SUPERJUNCTION CONCEPT IN POWER MOSFET

RICHU JOSE CYRIAC

M120128EC

Overview

Introduction

Superjunction concept

Limitation

Conclusion and future work

Introduction

Only concept which proved wrong theoretical study on the limit of silicon in high voltage devices.

The relation in power MOSFET without superjunction is [1]

The idea of a superjunction has been used to improve this relationship from super-linear to linear [2].

5.2BVRon

Superjunction concept

Superjunction concept

The drift region of superjunction device is formed of multiple, alternate n and p semiconductor stripes.

p pillar does not contribute to on-state conduction in the on-state.

Cross-sectional area of the drift region is halved, Ron will be doubled for the super-junction but with increased doping Ron reduces significantly.

Poisson’s equation for 1D electric field

In a superjunction device, electric field is 2D

E

x

Ex

y

E

x

E yx

y

E

x

E yx

Since the widths of the p and the n pillars are very small as compared with the height, the horizontal depletion takes place at a relatively low drain voltage.

n and the p pillars will be completely depleted well before the breakdown voltage is reached.

Due to the full depletion of the p and the n pillars, they should not create a maximum electric field for breakdown, Ec (critical field), at the vertical junction.

Designer’s freedom Doping profile of n region Design and pitch of p columns

In normal Si VDMOSFET In superjunction Si VDMOSFET

Flat electric field profile instead of a triangular one as in a VDMOS transistor[3].

Limitation

Difficulty of fabrication process. Higher aspect ratio of pillars requires large number of steps and higher costs.

Conclusion and Future work

Semi SJVDMOSFET is an option in which a bottom assist layer is provided, so there can be some relaxation in aspect ratio.

Charge sheet super junction in which say p- pillars in SJVDMOSFET is replaced by negative charge sheet.

Al2O3 or SiO2 can be used as charge sheets. Tunable charge compensation technique can be

implemented using YFET concepts. Fabrication of SJVDMOS on wide gap

semiconductors like SiC, GaN is a research focal point.

Reference

1. Silicon Carbide Power devices, B Jayant Baliga.

2. Jian Chen, Weifeng Sun, Long Zhang, Jing Zhu and Yanzhang Lin, “A Review of Superjunction Vertical Diffused MOSFET”, IETE Technical review, Vol29, Issue1, Jan-Feb 2012.

3. Pravin N. Kondekar and Hawn-Sool Oh, “Analysis of the Breakdown Voltage, the On- Resistance, and the Charge Imbalance of a Super-Junction Power MOSFET”, Journal of the Korean Physical Society, Vol. 44, No. 6, June 2004, pp. 1565-1570.

4. Dr. Gerald Deboy & Dr. Florin Udrea, “Superjunction devices & technologies – Benefits and Limitations of a revolutionary step in power electronics”, EPE 2007

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