noc19 ee41 lec03

Summary

In this enlightening lecture by NPTEL - Indian Institute of Science, Bengaluru, the focus is on the intricacies of sensor fabrication, particularly for medical applications. The module delves into the types of sensors available, such as micro heaters, interdigitated electrodes, and their application in measuring the impedance of cells, which can be crucial in distinguishing between healthy and cancerous tissues. Various techniques like physical and chemical vapor deposition are discussed as methods for sensor creation. The course also touches upon thermal properties of tissues and the potential applications of these sensors in tissue diagnostics and treatment.

Highlights

• Discusses different sensors and their applications in the medical domain 🚑
• Explains the role of micro heaters in cell analysis 🔥
• Describes the use of interdigitated electrodes for impedance measurement ⚖️
• Mentions piezoelectric and piezo resistive sensors for mechanical stress measurement 📏
• Showcases the importance of sensor design in detecting cancer 👩‍🔬

Key Takeaways

• Understanding sensors helps in treating diseases effectively 💡
• Different sensors for different medical applications! 🏥
• Microfabrication is key for sensor development 🔬
• Temperature control is crucial for maintaining cell viability 🌡️
• Interdigitated electrodes can measure impedance changes ⚡

Overview

In this lecture, we dive deep into the world of sensor fabrication with a focus on their applications in the medical field. The instructor elaborates on various types of sensors including micro heaters and interdigitated electrodes, explaining their design and function in detail. Such sensors are pivotal in distinguishing between healthy and diseased cells by measuring changes in electrical impedance - a technique particularly useful in cancer detection.

While highlighting the significance of sensor design, the talk also underscores the importance of maintaining an optimal temperature for cell viability. The instructor details how sensors are fabricated using techniques like physical and chemical vapor deposition. Such insights into fabrication equip learners with the knowledge to innovate new sensors and actuators not just for medical diagnostics but other varied applications too.

The session further explores piezoelectric and piezo resistive sensors, explaining how these help in understanding the mechanical properties of tissues. This kind of innovation holds promise in the realm of biopsy and tissue analysis, providing crucial insights into disease progression based on tissue elasticity and thermal properties. Overall, the lecture emphasizes the vast potential and exciting applications of sensor technology in revolutionizing medical diagnostics.

