Dr Stuart Higgins, The University of Cambridge
Silicon is great but what if it could be cheaper, bendier and printable? Maybe then we could get our food talking to our fridge. Naked Scientists regular and circuit bender extraordinaire Stuart Higgins is trying to make smart food a reality...
Stuart - In my left hand I have a silicon wafer; itís like a shiny blood colour; it looks very metallic and itís hard and, if I were to drop this, it would smash like glass.
Smith - Itís a disk. Itís what 4 or 5cms across and thin, shiny - itís like a CD really.
Stuart - Yes, it looks very similar to a CD. Itís got the same kind of rainbow colours if you look at the surface of it. This is silicon, so if you think in terms of your phone and the chips inside your phone or your computer, this is what theyíre made on - this is this hard material. Now thatís great but, as I said, if I drop this itís going to smash - itís not going to be so good. What if there was a way we could make electronics using plastic, with the benefits of plastic but also with the electrical benefits of silicon.
Smith - Why would you want to do that?
Stuart - Has anyone ever dropped their smartphone? So if you drop something like a glass screen or if you drop something thatís a hard crystal substance like silicon, itís going to smash - itís going to shatter to shatter into lots of pieces. So Iím looking in my research at ways of taking new materials that are based on plastics that can also be semiconductors; can also be electrical in their nature. So we often think of plastics as insulators; thatís why we make our plug sockets out of them; thatís why we make our cables out of them because we donít want electricity to get through. But, actually, it turns out that there are special kinds of plastics that can act as conductors; they can conduct electricity and they can also act as semiconductors and a semiconductor is something that, in the right circumstances, turns into a conductor.
Smith - And thatís what youíve got here is it?
Stuart - Yes. So in my right hand I have this flexible piece ofÖ well itís a piece of plastic.
Smith - Okay. So this is about the same size as the wafer of silicon. I can see through it; itís completely transparent, thin piece ofÖ looks like cling film but a bit thicker and itís got some coppery coloured stuff on it.
Stuart - Yes, so what weíre looking at there - actually itís gold. So if you look closely at this substrate you see this kind of pattern of gold wiring, essentially, and all of these wires are connected together with little devices called transistors and a transistor is a switch. Itís like an electrical switch where you press it and turn it on and you turn if off and itís the fundamental building block inside every microprocessor. So when your computer does calculations, itís transistors that are switching on and off.
Smith - How might we make that?
Stuart - The benefits of plastics are that you can actually turn them into inks so, if youíre doing something like silicon, you have to use very industrial processes - itís a very hard material to work with. But, if youíve got a semiconductor thatís also a plastic, you can dissolve it, you can turn it into an ink that could go into a printer, for example. An inkjet printer like we have at home. So one of the things we look at is ways of printing circuits on plastics. We send the design from the computer to the printer and it prints out the circuit on the piece of plastic and in that way weíre looking at ways of building up layers and creating these kind of flexible circuits.
Smith - What sorts of things could you make that do with that same technology because I know what my phone can do but, am I close to having a roll up phone?
Stuart - You're a little away from it yet because the silicon technology is so far developed; itís had many, many years of development. The phone inside your pocket has a billion transistors in it - incredibly complicated. This piece of plastic I have here has 120 transistors. Weíre still years and years behind but one of the things we are looking at doing is incorporating it into other kinds of products. So, in my particular research I look at radio tags and Iím interested in seeing whether we could make a flexible radio tag. A bit like your smart card or you security card when you swipe it on a door and looking at ways we can make that onto a flexible substrate. And the reason for doing that is if you can make things flexible, and you can print circuits, and you can do that cheaply and easily, then you could think about putting circuits where you wouldnít normally find them, for example, maybe on packaging. So, as you referred to earlier, imagine having a milk carton in your fridge thatís talking to the fridge itself and can actually tell you when the milk is about to go off. Or that you know by looking at your smartphone, whatís in your fridge when youíre out shopping so you know what to buy next.
Smith - It would be food for thought, wouldnít it?
Stuart - Exactly. Thatís where the idea is that if we can develop new materials and we can develop processes and ways of making these circuits that do that, then it opens up a huge new range of technologies.
Smith - Itís an obvious question. Why arenít we doing it now?
Stuart - Well, the problem is that these plastics, while theyíre good, is there not that good. Theyíre still quite a lot worse than silicon and, in particular, the charges, the electricity going on inside this circuit is moving a lot slower than it would in silicon.
Smith - Now I asked you for a bit of a demo to show us the speed of these things. What demo have you got lined up for us?
Stuart - So, Iím trying to illustrate here what happens if youíve got a slow transistor; if youíve got a slow switch that turns on and off. Now, in some ways, if youíve got your smartcard talking to the reader and itís kind of speaking very slowly and youíve got the reader speaking very fast in return and trying to get things really quickly, those two canít talk to each other, they canít understand each other, and particularly if youíve got transistors that can also be used as an amplifier. If that amplifier canít see all the frequencies then you start to miss information.
In this first clip Iím going to play a spoken recording and itís going to have all of the high frequencies cut out as if the transistor wasnít switching fast enough. So, weíre going to listen to that and try and understand whatís being said and see how difficult it is to hear whatís happening. After that Iím going to play the second clip with all the frequencies present so we can hear what it says.
Smith - Letís do itÖ
Audio - [Muffled]
Audio - I am sometime able to eject a very fine spray of saliva out of my mouth. Why are we evolved to do this?
Smith - Right. So why do they sound differently intelligible between the two?
Stuart - So, in that first clip we were hearing only the low frequencies and actually, in order to gain all the information and for our brains to be able to interpret it all, we need to have at least some of the frequencies there. We need to have as high a range of frequencies as possible so in the second clip when we can hear everything, itís much clearer.