 So, the next talk will mainly focus on the MEMS technology, I felt like all of us should know mechatronics engineers basically or who are involved with mechatronics application should know some of the fundamental details of this MEMS technology, it is drastically changing the way the mechatronics is done today. So, say for example, some of the sensors that are based on MEMS, they are much higher performance with much lesser cost. So, we need to know some of the fundamentals of the MEMS technology to evaluate whether this sensor would be better or like not or whatever ok. And maybe you may get into the MEMS in the field itself ok, because lot of mechatronics based things are used for development of this MEMS technology and its characterization ok. So, that way also like mechatronics and MEMS they go very hand in hand ok. So, let us see some of the details of this MEMS devices ok. So, this is the outline of my talk like first we will see what are the MEMS and MEMS and why they are becoming important, what is their importance right now ok. Then we will talk about some materials for MEMS and MEMS, then some of the fabrication processes ok. Here the idea is just to give you the flavor of this technology ok, which is very very different from conventional mechanical way of thinking ok. So, there is basic difference in the technology in basic philosophy of design and I mean development of these. So, I mean the aim is not to get into the design and development, but like give you the flavor ok. What all basic things are happening in MEMS and how the MEMS based sensors and things actuators things can be used for like making the mechatronics application better and lesser costly ok. So, that is the goal. And then we will talk about some of the mechatronics that is going into this MEMS characterization technology and some other applications depending upon like what time permits ok. So, MEMS and MEMS refer to micro or nano electromechanical system ok. So, they are basically mechatronics systems itself like, but at the micro and nano scale ok. And the difference is there like the unlike normal way of fabricating, they are fabricated using something called VLSI technology ok. This VLSI technology those who are electrical engineers they would be knowing it what it is, it is a very large scale integration ok. The basic idea started from the fact that in the VLSI technology we are able to create large number of components. Say for example, you know what are how many number of components are there on the Pentium chip millions and billions ok. So, so there is a technology available to create these many number of electronic components on the on the surface of the silicon wafer. Why not to use this technology to create some of the mechanical components? That is that is a route where this this thing started ok. So, the researchers started like thinking about how we can create mechanical components on the substrate, on the silicon substrate. So, that we can immediately integrate them into the electronics also whatever processing electronics your sensor needs. And then like you will have a wonderful sensor developed ok. So, that is the idea that got started and picked up in the recent years ok. And because like you have processing electronics on board the noise problem is reduced. And because like you are now fabricating very small mechanical components ok, your inertia which is a like a major deciding factor for the response time of your sensor ok. How fast the sensor will respond will depend upon how much mass the sensor in the sensor is getting moved ok. Say for example, you have a acceleration sensor ok. If you have a big accelerometer of this size, there is a lot of mass that is going to be like it should be moved like before your acceleration accelerometer gives a signal. But in the case of MEMS devices if you have very tiny mass, I mean as small as your hair ok, some some that kind of a dimension very small dimension mass if it is moved ok, it will give much better sensitivity ok. It is going to give you naturally because like the frequencies because mass has reduced the frequencies has has gone down gone up to a big extent ok. So, that is the so, so, so, you have a system where you have higher performance or higher high frequency specifications ok. Because of the high frequency you will have higher sensitivity. So, that is why the the high performance is there and because they are bulk fabricated. See you imagine now instead of like having millions of electronics components, you have millions of mechanical components of this kind of a sensors fabricated on the on your wafer. Per sensor cost is going to go down drastically ok. So, there is a there is both performance enhancement and cost cutting which is which is ideal for industrial growth ok. That is why these areas are these areas are picking up nowadays because you have like I mean see industry is always driving for higher performance and lower cost ok. Anything that gives will will will get industry money ok and then that becomes that becomes like a trend in the and then like it becomes established technology that is like a process of technology development ok. So, that is how that is why like these MEMS and M's are getting importance in in today's world ok. So, apart from these like there is there is a apart from what like reduced cost and like higher performance. We can also have revolutionary features and products I mean that people who had not thought of before I mean it was not possible and I mean because this technology is available now we can think of some some very very like tangent kind of applications where I mean it it becomes very easy. So, I will I will give you some of those kind of applications ok. Especially in the bio MEMS area there are lot of applications people are coming up with for bio diagnostics bio drug delivery systems and things like that ok. So, this is a accelerometer chip from this analog devices it is a it is a leading company in accelerometers and we have I mean some of these chips with us then this very small chips ok and that can have higher sensitivity and higher