Bendy circuits for smart food

15 March 2016

Interview with

Dr Stuart Higgins, The University of Cambridge

Silicon is great but what if it could be cheaper, bendier and printable? Maybe then Integrated circuit chipwe 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; it's like a shiny blood colour; it looks very metallic and it's hard and, if I were to drop this, it would smash like glass.

Smith - It's a disk.  It's what 4 or 5cms across and thin, shiny - it's like a CD really.

Stuart - Yes, it looks very similar to a CD.  It's 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 they're made on  - this is this hard material.  Now that's great but, as I said, if I drop this it's going to smash - it's 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 that's a hard crystal substance like silicon, it's going to smash - it's going to shatter to shatter into lots of pieces.  So I'm 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; that's why we make our plug sockets out of them; that's why we make our cables out of them because we don't 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 that's what you've got here is it?

Stuart - Yes.  So in my right hand I have this flexible piece of... well it's a piece of plastic.

Smith - Okay.  So this is about the same size as the wafer of  silicon.  I can see through it; it's completely transparent, thin piece of... looks like cling film but a bit thicker and it's got some coppery coloured stuff on it.

Stuart - Yes, so what we're looking at there - actually it's 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.  It's like an electrical switch where you press it and turn it on and you turn if off and it's the fundamental building block inside every microprocessor.  So when your computer does calculations, it's 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 you're doing something like silicon, you have to use very industrial processes - it's a very hard material to work with.  But, if you've got a semiconductor that's 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 we're 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; it's 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.  We're 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 I'm 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 wouldn't normally find them, for example, maybe on packaging.  So, as you referred to earlier, imagine having a milk carton in your fridge that's 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, what's in your fridge when you're out shopping so you know what to buy next.

Smith - It would be food for thought, wouldn't it?

Stuart - Exactly. That's 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 - It's an obvious question.  Why aren't we doing it now?

Stuart - Well, the problem is that these plastics, while they're good, is there not that good.  They're 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, I'm trying to illustrate here what happens if you've got a slow transistor; if you've got a slow switch that turns on and off.  Now, in some ways, if you've got your smartcard talking to the reader and it's kind of speaking very slowly and you've got the reader speaking very fast in return and trying to get things really quickly, those two can't talk to each other, they can't understand each other, and particularly if you've got transistors that can also be used as an amplifier.  If that amplifier can't see all the frequencies then you start to miss information.

In this first clip I'm going to play a spoken recording and it's going to have all of the high frequencies cut out as if the transistor wasn't switching fast enough.  So, we're going to listen to that and try and understand what's being said and see how difficult it is to hear what's happening.  After that I'm going to play the second clip with all the frequencies present so we can hear what it says.

Smith - Let's do it...

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, it's much clearer.

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