Fabrication Techniques for MEMS-based Sensors (PDF)

Fabrication Techniques for Mems-based Sensors: Clinical Perspective Prof. Hardik J Pandya Department of Electronic Systems Engineering Indian Institute of Science, Bangalore...

Fabrication Techniques for Mems-based Sensors: Clinical Perspective Prof. Hardik J Pandya Department of Electronic Systems Engineering Indian Institute of Science, Bangalore Lecture – 01 Introduction to Microengineering Devices Hi, welcome to this course, this course is about Fabrication Techniques for MEMS-based Sensors from Clinical Perspective. So, when we talk about clinical research what does that mean? And how is it really useful? So, there is a saying which goes like this, solutions to big problems lie in small things that is true for our actual life as well as in the case of research. When we understand the properties from the micro and nano perspective, we can really understand what kind of problem lies and what kind of solutions we can design. So, when you talk about micro and nano what do you mean by micro and nano? And how it can be useful? So, in this particular course, we will be understanding several devices that we can fabricate using a technology called microtechnology. And in particular, we will focus on microelectromechanical systems-based technologies as well as based sensors. This can be a microchip, it can be a flexible sensor, it can be a microfluidic chip. It can be a device for drug screening it can be a device for evaluating the efficacy of the drug. It can be a device that can measure the weight of a fly, a housefly. So, how can we design these devices? And how what are the process for designing these devices? So, we will take each device into detail and understand from a research point of view about how you can use this device to solve a particular problem in clinics. So, when I talk about this kind of problems we should understand first that where exactly we are talking about and when what exactly we are talking about. So, it is not just from the clinical perspective that we can make these devices, but these devices are used in several other applications. 1 (Refer to Slide Time: 02:43) So, if you see the slide, if you see the screen what we see is that we are talking about 10 -6 which is about 1 micron to 10-9, which is about 1 nanometer. And if you talk about our human hair it is around 100 microns, the average human hair thickness is about 100 microns. But, we are talking about one-tenth of that we are talking about 1 micron. In fact, we are talking about 1 nanometer; that means, a micro means a mean 1 millionth you see 1 by 10 lakh. If I want to just say in terms of lakh it is 10 lakh, 1 by 1 millionth or a when you talk about nano it is 1 billionth 1 by 1 billionth. So, these are extremely small values. And it is extremely important to understand something called a recipe or process flow. So, it is very important to understand what is a recipe and what is a process flow. So, when we talk about molecular manufacturing; molecular manufacturing what does that mean? Precision down to the atomic level, when you talk about nanotubes, we are talking about building advanced lightweight material as an advancement in LCD technologies. When talking about medicines we have devices that will flow through the circulatory system as well as devices that can evaluate the efficacy of the drug, as well as devices that can understand and help us to screen the drug. As well as devices that can be used for several surgical applications. So, we will see these devices we will focus more on this particular aspect. 2  Then we can also use this technology for nanocomposites, that is. assisting in a vast improvement in material compositions. Finally, this technology is also used in electronics. When talking about electronics we talked about MOSFETs, complementary MOSFETs, complementary metal-oxide semiconductors and how we can fabricate this MOSFETs and circuits that are used in electronics. So, you see that when you understand the concept of micro and nano, and the technology behind it, then you can apply your knowledge into several fields. It is not just limited to the clinical perspective but it can be used for electronics, it can be used for robotics, it can be used for building novel materials, it can be used for understanding the molecular manufacturing. So, it has a vast application. So, today’s lecture is focused on showing you a few devices that can be used in clinics or to solve problems which are related to medicine. So, let us see and we will talk about these devices in this particular lecture and we will take each device and see how it can be fabricated. So, when you understand fabrication from process flow to the recipe of each device then you can use this device by using the cleanroom. And understanding how the cleanroom can be used or how the equipment in the cleanroom should be used so to fabricate these devices. (Refer to Slide Time: 07:03) 3 So, let us see this slide, the first slide that you can see here what are these slides? It is showing micro heaters. So, when I talk about micro heaters you can see very clearly that this is the bar is about 3 millimeter. And the width of this line is about 100 micrometers. The spacing is about 100 micrometers. So, the width is 100 micrometers. And if you see this particular image this is a silicon wafer you can see it is an oxidized silicon wafer. And then on oxide we can if you see this part then it is chrome gold what is it? Chrome gold. So, now the question is why we have designed this particular heater in this particular fashion? (Refer Slide Time: 08:59) So, what is resistance? Resistance if we say R equals to rho l by A; that means, if I want to have a resistance of a higher value, I should decrease my area and or I can increase my length. For a given metal, resistivity remains constant. So, hereby using this design which is a design of a coil as an annular coil we are increasing the length and hence the resistance. Did you get it? We are increasing the length and hence the resistance one thing. Second thing, where are these micro heaters used? Micro heaters are used in a lot of applications such as sensors. 