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  • Good morning to all of you. Welcome to the course on Microsystems and MEMS. So, MEMS

  • the full name is microelectromechanical systems and this is a very emerging area today and

  • lot of work is going on around the globe on MEMS and Microsystems and it has got enormous

  • applications. Today, we will highlight the basic applications and some of the introduction

  • on MEMS and Microsystems.

  • Now, the MEMS topic or microsystems is an offshoot of the microelectronics and so to

  • start the course on MEMS and Microsystems, we will start from microelectronics and let

  • us look back little bit into the back of the present MEMS which is microelectronics and

  • we will look into the history on microelectronics.

  • So, this particular figure you can see the three scientists who are the Bardeen, Brattain

  • and Schokly from the Bell Laboratories and you know these three scientists first discovered

  • the Point Contact Transistor which is in 1947. For that discovery they got Nobel Prize in

  • 1956 and that was the first time Nobel Prize was awarded for an engineering device. You

  • know Nobel Prize is not given for any engineering branch. It is given on basic science, physics,

  • chemistry, mathematics, and etcetera. But here the Nobel Prize was given in physics

  • for engineering device.

  • Later on these three scientists developed a technique by which silicon can be oxidized

  • and oxidation demonstrated by them in 1953 at Bell Lab. Because of that demonstration

  • of oxidation from silicon, basically the people started thinking why we cannot make the transistor

  • on silicon monolithically. The first invention on transistor was a point contact that is

  • a diskette. Basically, they combined three pieces of silicon N P N and something like

  • that and then they took contact on each point and they got the transistor action.

  • This figure you can see is Jack Kilby and he invented integrated circuit in 1958.You can see here so that is the US patent and

  • which was submitted in February 6, 1959 and this was in September 1958 the patent was

  • written and that was the first monolithic integrated circuit you can see the picture

  • here and this gentleman is Jack Kilby and he got again Nobel prize for this particular

  • device in the year 2000.

  • So, from that time onwards people are not seeing back and they are proceeding forward,

  • particularly in the context of miniaturization of different components and making the integrated

  • circuits. Now this picture you see is the MOS transistor which contains over one million

  • MOS transistors and that is in early 1990s. Now if you look back to compare the revolution

  • in the integration of the components, we have to go back to the first transistor which is

  • also monolithic and that was made in 1960s, where four BJTs and several resistors are

  • connected together with some metal line. You can see this is a metal contact, this is a

  • metal born pad, here is another metal born pad and the four transistors and several resistances

  • were integrated to get some functions off to get some circuit.

  • Now, after that if we see the what is the status and the what are the trends of silicon

  • ICs, we have to see this particular figure where this has been obtained from CR route

  • map and here in one side you can see the minimum feature size of the transistor starting from

  • 1970 to 2020 and on the other side you can see the number of transistors for DRAM chip.

  • So now look at this figure, here in 1980 where these minimum feature sizes was nearly say

  • 2000 nanometer and then if you go, at present this is the present line 2004 and there you

  • can see the feature size is nearly 100 nanometer.

  • So, on the other side, the DRAM chip which is basically always cited the integration

  • level and that integration level starts from the 4 Kilobyte this is the nineteen four kilobit

  • DRAM which has come in 1970 and later on you can see from 4 Kilobyte to 64 Kilobyte then

  • 1 Megabyte to16 Megabyte and so on. At present 256 Megabyte DRAM, where this is nearly in

  • 1998 or 99 it came and there transistor count you can see here is one 10 to the power 9

  • so that means is nearly people are thinking at the moment so transistor level has come

  • of the order of 10 to the power 10 transistors for DRAM chip.

  • Now, if you here is one limit by 2010 and 2012, we can see the number of neurons in

  • the human brain in 15 centimeters cube is nearly 10 to the power 11. 11 is the total

  • number of the neuron cells and people are speculating that, by that time the number

  • of transistors for IC or DRAM chip will achieve in that level.

  • So now, this is another picture you can see which is basically Moore's Law and that gives

  • you the scaling of the CMOS. That means year to year how the integration is taking place,

  • you can see from here the model CMOS in 1980 which is nearly one micron technology and

  • then at present in 2004, the transistor size has come down to 19 nanometer only. Here basically

  • a route map is given by an international organization and that is the semiconductor route map they

  • call it, and in the last 34 years the scaling history is such that every generation feature

  • size sinks by 70 percent.

  • What do you mean by the generation? The generation basically, on an average of every 2.9 years

  • they speculate something, they foresee something and after that on that particular year again

  • depending on the progress of the design and progress of the technology they again just

  • to control something so the next two years what will happen, so that is basically the

  • route map. Earlier this generation is nearly 2.9 years but later on the progress is so

  • fast that has been changed to 2 years recently every two year they are speculating something.

  • Before that time target achieved, they got something else, much more progress has been

  • done.

  • Now, basically the scaling of the CMOS if you can see that the beginning of the some

  • micron era is started nearly say mid of 85, a mid of 80s that is 1985 nearly in that after

  • that deep UV lithography then 19 nanometer in 2004. So if you continue in this fashion

  • so reasonably by 2020, they will come to a limit and that limit of scaling, that means

  • there the problem is the lithography alignment or which will be the source of lithography.

