principles of electrochemical micro- and nano-system technologies

Electrochimica Acta 47 (2001) 3–21

www.elsevier.com/locate/electacta

Principles of electrochemical micro- and nano-system technologies�

Joachim Walter Schultze *, Arnd BresselAGEF eV-Institut, Heinrich-Heine-Uni�ersitat Dusseldorf, Uni�ersitatsstrasse 1, D-40225 Dusseldorf, Germany

Received 1 March 2001; received in revised form 16 April 2001

Abstract

The paper gives an introduction to this Special Issue and corresponding book ‘Electrochemical Micro- and Nano-SystemTechnologies’ (Elsevier). Interdisciplinary aspects are demonstrated by microgalvanics, engineering, electrochemical materialsscience, electroanalysis and biology. Moreover, the continuous scaling down to molecular systems is described. Experimentalparameters like topography, current densities, field strengths and hydrodynamics are characterised in double logarithmic plots.Types of reactions and materials properties determine the possibility of localisation and production rate. The EMT-number isintroduced to differentiate maskless processes: delocalising 2D conditions (EMT�1) can be distinguished from localising 3Dprocesses (EMT�1). Nanoscopic localisation can be achieved using microelectrode arrays or micromechanical devices. Micro-scopic local elements play an important role in unwanted corrosion or intended structuring like phosphating. Examples oftechnical EMST applications are given and, for the case of phosphating, characterised in a flow-diagram and the Pourbaix-dia-gram. © 2001 Elsevier Science Ltd. All rights reserved.

Keywords: EMST-definition; Characterisation of systems; Microelectrodes; Microcells; Reactions; Materials properties; Substrate properties;Corrosion; Localisation of processes; Spectroscopic techniques; Scaling down; Fundamentals; Pulse measurements; Flow diagrams; Micro- andnano-technologies; Biological applications

1. Introduction: subjects and definitions

1.1. De�elopment of Electrochemical Micro- andNano-System Technologies (EMST)

Traditional macroscopic electrochemistry started 200years ago with a strong technological connection toenergy technology and electrolysis. In the last ten years,electrochemical nanotechnology has been favoured, butin fact it is a field for fundamental science. As a linkbetween these different fields, microelectrochemistry isa fast growing part of electrochemistry forming inter-disciplinary bridges to science and medicine [1–9].Moreover, it finds growing application in various fieldsof technology. The new subject of ElectrochemicalMicro System Technologies (EMST), includes and ex-

tends the fundamental knowledge of electrochemistry,but in difference to fundamental science, it emphasisesthe technological application [6–8]. Due to the require-ment of a continuous scaling down, technologies andsystems should be miniaturised to close the recent gapbetween micro- and nanotechnology. This will be takeninto account in this book. In distinction to a book on‘Electrochemical Micro System Technologies’, whichemphasizes reviews and general aspects of EMST [9],this book emphasizes actual developments of electro-chemical micro- and nanotechnologies presented at the3rd EMT in Garmisch-Partenkirchen in September2000. Due to the connection with Interfinish 2000,microgalvanics, micromaterials and microcorrosion willplay a dominant role in this book.

The emphasis of EMST is an urgent activity sinceotherwise electrochemists do not realise the wide appli-cation of their own field, and, on the other hand,electrochemical methods are used without sufficientbackground and efficiency. Special developments incorrosion research, microelectronics and biology char-acterised this insulation of highly specialised fields ofengineers and scientists in recent years. During the first

� Parts of this article are taken frof ref. [9] with permission ofGordon & Breach.

* Corresponding author. Tel.: +49-211-81-14750; fax: +49-211-81-12803.

E-mail address: [email protected] (J.W.Schultze).

0013-4686/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.PII: S 0 0 1 3 -4686 (01 )00584 -9

J.W. Schultze, A. Bressel / Electrochimica Acta 47 (2001) 3–214

International Symposium on Electrochemical MicroSystem Technologies in Dusseldorf-Grevenbroich [7],the interdisciplinary character of EMST became evi-dent. It is explained in Fig. 1 and will be maintained inthe concept of this book. Examples are taken fromvarious articles: crystallographic information on poly-crystalline Ti from Ref. [10], electronic and engineeringaspects from Ref. [11], electrochemical application ofinsects from Ref. [12] and the electrochemical cell fromRef. [13].

The encouraging aspect of interdisciplinary connec-tions is caused by the reversibility of information: elec-trochemistry as well as the special field profit from newsolutions of problems and new technologies. It is achallenge to integrate all these experiences from variousfields and to use it for a general improvement ofEMST. In the present stage this cannot be done as anencyclopedy, but with typical examples of highly devel-oped processes or systems.

1.2. Subjects of this �olume

1.2.1. Introduction and fundamentalsOsaka describes in his introductory paper the histori-

cal and future aspects of EMST with materials formagnetic recording as an example [11]. His papergives a general introduction to principles of EMST.

P. Unwin, who was awarded by the K.J. Vetter Prizefor Electrochemical Kinetics, describes the hydrody-namic phenomena in microscopic jet streams [14].

The relevant principles of physical chemistry, electro-chemistry, kinetics and experiments are described inRef. [9]. This is necessary due to the decrease of elec-trode size, which causes the change from linear tospherical symmetry and the decrease of system dimen-sions to that of the diffusion layer of the electrolyte andthe grain size of materials. Microelectrochemistrystarted with kinetics of homogeneous reactions[1,15,16]. This is a field which profits from microelectro-chemistry, but simultaneously the clarification of com-plex mechanisms is very helpful, especially for theScanning Electro Chemical Microscope (SECM) [17],and for EMST in general.

1.2.2. Microgal�anics and microstructuringThe technologies of microgalvanics are now well

established [6,18–23]. EMST started in electronics withthe invention of the printed circuit board in the mm-range, but the dimensions were decreased continuouslydue to the requirements of electronics [6]. Lithographyis now a dominating technology [24,25]. The number ofinterconnections increased and they had to be minia-turised. While galvanic processes are applied in the nmrange for micro- and nanoelectronics [26], packaging in

Fig. 1. EMST with connections to and applications in electrochemical materials science, microengineering, electrochemical engineering and biologyand medicine. Many special subjects are located in between, because they belong to various topics. Examples are taken from Ref. [10] for surfaceanalysis of Ti, from Ref. [11] for harddisc head, from Ref. [13] for the microcell, and from Ref. [12] for the insect antenna.