4 (Refer to Slide Time: 09:55) And when I talk about sensors these are gas sensors. Then these micro heaters are used in something called chip for antibiotic resistance, antibiotic resistance chips. These sensors are used for microfluidics. So, when you say the sensors when the sensors consist of the heater and or directly heaters are used for microfluidics, heaters can be used in a sensor that is used for antibiotic resistance. Heaters are used in sensors that are used for measuring different gases or measuring different volatile organic compounds. So, when you talk about a volatile organic compound, what does a compound mean? VOC means a compound that is organic in nature and that is volatile also in nature. So, what are the example of VOC S when you talk about VOC S. 5 (Refer to Slide Time: 11:31) What are these volatile organic compounds? So, like I said it is organic and volatile, but can you give me an example? The example is gasoline so, we say here petrol, it can be diesel, it can be acetone, that we use in nail polish remover. It can be ethanol, it can be methanol, it can be isopropyl alcohol, it can be butanol. And if you want to detect this VOC S and we will see one application if you want to detect this VOC S, then you need to design a sensor and this sensor the sensing material works better at a higher temperature. So, to raise the temperature of the sensing material we have to use a heater. And for the sensors, are all micron in size or they consist of different patterns which are microns in size. And here we have to use heaters also in micro dimensions and that is why there is an importance of microheater. So, we will see how we can fabricate a microheater on an oxidized silicon substrate. The reason for using oxidized silicon substrate is that when we use silicon and directly if we deposit metal then we will not get actual value of metal because there is a semiconductor below it. So, silicon is a semiconductor, we cannot deposit metal on the semiconductor. So, we have an oxide layer on the silicon wafer and then on that oxide layer, we can deposit a metal. And this oxide layer will act as an insulator. 6 So, now when we have to fabricate this micro heater what are the process flow? And what is the recipe? We will see in this particular lecture series. (Refer to Slide Time: 14:21) Let us see another device. What do you see here? We see here that there are interdigitated electrodes, it is called interdigitated. That means, you have digits this is 1 digit, this is 2nd digit, 3rd digit, 4th digit, 5th, 6th, 7th, 8th, 9. If digits are interlocked like this interdigitated and if I measure an impedance, if I measure resistance or impedance across this it will be infinite correct because there is nothing it is not touching. But, if I deposit any material on this then I can see the change in the resistance. So, these are the electrodes that are used to measure the change in resistance or impedance of the material. 7 (Refer to Slide Time: 15:23) So, this particular structure if you closely see there is a microheater here, this is a contact for micro heaters. (Refer to Slide Time: 15:36) And if you see this particular diagram this one you can see micro heater over here and then on that micro heater it is interdigitated or there are interdigitated electrodes. But, again you cannot have let us say this is silicon dioxide, then this is the heater. The heater is of metal, 8 interdigitated electrodes this one inter digited electrodes is also written as IDES are also made up of metal. And you cannot have metal on metal; that means, that you should have an insulating layer on which you can design interdigitated electrodes. So, this one is where there is an insulating layer. So, if you see any of this device any of this one, this one there is a microheater at the bottom on which there is an insulator which can be a silicon dioxide or silicon nitride on and on that we have patterned. (Refer to Slide Time: 16:52) We have pattern interdigitated electrodes, you can see here in this particular diagram and there is oxidized silicon wafer and on which is silicon wafer with silicon dioxide, on which there are micro heaters or there is a microheater here there is a single microheater as you can see. On which there is an insulator, on which there are interdigitated electrodes which are patterned using lithography. And we will see the application of these interdigitated electrodes on SiO 2, on the micro heater in few examples later on. So, now we are complicating the design of the sensor. Earlier we have just seen microheater, now we are talking about microheater on that another layer of silicon dioxide, another layer of interdigitated electrodes. So, this will get on complicating when we design complex 9 sensors. This very simple example micro heater insulator and interdigitated electrodes, but there can be more complex examples that I will see. If you go to the next slide what we will see? (Refer to Slide Time: 18:24) Another device and this is a flexible catheter, force sensors for catheter or flexible catheter force sensors for atrial fibrillation. So, what is atrial fibrillation? What does atrial fibrillation mean? And how we can design a flexible force sensor for such