Microfabrication with Glass-Like Carbon

Summary

This script delves into microfabrication using glass-like carbon, emphasizing the benefits of smaller structures for quality and thermal management. It discusses challenges like trapped bubbles and impurities in larger structures, advocating for microscale fabrication for better carbon quality and efficient defect annealing. The speaker explores various microfabrication techniques, including traditional methods like drilling and EDM, and advanced lithographic processes. The goal is to create microscale devices with high surface area for enhanced functionality in sensors and batteries, while also touching on the distinction between microscale structures and devices.

Takeaways

• 🔬 Micro scale structures are those in the micrometer size range, and their quality can be optimized by reducing their size to allow for better annealing of defects and trapped bubbles.
• 🌡️ Heat treatment temperatures can be lowered for smaller structures due to increased surface area, which facilitates the annealing process and reduces impurities.
• 💧 Defects in carbon structures, such as non-six-membered rings, are higher energy structures that can anneal out to form more energetically favorable six-membered rings, leading to a more graphitic order.
• 🧊 The transition from large to smaller structures (from centimeter to millimeter, and micro to nano) is beneficial for material quality and allows for batch fabrication, reducing material use and increasing efficiency.
• 🔋 Smaller structures have a higher surface area to volume ratio, which is advantageous for applications like biosensors and batteries where interaction with the environment is crucial.
• 🏭 Industrial glassy carbon devices or large scale structures should ideally be smaller than 5 millimeters to maintain optimal properties.
• 🔩 Microfabrication techniques are specialized and differ from traditional manufacturing methods, often involving photolithography and other non-traditional methods to create microscale structures.
• 📡 MEMS (Micro Electro Mechanical Systems) are a class of microscale devices that utilize mechanical properties to obtain electrical signals or vice versa, but not all microscale devices are MEMS.
• ⚙️ Traditional manufacturing techniques like drilling, EDM, and ECM can also be adapted for microfabrication, showing the versatility in approach to creating microscale structures.
• 🔬 Lithographic techniques such as photolithography, electron beam lithography, and nano imprint lithography are crucial for patterning polymers in microfabrication processes.

Q & A

What are microscale structures in the context of manufacturing with glass-like carbon?

Microscale structures refer to structures that are in the micrometer size range, which can be created using glass-like carbon through various microfabrication techniques.

Why might large structures made of polymers have bubbles when converted into carbon?

Large structures made of polymers may have bubbles trapped inside due to byproducts like tar-like materials and synthetic gases released during pyrolysis. The large size of these structures can prevent efficient annealing of these bubbles.

How does the thermal conductivity of a carbonizing matrix affect the quality of glassy carbon structures?

The thermal conductivity of a carbonizing matrix can vary, with higher carbon fractions leading to increased conductivity. However, impurities and trapped bubbles in the core can lower thermal conductivity, affecting the overall quality of the glassy carbon structure.

What is the optimum size for industrial glassy carbon devices to avoid issues related to trapped bubbles and impurities?

The optimum size for industrial glassy carbon devices or large scale structures is smaller than 5 millimeters to minimize issues related to trapped bubbles and impurities.

Why is it beneficial to reduce the size of structures from centimeter to millimeter, and further to micrometer or nanometer?

Reducing the size of structures allows for better quality carbon due to lower heat treatment temperatures required for annealing out byproducts and defects, and it also increases the surface area to volume ratio, which is beneficial for various applications.

What is the significance of a higher surface area in microscale structures for sensor applications?

A higher surface area in microscale structures is significant for sensor applications as it allows for better capture of target molecules, even at low concentrations, due to increased contact with the surrounding liquid.

How does the size reduction of devices impact their functionality and sensitivity in applications like batteries?

Reducing the size of devices can lead to a higher surface area, which is beneficial for applications like lithium-ion batteries. This allows for more efficient charging and discharging as ions can move in and out of the structure more effectively.

What are the requirements for a polymer to be used in microfabrication for creating glass-like carbon structures?

A polymer used in microfabrication for creating glass-like carbon structures should undergo coking without becoming too soft to lose shape, have a high carbon content, and be compatible with both the fabrication techniques and the carbonization process.

Why is batch fabrication preferred in microfabrication processes?

