mems technology - DSpace at CUSAT

Transcription

MEMS TECHNOLOGY
SEMINAR REPORT
Submitted by
ARVIND KUMAR JHA
in partial fulfillment for the award of the degree
of
BACHELOR OF TECHNOLOGY
in
COMPUTER SCIENCE & ENGINEERING
SCHOOL OF ENGINEERING
COCHIN UNIVERSITY OF SCIENCE & TECHNOLOGY
KOCHI-682022
OCTOBER-2010
Division of Computer Engineering
School of Engineering
Cochin University of Science & Technology
Kochi-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
Head of the Division
MS. PREETHA M S
Seminar Guide
Micromechanical System for System-on-Chip Connectivity
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.
Division of Computer Engineering ,CUSAT
1
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
2
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
3
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, biomedical 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.
4
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
5
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.
6
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.
7
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.
8
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.
9
MEMS
Acoustical
Array
Module
MEMS
Socket
Interface
Analog CMOS
Signal
Conditioning
CMOS
A/D
Converter
Digital
Digital
Array
SoC
Signal
Beamforming
Control
PCI
& Beam
Processing
Interface
Bus
Steering
Engine
Figure 3: Block Diagram of Hearing Aid Instrument
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
10
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
11
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
12
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.
13
Figure 5a. Top view of MEMS micropackage
14
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
15
Figure 6. 3D model of MEMS microbus card
16
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
17
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, lowcontact 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.
18
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.
19
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.
20
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.
21
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.
22
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.
23
DIFFERENCES BETWEEN THE MICRO- AND THE
MACRO-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
24
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).
25
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
26
(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.
27
ADVANTAGES AND DISADVANTAGES
ADVANTAGES

High efficiency

Cost effective

Flexible

High accuracy precision
DIS ADVANTAGES

Complex design

Complex fabrication procedures
28
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.
29
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
30
BIBLIOGRAPHY
1. www.darpa.mil
2. www.sanyo.co.jp
31

mems technology - DSpace at CUSAT

Transcription

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