1200 V SiC Schottky Rectifiers optimized for ≥ 250 °C operation

1200 V SiC Schottky Rectifiers optimized for ≥ 250 °C
operation with low junction capacitance
Ranbir Singh* and Siddarth Sundaresan
GeneSiC Semiconductor Inc.
43670 Trade Center Place; Suite 155
Dulles, VA. USA
[email protected]
Abstract— Electrical Characteristics of Industry’s first
commercially available 1200 V rated SiC Schottky rectifiers,
specially designed for operation at ≥ 250 °C are presented. These
high-temperature SiC rectifiers fabricated in 1, 5, and 20 A
current ratings feature reverse leakage currents of < 3 mA/cm2
at 1200 V up to temperatures as high as 300 °C. GeneSiC’s 1200
V/20A High Temperature Schottky (designated SHT) rectifier
offers a 10x reduction in leakage current and a 23% reduction
in junction capacitance when compared to its nearest SiC
Schottky rectifier competitor. In addition, these SHT rectifiers
demonstrate superior surge-current ratings, and temperatureindependent switching capability up to their rated junction
To address the emerging need for high-temperature (>200
°C) capable high-voltage rectifiers in down-hole oil drilling,
geothermal instrumentation, aerospace and other military
applications, GeneSiC has successfully commercialized the
industry’s first 1200 V SiC Schottky rectifiers designed and
fabricated for low-leakage performance at > 200 °C junction
These high-temperature Schottky (SHT)
rectifiers are uniquely designed and fabricated to fully exploit
the superior high-temperature capability of the 4H-SiC
material and associated metallizations, fabrication techniques
and designs. A detailed investigation of the on-state, blocking
voltage, switching, capacitance-voltage (C-V), and long-term
reliability characteristics of these novel SiC SHT rectifiers are
presented in this paper. The SHT Rectifiers presented in this
paper are excellent diodes for use in conjunction with
GeneSiC’s SiC “Super” Junction Transistors (SJTs) [1], which
offer superior electrical performance over competing SiC
transistor technologies (MOSFETs, JFETs) at > 200 °C
operating temperatures.
Device designs and fabrication processes were developed
at GeneSiC to enable the SiC SHT rectifiers to block their
rated voltage, even at temperatures as high as 300 °C with low
leakage currents. The topside metallization for these SHT
rectifiers was formed by either thick Al or Au to be
compatible with wire-bonded or fully soldered packaging,
respectively. The 1200 V SHT rectifiers were fabricated with
three different chip sizes, corresponding to 1 A, 5 A and 20 A
chip current ratings. When these chips are packaged in
different packages with different thermal characteristics, they
offer correspondingly different current ratings. These devices
are packaged in industry standard 3-leaded TO-257 and
Surface Mount (SMB05/TO-276) packages, as shown in
Figure 1.
Figure 1: Isolated TO-257 (Left) and Surface Mount SMB05
(TO-276) packages were used for packaging of high
temperature SiC Rectifiers.
Although these packages and associated solders and
encapsulations were rated for <250oC junction temperatures,
these devices were electrically characterized up to 300 °C. It
is assumed that the pulsed measurements do not affect device
characteristics appreciably.
A. Voltage Blocking Characteristics
Very low leakage currents are measured on a 1200 V/1 A
SiC SHT rectifier up to 300 °C (Figure 1). A clear signature of
avalanche limited breakdown can be inferred from the positive
temperature co-efficient of the breakdown voltage as observed
in Figure 2.
SHT rectifier at temperatures as high as 250-300 °C, without
excessive leakage currents.
B. On-State Performance
The forward I-V characteristics of a 1200 V/5 A SiC SHT
rectifier are shown in Figure 4. The on-state voltage drop
shows a modest increase at the rated 5 A from 2.18 V at 25
°C to 3.6 V at 250 °C.
Figure 2: Reverse Blocking I-V Characteristics of (Left, a)
1200 V/1 A SiC Schottky rectifier up to 300 °C.
Leakage currents at rated voltages of the SHT Schottky
rectifiers were compared with Schottky rectifiers from other
manufacturers. The leakage current comparison is shown in
Figure 3.
Figure 3: Comparison of blocking characteristics of
standard and high-temperature 1200 V/1-20 A SiC
Schottky rectifiers fabricated by GeneSiC. Datasheet data
from 1200 V SiC Schottky diodes fabricated by other SiC
device manufacturers are also shown for comparison.
