June 2006

Silicon-On-Insulator Precision Timers for Extreme Temperatures

Richard Patterson, NASA Glenn Research Center, U.S.A.

Ahmad Hammoud, QSS Group, Inc. / NASA GRC, U.S.A.

Gonzalo Picun, Cissoid Company, Belgium

**Background**

Space exploration missions require electronic parts and circuits capable
of efficient and reliable operation under extreme temperatures. Exposure
to cryogenic temperatures, for example, is anticipated in the
environments of the James Webb Space Telescope (-236 °C), lunar craters
of the moon (-223 °C), Mars (-140 °C), and other space platforms deep in
space away from the sun. Presently, spacecraft and probes operating in
the cold environment of deep space utilize some form of heating system
to maintain an operating temperature for the on-board electronics of
approximately 20 °C. Electronics capable of operation at cryogenic
temperatures will eliminate the need for the thermal control elements,
enhance efficiency of space electronic systems, improve their
reliability, and simplify their design. Silicon-On-Insulator (SOI)
technology is being pursued by the electronics industry due to the
advantages it offers in terms of fast switching, reduced leakage,
improved radiation-tolerance, and less power consumption when compared
to its silicon counterpart. In addition, SOI-based devices are tailored
through their design for high temperature applications. Very little
data, however, exist on the performance of such devices under cryogenic
temperatures.

**Scope of Work**

Three devices of type CHT-555 SOI timers, which were designed and
furnished by Cissoid Company, were evaluated under extreme temperatures.
The CHT-555 is a low power, high temperature, highly stable timer for
producing specific oscillations or generating accurate time delays
\[1\]. The device operates in both astable and monostable modes, and is
rated for temperature operation between -30 °C and + 225 °C. Table 1
shows some of the device manufacturer's specifications \[1\].

Table I. Specifications of the CHT-555 SOI high temperature timer \[1\].

  -------------------------------------------------- --------------------
  **Parameter (Unit)**                               **CHT-555**

  Supply Voltage, V~DD~ (V)                          4.5 to 5.5

  Current Consumption, I~S~ (µA)                     297 to 337

  Drift with Temperature (ppm/°C)                    -35 to 120

  Linear Sensitivity, (mV/°C)                        -1.56

  Temperature Range, T (°C)                          -30 to +225

  Package                                            TO-5

  Lot \#                                             LOT 151
  -------------------------------------------------- --------------------

The timers were configured in a monostable configuration and were
evaluated in terms of their output waveform, pulse duration, and supply
current as a function of temperature between +100 °C and --195 °C using
a liquid nitrogen-cooled environmental chamber. These characteristics
were obtained at various levels of supply voltage and trigger signal
frequency. Cold-restart capability, i.e. power switched on while the
device was at a temperature of -195 °C, was also investigated. In
addition, the effects of thermal cycling under a wide temperature range
on the operation of these timers were determined. The devices were
exposed to a total of 7 cycles between ‑195 °C and +100 °C at a
temperature rate of 10 °C/minute. Following the thermal cycling, circuit
measurements were then performed at the test temperatures of +20, ‑195,
and +100°C. As was mentioned earlier, each timer was configured in a
monostable circuit configuration, as shown in Figure 1. In this mode,
the pulse duration (t~p~) of the output is governed by the values of the
resistor (R~a~) and the capacitor (C) according to the equation t~p~ =
1.1R~a~C. The resistor, R~a~, was a metal-film type with a value of 9.97
kΩ, and the capacitor was a 0.01 µF NPO ceramic part. These components,
which are stable with temperature variation, will yield a pulse duration
of about 109 µs.

![](media/image1.wmf){width="3.3055555555555554in"
height="1.9479166666666667in"}

Figure 1. Monostable CHT-555 timer circuit.

**Results and Discussion**

Due to the similarity of the results for the three timers, only data
from one of the timers are presented and discussed.

*Temperature Effects*

The trigger, output, and threshold voltage waveforms of the timer
circuit obtained at room temperature are shown in Figure 2. These
waveforms were also obtained at test temperatures of -50, -100, -150,
-195, and +100 °C. Except for a very minute change in pulse duration, no
major distortion was observed in the generated waveforms as test
temperature was changed throughout the range of -195 °C to +100 °C. For
illustrative purposes, only those waveforms obtained at the extreme
temperatures, i.e. -195 °C and +100 °C are presented here as shown in
Figures 3 and 4, respectively. These waveforms, which were obtained
using a supply voltage of 4.7 volts and a triggered signal with a
frequency of 25 kHz, show a very slight decrease in pulse duration as
temperature was decreased. Measurements obtained at other trigger
frequencies of 5 kHz, 52 kHz, and 100 kHz produced similar results. This
effect of temperature on output pulse duration, t~p~, is depicted in
Figure 5 for various trigger frequencies. It can be clearly seen that
for a trigger frequency of 5 kHz, for example, t~p~ decreases by only
0.3% when temperature decreased from +100 °C to -195 °C. This trend was
the same at the other trigger frequency levels. It is important to note
that regardless of the test temperature, increasing the trigger
frequency was found to slightly (\< 3.5%) increase t~p~.

![](media/image2.png){width="3.5840277777777776in"
height="2.3194444444444446in"}

Figure 2. Waveforms of trigger (1), output (2), and threshold (3)
signals at +20 °C.

![](media/image3.png){width="3.573611111111111in"
height="2.3493055555555555in"}

Figure 3. Waveforms of trigger (1), output (2), and threshold (3)
signals at -195 °C.

