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Today I will discuss on applications of MEMS and Microsensors. In the first class already
I have told you that there are various applications of MEMS in different spheres of life. For
example, in military, in aerospace, in entertainment, in industrial control, in biology, like that
lots of applications are there and today I will discuss some of the applications in detail.
And details of the devices made using the MEMS technology and sensors will be discussed
later on in individual classes on sensors and microsystem.
And you can see in the picture there are some structures which are very small in size, which
were earlier made using some mechanical engineering devices machines like lathe machines, grinder,
polisher, and etcetera. And here you can see the structure shows here, some gear train,
so lot of gears are connected and they can rotate in clockwise as well as anticlockwise.
And you can see different teeth are there and they are coupled from one ring to another
ring through those teeth. And using some electromechanical energy or electrostatic drive you can have
movement of the individual wheels and as a result of which the other wheels also will
rotate either in clockwise direction or anticlockwise direction. And these miniature structures
have been developed using the MEMS technology particularly micromachining. In some cases
they use bulk micromachining and in some cases they use surface micromachining. In this side,
if you have an idea of the size of the flexures or size of the wheel, the length this is 10
micrometer as shown here. So now, the overall the dimension or wide width of this the beam
will be nearly say 80 to 100 micrometer. And similarly here you can see one pivot and all
those pivots are made using either bulk or micromachining technology. And obviously you
can see, if there are different layers are there, all the layers are individually fabricated
and then they are bonded together to have the complete structure. And this is a mechanical
link and mechanical components are coupled with each other so that the complete structure
is obtained and you can have some mechanical actuations or movement using either magnetic
drive or electrostatic drive.
In the next figure, you will see another structure this is, these are again gear trains and is
a basically is a part of mechanical digital to analog converter. You have come across
the term DAC in case of electronics, similarly in case of mechanical area, mechanical arena
also one can have DAC digital to analog converter. Here it means that, digital means a discrete
movement and analog means continuous movement. So the mechanical structure when it needs
continuous movement, then we call it as analog mechanical movement or mechanical signal coming
from that and it is some jerk or some discrete movement is there, with small time interval,
if some mechanical movements are there again it stops so we call it is a digital mechanical
movement. So from a jerk to continuous movement, the jerk frequency may be very small or very
high, you can adjust that, so depending on that you can have some continuous motion of
the mechanical gear, mechanical train. And that can be done using some links or some
wheels which are connected you can see here, one to other, then other and this is a another
layer, some kind of say actuator things, so they are interlinked and these are fabricated
in a lab in Sandia National Lab. So they have successfully done a lot of mechanical micro
structures and with those micro structure they can drive some of the micro mechanical
system.
Now in another picture I can show you some of the hinges. So these are scissor hinge,
again this length is ten micrometer. Obviously you can imagine this particular side is locked
of inch by inch but it is at the best few millimeters by few millimeters. And there
are two kinds of scissor hinges are there and these are very useful in any of the mechanical
systems so these are only micro structures.
Now, here pair of thermal actuators is also shown. That means here actuation is done with
the help of not magnetic energy or not with the help of electrostatic energy but with
the help of thermal energy. So thermal energy, there are lot of materials which can expand
if you apply thermal energy. And if you make a very small steep and thin, thickness very
thin so then, those beams will bend or you can applying the thermal energy, you can change
the shape of these flexure. For example, you have seen the biometallic structure, different
thermal expansion coefficient. So if you apply thermal energy, so they will take some shape
depending on whose thermal expansion coefficient is higher and which is lower, how you are
placing it like that. So in a similar fashion if you make some thin sheet of the biometallic
structure, there if you have applied thermal energy, so then if some flexure takes the
shape of some bend and consequently if it is linked with some of the other mechanical
structure, so they will also started moving. So that means some actuation can take place
by using the thermal energy. Earlier we have seen in the motor that is the MEMS micro motor,
there electrostatic energy is used for some sort of movement. Similarly thermal energy
can be used for movement. So everything you should remember is not in a very high energy
is a small energy and slow movement and slow actuation and that slow movement you can increase
the movement just amplify those thing by using the different shape of the gear, wheel etcetera.
So that is similar principle that used in mechanical engineering mechanical drive also.
