Solid-state electronics are those circuits or devices built entirely from solid materials and in which the
electrons, or other
charge carriers, are confined entirely within the solid material. The term is often used to contrast with the earlier technologies of
vacuum and
gas-discharge tube devices, and it is also conventional to exclude electro-mechanical devices (
relays,
switches,
hard drives and other devices with
moving parts) from the term solid state. While solid-state can include
crystalline,
polycrystalline and
amorphous solids and refer to
electrical conductors,
insulators and
semiconductors, the building material is most often a crystalline semiconductor. Common solid-state devices include
transistors,
microprocessor chips, and
RAM. A specialized type of RAM called
flash memory is used in
flash drives and, more recently,
solid-state drives to replace mechanically rotating magnetic disc
hard drives. A considerable amount of
electromagnetic and
quantum-mechanical action takes place within the device. The expression became prevalent in the 1950s and the 1960s, during the transition from
vacuum tube technology to semiconductor
diodes and
transistors. More recently, the
integrated circuit (IC), the
light-emitting diode (LED), and the
liquid-crystal display (LCD) have evolved as further examples of solid-state devices.