Page 37 - Curriculum Visions Dynamic Book

Quartz crystal
Microchip
Watch case
Liquid crystal (LCD) display
The crystal structure of quartz
The crystal structure of quartz is responsible for many of its unique properties. For example, a quartz crystal placed under pressure will produce electrical charges at each end of the crystal. A voltage applied across it results
in minute changes in shape. These two phenomena make up the piezoelectric effect.
The piezoelectric effect can be used as a pressure gauge or an electrical oscillator (a device that vibrates). Quartz crystal oscillators are at the heart of every digital watch and the clocks that help to control computers.
Quartz oscillators are also used in radios and other receiving and transmitting devices.
ICs (integrated circuits)
By carefully placing the doping impurities on a wafer of silicon, the wafer can be made to behave as though it were a myriad of separate components.
This is possible because silicon can
be made to change its conductivity over very short distances. In turn, this makes it possible for the circuit components to be microscopically small.
The principle of an IC is simple, but making ICs is extremely difficult because of the miniaturisation and accuracy required. A circuit is first drawn at a large-scale and made up as a photographic transparency. A light is shone through the transparency and focused onto a silver-based, light-sensitive coating on the surface of the chip.
The chip surface is next etched so that only the silver that will make the circuit remains. At the same time impurities have to be introduced into the surface of the wafer so that the chip can act as transistors, diodes, resistors, etc., and thus complete the circuit.
The whole of this circuit, and the aluminium leads that will be used to connect the IC to the “wider world” are encased in a plastic block.
 A modern IC, showing the multitude of external connections.
 A quartz watch uses the piezoelectric effect to keep superb accuracy at very low cost.
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