independently, being mechanically disconnected
from the other metal surfaces (yet maintaining good electrical and thermal contacts).
3.3.3. The Guard Rings
As far as Zener, controlled avalanche and suppressor diodes are concerned, their precise reverse
breakdown voltage should depend primarily upon the value of the semiconductor doping level.
The edge breakdown or leakage remain a vulnerability, that is mitigated by different means for
the various voltage ranges. The very low Zener voltages up to 6.8 V were obtained by simply
using shallow planar junctions (formerly there were alloyed pn junctions instead of the diffused
ones); for the next Zener voltage range up to 10 V a guard ring was used around the planar
diffusion; finally, the highest voltage Zener diodes were realized in mesa technology with
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deeper diffusion for the junction. The Schottky diodes were realized also in planar technology
with guard ring lateral protection.
3.4. Technologies and Products
The power silicon devices were manufactured by Section 2300 on high resistivity (low doping)
silicon wafers, with high temperature deep diffusion of impurities at lower concentrations to
form the high voltage junctions, and shallow, higher concentration diffusions for ensuring a
metal-semiconductor contact with very low resistance. The largest wafers in use in Section
2300 had a diameter of 3 inches. The wafer thicknesses ranged from 150 microns (for fast
rectifying diodes) up to 700 microns for 2400 V thyristors and could go up to one millimetre
for 4-5 kV rectifying diodes.
The main manufacturing steps – also called “unit processes” - are quite similar for all products
manufactured in Section 2300, although it will depend upon the product which unit processes,
with which recipe and parameters, and in which order will be integrated in the manufacturing
flow.
In generic terms, for all products there will be a manufacturing sequence that will be applied to
the wafer, and may include: oxidation and possibly lithography to open windows in the oxide
and define localized area on the chip; doping either selectively (i.e. in the windows defined by
photolithography) or non-selectively; metal deposition; and the definition of the mesa bevel.
Then the chips are separated from the wafer (dicing), the dice are attached and contacted to the
metallic parts of the future package, then the package is formed and protected. A crucial step is
the etching and passivation of the mesa bevel, which may be performed either on wafers before
separation, or after soldering the dice to the case parts. This is of course the case for smaller
dice, when many of them would fit on the same wafer. For ultra-high voltages it may be
necessary to use several wafers, stacked one atop of another and separated by aluminium disks
to assure the mechanical strength. When the product must handle extremely high currents, it
may be necessary to use the entire wafer for one or very few silicon structures. The silicon
structure is alloyed with aluminium on a disc of molybdenum as interposer between the silicon
and the copper package parts to ensure the mechanical rigidity and to attenuate the mismatch
in the thermal expansion coefficients, in order to avoid the silicon micro-cracking. It is this
sandwich that will go in the final package. In the following we will indicate the typical
operations for the main product families.
3.4.1. Low and medium power diodes, thyristors and triacs
Uniformly low-doped wafers, with appropriate thicknesses are used.
For diodes, the junction is defined by high temperature deep diffusion at low concentrations,
while shallow, high concentration diffusions will be performed in the contact areas to ensure
high conductivity, ohmic contacts. The wafers are then electrochemically plated with a nickel-
gold metal layer, then the dice are separated from the wafer into square, hexagonal or round
chips, from 1mm to 1 cm on a size, by a chemical etching process which also defines the lateral
mesa profile. In a subsequent processing step, the bevel is passivated with organic resins or
thermally sintered glass. As an exception, the very small chips of the 1 A diodes are separated
by wafer sawing with diamond edge disk and are fixed between two silver-coated copper disks
to form a sandwich for safer mechanical handling; next they are chemically etched to define
and smoothen the lateral mesa profile; after being further soldered to the copper piston-shaped
terminals, the sandwiches are passivated with organic resins.
For thyristors and triacs, the junctions are defined by high temperature deep diffusion at low
concentrations, while shallow, high concentration diffusions will be performed under the
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contacts. The grooves of the mesa profile are chemically etched, then passivated with a
thermally sintered glass layer, or in some cases with organic resin. The chips are selectively
metalized by chemical deposition of a nickel layer. The selective diffusion, etching and
metallization processes involve single and even double face aligned photolithography (e.g. for
low/medium power thyristors or for triacs) making it a mesa-planar technology. The double
face alignment process was the result of the successful in-house research. The capability for
double face photolithography developed by the Section 2300 was unique in Romania! The
deposited metal is later covered with soft solder alloys. The dice are separated by wafer sawing
with a diamond edge disk.
