Plastic Electronics is a very strange concept, because most people consider electronics to require some sort of conducting material and almost everybody considers plastic to be an insulator.
‘Plastic’ is an umbrella-term for a polymer. A polymer is a chain of repeating identical molecules - called ‘monomers’ - chemically linked up to form one long molecule; the obvious analogy are the links in a chain being the monomer, with the chain they constitute being the polymer. Similarly to this analogy, the polymer (chain) has different properties to that of the monomer (chain-link). A good question now is, “How can plastic conduct charge?’.
Conduction - as your early science lessons and classes should have taught you - is the ability to allow charge to pass through a material. The most obvious example is in a metal where the metal ions are arranged in a regular lattice, while the free electrons can float around. These electrons that are free to ‘float’ around are said to be ‘delocalised’. As you may guess, the fact that the electrons can move about means that charge can be conducted through the metal!
A POLYMER CONDUCTS BY THE SAME PRINCIPLE!
Polymers have a linear array of carbon atoms, which are bonded in such a way as to allow the passage of charge. This I think is best explained by analogy:
Consider a polymer as a row of seats (the monomer units all linked up), one next to another, as in a lecture theatre or concert hall. Now put people (electrons) on these seats. Now, remove one person from this system (i.e. remove an electron from the polymer, which is called oxidising the polymer). This means there is space for the electrons to move to, and as such, with a domino-like effect, charge can be moved across a polymer. It really is quite simple!!
According to the above description, these polymers can be, indeed are, classified as semiconductors. By this I mean that they only conduct under certain conditions, i.e. when there is an electron removed (a.k.a. a hole inserted), which is a process known as doping. Until the polymers are doped - which can be done electrically, such as by attaching electrodes and directly providing the charge, or chemically, by using something that is easily reduced and thus oxidises the polymer (Iodine is a popular choice) - they are insulators. They are organic semiconductors, which is another term commonly found in the press and journals. The relevance is that semiconductors are used in almost everything that requires a microchip. Silicon is the most commonly used semiconductor.
The promise of these organic semiconductors is for them one day to be more efficient than silicon, and could be easier and cheaper to process, enabling complete replacement of the currently macroscopic-scale silicon transistors with atomic-scale organic semiconductor-derived transistors. This is vital if the chip manufacturers are to keep with their self-set pace of development and improvement (see below).
The problem of using silicon in computer processing chips is only apparent when one examines how the silicon is used in a chip. It is used mainly in the millions or even billions of transistors which are on each chip. In fact you may have heard of Moore’s Law (of Gordon Moore; co-founder of the chip giant Intel), which states that every 18 months or so there will be twice as many transistors on a chip. Well, this law/guideline has been the driving force behind the silicon chip industry ever since it was stated in 1965, and means that these transistors must be made smaller and smaller each year, which has been fine for the past 30 years or so. However, part of the transistor called the gate-oxide(see diagram below) which acts as an insulator (and is made of silicon) can only become so small before it no longer can act as insulator. It is this which is causing so much hassle.
Schematic of a transistor adapted from library.thinkquest.org
As a consequence, new materials with different dielectric constants have been looked at to take over when silicon reaches the end of its usefulness. Alloys of Hafnium have been considered, and indeed utilized in some recent chip designs (see The New York Times article from 27 Jan 2007). Another answer to this problem however is the use of organic semiconductors, which, one day (again - the potential is there, but the means is still in the making!) could allow the fabrication of molecular sized transistors! This is the goal.
Other components are also being considered, with the obvious examples of OLEDs, which are already being made available commercially (See blog 13/06/07 OLEDS: Universal Display Corporation Awarded Grants), and photovoltaic devices (See blog 14/07/07 Plastic Solar Cells get Boost in Efficiency), whose efficiencies are approaching commercially viable levels.
There is still a long way to go until we have tiny computers made of pure plastic sitting on desks, transmitting wirelesly to a thin flexible piece of (you guessed it!) plastic, which displays information in high resolution, all powered by the ambient light that that same screen has absorbed during the day and stored in capacitors…but I am not at all frightened to say that this is not a question of if - just a case of when.
I hope this short introduction into plastic electronics has made it slightly clearer as to what all the fuss is about, what some of the science entails, and what progress is being made.
If anyone has ANY QUESTIONS please just ask. I will do my best to give factually correct information (if and when I can!); but seriously, any feedback is massively welcomed, negative or not.
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