J.W. Schultze, A. Bressel / Electrochimica Acta 47 (2001) 3–21 5

�m dimensions is still a limiting factor [27]. Simulta-neously, the development of the LIGA-process[20,28,29] opened the electrochemical mass productionof micro mechanic and opto-electronic tools, whichnow enhance the development of micro reactors forchemical synthesis [30], mixers and other tools.

1.2.3. Electrochemical materials science in the �m-scaleElectrochemical Materials Science (EMS) is a new

field of materials science [31], which yields fundamentalinformation on mechanical, electronic and optical prop-erties. It needs microscopic and molecular informationon the surface and bulk, and, therefore, it profits verymuch from the progress of EMST [32–49] and opticalmeasurements [50]. On the other hand, fundamentals ofnucleation and growth determine the deposition rate aswell as the quality of various microstructures [51–59].Miniaturisation of cells and electrodes allowed greatprogress in characterisation of micromaterials[10,13,43–49]. Electrochemical in situ and ex situ tech-niques and metallographic methods allow the investiga-tion of the microstructure. Moreover, the gap betweentechnical materials and single crystal experiments canbe closed: electron back scattering diffraction (EBSD)now allows the crystallographic determination of singlegrains [10].

Great progress has been achieved in corrosion re-search [60–62] and microscopic or even nanoscopicmodification of surfaces and films [54,63–65]. The con-ditions of electrochemical machining (ECM) [65–68]are similar to those of pitting corrosion [69].

1.2.4. Electroanalysis and biological applicationAnother highly developed field of EMST can be

found in electroanalysis [12,70–85]. Requirements ofmass production can be solved by miniaturisation [86–90]. Terms like ‘Micro Total Analysis Systems �TAS’and ‘Lab on the chip’ represent the successful miniaturi-sation of electrodes and sensors which is of specialinterest for biosensors [90,91]. New concepts of combi-nation of natural systems like a beetle antenna [12] andsemiconductor technology [87] form a bridge to theapplication in biology and medicine, which is continuedby combination of neurons on a chip [92].

1.2.5. NanoelectrochemistryClassic scientific considerations like those of Stranski

for the crystal growth took the atomistic structure ofsmall particles and surfaces into account. Since theinvention of STM, there is a renaissance of atomisticconsiderations giving the nanoelectrochemistry greatimpetus. Now, nanoelectrochemistry allows a furtherscaling down of EMST to the nanoscale, which wasemphasized in Garmisch. Thus, the last part of thisbook describes nanotechnology in relevance to electro-chemistry. This development will be continued in Dus-seldorf 2002 at the 53rd ISE Meeting.

1.3. Definitions for EMST

After this description of the range of subjects wehave to define the term EMST to distinguish it fromelectrochemistry and Micro System Technologies(MST). Electrochemistry covers the whole field fromthe molecular reaction to process, product and finalsystem. For example, the electrochemical detection ofNO molecules includes mechanistic models and trans-port reactions as well as material aspects of the sensor[73]. EMST, on the other hand, concentrates on theminiaturisation of single parts and the whole system.Photo electrochemistry treats the general aspects ofsemiconductor electrochemistry and photons, whileEMST uses the principles for micro- and nanoscopicsurface analysis and modification, e.g. [55].

Following the description in Ref. [6], we defineEMST in the following way:

Electrochemistry describes all processes of ions ormolecules at charged interfaces, i.e. faradaic as well aselectroless processes. They usually take place at solid/liquid interfaces, but liquid/liquid interfaces may beincluded, too [93].

Micro limits the systems and processes to the rangebelow 1 mm in all three dimensions (x, y, z). This yieldsa clear difference to the well-known field of thin filmtechnology, which limits only the vertical dimension(z). Therefore, lateral effects in (x, y)-direction becomedominant in EMST. For examples see Fig. 4 later.

Nano: the lower limit of 1 �m is not sharp in EMST.For example, the miniaturisation to ultra microelec-trodes of nm dimensions is in progress with commontechnologies. But a lot of physicochemical phenomenachange in the nm range, for example the thermodynam-ics of small particles [51]. Moreover, techniques changein the nm range, e.g. the diffraction of photons, or theappearance of new SXM techniques like STM.

System means a combination of two or more parts ordevices. A single microelectrode is essential for anelectrochemical microsystem, but it represents only apart of it. At first, EMST includes micro- and nanosys-tems with an electrochemical function. But due to thelarge applications, EMST includes electrochemical pro-cesses for both production and characterisation of mi-crosystems, as well.

Technology limits the field of processes and proce-dures with general relevance and good reproducibility.As will be discussed in Section 4, we interpret EMSTin two directions: electrochemical processes for micro-technologies as well as microtechnologies forelectrochemistry.

1.4. Characterisation of microstructures and systems

The discussion of any structure and system needs acharacterisation at first [94]. Between fundamental


Fig. 2. (a) Classification of microstructures by order, symmetry, aspect ratio and material combination. (b) Signal density l and intensity Ldependence on the electrode radius r. L0= intensity of standard signal. For masking and focussing signals see Fig. 15 (by permission of Gordonand Breach).

microelectrochemistry and EMST there is a large differ-ence of relevant systems. As shown in Fig. 2a on theright side, fundamental research in microelectrochem-istry prefers homogeneous, symmetric single systemswhich are preferably flat to ease numerical simulations.In production, on the other hand, technical require-ments dictate the topography and other parameter likedegree of heterogeneity and symmetry (Fig. 2a, leftside), leading to more complex microsystems.

According to multiplicity, we have to distinguishsingle and multiple systems. While single systems de-pend on the radius r only, r and the distance d have tobe given for multiple systems. This difference has alarge impact on current density or signal intensity L asshown in Fig. 2b. We have to distinguish the intensityL0 of the incident signal, the signal density l (cm−2)and the resulting signal L of the microelectrode with aradius r. For single systems and illumination throughmasks, l is constant, but L decreases with miniaturisa-tion (L�r2). This yields a lower detection limit forsmall electrodes. For periodic systems with multipleelectrodes, on the other hand, L is almost constant,L�r0, and common equipment can be used. In case offocussing techniques, the signal intensity L0 can bemaintained, but the signal density l increases with de-creasing r, l�1/r2. This has an important consequence,e.g. for laser focussing, if enhanced signal densitycauses an increase of temperature [95].

Periodic systems (e.g. arrays [96,97]), irregular sys-tems (printed circuit boards [98]), and statistic systems(e.g. phosphate layers [6]) differ by their order. Inelectroanalysis, disc electrodes are preferred, while in

technical systems lower symmetries occur. Another im-portantcharacter is given by the aspect ratio A=depth z/width x which often increases up to 100 for technicalsystems. Finally, the material composition in vertical orlateral direction is important. We will distinguish insu-lators I, metals M and semiconductors S according totheir electronic conductivity (see Section 3.2 and Fig. 10for further examples).