Chapters

• 00:00 - 10:30: Introduction and Overview of Medical Sensors This chapter introduces the topic of medical sensors, providing an overview of their importance and applications in the medical field. The introduction sets the stage for a deeper exploration into various types of medical sensors, their functionalities, and the role they play in modern healthcare solutions. The content aims to equip readers with foundational knowledge to understand how these devices contribute to medical diagnostics and patient monitoring. The chapter begins with a welcoming note, setting a positive tone for the learning experience.
• 10:30 - 21:00: Micro Heaters and Interdigitated Electrodes The chapter introduces the topic of sensor fabrication, focusing specifically on micro heaters and interdigitated electrodes. It begins with a recap of the previous module, which covered various sensors and their applications. The instructor promises to delve deeper into the fabrication details of each sensor type in the upcoming modules, aiming to provide comprehensive knowledge as part of the course. The immediate focus, however, is on understanding the variety of sensors available and their respective applications.
• 21:00 - 31:30: Force Sensors and Strain Gauges The chapter focuses on the medical domain to understand how the basics of microfabrication, technology, and sensor design can help in fabricating various sensors and actuators. These technologies, commonly used in the medical field, have diverse applications across different areas. The chapter also discusses various physical and chemical vapor deposition techniques.
• 31:30 - 42:00: Cantilever Sensors and Tissue Elasticity The chapter titled 'Cantilever Sensors and Tissue Elasticity' begins by discussing various deposition techniques, focusing on fabrication methods for specific devices.
• 42:00 - 52:30: Interdigitated Electrodes for Tissue Analysis The chapter discusses the concept of interdigitated electrodes in the context of tissue analysis. The focus is on the structure and connectivity of these electrodes, which involve metal lines and contact pads. The importance of measuring resistance or impedance is highlighted, pointing out that without proper connection or structure, the impedance would be infinite.
• 52:30 - 63:00: MEMS-Based Cancer Diagnosis The chapter discusses the use of interdigitated electrodes in MEMS-based cancer diagnosis. It highlights the principle of measuring impedance changes when different materials are placed on these electrodes. Specifically, when cells are loaded onto the electrodes, their impedance can be measured, which is a critical aspect of the diagnostic technique.
• 63:00 - 73:30: Fabrication of Interdigitated Electrodes The chapter discusses the measurement of electrical properties of cells, specifically impedance, in normal versus diseased states. It highlights how cells from a healthy person and those from a person with cancer have different impedance values, indicating changes in electrical properties. The focus is on the methods used to measure these differences in impedance.
• 73:30 - 84:00: Analyzing Tissue Elasticity and Thermal Conductivity The chapter delves into the analysis of tissue elasticity and thermal conductivity, particularly in relation to the body's natural conditions. It highlights the typical temperature inside the human body, which is around 37 degrees centigrade, and considers environmental factors such as CO2 levels at approximately 5% and humidity around 95%. Understanding these parameters is crucial as they influence energy dynamics within the body.
• 84:00 - 94:30: Conclusion and Preview of Next Module The chapter discusses the optimal temperature conditions for keeping cells alive, specifically at 37 degrees centigrade. It contrasts this with the current temperature from where the lecture is being taken, which is 20 degrees centigrade. The chapter seems to focus on the practical implications and considerations of cell preservation at specific temperatures, providing insight into the ideal conditions needed for maintaining cell vitality. It serves as a conclusion and possibly hints at further exploration or practical steps in a subsequent module, although the exact details of the preview are not provided in the transcript snippet.

