mems technology

Micromechanical System for System-on-Chip Connectivity

INTRODUCTION

MEMS technology has enabled us to realize advanced micro

devices by using processes similar to VLSI technology. When MEMS

devices are combined with other technologies new generation of innovative

technology will b created. This will offer outstanding functionality. Such

technologies will have wide scale applications in fields ranging from

automotive, aerodynamics, hydrodynamics, bio-medical and so forth. The

main challenge is to integrate all these potentially non-compatible

technologies into a single working microsystem that will offer outstanding

functionality.

The use of MEMS technology for permanent, semi permanent or

temporary interconnection of non-compatible technologies like CMOS, BJT,

GaAs, SiGe, and so forth into a System-on-Chip environment can be

described using an example application. It is a hearing instrument in which

an array of acoustical sensors is used to provide dynamic directional

sensitivity that can minimize background noise and reverberation thereby

increasing speech intelligibility for the user. The micro array can provide

dynamically variable directional sensitivity by employing suitable beam

forming and tracking algorithms while implanted completely inside the ear

canal.

Dept. of AEI MESCE Kuttippuram1


MEMS ACCOUSTICAL SENSOR ARRAY FOR A HEARING INSTRUMENT

In this application an array of capacitive type sensors are used in a

hearing instrument to provide dynamic directional sensitivity and speaker

tracking and can be completely implanted in the ear canal. The directional

sensitivity is obtained by the method of beam forming. The microphone

array is developed using MEMS technology and which can be used to form

beam to provide directional sensitivity.

BEAM FORMING USING MICROPHONE ARRAY

The microphone array consists of nine capacitor type microphones

arranged in a 3*3 array and utilizes the classical phased array technique for

beam forming. In this technique, the relative delay or advance in signal

reception is eliminated by applying a delay or advance is that the signal out

puts from different microphones can be added to form a beam as shown in

figure 1.



Figure 1. Beam pattern of a transducer array: normal beam

It is also possible to steer the direction of the beam by providing

additional delay factor that is equal to the negative of the relative delay to the

out put of each microphone in the array when a signal arrives from that

direction. Figure 2. illustrates the beam steering concept.



Figure 2. Beam pattern of a transducer array: steered beam

Similarly, it is possible to form multiple beams out of the single

array employing different delay factors and use such beams to scan the

direction of the potential speaker. This scanning beam can easily realized by

continuously steering the beam from top to bottom or from left to right by

dynamically changing the steering delay using digital filters. An algorithm

will detect a speech signal above some threshold level and will steer the

main beam towards that direction. The block diagram for such a system is

shown in figure 3.



To avoid spatial aliasing at all steering angles the spacing d between the

microphones of the array is required to be

D < πc/ω

= πc/2πf

= λ/2]

Where λ is the wavelength of the incident acoustical signal and f is

the frequency in Hz. c is the velocity.

If the sensor array is to be inserted inside the ear canal, the spacing between

the microphones will be much smaller than the required. This constraint can

be overcome by introducing additional delay factor to compensate for the

difference in delay due to the required spacing d and the delay due to

physical microphone spacing.


SoC PCI Bus

Array Control Interface

MEMS Acoustical

Array Module

MEMS Socket

Interface

CMOS A/D

Converter

Analog CMOS Signal

Conditioning

Digital Beamforming

& Beam Steering Engine

Digital Signal

Processing

Figure 3: Block Diagram of Hearing Aid Instrument


MEMS MICROPACKAGING SOLUTION

The MEMS technology can be used to create necessary structures

for die level integration of MEMS devices or components and CMOS or

non-CMOS, like BJT, GaAs, and Silicon-germanium devices. The basic

structure of the proposed mechanism is a socket submodule (figure 4) that

holds a die or device. The required no of submodules can be stacked

vertically or horizontally to realize a completely system in a micropackage.

Figure 4a. 3D model of socket submodule



Figure 4b. top view of socket submodule

Connectivity between submodules is achieved by means of

microbus card (figure 6.) constructed with heat deformed, gold coated

polysilicon cantilever microspring contacts and platinum coated microrails

fabricated inside an interconnection channel that is presented in each socket

submodule. An illustration of the micropackaging system is shown in figure

5.



Figure 5a. Top view of MEMS micropackage

Figure 5a. MEMS micropackaging system: cross section through AA’



Microorganisms and moisture inside the ear canal may contaminate

the microsensor array. This can be helped by the submodule type sensor

array, which can be removed easily for cleaning or replacement.