Now here, I will show you some of the sensors now. And the picture shows the pressure sensor,
piezoresistive pressure sensor. That means here, the change of resistance by changing
this trace of strain is the basic principle of making this sensor. The silicon is a very
good mechanical material and not only is that silicon a piezoresistive material, that means
here, this is the cross sectional structure of the sensor, this is the top view of the
sensor. Now, this is the basically beam and this is the membrane and here n type epitaxial
layer, 8 to10 micron thick epitaxial layer is here. There what we have done, so we have
defused the p type impurity into the n epitaxial layer to make some resistance. And those resistances
are made, you can see this is the membrane and at the edges of the membrane the resistances
are made. The reason behind it is that so and if you apply some pressure on the membrane,
the membrane will bend it will deform. And if you do the simulation on the mechanical
simulation or if you do the strains analysis of that particular membrane, then we will
find that maximum space region is at the edges of membrane. Details of that simulation results
I will show you when I discuss in detail the pressure sensor its principles and fabrication.
Now here, the piezoresistance are fabricated at the edges of the membrane and all these
piezoresistance are connected in a Wheatstone's bridge like this. And if you apply signal,
this point to this point with respect to ground, if you apply certain voltage here, so we obviously
as per the log of the Wheatstone bridge or principal of the Wheatstone bridge you know,
if all the resistance are same, then you will not get any output voltage it will be low.
Now any of the resistance is changed, others are fixed then the bridge will imbalance and
it will show some output voltage. So now depending on the how much pressure we are applying from
the top, then the beam or membrane here will deflect down or if you apply pressure from
the top, so it will deflect downward. So now, as a result of which some of the piezoresistance
will experience tensile stress and some will experience compressive stress.
So, as a result of which in some cases resistance will increase, in some cases resistance will
decrease. So in that case, the four resistance will not increase or decrease in the same
fashion. Some will increase and some will decrease as a result of which the bridge will
be unbalanced and you will get output voltage. So how much pressure we are applying on the
membrane, depending on that, we will get the output voltage. So the output voltage is directly
proportional the pressure applied on the membrane. So this is the basic principal of the piezoresistive
pressure sensor. And at the same time all the resistance were, when you are connected
in an electronic circuit like Wheatstone bridge so you have to have the whole structure must
not float you have to have some ground plain ground connection. So here in this structure,
you can see here the blue color n plus diffusion, so that here the substrate contract is there.
So here the n plus n epilayer and there if you want have only contact, you have to have
n diffusion.
So this is the n plus diffusion so that you will have the substrate contact and this substrate
you can keep it at certain floating, they should not float, floating potential you should
not keep the complete substrate. So in that case, if you plotted then the outputs, the
reading may not be stable, it may flexure. To have a stable output, we have to keep this
substrate and a fixed potential maybe it is the ground potential. So this is the complete
structure of the piezoresistive pressure sensor and here is the picture or microphotograph
of that piezoresistive pressure sensor. So another kind of pressure sensors is available.
They are fabricated based on the capacitance change principal and those are known as the
capacitive pressure sensor.
Now in this diagram you can see the capacitive pressure sensor. This particular sensor will
have three parts. Say one part is the silicon diaphragm on membrane which will act as the
sensing element, the second part will be a cavity which creates a capacitive gap and
third part a metalized glass plate provides the capacitive reference plate. So these are
the three parts in this capacitive pressure sensor. So here what we do using the MEMS
technology, we fabricates some parallel plate capacitance. So parallel plate capacitance
means, there will be two electrodes and there will be a gap or some di electric in between
the two electrodes. So one electrode will be bottom the glass plate which is coated
with conducting film. So that is here metalized glass plate will be the one electrode and
top electrode will be a membrane. This is the thin diaphragm. So thin diaphragm, the
inside of the diaphragm if you coat with metal film and top side of the bottom glass plate
if you coat with the again metallic film so then, those two will act as a parallel plates.
So in between those two plates, there will be either here or you can put it some other
directive material so better here with certain pressure. So now all you can keep it atmospheres
pressure, so that the atmospheres pressure will be the reference pressure.
Now if you apply pressure on the diaphragm, then the diaphragm, the top diaphragm, this
will the deflect it pressure is given from the top so it will deflect from the bottom
and from the top to downwards. So as a result of which the gap between the bottom glass
plate and the top electrode will change. And as a result of which the capacitance also
will change. So depending on the deflection of the diaphragm and that deflection again
depends on how much pressure you are applying at the top. So accordingly the capacitance
will change. So now the change of capacitance you have to measure. So obviously you have
to have the signal pickup circuit. So that means here, the change of capacitance must
be reflected change of either voltage or some other electronic parameters would change there.