noc19 ee41 lec03 Transcription

• 00:00 - 00:30 [Music] hi welcome to this particular module
• 00:30 - 01:00 last module we have discussed a few of the sensors and the application right but as I have promised you that I will teach you each sensor fabrication in detail in the in the few of the modules right as a part of this particular course right now our focus is on understanding what kind of sensors are available and how what are the application of those sensors and
• 01:00 - 01:30 we will be focusing on medical domain so that you can understand that how understanding basics about micro fabrication and technology and sensor design technology can help you to fabricate several sensors and actuators for medical domain the same sensors and actuators can be used for other applications as well we will be discussing those applications in detail including different physical vapour deposition techniques chemical vapour
• 01:30 - 02:00 deposition techniques please ah graphite techniques to fabricate those devices alright so if you recall yesterday what we discussed was micro heaters right and then we discussed why we had to fabricate a micro writer how we can fabricate micro eater and how can have the resistance values right then we discussed how you can have an inter digitated electrodes on the micro heater now just to help you this is digits okay
• 02:00 - 02:30 this is inter digit digits inter digit now if you assume that this to our metal metal lines and if I'm not connecting to metal lines what will end these are the area these are the contact pads alright so these are the contact pads this one and this one alright and this is these are metal lines so if I measure the resistance right or impedance what will be resistance or impedance it would be it would be in finite right because
• 02:30 - 03:00 there is no connection it would be infinite now if I place anything on this particular two electrodes I see the change in the impedance values depending on the material that I have placed on these particular electrodes isn't it so the point that I am making here is that this inter digitated electrodes can be used to measure the impedance of different materials now if I load cells on this particular individual electrodes then I can measure
• 03:00 - 03:30 the impedance of a cell so if I take a per cell from a normal person and if I take a cell from a deceased person let's say we talk about the cancer so cell from the person suffering from a cancer then are the cells changing their electrical properties if you want to measure the cells from a normal person and cells from the person suffering from cancer you will see that the impedance values are different that means the electrical properties are different how can measure impedance with the help of
• 03:30 - 04:00 the inter digitated electrodes now what what is the the situation within our body right what I mean by situation is what is the temperature of inside the body around 37 degrees centigrade correct how much amount of co2 is there around 5% how much humidity around 95% energy right so the point is that at 37
• 04:00 - 04:30 degree the cells would be alive we can keep the cells alive at 37 degree centigrade - now right now where I am taking this lecture the temperature is about 20 degree centigrade okay I want when I take the cells from a normal person and energetic a sense from a
• 04:30 - 05:00 cancerous person I want their cells to be alive and to keep the cells alive we require 37 degree centigrade to Reece 37 degree centigrade we have to heat these cells or heat the device from 20 degree to 37 degree you got it how can we heat with the help of a micro heater so now if you have a micro heater and if you have a inter digitated
• 05:00 - 05:30 electrodes or the micro heater now interdit electrodes are made up of metal heater is made up of metal if I place two metals together what will happen it will be short circuit why it will be short so I cannot place one metal on the top of another matter right what I can do is I can have a insulating layer in between I can place one insulator in between the two metals now there is no
• 05:30 - 06:00 short there is no short correct so the point here is that if I have a heater and I have an insulator which can be my silicon dioxide which can be my silicon nitride and over that if I place interdigital electrodes then I can heat my device with the heater and I can measure my impedance with the help of inter digitated electrodes when I place any sample on the inter digitated electrodes you got it that's what we
• 06:00 - 06:30 have seen yesterday how to fabricate the heater and how to fabricate an inter digitated electrodes with a sandwich lever in between when I say fabricate you are just you have just seen the device right we will see the process flow in detail and the recipe also for that so that was the second sensor the third sensor that we have as we were talking about is a force sensor right
• 06:30 - 07:00 what can be a force sensor it can be a piezoelectric sensor it can be a piezo resistive sensor piezoelectric is when you apply a pressure that is changing the voltage right so the mechanical you know parameter is changed to an electrical parameter or vice-versa right while intakes are in case of P so resistor when you apply a pressure or force there is a change in the resistance right now if I talk about the
• 07:00 - 07:30 strain gauge strain gauge when I apply a pressure there is change in the resistance high because of the strain on the sensor now we should also know when you talk about any strain gauge you should talk about God factor or gauge factor the the accent would be different it will be G a you GE a gog gog god
