Solid-state refers to electronic components, devices, and systems based entirely on the semiconductor . The expression was especially prevalent in the late 1950s and early 1960s, during the transition from vacuum tube technology to the semiconductor diode and transistor . 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.
In a solid-state component, the current is confined to solid elements and compounds engineered specifically to switch and amplify it. Current flows in two forms: as negatively charged electrons, and as positively charged electron deficiencies called holes. In some semiconductors, the current consists mostly of electrons; in other semiconductors, it consists mostly of holes. Both the electron and the hole are called charge carriers.
An example of a non-solid-state component is a cathode-ray tube ( CRT ). In this device, electrons flow freely through a vacuum from an electron gun, through deflecting and focusing fields, and finally to a phosphorescent screen.