Overview

The charge-coupled power MOSFET structures discussed in the previous chapter allow drastic reduction of the on-resistance of the drift region by utilizing the two-dimensional charge coupling between a source-connected electrode located within deep trenches and the donors in the drift region. By using a linearly graded doping profile, a rectangular shaped electric field profile can be generated in the drift region with doping levels ranging above 1 10 ¹⁶ cm ^?3. In addition, it was shown in the previous chapter that the charge coupling phenomenon distributes the electric field primarily in the N-type drift region with very little voltage developed across the P-base region. This allows reduction of the channel length which is beneficial for high frequency operation.

In the CC-MOSFET and GD-MOSFET structures described in the previous chapter, the channel is formed on the sidewall of the same trench within which the source-connected electrode is located. This imposes fabrication challenges because of the need to isolate the gate and source electrodes within the trench. In addition, the source-connected electrode in the trench must be periodically brought to the surface to make its electrical connection which disrupts the gate layout in the third dimension.

In this chapter, an alternate structure that utilizes the charge coupling concept is described with the gate region formed on the top surface ^[1]. This structure, named the super-linear (SL) MOSFET structure, can utilize either a uniform or a graded doping profile. In the previous chapter, it was shown that the...