Applying these characteristics, the Pt disc microelec-trode used for amperometric measurements is describedas a single, flat (A=0), metallic microsystem with2D-(circular) symmetry suitable for high current densi-ties and exact simulations. In contrast to that, thethrough hole plating of printed circuit boards repre-sents a multiple, irregular insulator/metal system with ahigh aspect ratio (A�5) suitable for chemical deposi-tion of polymers and galvanic processes at low currentdensities only [98]. ECM [66–68] yields negative mi-crostructures in a homogeneous material with aspectratios near 1.

1.5. Inorganic �ersus biological systems

The increasing interaction between electrochemistry,pharmacy, biology and medicine was a great surprise atthe 1st EMT. The 60-year effort of scientists of thisfield in electrochemical sensor miniaturisation [99], cul-minating in the award of the Nobel prize to Sakmannand Neher [3] demonstrated that EMST has alreadybeen highly developed in biology and medicine 15 yearsago [100]. The invention of the LIX-microelectrodedesign [101], the patch-clamp technique [3] and the


detection of ionic currents through membrane channelsmark the first achievements. The control of cell proper-ties like changes of its volume demonstrates the pro-gress [102]. Microelectroporation of cell membraneswill be applied in tumour therapy [103]. Other examplesrefer to bacteria manipulation and deterioration [104]which could not be discussed here in spite of greatfuture potential. But it should be emphasised that inbiological systems the relevant field strength is oftenmuch smaller than in common electrochemical systems.

At a bird’s eye view, a common treatment of scien-tific, engineering and biological problems seems to beimpossible. However, this is not true, as will be ex-plained in Fig. 3 for some processes of inorganic andbiological systems, and later in Fig. 7. All of them aregoverned by the electric field and mobility of electrons,ions or larger particles. Electron transfer reactions,ETR (a) take place in the double layer between metaland small ions or large molecules like DNA. Transportof larger molecules is well known from electrophoresis(b) and similar phenomena occur during localisation ofbacteria in the electric field [104]. Polarisation (c) isimportant for insulating films and biological cells. Al-though strongly differing from the molecular view,channel formation occurring in pitting corrosion [69]

and lipid membranes (d) can be characterised by thesame electrochemical transient techniques.

2. Scaling down in electrochemistry

2.1. Micro- and nanoscopic dimensions

In microscopic dimensions, there are similarities anddifferences to the macroscopic electrochemistry. Forexample, charge transfer reactions and nucleation phe-nomena at the solid/liquid interface are identical. Prin-ciple transport and reaction mechanisms in solution arealso the same, but the dimensions of the system becomecomparable with those of the diffusion layer. Thermo-dynamics predict an increase of the chemical potential� for a particle radius r�0.1 �m, while micromaterialsexhibit the same � as the bulk. Due to the transitionfrom linear to spherical layer symmetry, the diffusion isenhanced, the limiting current density increases, id�1/r,and the ohmic drop decreases with decreasing r, R�r[6,15]. This difference between macroscopic and micro-scopic systems is maintained for electrode arrays withdistances d�r, but it vanishes for periodic systems withd�r or at least d similar to r. The influence of the celldiameters on the diffusion layer also becomes apparentin hydrodynamics, see Section 2.7.

Another important difference arises if random phe-nomena such as nucleation, pit formation or accumula-tion of impurities become dominant. For example, at atypical nucleation rate of 106 cm−2 s−1, only a singlenucleus is formed on 1 �m2 in 100 s! Therefore, proper-ties of micromaterials become sensitive to nucleationrate, and those of nanomaterials even more.

In contrast to thin film technologies, lateral dimen-sions have to be considered if the components of x andy become smaller than that of z. The aspect ratioA=z/x (more general, A=2z/(x+y) for systems withlower symmetry) is important for transport reactions inthe electrolyte. Fig. 4 shows a summary of relevantsizes of lateral and vertical solid systems in a doublelogarithmic plot. For comparison, typical phenomenaof the electrolyte are included in italics.

The molecular structure of interfaces represents atraditional domain of electrochemistry. The doublelayer, UPD-layers, molecular films of organic moleculesor inhibitors and oxide films [105] are described in eachtextbook. In addition to them, EMST applies SAMs,defined multi-layers and tailored materials.

2.2. Microelectrodes and microcells

During the 1990s, large progress was made by minia-turisation of electrodes [6,15]. Today, problems evolvefrom mechanics of electrode production, sensitivity andinsulation or leakage currents. Glass technologies com-

Fig. 3. Similarity of fundamental processes of inorganic and biologi-cal systems: (a) electron transfer reactions, ETR; (b) electrophoresisand localisation of bacteria by AC polarisation; (c) polarisation ofthin films (oxide or cells); and (d) formation of pits in passive films orchannels in membranes.


Fig. 4. Survey of electrochemical phenomena in a double logarithmicplot. Lateral systems (x�z) and vertical systems (z�x) are sepa-rated by the line for aspect ratio A=1. Values of the electrolyte(Helmholtz layer, Nernst diffusion layer, and whirls) for comparison.

dimensions, while the exposed electrode surface remainsin the �m range. For measurements in micro systemswith high aspect ratio, needle shaped, modified or metaldisc electrodes are applicable [84,85]. For research anddevelopment, an electrode array with multiple electrodeshapes was developed in silicon technology [107], whileperiodic microelectrode arrays are used in medical re-search [96,97].

Various cells for surface modification or investigationwere developed which are summarised in Fig. 5. Themain characteristics are given by limitation of cellvolume, distance of the electrodes, electrolyte flow, andoptical transparency [32]. The SECM [17] is realised ina macroscopic cell, but the local resolution is achievedby limitation of diffusion. Microelectrodes surroundedby a photoresist can be measured, if they are wetted bya nl droplet with introduced counter and referenceelectrodes. Various modifications of the capillary celland the optical microcell are described by [32,60]. Theyare similar to the concept of a movable mask. Thesmallest electrochemical cell with two electrodes is re-alised by vapour condensation between a substrate anda SPM-tip [108,54]. It is useful for preparation of S/Istructures in the nm range. Biological cells representnatural microcells with a large electrolyte volume out-side of the cell. They are described in Ref. [102].

2.3. Current and charge densities and deposition rate

In EMST, current densities in the range between�A cm−2 and A cm−2 are applied in potentiostatic orgalvanostatic experiments. Typical ranges and applica-tions are shown in Ref. [6].

