1 00:00:00,000 --> 00:00:10,089 [MUSIC] 2 00:00:10,089 --> 00:00:13,408 Hi, welcome to Coursera's Nanotechnology, The Basics. 3 00:00:13,408 --> 00:00:15,250 My name, my name is Daniel Mittleman. 4 00:00:15,250 --> 00:00:15,968 Thanks for joining me. 5 00:00:15,968 --> 00:00:19,496 Today, we want to talk about some of the spin-off technologies, 6 00:00:19,496 --> 00:00:23,088 that have been enabled by rapid advances in the semiconductor in. 7 00:00:23,088 --> 00:00:24,924 So, as we have seen, earlier, 8 00:00:24,924 --> 00:00:28,120 in the lectures this week, semiconductor electronics 9 00:00:28,120 --> 00:00:33,264 industry has been driven to maintain their pace on the Moore's Law of prediction. 10 00:00:33,264 --> 00:00:35,114 as a market forecast, really 11 00:00:35,114 --> 00:00:38,666 and in order to stay on that, they've really been driven 12 00:00:38,666 --> 00:00:43,660 to innovate in a number of areas, associated with processing silicon wafers. 13 00:00:43,660 --> 00:00:45,190 So, what you're seeing here is a picture of a 14 00:00:45,190 --> 00:00:48,590 bare silicon wafer, which is really just a mirrored surface. 15 00:00:48,590 --> 00:00:51,120 And, how it gets turned into a processed 16 00:00:51,120 --> 00:00:54,210 wafer with, nanoscale components and patterns on it. 17 00:00:54,210 --> 00:00:56,010 In order to do that, you need a lot of 18 00:00:56,010 --> 00:01:00,910 different process tools, and techniques, and technologies, that enable laying 19 00:01:00,910 --> 00:01:05,240 down layers with fine precision, removing pieces with fine precision. 20 00:01:05,240 --> 00:01:06,610 And, all of this has been developed, with 21 00:01:06,610 --> 00:01:10,780 the idea of enabling advances in the semi-conductor industry. 22 00:01:10,780 --> 00:01:13,382 But, of course, all of these ideas, also, can be spun off 23 00:01:13,382 --> 00:01:17,630 and applied in areas that have nothing to do with the electronics industry. 24 00:01:17,630 --> 00:01:20,230 And that's really what we want to talk about in today's lecture. 25 00:01:20,230 --> 00:01:23,050 Some of those spin-off technologies, were really there are too many to 26 00:01:23,050 --> 00:01:26,440 mention, but I can highlight a few of them in these pictures here. 27 00:01:26,440 --> 00:01:30,670 So, for example microsurgery or micro machines or 28 00:01:30,670 --> 00:01:34,460 micro fluids, all of these are ideas which. 29 00:01:34,460 --> 00:01:37,960 on the face of them have very little to do with electronics, in 30 00:01:37,960 --> 00:01:39,300 the sense, that they are not about 31 00:01:39,300 --> 00:01:42,940 creating new electronic circuits, or integrated circuits. 32 00:01:42,940 --> 00:01:47,660 But, they leverage the advances made by the electronics industry, to 33 00:01:47,660 --> 00:01:51,470 enable the construction of devices which, which have impact in all of 34 00:01:51,470 --> 00:01:52,290 these other areas. 35 00:01:52,290 --> 00:01:55,771 And, I'd like to highlight just a few of those advances, some of 36 00:01:55,771 --> 00:02:00,315 those innovations in the industry which have done all, all of this enabling. 37 00:02:00,315 --> 00:02:04,700 slow, the ability to lay down thin layers of materials with fine precision. 38 00:02:04,700 --> 00:02:08,870 The ability to carve away small channels, or narrow channels in silicon. 39 00:02:08,870 --> 00:02:10,420 And, the ability to create more 40 00:02:10,420 --> 00:02:12,820 complicated structures, such as, for example, cantilevers. 41 00:02:12,820 --> 00:02:16,870 So, the first one I want to talk about, is the ability to lay down layers 42 00:02:16,870 --> 00:02:19,650 of material on the substrate, with very high precision. 43 00:02:19,650 --> 00:02:20,970 There are quite a number of ways of 44 00:02:20,970 --> 00:02:23,570 doing that, I'm only illustrating two of them here. 45 00:02:23,570 --> 00:02:26,270 On the left, you're seeing a picture of a device, 46 00:02:26,270 --> 00:02:29,320 that was fabricated with a technique known as physical vapor deposition. 47 00:02:29,320 --> 00:02:31,600 And what you see here is a cross-section of the 48 00:02:31,600 --> 00:02:34,960 device, where you can see alternating layers of different materials. 