The dice are soft-soldered with lead-tin-(sometimes)silver on copper case parts, while the gate
for thyristors and triacs is contacted by thermosonic wire bonding. They are packaged in both
electrically welded metal-glass or metal-ceramic cases, as well as in moulded plastic cases.
From an organizational perspective, these products were consolidated in an integrated module
for medium power diodes and thyristors.
3.4.2. High Power Diodes and Thyristors
Thicker silicon wafers with lower doping will be used.
Deep non-selective impurities diffusion at high temperatures are used to define the high voltage
diode junctions. For thyristors and triacs, in addition to the deep non-selective and selective
diffusions there is an additional diffusion for the control gate. Moreover, in order to be able to
uniformly trigger the thyristor/triac anode current, the anode presents holes (dots) through
which the gate-to-anode contacts are distributed across the whole area. Photolithography must
be used to define these localised features; hence this is a mesa-planar technology. Of course,
shallow high concentrations layers are also diffused on all devices, to ensure good ohmic metal-
semiconductor contacts. The wafers are cut into round structures by sandblasting, or by laser
cutting for larger diameters, laser cutting being also capable to separate structures with different
diameters from the same wafer, useful to optimize the material usage. The silicon disks are
vacuum plated with thin metal layers; to assure rigidity, they are pre-assembled in sandwiches
by high temperature alloying of the silicon structures with aluminium on a molybdenum
interposer matching the expansion coefficient to that of silicon. The mesa lateral profile is
defined by mechanical wet-powder grinding, then refined by chemical etching, followed by
passivation with organic resins. The sandwiches are contacted to the copper parts of the cases
either through soft soldering, or by pressed contacts11 (on one or on both faces) conceived for
avoiding mechanical tensions between the sandwich and the case parts, making sure that the
product will reliably operate during thermal cycling. They are packaged in metal-glass or metal-
ceramic welded cases, as well as in moulded plastic cases.
From an organizational perspective, these products were consolidated in an integrated module
for high power diodes and thyristors.
3.4.3. Specialty Technologies
In the early phases of the Section 2300 the silicon wafers for fast switching rectifying devices
were doped with gold through high temperature diffusion. Later, the expensive gold doping
process was replaced by a revolutionary nuclear technology, not only cheaper but also much
more effective; it has been protected by patents and was applied across the board, with the
exception of the planar ultra-fast diodes that remain gold-doped.
11 V. Banu – CAS Proceedings, 8 (1985). Re. power devices with pressed contacts.
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3.5. People and their areas of responsibility
The intention of this chapters is to mention the names of the technologists as well as their main
contributions to the growth of the Section 2300, the „heroes” of this success story.
3.5.1. Management
The Section 2300, later changed into the Factory for Power Semiconductor Devices, was led
by eight successive management teams:
(1) phys. Doina Didiv (manager) with dr. eng. Nicolae Iosif (deputy);
(2) dr. eng. Nicolae Iosif with eng. Gheorghe Florea;
(3) eng. Gheorghe Florea with dr. eng.Petru Dan;
(4) dr. eng. Petru Dan with dr. eng. George Mânduțeanu;
(5) dr. eng. Petru Dan with eng. Eugen Popa;
(6) eng. Eugen Popa;
(7) eng. Marian Udrea-Spenea;
(8) phys. Marius Jidveian was the last manager of the Factory.
3.5.2. Product Families
It was already mentioned that the products of the Section 2300 have been basically split in two
big families mainly as a function of the power they could handle (plus a few other
characteristics). For a better coordination and management of the design and manufacturing
chains, a concept of integrated modules for designing / wafer processing / assembling /
measuring and testing was established and implemented. and the technology portfolio of the
two modules has been described before, here we will also list their main products. In addition,
these two modules did not cover the entirety of the activities in the Section 2300, two more
specialty chains emerged, as shown below:
1) Integrated module for medium power diodes and thyristors under the leadership of Petru
Dan produced mesa diodes between 1-80 A and mesa thyristors and triacs between 1-40 A (also
the above-mentioned planar Zener and ultra-fast diodes). Other products, more or less similar
with these, included monolithic rectifier bridges or rectifying stacks, as well as monolithic
power modules with diodes and thyristors.