So either you can use a capacitance bridge or you can connect the capacitance in a circuit
were the circuit frequency will change, by the change of capacitor. So you can have a
calibration curve change of capacitance versus the frequency change if you apply tuning circuit
at the output that also is possible. So different the signal conditioning circuits are available
different signal pickup circuits are available from the sensor. So you can use any of them,
so that we will discuss later on in detail how the change of capacitance is going to
change in voltage current frequency, any of the electronic the signal parameters. So this
is another kind of capacitive another kind of MEMS pressures sensor where the basic principle
is a change of capacitance by changing pressure.
So another device here I would like to highlight is inertial sensors. So inertial sensor are
two kinds of sensors, there is only actuator sensor and another is a rotation sensor. Rotation
sensor name is called the gyro sensor. Now here, the picture shows the accelerometer
and that accelerometer was developed by Analog Devices, a renowned company in USA. Now in
what is the basic principle the basic principle of this particular the actuator is that, you
can see here the comb like structure. So in the comb like structure there are few electrodes
are fixed and now these two sides, these electrodes are fixed. At the peripherally, these electrodes
are fixed here and in between you see this, a vertical rim and there are some fingers
are there. Now if you fix that, these are the fixed electrode. And if you whole structure
is fixed but this can move. So with the acceleration, if you applied acceleration in this direction,
so because of the mass of this structure, this will go down.
So as a result of which you can see the gap between the top electrode and the middle will
increase and the bottom electrode and the middle electrode will decrease. So that means
these are basically the two capacitances C1 and C2. One capacitance because of the increase
of the gap will decrease and in the bottom capacitance, because of the decrease of the
gap the capacitance will increase. So that means one is the capacitance will increase
in other case capacitance will decrease the differential mode capacitance. So basically
when there was no acceleration, the gap between the middle and the top and the gap between
middle and the bottom will be the same. So as a result of which capacitance of both the
top electrode and bottom electrode with the middle electrode will be the same. Now because
of the acceleration movement of this structure, so in this direction, so sometimes it will
bottom capacitance will increase and sometime top capacitance, that means capacitance with
top electrode will increase. So as a result of which, that if you can have
some change of capacitance, some will increase and some will decrease and with convenient
circuit along with the sensor you can sense how much is the acceleration. So that is,
this particular comb like structures is made using surface micromachining technology. And
that has been fabricated by analog devices at the beginning and they are marketing this
kind of the combed structure accelerometer which is based on change of capacitance with
acceleration. Now this kind of accelerometer can work in the range of 2 to 50g, g is basically
acceleration due to gravity. Cost of each sensor here approximately 10 US dollar per
sensor and you can make the design so that it can measure along the three axis; the acceleration
x axis, y axis and z axis. It has got lot of application in automobile sector, in industrial
sector, consumer and military. And individually, the area wise, its applications in automotive
within the airbag, alarms, ABS, door locking and brake lights; industrial application earthquake
detection, gas shutoff, machine, health; consumer application navigation, computer peripherals,
sport devices; military application navigation purpose, munitions and simulation. So these
are various kinds of application of inertial sensors.
Other kind of inertial sensor is a rate grade inertial sensor which is known as gyro sensor,
which sense the rotation and here this kind of sensors are used in case of the munitions.
For example, in in civil applications or in different kind of toys or this entertainment
electronics you can see where some rotation is required. That means, the for example the
joystick, you rotate joystick so there also some kind of rotation sensor is required and
it will use this rate sensor. For example, in case of missile, there also the gyros are
very much essential, in avionics the rotation sensors are in are important component and
part of that system. So here, this picture shows some rocket 2.75 inches rocket which
is very small inside and there you can have you can see here, this is the rate grade inertial
MEMS sensor and this is the picture of the chip you can see how small it is and it is
fixed at this head of this rocket and so that when it makes movement, then from the ground
control you can rotate the rocket which direction it will move. So that can be controlled remotely
by using this acceleration sensors or rotation sensors.
