Question

What is used to higher the speed of operation in MOSFET fabrication?

(a) Ceramic gate

(b) Silicon dioxide

(c) Silicon nitride

(d) Poly silicon gate

The question was asked during an interview.

This intriguing question originated from MOS Digital Integrated Circuits in chapter Logic Families of Digital Circuits

Answer 1

Right option is (d) Poly silicon gate

To elaborate: In conventional metal gate small overlap capacitance is present, which lowers the speed of operation. With the presence of self aligning property of the poly silicon gate it eliminates this capacitance. Using a process called ion-implantation, polysilicon, the drain and the source get doped. However, the thin oxide under silicon gate acting as a mask for the process and thus develops the gate aligning property.