Batch fabrication is preferred in microfabrication because it allows for the creation of multiple structures or devices at once, which is more efficient and cost-effective compared to individual, serial manufacturing techniques.

What is the difference between microscale structures and microscale devices?

Microscale structures are physical forms at the micrometer scale, while microscale devices are systems that perform a specific function or operation at the microscale, with their functional elements being smaller than 100 micrometers.

How do top-down and bottom-up approaches differ in microfabrication?

Top-down approaches in microfabrication involve starting with a larger piece of material and removing unnecessary parts, while bottom-up approaches build structures by adding layers or components, starting from smaller molecules or cells.

Outlines

00:00

🔬 Microscale Structures and Glassy Carbon

This paragraph discusses the challenges and considerations of creating microscale structures using glassy carbon derived from polymers. It explains that large structures made from polymers, when converted to carbon, may trap bubbles and impurities due to the byproducts of the pyrolysis process. These trapped defects can lead to variations in thermal conductivity and prevent the material from being classified as true glassy carbon. The speaker suggests that optimizing the size of the structures can mitigate these issues, as smaller structures allow for more efficient annealing of defects and require lower heat treatment temperatures. The concept of defects in carbon structures is also introduced, with a focus on non-six-membered rings that cause strain and distortion in the material. The speaker emphasizes the importance of achieving a more graphitic order through the annealing process to improve the quality of the glassy carbon.

05:03

🛠️ Microfabrication Techniques and Materials

The second paragraph delves into the specifics of microfabrication techniques and the materials used in the process. It highlights the need for polymers that are compatible with both microfabrication techniques and the carbonization process. The paragraph also touches on the advantages of reducing the size of structures to the micrometer scale, which include using less material, enabling batch fabrication, and increasing the surface-to-volume ratio. This leads to improved performance in applications such as biosensors and batteries. The speaker also introduces the concept of substrates in microfabrication, which serve as the base for creating devices or structures. The benefits of higher surface areas for sensing and energy storage are discussed, along with the importance of specialized fabrication techniques and materials for creating microscale devices.

10:06

📡 Microscale Devices and MEMS

This paragraph focuses on defining microscale devices and systems, with an emphasis on the functional elements that characterize them. It explains that a device is considered microscale if its functional element is smaller than 100 micrometers. The paragraph also introduces the concept of MEMS (Micro Electro Mechanical Systems), which are a class of microscale devices that utilize mechanical properties to obtain electrical signals or vice versa. The speaker clarifies that not all microscale devices are MEMS, but all MEMS are microscale devices. Examples of MEMS and other microscale devices like biosensors are provided to illustrate the diversity within the category. The paragraph concludes with a discussion of microfabrication techniques, distinguishing between traditional manufacturing methods that can be adapted for microscale work and newer techniques developed specifically for microfabrication.

15:07

⚒️ Traditional and Advanced Microfabrication Techniques

The fourth paragraph explores both traditional and advanced microfabrication techniques. It begins by acknowledging that some conventional manufacturing methods, such as drilling and electrochemical machining, can be applied to create microscale structures. The speaker then transitions to discuss advanced lithographic techniques, which are central to microfabrication. The paragraph explains that lithography involves creating patterns on a substrate, typically using a polymer film that is selectively removed to form the desired structure. Various lithographic methods are mentioned, including photolithography, electron beam lithography, X-ray lithography, and nano imprint lithography, each utilizing different energy sources or mechanisms to pattern the material. The paragraph emphasizes the importance of these techniques in the microfabrication process and how they enable the creation of intricate microscale structures.

Keywords

💡Glass Like Carbon

Glass Like Carbon (GLC) is a form of carbon material known for its high strength and resistance to thermal shock. In the video, it is discussed as a material that can be used to create microscale structures. The process of converting polymers into GLC involves careful control of pyrolysis to avoid trapping bubbles and impurities, which can affect the material's properties. The video emphasizes the importance of optimizing the size of structures to ensure quality and homogeneity in the final carbon product.