So now, another application of those the MEMS is a micro resonator. So here you can see
a picture of micro mechanical resonator with non-intrusive supports and it reduces the
anchor dissipation and as a result of which you will have higher Q and this resonator
has been developed. And it works at 92.25 Megahertz is a resonance frequency and it's
Q is 7450 and you can see here, these are basically drive electrode and drive electrode
are given by electrostatic energy and these two are support beam and is an extra, this
is the flexures and these are the anchor and the anchor is supported with a beam and this
beam length is 10.4 Micrometer and it's width is thickness is 1micrometer and width is in
the range of say about 2 to 4 micrometer. So this anchor is fixed here and now the whole
structures is a resonate depending in how much the drive you are applying from this
electrode. So the length, dimension is mentioned here the width, length and thickness and you
can see the total structure will be say 1 millimeter by 2 or 3 millimeter total dimension
and it will resonate at a frequency of 92 Megahertz nearly and its Q is 7450 and 10
Millimeter the pressure.
So these are really useful in many applications and now this picture shows some RF filters
which can be tuned. That means, filters tune means you can change its pause band or stop
band frequencies. So any kind of the filter you require some the passive components like
inductive and capacity particularly it is in RF filter, so we do not use resistances,
all though RF filters are normal made using some capacitance and inductors. So these are
the tunable filter structures where if you want to tune the frequency response of the
filter, obviously you have to tune the value of the capacitance. So tunable capacitance
can be made here are some of this structure you can see here. So here, how the capacitance
are made, so here is you see the electrode, top electrode, the bottom electrode and these
are directive layer. Now the capacitance value can be changed if we change the gap between
the top and bottom electrode. Just few minutes back I mentioned that. Now, for that you have
to have certain mechanism by which these top electrodes can go down like this. So that
means, that going down that means bending of this top electrode or deflection of the
top electrode can be done by certain techniques.
One of the techniques is applying some electrostatic energy or applying some if you keep it in
some closed chamber and if you increase the pressure, so pressure also deflects that.
So now by some mechanism if you can change the gap, so capacitance can be tuned. So that
capacitance you can connect with this filter, so as a result of which the total frequency
response of the filter is changed. So here, you can see the total wafer and in that wafer
the tunable capacitance is one chip looks like this and the cross section diagram is
like this and here you can see variable 6 bit MEMS capacitors are fabricated. There
are 6 capacitance are there and its values change depending on the how much area top
and bottom electrode you are allowing. So here in the left side you can see some picture
those are the high Q indictors that are also being made using the MEMS technology now a
days and those indictors and those capacitors are connected here to get this tunable filters.
So here is the microphotograph or the filter, the circuit is shown here. So now the values
of the capacitance are mentioned also, it ranges from 1.16 Pico Farad to 2.25 Pico Farad
and its inductances are in the order of the few Nano Henry. So these are possible now
a days using MEMS technology and as a result with which the RF filters, RF switches are
being fabricated using the MEMS structures.
Now here are some applications and this is a pressure sensor belt on jet plane. So here,
in a jet plane, in the belt lot of pressure sensors are corrected in different arrays.
And those pressure sensors normally measure the pressure outside of the plane as well
as inside pressure is also monitored. So for that, outside in the belt there are lot of
thin film or the micro machine, the pressure sensors are indicated, the picture is shown
here. And those capacitances are connected with some circuits and those circuits are
some kind of ASIC and there are interconnect each other and how the interconnections rounds
to the surface of different external surface of the jet plane is shown here and obviously
when the jet plane moves, it moves with a tremendous high speed as well as the off side
pressure is not atmospheres pressure, you now if a depending on the height the pressure
also goes down. So that monitoring of the pressure is very important so that inside
pressure will be control and inside pressure you have to keep in atmospheric pressure for
survival and outside pressure changes accordingly. So the movement of the total structure how
will guide it, how will the make this turn, all everything depends on the pressure. So
in each part lots of pressure sensors are fixed in different direction and different
places of the body of the planes. So accordingly you can get the monitoring of the pressure
at different direction.
So another application is the actuators for aero dynamic control. These are some of the
actuator array on the leading edge of the wing and of the mirage fighter. So in the
modern, all kind of the all kind of the avionics or airplanes, they are taking advantage of
miniatures and level operation of the miniature size and level operation of the MEMS devices
and here are some sort of actuators is shown. These are flexible sensor stroke actuator
scheme something like that. So it can deflect, it can change its shape depending on how much
some kinds of materials are safe memory alloy. So its shape can change by changing some magnetic
energy, so that can be used as actuators also.
