1. SUPERJUNCTION CONCEPT IN POWER MOSFET
RICHU JOSE CYRIAC
M120128EC

2. Overview
 Introduction
 Superjunction concept
 Limitation
 Conclusion and future work

3. 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].
5.2
BVRon

4. Superjunction concept

5. 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

6.  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

7. In normal Si VDMOSFET In superjunction Si VDMOSFET
 Flat electric field profile instead of a triangular one as in a VDMOS transistor[3].

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

9. 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.

10. 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