💡Microscale Structures

Microscale structures refer to structures that are in the micrometer size range. The video discusses the challenges and benefits of creating such structures from materials like polymers, which are then converted into carbon. Smaller structures allow for better control over the carbonization process, leading to fewer defects and bubbles. The video also suggests that reducing the size from centimeter to millimeter, and further to micrometer or nanometer, can improve the quality of the carbon structure.

💡Pyrolysis

Pyrolysis is a thermal decomposition process used to convert organic polymers into carbon materials. In the context of the video, pyrolysis is crucial for creating glass-like carbon from polymers. The script mentions that byproducts like tar-like materials and synthetic gases are released during pyrolysis, which can lead to trapped bubbles in the material if not managed properly.

💡Thermal Conductivity

Thermal conductivity is the ability of a material to conduct heat. The video explains that the thermal conductivity of carbonizing matrix can vary, with higher carbon fractions leading to increased conductivity. However, impurities and trapped bubbles can reduce thermal conductivity in the core of the material, affecting the overall properties of the structure.

💡Annealing

Annealing in the context of the video refers to the process of heating and cooling a material to relieve internal stresses and improve its crystalline structure. It is mentioned that smaller structures allow for more efficient annealing of defects and trapped byproducts, leading to a more uniform and higher quality carbon material.

💡Defects in Carbon

Defects in carbon, as discussed in the video, can include non-six-membered rings which are non-crystalline structures causing strain. These defects are higher energy structures that can anneal out during the heat treatment process. The video emphasizes the importance of reducing these defects to achieve a more graphitic and ordered carbon structure.

💡Graphitic Order

Graphitic order refers to the arrangement of carbon atoms in a hexagonal, crystalline pattern as found in graphite. The video explains that achieving a more graphitic order in carbon materials is desirable for improving their properties. This can be accomplished by ensuring all six-membered rings are present, which allows for the characteristic ABABAB stacking pattern of graphite.

💡Microfabrication

Microfabrication is the process of manufacturing structures and devices at the microscale. The video discusses various techniques and materials used in microfabrication, emphasizing the need for specialized methods due to the small size of the structures. The script also highlights the advantages of microfabrication, such as reduced material use, increased surface area to volume ratios, and the ability to perform batch fabrication.

💡MEMS Devices

MEMS stands for Micro Electro Mechanical Systems. These are a class of microscale devices that combine electrical and mechanical properties. The video explains that MEMS devices can convert mechanical movements into electrical signals or vice versa. While not all microscale devices are MEMS, they represent an important category within microfabrication, with examples ranging from sensors to actuators.

💡Lithography

Lithography in the context of the video refers to a set of techniques used to pattern materials at the microscale. The script mentions various types of lithography, including photolithography, electron beam lithography, and nano imprint lithography. These techniques are essential for creating precise microscale structures and devices, and they involve the use of light, electrons, or mechanical pressure to transfer a pattern onto a substrate.

Highlights

Micro scale structures are defined as structures in the micrometer size range.

Large polymer structures converted into carbon may trap bubbles due to byproducts released during pyrolysis.

Optimum size for industrial glassy carbon devices is smaller than 5 millimeters to prevent trapped bubbles and ensure quality.

Reducing structure size to micro or nanometer scale allows for lower heat treatment temperatures and better annealing of defects.

Defects in carbon structures, such as non-six-membered rings, are higher energy structures that can anneal out under certain conditions.

The presence of defects and bubbles in curved carbon structures can impede the annealing process.

Micro fabrication techniques are necessary for creating glass-like carbon structures due to the specific requirements of polymers and carbonization.

Batch fabrication processes are advantageous for micro scale structures due to the ability to create many devices simultaneously.

Higher surface to volume ratios in micro scale structures can improve the performance of devices like biosensors and batteries.

MEMS devices are a class of micro devices that utilize mechanical properties to obtain electrical signals or vice versa.

Not all micro scale devices are MEMS; other types include biosensors and battery electrodes.

Micro fabrication can use both top-down subtractive techniques and bottom-up additive techniques.

Traditional manufacturing techniques like drilling and EDM can be adapted for micro scale fabrication.

Lithographic techniques, including photolithography and electron beam lithography, are used for micro scale structure fabrication.

Nano imprint lithography uses mechanical pressure to pattern polymers in micro fabrication.

