The vacuum tube was invented in 1910 and was the preferred electronically-controlled amplifier/switch for half a century; it was the fundamental building block that made the electronic revolution—including radio, television, radar, sound recording and reproduction, telephone networks, computers, home appliances, cryptography, and industrial process control—technically and economically feasible.
The vacuum tube made it possible to control a high-power electronic signal with a low-power signal, thereby serving as an electronic amplifier and switch.
Vacuum tubes have several downsides.
- they are not very reliable: offgassing and leakage through the tube seals can eventually poison the cathode, reducing its ability to thermionically emit electrons; cathode materials can also be depleted as materials boil out of them; repeated heating and cooling of the electrodes strains components and can lead to mechanical failure.
- they are expensive to produce: vacuum tubes are quite large and required a high-quality vacuum to operate.
- they are electrically inefficient: because the cathode has to be maintained at a constant high temperature, each vacuum tube requires significant wattage to operate. The ENIAC computer used over 17,000 vacuum tubes and consumed 150kW of electrical power. This also posed significant cooling challenges (and expenses).
While vacuum tubes still find use today in specialized audio and high-frequency power amplifiers and a few technical devices, they have been replaced in virtually all applications by solid state devices such as transistors.
'MOSFET' stands for 'Metal Oxide Semiconductor Field Effect Transistor'. The MOSFET is an important component in modern solid state electronics and a model device for exploring how a series of very thin semiconducting films can be engineered to serve a particular function.
A technique for doping a semiconductor material. Doping modifies the density of free charges in the material, changing the conditions under which the material will conduct.
A typical ion implanter consists of an ion source and an electromagnetic particle accelerator, by which ions are produced and accelerated into the material placed in the target chamber. Ions can be accelerated to 1-1000 keV to control the depth to which the ions penetrate the target.
After ion implantation, the material is annealed at elevated temperature to allow the dopant to diffuse into substitutional positions within the semiconductor.