gate dielectric

{{Short description|Field-effect transistor}}

{{Ref improve|date=December 2006}}

A gate dielectric is a dielectric used between the gate and substrate of a field-effect transistor (such as a MOSFET). In state-of-the-art processes, the gate dielectric is subject to many constraints, including:

• Electrically clean interface to the substrate (low density of quantum states for electrons)
• High capacitance, to increase the FET transconductance
• High thickness, to avoid dielectric breakdown and leakage by quantum tunneling.

The capacitance and thickness constraints are almost directly opposed to each other. For silicon-substrate FETs, the gate dielectric is almost always silicon dioxide (called "gate oxide"), since thermal oxide has a very clean interface. However, the semiconductor industry is interested in finding alternative materials with higher dielectric constants, which would allow higher capacitance with the same thickness.

{{Further|high-κ dielectric}}