The submodules are connected by means of a MEMS microbus

with gold coated polysilicon cantilever microspring contacts and platinum

coated microrails fabricated inside an interconnection channel that is

presented in each socket submodule. Figure 6 shows the 3D model of

microbus

Figure 6. 3D model of MEMS microbus card



DIE TESTING CONFIGURATION

The concept of socket submodules and connectivity can also be

used in a die testing platform. The establishment of temporary connectivity

for testing a die without exposing the die to otherwise harmful energy

sources or contaminations during the test cycles is a major technological

challenge. The MEMS submodule can be reconfigured to establish

temporary connectivity for die testing with out exposing the die to any

contamination while carrying out necessary test procedures. Figure 7

illustrates the die testing configuration using MEMS socket type structures.

Figure 7. MEMS die testing configuration



In this set up, two different type of MEMS sockets are used: a fixed

one connected permanently to a Tester-on-Chip (ToC),which is a die testing

SoC using an enabling gold–to-gold thermo sonic bonding technology and a

removable socket that acts a die specific carrier. The contact springs on both

sides of the removable socket undergo deformation due to a compression

mass on the top of the die and generate the necessary contact force. The

removable MEMS socket can be redesigned to connect a die that is larger

than the ToC. This makes the system a flexible one. The major design

objectives of contact spring mechanism is to develop a proper –contact force,

low-contact resistance, small area, and short contact path while having the

ability to tolerate some torsional misalignment. Another important

requirement is to maintain the contact surface that will remain reasonably

flat even under torsional deformation to realize a higher contact area. Based

on these constraints designs two of contact springs are given in figure 8.



Figure 8. Two types of micro spring contacts

ADVANTAGES AND DISADVANTAGES

ADVANTAGES

High efficiency

Cost effective

Flexible

High accuracy precision

DIS ADVANTAGES

Complex design

Complex fabrication procedures



CONCLUSION

MEMS technology offers wide range application in fields like

biomedical, aerodynamics, thermodynamics and telecommunication and so

forth. MEMS technology can be used to fabricate both application specific

devices and the associated micropackaging system that will allow for the

integration of devices or circuits, made with non compatible technologies,

with a SoC environment. The MEMS technology allows permanent, semi

permanent and temporary connectivity. The integration of MEMS to present

technology will give way to cutting edge technology that will give

outstanding functionality and far reaching efficiency regarding space,

accuracy precision, cost, and will wide range applications. Describing typical

application of MEMS in a hearing instrument application the flexibility and

design challenges and various innovative features of MEMS technology is

made to understand. In the hearing aid instrument microphone arrays are

used to produce directional sensitivity and improve speech intelligibility. The

various components and necessary signal conditioning algorithms are

implemented in a custom micropackaging that can be implanted inside the

ear canal is described.



REFERENCES

1. Sazzadur Choudhury,M. Ahmadi, and W.C. Miller , Micromechanical

system for System-on-Chip Connectivity’, IEEE Circuits and Sytems,

September 2002

2. New battery may jump-start MEMS usage, ISA InTech April 2002

BIBLIOGRAPHY

1. www.darpa.mil

2. www.sanyo.co.jp



ABSTRACT

Micromechanical systems can be combined with microelectronics,

photonics or wireless capabilities new generation of Microsystems can be

developed which will offer far reaching efficiency regarding space, accuracy,

precision and so forth. Micromechanical systems (MEMS) technology can be

used fabricate both application specific devices and the associated micro

packaging systems that will allow for the integration of devices or circuits,

made with non-compatible technologies, with a System-on-Chip

environment. The MEMS technology can be used for permanent, semi

permanent or temporary interconnection of sub modules in a System-on-

Chip implementation. The interconnection of devices using MEMS

technology is described with the help of a hearing instrument application and

related micropackaging.



CONTENTS

1. INTRODUCTION 1

2. MEMS ACCOUSTICAL SENSOR ARRAY FOR A HEARING

INSTRUMENT 2

BEAM FORMING USING MICROPHONE ARRAY 2

3. MEMS MICROPACKAGING SOLUTION 6

4. DIE TESTING CONFIGURATION 10

5. ADVANTAGES AND DISADVANTAGES 12

6. CONCLUSION 13

7. REFERENCES 14

8. BIBLIOGRAPHY 14



ACKNOWLEDGEMENT

I extend my sincere gratitude towards Prof . P.Sukumaran Head of

Department for giving us his invaluable knowledge and wonderful technical

guidance

I express my thanks to Mr. Muhammed kutty our group tutor and

also to our staff advisor Ms. Biji Paul for their kind co-operation and

guidance for preparing and presenting this seminar.

I also thank all the other faculty members of AEI department and my

friends for their help and support.


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