MEMS TECHNOLOGYdspace.cusat.ac.in/jspui/bitstream/123456789/2208/1... · MEMS TECHNOLOGY SEMINAR...

MEMS TECHNOLOGY

SEMINAR REPORT

Submitted by

ARVIND KUMAR JHA

in partial fulfillment for the award of the degree

of

BACHELOR OF TECHNOLOGYin

COMPUTER SCIENCE & ENGINEERING

SCHOOL OF ENGINEERING

COCHIN UNIVERSITY OF SCIENCE & TECHNOLOGY

KOCHI-682022

OCTOBER-2010

Division of Computer EngineeringSchool of Engineering

Cochin University of Science & TechnologyKochi-682022

CERTIFICATE

Certified that this is a bonafied record of the seminar work titled

MEMS TECHNOLOGY

Done by

ARVIND KUMAR JHA

of VII semester Computer Science & Engineering in the year 2010 in partial fulfillment of the

requirements for the award of Degree of Bachelor of Technology in Computer Science &

Engineering of Cochin University of Science & Technology

Dr.David Peter S MS. PREETHA M S

Head of the Division Seminar Guide

Micromechanical System for System-on-Chip Connectivity

Division of Computer Engineering ,CUSAT 1

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 .

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 5

BEAM FORMING USING MICROPHONE ARRAY 8

3. MEMS MICROPACKAGING SOLUTION 12

4. DIE TESTING CONFIGURATION 18

5. ADVANTAGES AND DISADVANTAGES 20

6. CONCLUSION 29

7. REFERENCES 30

8. BIBLIOGRAPHY 31



ACKNOWLEDGEMENT

We take this occasion to thank God, Almighty for blessing us with his

grace and taking our endeavor to a successful culmination. We extend

our sincere and heartfelt thanks to our esteemed guide, Ms. PREETHA

M.S. for providing us with the right guidance and advice at the crucial

junctures and for showing us the right way. We extend our sincere

thanks to our respected head of the division Dr. David Peter , for

allowing us to use the facilities available. We would also like to

thank the our class co-ordinator Mr. Sudheep Elayidom for his kind

suggestion towards the initiative of this seminar.We would like to thank

the other faculty members also,at this occasion. Last but not least we would

like to thank friends for the support and encouragement they have given us

during the course of our work.

.

ARVIND KUMAR JHA



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 micro array can provide dynamically variable directional

sensitivity by employing suitable beam forming and tracking

algorithms while implanted completely inside the ear canal.

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.



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








MEMS ACCOUSTICAL SENSOR ARRAY FOR A HEARINGINSTRUMENT

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.

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 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

SoCPCIBus

ArrayControl

Interface

MEMSAcoustical

ArrayModule

MEMSSocket

Interface

CMOSA/D

Converter

Analog CMOSSignal

Conditioning

DigitalBeamforming

& BeamSteeringEngine

DigitalSignal

Processing

Figure 3: Block Diagram of Hearing Aid Instrument



compensate for the difference in delay due to the required spacing d

and the delay due to physical microphone spacing.

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



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

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.



The micromachining technology that emerged in the late 1980s can

provide micron-sized sensors and actuators. These micro transducers

are able to be integrated with signal conditioning and processing

circuitry to form micro-electro-mechanical-systems (MEMS) that can

perform real-time distributed control. This capability opens up a new

territory for flow control research. On the other hand, surface effects

dominate the fluid flowing through these miniature mechanical

devices because of the large surface-to-volume ratio in micron-scale

configurations. We need to reexamine the surface forces in the

momentum equation. Owing to their smallness, gas flows experience

large Knudsen numbers, and therefore boundary conditions need to be

modified. Besides being an enabling technology, MEMS also provide

many challenges for fundamental flow-science research.



Microvision's MEMS scanning mirror is a silicon device at the center

of which is a tiny mirror. This mirror is connected to small flextures

allowing it to oscillate. The 2D MEMS scanner oscillates vertically

and horizontally to capture (imaging) or reproduce (display) an image

pixel-by-pixel. 2D MEMS scanners are used in the PicoP display

engine that powers Wearable Displays, Vehicle DisplaysPicProjector

Displays.A1D MEMS scanner,as used in the ROV Scanner, oscillates

along one axis only and is useto capture a bar code image.