G range sensing and another advantage that they provide is because there is a actuation and sensing on board you can calibrate the sensor in a in a literally a minutes time ok. So, you have the actuator you have the sensor both are there on the on the system and like like say for example, you have used this accelerometer for say a month's together and you you you are not too sure about how the calibration would have changed. So, you can recollect recalibrate in a minutes time because both actuation and sensing is there on board that is another advantage that these MEMS sensors provide ok. Then this autonomous airplane technology like they are using lot of these MEMS basically because like the conventional ways of sensing the direction gyro those those are very heavy I mean. So, so you you need for airborne vehicles ok to have as less weight as possible towards that end like you need to reduce like as much electronics or as much mechanical sensing gyro then all they are really of big size. So, if they are reduced in size and you can do the same job with a small chip of small size I mean that would be that would increase the payload that it can carry in the autonomous vehicle ok. No, no, no these are not in phenometer these are like vibrating gyroscopes ok. There is a vibrating MEMS device and like you you change the direction I mean you rotate I mean give some like omega and it will start vibrating in the perpendicular direction ok. So, so that is a basic principle that it is using ok. This is actuator MEMS in actuators in your day to day use like the inkjet printers they are using this small inkjet actuation at a precise location on your paper to produce like whatever printout that you want to ok. So, this is I mean we have taken this directly from nozzle on the printer cartridge I mean directly from the printer cartridge and if you see the printer cartridge at the bottom you will see some gold I mean I do not know if you have observed it carefully, but it has like that gold plate you will see at the bottom. So, it has actually the ink holes whatever the they are seen 160 micron holes seen in this figure they are they are already there on that plate, but our eyes cannot see that. If you just rub your hand you will get the ink on the hand, but like it is really coming through this very small pores and at the back of this pores you see as in here there are some electrical contacts ok. When you excite that contact ok these are the these are more like these pads gold pads actually contact the other part like where your cartridge is fitted in the printer ok. So, these contacts go to this this pore level and when you when you give voltage in those contacts I mean because of small resistance of a of a thing there is a resistive heating resistance of a ink there is a resistive heating of a ink and the bubble is created because of the heating and that bubble pushes the ink in a in a form of a jet ok. That is the way this process goes on and this we are using day in and day out like I mean printer cartridges. So, already there this MEMS technology is at our door steps actually ok. So, this is another example from Bell Labs like where there is a optical switch to switch between this like say input signal is coming from this fiber and whether to give it out in this fiber or this fiber a switching will be decided by this MEMS best switch. Similarly, this is more of a more I mean kind of a MEMS mirror which is used for switching I mean this is an array of switching the each of the elements shown here is of of this kind ok. And now whether to direct this light coming from this fiber to one of the arrays from the aside I mean things which is placed on the side the which fiber on the side that it can decide based on the angle of this mirror and it can switch. So, that is a switching application micro arrays of arrays of micro motor for switching application. And this is useful in say for example in your networking ok all like optical fibers that carry the signal that can be routed in a different direction by using these kind of a switches. This is just demonstration application for micro motor based on the similar principle to your stepper motor, but with the electrostatic actuation not with the magnetic electromagnetic actuation ok. So, these poles like you can excite in a sequential manner and then like you can have this motor run. And this motor like particularly you can go up to the speeds of like 300,000 or 500,000 rpms is a is a normal speed for these motors ok. Because of the reduced inertia you can see now that you can run the motor at much much higher speeds then it can be possible at the at the macro domain. Now the problem with this is basically the friction and wear like the you cannot run more this motor for more than a minute or so. Because of like lot of friction wear wear takes place and then like your motor gets worn out ok. So, that is the limitation. So, that is why I told you those flexure kind of a ways are more appropriate for MEMS level actuation ok. This is another application where this is useful in endoscopy where you have all the sensing sensor elements are here there is a light in the capsule there is a camera in the capsule and it takes images at a rate of 2 images per second and it will transmit it on a small device pager like device which is sitting on your bed and then doctors can analyze those images later on. So, endoscopy which is so painful process like for patient I mean that can be avoided the pain can be avoided by using this kind of a capsule ok. And this is already FDA I mean federal drug administration has approved this in the US and people are using this product ok. This is another application again this is totally mechatronics kind of a thing where you have mirrors like area of mirrors sitting on a chip and you are processing the light using these mirrors ok. So, these are called digital light processing chips ok. Texas instrument was working like for long time as long as like about 7 and 8 years without anybody's knowledge on this technology and then they launched like I think in 2001 98 99 that time they