The measured current, I�r2 decreases with minia-turisation. The lower limit for electrochemical experi-ments is in the range of about 10 fA [13] for Dc and

pete with etching of metals and silicon technology.Some examples of microelectrodes and electrode arraysare shown in Refs. [6,106]. Microelectrodes have beensuccessfully applied in electroanalysis [86] and studiesof nucleation and growth [51]. In biological research,pH sensitive electrodes in glass technology have beenapplied. Even four-barrelled, multi-functional elec-trodes and four-functional electrode arrays with highaspect ratio (A�10) are available [102].

In STM experiments, nanosized metal electrodes areapplied. The resolution measured by the tip is in atomic

Fig. 5. Cell constructions for microelectrochemical experiments: (a) water droplet on a photoresist electrode [50]; (b) water droplet in oil [32]; (c)movable mask [6]; (d) scanning droplet or capillary cell [32]; (e) optical microcell [109]; (f) biological cell [100]; (g) vapour condensation cell withtwo electrodes or ‘electrochemical nano cell’ [54]; and (h) SECM [17] (by permission of Gordon and Breach).


Fig. 6. Test of electrochemical data of quadratic electrodes dependence on electrode length a (a�2r). (a) Charges Q and charge densities q ofoxide formation on gold microelectrodes measured on various electrode arrays. (b) Double layer capacity. Deviations at a�10 �m are caused byparasitic capacities [111] (by permission of Gordon and Breach).

100 pA for AC measurements. For lower current densi-ties, use of electrically connected multiple microstruc-tures often is the only alternative. Technical processescan be carried out with common techniques, since theyare usually taking place at periodic systems.

Faradaic, capacitive or electronic tunnel currentshave to be distinguished [54]. In STM experiments,currents are measured at single surface atoms, i.e. for10−15 cm2, but they are caused by very large electronictunnel currents of I�10 pA [6]. The minimum quantitywhich can be measured is also limited by the minimumcharge which has to flow: this is about a few fC as longas no multiplication techniques are available. Thus, fastfaradaic processes may be detected for S�10−10 cm2,but capacitive currents for 10−7cm2 only. Surface reac-tions could be measured in case of oxide formationdown to 100 nm, while Bard could detect single ionsdue to repeated transfer between two electrodes [110].

A verification of such considerations on the experi-mental limitations was carried out by Buß [111] withvarious microelectrode arrays for research and develop-ment. On gold electrodes, the charge of oxide forma-tion was determined as well as the double layercapacity. Results are shown in Fig. 6 in dependence onthe electrode length a (a�2r) of quadratic microelec-trodes. The faradaic charge of oxide formation is pro-portional to r2 for r�2 �m. Edge effects (e.g.delamination) cause errors for the oxide charge at smallr in dependence of the passivation quality [111,112].But for double layer capacities, the surface area of theelectrode is not the only source. Parasitic capacities ofleads and the Si substrate have also to be considered.Therefore, deviations occur for r�10 �m already.Thus, the minimisation of the RC-value of microelec-trodes requires special care.

The current density of deposition or dissolution,respectively, can be converted into a growth rate by Eq.(1)

dzdt

=−Vmol i

zF(1)

where Vmol is the molar volume. For rough estimationstypical values of Vmol=20 cm3 mol−1 and z=2 can beused. Applying these values, we obtain dz/dt=1 �m s−1 (i/A cm−2) as a typical growth rate. Thisimplies, that even in solutions with high concentration(c�1 M), where i=1 A cm−2 can be achieved, deposi-tion rates of only 1 �m s−1 can be realised. For ECM,on the other hand, where current densities of10 A cm−2 and more can be applied, high dissolutionrates of 10 �m s−1 can be achieved. Electroless pro-cesses are usually much slower, for examples see Ref.[47].

2.4. Field strength in microstructures

Another important parameter is given by the poten-tial U and the field strength F (V m−1), respectively.This will be explained in Fig. 7 for some inorganic andbiological systems as example. The potential differencesare in the range of some V for most electrochemicalexperiments and biological systems. For conductingelectrolytes of sufficient concentration, electrochemistryis concentrated at the interfaces in the nm range. Thus,electrochemical electron and ion transfer reactions,ETR and ITR, take place at F in the range of109 V m−1. In systems with insulating substances asimilar high field strength of 108–109 V m−1 is neces-


Fig. 7. Double logarithmic plot of field strength F vs. distance z forchemical and biological systems. Typical cell voltages (kV, V) andapplied electrode potential differences (V, mV) as parameter. Thefield strength of photodesinfection (e.g. on TiO2 [135]) and fielddesinfection is similar, but the voltages differ. For electroporation see[103]. Localisation of bacteria [113], field potentials in brain [116] (bypermission of Gordon and Breach).

in biological membranes at sub-�m ranges. In thiscontext, the outstanding natural ability of several fishspecies to generate high voltages (e. g. the electric eel[114]) or to detect extremely low field strengths (e. g.sharks [115]) should be mentioned.

2.5. Electrochemical, spectroscopic and other in situtechniques

Full understanding of electrochemical phenomenarequires energetic, topographic and other informationavailable from spectroscopy, mechanics and other fields[31,50]. Here, we will mention the in situ methods,which are available for EMST.

The interaction with photons yields structural, en-ergetic and kinetic information. A classification can bederived from input and output signal, differentiatingbetween optical (photons) and electrical (i, U, C) sig-nals. Table 1 gives a survey on typical methods, theirinformation and resolution. For the optical methods adescription will be given by Ref. [50].

Mechanical properties like hardness, friction andother interactions in the �m and nm range can bemeasured by AFM, nano indenters and similar tech-niques. This is described in Refs. [52,89,117].

2.6. Resolution of time and space

The resolution of processes in time and space is acomplex problem. Fig. 8 gives a double logarithmic plotof general phenomena. At first, we will discuss theresolution in time, since EMST takes place in threedifferent time scales:� Preparation of the microstructure. That includes nu-

cleation (within �s), growth or etching (up to someks) and post treatment (usually ks to Ms). Theadjustment of nucleation, diffusion, migration andion transfer reactions sometimes requires special po-tential time programs as in pulse plating [35,51] or inECM.

sary, e.g. for the growth of oxides. Then, however, thepotentials can increase up to 100 V and more [31]. Thecorrespondent field strength decreases with increasing zas long as no space charges are present.