![](media/image4.png){width="3.573611111111111in"
height="2.310416666666667in"}

Figure 4. Waveforms of trigger (1), output (2), and threshold (3)
signals at +100 °C.

![](media/image5.wmf)

Figure 5. Output pulse duration as a function of temperature.

The output pulse duration was also determined as a function of input
voltage. Data obtained for supply voltages between 3.9 and 5.1 volts are
shown in Figure 6 at the test temperatures of +20, +100, and -195 °C.
While variation in the supply voltage did not produce any effect on the
pulse duration at either +20 °C or +100 °C, the timer exhibited a
gradual, but very slight decrease, in its output pulse duration at the
cryogenic temperature of -195 °C. This decrease in t~p~ amounted only to
about 0.38% when supply voltage was increased from 3.9 to 5.1 volts.

![](media/image6.wmf)

Figure 6. Output pulse duration versus supply voltage at different
temperatures.

Figure 7 shows the supply current of the SOI 555 timer as a function of
temperature and at various trigger frequencies. It can be seen that the
supply current decreased, in a linear fashion, as temperature was
decreased. This behavior was the same regardless of the frequency of the
trigger signal. At 5 kHz trigger signal, for example, the supply current
decreased from its room temperature value by 17.9% at -195 °C, and it
increased by about 6.2% at the elevated temperature of +100 °C.
Increasing the frequency of the trigger signal tends to cause a slight
decrease in the supply current of the timer, at a given test
temperature.

![](media/image7.wmf)

Figure 7. Timer supply current as a function of temperature.

*Cold Re-Start*

Cold-restart capability of the SOI CHT-555 timer was investigated by
allowing the device to soak at -195 °C for at least 20 minutes without
the application of supply voltage or trigger signal. Power was then
applied, and measurements were taken on the output characteristics. The
timer was able to successfully cold-restart at -195 °C, and the results
obtained were the same as those obtained earlier at that temperature.

*Effects of Thermal Cycling*

The effects of thermal cycling under a wide temperature range on the
operation of the CHT-555 timer were investigated by subjecting it to a
total of 7 cycles between -195 °C and +100 °C at a temperature rate of
10 °C/minute. Output and threshold voltage waveforms were then recorded
at +20, -195, and +100 °C. A comparison of these waveforms, which were
obtained using a 5 kHz trigger frequency, at test temperatures of +20,
-195, and +100 °C for pre- and post-cycling conditions are shown in
Figures 8, 9, and 10, respectively. It can be clearly seen that the
post-cycling waveforms at any given test temperature were the same as
those obtained prior to cycling. Similar results were obtained when the
trigger frequency was varied from 5 kHz to 100 kHz. Therefore, it can be
concluded that the extreme temperature exposure and the thermal cycling
did not induce much change in the behavior of this SOI timer. This
limited thermal cycling also appeared to have no effect on the
structural integrity of this device as no structural deterioration or
packaging damage was observed.

![](media/image8.png){width="2.8958333333333335in"
height="2.4590277777777776in"}

Pre-cycling

![](media/image9.png){width="2.8965277777777776in"
height="2.4583333333333335in"}

Post-cycling

Figure 8. Pre- and post-cycling waveforms of CHT-555 timer at +20°C.

![](media/image10.png){width="2.9in" height="2.4611111111111112in"}

Pre-cycling

![](media/image11.png){width="2.8979166666666667in"
height="2.4611111111111112in"}

Post-cycling

Figure 9. Pre- and post-cycling waveforms of CHT-555 timer at -195°C.

![](media/image12.png){width="2.9006944444444445in"
height="2.4590277777777776in"}

Pre-cycling

![](media/image13.png){width="2.9in" height="2.4583333333333335in"}

Post-cycling

Figure 10. Pre- and post-cycling waveforms of CHT-555 timer at +100°C.

**Conclusions**

The operational characteristics of three silicon-on-insulator 555
timers, which are mainly designed for high temperature applications,
were obtained over the temperature range of -195 °C to +100 °C. The
devices were evaluated in terms of output waveform and pulse duration,
and supply current as a function of temperature at various trigger
frequencies and supply voltage levels. The effects of thermal cycling
under a wide temperature range on the operation of these devices and
cold-restart capability were also investigated. The three timers,
configured in a monostable circuit configuration, displayed virtually
identical characteristics and were able to maintain good operation
between -195 °C and +100 °C with minimal changes in its characteristics.
The limited thermal cycling performed on the devices had no effect on
their performance, and all three timers were able to cold start
successfully at -195 °C. These preliminary results indicate that these
SOI-based high temperature timers could be potentially used in space
exploration missions under cryogenic environments. Further testing under
long-term cycling is, however, recommended to fully establish the
reliability of such devices and to determine their suitability for
extended use in extreme temperature environments.

**References**

1.  Cissoid CHT-555, "High Temperature Precision Timer", preliminary
    datasheet, version 0.4 (04/2005).

**Acknowledgments**

This work was performed under the NASA Glenn Research Center GESS
Contract \# NAS3-00145. Funding was provided from the NASA Electronic
Parts and Packaging (NEPP) Program Task "Reliability of SiGe, SOI, and
Advanced Mixed Signal Devices for Cryogenic Power Electronics". The
efforts by Mr. Laurent Demeus of Cissoid Corporation in Belgium are
greatly appreciated for providing the test samples.