Material selection is crucial for compatibility with micro fabrication techniques and carbonization processes.

Transcripts

Hello everyone now, since we are on the topic  of Manufacturing with Glass Like Carbon,  

let us also talk about making micro  scale structures using glass like carbon.  

So, what are micro scale structures? These are the  structures that are in the micro meter size range. 

You know we discussed this in detail that if you  have very large structures made of polymers and  

then you convert them into carbon what happens  is; these thick structures, they may end up  

having some bubbles trapped inside of them,  trapped inside in in the core of the material. 

These bubbles are caused by the by  products with the the tar like materials,  

the synthetic gases that that are released  during the the pyrolysis of the polymer and now,  

since the structure is too big they are not able  to anneal out in an efficient manner and also the  

carbonizing matrix it is a very complex material  and it is thermal conductivity may also differ. 

, At the so once, it becomes more carbon  you know it has a higher fraction of carbon  

then the thermal conductivity may increase, but  what you have in the core may have a lower thermal  

conductivity, because of higher impurities and  also the trap bubbles and then it becomes you know  

then your overall structure you cannot call it  glassy carbon structure, because some of it is not  

glassy carbon really or it has different property. So, what do you do? You try to optimize your size.  

So, in the case of industrial glassy carbon  devices or large scale glassy carbon structures  

the optimum size is smaller than 5 millimeter  ok. Now, the point is if we can go down from  

centimeter scale to millimeter scale, why not  millimeter to micrometer or micro to nanometer? 

The idea is that the smaller the size the better  the quality of your carbon or not better quality,  

but in that case you require slightly lower  heat treatment temperatures, because you now  

are able to provide more surface area for your  by products as well as defects to anneal out. So,  

why by the way defects also would like to anneal  out? What are defects? In the case of elemental 

So, let us not talk about you know doping induced  defects and so, for an element defects are in the  

case of carbon non 6 membered rings. So, non  crystalline structures structures that are,  

that have a certain strain ok or these are  the kind of structures which will also lead to  

distortions in your otherwise graphitic material. These structures are actually higher energy  

structures and they will try to anneal out as long  as you know it is possible, it is not possible if  

you have these strongly curved carbon structures  or if you have some of these strongly curved  

structures completely they convert into fullerene  like structures, they become completely closed. 

So, they are spherical now or  cage like structures that we call  

so once you have a defect or a bubble or a void  trapped inside these curved carbons, then it  

will be very difficult for it to to break that  structure and you know get out of the material,  

but there are also several voids which are not  really with for them it is possible to anneal out. 

But what we need to do is? We need to provide  it certain energy in the form of heat and  

also you should remember that when these defects  anneal out, lets say for 7 membered ring,  

tries to convert into a 6 membered ring  which is its most you know energetically  

favorable state in that case you will also  have a more graphitic order which means you  

will have more a b a b a type organization. Because now, there is a possibility when you  

have all 6 membered rings it is possible to have  this kind of hexagonal graphite like arrangement  

crystalline arrangement which was otherwise,  once you have 5 membered rings, then you will  

only have this random rotation of of the sheets  on top of each other what you would call graphenic  

sheets and not graphene sheet, we are not calling  them graphene, because they contain defects ok. 

So, these are the fundamental concepts also in  the case of micro fabrication you have the same  

other same principles are the same. So, if you  want to get glass like carbon what do you want?  

You need a polymer which undergoes coking, but it  does not become so, soft that you lose the shape. 

This is also again valid for the large scale  structures as well so, that is number 1 and number  

2 you should have the right fabrication techniques  which the fabrication techniques is what we are  

going to talk about. Your carbon content in the  polymer should be high. So, these are again, these  

are the things that are valid for for everything. The only thing is that now we have ok we we need,  

because we have very specialized micro fabrication  techniques now, we are not using the traditional  

milling and drilling and turning techniques,  because micro fabrication have its own set of  

fabrication techniques, this is  what we are going to talk about. 

So, we need polymers that are compatible  with those fabrication techniques  

and that are compatible with your carbonization.  So, both conditions should be satisfied. Also,  

one more additional factor is that when  you are doing micro fabrication you are  

typically making structures onto a substrate. Substrate means; yeah any flat structure you know,  

on top of that you will make your your  devices or structures so whatever is,  

because micro meter scale things can  be very small you can imagine that.  

