IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 64, NO. 1, JANUARY 2017 217
Optimization and New Structure of
Superjunction With Isolator Layer
Wentong Zhang,
Student Member, IEEE
, Bo Zhang,
Member, IEEE
, Ming Qiao,
Member, IEEE
,
Zehong Li,
Member, IEEE
, Xiaorong Luo,
Member, IEEE
, and Zhaoji Li,
Member, IEEE
Abstract
— An optimization theory is developed for the
balanced symmetric superjunction with the interface iso-
lator layer (I-SJ) in this paper. The theory includes two
parts: the electric field calculation by the Taylor series
method; the design formulas by the minimum specific on-
resistance
R
ON,min
optimization. Based on the theory, a new
I-SJ structure with a single cell is proposed, which shows
the minimum
R
ON
among the superjunction (SJ) devices
with the 1 µm shallow depths.
R
ON
of the new device is
reduced by 53.5% compared with that of the conventional
SJ lateral double diffused metal-oxide-semiconductor field
effect transistor (LDMOS) and 67.6% with the conventional
LDMOS under the same breakdown voltage
V
B
of 658 V.
Index Terms
— I-SJ,
R
ON,min
optimization, specific
ON-resistance, Taylor series method, theory.
I. INTRODUCTION
T
HE superjunction structure with the interface isolator
layer (I-SJ) was proposed in [1] to reduce the specific
ON-resistance R
ON
for a given breakdown voltage V
B
. The thin
isolator layer (I-layer) was also used to overcome the interdif-
fusion problem of superjunction (SJ) in both the vertical and
the lateral devices [2], [3]. For the conventional SJ without
the I-layer (C-SJ), the analytical theory is mainly based on the
Fourier series approximation method (F-method) [4]. Besides,
the electric field can also be obtained by the method of
separation of variables [5], [6]. The similar analysis for the
I-SJ structure is more complex, because two Poisson equations
in the n and p silicon regions and one Laplace equation in the
I-layer must be solved. Up to now, the optimization theory of
the I-SJ has yet to be found.
Instead of solving three complicated equations, this paper
proposed an optimization of the balanced symmetric I-SJ
based on the Taylor series approximation method (T-method).
With the calculated 2-D electric field, the minimum specific
ON-resistance R
ON,min
method [7] is used to optimized the I-SJ
in the nonfull depletion mode [8] to realize the lowest R
ON
.
Based on the optimization method, a new I-SJ LDMOS with
Manuscript received September 17, 2016; revised November 6, 2016;
accepted November 8, 2016. Date of publication November 28, 2016;
date of current version December 24, 2016. This work was supported by
the National Natural Science Foundation of China under Grant 61376080
and Grant 61474017. The review of this paper was arranged by Editor
S. N. E. Madathil.
The authors are with the State Key Laboratory of Electronic Thin Films
and Integrated Devices, University of Electronic Science and Technol-
ogy of China, Chengdu 610054, China (e-mail: wentwing@126.com;
zhangbo@uestc.edu.cn; qiaoming@uestc.edu.cn; lizh@uestc.edu.cn;
xrluo@uestc.edu.cn; zjli@uestc.edu.cn).
Color versions of one or more of the figures in this paper are available
online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TED.2016.2628056
a single cell is optimized, which has the similar typical sizes
as those in [9]–[16] and shows the lower R
ON
.
II. I-SJ T
HEORY
The optimization includes two parts: the 2-D electric field
based on the T-method; the R
ON,min
method for the I-SJ.
A. Electric Field Distribution of I-SJ Based on T-Method
The I-SJ cell structure is shown in Fig. 1(a),inwhich
W, L
d
,andN are the width, length, and doping concentrations
of the n- and p-regions; W
I
is the width of the I-layer. In the
expressions, q is the electron charge; ε
s
and ε
I
are dielectric
constants of the silicon and the isolator, respectively.
The electric field E(x, y) of the I-SJ is a superposition of
the charge electric field E
q
(x, y) and the potential electric
field E
p
[7], in which E
p
= V
B
/L
d
is a constant. The
T-method is used to calculate E
q
(x, y) of the I-SJ and detailed
in Appendix A, from which the charge electric field along the
half integral path CO with 0 ≤ y ≤ L
d
/2 is
⎧
⎪
⎪
⎨
⎪
⎪
⎩
E
q,x
(y) = E
T
0.5W
T
c
exp
E
T
E
p
y−L
d
/2
T
c
E
q,y
(y) =−E
T
exp
−
y
T
c
(1)
where E
T
= qNT
c
/ε
s
and T
c
, defined as the characteristic
thickness, is a size-dependent parameter with W and W
I
T
c
=
W
2
√
2
1 +
2ε
s
W
I
ε
I
W
. (2)
As shown in Fig. 1(b), the positive E
q,x
(y) reduces fast as
it gets farther away from point O. The negative E
q,y
(y) only
has the larger absolute values within the distances of 2T
c
from
the points C and is almost zero in the charge balance region
from 2T
c
to L
d
−2T
c
.IfL
d
< 4 T
c
, the SJ loses its function
to reduce R
ON
efficiently. Therefore, T
c
is the measurement of
the charge balance between the n- and p-regions.
From Appendix A, it can be seen that the T-method has
the following features: E(x, y) is obtained by solving the
simplified Poison equation using the Taylor series rather than
solving the two Poisson equations in the n- and p-regions and
one Laplace equation in the I-layer; the physical significances
of the parameters are clear and the method is useful for the
C-SJ with W
I
= 0 in (2). Therefore, compared with the
F-method, the T-method is a simple and universal method for
both the I-SJ and the C-SJ devices.
0018-9383 © 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.
See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.