Editing Sapphire (section)

====As substrate for semiconducting circuits====
{{main|Silicon on sapphire}}
{{More citations needed section|date=March 2021}}

Thin sapphire wafers were the first successful use of an insulating [[substrate (semiconductor)|substrate]] upon which to deposit silicon to make the [[integrated circuit]]s known as [[silicon on sapphire]] or "SOS"; now other substrates can also be used for the class of circuits known more generally as [[silicon on insulator]]. Besides its excellent electrical insulating properties, sapphire has high [[thermal conductivity]]. [[CMOS]] chips on sapphire are especially useful for high-power radio-frequency (RF) applications such as those found in [[cellular telephones]], [[police radio|public-safety band]] radios, and [[satellite communication]] systems. "SOS" also allows for the monolithic integration of both [[digital electronics|digital]] and [[analog electronics|analog]] circuitry all on one IC chip, and the construction of extremely low power circuits.

In one process, after single crystal sapphire boules are grown, they are core-drilled into cylindrical rods, and wafers are then sliced from these cores.{{citation needed|date=October 2014}}

Wafers of single-crystal sapphire are also used in the [[semiconductor]] industry as [[substrate (semiconductor)|substrates]] for the growth of devices based on [[gallium nitride]] (GaN). The use of sapphire significantly reduces the cost, because it has about one-seventh the cost of [[germanium]]. Gallium nitride on sapphire is commonly used in blue [[light-emitting diodes]] (LEDs).<ref>"Gallium nitride collector grid solar cell" (2002) {{US patent|6447938}}</ref>