So, these you will not make them individually you  will rather do a batch fabrication process which  

in fact, is the advantage of micro fabrication. So, the overall idea, the fundamental idea of  

micro fabric or reducing the size  of the structures and devices is 2,  

number 1 be able to use less material and do batch  fabrication, number 2 you have higher surface to  

volume ratio in all of these structures. So, higher surface area always helps.  

How? Lets say if you take an example of a of a  biological sensor. What does this sensor have  

to do? What do sensors do? They sense something  biosensor would sense some biological molecule  

which can be a disease antibody or antigen or any  any bacteria or virus, this device has to sense  

it, to catch it, to chemically attach to it. If it has a larger surface area then it will  

be able to catch your whatever is the desired  molecule from you know even when it has a very  

low concentration, because now it is in contact  of more liquid, because it has more surface  

area. Similarly, if you think of batteries,  batteries, let us say lithium ion battery. 

So, lithium ion requires more surface area to go  inside the structure and come out charging and  

discharging. So, these are also so that increasing  surface area reducing the overall footprint  

of the device. Overall footprint means;  overall size. So, if you want a chip that  

fits inside your you know mobile phone  then you do not want it to be too large. 

So, the weight is reduced, the size is reduced,  and the functionality, the sensitivity is  

increased. So, this is the overall idea anyway  of micro fabrication and that is why you want to  

have specialized fabrication techniques,  specialized materials, and let us see if we  

convert them into carbon, is there any advantage  of that. We know the advantages of carbon. 

So; now, let us talk about what are the things  that we do and how do we make these devices. So,  

you want to remove the the byproducts and defects  yes, ok. Now, as I also mentioned that you may get  

more graphitic order at lower pyrolysis or heat  treatment temperatures if you have, annealing,  

easier annealing of defects and also some carbon,  some polymer there we will talk about this. 

So, there are some polymers which are used for  many microfabrication techniques specially,  

photolithography these are actually able to give  you glass like carbon. So, this is what we will  

talk about. So, before that let me talk about some  very fundamental things about microfabrication.  

So, I am assuming that you do not know  anything about micro fabrication at this point. 

So, what is micro? Micro is 10 power minus 6  meter that you know. So, it is a here I have  

I have shown a scale where you can see so, if you  plot it on a logarithmic scale plot then you will  

have the same distance between 1 meter and 1  kilometer that you have between 1 micrometer  

and 1 nanometer, which is the order of 3. So, you can see in in terms of powers of  

10 how do these different length scale  with different dimensions look like. What  

we are talking about right now is the micro meter  scale fabrication and not nano scale fabrication. 

Also, another important thing is that we would  typically call it micro fabrication and not  

micro manufacturing, but in principle we are  making something, you can call it fabrication,  

you can call it manufacturing or anything. The idea is that fabrication is just the  

term which sounds little more sophisticated. You  know manufacturing sounds like you need good old,  

good old fashioned big machines machines and you  require physical labor. So, just to make it sound  

you know softer in a way you you know you can use  the term fabrication which is more commonly used,  

but manufacturing you are making  something you you know that ok. 

So, now what device so, let us talk  about device. What device would I call  

micro device? Anything which is smaller than you  know anything which has its dimensions in 10 power  

minus 6 meter scale, can can I just call it  micro microscale device or is it number 1. 

Number 2 should I have all the parts  of that device in the micrometer scale  

then the overall device will itself be very  small, then we know when you see the chips that  

are on your inside your phone or something not  every part of it so, some part of it which you  

know the the circuitry and so on that might  be in millimeter scale. So, does the entire  

device have to be in the micrometer scale? So well there is another this this rather  

formal definition of microscale device  is that when your functional element is  

smaller than 100 micrometer in size then you call  the device micro device and same thing actually  

is also applicable to nano devices there the  functional element is smaller than 100 nanometer.  

What is a functional element? Every device has a function.  