• 07:30 - 08:00 factor and what is the exactly god factor is quad factor is a ratio of J stress by strain that is Delta R by R divided by Delta L by L that means that when I apply a pressure on a piezo resistor then their resistance of the phaser resistor would change and because
• 08:00 - 08:30 of Pisa resistor let's add this up is a resistor embedded lesser this app is a resistor okay and the register is embedded onto this material so when I apply a pressure this will change this will Bend like this so bending will cause the change in length Delta L L Delta L L Delta and there is because it's bands there is a stress and if there is a resistor inside there is a change in the resistance values so now
• 08:30 - 09:00 we have Delta R because we had an original register and there is a change in resistance value and we have Delta L in there was Orion length and there is a change in length so Delta R by R divided by Delta L by L will give you the COS vector how you will use this values because depending on the god factor of what filter value is higher the sensitivity is better right so if you
• 09:00 - 09:30 compare a metal and if you compare a semiconductor the semiconductor goes factors are generally better than the metal god factors right so we took an example of arrhythmia and I was talking about the beating of heart and then I give an example that there is a catheter which you can you know place inside the body and not you of course it's a surgeon will place inside the
• 09:30 - 10:00 body and the heart will be that particular region which is misfiring the signal will be burnt and that burning would be with the help of RF side of ablation and when you press it you should know what is a force at the tip of the catheter right and if the if the force is less the recurrences are if a force is more then the other parts of the tissue heart tissue will get burned in both the cases is not good for us we
• 10:00 - 10:30 require an optimized force value and to get that optimized first value we need to design a force sensor so we will see how to design a force sensor for that particular application cool all right the next sensor that we discussed was the cantilever right the resistor cantilever and we saw that how a ballista cantilever can be used to measure the change in the mechanical properties of tissue now the same
• 10:30 - 11:00 cantilever can also be used to see the change in the mechanical properties of cells how these cells from a normal to cancer the mechanical properties changes what I mean by mechanical body elasticity of the cell would change a cell which is cancerous would have different elasticity compared to cell which is normal if that is the case from the cells can be and I organized that okay a person is suffering from cancer right but group of cells together makes
• 11:00 - 11:30 a tissue if you work on tissue and if you press the tissue what will happen you may have a property that from the onset of the disease to its disease progression how the mechanical properties of tissue is changing right and that you can convert to an elasticity value all right so you can either Pisa register and assuming that this is a tissue you can apply a force
• 11:30 - 12:00 the tissue depending on city of the tissue or stiffness of the tissue that the sensor will bend this bending will cause change in resistance because there is we have diffused a piezo resistor inside the cantilever and that change in resistance will help us to understand what is the elasticity of the tissue of course this change in the distance with applying or the tissue before that you have to calibrate it with the commercial force sensor and you also also want to know that what is just what is a change in the tissue in the
• 12:00 - 12:30 stress of the cantilever by using some hard material you can press it it will Bend and you will know the calibration protons all right now if you say that a cell or a tissue is changing its property or property elasticity right why because there is a calcification right and different different biological terms let's not go into that biology but
• 12:30 - 13:00 we know that the tissue elasticity is changing now when the tissue elasticity is changing if I go for a scanning electron microscopy you have I have written yesterday you have seen some images interdigital electrodes on the heater that were SEM images right so if I do a fill electron or field emission field emission in scanning electron microscopy which is Fe SEM then I can understand the structure of the tissue
• 13:00 - 13:30 so if I take a normal tissue and if I take a cancerous tissue and if I see the structure of the tissue or with the help of Fe SEM what I will have or a topography of the tissue if I see what I will have I I see that there is a change in the roughness of the tissue a cancerous tissue is rough compared to the normal tissue or normal tissue is much more smoother compared to cancerous tissue okay so when the tissue is rough
• 13:30 - 14:00 or tissue is smooth what will happen the resistance would change right a resistance of a smooth material would be different than the resistance of a rough material the resistance would change as per the tissue property and what I told you the cancerous tissue normal tissues
• 14:00 - 14:30 are different than the cancerous tissues in terms of the surface roughness can we use this property and understand the change in the tissue property so that means that if the roughness is different resistance is different that means I can change see the change in the resistance of the tissue as cancer progresses right now you had to keep the tissue alive to keep the tissue alive or no not and I out the tissue to get dry right a design