High electric field strengths above 1 kV m−1 or steepfield gradients in nm range cause the destruction ofbiological material in most cases, whereas fieldstrengths resulting from mV to some 100 V acrosslayers of �m to mm range may be applied for theintroduction of chemicals by non-destructive electropo-ration of the cell membrane [103] or for the localisationand sorting of individual cells [113]. Lower electric fieldstrengths below 1 V m−1 are responsible for conduc-tance phenomena in mm range, but can also be found

Table 1Electrical and optical in situ methods for EMST

Process Signal out Result Information ResolutionSignal in

I(U)ElectricalElectrical 1 �m, (photoresist) nmFaradaic process(STM)10 �mDouble layer charging Electrical U(q) or q(U) Capacity C, thicknessElectrical

Electrical nm (STM)Topographic, electronicI(U,z)Electricale-TunnelingElectrical Optical E=h� Electronic, band structureLight emission

I(U, E=h�) Electronic, band structure 10 �mOpticalPhotocurrent Electricalmeasurements

50 �mAME, Ellipsommetry Optical Delta, psi,Optical Structuralalpha

10 �mOptical Electronic, optical�-Reflectommetry Intensity (�)OpticalVibration, crystallographic structureV �OpticalOptical�-Raman �m


Fig. 8. Resolution of electrochemical effects in time t and depth z ina double logarithmic plot. Effects of inorganic systems: atom vibra-tions, nucleation, pits etc. Effects of electronic systems: devices,electronic conduction, information. Effects in biological systems:channel formation in membranes, measurements on bacteria andneurons, application in medicine (by permission of Gordon andBreach).

The geometric extension gives the second parameter.From the dimensions of an atom via that of a nucleusand channel up to a microstructure we realize an in-crease by 5 and more orders of magnitude.

The processes which have to be considered take placein ns via mm (electronic conduction) or within monthsor years in application of electronic or medical systems.

The electrochemistry of microstructures changes independence of the surrounding electrolyte and gas at-mosphere, respectively. Due to the small dimensions ofthe microstructure, pits, cracks and other corrosionphenomena can cause a complete failure within someseconds. Therefore, the efficient and economic prepara-tion of corrosion stable microstructures requires a lot ofspecial know-how [112].

2.7. Hydrodynamics

Microfluidics are of great interest for special prob-lems, but they were scarcely investigated [14]. Fields ofinterest exist for microreactors, sensors [70], ECM [66–68] and fast galvanics [14,118,119]. The thickness of theNernstian diffusion layer and the Prandtl layer are inthe same order of magnitude as the structure (see Fig.4). Therefore, a laminar flow is assumed for mostsystems. Moreover, many systems are operated in qui-escent solution. Experiments were carried out in theoptical microcell at flow rates up to 1 m s−1. Calcu-lated Reynolds numbers R �100�Rcrit=2300 indi-cate a laminar flow [118]. Results are shown in Fig. 9for a model reaction in a microcell.

In jet experiments by Unwin [14] and in ECM [120],velocities up to 30 m s−1 are realized. Then, micro-scopic whirls have to be taken into account, which cancause rough surfaces [65].

� Period of standby/storage of the structure (up to 10Ms).

� Application (between �s and Ms), which dependsvery much on the type of application.An example proving the extreme conditions is given

by the airbag sensor which is electrochemically pro-duced in some ks, stands by for (hopefully) many Msencapsulated in an inert atmosphere, but has to react(mechanically) within ms.

Fig. 9. [Fe(CN6)]3− reduction in a microcell (described in Ref. [109]). (a) Experimental current density in dependence on the flow rate. A flow rateof 1 �l s−1 corresponds roughly to a velocity of 2.2 cm s−1. (b) Limiting current dependence on the flow rate under potentiostatic (U= −0.7 V)and potentiodynamic conditions from Fig. 2.9a [52] (by permission of Gordon and Breach).


Fig. 10. Typical combinations of materials for microstructures: M, metal; I, insulator; S, semiconductor; O, oxide; Pol, conducting polymer;Comp, composite film. (a) Lateral metal structure 12 � M � 12 on top of insulator � 1; (b) composite film on metal M2 for sensors; (c) microstructurewith three metals, M2 as sacrifice layer; (d) metal on insulator with an interfacial layer X for adhesion or nucleation; (e) vertical structuremetal/conducting polymer/insulator, e.g. in holes of printed circuit boards with M,M�=Cu; (f) vertical MOM structure, e.g. Cu/TiO2/Ti [134]; and(g) lateral structure conducting polymer Pol/O/Pol on S, e.g. PBT/SiO2/PBT on Si [94] (by permission of Gordon and Breach).

3. Reactions and materials

3.1. Reactions of micro- and nanoelectrochemicalprocesses

In principle, all electrochemical reactions known in amacroscopic system can occur in microstructuring pro-cesses as well. For the formation of positive or negativestructures, reactions involving Ion Transfer Reactions(ITR) from the electrolyte to the solid phase or viceversa can be used. Besides that, ITR can be induced byETR, e.g. in chemical reactions. Electrophoretic reac-tions are also used.

Typical reactions are metal deposition or dissolution,oxide formation and polymerisation. Gas evolving reac-tions like hydrogen evolution or pure ETR take placeand have to be taken into account in electroless pro-cesses. Pure ETR are important for the SECM, but notfor microstructuring. Table 2 gives a summary of mostimportant reactions.

3.2. Materials properties and combinations in EMST

As can be seen from Table 2, the choice of combina-tion of substrate and product materials allows a largevariety of ITR, ETR or photo electrochemical reac-tions. Systems can be built up by a single element,compounds of the same element or various element/compound combinations. Even for the same element,the preparation of a microstructure can produce combi-nations of metals or semiconductors with insulators.The formation of conducting, semiconducting or insu-lating oxides on a metal or semiconductor yields verydifferent combinations [51]. Applying the physicalnomenclature, possible substrate/product combinationscan be characterised by the electronic conductivity,using the symbols M (metal), S (semiconductor) I (insu-lator), O (oxide), Pol (polymer), X (others), E (elec-

trolyte). For systems like batteries or sensors, the ionicconductivity has also to be defined. For preparations,we have to distinguish between lateral and verticalstructures according to Fig. 2. While the galvanic in-dustry prefers hard materials, for many functional sys-tems, e.g. sensors, soft materials like polymers have tobe applied.

