February 11, 2005

NASA Electronic Parts and Packaging Program

Performance of Vishay Siliconix U430 JFET Transistor at Extreme
Temperatures

Richard Patterson, NASA Glenn Research Center

Ahmad Hammoud, QSS Group, Inc. / NASA GRC

Malik Elbuluk, University of Akron

**Scope**

Cryogenic temperatures are typically encountered in planetary
exploration and deep space applications, such as Mars and Saturn
environments. Minimum temperature on the earth's moon has been estimated
to be as low as -235 °C. Electronics on board of current spacecraft are
maintained at about room temperature, through the use of various thermal
control elements, for proper operation. Great benefits would be gained
if the electronics were made to function properly at the extreme
temperatures without the use of these heating accessories. These
benefits include improved reliability, increased payload capacity, and
decreased electronic system development and launched costs, to name a
few. Very little data exist on the performance of many electronic
devices and circuits under cryogenic temperatures. In this work, the
performance of an N-channel JFET (Junction Field Effect) transistor was
evaluated under low temperature and thermal cycling. The investigations
were carried out to establish a baseline on the functionality and to
determine suitability of this device for use in space applications under
cryogenic temperatures. This device was chosen because it is being
considered by the NASA Jet Propulsion Laboratory (JPL) for use in
electronic circuits on future space missions.

**Test Procedure**

The device investigated in this work comprised of Vishay Siliconix U430
device. Each device had matched pair of N-channel JFET transistors. This
type of transistor is a depletion mode device with high slew rate, low
noise and low offset/drift voltage, and can be used in wideband
differential amplifiers, high speed comparators, and impedance
converters \[1\]. The transistor pair was examined for operation between
-195 °C and +100 °C. Performance characterization was obtained in terms
of their switching characteristics, using a Sony/Tektronix 370A
programmable curve tracer, at specific test temperatures. Cold-restart
capability, i.e. power switched on while the devices were at a
temperature of -195 °C, was also investigated. Thermal cycling effects
were also investigated over a wide temperature range. The devices were
exposed to a total of 10 cycles between -195 °C and +100 °C at a
temperature rate of 10 °C/minute. At each test temperature, the device
was given a soak for 20 minutes before data were taken. Following the
thermal cycling, measurements were then performed at the test
temperatures of +20, -195, +100, and again at +20 °C. Some of the
manufacturer's specifications for this JFET transistor are shown in
Table I \[1\].

Table I. Specifications of Vishay Siliconix U430 JFET transistor \[1\].

  ----------------------------------- --------------- -------------------
  **Parameter**                       **Symbol**      **U430**

  Operating Temperature               T(oper)         -55 °C to +150 °C

  Max Drain Current                   I~D~            30 mA

  Max Gate-Source Voltage             V~GS~           -25 V

  Total Power Dissipation             P~D~            0.5 W

  Drain-Source On-Resistance          R~DS(on)~       \> 27 Ω

  Package                                             TO-78
  ----------------------------------- --------------- -------------------

**Test Results**

Although two units of this transistor were evaluated, data pertaining to
only one device is presented due to the similarity in their results.

*Temperature Effects*

The pre-cycling switching characteristics of the U430 device at +20 °C,
-195 °C, and +100°C are shown in Figures 1, 2, and 3, respectively.
These output characteristics are defined as the drain current (I~D~)
versus drain-to-source voltage (V~DS~) family curves at various gate
voltages (V~GS~). In this test gate voltages (V~GS~) ranged between 0
and -1.6 Volts. Two deviations can be noted in the output
characteristics with change in temperature. The first is the downward
shift of the switching curves, for a given gate voltage, as temperature
moved away from room temperature. This behavior, which is more profound
at low temperatures, is an indicative of the increase in the gate
threshold voltage with decreasing temperatures. At the high test
temperature, i.e. +100 °C, this change is insignificant as the
temperature is still within the device's operating temperature range.
The second deviation represents the variation, albeit minimum, in the
slope of the switching curves in the linear region, for a given gate
voltage, as the test temperature is changed. This phenomenon is caused
primarily by the dependence of the drain-source on-resistance
(R~DS(on)~) on test temperature.

*Cold Re-Start*

Cold-restart capability of the Vishay Siliconix U430 matched N-channel
JFET pair transistors was investigated by allowing the devices to soak
at -195 °C for at least 20 minutes without the application of electrical
bias. Power was then applied to the device under test, and measurements
were taken on the output switching characteristics. Both transistors
were able to cold-start successfully at -195 °C, and the results
obtained were the same as those obtained earlier at that temperature.

![](media/image1.wmf)

Figure 1. Pre-cycling output switching characteristics at 20 °C.

![](media/image2.wmf)

Figure 2. Pre-cycling output switching characteristics at -195 °C.

![](media/image3.wmf)

Figure 3. Pre-cycling output switching characteristics at +100 °C.

*Effects of Thermal Cycling*

The effects of thermal cycling were investigated by subjecting the
devices to a total of 10 cycles between -195 °C and +100 °C at a
temperature rate of 10 °C/minute. Switching characteristics of the
transistors were then taken at +20 °C,\
-195, and +100°C. Figure 4 shows this post-cycling data at these
selected temperatures. It can be clearly seen that the post-cycling
family of switching curves for these transistors were the same as those
of pre-cycling for a given test temperature. Also, little change
occurred in the drain-source on-resistance (R~DS(on)~) of the
transistors as depicted in Table II. Therefore, the extreme temperature
and the thermal cycling did not induce much change in the behavior of
these transistors. This limited thermal cycling also appeared to have no
effect on the structural integrity of these devices as no structural
deterioration or packaging damage was observed.

Table II. Pre- and post-cycling on-state resistance R~DS(on)~ versus
temperature.

  --------------------- ------------------------ ------------------------
  **Temperature (°C)**  **Pre-cycling R~DS(on)~  **Post-cycling R~DS(on)~
                        (Ω)**                    (Ω)**

  -195                  58                       55

  +20                   48                       48

  +100                  67                       68
  --------------------- ------------------------ ------------------------

![](media/image4.wmf)

Pre-cycling at 20 °C

![](media/image5.wmf)

Pre-cycling at -195 °C

![](media/image6.wmf)

Pre-cycling at +100 °C

![](media/image7.wmf)

Post-cycling at 20 °C

![](media/image8.wmf)

Post-cycling at -195 °C

![](media/image9.wmf)

Post-cycling at +100 °C

**Conclusions**

Two Vishay Siliconix U430 N-channel JFET devices were evaluated for
operation between -195 °C and +100 °C. Each device had a matched pair of
transistors. The effects of thermal cycling under a wide temperature
range on the operation of these transistors and cold-restart capability
were also investigated. Both devices were able to maintain operation
between -195 °C and +100 °C with minimal changes in their
characteristics. The temperature-induced changes included an increase in
the gate voltage at cryogenic temperatures, and a slight increase in the
on-resistance at 100 °C. The limited thermal cycling performed on the
transistors had no effect on their performance, and both devices were
able to cold start at -195 °C. Further testing under long-term cycling
is required to fully establish the reliability of these devices and to
determine their suitability for extended use in extreme temperature
environments.

**References**

\[1\]. Vishay Siliconix, "U430 Matched N-Channel Transistor Pairs", Data
Sheet Document Number 70249, Rev. E, June 2001.

**Acknowledgements**

This work was performed under the NASA Glenn Research Center GESS
Contract \# NAS3-00145. Funding was provided by the NASA Electronic
Parts and Packaging (NEPP) Program.