launched these DLP chips it was it is amazing like the way the projection like the technology got changed because of these ok. So, this is based on like micro mirrors which are seen in this figure and like whatever pixel you want to have like you turn this micro micro mirror such that that only pixel is illuminated on the screen or on the projection system ok. So, that is a way like you control the light and there are thousands and thousands of these kind of mirrors on a single chip and Texas instrument being a company in chip development as parallely developed chips which can be processed I mean which can process these I mean which can give commands to these kind of a DLP chips ok. So, your computer can be interface to these DLP chips through like whatever chips developed by Texas instrument ok. And then algorithms and other things they have whole bunch of products developed on this concept and we also have like recently we have received this kind like micro mirrors, but not based on these technologies it is a different technology and where we have more precise control these are combactuated mirrors ok. Let us see if time permits I mean I mean talk about. So, this company has approached us for developing controllers for this combactuated micro mirrors which can produce really nice I mean applications ok. So, this is a micro robots which can walk ok these are based on the heat actuators. So, when you pass current like there will be heat generated and then differential thermal or thermal expansion basically you use it for actuation. So, this is a video of like that robot moving which is based on ok I think it is not working let us move on. Basically this video showing like this particular robot which is you can see the scale here starts walking ok it has like at the legs which we saw in the last water actuators we saw in the last slide I mean they are there at the legs. So, at the joints of the legs so, it can walk ok. So, people have achieved I mean the point is like the people like a lot of tremendously lot many things can be possible ok. And whatever you are thinking may not be the only kind of a solution they can be better solution available. So, that you should be open for those kinds of solutions. And now we will see how these are like whatever different things we have seen like how these can be created by using MEMS technology. What is the basic fundamental ways in which people create these kind of small products ok. So, the basic material that is used is silicon and the silicon has this kind of a crystal structure that is very important I mean in some of the things we will see anisotropic machining specifically this kind of a structure is very important. Silicon has like very different properties which are much better than many other materials and it is available in the form of wafers ok. So, 2 inch, 4 inch, 18 inch diameter wafers are available for silicon. And then silicon derived materials like there are a lot of other materials and then you have metals which can be compatible with I mean it can like have a good adhesion. Like say for example, you can deposit chrome and gold on silicon surface and thing like that you can create like. So, it is a deposition process in which you can have this other materials polymers gold can be possible on the surface ok. Now, the fabrication process for the MEMS is basically divided into major 3 categories ok. These are the only 3 categories you will find for any of the MEMS process. First is lithography which is patterning. It is like the what happens when you take a picture in your not with the digital camera with the like what your analog camera ok. Where you have a negative at the back and when you take a picture that the light affects that negative at some appropriate places and then like your picture is created, imprint is created on the negative. So, similar process is lithography. There are 2 categories in that. First is a positive photoresist thing. So, you have this silicon wafer on which you put a drop of a photoresist ok. This is like a material for negative I mean chemical that is there in your negative ok. You spin it at very high speed and then it will get spread uniformly on the surface of the wafer ok. Then like you use a mask ok. This whatever material you have deposited is sensitive to light ok. So, you create a mask which can permit light to pass through some area and allow not to pass through other area and then that thing will get affected ok. Now, you put it in the developer and this will get dissolved whatever is affected will get dissolved and then that cavity is created on the surface ok. Now, you put any etchant for silicon and that kind of a machining will be possible on the surface of silicon. This is at a core of all the MEMS based processes ok. So, you typically post bake it to make it hard. So, that like no chemical effects other than the chemical I mean which you want to remove I mean remove this finally ok. So, this is in the case of positive photoresist. Now, negative photoresist is a opposite thing like you spread you expose it to light and affected area will remain and other area will go off ok. That is there are two variants in the photoresist and then you can post bake it and use it for further processing. Now, that previous thing was a mask based lithography. So, in a mask based thing like ok. Now, first the question will come how to prepare mask ok. What I am talking about here the dimensions are really in a in a in a micron range ok. So, to create mask also of that size how do you do that? Well that is a question that naturally comes in the mind and the the the answer is like there is a e-beam lithography machine that you can use where electron beam is scanning on the surface of the whatever substrate and then it is producing like whatever you want to produce ok. So, there is no necessity for mask and it can be used for actually preparation of mask and then because e-beam has the wavelengths which are very small ok, you can really go for sub micron features ok. The actually you know the size of the thing which is limited I mean like the features is