So these are some examples I am showing here had another example so some jet engine there
also they use some strain gage and which will have 10000 times sensitivity of metal foil
strain gage. So strain gage is a very important part of any of the civil structures and they
earlier are the metal foil strain gages were used and they have been replaced by the MEMS
strain gage. And some of the structures is shown in this diagram shows the cold flow
and hot flow. Depending on that, this shape will change and as a result, if the shape
changes, how much this strain is developing the structure, that you have to measure. So
that can be used with the help of some thin films material on some membrane or flexures
and accurately so its sensitivity also increases nearly 10000 times more than the metal foil
strain gage.
So another application here is the chemical sensing, that is remote chemical sensing.
So that is also possible and here you can see the structure here, this is silicon wafer
and the individually adjustable array of driver electrodes are fabricated on the silicon wafer
and on silicon there is a silicon dioxide, on silicon dioxide top this the array of driver
electrodes are formed. And then in this direction, you can see lot of deflectable, the micrometer
grating elements. Basically the gratings are made using the MEMS technology. And this grating
when a broadband light is incident over the grating, the grating will defect and the deflected
lights is analyzed using polychromatic spectrum analyzer. So you can have the spectrum of
this and intensity versus if you look into that this the spectrum, then from this pick
you can you can identify what are the different kinds of chemicals are available in that particular
area.
So by using remote energy, for example, some of the chemicals available on the surface
or in environment can be detected using this miniaturized MEMS polychromator. So one of
the advantages is, programmable and you can use in a remote way so that in the distance
place where you cannot go, those particular location you can have some idea regarding
the chemical composition or regarding the hazardous gas composition available in that
particular area. That is using the MEMS polychromator is the device and that is used basic principal,
is the diffraction of light and that diffracted light is analyzed using this spectrum analyzer.
And the frequency response, that means the peaks you can identify from there you can
guess the composition of that those chemicals and another things.
So now here, another application is Pico Satellite. Pico Satellite, there all the components mostly
are the RF switch, RF components are there and the first demonstration of the Pico satellite
was made by the USA Air Force and Machine System Center in January 2000 in 26 January
2000, two Pico satellites are linked by 30 meter long. This is the tether and it was
monitored by mother ship OPAL Stanford and it was just 7 February 2000, it was first
demonstration was being made and it operates MEMS RF switches in space and these are basically
for tracking and communication this is the tether 30 meter long.
And these are the small kind of switch which is shown also here the MEMS RF switch. The
complete the diagram here is a basically Pico satellite and its size you can see 2.5 by
seven point by 10 centimeter and its total weight is 250 gram, that is the weight of
the complete satellite and inside at the same time you can see a switch and that is MEMS
RF switch and there are three satellites; one, two, three, everything is controlled
from the ground station here. So one advantage is the less weight you can see 250 grams satellite,
that it is known as a Pico satellite. Now a day the satellites widths are in the range
of plutons.
So if you reduce into the few grams, so automatically the launching of satellite will be very easy.
And there the cost is less, well requirement is less and only thing is the reliability
how long it will work, that is need to be tested but lot of work is going on in this
direction to make the Pico satellite and to see a its reliability and how much information
it can provide at the ground to monitor the environment and other things. So these are
the Pico satellite program, there also MEMS is plying a major role in terms of this switches,
in terms of the filter, in terms of the RF, what about the RF circuit you require and
that are being made using to MEMS technology.
Now here is the automobile application is the picture you can see the smart car and
here lot of sensors MEMS sensors are used and some of the picture are shown in different
places. Here you can see the silicon nozzle for fuel injection and how the nozzle, this
is the picture of a nozzle 50 micron by 50 micron and this is the area of nozzles which
is used for fuel injection. Here you can see another sensor which is the structure, which
is basically the wheel and it can depend on the nozzle fluid and it can rotate here also
by fuel. This is the fuel pressure sensor. Here you can see the airbag; micromachine
accelerometer airbag is here. So for example, these are thin pressure sensors which are
connected, which are fixed at the tyre.