For the rate of vertical structure formation (deposi-tion or removal), the local field distribution at theinterface and within the structure is important. It de-pends on the conductivity of the deposit. Examples

Table 2Typical reactions for microstructuring: ion transfer reactions ITR,electron transfer reactions ETR, photoreactions

Process Type of Reaction Formula

Mz++ze−�MITRi−: Metal deposition;i+: etching, ECM

Anodic oxidation M+zH2O�ITRMOz+2zH++2ze−

Anodic oxidation+h� M+zH2O�ITR induced bylaser light MOz+2zH++

2ze−

Mz++ze−�MChemical metal Cathodic ITR,deposition anodic ETR

CH2O+H2O�CO2+4H+4e−

Rx�COO−+H+PrecipitationElectrodeposition of paintinduced by ETR �RxCOOH

H++e−�1/2H2

ITR, induced byPhotodissolution, Si+6HF+4p+

+h��SiF62−laser lightphotocorrosion

+6H+

R�H2+h��Photopolymerisation ITR/ETR, inducedRn+2H++2e−by laser light


Fig. 11. Delocalisation (2D) or localisation (3D) of maskless electro-chemical processes dependence on resistances: Double logarithmicplot of Rpol vs. Rel. The ratio yields the EMT number. EMT�1allows a maskless micro- or nanostructuring. For EMT�1 geometricbarriers are necessary.

electrolyte systems (MM�E). Using the materialsproperties of substrate and electrolyte, this can beexplained. A localisation of the electric field is onlypossible, if the resistance of the electrolyte Rel exceedsthat of the electrode Rpol=RS+RD which is given bythe series resistance of the substrate RS and the transferresistance RD. To demonstrate the problem, Fig. 11shows a double logarithmic plot of Rpol versus Rel. Incase of metallic electrodes with a small Rpol, this is nomajor problem. But in case of insulating substrates orinsulating structures, their inner resistance becomes toohigh even for pure water. In that case, the ‘Electro-chemical Nano Cell’ has to be used with molecularwater films of sufficient high resistance [54]. Similar tothe Wagner-number defined for metal electrodes [124],we here define the EMT-number by the ratio

EMT=Rpol

Rel

(2)

The diagonal in Fig. 11 separates the fields for 2Dsystems, where the electrochemical reaction is delo-calised over the whole surface, from the field for locali-sation, i.e. 3D structures. For a localisation of theprocess in electrolytes without boundaries, the condi-tion EMT�1 must be fulfilled. For other electrochem-ical processes like the electrochemical deposition ofpaint [122], the aim is just the opposite of structuring:the delocalisation of the electrochemical process by theinhibiting paint layer yields the desired homogeneousdeposition in pores and cracks, as well.

3.4. Substrate properties and preparation

Typical substrates of EMST are Si, Ti, Fe or insulat-ing polymers. In general a clean, homogeneous flatsurface is preferred, but adhesion requires a roughsurface or a seed for nucleation of the microstructure[47]. Therefore, electrochemical surface treatment of thesubstrate is often necessary. For negative microstruc-tures, on the other hand, ECM represents a successfultechnology for high aspect ratios [66]. A survey ofsmoothing and etching technologies is given in Refs.[9,31]. The great advantage of ECM for EMST com-pared to classical production processes is given by theremoval of the surface atoms without the risk of me-chanical or electrical stress within the substrate.

Chemical properties of the substrate are importantfor the interaction with the first layer of product and,therefore, for the adhesion. Dislocations and surfaceinhomogeneities determine the nucleation. EDX andScanning Auger microscopy will be used to checkchemical impurities and surface layers. Details of theelectronic structure are important for rate of processes,especially at semiconductor surfaces. Porous silicon is atypical example.

were demonstrated in Refs. [31,105] for metals, semi-conductors and oxides. While at the surface of conduct-ing phases the potential drop is concentrated in theHelmholtz layer, in semiconducting or insulating phasesa large potential drop may occur in space charge layersor across the whole insulator. Therefore, the formationof thicker deposits is easy for metallic phases and, atsmall overpotentials, for semiconductors. But for non-conducting phases, it requires high potentials [31]. Forinsulating films on metals, the high field law causes aconstant growth of a typical thickness proportional toU, e.g. d=2 nm V−1. For n-Si and other n-type semi-conductors, the potential drop within the semiconduc-tor has to be considered. It can be eliminated, however,by illumination.

The field distribution has a large impact on micro-and nanostructuring. For example, vertical nanostruc-tures of insulating SiO2 can be prepared on p-Si (andon n-Si by illumination) by a field dependent processonly in almost monomolecular films of condensed wa-ter, but not in an extended electrolyte, which dissipatesthe field necessary for film growth [54]. On the otherhand, self-catalysing reactions like pitting enhance thelocalisation.

Electrodeposition of paint [121,122] is used to insu-late metal tips or for fixation of functional substances,e.g. on ion selective electrodes [123].

3.3. EMT-number for structures

The question arises, why electrochemical nanotech-nologies up till now are concentrated on metal/metal�/


Since single crystals are expensive, polycrystallinematerials with electropolished surface are often pre-ferred. Then, however, the surface structure becomesimportant. This can be studied by Anisotropy MicroEllipsometry (AME) in case of anisotropic materials[50] or by EBSD [10]. The latter one can determine allthree Euler angles with an accuracy of 1° with a highlocal resolution of 1 �m. Based on such a principalinvestigation, other effects which are strongly con-nected with the grain orientation can be used, too. Asan example, the EBSD-analysis of a Ti-surface and theinterference colours of anodic films on it can be usedfor determination of the surface orientation, which hasa great impact on corrosion and reactivity [10].

3.5. Nanoscopic materials properties and topographiccorrelation

In molecular dimensions, the atomic and electronicstructure of the surface plays the dominant role. STMand other SXM techniques revealed the influence ofsingle atoms. For a long time, however, the SXM-pic-tures could not be coordinated with micro or evenmacroscopic pictures. Two different approaches arereported in this volume: Microelectrode arrays can beused to locate the SXM-picture [54]. Using microme-chanical techniques, the combination of SXM and mi-croelectrodes was achieved in Ref. [53]. In EMS, thecombination of nucleation, growth and diffusion pro-

cesses can be applied to prepare nanomaterials whichare now of great interest in electrocatalysis. Some ex-amples are described in Refs. [55–59].

3.6. Corrosion of microsystems

After discussion of reactions (Table 2), time scale(Fig. 8), and materials properties (Fig. 12), it becomesclear that the stability of microstructures in electrolytesor wet atmospheres requests special care. In principle,corrosion in the gas phase can be avoided by encapsula-tion, e.g. for electronic devices, but simpler passivationfilms are preferred for economic reasons [112]. In elec-trolyte, penetration of water and aggressive ions can befast. Thus, depending on the environment the sensor isexposed to, even a stability of some days might besatisfactory. The corrosion of microdevices was studiedusing microelectrode arrays with various passivationfilms [112b].

