Vol. 30, No. 11 Journal of Semiconductors November 2009
Novel lateral IGBT with n-region controlled anode on SOI substrate
Chen Wensuo(陈文锁)
†
, Xie Gang(谢刚), Zhang Bo(张波), Li Zehong(李泽宏), and Li Zhaoji(李肇基)
(State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China,
Chengdu 610054, China)
Abstract: A new lateral insulated-gate bipolar transistor (LIGBT) structure on SOI substrate, called an n-region
controlled anode LIGBT (NCA-LIGBT), is proposed and discussed. The n-region controlled anode concept results
in fast switch speeds, efficient area usage and effective suppression NDR in forward I–V characteristics. Simulation
results of the key parameters (n-region doping concentration, length, thickness and p-base doping concentration)
show that the NCA-LIGBT has a good tradeoff between turn-off time and on-state voltage drop. The proposed
LIGBT is a novel device for power ICs such as PDP scan driver ICs.
Key words: turn-off time; on-state voltage drop; NDR; power ICs
DOI: 10.1088/1674-4926/30/11/114005 EEACC: 2560
1. Introduction
The lateral insulated-gate bipolar transistor (LIGBT) is
a promising power device for power ICs due to its combina-
tion of the high input impedance of the MOS gate and the
conductivity modulation effect of the bipolar transistor. The
conductivity modulation permits the LIGBT to have a low
on-state voltage drop, but it also causes slow turn-off due to
the removal of stored electron-hole plasma in the drift region,
which is strongly dependent on the recombination process of
the electron-hole pairs during the turn-off period
[1, 2]
. Various
approaches have been reported in the literature to improve the
switching performance or to make a good tradeoff between
on-state voltage drop and turn-off time for the LIGBT. These
include the shorted anode LIGBT (SA-LIGBT)
[2, 3]
, NPN con-
trolled anode structure
[4]
, the segmented anode concept
[5, 6]
,
multi-gate devices
[7−10]
and lifetime control engineering
[11, 12]
.
The use of lifetime control engineering to reduce carrier life-
time increases cost due to the addition of a further process step.
The NPN controlled anode structure suffers from large forward
voltage drop because of its low current gain. The asymmetric
anode structure allows the segmented anode structures to suf-
fer from disadvantages such as asymmetrical current flow in
the n-drift region. Multi-gate devices require complex control
circuitry to switch the gates at the anode (high voltage) end.
The shorted anode concept offers the simplest solution but in-
troduces undesirable voltage snapback or negative differential
resistance (NDR) into the forward current–voltage (I–V) char-
acteristics due to the change-over from unipolar to bipolar cur-
rent conduction, which can lead to system instability
[13]
. Fur-
thermore, to prevent punch-through breakdown, a highly con-
ductive n-buffer region should be employed in the anode re-
gion. Therefore, a very long p injector is required to suppress
the NDR regime. This makes the device less area-efficient,
especially for the middle breakdown voltage (above 200 V)
power devices because of the small n-drift length. In this pa-
per, a novel fast switching speed n-region controlled anode
LIGBT on silicon-on-insulator (SOI) substrate is proposed and
discussed. SOI substrates overcome the deep plasma injection
into the substrate for junction-isolation substrates
[14, 15]
.
2. Device structure and operation
2.1. Device structure
A schematic cross section of the proposed LIGBT on SOI
substrate is illustrated in Fig. 1.
Distinct from the conventional LIGBT anode structure
only including a P+ region, the NCA-LIGBT anode has a spe-
cial design including a P+ region, N+ region, p-base region
and n-region. The anode n-region, which can be formed by
high energy phosphorus implantation after p-base region for-
mation, is a key concept for the NCA-LIGBT to have fast
turn-off speeds and efficient area usage. The n-drift region
doping concentration was optimized to fulfil the RESURF
condition
[16]
. Table 1 shows the device parameters used in the
numerical simulation.
2.2. Operation
When a voltage above the threshold is applied to the gate,
the proposed device is turned on. At a low forward bias, elec-
trons that flow from the channel through the drift region are
collected by the anode n+ region, and the transistor operates
Fig. 1. Schematic cross-sectional view of the proposed LIGBT.
† Corresponding author. Email: wensuochen@uestc.edu.cn
Received 12 May 2009, revised manuscript received 12 June 2009
c
2009 Chinese Institute of Electronics
114005-1