49 00:02:34,960 --> 00:02:37,150 In this case, two different kinds of oxides, 50 00:02:37,150 --> 00:02:40,086 it's a silicon dioxide and a tantalum oxide. 51 00:02:40,086 --> 00:02:42,430 And when you would lay down alternating layers, 52 00:02:42,430 --> 00:02:44,100 with precisely controlled thickness and 53 00:02:44,100 --> 00:02:47,400 precisely controlled morphology and, and chemistry, 54 00:02:47,400 --> 00:02:52,280 then what you can create are optical components with extraordinary properties. 55 00:02:52,280 --> 00:02:56,910 And, and, of course, nanometer scale size, or anyway, micron scale size. 56 00:02:56,910 --> 00:03:01,390 if you need finer precision than that, you can go to this other technique that's 57 00:03:01,390 --> 00:03:02,980 illustrated by the cartoon on the right 58 00:03:02,980 --> 00:03:05,130 here, which is known as molecular beam epitaxy. 59 00:03:05,130 --> 00:03:07,540 And this is, somehow, the gold standard or the, 60 00:03:07,540 --> 00:03:10,310 the highest level of precision that one can obtain. 61 00:03:10,310 --> 00:03:15,030 This is done inside an ultra high vacuum, and one can really lay down atomic layers 62 00:03:15,030 --> 00:03:18,210 of almost any material on a substrate with, 63 00:03:18,210 --> 00:03:20,590 with precision of one atomic layer at a time. 64 00:03:20,590 --> 00:03:25,170 So, you can control the thickness of these layers, you can control their composition. 65 00:03:25,170 --> 00:03:29,070 their atomic composition by putting down different materials at different times. 66 00:03:29,070 --> 00:03:32,920 And you can really create very sophisticated and complicated structures 67 00:03:32,920 --> 00:03:34,230 using these sorts of techniques. 68 00:03:35,310 --> 00:03:40,790 these ideas are pervasive in our daily lives anybody 69 00:03:40,790 --> 00:03:44,220 for example, who wears eyeglasses that have anti-reflection coating 70 00:03:44,220 --> 00:03:48,044 or uses a reasonably good camera that has anti-reflection 71 00:03:48,044 --> 00:03:52,190 coating lenses coating on the lenses or anti-scratch coatings. 72 00:03:52,190 --> 00:03:57,550 These are all created by putting down multiple layers of oxide materials. 73 00:03:57,550 --> 00:03:58,000 a little 74 00:03:58,000 --> 00:04:02,310 bit less visible to the consumer but perhaps equally important are things like 75 00:04:02,310 --> 00:04:06,680 the laser in your DVD player, or the hard drive in your computer. 76 00:04:06,680 --> 00:04:09,060 what you're seeing in, on the cartoon on the bottom here, is a 77 00:04:09,060 --> 00:04:13,940 cross section of what the laser in a DVD player typically would look like. 78 00:04:13,940 --> 00:04:15,840 And you can see again, there are multiple layers of 79 00:04:15,840 --> 00:04:19,030 different materials layed down in some sort of alternating pattern. 80 00:04:19,030 --> 00:04:20,941 With typically nanometer sort of thickness, 81 00:04:20,941 --> 00:04:22,999 so there's an eight nanometer thickness layer, 82 00:04:22,999 --> 00:04:26,184 and you see in this particular example the materials are semi-conductors, 83 00:04:26,184 --> 00:04:27,703 they are gallium arsenide and indium 84 00:04:27,703 --> 00:04:30,490 gallium arsenide and aluminium gallium arsenide. 85 00:04:30,490 --> 00:04:33,490 And these are laid down with exquisite precision in terms of the 86 00:04:33,490 --> 00:04:36,020 composition, the smoothness of the interfaces, 87 00:04:36,020 --> 00:04:37,670 and the thickness of each layer. 88 00:04:37,670 --> 00:04:40,570 Typically one can lay down dozens of layers, or hundreds, or in some 89 00:04:40,570 --> 00:04:42,970 cases even thousands of layers to create 90 00:04:42,970 --> 00:04:44,740 structures that have all sorts of functionality. 91 00:04:46,390 --> 00:04:47,820 So putting down layers is good, 92 00:04:49,030 --> 00:04:50,950 but removing material is also good. 93 00:04:50,950 --> 00:04:53,210 Obviously, it's not enough to be able to put stuff down, you 94 00:04:53,210 --> 00:04:57,180 also have to be able to take stuff away in selective selectively. 