The 24th IEEE International Conference on Micro Electro

Mechanical Systems (MEMS 2011) is one of the premier annual

events reporting research results on every aspect of microsystems

technology. This Conference reflects the rapid proliferation of the

commitment and success of the microsystems research community. In

recent years, the IEEE MEMS Conference has attracted more than 700

participants, 800+ abstract submissions and has created the forum to

present over 200 select papers in podium and poster/oral sessions. Its

single-session format provides ample opportunity for interaction

between attendees, presenters and exhibitors. MEMS 2011 will be

held in Cancun, Mexico on January 23 - 27, 2011 at the Hilton

Cancun Golf and Spa Resort.



APPLICATIONS

The applications of MEMS devices are manifold but due to their size and

supporting functions they are hardly ever noticed by the average end-user.

The first applications for MEMS devices in the 1990s were inkjet-printer

nozzles followed by ESP (Electronic-stability-program) for the automotive

market and acceleration sensors actuating the airbags in cars. At present a

new mid-range car contains something like 40 MEMS sensors upwards, for

Tire-Pressure-Monitoring, various sensors for airbags, driver presence

detection etc. Also in the last 5 years MEMS devices have started to

penetrate the consumer-product markets with gyroscopes in digital cameras

and navigation systems, acceleration sensors in game console controllers

and mobile phones. This trend of consumer electronics driving the MEMS

market is expected to continue with the sensors increasingly being used for

assisted living and identification applications.



DIFFERENCES BETWEEN THE MICRO- AND THEMACRO-WORLD

Imagine you have a box filled with several glass marbles. Now you give

the box a good shake and place it on a table. When opening the box now,

where would you expect to find the marbles? Well, our everyday

experience tells us, they will be on the bottom of the box.

Now imagine we use the same box but replace the glass marbles by tiny

ones with a diameter of several micrometer (the thousandth part of a

millimetre). Now we close the box again and give it a good shake. When

opening the box now, where would you expect to find the marbles?

On the bottom again?

This is where our macro-world experience mislead us. The marbles would

be equally distributed on each surface of the inside of the box, sticking to

bottom, side-walls and the lid. This is due to the fact that when reducing

the size of a body to micro-dimensions the gravitational force becomes

more and more unimportant compared to other forces acting on the body.

More specific, the gravitational force being a volumetric force scales with

L3, whereas surface forces like the electrostatic force scale with L2. This

means when reducing the dimensions of a body by a factor of 1000, the

gravitational force is reduced by a factor of 1000-3 = 10-9 whereas the

electrostatic force is reduced by 10-6.

Therefore, the weight of a body can be neglected in almost all instances



when dealing with MEMS devices, except in special devices such as

accelerometers.

The other major differences when dealing with the world of MEMS are

Surface tensions, which causes surfaces to stick together and is a

common critical failure for MEMS devices.

Mixing of fluids is very difficult on a micro-scale as most fluid flows

are laminar rather than turbulent. Special designs are required to mix

two substances.

The stability of manufactured structures. When looking at MEMS

devices often they look as if they can impossibly survive, such as

bridges which are just 0.5 um thick, 40 um wide and 1000um long.

(In the macro world this would equal an unsupported bridge 0.5 m

thick, 40 m wide and 1 kilometer long, which would collapse at once

due to its weight).



MANUFACTURE PROCESSES

Most of the MEMS manufacturing technologies where originally

developed from existing semiconductor manufacturing processes. Over the

last 20 years, these have been adopted to meet the specific needs of MEMS

devices.

In general MEMS manufacturing technologies can be divided into these

categories:

Bulk micromachining, the first MEMS manufacture technology, in

which the Silicon wafer is etched to create structures such as groves ,

bridges and apertures with near 90 degree sidewall angles.

Surface micromachining, which uses predominantly additive

processes using the Silicon wafer as substrate. Devices formed using

surface micromachining tend to be considerably thinner than bulk or

HAR devices.

High aspect ratio micromachining (HAR) combines some of the

aspects of both surface and bulk micromachining . A process which

is commonly associated with this technology is the DRIE-process

(Deep Reactive Ion Etching), w hich allows for silicon structures

with extremely high aspect ratios through thick layers of Silicon



(hundreds of nanometers up to hundreds of micrometers). This is

achieved through a cycled etch process in which the deposition of a

passivation material on the sidewalls of the etched material and the

actual etching process alternate.

Specialised processes for niche applications.



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

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