A special phenomenon is given by local elements inmicroscopic dimensions. Fig. 13 shows the negativeresults of this local element formation for a technicaldevice [112a]. On the other hand, microscopic localelements are helpful in the technical process of phos-phating. Fig. 14 shows a model for phosphating of steelin a modern Ni-containing bath [125]. While steel cor-rodes, Ni is deposited on the steel surface. A continu-ous nickel plating is hindered by further progress of

Fig. 12. Log/log-plot for materials properties: (a) metals (grains, screw dislocations, crevices, welds); (b) coatings. A=aspect ratio (by permissionof Gordon and Breach).


Fig. 13. Bimetallic (galvanic) corrosion of Ti�TiN�Al�TiN� stack [31](by permission of Gordon and Breach).

reactions (reduction of accelerator, protons and Ni-ions) are preferred on the Ni-islands. Finally, a statistic,microstructured lateral M/M�, I/E system results.

3.7. Localisation of processes

For the preparation of microstructures, the localisa-tion of electrochemical reactions has to be realised.Depending on the intended profiles shown in Fig. 2,methods with sharp blocking or a focused signal can bechosen. Fig. 15 gives a summary of principles [9].

Geometric blocking, e.g. by a photo-resist [24], givesthe sharpest structures. Therefore, lithography [41] iswidely applied with all variations. However, complica-tions arise for thicker structures, if the reaction mainlytakes place at the boundary, which is observed forchemical deposition or formation of conducting poly-mers. Chemical modification can be used for localinhibition or catalysis. Local induction of nucleationand growth by foreign clusters is used for electrolessdeposition, e.g. by Pd deposition on insulators etc.Localised deposition of a solid-state reactant causes agood localisation of the product [94]. Local insulationby adsorbed poisons, inhibitors, or by surface modifica-tion, e.g. ion implantation [47], gives sharp boundariesfor the first atomic layers only.

Focused signals, e.g. electric field, laser light etc.,usually yields Gaussian profiles. Localisation by surfacetension is well known from preparation of insulatedSTM-tips, and it is used for the scanning droplet cell[32]. Transport of educts can be focussed by the SECMor in a jet [14].

Fig. 14. Formation of microscopic local elements during phosphatingin a Ni2+-containing bath by ion and electron transfer reactions ITRand ETR. Anodic corrosion of Fe (local anode) causes a cathodicdeposition of Ni. Cathodic ETR are enhanced on Ni, which forms alocal cathode. Local elements are connected, separated and partiallycovered by Zn-phosphate [125].

iron corrosion and by insulation by phosphate crystalsdeposited on the surface, too. Thus, the anodic currentdensity prevails at the steel surface, while the cathodic

Fig. 15. Principles of localisation of electrochemical reactions by geometric blocking [94], chemical modification, localised signals [94] or transportlimitation by a jet or the SECM [117,17] (by permission of Gordon and Breach).


Fig. 16. Schematic representation of primary and secondary effects ofmicrostructuring: primary effects by focussing of the signal, sec-ondary effects by dissipation of heat, migration of holes, and lightscattering (by permission of Gordon and Breach).

example is given by the fuel cell development: while thecatalyst has dimensions of few nm, the membraneelectrode assembly (MEA) requires micro technologicalprocedures, but the production of the fuel cell presumesa lateral scaling up to a cell in the cm-range. Finally,these cells have to be multiplied in the stack to the finalaggregate. Thus, we have two different multiplicationsteps yielding the final product. Ref. [6] gives the rela-tion between particles, sizes and area. This demon-strates the long way from fundamental science via EMSto micro system technologies and the industrial produc-tion at the end.

Multiplication of the microstructure in a commontechnical process yields mass products, and the lowprize allows the application of the microstructure as athrow-away product. This consequence gives MST andEMST the same economic chance as microelectronicshas already.

4.2. Flow diagrams

In most examples of EMST, a sequence of verydifferent production steps is necessary. Typical exam-ples are substrate preparation, prestructuring of thesubstrate and modification by activation which all takeplace before the main process of materials deposition orremoval. Then, one or more process steps of depositionfollow. After that, a post treatment (annealing, illumi-nation, fixation) is often applied [6,94].

Processes take place at different chemical and electro-chemical conditions. Hence, an extended description ofregulation of temperature, potential (or current), pH,etc. is necessary. Flow diagrams and a description inthe Pourbaix diagram are appropriate [6,9,98]. As anexample, the phosphating of steel or zincated steel andfollowing cathodic electrodeposition of paint (EDP)will be discussed. This process is widely applied inautomotive industries. Typical production rates of afactory are some 10.000 m2 day−1 of Fe or Zn which iscovered by about 1011 phosphate crystals of about 2 �mthickness, and between the phosphate crystals the mi-croscopic local elements Fe/Ni or Zn/Ni exist whichwere explained in Section 3.6. An exciting technologywith a low prize of less than 1 DM m−2!

The multi-step process is qualitatively characterisedin Fig. 17a by the microscopic structure of the inter-face, the aim of the process step and some of theimportant parameters (potential, thickness, pH andprocess time). Other parameters (temperature, concen-tration, stirring) have been omitted for reasons of sim-plicity. It should be pointed out that the relevantdimensions change from activation (nanosized titaniumphosphate) to the zinc phosphate (2 �m) and the EDPlayer (30 �m) and that the electroless processes takeplace at intermediate potentials, while the EDP needspotentials down to −100 V. The steps A, B, C, D and

In case of focused signals, primary and secondaryeffects have to be distinguished. Primary effects are dueto focused signal. Usually, secondary effects broadenthe microstructure. They can be caused by transport ofeducts, products or heat as is schematically shown inFig. 16. Typical examples are given by laser-inducedreactions [126]. Diffusion of holes or electrons in thesubstrate dissipates the focused signal. Formation ofgas bubbles with a scattering effect gives another exam-ple. In the anodic polymerisation, on the other hand,diffusion of oligomers usually causes broad deposits.The heat transport is important for laser-induced metaldeposition [127].

4. Special aspects of EMST

4.1. Scaling down and multiplication

The scaling up of a process for industrial realisationis well known as a standard problem of chemical engi-neering. In EMST, the problem is opposite: the firststep consists of scaling down or the miniaturisation ofproducts. After clarification of the micro system, thetechnical realisation does not require the scaling up of asingle process, but the multiplication (‘numbering up’)of the micro system yielding a multiple, more or lessperiodic system. The phosphating process is a goodexample [6,31]. The first step required scaling downfrom a laboratory single crystal to crystals on steel. Ina next step, nucleation density was adjusted to thetechnical system. Then, layer properties were improvedby microscopic local elements. Finally, the multiplica-tion in the technical car production with about 1012

crystals per car body has to be achieved. Another


E take place at very different sites in the Pourbaix-dia-gram, e.g. that of Zn in Fig. 17b.