2) Integrated module for high power diodes and thyristors led by George Mânduțeanu
delivered diodes between 100-3000 (exceptionally 5000 A) and thyristors between 50-1000 A
(including related versions like gate turn-off thyristors GTO).
3) Three-phases rectifier bridges for automotive applications was a third distinct family that
emerged due to the increasing demand for automotive parts. It was led and developed by Eugen
Popa. He took over these products form engineer Traian Cârcu, future manager of Section
2500, and engineer Dănuț Bodea, future manager of the export department, who initiated the
production of the first type of such bridges responding to a customer demand.
4) The ready-to-use modules with power devices was a fourth, future-oriented avenue opened
thanks to the technical skills and innovative creativity of some application-oriented people.
Most of the products were custom-designed, generating a considerable added-value; some of
these products were designated in the world as „mechatronics”. The leader of this department
was eng. Mihai Chiș, a brilliant professional coming from one of the main customers,
ELECTROTEHNICA SA.
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3.5.3. Wafer and Chips Processing
The Silicon wafer processing, including oxidation, doping by diffusion, heat treatment,
chemical deposition of nickel and gold, followed by acid mesa defining and etching, for low
and medium power diodes, were initially handled by phys. Elisabeta Tsois and eng. Iosif
Lingvay, and later by phys. Eugen Lakatoș (high temperature processes) and eng. Elena
Seremeta (chemical processes).
The silicon wafer processing (same kind of processes as above, plus photolithography) for high
power devices with mechanically defined mesa structure, as well as for the whole range of
thyristors and triacs, including the double face aligned photolithography were led by physicists
Carmen Liiceanu, Florian Țurțudău who were later joined by the younger engineers Gabriel
Dumitrescu and Mihai Apostolescu. The planar processing of the wafers for low voltage Zener
diodes, ultra-fast diodes and Schottky diodes was entirely the responsibility of eng. Mihai
Bucur, a colleague „borrowed” from the staff of the Section 2500, where performed the related
processes. Phys.Mihai Răuță contributed here with an innovative design procedure for guard-
ring Zener diodes.
The contact between the semiconductor and its metal electrodes may dramatically influence the
electrical and thermal behavior of the device, as well as its reliability. The real metal-
semiconductor interface is very different from the ideal model of the metal-semiconductor
contact. Obtaining a very good ohmic contacts or a high performance Schottky contact is a
matter of technological art. That is why an extensive research on this topic was developed by a
joint team of academics and technologists12,13,14,15,16.
The neutron irradiation technology17 mentioned above for fast semiconductor devices was
invented, developed, and implemented by phys. Eugenia Hălmăgean. She also developed a
technique of doping silicon ingots by nuclear transmutation of the silicon into phosphorus,
capable to considerably improve doping uniformity.
Eng. Viorel Banu was running the vacuum metal deposition, such as titanium-nickel-silver or
chromium-nickel-silver for low and medium power devices; chromium-gold, chromium-gold-
chromium and nickel-silver for high power devices; as well as aluminium for alloyed Zener
diodes and high voltage rectifying stacks. He replaced the previously expensive gold plating of
the molybdenum disks with silver. By using an equipment for plasma enhanced chemical vapor
deposition designed and built by IPRS Băneasa in collaboration with the enterprise ICRET
Bucharest he obtained super-low forward voltage Schottky diodes with a maximum voltage
drop of 0.25 V at a current of 10 A. He also realized an innovative technique for ultra-fast
12 P.Al. Dan - Contributions to the study of the metal-semiconductor contact (in Romanian), Ph.D. Thesis, Faculty
of Electronics and Telecommunications, IPB, , Romania, 1988.
13 D. Dascălu, G. Brezeanu, M. Suciu, P. A. Dan – Solid State Electronics, 27, 359 (1984). Re. effect of geometry
and heat treatment on non-ideal aluminium-silicon contact.
14 P. A. Dan, G. Popovici, D. Dascălu, G. Brezeanu, A. Popa – Journal of Electrochemical Society, 130, 2472
(1983). Re. chemically deposited nickel-silicon contacts.