95 00:04:57,180 --> 00:05:00,880 So, there're again quite a few different technologies that can be used to do this. 96 00:05:00,880 --> 00:05:03,950 Here, I'm illustrating probably one if the most commonly 97 00:05:03,950 --> 00:05:07,140 used of those, which is called reactive ion etching, 98 00:05:07,140 --> 00:05:09,450 and on the left you see some text which 99 00:05:09,450 --> 00:05:12,030 describes a three-step process as to how this works. 100 00:05:12,030 --> 00:05:14,210 Briefly speaking, you use microwaves 101 00:05:14,210 --> 00:05:19,530 to create a plasma, which is just a gas of charged atoms, charged ions. 102 00:05:19,530 --> 00:05:22,280 with positive charge and you create those near a positive 103 00:05:22,280 --> 00:05:25,390 electrode and then they are accelerated towards a negative electrode. 104 00:05:25,390 --> 00:05:27,810 And those accelerating ions, in between you place 105 00:05:27,810 --> 00:05:29,680 the sample that you want to etch, and those 106 00:05:29,680 --> 00:05:31,450 ions run into the sample, and because they 107 00:05:31,450 --> 00:05:34,070 are charged they will react chemically with the surface. 108 00:05:34,070 --> 00:05:38,420 And create some sort of reactive species that is then removed by your vacuum pump. 109 00:05:38,420 --> 00:05:39,700 So, you can remove material. 110 00:05:39,700 --> 00:05:41,400 And because these ions are accelerated in 111 00:05:41,400 --> 00:05:44,330 one particular direction, they have a, a, the 112 00:05:44,330 --> 00:05:46,270 etch is highly anisotropic so, etch in 113 00:05:46,270 --> 00:05:48,320 one direction, but not in the sideways direction. 114 00:05:48,320 --> 00:05:51,792 So, you can create for example deep trenches using this sort of technique. 115 00:05:52,830 --> 00:05:57,540 It's obviously not enough to simply remove everywhere on a surface. 116 00:05:57,540 --> 00:05:59,660 You might want to material from some parts of the surface 117 00:05:59,660 --> 00:06:02,170 but not others, so you need to be able to protect. 118 00:06:02,170 --> 00:06:04,990 Areas of the surface that where from which you do not want to remove 119 00:06:04,990 --> 00:06:07,380 materials, and one typical to do this would be 120 00:06:07,380 --> 00:06:09,520 put down a layer of what's called a photoresist. 121 00:06:09,520 --> 00:06:11,592 Which is basically just a thin plastic layer 122 00:06:11,592 --> 00:06:13,832 that protects the surface from the etching ions 123 00:06:13,832 --> 00:06:15,736 and so the etching would not happen there 124 00:06:15,736 --> 00:06:18,310 and it would happen in the other locations. 125 00:06:18,310 --> 00:06:21,268 In order to create back that photoresist pattern, which may 126 00:06:21,268 --> 00:06:25,040 have nanometer sized features, or apertures or structures in it. 127 00:06:25,040 --> 00:06:26,690 You would typically use photolithography. 128 00:06:26,690 --> 00:06:30,040 So you can see we're going to use a combination of the tools that have 129 00:06:30,040 --> 00:06:32,400 been developed for creating integrated 130 00:06:32,400 --> 00:06:35,180 circuits, photolithography, etching, and so on. 131 00:06:35,180 --> 00:06:37,740 In order to create other sorts of structures as well. 132 00:06:37,740 --> 00:06:39,680 And, and I didn't mention, but this 133 00:06:39,680 --> 00:06:42,150 photoresist would be a temporary protective structure. 134 00:06:42,150 --> 00:06:43,770 It could be subsequently removed. 135 00:06:43,770 --> 00:06:46,830 By simply dissolving it in acetone or something like that. 136 00:06:46,830 --> 00:06:49,450 So, the kinds of structures that can be made with reactive 137 00:06:49,450 --> 00:06:53,610 ion etching are, for example, trenches, where you could flow liquids. 138 00:06:53,610 --> 00:06:55,900 So, this gives rise to a whole 139 00:06:55,900 --> 00:06:59,860 area of endeavor known as microfluidics, the idea of having 140 00:06:59,860 --> 00:07:05,270 microliter or smaller volumes of liquids flowing in thin channels. 141 00:07:05,270 --> 00:07:07,470 And this enables a whole range 142 00:07:07,470 --> 00:07:10,610 of interesting applications in biology and medicine. 143 00:07:10,610 --> 00:07:12,600 I want to particularly highlight this one here which 144 00:07:12,600 --> 00:07:14,310 is called the lab on a chip application. 