an application? What is the use of actually designing a force sensor for atrial fibrillation? we have to understand that. So, we will understand what exactly atrial fibrillation means, we will see how we can design a force sensor and how we can integrate this force sensor on the catheter. So, that it can measure the character contact force. So, that it can measure the catheter contact force. So, we will see how we can design this particular sensor and what kind of experiment we can perform to understand the characteristics of the force sensor that we have designed. And this is again a medical application because we are designing a force sensor for atrial fibrillation something to do with the heart. So, if I know microengineering, if I know micro fabrication I can design a sensor that can be used for surgical applications. You see it is used for catheters that are used for atrial fibrillation which is a disease in the heart. So, we will see through this application. 10 (Refer to Slide Time: 20:17) If I go to the next slide what I can see? I can see that there are cantilevers and if you closely see there is a piezoresistor embedded in oxidized silicon or embedded in polysilicon, not oxidized silicon piezoresistive embedded in polysilicon. (Refer to Slide Time: 20:53) And at the end of the cantilever, at the tip of the cantilever or at the end of the edge of the cantilever in this side this one there is an SUA tip there is an SUA tip. So, this cantilever. The thickness of this cantilever is 2 micrometer. 11 We are talking about human hair having a thickness of 100 micrometers. We are looking at the cantilever which is about 2 micrometers and the reason for having a piezoresistor is that when we press this cantilever there will be a change in resistance. That is a property of piezoresistor, when you apply pressure when you apply force there is a change in resistance of piezoresistors, because of the strain created in the piezoresistor. So, because when we apply a force like this it will bend in this direction like this, then there is a strain in this area. This strain causes a change in the resistance of the resistor embedded in the cantilever. Now, we can also see here. (Refer to Slide Time: 22:07) In this particular diagram that there is a piezoresistive cantilever once again which is bent. What is the reason for bending? Why it is bent? And why this is not? That is because of the recipe that I was talking about. So we should know; what is the recipe for fabricating these devices if the recipe is wrong then you will have this kind of device, but what we require is this one. So, we will see how we can fabricate this piezoresistive microcantilever and how it can be used for several applications including measuring the properties of tissue. 12 (Refer to Slide Time: 23:09) Including measuring the properties of tissue; so when you talk about tissue, the stiffness of the tissue. Can we measure a stiffness using piezoresistive microcantilever? That is a question. Can we measure the stiffness of the tissue using piezoresistive microcantilevers? And if we can measure the stiffness of tissue then we can use this for diagnosing a case called breast cancer. So, we will see how it can be used for understanding the mechanical properties of the tissue let us go next. 13 (Refer to Slide Time: 24:09) Now, the same example which is your interdigitated electrodes, you can see here interdigitated electrodes. And if I have an interdigitated electrode what are the applications? I told you that one application of the interdigitated electrode would be measuring the resistance or impedance. So, when you talk about resistance or impedance you require some material to be kept on the interdigitated electrodes. So, if we keep a tissue on the interdigitated electrodes what we can measure? We can measure impedance. Why because there is a solution required to keep the tissue alive and that is PBS is the solution. So, if I have interdigitated electrodes and on that, if I place a tissue on which I have a solution then I cannot just measure resistance because there are several parasitic components that come into play such as double-layer capacitance. So, now instead of measuring resistance what I will measure? I will measure impedance, I will measure the impedance of the tissue. So, now if your device or if you can design a device that can measure the impedance of tissue or it can measure the impedance of cells as the disease progresses then you are measuring the electrical property of tissue or cell, is not it? So, what we will do by measuring the electrical property of tissue? What we need by measuring the mechanical property of tissue? The same thing will do by electrical property of tissue. That means that if I can see the change in the tissue properties as the disease 14 progresses. And let us take an example of a breast cancer or oral cancer or any other cancer- related tissue and my sensor can give these changes, can measure the signature, can measure the electrical and mechanical signature of the tissue or of the cell I can diagnose, I can use this device as a diagnosing device for cancer. So, now we are using interdigitated electrodes without any heater for understanding the properties of tissue and these are the electrical property of tissue. But, when I talk about the electrical property of tissue I need to first have interdigitated electrodes. And when we are talking about that this tissue is there we have to load the PBS which is a solution. Then if I load this solution on the glass slide it will do not stay on the point. So, we had to create a well to hold the solution. So, we will see how we can create this kind of device. There are interdigitated electrodes within a SU 8. That is another device that we can design from the biomedical application, from the clinical perspective. (Refer to Slide Time: 27:37) So, this is what we can see here on the slide that the tissue is placed on the interdigitated electrodes and you can see here the interdigitated electrodes are fabricated using chrome and gold. And the spacing and width, the width and spacing of these interdigitated electrodes is 10 micron. And the well is made up of SU 8, well is made about made up of SU 8. So, we will see how we can use this kind of device for measuring the tissue property particularly electrical property of tissue. 