limited not by the wavelength, but by the spread of the electrons ok. These electrons are very light in in mass I mean if the mass of electron is I mean very small. So, whenever this electron beam is hitting your substrate they always start spreading. Now, when they spread like your that spread will determine the the feature size rather than like the wavelength at which these electrons are going ok. So, typically 20 nanometer is is a best resolution that you can get with the electron beam writing ok. And for higher resolution further higher resolution you can use ion beam or x-ray lithography ok. Now, what do you do with these pieces I mean our substrates which have this kind of a patterns generated on the surface ok. The further processing step is either this etching or is deposition ok. So, material adding or material removal ok. So, where to add where to remove is decided by this mask ok, mask based lithographic process that we have seen ok. Where to add and where to remove is decided by that and all the other processes I mean we will just go little faster over these processes. They are just either material addition or material removal processes with some some minor differences here and there ok. So, we will not get into the integrities of these processes, but we will just see their animations ok. So, without aditation if you keep your silicon wafer with a window open this typically is called window open you have opened this small window on the surface of silicon wafer ok. So, if you keep that wafer in the etchant which is like there are many chemicals that are available it is not going to details. For a for a 5 minutes or like for longer time they will start etching away the silicon and this is a isotropic way like the etching is is uniform in all the directions ok. So, that is producing this kind of a over hung ok. You intended to produce this size on the surface, but actually what is getting produced is this size ok. So, you need to be careful about all these multiple details ok. Now, with agitation you produce like deeper cavities ok. The anisotropic etching has this kind of a structure that I was talking about play important role in the anisotropic etching because like some of the etchants like these KOH and EDP they have a selectivity of these planes ok. So, this etching selectivity etching is more in one direction than the other. So, you can produce like precisely this angle will be decided upon by this surface ok. So, so I mean you can use 1 0 0 surface wafer meaning like 1 0 0 the crystals in this wafer are oriented in this precisely this fashion which is indicated here. So, that like 1 0 0 vector of a crystal direction is pointing up perpendicular to the surface. So, this is very important like if you have any other direction pointing up the same like kind of a mask will produce different cavities ok. Then there is plasma etching where you have to between these 2 electrodes a plasma is created. So, because of the ions moving in the plasma like they will hit the surface and physically remove the metal or whatever the silicon in this case from the surface ok. So, this is a physical metal removal process material removal process by using plasma and you can have in addition to physical material removal you can have reactive ion etching where like if you instead of like the neutral gas like argon if you use the chemically reactive species of gas there then it will have chemical reaction also taking place at the same time and that will be much faster process of material removal and that is called reactive ion etching process ok. It can produce really deep trenches like I mean with aspect ratio like if this width is 1 this width is 1 you can go as deep as 20 micron ok. So, very high aspect ratio structures can be produced ok. This oxidation process is just keeping the silicon wafer in the oxygen environment for higher temperature at higher temperatures and it will grow oxide on the surface of the wafer. So, that is a that is I mean very precisely known process you can create these oxides of very precise thickness for various applications ok. So, this oxide silicon oxide is nothing, but a glass ok. So, silicon dioxide is basically. So, then the there is this pattern where now like the electrode is switched ok in plasma etching like whatever electrode was I mean your substrate was seeing the heating of ions. Now, you have switched the electrodes because of which like the target substrate is seeing those high velocity ions and the material is removed from the target substrate and deposited on the surface of your wafer that is the process of sputtering ok. And all these all these processes by the way are available in our lab here like micro electronic facility we have all these processes we can carry out and I mean I will show you some of the things which yeah which I have some of the slides which we have created those micro components over here ok. Then chemical wafer depositions. So, like that there are various deposition processes let us not get into this. Here if the the idea is like you have the two gases entering in the chamber they react in the chamber with each other and then like the products of the reaction are deposited on the substrate of your wafer ok. Now, how we can use this to create like say for example, cantilever kind of a structure ok that is demonstrated here. So, you have this wafer you have created this window by using a lithography step and then you can deposit like say some for example, polysilicon material ok. You want to create a polysilicon cantilever on the surface then you use another mask use another lithography step and you produce some some kind of a mask like this on the surface is a negative photoresist. Then you start etching like first you have removed the photoresist and then you have removed the polysilicon which is which is not under mask which is not protected by the mask and then you you can remove this baked photoresist self and you can you have a free standing cantilever created on the surface of the wafer ok. So, that is a basic these are this is a basic process called surface micro machining