• 14:30 - 15:00 and in a different way you have to load that issue with some saline solution like PBS forceful buffer saline all right and you want to measure the resistance but now since you have added the Saline you cannot directly go and look at the resistance values you have to go for an impedance value so what I mean by that so if you see the screen these are the inter digitated electrodes
• 15:00 - 15:30 here okay and what will be the impedance of this impedance of this would be infinite or extremely high why because there is nothing on this individual electrodes and only there are metal lines not connecting with each other right you see here there are metal lines not connecting with each other these are lines which are not connecting with each other correct now on this if I place a tissue
• 15:30 - 16:00 your place a tissue which is this particular image right you can see the tissue here right placed on the inter digitated electrodes what will happen there will be change in the impedance value the Z would change right the z of this and the Z of this this would be some kilo ohms or megohms this will be close to infinity understood
• 16:00 - 16:30 right now you can design this kind of inter digitated electrodes which are also called sensors because it will sense the change in the impedance impedance of or impedance of normal tissues and cancerous tissues right so the impedance change of the normal tissues and the concerns tissues can be
• 16:30 - 17:00 measured with the help of inter digitated electrons right what is impedance impedance is an electrical parameters so we are measuring the electrical characterization of breast tissues to the help of interdigital electrodes so we said MEMS based M stands for micro distance for micro electro mechanical
• 17:00 - 17:30 systems micro electromechanical systems MEMS okay MEMS based best cancer diagnosis now this is tissue based devices so it's a biopsy based tissues will discuss this thing when we discussed this device in detail how to fabricate it because that's a part of this particular course it should be expert in understanding the process flow and the recipe and the fabrication of
• 17:30 - 18:00 different sensors all right so if I want what is this if I draw a cross-section of this this is nothing but you have this silicon wafer and on silicon wafer whether you have silicon wafer and you have a glass as a substrate all right this is silicon this is glass what I want to have I want to have inter digitated electrodes on the substrate silicon and glass our
• 18:00 - 18:30 substrate so if this is a glass right then I can deposit a matter this is chrome gold alright this is glass then you deposit a metal and then
• 18:30 - 19:00 you perform photolithography then you were from photolithography to pattern this chrome gold to form inter digitated electrodes right in case of silicon let me draw a little bit small schematic silicon can I deposit a metal can I
• 19:00 - 19:30 deposit a metal directly on silicon this is my chrome code on silicon wafer my question is in case of glass I could directly
• 19:30 - 20:00 deposit chrome gold on glass and pattern it to form individual electrons in case of silicon can I do the same thing I cannot write why because glass is an insulator while silicon is a semiconductor right so what should I do for if I want to make the device on silicon wafer I had to first grow
• 20:00 - 20:30 silicon dioxide I the first grow silicon dioxide right this is sio2 what is sio2 sio2 easier glass on this sio2 I can deposit a metal
• 20:30 - 21:00 I can deposit a matter and I can do a little graphic I can perform a photolithography alright so this is my
• 21:00 - 21:30 interdigital electrodes inter digitated electrodes this is my silicon dioxide and this is silicon you got it now don't worry about how the photo lithography is performed that I will teach you for toe little Gaddafi is
• 21:30 - 22:00 performed I I'll teach you right now just understand that if I can if I want to use silicon as a substrate I haven't to use glass as a substrate what is the difference glass being an insulating material I can directly deposit a metal write and perform photography to to fabricate inter digitated electrodes in case of silicon since silicon is a semiconductor I need to make an insulating layer or deposit or grow an insulating there over which I
• 22:00 - 22:30 will deposit metal right and then I will for a performer photography to form industry electrodes this metal is grown using a technique called physical vapour deposition silicon dioxide is grown using thermal oxidation alright now what is silicon dioxide silicon dioxide is nothing but glass right silicon dioxide is nothing
• 22:30 - 23:00 but yes so this is how you can fabricate inter digitated electrodes will they will discuss the process flow later on in the in the few models from now okay now you have seen and heater and inter digitated electrons right you have seen this fabrication you have seen this fabrication now on this inter digitated electrodes if I add a pure resistive material piezo resistive material right
• 23:00 - 23:30 and if I place a tissue on this and if I apply a force force f1 this piece of resistor visionaries - material is nothing but these are the sensors now because how many sensors 1 2 3 & 4 there are 400
• 23:30 - 24:00 digital electrodes so I have for visual registers on which I have placed a tissue and applying unknown force right so the piezo register will change the resistance based on the force that we have applied but the amount of force that we applied an amount of force reaching the prison resistor depends on the elasticity of the tissue isn't it
