Microfabrication with Glass-Like Carbon
Summary
TLDRThis 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
🔬 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.
🛠️ 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.
📡 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.
⚒️ 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.
Mindmap
Keywords
💡Glass Like Carbon
💡Microscale Structures
💡Pyrolysis
💡Thermal Conductivity
💡Annealing
💡Defects in Carbon
💡Graphitic Order
💡Microfabrication
💡MEMS Devices
💡Lithography
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.
Weitere ähnliche Videos ansehen
Surface Area Analysis of Carbon Materials
Surface hardening of steel | flame, induction, laser beam, case hardening and nitriding
Introduction to SACS: Structural Analysis for Offshore Engineering
Introduction to Structural Dynamics Course by Prof. Pradeep Kumar Ramancharla, EERC, IIIT-H
Application and Analysis of Switches I
Introduction to Modern Broiler Production (all subjects combined)
5.0 / 5 (0 votes)