15 G. Brezeanu, C. Căbuz, D. Dascălu, P. A. Dan – Solid State Electronics, 30, 527 (1987). Re. silicide-silicon
contacts of vacuum deposited platinum and chromium.
16 G. Brezeanu, D. Dascălu, P. A. Dan, S. Negru, V. Trăistaru – Microelectronics and Reliability, 28, 205 (1988).
Re. aluminium-titanium-silicon contacts.
17 E. Hălmăgean – CAS Proceedings, 2 (1979). Re. lifetime reduction through irradiation with fast neutrons.
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power devices18,19, which consisted of combining gold diffusion with electron irradiation for
improving the mitigation between forward conduction and reverse blocking.
The classical passivation of low and medium power devices was based on organic silicone resins
polymerized at moderate oven temperatures. It was generally performed on chips already
attached to the copper base of their case. A genuine alternative solution was the chemical
etching and passivation with organic resin of separated dice tightly pressed between acid-
resistant foils, a patent developed by eng. Vasile Obreja from ICCE. A substantial
improvement occurred for devices manufactured with glass-passivation20,21 (instead of organic
passivation), with nickel metal plating covered by soldering alloy, based on an original idea by
eng. Sever Grigorescu, further developed by eng. Anca Nichita. The glass passivation also
enabled a major improvement in manufacturing controlled-avalanche devices22. Another
original passivation alternative for the nickel-gold plated mesa chips invented and patented by
eng. Mircea Romanescu consisted of passivating the chemically etched grooves on the wafer
with a thixotropic organic resin (used before only in aeronautic technologies) having very good
chemical and dielectric properties and a short hardening time by thermal treatment, then
mechanically dicing the wafer by sawing with diamond edge disk. This technology was
particularly successful for mesa Zener diodes over 10 V, where the planar technology was no
more appropriate.
3.5.4. Assembly and Chemical Protection
The low and medium power devices chips (either already passivated or not) were assembled by
soldering the chips with special alloys containing tin, lead and silver on metal parts (bases) of
metal-glass or plastic cases, through a heat treatment in inert (nitrogen), then reducing
(hydrogen) atmosphere in belt furnaces, followed by sealing (electric welding of metal cases)
or moulding (plastic cases). In the case of non-passivated chips, a chemical etching was used
after soldering for refining the mesa edge and before applying the resin passivation on the bevel.
For high power devices the chemical mesa processing and the organic passivation were always
performed on sandwiches. The alloying of high-power silicon-molybdenum sandwiches, as
well as the soldering of these sandwiches to the copper package parts were performed in similar
kind of furnaces. The sandwiches were then either sealed in metal-ceramic packages by
electrical welding or moulded in plastic packages.
The assembly and test production line for low power diodes was led by phys. Carmen Nan,
and later by eng.r Gheorghe Lazăr. Eng. Cătălin Georgian succeeded to implement here the
more economic use of glass-passivated chips, instead of the organic-passivated sandwiches, for
1 A diodes. Some similar technology for assembling diode chips in single-phase moulded or
resin-filled rectifier bridges was used and diversified by eng. Doru Liiceanu for general
applications.
18 V. Banu, G. Dinoiu, E. Iliescu, E. Lakatoș, C. Liiceanu, F. Țurțudău – CAS Proceedings, 12 (1989). Re.
irradiation with electrons versus gold and platinum diffusion.
19 V. Banu, E. Iliescu, Anastase Niculescu – în Electrotehnica, Electronica și Automatica, 33 (1989). Re.
manufacturing process for fast high power thyristors.
20 M. Udrea-Spenea, S. Grigorescu, A. Nichita – CAS Proceedings, 6 (1983). Re. glass passivation.
21 M. Niculae, A. Nichita, M. Udrea-Spenea, S. Grigorescu, V. Marinescu – CAS Proceedings, 8 (1985). Re.
breakdown of glass passivated versus organic passivated chips.
22 E. Popa, A. Stan, M. Udrea-Spenea, A. Nichita – Electrotehnica, Electronica și Automatica, 33 (1989). Re.
medium power suppressor diodes.