So, let us say if I have the sensor the the part  of that device that is actually doing the sensing,  

the rest of it may be some cables or some you  know, because you wanted to you made contact pads,  

because you need a readout from the device. So, there will be you know for the circuitry  

you will do a lot of things, but the part that  is actually performing the sensing you know  

function that is what should be smaller than 100  micrometer in the case of micro scale devices.  

Now, micro scale devices are also called micro  systems, because you know we are talking about  

devices right now, we are talking about the entire  system and not just one one individual structure. 

So, when you have this system which  performs a micro scale operation or function  

your functional element is smaller  than 100 micrometer then you call it  

micro system or you call it micro device ok. Now, they can be further divided of course, they  

can be sensors, they can be you know actuators,  they can be batteries also micro scale, battery  

electrodes there can be many other you know  definitions or classifications of these devices. 

One important class of micro scale  devices is what is known as MEMS devices.  

These the so, the the the full form of  MEMS is Micro Electro Mechanical Systems.  

So, as the name itself suggests you have  something to do with electrical properties  

and something to do with mechanical properties  and these are electro mechanical systems. 

So, the definition of MEMS is that  this is the class of micro devices  

where you either utilize mechanical properties of  that material or of that structure to gain. So,  

or to to obtain an electrical signal or a  readout or the other way around, either you  

use the mechanical properties to get electrical  signal or you use the electrical properties  

to let us say mechanically vibrate your structure. So, these type of devices are known as  

MEMS devices, but not all micro scale  devices are MEMS that you need to  

to remember. So, there is some examples of MEMS  you can actually do in internet search and find  

out lot of examples of MEMS, but remember that  there are not all micro scale devices are MEMS. 

That is very important, because there are other  than MEMS, there are other types of microscale  

devices for example, a battery electrode that has  an electrochemical property an electrochemical  

function. You do not call it MEMS device, because  that is passive that does not you know there is no  

mechanical movement of that structure. Also you are not getting an electrical signal,  

because of the mechanical movement and  so on. So, there is they are not they,  

but they are if their dimensions are in  micro scale and if the functional element is  

smaller than 100 micrometer, you will still  call them micro scale structures or devices. 

So, there are also other examples like biosensors,  if I have a micro scale you know structure and I  

immobilize some enzymes on top of it and those  enzymes are then performing certain function and  

they are sensitive to certain biological molecule,  this entire setup may not be a MEMS device,  

but it is a micro scale device. So, basically  the idea is that all MEMS are micro devices,  

but not all micro devices are MEMS ok. So; now, let us talk about the the micro  

fabrication technique. So, now, you understand  the fundamentally, what is the definition of  

microscale device and so on ok. What are  the microfabrication techniques? Well,  

as I said that you may not always use  the traditional manufacturing tools, but  

sometimes you may also some of the manufacturing  tools can also be used, but before that let us  

talk about what is the device anyway. So, we device should have a function,  

device should have a functional element, but  sometimes when you say micro scale structure  

remember that the structure may not be a device.  So, there is a difference. What is a material?  

Material is something like carbon. So, you see in this this image material is  

a material, we generally use the term material for  anything, anything that is bulk, that is tangible,  

that has you know some form. So, that is a  material carbon in the in a in a very general  

way we can call carbon a material, we can call  graphite a material, glass like carbon a material. 

We can also call carbon nanotubes a  material, but since it has a certain  

well defined structure as the nanoscale, then  we call it a nano material ok. So, material,  

nano material, these are still you know we have  not utilized them in a any specific fashion. 

However, now if you take this carbon  powder or carbon nanotube powder  

and then you let us say you mix it into a resin  and you print it on top of a of a substrate and  

that is why I said the substrate becomes  important in the case of micro scale. 

So, you make lines out of it which look like some  interdigitated electrodes these are called. So,  

these are not yet electrodes in a way, but  you want to make microelectrodes array. So,  

even if you make so, whatever design you had in  mind, once you make it on top of a substrate then  

you call it a structure, micro scale structure. And then you also make the contact pads you also  

make everything else you know whatever you know;  however, you get the readout from your material,  

you may actually integrate certain CMOS chips,  you can use, you know when you are completely  

fabricating a system which can perform a  certain function then you call it a device. 

So, this is the difference between structures  and and devices ok. That that is something you  

already know, but just to keep in mind ok.  Now, similar to large scale manufacturing  

you can also perform your micro fabrication using  top down or bottom up manufacturing approaches. 