by which you can create like MEMS components on the surface ok. So, this is in 3D this looks like this ok you have created first cavity on the in the in the on the surface of wafer and then like you have deposited actually and this is a deposited and pattern polysilicon and then this is a release sacrificial edge. So, you have a released structure of cantilever standing on the surface of a wafer ok. So, so now there is there is this electroplating process. So, you can have addition of like all these different processes basically using these patterns and then you can now add electroplating to it you can add molding to on the on the same pattern which you have electroplated. So, so those those kinds of processes you can add and like you can create your own kind of a processes ok. So, here now you have first created these cavities in like this photoresist which is typically PMMA which is very high aspect ratio for photoresist and then like you can fill them by using electroplating ok. You keep it this keep this dip this in into the electrochemical and like have the electrochemical deposition take place and it will be only filled in these cavities because this is not not conducting material ok. And then you can remove that material and now you have freely standing these patterns on the substrate metal metal rods in the substrate ok. Here it is some other other combination with molding. So, you have created this freely standing things on the and then you use it to create a mold out of this pattern ok. And this is like a you can use PDMS material for example, for mold and then like you can strip off like I mean this literally like you can as we remove the cellotip from substrate like you can remove this thing and then it will have those patterns that cavities will be there on the on the surface ok. So, these are some of the components fabricated micro fabricated ok. These are other micro fabrication techniques let us not get into details I mean this is a this is a technique where like you layer by layer you create this micro component you write the first layer then deep the stage into the photopolymer liquid tank and then like you write a second layer and go on writing different layers to create really three dimensional very complex kind of micro components. Actually we have in our lab we are developing this technology in house actually in the mechanical engineering department and we are using like very I mean this is now pretended technology that we the pretend is in process on the technology. Some of the technological limitations that current literature shows those processes we have we have taken care of that to get a high speed fabrication possible ok. So, this is just an animation showing you like how each layer will be written ok. Say for example, this is kind of a circular thing we want to write ok. So, you scan line by line and then like develop this layer and then like this way we will get developed on the stage and then you insert the stage in the liquid and then like you develop next layer. These are various sensing methods that are possible that can be possible at the MEMS sensors level ok. The resistive sensing you can create by like creating resistors on your device ok. Say for example, pressure diaphragm ok you can dope it differently and then like you can create your resistors sitting on the pressure diaphragm itself ok. So, entire your withstone bridge can be on the device itself you do not have to connect wire separately to your string as you do in the strain gauge ok. That is advantage in this case you are I mean you are not mounting separately any strain gauge on your pressure diaphragm like the the pressure diaphragm is integrated with the resistors ok. So, that resistance change you can like take out and then like process to get the output corresponding to the pressure ok. So, that avoids like number of components also and that enables like the noise reduction and gives you more precise way of like sensing pressure ok. So, based on temperature you can have like two different material layers and then like like temperature change would cause the material I mean this kind of cantilever to bend because of the differential thermal expansion and that you can use as a sensing of a temperature. So, like that you can have many different ways in which you can measure the temperature. Capacitive sensing you can have as I said in a like pressure diaphragm when it changes like you can have another plate parallel plate on the top of that and then it is change in the capacitance you can sense. There are in in capacity also there are combs possible that we will see in the later some examples. So, so these these are the effects I mean sensing methods that are like popular at the MEMS level and there are a lot of optical measurements also possible I mean optical sensing ways also possible and people are developing opto MEMS actually like where optical components are integrated in the MEMS structure itself ok. So, that is a very heavy I mean like very current research area actually and the most difficult thing in the opto MEMS I mean opto electronic MEMS is basically to generate the optical source on the on the chip itself ok. So, we cannot have laser like generated on the chip I mean that is that is a technology there are technological limitations to that. So, that is a very active research area right now ok. Yeah laser diodes are small enough, but then integrating them with the chip is where the problem is. You cannot create them on chip like you can create separately, but again there will be problem of how to assemble. So, that the laser is precisely in one particular direction that is a technological limitation ok. So, this is just a quick demonstration of like creating a pressure sensor out of your silicon wafer ok. So, this is by electrochemical etching you can have these are the contact pads and these are the these are the gold contact pads and these are the resistors which are used for sensing strain gauges. And then this dimension is precisely maintained by using this anisotropic etching at the bottom from the back side of