SOLID STATE (ELECTRONICS)

The term 'solid state' was introduced in the 1960s to describe electronic devices whose circuits contained neither vacuum tubes nor mechanical devices such as relays, as transistors replaced vacuum tubes in most consumer electronics.
As long as tubes still were being used, the 'solid state' term was used in semiconductor products. In the early 1970´s when tubes no longer were used in standard consumer electronic products, this term went silent.
In solid state components, electrons flow through unheated solid semiconductor materials (such as Germanium (Ge) or Silicon (Si)), instead of through a heated vacuum, as in vacuum tubes. Solid-state devices are typically far more reliable than their thermionic counterparts, due to the superior resistance to shock, vibration and mechanical wear that transistors provide.
As vacuum tubes rapidly became obsolete in consumer electronics, the term "solid state" was retained as a synonym for "contains no moving parts". For example, digital audio players that store all their data in flash memory are often described as ''solid state'', to differentiate them from hard disk players. Like the earlier usage, this new usage is intended to connote increased durability and shock resistance.
Vacuum tubes continue to be used in amplifiers, high-voltage devices (such as CRT-based televisions and computer monitors), radio transmitters, and optical sensors.