So, top down means when you you know you take  a bigger piece of something and then you remove  

the unnecessary parts. So, you also can call it  a subtractive technique or you can use bottom up  

which is called the additive technique, techniques  like 3D printing, layer by layer arrangement of  

something or certain biological processes where  smaller molecules or cells will make a larger  

organ together that is also a bottom up process. A lot of natural biological processes are rather  

in fact, in fact, bottom up processes. So, you  can use both of these techniques, depending upon  

the material that is available to you and  depending upon also the ease of fabrication  

and the overall cost and and keeping all of these  things in mind also whether you want to use batch  

fabrication or you want to use individual  fabrication, serial manufacturing techniques. 

So, based on all of these things,  but you have both types of techniques  

bottom up and top down also in the case of micro  fabrication ok. Now, some of the traditional  

manufacturing techniques are actually also usable  for micro meter scale structure fabrication. 

So, actually you will be surprised to know  that there are drill bits that are you know,  

you can find drill bits in which are which can  actually precisely give you 50 micrometer diameter  

hole. So, it is not impossible there are  certain techniques which which have been  

translated into the micrometer scale. Some other examples I have mentioned here  

for example, EDM and ECM, electric discharge,  machining electrochemical machining, wire EDM's  

specially, these are the techniques that are  also used for making micro microscale structures. 

In fact, sometimes also in the past people did  make micro micro scale structures, but they did  

not, those were not the functional elements in  most cases. So, that is why the the technology  

was not so so, widely utilized, but micro scale  fabrication has also a lot of gold jewelry. 

You will if you go to a gold, good old fashioned  gold jewelry manufacturer in a in in in Jaipur  

or something like that you will realize  that actually they are using a lot of  

techniques which are giving  you micro scale structures,  

but they are not devices. You are making jewelry out of it,  

you are not really making electronic devices you  know. So, fabrication techniques were available,  

but there now we are using them more for for  for the devices and also now there is a market  

for these devices. Now, you have you know larger  equipment that require micro micro scale devices. 

So, it is this nowadays thats why a  microfabrication has become popular in  

a different way, but as I mentioned some of  the traditional techniques can also be used  

for making micro scale structures ok, but  then there are also certain new techniques  

which have developed which have been developed  specifically for micro fabrication applications. 

So, they may not be used at larger scale for  example, various lithographic techniques.  

Now, the the the term lithography actually means;  litho means a stone and graphy means carving  

something. Graphy is is a term which graph,  graphy, and even graphite is related to that. 

This this term is is actually used for making  drawing things, to graphy's to draw something  

ok and since, graphite was used for drawing things  you know that is why it is called graph-ite ok. 

So, these all words are related, but  lithography as such is a technique which is  

used for, which this term was used  for carving structures onto the stones  

and now we carved structures  on top of silicon wafer. 

So, we call that also lithography and how  do we carved structures on top of silicon  

wafers? We do not sit and scratch the  silicon wafer we we, what we do is; we  

make a polymer film on top of a silicon wafer or  any other substrate for that matter, but silicon  

wafer is the most commonly used substrate. So,  you make a film of polymer and then you remove  

the undesired parts and keep the desired parts. So, it is as simple as that that would be called  

your lithography, but now the question  is how do you remove the undesired parts  

and how do you determine what structure you  want to make and how do you actually make that  

structure. So, this is where the lithographic  techniques they that is where we need to learn  

about the various lithography say actually,  there is not just one lithography, there are  

various lithographic techniques that will depend  also on the polymer on the size of the structure. 

So, for example, photolithography, as the name  suggests, it has something to do with photons,  

something to do with light. So, this is the  technique where you utilize the UV light  

as your tool that is what is used for  removing the undesired parts of the material. 

Similarly, there is something called electron  beam lithography. So, you have beam of electrons  

that is used for carving the structures out into  your into your into your polymer, there is X-Ray  

lithography where you would use X-Rays, there  is something called nano imprint lithography  

where you will actually use a mechanical  push to to to to pattern your polymer. So,  

all of these techniques are used now  in in the case of micro fabrication.