fieldplate

A field plate is a conducting plate placed over a semiconductor surface and connected to a defined bias. Its purpose is to shape the electric field within and near a device, spreading out the field lines to reduce peak electric fields at edges, interfaces, and passivation layers. By redistributing the potential near a junction, a field plate helps increase breakdown voltage and reduce surface leakage and premature breakdown in high-voltage devices.

Field plates are commonly implemented in high-voltage power devices, including lateral and trench MOSFETs, IGBTs, and diode structures, as well as in wide-bandgap technologies such as SiC and GaN devices. The plate can be a metal region or a heavily doped semiconductor that extends over the device surface and is separated from the underlying regions by a dielectric or passivation layer. It is biased to a potential (often near the source or drain, or to a separate bias rail) that modifies the electrostatic landscape so that field lines terminate more evenly rather than concentrating at the junction edge.

Design considerations include the plate’s length, overlap with the junction, and spacing from the active region, along with the dielectric thickness and bias connection. While a field plate improves breakdown performance and reliability, it also adds capacitance and can affect switching speed and parasitic interactions. Proper layout must balance these trade-offs and, when used with other edge-termination techniques such as guard rings, provides a robust method for field management in high-voltage semiconductor devices. Field plates are regarded as a standard tool for field relief and edge termination in power electronics.