So that tyre pressure can be continually monitor and these are the exhaust gas sensor. At the
back you can see some crash sensor; so that it can it can give you some signal before
crash so these are the fuel level sensors the airbag side impact sensors are here, side
impact. So air condition compressor sensor is connected here, so the pressure sensors
are inside in not only wheel but also the outside pressure, inside pressure you can
monitor. Mass flow air sensors is connected here. So you can see full of sensors are indicated
in whole body of this automobile so that it can safely run without any problem as well
as without any danger. Before any danger comes, so it can give some signal to the driver also
so that he can take care of.
So lot of sensors MEMS sensors are used in automobile. Here particularly one sensor I
am highlighting, that is the airbag sensor. That airbag sensor is basically the one safe
guard it protects from during accident the airbag blows and it prevents accident of the
driver whose is sitting near the wheel. So that that particular sensor is day by day
a great demand and different countries governments are making compulsory rule so that all the
automobiles must have the airbag sensor inside the car. So that sensor is in great demand
and that can be fabricated using the MEMS technology this is basically the acceleration
sensor and either by capacity or piezoresistive we can make it.
So now, this is a health monitoring application, you can see the picture here micromachined
transducer. And here again some kind of pressure sensor which can sense the blood pressure,
is you can connect here that is the blood pressure sensor is inside we will show here.
And not only that blood pressure, here is one sensors is connected here, which can simulate
the muscle, simulator. Another sensor is used which is here which is pacemaker. So pacemaker
is another kind of pressure sensor, so that is also embedded inside the different parts
of the body for a health monitoring purpose. Biological applications are enormous.
Here is another pressure sensor which is connected at the tip of a catheter. And this total guide,
well length is nearly 1.8 meter and a total thick side which is connected here, so that
is nearly 100 micrometer by 150 micrometer by 1300 micrometer and total diaphragm length
of the sensor is 130 micrometer. By 130 micrometer it can measure the pressure in, is 25 to 300
millimeter of mercury and accuracies plus minus 2 millimeter and it can work in the
temperature 935 to 40 degree centigrade and it basic principle is piezoresistive. So this
kind of the catheter tip pressure sensor is used for medical diagnostic or during the
surgery. Doctors are also using the catheter, some kind of pressure sensor is a surface
micromachine pressure sensor that is used for cardiovascular pressure measurements.
So another fluidics application and fluidics are liquids or gasses, so those flow measurements
can be done using some flow sensors. And it has got enormous application not only in biology
but also in fluid dynamics. So some of the applications are drug delivery systems in
DNA sequencing, drug and gene discovery, and its size is very small about say 170 centimeter
cube and its weight is 300 gram that is specification of the mass spectrometry. The chip that is
also for analyzing any of the biological fluidics you need those kinds of devices.
So some other biosensors are here. These are cell based biosensor with microelectrode array.
These are the typical cells and the cells may contain some of the chemicals or agents.
And these are the some channels and some electrodes are there, which you can apply certain field
here. So as a result of which they can decompose and you can analyze those composition using
some technique. And their main advantage is the reasons requirement is very small and
you can have reliable measurement on a small miniature from small body. So in this picture
you can see some of the neural probes, silicon neural probes. These are used for the neurology
application as well as some neural researches is lot of neural researches taking place in
different labs. So for then they need some neural probes and these are successfully made
using the silicon technology. The tip of this neural probe are of the order of shape 1 or
2 or 3 micro micrometer and these are successfully made using the MEMS technology.
These are that DNA chip you can see total DNA chip and each cell is shown is here, lot
of the silicon nitrides are used as a passivation layer and DNA synthesis DNA analysis are being
made using the DNA chip and these are the electrode arrays and this is the cross section
of the individual the cell and in bio MEMS, I will discuss a little bit in detail in the
bio MEMS. In different class there I will again explain the detail function of those
DNA chip.
Now, these are some of the micro electrostatic comb drive motors which also I have shown
in earlier. So these are the comb drive, electro static comb drives and these are the motors
and it requires some of the electrostatic energy and it is an electrostatic drive micromotors
and I have explained earlier the functioning of this particular comb drive motors.
So here is another application, this is the microvalves and micropumps. So you can see
here, in this particular picture you can see 3 or 4 pieces 1, 2, 3 and 4. Now that is,
2 way check valve. We see individual pieces are made separately using the MEMS technology.
