Backgating

Backgating is a term used in semiconductor device physics and electronics to describe the influence of a voltage applied to the back side or substrate of a device on the operation of its front-side gate or channel. It is most commonly encountered in devices where the channel is insulated from a back electrode, such as silicon-on-insulator (SOI) transistors or thin-film transistors. The back gate, often the substrate or a dedicated conductor under an insulating layer, modulates the channel by shifting the body potential, thereby affecting the threshold voltage and drive current.

Mechanism: The body effect occurs when the substrate potential changes, influencing the depletion region and the effective threshold. In dual-gate devices, both gates can independently tune the channel behavior. In SOI devices, the buried oxide separates the back gate from the front gate, but a back-bias can still modulate the channel to adjust performance.

Applications: Backgating can be used to tune device performance after fabrication, compensate for manufacturing variations, enable dynamic threshold adjustment for low-power operation, and in some sensor or memory devices to calibrate response. It is a technique in back-gated field-effect transistors (BG-FETs) and dual-gate transistors, where a second gate provides additional control over conduction.

Challenges and considerations: Backgating introduces coupling between gates and can complicate circuit design, requiring careful isolation and control of substrate bias to avoid leakage, instability, or increased noise. Radiation or charge trapping in the substrate can also cause unintended backgate effects, particularly in radiation-sensitive applications.

See also: body bias, threshold voltage, SOI transistor, dual-gate transistor.