the wafer ok. And then precisely controlling the time for which this etching is happening ok. So, you get precisely whatever size diaphragm you need on the on the wafer I mean on the pressure sensor. And then like you have this contact pads and doping done in this fashion to have that sensing happening ok. Then you can package it with the glass on the top and then like you can put your. So, it will look something like this in three dimension ok. So, pressure cavity you have a diaphragm and then all these sensors are located at appropriate places and back side you have a vent to give the pressure ok. Then similar thing accelerometer will not again go get into details, but like ok. This is again anisotropic etching on both the sides and then you have a big mass here ok. Big I mean like big in this case is a maybe 200 microns ok. So, so that is the dimension that we are talking about. And here you can produce like on this hinge here you can have again the doping and resistor created here and contact that and like you will get your pressure I mean the acceleration change recorded by the change in the resistance ok. So, now like mechatronics in characterization of MEMS and MEMS I mean mechatronics is playing a big big role in the basically the characterization processes that have been developed or characterization tools that have been developed so far for MEMS devices ok. The basic device that is based on is like SPM like scanning probe microscopy technology ok. So, will we see little bit glimpses about this technology in the coming slides and that will understand how what role the mechatronics has to play and what kind of sensors and actuators they are using at that scale ok. Now considering a microscopy the basic question is like optical microscopy if you like you all have used microscopy in at some point. This optical microscope how big it can see I mean how small it can see. Exactly. So, wavelength of visible light is a limitation ok whatever light you are using I mean usually that is a UV light for use for microscopes, but the wavelength of light is a limitation for what you can see in microscope ok. It is not that like you can go on like having higher and higher magnification and you will get to see everything ok at the nanometer scale also no that is wrong impression if you have. So, wavelength of visible light or whatever light you are using for microscopy is a limitation on what you can see ok. So, that is you know what is the wavelength of light is say for example, green light 1000 I mean it is in the range of like to be precise 5000 angstroms or 500 nanometers ok. So, like so, you can see only up to 500 not even 500 like it will be very difficult to see, but that kind of a range with your microscope ok. So, you to really see 20 nanometer feature or 10 nanometer feature what is. So, that was the question I mean that people were trying to address like couple of years ago ok. And then the solution for that is scanning tunneling microscope ok. So, so this was this was invented early 80s by these two gentlemen for this invention they got a noble price ok. Now ok, so that technology is like using this kind of a tip and scanning it over your surface ok and passing some current through this tip ok. At us on the surface there will be some kind of a like ups and downs ok which you want to really see in the microscope. So, those at that point the current will change ok. The current has really exponential order of magnitude change or exponential relationship with the distance ok. As a distance changes like current will change a huge lot ok that is how you get a better sensitivity for sensing the distances. So, this is a atomic I mean atomic level picture it is shown here is a electron gas or like electron cloud around your atoms on the surface. And then like these clouds interact and then there is a tunneling of electrons through this this gap ok. And then this gap we are talking about is really really small ok. It is in the nanometers or angstrom level change ok. So, this typically is 10 angstrom or 1 nanometer ok. So, there are more details about the technology, but basic idea is to scan on the surface. Now you can do it in the mechatronics way like having closed loop control and maintain this distance constant and see what is the change in current or you can do other way like you can like do it in the open loop ok. There is no feedback taken from the current and then like you just see what is the change in current as you move linearly on the surface ok. So, these are I mean people have come up with different modes and, but basic fundamental idea is what you need to be aware of what ok. So, I mean these ideas can be used I mean really in a in a in a like bigger scale also for some applications if they may be useful for you to use ok. So, you can get really atoms atomic picture of devices using this tunneling. So, this is image of plain surface of copper and nickel ok. So, now the limitations of STM is basically like you need a thing to be conducting for electrons to transmit like from one place so, only metals can be imaged with STM. So, what about non metal? So, to avoid I mean to overcome this problem people have created the thing like this where you have this cantilever which is having some kind of a reflective surface at the tip and then you place this laser light at a very large distance ok. And then it is getting reflected and falling on this photodiode or ok this is coming from the laser and falling on this photodiode and this photodiode I mean as this distance increases like you will have a higher and higher resolution that what the movement of cantilever you can see ok. So, as cantilever moves on a sample ok the sample will have like typically ups and downs on the tip will interact with those and then like tip will move when tip is moving up if you sense that distance it see if the tip moves up then this angle of the cantilever changes and then that changes the place where it is falling on the photodiode surface. This is typically a quadrature photodiode ok it has four quadrants and I mean let us not get into details like I mean