  • So, optical lithography is a commercial technique, you know after they highlight, they proceed

  • to UV, deep UV and then after deep UV there are certain other lithography techniques which

  • are basically x-ray or lithography but those are not commercially viable.

  • The people want to stick on optical lithography itself so that's why optical lithography create

  • some problem after the 90s nanometer and below. Lot of intervention and techniques people

  • are using in the optical lithography so that they can get the feature size below these

  • 90 or now at present 60 or 65 nanometer people are working on.

  • But now the silicon microelectronics basically if you see, that is the silicon wafer is 1

  • 0 0 crystal orientation wafer. Now, at present the standard size of the silicon wafer in

  • industry is nearly 12 inches. Normally in some cases the 4 inch or 6 inch and 8 inch

  • wafers are also used in some of the small fabs but in big fabs they are working on 8

  • to 12 inches. Now, you know the lots of circuits are made on silicon wafer and individual single

  • chip and that is of the order of 2 centimeter square.

  • I am talking about a larger chip size which you can make now days, is of the order of

  • 2 centimeter square that does not mean that feature size is also very large. Feature size

  • is very small and if you can get the larger die side that is another achievement. Feature

  • size goes down and this is known as the die and the die size goes up so that is the challenge

  • of the technology. Now currently what I just mentioned few minutes back, that the number

  • of transistors per chip has exceeded the 1000 million. So this is heading towards the billion

  • and projection in 2014 is 20 billion transistors per chip and that is

  • the projection at the moment.

  • Now, here is another diagram, where you can see the feature size goes down, so if you

  • look into the integrated circuit history, below this is a 0.1 micrometer and this is

  • 10 nanometer range, this is the one transition 0.1 to 10 nanometer and then another transition

  • level is 10 nanometer to 1 nanometer. So 1 nanometer means this transition is very important

  • to people and is basically the quantum devices. Now you know the lattice, the constant of

  • silicon is nearly 3 or 4 or 5 nanometer. Now if you go into 10 nanometer that means few

  • 2 or 3 the atomic diameter is like that. So, that means the few monolayers of silicon within

  • that if you go into this region then you have to make the devices.

  • So there, the normal physics of the transistor may not be valid and you have to go into the

  • quantum mechanical analysis and those are basically the quantum devices. Below that

  • are atomic dimension and the automatic atomic dimension level, when you make the transistor

  • lot of other problems will come into the picture. Then here is another table which shows that

  • the trend of the feature size as well as the wiring levels the mask count and supply voltage

  • that all this figure tells that is in 1997 where the supply voltage is nearly 2 volts

  • and in 2003 it is 1.2 volts and people are looking for the circuits and devices which

  • will work in the 1 volt and at 2012 it's a 0.5 to 0.6 volt.

  • So, you see how the feature size goes down and at the same time the chip size is going

  • up as just now I mentioned to 80 millimeter square so they are speculating in 2012 it

  • will be 1580 millimeter square. The number of transistors in that regime is 1.4 billion

  • and that is wiring level. That means in the present all the microprocessor chips, the

  • seven or eight level of metallization is being done there. You know if the number of levels

  • is more the technology is getting much more complicated and obviously the yield is another

  • important point which is another yardstick. So, how your technology is good, how it is

  • commercially viable etcetera, so yield should be very good.

  • So, for that if number of levels of metallization increases, so then automatically you have

  • to compromise with some yield but you have to make a compromise on a good yield. At the

  • same time, number of wiring level increases that is the motto and target. And mask count

  • is going to increase if the levels are more. So that the interlevel metal you have to have

  • a dielectric layer then some metal pattern then again another dielectric layer so automatically

  • the mask level will also increase. So that was the present scenario.

  • Now the size what i am discussing does matters how you can see this figure here. So, this

  • is the the area of the micromachining and this Nano machining. So another word you are

  • coming across now is machining. So machining, the terminology initially it was in mechanical

  • engineering, people they used to point machining, that means from a huge bulk steel or any of

  • the metal beam they used to machine it to get small miniature structures. Well later

  • on the machining is used in microelectronics laboratory also to fabricate the MEMS devices.

  • Now here you can see the 1meter, that is that elephant and then is gone down to 0.1 so that

  • is the chip size is you say this is the area where 0.01 meter to 1 centimeter in that area

  • you can get the IC chip.

  • Then this is the size of 1 millimeter the grain of sand and then biological cell comes

  • nearly 0.01 millimeter to 10 micrometer and then

  • comes 1 micrometer which is the smallest feature size 0.35 micrometer is sometimes back may

  • be in 1996,97 where that level is micro. Now, if you go beyond that 0.1 micrometer below,

  • that is entering to the nano area and there some of the examples are shown that the atomic

  • littering using the scanning telling microscope. This is

  • 1 nanometer, they are obtained from the feature size then DNA is of the 2 nanometer wide that

  • is the size.