15 (Refer to Slide Time: 28:20) Let us move to the next slide now we will also understand how we can design a tool that can be used for diagnosing cancer. And to understand the designing of this tool that can be used to diagnose cancer we again need the basic understanding of what we call micro technology microtechnology. So, here we will be understanding or we will be studying several modalities. (Refer to Slide Time: 29:02) 16 When I say several modalities one is mechanical, another is electrical, another is thermal. Hence mechanical, electrical, thermal. All 3 properties of the tissue if I want to measure can I design a sensor that can measure all 3 properties or can I design a biochip that can measure all 3 properties of tissue, when I say all 3 properties the electrical properties, mechanical properties, thermal properties. And I do not want only one to design the biochip, but I also want to integrate this biochip into a tool. Such that when the tissue is taken from the biopsy we will see how the tissues are taken out. Once the tissue is out from the biopsy, I can place a tissue on this tool and I can just press a button. Or a pathologist if it is a pathology lab the pathologist will just press a button and he or she will be able to see what are the changes in the tissue properties. And thus this can be an aid to the surgeon. So, why do we require an aiding tool for the surgeon, is the gold standard not enough? now how cancer is diagnosed? So, we have to understand these things and then only we can design a particular tool that can be used for understanding the tissue properties. So, now we started from the microheater, then we come came to interdigitated electrodes, then we make to cantilever and then we went to interdigitated electrodes within SU 8 well. Now we are talking about a one more sensor that can be integrated and that is the thermal sensor. So, a thermal sensor can be micro heater we can use microheater for thermal sensing, we have to use a piezoresistive material that is we can use any piezoresistive material example is P DoT PSS which is a conducting polymer, and then we have to use an electrical sensor to measure the tissue properties. So, all 3 sensors integrated on a biochip. How can we do that? So, we will see in this series of lecture how we can fabricate such a kind of device now. 17 (Refer to Slide Time: 31:23) Let us see another device and this device is used for drug screening. So, how we can design this drug screening device? And what is the use of this drug screening device? So, now if a patient has to be given a particular drug, which drug will be more effective from a patient point of view? Every drug and every patient responds to the drug in a different way. So, can we design a device that is patient-centric? What is it? Patient-centric such that we take the cells from the patient and we load in the device and we pass different drugs next to the cells and see the response of the cells or tissue with respect to different drugs then we can understand which drug is more effective. So, to measure this response either we can use impedance or we can use the fluorescence technique now is used in bio labs. So, what I was saying that if I take a cell; let us say if I take a cell from my hand let us say from here I take a tissue. I take a tissue I place the tissue in the microfluidic chip I slice the issue place the issue in microfluidic chips. Pass the drug and if the drug is effective tissue will start dying. That the death of the tissue if I can measure by using some sensor that is integrated within this microfluidic chip. Then I can understand which drug is more effective for my body. Now, we are not talking about just if I get sick and I had to dig out the tissue, we are not talking about that kind of device. We are talking about a device when it is cancer and when the drug that is administered to the patient or drug that is given to the patient is extremely 18 important. Because it is a matter of life and death. Which drug will be more effective and which not because every patient will respond differently. So, now, as an engineer is a micro engineer who knows microengineering and microtechnology can you design a device that can be used from a patient-centric point of view for rapid drug screening you get it? We will see how you can design this device; so that when we use this device then based on the result a proper drug can be given to a proper patient. And it may change from patient to patient, thus making the delivery of the drug, thus making the screening of the drug more effective. (Refer to Slide Time: 34:37) So, if you see the screen what we see? That there is a microheater on which there should be an insulator on which there are electrodes and this everything. So, this one and this one should be on one chip. And for flowing I need channels, these channels I can fabricate using soft lithography, using soft lithography. 