so, but I mean any change of position where it is falling on the surface ok will be able to detect that ok. And as the distance is increased like you will have higher and higher sensitivity. So, there are then again more details are there about this technology like you can have contact measurement and non contact kind of a measurement you can like this is now kind of a mechatonic system ok I will show you. So, so contact and non contact modes are basically these. So, you can have constant height kind of a scanning and then then you can have constant force kind of a scanning ok. So, see the important idea here is that ok the force between the tip and the sample varies as you change the distance tip samples separation as you change this distance the force is first attractive and then it becomes repulsive when it is close to making contact or when that distance or gap is becoming 0 and these distances are of the order of nanometer and angstrom ok. So, depending upon various I mean different materials like you have different characteristics for those curves, but typically that is the nature of the curve ok. So, you have initially like initially as you bring the sample close to the substrate you first have attraction and then like you have a repulsion ok. So, using this kind of a curve like you can plan out different strategies for measurement that is what is the non contact and contact strategy people have designed and developed ok. So, let us not get into detail. So, there are there can be other ways possible. So, so basically the system if you see that that can do this will typically have I mean all the mechatronics put together ok. So, you see this is a this is actually SPM device you see that the device is really really small. I mean the system total system cost will be about to the order of like 50 lakhs and this is the major cost factor. Ok, this has the entire like whatever amount is put I mean is major mainly in the development of these ok. So, the details here are like here we may not be able to get into all the details, but basic idea is like you have a sample holder here and SPM tip which is somewhere here in this cavity and like you will have the laser light ok. There will be some source here and there will be a laser light coming out and falling in the camera which is inside and on the screen you will see the image of the laser spot. I mean to do carry out kind of a initial adjustments of these norms to make sure that the laser light is basically falling on the photodiode. See it may be possible when you replace the sample tip I mean the SPM tip from here the laser light may go astray I mean because like this is very high sensitive. So, so it is very highly sensitive to any of the misalignment like if you have misalignment of even few microns this may change the picture drastically. So, you need to provide for this system like various kind of adjustments to bring it back and then once it is once you see that laser light is falling on the photodiode then you can see that this will start giving some signal ok. So, A, B, C and D they are like a quadrature, quadrant photodiodes quadrature photodiode signals A, B, C and D are 4 quadrants of a photodiode ok. So, this is more detail about this ok. So, so we have seen some of the devices MEMS devices these are more devices people have fabricated so far. So, pressure sensors are very popular MEMS based pressure sensors accelerometers vibrating gyroscopes they are people have developed. Then in micro actuators, thermal actuators, piezo actuators, comb based actuators which we will see. Then micro gears, micro engines also people have developed in the research and microfluidic systems ok inkjet printers and drug delivery system I mean people have developed. Like say for example this drug delivery simple system I mean the that has been developed is like some capsule sitting in your body and as soon as like your sugar level goes high insulin will be automatically released in the bloodstream to like and take care of that. So, that is a kind of a drug delivery like automatic drug delivery that has been already in place ok. I mean there are issues about its use and not I mean whatever but the technology has reached I mean that stage right now ok. So, there are many more devices here to come and there is this is a lot of gray area like I mean there you have a bright idea you can just implement it and like you can be like contributing to a new sensor or whatever new application of the existing sensor thing like that. So, there are a lot of possibilities in these MEMS right now. So, these are the comb actuators that I was talking about like you have like just intermingling fingers and which you can give voltage and they will be in electrostatic attraction ok. So, these are the comb drives people call it and as you increase the number of combs like you will have a higher and higher force that can be produced by these comb drives ok. We have developed some devices based on the comb drives that I will show you some pictures of. This is a micromotor. So, yeah this is a comb drive like ok. This is a XY nano stage which we have developed at IIT and actually this was not fabricated at IIT this was designed at IIT and then like there is a there is a fab called polymorphs fab. We have some collaborative arrangement with the University of Colorado Boulder where we had sent our designs and then those designs were implemented and they sent us this chips which were fabricated the photograph of one of the chips. So, the idea here is that you have comb drive here and these places. So, these two are used for actuation in x direction and these two are used for actuation in y direction and we have used this flexure mechanism ok. This part is fixed these links are free to bend they basically like make sure that the combs are moving parallel to itself ok and then they are giving x and y direction motion to the stage ok. So, that is the whole idea of this flexure mechanism and because of the flexure there is no rubbing any part rubbing against each other ok. So, that is the whole idea. So, that like this can be used