They are sensitive to radiation and cosmic rays (special radiation-hardened chips are used for spacecraft devices). In audio applications, transistors lack the lower-harmonic distortion – the so-called tube sound – which is characteristic of vacuum tubes, and is preferred by some. Types Classification |- style="text-align:center;" |||PNP||||P-channel |- style="text-align:center;" |||NPN||||N-channel |- style="text-align:center;" |BJT||||JFET|| |- style="text-align:center;" |||||||P-channel |- style="text-align:center;" |||||||N-channel |- style="text-align:center;" |colspan="2"|MOSFET enh||MOSFET dep|| Transistors are categorized by Structure: MOSFET (IGFET), BJT, JFET, insulated-gate bipolar transistor (IGBT), other types. Semiconductor material (dopants): The metalloids; germanium (first used in 1947) and silicon (first used in 1954)—in amorphous, polycrystalline and monocrystalline form. The compounds gallium arsenide (1966) and silicon carbide (1997). The alloy silicon-germanium (1989) The allotrope of carbon graphene (research ongoing since 2004), etc. (see Semiconductor material). Electrical polarity (positive and negative): NPN, PNP (BJTs), N-channel, P-channel (FETs). Maximum power rating: low, medium, high. Maximum operating frequency: low, medium, high, radio (RF), microwave frequency (the maximum effective frequency of a transistor in a common-emitter or common-source circuit is denoted by the term , an abbreviation for transition frequency—the frequency of transition is the frequency at which the transistor yields unity voltage gain) Application: switch, general purpose, audio, high voltage, super-beta, matched pair. Physical packaging: through-hole metal, through-hole plastic, surface mount, ball grid array, power modules (see Packaging). Amplification factor , (transistor beta) or (transconductance). Working temperature: Extreme temperature transistors and traditional temperature transistors (). Extreme temperature transistors include high-temperature transistors (above ) and low-temperature transistors (below ). The high-temperature transistors that operate thermally stable up to can be developed by a general strategy of blending interpenetrating semi-crystalline conjugated polymers and high glass-transition temperature insulating polymers. Hence, a particular transistor may be described as silicon, surface-mount, BJT, NPN, low-power, high-frequency switch. Mnemonics Convenient mnemonic to remember the type of transistor (represented by an electrical symbol) involves the direction of the arrow. For the BJT, on an n-p-n transistor symbol, the arrow will "Not Point iN". On a p-n-p transistor symbol, the arrow "Points iN Proudly". This however does not apply to MOSFET-based transistor symbols as the arrow is typically reversed (i.e. the arrow for the n-p-n points inside). Field-effect transistor (FET) The field-effect transistor, sometimes called a unipolar transistor, uses either electrons (in n-channel FET) or holes (in p-channel FET) for conduction. The four terminals of the FET are named source, gate, drain, and body (substrate). On most FETs, the body is connected