19 (Refer to Slide Time: 35:24) And the material that you can see here this material neither cube is PDMS, the material is PDMS. So, can we design a tool or can we design a device that can be used for rapid drug screening? So, we will see this device, how we can fabricate this device and how it can be used; and what are the preliminary results that I obtained using this particular device. Similarly, these are all the research problems you can work on, you can design these devices. By understanding this we are gaining expertise or we are understanding or we are improving our knowledge for designing several sensors that can be reused from the research point of view. Can you do some kind of research by gaining this experience from this course? There is an idea for this particular course. At least you know the process flow, once you know the process flow when you go to clean room for the fabrication of the device you will not be blank. You will know these devices or this equipment is used for this particular device. We will also see kind of equipment that is used for fabricating device not only process flow and recipe. 20 (Refer to Slide Time: 36:51) So, if I go to the next slide and the next slide is for antibiotic susceptibility. We will see how we can design a microchip that you can see here over here for understanding antibiotic susceptibility. Now what does, that mean? What does that mean and we can also design a microfluidic chip for understanding the antibiotic susceptibility. So, if you ever went to doctor if you went to a doctor and you have some kind of infection, the doctor will generally prescribe topical antibiotics that are 3- 4 antibiotics to eat. And we take this medicine and we pay the doctor. Why eat 3- 4 medicines? Why not 1? Why not 1? Why do we eat 3- 4 tropical antibiotics? Because first which antibiotic would be useful we do not know. Even we know that this is a bacterial infection and this infection is due to particular bacteria and there are medicines antibiotics meant for killing those bacteria, still we have to take 3- 4 antibiotics. Because we do not know which antibiotic would be useful for killing this bacteria or will the bacteria would be having resistance against the antibiotic. We do not know neither does the doctor. So, we are given the antibiotic, second is we had our blood taken or a urine sample was taken for further understanding what bacteria and suppose bacteria is known what antibiotic to give. And the results from the pathology come in 24 to 48 hours, in some cases even more. Some cases even more time is taken for giving you the results ok. This antibiotic would be more 21 effective with these particular bacteria since the patient is suffering from this particular disease. It is known if I have a urinary tract infection then I know that the E Coli that is bacteria called E coli would be in higher concentration. But, which antibiotic to use, a doctor can generally understand based on the reports from the path lab. Now, it is ok, it is ok, I do not say that the current way of medicine is wrong. It is what it is, this is what we know. But, the idea is why we cannot reduce this time? Why we have to wait for 24 hours? Why we have to wait for 48 hours to get the report. Can you design a device that can perform the analysis within a shorter period of time by requiring us a lesser sample? Why do we have to give like 10 ml of blood? Or even 20 ml of blood? Or even 1 ml of blood. How about microlitres; how about similar to glucometer I just puncher and that is it that is enough for me to give. So, reducing the sample size, rapidly getting the diagnosis and giving a correct antibiotic to the patient and correct antibiotics, by the way, the antibiotic that will be effective for this particular bacteria. If we can do this whole thing within a shorter period of time using a device then that will be really awesome is not it. Now, again you understand from our point of view if I have a bacterial infection if a doctor gives me an antibiotic I can take the antibiotic and wait for 2 days. Even for this antibiotic one of the antibiotic is useful, another one is not. If my immune system can take it, but, what about neonates? What about babies? There is a lot of bacterial infection in neonates and the immune system of a baby is extremely weak. So, in that case, waiting for 24 to 48 hours may cause death or life-threatening issue for a neonate. Thus this kind of device that can do rapid testing of antibiotic medicines that are antibiotics and can tell that the bacteria is resistance or not it is extremely useful. So, for that, we will see how we can design a microchip or a microfluidic device. So, that is what we see on this screen a microfluidic chip for the rapid bacterial antibiotic, susceptibility testing, we will see this device how we can fabricate this device. 22 (Refer to Slide Time: 42:10) Now, I go to another device and this is microfluidic chip again you can see it is a microfluidic chip. These are SEO images of the microfluidic chip and this is just an image of the mold that is made in silicon. And we will see why we have made this mold in silicon, what is the use of this device we see everything. So, what is the idea? The idea is that if I want to understand which drug can be used for killing this cancer. (Refer to Slide Time: 42:52) 23 Suppose this is a cancerous tissue and you can see here vessels, blood vessels supplying oxygen and nutrition to the cancerous tissue. Supplying oxygen and nutrition to the cancerous tissue and then you can see here there is an extracellular matrix. So, I want to test a drug that will start or stop that will stop growing of these vessels. If the vessels are stopped, if the growth of vessels are stopped or the vessels are destroyed, the vessels that are providing nutrition and oxygen to the tumor are destroyed. Then