It can be seen from Figure 3 that the GeneSiC SHT
rectifiers offer the lowest reverse leakage currents among
commercially available 1200 V SiC Schottky rectifiers at all
current ratings. A 20 A SHT rectifier shows a 10x reduction
in reverse leakage current at 1200 V and 175 °C, when
compared to its nearest SiC Competitor. The special lowleakage process used for GeneSiC’s SHT rectifier fabrication
results in a further 27% reduction in leakage current at 175
°C, as compared to GeneSiC’s standard Schottky rectifier,
named SLT rectifier. This enables the operation of the SiC
Figure 4: Temperature dependent on-state characteristics
measured on a 1200 V/5 A SiC SHT Rectifier.
Almost temperature independent Schottky barrier
heights of 1.2 eV and ideality factors < 1.05 (Figure 5) are
extracted from low-current (10-9 A to 10-5 A) forward I-V
characteristics measured at different temperatures on the 1200
V/5 A SHT rectifiers, which are evidence of an homogenous
Schottky barrier interface, even at temperatures in excess of
200 °C.
Figure 5: Ideality factor and Schottky barrier height
extracted from the I-V-T measurements.
C. Capacitance-Voltage (CV) Chracteristics
The reverse recovery loss in a majority carrier SiC Schottky
diode originates entirely from charging and discharging of its
junction capacitance (Cj). Therefore a measure of
Capacitance, especially at near-zero bias, is considered to be
an important parameter used to compare the performance of
these type of devices. From the C-V characteristics shown in
Figure 6, a 1200 V/5 A SHT rectifier shows 9% reduction of
Cj at 1 V reverse bias and a 15% reduction in capacitive
charge (Qc) at 800 V, when compared with a 1200 V/5 A
SLT (standard-design) rectifier.
Figure 6: Comparison of C-V characteristics measured on
GeneSiC’s 1200 V/5 A standard (SLT) Schottky and SHT
As shown in Figure 7, GeneSiC’s 1200 V SHT rectifiers
offer the lowest near-zero bias (at Anode-Cathode bias,
VAK=-1 V) junction capacitance (Cj) among all commercially
available 1200 V SiC Schottky rectifiers at all current ratings.
A 20 A GeneSiC SHT rectifier shows a 23% lower Cj when
compared to a 20 A SiC Schottky rectifier from Competitor
#1. Thus, these SHT rectifiers offer the fastest switching
capability and lowest-in-class switching losses in the 1200 V
Schottky rectifier class.
D. Switching Characteristics
The 1200 V SHT rectifiers were inserted as free-wheeling
diodes with a 1200 V/25 A Si IGBT, and a standard double
pulse scheme was used for obtaining the switching
waveforms. The cathode current waveforms obtained for
switching a 1200 V/20 A SHT rectifier under a high reverse
dI/dt condition (50 A/μsec) and reverse bias 960 V, at 25 °C
and 205 °C are shown in Figure 8.
Figure 8: Diode turn-off current waveforms measured on
a 1200 V/20 A SiC SHT rectifier at 25 °C and 205 °C. The
turn-off measurement was performed to a reverse bias of
960 V.
A very low peak reverse recovery current of <0.5 A is
observed from the cathode current waveforms, even for
switching at such high (960 V) voltages. Moreover, there is
no difference in the switching transients measured at 25 °C
and 205 °C, which confirms the majority carrier
characteristics of the SiC SHT rectifiers.
Experimental Results were presented in this paper on the
Industry’s first 1200 V high-temperature SiC Schottky
rectifiers specially designed for 250-300 °C operation.
Desirable features of these SiC SHT rectifiers include ultralow (< 1mA/cm2) reverse leakage currents at 250 °C, lowestin-class junction capacitance leading to reduced switching
losses, and temperature-independent switching performance.
Detailed comparisons with several commercial SiC Schottky
rectifiers were performed and the performance benefits of the
SHT rectifiers were quantified.
Figure 7: Comparison of junction capacitance of
GeneSiC’s 1200 V SiC Schottky rectifier product line with
SiC Schottky diodes from other manufacturers (data from
respective device datasheets).
R. Singh, S. Jeliazkov, E. Lieser, “1200 V-class 4H-SiC “Super”
Junction Transistors with Current Gains of 88 and Ultra-fast Switching
Capability”, Materials Science Forum, 717-720, pp.1127-1130 (2012).