Overview

The super-linear (SL) MOSFET structure described in Chapter 7 utilizes the charge-coupling concept to reduce the resistance in the drift region. The charge-coupling is achieved by forming a source connected electrode within a deep trench that surrounds the (mesa) drift region. In addition to allowing high doping concentrations in the drift region, the charge-coupling distributes the electric field below the P-base region resulting in a low electric field at the surface. This enables maintaining the channel in the linear mode of operation even at high drain bias voltages an essential feature to obtain the desired super-linear behavior. The planar gate structure for that device is formed on the mesa surface. Electron transport occurs from the N ⁺ Source region and the inversion layer channel region through a transition region into the N-drift region. The constriction of current flow in the transition region adds to the on-resistance of the structure and limits the maximum drain current (i.e. the compression current).

In this chapter, a super-linear (SL) MOSFET structure is described which utilizes the charge-coupling concept exploited in the above device structure but relies up on a trench gate region formed within the mesa region ^[1]. The trench gate structure eliminates the transition region resulting in superior on-resistance and compression current. When compared with the trench gate GD-MOSFET structure described in Chapter 6, this structure is easier to fabricate because the gate is not formed within the same trench as the source connected deep trench electrode. The super-linear...