4.3. Microtechnologies for EMST

In multi-step processes of micro system productions,electrochemical technologies are involved in varioussteps of pretreatment, structuring, posttreatment, andapplication. Therefore, EMST has three large fields[6,9]:� Micro system technologies, MST, for electro-

chemistry;� Electrochemical processes for MST (see Section 4.4);� Electrochemical micro systems (see Section 4.5).

MST for electrochemistry covers the necessary back-ground knowledge of electrochemists: it includes allnon-electrochemical techniques for deposition, removalor bonding of materials like PVD, silicon technologies,glass etching (Foturan [6]), spark erosion, milling,drilling, laser pulling of metal wires, glueing, passiva-tion etc. The relevance of MST is due to their impacton the following electrochemical processes and applica-tions. A summary is given in Ref. [6].

4.4. Electrochemical processes for MST

Electrochemical micro technologies for non-electro-chemical systems include all galvanic and electrolessprocesses, material preparations and anodic bonding.Typical examples can be found in electronics. A surveyis given in Refs. [9,19]. For example, a large group ofelectrochemical work has been done by preparation ofnano- and micromaterials. Especially magnetic materi-als are important [11,31,128].

The LIGA process is used for clock manufacturing.Magnetic materials are necessary for computer hard-disk heads [128]. Further, the production of airbag

sensors and inkjet cartridges have to be mentioned. Theapplication of ECM has been known for macrosystemsfor a long time. In EMST, it is an essential technologyfor metal removal. Mechanic technologies like drillingand sawing are limited to simple geometries down to0.1 mm, damage the surface and leave burrs. ECM, incontrast, can be applied for special removal withoutstrain, special topographies and deburring. It is nowapplied for production of jets, razor heads and masksfor microelectronics. For electronics, the production ofPCBs and packaging is very important [6,27]. Phos-phating was already described.

Microgalvanic processes are now necessary for chem-ical engineering. Chemical reactors and mixers alreadyrepresent micro systems with growing importance [30].Micro flow systems are required for analytical systems[129].

4.5. Electrochemical micro systems

In the following, electrochemical micro systems andproducts of EMST will be mentioned. Many of themare just under development. The application of suchsystems presumes a high lifetime and corrosion stabil-ity, which is a challenge for construction of microsystems as corrosion protection has to be scaled downproportionally as well [112].� Electrochemical microreactors [30,130] and fuel cells

represent electrochemical micro systems. Due totheir small volume, they can be optimized for heatdissipation, defined lifetimes of intermediates andfast transport processes.

� Microcells for local galvanic processes or modifica-tions of surfaces [32] belong to the larger group ofmicroreactors. They differ due to their attachment tospecial surfaces. The jets for electrolyte allow highcurrent densities for galvanic processes [119].

Fig. 17. (a) Flow diagram and (b) Pourbaix diagram of phosphating and cathodic electrodeposition of paint.


Fig. 18. Capacitive systems for MST in a double logarithmic plot ofC vs. z. Active materials for batteries with C�z (m=1), andcondensors with C�1/z (m= −1). Full line: microcapacitor with10×10 �m2, dotted line for a macro system with 1×1 cm2. Forsemiconductors the space charge layer dsc= f(U,N) must be consid-ered (by permission of Gordon and Breach).

5. Conclusions

The young field of electrochemical micro system tech-nologies (EMST) is fast developing. It enriches manyfields of science and technology, since it offers alterna-tive approaches to mechanical or physical techniques.Advantages are due to:� the localisation of the electric field at the solid/liquid

interface;� the absence of mechanical stress and tenses below

the surface;� the regulation of process rates by potential or

current;� the high sensitivity;� the large variability of materials with differing elec-

tronic or ionic conductivity;� the flexibility of chemical processes and properties.

On the other hand, EMST is not an unique, isolatedtechnology. It needs other technologies and integratesthem, and often it has to compete.

The dimensions and experimental limits of EMSTbecome smaller and smaller. Higher sensitivity of elec-trochemical equipment, progress in mechanical tech-nologies by application of piezo techniques andimprovement of other MST allows a continuous pro-gress of miniaturisation. Starting from the mm-rangeabout 20 years ago, many techniques are now availablein the �m-range. In contrast to the - at first - insulatedsuccess of STM in the nm range, EMST maintained theconnection to neighbouring dimensions. This givesEMST the chance to form a bridge between the tradi-tional macroscopic electrochemistry and the electro-chemical nano science. That was the reason to changethe title of the International Symposium on Electro-chemical Micro System Technologies into ‘Interna-tional Symposium on Electrochemical Micro and NanoSystem Technologies’, which will be held in Dusseldorf2002. We are sure that this book will catalyse furtherprogress in that field.

Acknowledgements

The support of this work by the Ministerium furSchule, Wissenschaft und Forschung of Nordrhein-Westfalen by the joint projects ‘Integrierte Mikrosys-temtechnik fur Fest/Flussig-Systeme IMST’ und‘Elektrochemische Mikro- und Nano-Systeme Elminos’is gratefully acknowledged. We gratefully acknowledgethe permission by Gordon and Breach Science Publish-ers to reproduce parts of a similar article from the bookElectrochemical Microsystem Technologies, J.W.Schultze, T. Osaka, M. Datta (Eds.), Gordon andBreach, 2001.

� Many micro systems and high tech products dependon electrical energy delivered by batteries or capaci-tors within the micro system [131,132]. Systems forcharge storage include condensors for small chargesand high voltages and batteries and supercaps forlarge charges and low voltages. Fig. 18 shows theopposite dependence of these systems on the thick-ness of the functional layer [112].

� Microcoulometers can be discussed here, too.� Miniaturised electrochemical sensors are widely ap-

plied in analytical chemistry, biology and medicine[12,70–77,86–88]. For medical applications, all theadvantages of mass production are used.

� An advanced version of electrochemical sensors isgiven by multi-sensor systems [71] and finally by theMicro Total Analysis System �TAS or the ‘Lab onchip’.

� The chances of micro capillary electrophoresis weredemonstrated by Manz et al. [133].

� Other microsensors use electrochemical principles fordetection of physical data. For example, microinclinometers are based on the field distribution in aconducting electrolyte.

� Fluid systems are strongly connected to electrochem-ical systems, even if the working principle is not anelectrochemical one. Mixers, emulsifiers [30], ink jets,dosimeters and flow detectors should be mentionedin this group.


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