Three-Dimensional Varying Density Field Plate for Lateral Power Devices

Field plate (FP) is a widely used electric field optimization technique in lateral power devices. However, the electric field optimized by 2-D-FP still has limited distribution distance and poor distribution uniformity, which are disadvantages for lateral power devices. To investigate the disadvantages deeply, this paper extracted the charge density (D
_ch
) on 2-D-FP by simulation for the first time. Our investigations found that the disadvantages of 2-D-FP come from the nonuniform distribution of D
_ch
on 2-D-FP, which cannot fit the requirement of charge balance. To solve the problem, the method to modulate D
_ch
on FP by designing the FP in the width direction is studied. In this way, the 3-D varying density FP (3-D-VDFP) that has relatively uniform D
_ch
distribution is proposed. Our studies based on a lateral double-diffused MOS (LDMOS) proved that the 3-D-VDFP alleviates the disadvantages of 2-D-FP effectively and realized the charge balance without introducing p-type region for the first time. The corresponding experimental results show that the LDMOS with 3-D-VDFP has lower specific on-resistance than the buffered step doping super junction LDMOS because the drift region is not wasted at all when the charge balance is realized by 3-D-VDFP.