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Petru Dan was the manager of the assembly and test line for medium power devices, as part of
the module he was leading. The team was great; it included engineers Viorel Marinescu,
Mircea Romanescu, Grigore Popovici, Adrian Albu, Nicolae Popescu and Any Ichim. The
latter two invented, registered and implemented a technology for alkaline etching of nickel
plated mesa chips (thus avoiding the additional expensive gold plating), soldered with lead on
the copper case base, followed by organic passivation.
The assembly and test of high-power devices were led in the early days by eng. Marian
Niculae, and later by phys. Marius Jidveian. It included the sandwich processing, assembling
with case parts, sealing or moulding, and finally testing and sorting. Eng. Mihai Luca worked
there for a while, for measurement and testing. The electronic maintenance of the whole
production line for high-power devices was taken care of by eng. Dan Halip.
The sealed devices (either in metal or plastic case) were protected by electro-chemically
deposited metal cover (like nickel or tin), the related processes being led by eng. Ștefan
Armeanu. He was also in charge with supplying the high-grade de-ionized water, whose high
purity was crucial for the quality of mesa technologies.
3.5.5. Rectifier Bridges and Modules with Diodes and Thyristors
Part of the medium power diodes and even chips where further used to build three-phase
rectifying bridges for automotive alternators, with average currents up to 100 A. Before 1990
it was a substantial demand mainly from the Romanian car manufacturers, established as state-
owned enterprises, as well as from the famous motorcycles manufacturer Java in
Czechoslovakia. The latter was the biggest export business of IPRS Băneasa. After 1990 the
international market demanded an unexpectedly large spectrum of design versions, with diodes
either soldered, or press-fitted on heatsinks, or even with passivated chips directly soldered on
heatsinks. The creativity of Eugen Popa and his team, where Florian Țurțudău played a major
role, led to ingenious custom-designed solutions for all three kinds of designs, part of them
protected by patents, enabling the successful entry and growth on the worldwide automotive
market. This development required extensive in-house design efforts for the mechanical parts
and corresponding tooling, professionally assumed by eng. Sorin Dobrinescu.
A particular interest emerged for modular assemblies of power diodes and thyristors together
with other components, exhibiting significant added value, in discrete version fixed/pressed on
aluminium heatsinks like the so-called „application kits” conceived and developed by eng.
Mihai Chiș, as well as in monolithic versions, moulded or filled with epoxy resins, designed
by eng. Milan Peleanu. Due to the impetus of these developments and the additional space
requirements, the production of the heatsink-mounted assemblies led by Mihai Chiș was located
in the older germanium unit, Section 2200.
3.5.6. Test, Quality and Reliability Assessment
The resulted final devices and assemblies were submitted to complete electrical testing and
sorting. This was a 100% screening and sorting process done in the assembly and test
department. In the beginning of Section 2300, when SILEC diodes were manufactured under
license, the responsibility was with eng. Gheorghe Florea, then it was assumed by Eugen Popa
together with eng. Eva Rado after thyristors have been introduced.
At the same time, the quality assurance pulled random samples from all batches and performed
checks and assessments, as well as reliability evaluations. The quality assurance methodology,
formerly dealt with by eng. Radu Dragomir, became rather obsolete after two decades of
classical approach and was upgraded when Florian Țurțudău got involved in implementing
the ISO standardization and in establishing an up-to-date quality system, which strengthened
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the competitive advantages of the products, mainly after expanding the presence on the
international market after 1990.
The reliability sector had a spectacular development, in line with the development of the
company, and allowed the manufacturing of high reliability components, which were classified
according to the specific operation conditions: (a) „yellow program” with reference to
components for industrial applications requiring guaranteed reliability; (b) „red program” for
professional components with a minimum reliability index λ 10-6 h-1; (c) „blue program” for
components with special protection for naval and aviation applications; (d) components for the
Romanian Railway Company; (e) components for military applications. The annual reliability
report became one of the most effective instruments for the continuous quality improvement.
The reliability evaluation had been started by phys. Barbu Constantinescu, but later it was
broadly developed, upgraded and extended by eng. Marian Udrea-Spenea23 to cover a wide
range of power domains (i.e. up to very high voltages and currents, including unusually high
surge values to be checked), for almost all device types (rectifier and controlled avalanche
diodes, thyristors, triacs, rectifier bridges, modules), and for an extended span of controlled
performances (electrical, thermal, mechanical, environmental, aging under full charge
conditions). Marian Udrea-Spenea had contributed also to the progress of Section 2300 with
several new products and processes. Eng.Augustin Stan added valuable knowledge about
failure mechanisms in power devices24, based on his previous work for the assembling of low
power diodes and automotive products.