over and over again at I mean there is I mean the materials are known not to fatigue at the smaller scale ok. Like people have seen like materials which do not fatigue I mean millions of cycles they do not fatigue, but if there is a friction there is a problem like there is a wear is much higher at the M scale. So, that is that problem is avoided here by the smart design with the flexures ok. So, this is a more closer view of a comb drive is on that view ok. Then the nowadays these sensors ok for bio MEMS area I mean say for example, which we have which we just talked about like the insulin drug delivery. So, the sugar level when it is changed like how one can sense that or like any other biomolecule if that is there in your blood how one can see. So, for that people have developed like the sensors based on the cantilever type of array which is called affinity cantilever sensors. So, the basic idea is like allow biomolecules whatever the specific you are looking for allow them to sit on the cantilever surface by a process called immobilization. So, in that process only those selected molecules if they are there in your blood they will come and sit ok. How that happens and all will not get into details, but once that happens like interaction between those molecules they will cause some forces ok. Now this cantilevers we are talking about are like 100 micron in size or 50 micron in size that kind of a dimensions when they see this biomolecular forces they this cantilevers typically bend or show some change in the deflection or resistance I mean if you have a resistive element at the base of the cantilever it will show the change. So, there can be piezoresistive and optical detection possible and that change you can attribute to presence of biomolecule in whatever sample that you are testing and based on that. So, the tedious process of like observing them like I mean in the pathological laboratories and like. So, that process is quite time consuming. So, that process can be like avoided and there is a lot of research going on into this like reliability how reliable is this way of doing thing and I mean other things are going on. But essentially this is a idea and based on this idea only like this close loop I mean like say this is right now just sensing. So, you do not develop a close loop system unless like you have some kind of a way you affect this concentration in the blood. So, that is what the insulin based drug delivery sensor that we are talking about. So, there will be a sensor of sugar level and if it exceeds a particular limit then it will directly that sensor will release appropriate amount of insulin from the stored in that capsule in the in the main blood stream. And so, that is how the close loop system. I mean this is very futuristic kind of a thing, but it is possible to do with the technology. I mean technology is going in that direction. So, we are for example, developing sensor for myocardial infarction which is like early detection of heart attack like person like when the like this problem like doctors approached us for like when the patient comes into the hospital like they want to know whether that patient is really a heart patient or the chest pain is because of some other reasons. So, to isolate I mean and they found that like 60 percent of the cases are like not heart kind of a cases they are because of some different reason and you do not want to administer like the costly things like taking ECG and other kind of a checkups unless you know that this is really a heart patient kind of a case. So, to avoid that like you want to have a sensor which can detect that this is because of the heart problem. So, that the case of myocardial infarction is where like some of the molecules are released in the blood. So, there are specific molecules to that like way of getting a heart attack. So, those molecules if you detect like you will get to know that this is a patient who needs like further attention ok. So, that is what we have developed at IIT. It is a cantilever based product which is which can be used like you can just pass your the blood of a patient on the surface and it will tell you within say 15-20 minutes that this is a positive case for heart attack. So, he needs like special attention and so those kinds of things can be possible which people would not have imagined like how to detect whether like you are susceptible to heart attack or you will you are likely to get heart attack. So, that is where the technology is playing role. This is a illustration of like how one can have like various different kinds of diseases. I mean say for example, this cantilever is for one biomolecule, this cantilever is for another biomolecule and then you have a same sample of blood drop which is coming on the surface and like whatever you wash off and all. And then like this will attract only like if there is a this will detect if there is a bacteria for malaria in here. So, there are various kinds of like for example, HIV like kind of a disease like you have various possibilities ok. So, out of that what kind of a HIV infection is this for this particular patient that all you can determine based on the array kind of a sensing in a very low time ok. So, this is one of the sensors which is fabricated at IIT. These are some other sensors which have been fabricated. These are basically U shaped micro cantilevers for myocardial infarction that was and then then you can see here there is a pad which is for the mirror kind of a thing to reflect light to determine what is the deflection. So, in conclusion what we have seen is basic overview of MEMS and LEMS. Basic fabrication processes are only three like lithography, deposition and material removal ok. And these technologies are inevitable in the future consumer and industrial mechatonic systems as the sensors or actuators because of their higher quality as I said earlier higher quality and higher resolution at a higher quality and at a low cost it is offering you higher performance. So, they will be affecting the markets and they will be driving the economy ok. So, there we close.