Question

The purpose of a field oxide (FOX) in CMOS fabrication is to:

• A. Create conductive channels
• B. Act as a mask for doping
• C. Provide electrical isolation
• D. Improve gate switching speed

Hint:

FOX = Field OXide = Electrical isolation! It keeps neighboring transistors from interfering.

Answer 1

The Correct Option is C

In CMOS (Complementary Metal-Oxide-Semiconductor) fabrication, the field oxide (FOX) layer plays a crucial role in electrically isolating different components on the semiconductor wafer. It is typically formed using thermal oxidation in areas not involved in active device formation.
FOX helps prevent electrical interference or leakage currents between adjacent transistors or active regions. This isolation is essential for maintaining the integrity and reliability of individual transistors within an integrated circuit.
Clarifying incorrect options:

• (A) FOX inhibits conductive channels — not creates them.
• (B) While masking is a part of fabrication, FOX's primary role is isolation, not doping.
• (D) Gate switching speed is influenced more by gate oxide and transistor design, not the field oxide.

Thus, the primary function of FOX is to provide electrical isolation between devices.