Now all the 4 layers now bonded using some special kind of bonding machine. After aligning,
you can make bond by silicon to silicon or you can make bonding by silicon to glass and
if you bond, then you can have the complete structure. Now here you can see, so this is
the actuation chamber here and these are the electrodes; this one and this one. Now here
you can see the basic the valve, the basic pump diaphragm is here. So now these are 2
inputs inlet and outlet. Now this top portion is the actuation unit and the bottom portion
is the valve unit. Now, how actuation is being made? Now, you see here that top and bottom
these are, if you apply certain this is fixed. Now this is some kind of membrane. Now if
you apply certain electrostatic feel, so that the membrane can be attractive with the bottom
electrode top electrode. So that means there is a deflection here so this membrane is attracted
towards the top so as a result of which the volume in the chamber will increase. See the
volume in the chamber increases, so this valve will open it because of the pressure. Because
here initial it was closed, now you suck it. So here from outside pressure the valve will
open so if the valve will open so the fluid it can go here.
Now, after the fluid enters into the chamber, then you do one thing, this, the flexure you
release it. That means whatever the electrostatic energy you applied you just stop it. So, automatically
what will happen? This, the middle diaphragm will take its own shape. So it will go downwards.
So a result of which it will apply some pressure on the fluid here. So then what will happen
because, this valve opens in this direction it will be closed if you apply pressure in
downward. So the valve will be closed. So but this valve will open. So when this diaphragm
goes downward, so the valve open, so liquid goes in this direction. So by applying, that
is why this unit is known as the actuation unit, so in the actuation unit by changing
the potential, electrostatic potential or by applying or not applying the electrical
field, so the diaphragm flexure you can attract toward stop or you can release it so as a
result with it the liquid can suck and in the other valve it can eject. So this some
kind of the microvalve and micropumps using MEMS technology you can easily make it.
So here had another application, which is the micro thruster application it has been
developed at out laboratory. So here you can see, there are again 2 pieces; the bottom
is the silicon wafer which is safe like say the U shaped the some silicon is etched and
this is structure some immediate heater has been fabricated. This is the heater, micro
heater. So now there is another wafer, top wafer. You safe like that now you bond these
2 wafers by bonding machine. Now this is a vaporizing chamber. Now propellant, if you
insert the propellant here through a narrow tube, now if you heat these resistances by
applying current to the resistance, so the heat will be generated. As a result of which
here, the propellant which is inserted here, that will vaporize. Those propellants will
again, when it will vaporize, so it will exist to at nozzle. So when it exists to the nozzle,
it will apply some back thrust. It will apply some back thrust because through that nozzle
the wafer is ejected, as a result of which it will apply Newton's third law of motion.
In the high speed the liquid is rejected, so as a result, thrust is develop in the opposite
direction. So that is that is why it is known as the micro thruster and thrust force is
200 micro neutrons you can apply and total size is 12 millimeter, by 8 millimeter, by
0.6 millimeter. So this micro thruster is used proper positioning of the satellite in
space. Now here are some applications I am highlighting in different areas I am naming.
So in defense application or inertial navigation on chip for munitions distributed unattended
sensor for asset tracking border control environmental monitoring and other cases. Integrated fluidic
system for miniature analytical instruments, hydraulic and pneumatic systems, propellant
and combustion control. Weapons safing, arming and fuzing to replace current warhead and
weapons systems to improve safety, reliability and long term stability.
So, other applications are embedded sensors and actuators, mass data storage devices,
integrated micro optomechanical components, to identify the friend or foe systems, displays
and fiber optic switches. Here are MEMS for home appliance. Accelerations sensor or tilt sensor, it used in iron position control
vibration sensing in washing machine. Biochip is used in food control, chemical sensor in
water quality, electronic nose I will discuss in detail later on. Atmosphere monitoring,
flat panel for display, microfluidic chips dosing systems in washing machines, pressure
sensor so water level in washing machines, temperature sensor used in cooking, smart
dust is used household appliance monitoring. So MEMS in IT and entertainment. Here again
joystick and hard disk stabilization, there the accelerations sensors are used. Gyro is
used for camera stabilization system, hard disk drive heads in data storage, inkjet print
heads printing, optical mouse for computer mouse and micro displays projection portable
systems. Other area is telecommunication. There micro mirrors used in switching and
optical attenuation, V grooves used for optical fiber alignment, tunable filters are used
for tunable lasers, switches for signal routing, antennas for transmission and reception, inductors
and tunable filters also have shown earlier.