what kind of drug would be effective? Or what kind of combination of the drug would be effective? What kind of suppose there are 3 drugs 1, 2 and 3. One will be effective, second will be effective or third will be effective or combination of 1 and 2 will be effective or combination of 2 and 3 will be effective or combination of 1 and 3 will be effective or combination of all 3 will be effective. If I want to study this combination, we call combinational therapy. What can I do? (Refer to Slide Time: 44:40) I can design a microfluidic chip that mimics the same thing and I can test different drugs. I can test different drugs whether a drug is effective or not that is drug efficacy, whether the drug is effective in killing the tubules or in destroying the vessels that are supplying oxygen 24 and nutrition to the tumor. If the nutrition and oxygen are stopped then the tumor will start dying because a tumor is nothing but a group of cells growing abnormally. So, this is another device that we will be looking at the clinical perspective then we go to the next slide. (Refer to Slide Time: 45:16) This is a very interesting application of a flexible MEMS. Flexible microelectromechanical sensors or MEMS-based systems based sensors for phenotyping or understanding tissue properties. And we will see how the process flow happens, how this device looks like. If you see closely this device has this particular pattern and actually there is an array of these patterns. And these arrays are nothing, but strain gauge, what is that strain gauge? What is the use of strain gauge? Strain gauges are nothing, but when we apply strain its resistance will change, it is a kind of piezoresistor. So, I can make these array of sensors using P DoT PSS. P DoT PSS is a conductive polymer, what is it, a conductive polymer. Second, if I have an insulator on it and on the insulator if I have gold pads, you can see here gold pad patterns. And by the way, everything that you see here like here in the center it consists of piezoresistor and gold pad and SU 8 pillar. So, tiny super tiny you see this is 1 millimeter. So, it is about 1 millimeter within that area we have the sensors, within that area we have the sensors. So, anyway coming back to here. 25 If I have piezoresistors on which I have an insulator on which there is a gold pad and on gold pads, there are SU 8 pillars, there are SU 8 pillars. Then I have a sensor if the substrate is a flexible substrate then I can use these sensors. And in SU pillar we can make it conductive, we can make it conductive. I can use this sensor for measuring the electrical and mechanical property of a material. And we will see how we can use this device for measuring the electrical and mechanical property of the material. And you can see here the contact pads the, you see it is like zigzag, it is like here. It is not a straight-line why to have this kind of pattern? Why not have a straight line? What is the designing problem in this one or this one? Why we have selected this particular design? We will see that. So, you understand how you can design this kind of flexible sensors for your particular application. Because, you see I am showing some of the application of my work, my research. But, what about the problems that you come up with, if you come up with a unique problem and you want to find a solution for that particular problem, you have to design your own sensors. By better understanding, these flexible sensors what we were talking about can you use a concept and can you create your own sensor that is the idea, guys. So, what I will do is I will teach you how to fabricate these flexible sensors using MEMS technology. There are a few more devices that we have to see and those devices we will see in the second module. This is an introductory module where I wanted to you to get familiarized with a lot of devices, different kind of sensors and MEMS-based technology; and how these sensors or devices or microfluidic chips can be used for clinical applications. But please make sure or please understand this thing that this is not only one area where you can use the knowledge of microengineering. We will see the fabrication and you can use this fabrication for designing sensors for other applications as well. So, I will show you devices that are used for clinical perspective, but you can make devices which can be used for electronics, which can be used for robotics. For example, if I want to have a touch sensor or robot wants to have a touch sensor, can you design this touch sensor using the knowledge that you acquire in this subject that is the idea. 26 So, we will be looking at this from one point of view that if I want to design a flexible force sensor or a touch sensor what kind of changes in the design can be made. So, I will see you in the next module we will discuss a few more devices and then we will start understanding microfabrication. We will see the process flow how we can design a device, what are the techniques used for designing this device, such as what are the equipment used, how a clean room looks like, what are the equipment within the cleanroom. And then we will see each device in detail and how it can be used for solving a particular problem. Till then you again just look at the lecture at the end of this particular course you will understand how you can fabricate a device at least using the process flow, at least on paper. And then in the next course, I have, a plan to go to the lab and perform actual experiments. But, to go to that level first we need to understand how we can fabricate devices or how we can design the process flow for the device. So, I will see you in the next class, till then you take care. Bye. 27