145 00:07:14,310 --> 00:07:16,840 The idea here is that in the chemistry lab you would 146 00:07:16,840 --> 00:07:20,920 be mixing liquid components and creating reactant products and so on. 147 00:07:20,920 --> 00:07:24,240 And in microfluidic lab on a chip, you would be doing 148 00:07:24,240 --> 00:07:27,360 the same thing but on a, on a much smaller scale. 149 00:07:27,360 --> 00:07:29,360 it would be small, portable, chip, and so 150 00:07:29,360 --> 00:07:31,950 on and so that would be really advantageous. 151 00:07:31,950 --> 00:07:35,120 there's a laboratory at Rice University, the McDevitt Lab, who 152 00:07:35,120 --> 00:07:36,660 are doing exactly this sort of thing and who are 153 00:07:36,660 --> 00:07:41,470 developing diagnostics for for medical use in the third world, 154 00:07:41,470 --> 00:07:45,190 where a big chemistry is simply too expensive and not practical. 155 00:07:45,190 --> 00:07:45,790 And so, I would, 156 00:07:45,790 --> 00:07:50,320 I would also highlight this webpage here. Rice 360 is a group here. 157 00:07:50,320 --> 00:07:52,920 Rice that is pushing the development of technologies. 158 00:07:52,920 --> 00:07:57,800 Many of which are nanotechnology enabled for applications in the third world. 159 00:07:57,800 --> 00:07:59,760 Another interesting application is illustrated by 160 00:07:59,760 --> 00:08:02,820 this photograph on the right here. 161 00:08:02,820 --> 00:08:04,710 Which is a, a cell biology application. 162 00:08:04,710 --> 00:08:10,020 Here we have yeast cells growing inside of a serpentine shaped channel. 163 00:08:10,020 --> 00:08:11,070 And what's interesting here 164 00:08:11,070 --> 00:08:13,960 is that in ordinary media, the yeast cells grow straight. 165 00:08:13,960 --> 00:08:15,970 But in a curved channel the yeast grow curved. 166 00:08:17,710 --> 00:08:19,940 So, to take this one step further we can be even 167 00:08:19,940 --> 00:08:22,310 more sophisticated than simply drilling trenches 168 00:08:22,310 --> 00:08:24,600 we can create three dimensional structures. 169 00:08:24,600 --> 00:08:28,060 Again, out of silicon simply by etching selectively, 170 00:08:28,060 --> 00:08:30,380 and protecting, and then under-etching, and so on. 171 00:08:30,380 --> 00:08:34,040 And so, what you see here is a, is a, an array of cantilevers. 172 00:08:34,040 --> 00:08:36,270 A cantilever is, after all, just a diving board, 173 00:08:36,270 --> 00:08:38,390 which is anchored on one end and can vibrate. 174 00:08:38,390 --> 00:08:40,130 And we can imagine taking a diving board and 175 00:08:40,130 --> 00:08:42,610 shrinking it down to a micron size or smaller. 176 00:08:42,610 --> 00:08:44,790 And then we have something that will vibrate much more rapidly. 177 00:08:44,790 --> 00:08:45,650 But it's the same idea. 178 00:08:46,946 --> 00:08:49,762 the ability to make a cantilever really enables a lot 179 00:08:49,762 --> 00:08:52,962 of ideas in sensing, and I want to highlight one of those 180 00:08:52,962 --> 00:08:56,162 by pointing out this photo here which shows the underside of 181 00:08:56,162 --> 00:08:59,640 a cantilever with a sharp tip fabricated on to the structure. 182 00:08:59,640 --> 00:09:01,030 This is all still silicon. 183 00:09:01,030 --> 00:09:01,370 So, this is 184 00:09:01,370 --> 00:09:03,710 just carving pieces out of silicon, essentially. 185 00:09:03,710 --> 00:09:08,680 That sharp tip tapers down to a size that can be only a few nano-meters in size. 186 00:09:08,680 --> 00:09:12,660 And this really, this development really enabled a whole new way of 187 00:09:12,660 --> 00:09:14,370 thinking about ways to image the 188 00:09:14,370 --> 00:09:17,998 topography of a surface with incredible sensitivity. 189 00:09:17,998 --> 00:09:22,020 This is known as atomic force microscopy, as it's illustrated by this cartoon here. 190 00:09:22,020 --> 00:09:24,260 The idea here is to take your cantilever, which has 191 00:09:24,260 --> 00:09:26,450 a, a very sharp needle tip on the end of it, 192 00:09:26,450 --> 00:09:28,340 and essentially just drag it across a surface. 