So this is in process control and instrument in application. Accelerometer and tilt sensor
again for vibration monitoring. Biosensors quality control in food industry, biosensor,
gas sensors in oil platforms, magnetic sensor is used in rotation measurement, micro pumps,
pressure sensors and temperature sensors has got enormous application in process control
and instrumentation. And medical and biomedical. They are active patches for drug delivery,
hearing aids for hearing, accelerometers for heart pacemakers, implantable insulin pump
for drug delivery, needleless injectors again for drug delivery, smart pill for drug delivery,
pressure sensor for blood pressure. These are all biomedical applications. So these
are the few applications I mentioned, so other applications I will discuss when other topics
I will discuss in detail. Some typical applications also I will highlight during those time. Thank
You.
So today, we will discuss on materials which are used for MEMS
and microsensor devices. So you know, materials are the fundamental things or basic things
based on which we develop various kinds sensors. While exploiting the properties of materials,
the materials are of different class and all those classes little bit I will discuss in
today's lectures. So, the materials which are used for MEMS are basically from different
group. Some group belongs to the metals or metal alloys.
Some group are metals belongs to semiconductor particularly silicon, and metals and metal
alloys other than those, sometimes we use some ceramic materials also and polymers material.
So these are the 4 classes of materials which are used for making various kinds of microsensors.
Now let us concentrate first on metal and metal alloys for MEMS. So we use thick metal
films for those devices which are used for structural materials for final sensors and
sometimes it is also used as the mould which is inserted into the polymer on ceramic micromoulding.
What do you mean by micromoulding and what are the moulds? That I will discuss during
the micromachining class? These are the techniques by which you can make the mould or micromoulds
that is in chapter micromachining. Now, other than this micromoulding there are other techniques
which are mainly micro electroplating or photo forming. These are used to build thick metal
film structure for different components of the Microsystems or MEMS devices. Electroplating
is another technique which is used for making thick metal films. Thick means I want to say
several microns may be 20 micron, 30 micron, 40 micron in that range.
If you want to deposit the more than 10s of microns then, conventional the thin film evaporation
technique or sputtering technique cannot help. With that technique you can get films of the
order of maximum 2 to 3 micron and if you want more than that 10 microns, 15 microns,
20 microns like that, then you have to add of certain techniques, those are mainly the
CVD techniques and the electroplating technique. Electroplating technique is getting lot of
importance now a day because, this particular technique is a low temperature process and
that stage is known as thermal stage and because of that trace, some of the sensor behavior
or sensor output may also change. So that also you have to keep in mind. So, other than
the mechanical stress, another stress is also involved which is known as the thermal stress
hardness is another mechanical property. Physical hardness of the material is characterized
by Knoop hardness constant and is in kg per millimeter square. Knoop is basically name
of a scientist; he investigated that particular property of the material. That is why it is
characterized by Knoop hardness and it is defined by kg per millimeter square.
Now, others are creep and fatigue. These are all mechanical properties. What is a creep?
Creep is basically time dependent and permanent deformation of materials when subjected to
a constant load and stress below or close to the yield strength. It occurs at elevated
temperature and static stress. If temperature is elevated and a static stress is applied,
then this is known as the creep and other property is known as the fatigue. What is
fatigue? Change in material properties caused by cyclic loads at stresses much lower than
yield strength. That means you are applying stress lower than the yield strength, but
if you are applying cyclic stress that means once you are applying stress then release
it, again you are applying stress then release it, again you are applying stress then release
it, in a cyclic way if you apply stress and then release, then the material property that
particular mechanical property of the material will little bit change and that is known as
the fatigue.
As if the material reached its condition, it may not follow the linear stress ten relation,
so that is the fatigue. So these are various kinds of the mechanical properties, the axial
stress, shear stress, the yield strength, brittle, ductile, creep, and fatigue. These
are the various kinds of mechanical properties once you take care of when you are going for
design of any microstructure using silicon or any other single crystal or even using
the metal or metal alloys. So let me stop here today. So in next class I will discuss
on the different properties of the materials which are used for making Microsensors and
MEMS devices. Thank you very much.