3.6. Partners
A major support role in the research, design and development of the specific silicon devices
and the related technologies was played by the specialized research institute ICCE, as well as
by other research units such as ICPMS, IFA, IFIN, and by universities, mainly by the Faculty
of Electronics and Telecommunications of IPB (later UPB). This support was constantly
provided not only to Section 2300 but to all semiconductor production units of IPRS.
In the beginning of the operations of Section 2300, the early version of ICCE (at that time
CCPCE) was located in the facilities of sections 2200 and 2300, than moved in its own tall
building, over the fence of IPRS Băneasa. In spite of the large span of concepts, products and
technologies developed by ICCE, only very little interest was actually devoted to the power
semiconductor devices dealt with by Section 2300. It is worthwhile to mention here the
passivation technology with organic resin for nickel-gold plated chips for medium power
devices, as well as some technologies for fast and Zener diodes.
A much more substantial support was given by the Faculty of Electronics and
Telecommunications of IPB (later the Faculty of Electronics, Telecommunications and
Information Technology of UPB), mainly by the Chair CDE, which was renamed Chair of
Electronics Technology and Microelectronics (the later DCAE). A special emphasis is deserved
by the long lasting co-operation with Prof. dr. Dan Dascălu (nowadays member of the
Romanian Academy) and Prof. dr. Gheorghe Brezeanu in the fields of metal-semiconductor
contacts and Schottly diodes, Prof. dr. Adrian Rusu in the fields of Schottky diodes and
semiconductor device modelling, Prof. dr. Andrei Silard in the field of power thyristors, Prof.
dr. Mircea Bodea on various semiconductor theoretical and practical issues.
23 M. Udrea-Spenea, T. Mochi, A. Stan, R. Giurconiu, M. Dabija – CAS Proceedings, 14 (1991). Re. failure rate
of semiconductor devices.
24 E. Popa, A. Stan, A. Nichita – CAS Proceedings, 9 (1986). Re. thermal fatigue of medium power devices.
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3.7. Scientific Contributions
The high performance obtained in designing products, imagining new device concepts25,26,27
and managing production processes was per se rewarding for professionals working in IPRS
Băneasa. However, the production challenges led them to more ambitious goals, such as sharing
the acquired experience within the scientific community, or even to protect the results by
registered patents Thus, a lot of valuable results were presented at professional conferences like
the Annual Conference for Semiconductors CAS, or published in local and international
scientific journals, as well as in comprehensive books (Fig. 4, 6). Most of such contributions
were the result of joint activities with partners from universities or research institutes.
To provide a systematic view of such works authored or co-authored by people of Section
2300, it is worthwhile to classify them according to the approached topics: silicon processing
[1-6], power diodes and thyristors [7-25], fast switching devices [26-34], Zener, controlled
avalanche and suppressor diodes [35-42], Schottky diodes [43-45], metal-semiconductor
contact [46-74], mesa passivation [75-79], reliability of power devices [80-87], modelling and
characterization [88-97]. In the detailed reference list of this chapter a brief abstract in English
is added at the end of each reference, instead of the titles in Romanian.
The universities offered to IPRS specialists the opportunity to obtain advances degrees. Thus,
four people employed in Section 2300 engaged in PhD research and successfully defended their
thesis, while keeping their regular production responsibilities: Eugenia Hălmăgean got a PhD
in physics with the thesis on neutron irradiation of semiconductors; George Mânduțeanu
became a PhD in electronics with a thesis on modelling power silicon devices; Petru Dan got
a PhD in electronics with a thesis on metal-semiconductor contacts; Nicolae Iosif became a
PhD in power electronics.
3.8. Epilogue
The story of Section 2300, later the Factory for Power Semiconductor Devices, is not only about
a successful production unit belonging to the elite industrial company IPRS Băneasa, but it
offers also a panoramic view over the life cycle of one of the most advanced production units
of the Romanian industry. Its growth lasted for more than a decade, really impacting the
progress of many industrial sectors dependent on such devices. The maturity decade gave it the
chance to consolidate its strengths, to diversify its offer, to capture the local market and to open
doo
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