193 00:09:28,340 --> 00:09:30,750 And when it comes to a bump, it hops up and over. 194 00:09:30,750 --> 00:09:32,090 And, if you can sense the motion of 195 00:09:32,090 --> 00:09:35,810 that cantilever with nanometer scale resolution, then you 196 00:09:35,810 --> 00:09:37,930 can make a topography map of your surface, 197 00:09:37,930 --> 00:09:40,390 and measure bumps that are only a nanometer high. 198 00:09:40,390 --> 00:09:43,550 Or even smaller, in fact, the, the limit of this is less than a nanometer. 199 00:09:43,550 --> 00:09:46,650 The way we measure that. This is sort of another innovation. 200 00:09:46,650 --> 00:09:49,220 The way we actually measure that is by using a laser, 201 00:09:49,220 --> 00:09:52,120 and bouncing it of off the surface of the cantilever and 202 00:09:52,120 --> 00:09:54,220 then reflecting it onto a detector that is 203 00:09:54,220 --> 00:09:55,860 very sensitive to the position of the laser. 204 00:09:55,860 --> 00:09:58,430 So, as the cantilever removes, the laser beams move back and 205 00:09:58,430 --> 00:10:01,460 forth and you can measure that change in position and correlate that. 206 00:10:01,460 --> 00:10:03,650 With change in position of the cantilever. 207 00:10:03,650 --> 00:10:06,080 So, atomic force microscopy is really opened up a whole 208 00:10:06,080 --> 00:10:09,820 new world of how to image surfaces and their topography. 209 00:10:09,820 --> 00:10:13,610 it's also spun off it's own interesting technological ideas. 210 00:10:13,610 --> 00:10:17,240 For example you can take your cantilever, your sharp tip and 211 00:10:17,240 --> 00:10:20,400 bind it to a single molecule which is then attached to the surface. 212 00:10:20,400 --> 00:10:22,838 And by moving the cantilever up and down you can stretch 213 00:10:22,838 --> 00:10:26,890 one molecule and measure its spring constant or measure its tensile strength. 214 00:10:26,890 --> 00:10:28,400 So measuring the tensile strength of single 215 00:10:28,400 --> 00:10:30,540 molecule is something that ordinarily you would imagine 216 00:10:30,540 --> 00:10:34,270 would be very hard to do, but we can do that using these sorts of techniques. 217 00:10:34,270 --> 00:10:36,140 The other thing that's interesting about 218 00:10:36,140 --> 00:10:38,450 the cantilever idea, is that this vibration 219 00:10:38,450 --> 00:10:40,050 frequency, they have a natural vibration 220 00:10:40,050 --> 00:10:42,680 frequency, is incredibly sensitive to the mass 221 00:10:42,680 --> 00:10:43,680 of the cantilever. 222 00:10:43,680 --> 00:10:46,330 So, if we functionalize the top surface of that cantilever 223 00:10:46,330 --> 00:10:49,910 so that it binds for example, selectively to a specific protein. 224 00:10:49,910 --> 00:10:51,850 Then when that protein binds there, even 225 00:10:51,850 --> 00:10:54,170 if it's just one protein molecule, the change 226 00:10:54,170 --> 00:10:56,490 in mass of the cantilever will change 227 00:10:56,490 --> 00:10:58,780 that resonant frequency and one can measure this. 228 00:10:58,780 --> 00:11:02,200 So, you can actually measure the binding event of a single molecule on a surface. 229 00:11:02,200 --> 00:11:04,280 That's extraordinary sensitivity, which is enabled 230 00:11:04,280 --> 00:11:08,010 by our ability to fabricate these complicated 231 00:11:08,010 --> 00:11:11,230 structures in three dimension using etching of silicon, essentially. 232 00:11:11,230 --> 00:11:14,060 So, the ideas of this lecture are really two fold. 233 00:11:14,060 --> 00:11:17,870 Number one the need for smaller and smaller devices, which is to 234 00:11:17,870 --> 00:11:21,070 say the need to remain on the Moore's Law curve has driven the 235 00:11:21,070 --> 00:11:23,530 electronics industry to innovate in the 236 00:11:23,530 --> 00:11:25,900 development of new tools, and new techniques, 237 00:11:25,900 --> 00:11:30,702 and new approaches to structures silicon on the macro and eventually nano scale. 238 00:11:30,702 --> 00:11:33,570 And, those new tools and techniques have then, led to 239 00:11:33,570 --> 00:11:36,060 a whole range of spin-off technologies which 240 00:11:36,060 --> 00:11:39,640 have applications in areas far outside of electronics. 241 00:11:39,640 --> 00:11:41,360 I hope this has been an interesting lecture for you. 242 00:11:41,360 --> 00:11:41,940 Thanks for joining.