  • On the other hand if you see the machining, this is the micro machine gear which is nearly

  • 100 micrometer, then this is dust particle side you can compare with that which is a

  • 1 to 5 micrometer and these are some quantum electronic structures, the width of these

  • structures in nearly 200 Angstrom and the atomic level 1 to 4 Angstrom. So that means,

  • the size does matters because the with the reduction of the size and minimum feature

  • size all the technology is going to change and at the same time the equipments are going

  • to change and if you go below say 1 nanometer level, then physics of devices is going to

  • change.

  • So now, if you look here, the size also on the scale that is bottoms up and here it stops

  • down. So both are shown, here the few areas are is basically plant and animal cell and

  • this is the bacteria size is the 1 micrometer to 10 micrometer and 10 to 100 micrometers

  • are plant and animal cell. This is the area where basically the MEMS

  • are made and now if you go beyond that, which is not microelectronics that is basically

  • coming nano scales or nano electronic their size comes below the 100 nanometer to say

  • here is say 1 nanometer. And below 1 nanometer the different area so that 100 nanometer to

  • 1 nanometer, that the size of the virus, proteins and the helical turn of the DNA and this is

  • the minimum feature size of a MOS transistor in 2004 you can see here. So people are working

  • so 10 nanometer or 15 nanometer level, obviously, that is the nano scale for the nano and these

  • are 100 nanometers MOS transistor you can see the gate dielectric is from here to here.

  • So now, the science of miniaturization with that you can see in case of machine, how the

  • size is going to reduce. And here the size is basically an accelerometer and here is

  • a MEMS accelerometer. Now, side by side if you compare you see initially, the conventional,

  • the accelerometer, the mass was nearly 1.5 Kilo more than that and its size is 15 centimeters

  • by 8 by 5 centimeter and it requires power of the order of 35 Watts. And on the other

  • side you can see that, if a MEMS accelerometer if you use so that mass is only 10 grams so

  • instead of 1587, it has reduced to 10 gram and size is very small compared to these.

  • Power instead of 35 Watts, is only 1 Milli watt and cost instead of 20,000 Dollars, it

  • has come down to only 500 Dollars. So, at present the price is further down and you

  • can get nearly 10 or 50 or 100 Dollars to have MEMS devices.

  • So, although the microfabrication was originally limited to silicon, now the field is open

  • people have started using some other materials than silicon particularly the polymers and

  • ceramics and composite materials and also coming into the picture and people are using

  • those materials for the MEMS devices and microsystem fabrication. Why people are sticking at the

  • beginning only on silicon? There are certain reasons. Because silicon technology is fully

  • mature and there is no new research to be done for the processing of silicon. That is

  • why they do not want to deviate from the silicon. But later, on the other material particularly

  • polymer and organic material has some other advantage in certain areas, so they are going

  • to switch from the silicon to other nonconventional materials also non-silicon materials also

  • for making MEMS.

  • So now, the science of miniaturization, if you look into that, although lithography has

  • been the current method of defining patterns, many forms of direct right schemes are also

  • being used now a days. Traditional electroplating molding is being used in micro-domain. This

  • is not used in case of this normal microelectronics. But in case of MEMS we are going to use the

  • electroplating micro molding and in this liga, all these are coming into the picture and

  • all the techniques, I will discuss in detail in the future classes.

  • Now, this is a Micro or Nano world. If you look here, you can see various application

  • areas. Those application areas are basically, one is the say the physical MEMS or physical

  • sensors which deals with pressure sensor, force, inertial, sound means that these are

  • the area where MEMS devices are made. Other area is micro-optics, optical areas which

  • we call it as MOEMS Micro-Optical Electromechanical Systems. So there is the optical domain, there

  • are lots of devices made using mircomachining technology. Then another is micro-probing,

  • the STM and AFM. The AFM components are being made using the MEMS.

  • Others are the micro-fluidics. Micro-fluidics is a major application in the biology and

  • not only the biological application, there are others in flow of gas and flow of fluid

  • in a micro channel, that dynamics is a is a very interesting and there lot of devices

  • are being made now. This is another area of micro-fluidics. In Bio-MEMS, lot of work is

  • going and one emerging area of research at present Bio-MEMS area. And by the actuation

  • and motion that is basically the actuators are also very important. If you want to make

  • a microsystem, what do you need? You need the sensor, you need actuator and you need

  • the signal conditioning circuits or processing circuits.

  • So actuator is one part of the microsystem. So if you look into all the microsensor development

  • that will not complete the microsystem development. If you want to have some microsystem, you

  • have to see how the actuators can be made. And it cannot only make how it can be integrated

  • with the sensor and also the signal condition circuit. So that is why this is another area

  • of Micro Nano world, how can you make the actuator a precisely working actuator and

  • is very important which is integrable with the micro sensor.

  • Now let us look into the MEMS history and if you look there, the gentleman is a fine

  • man you know, and he basically got a Nobel Prize in 1959. In physics, again he had a

  • vision and at that time he declared that there is plenty of room at the bottom. That means

  • on silicon inside you can make lot of small miniature devices and that means there are