Body Contact

Body Contact is a design technique in SOI technology where an explicit electrical connection is made to the transistor body — providing a path for accumulated charge to escape, eliminating floating body effects at the cost of increased area and parasitic capacitance.

What Is a Body Contact?

• Implementation: An extension of the active region connected to a P+ (or N+) diffusion tied to ground (or VDD).
• Types:
• T-Shaped: Body contact extending from one side of the gate.
• H-Shaped: Body contacts on both sides.
• Body-Tied MOSFET: Integrated contact within the device layout.
• Area Penalty: 15-30% increase in transistor area.

Why It Matters

• Eliminates: Kink effect, history effect, floating body instability.
• Analog: Essential for SOI analog circuits where output resistance and gain must be predictable.
• Trade-off: More area and capacitance vs. better analog behavior and reliability.

Body Contact is the grounding wire for SOI transistors — sacrificing density to eliminate the unpredictable floating body effects.