• 24:00 - 24:30 the force our I am applying f1 and the force at P so register measures or it will reach the piezo register will depend on the elasticity or the stiffness of the material placed between the sensor and the indenter indenter is where you apply the force this is where you can say it is an indenter alright so
• 24:30 - 25:00 now what will happen from this we can measure the elasticity of that issue I'll teach you this is very interesting biochip right I'll teach you in detail right now just understand quickly now when I want to apply a force the piezo register will chain the piezo resistivity only when it will it is able to measure the change in the force so
• 25:00 - 25:30 suppose I have a silicon wafer and I have a silicon wafer with a diaphragm like this if I apply a force here and I apply a force here which one will Bend this is not going to bend because silicon is solid material hard material this will Bend so here what I see what I
• 25:30 - 26:00 what we are expecting is it will Bend like this right in this case nothing will happen so we need to create this diaphragm right we have to etch the silicon wafer to create the diaphragm how to etch the silicon wafer that there are there is a technique called micro machining micro
• 26:00 - 26:30 machining machining all of you have learned in the workshop right we machine the different metals right at micro level when you perform machining is called micro machining all right now the bulk of the silicon is machined is taken out right here you can see bulk of the silicon material is taken out that's why this process is called bulk micromachining bulk micromachining all
• 26:30 - 27:00 right so this is out the silicon will Bend then if I have a piezo resistor on this silicon wafer if I have a piece of register on this silicon wafer then what
• 27:00 - 27:30 do you see here there is a bending of the piezo register there is a bending of the pizzle register this bending will cause change in the resistance right so the stress in the prison resistor because in resistance so to help increase the sensitivity of the piezo resistive material we are performing a bulk micromachining technique by which we are etching the silicon wafer from
• 27:30 - 28:00 the backside and this is what you can see right over here all right the backside of this particular wafer this one on the backside there is a pit so it becomes a diaphragm becomes a diaphragm right so we will see how to create this bulk micromachining and this is also a sensors chip that can be used to understand the change in the mechanical and thermal properties how thermal
• 28:00 - 28:30 properties so now you have a heater on the chip right you have a heater and you have a PC resistor material right you have a heater insulator you have a heater insulator inter digitated electrodes on which you have a piece of resistive material now if I if I have a tissue let's assume that this is a chip and I place a tissue on the chip so let me place a tissue let's say this is a tissue all right I what is there in my chip my chip has a heater I heat this tissue and I have an indenter
• 28:30 - 29:00 something that presses that issue like this okay if this indenter has a thermistor what is this thermistor at the tip was the chip having chip is having a heater so I'm heating their bottom of the tissue and I am measuring the top temperature of the tissue the modern temperature I know top temperature I am measuring with the help off with the help of indenter because
• 29:00 - 29:30 indenter as a thermistor so I will get t1 is a temperature that I am heating at the bottom of the tissue and t2 which is a temperature at the top of the tissue right now depending on the tissue properties or depending on the stage this property would change whatever in my stage state 0 stage 1 stage 2 stage 3 stage 4 these are different stages in breast cancer right so the thermal
• 29:30 - 30:00 conductivity of the tissue can be measured with progression of the disease any tissue related cancer we can measure the thermal conductivity of that particular tissue using this particular sensor right which is our micro heater to measure the thermal conductivity with an inductor with the thermistor and then we have a piece of resistor so now if you again consider this as a chip
• 30:00 - 30:30 this is a tissue and there's a pressure resistance which will apply unknown force on the tissue and how much amount of resistive resistance is changing depends on how much force is actually translated through the tissue and that depends on the tissue elasticity you got it so now we are measuring D we can measure elasticity of the tissue we can also reserve the thermal conductivity of the tissue right that is a sensor that
• 30:30 - 31:00 we are talking about it's not ending we have many more to discuss right and let us see one more sensor or let us do like this let us stop here and let us meet in the next module because it will be too much for you to digest at one time it's it's a good to eat food in small proportions so I will meet you in the next module talking about few more sensors and there we will see what is a
• 31:00 - 31:30 microfluidic sensor and how can you use it for rapid drugs okay very interesting like I said once you understand how to fabricate a sensor how to fabricate an actuator you will be able to find enormous applications of these particular devices all right so till then you take care I'll see you in the next class bye