Silicon - Microchips and Semiconductors

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Silicon - microchips and semiconductors The macromolecule I have chosen is silicon. Silicon has four electrons in its valence shell, this allow them to form crystals, the four electron covalently bonds with four neighboring atoms creating a lattice. Electricity involves the flow of electrons, but all the outer electrons in a silicon crystal are involved in covalent bonds, pure silicon crystal is nearly an insulator, this is because the outer electrons can’t move around. (Wikipedia Contributors, 2012)(Brain, 2004) Silicon is a semiconductor because of its electrical conductivity being between that of an insulator and a conductor. For silicon to become more conductive we ‘dope’ the silicon, the procedure is known as ‘doping’. In doping, we mix small amount of impurity into silicon crystal. There are two types of impurities - N-type and P-type. N-type doping involve adding phosphorus or arsenic in small quantities, phosphorus and arsenic each have five electrons in the valence shell, when bonded to a silicon lattice the fifth electron has nothing to bond to, so it’s free to move around. P-type doping involving adding boron or gallium to silicon, boron and gallium both only have three electron in the valence shell. When added into a silicon lattice they create ‘holes’ in the lattice where a silicon electron has nothing to bond to.(Brain, 2001) A diode is the most basic semiconductor device and it consist of putting P-type and N-type silicon together. A diode only allow current to flow in one direction and not the other. A transistor is a more advance version of diode, instead of using two layers it uses three, in one of these configuration NPN or PNP sandwich. When applying a small current to the center layer of the sandwich, a larger current can flow through the sandwich, this gives a transistor its switching behavior.(Brain, 2001) The larger current oscillate

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