Semiconductor chips based on MEMS (Micro-Electro-Mechanical Systems) technology, such as sensors, transducers, and actuators, are becoming widely used in today s electronics due to their high performance, low power consumption, tolerance to shock and vibration, and immunity to electro-static discharge. In addition, the MEMS fabrication process allows for the miniaturization of individual chips as well as the integration of various electronic circuits into one module, such as system-on-a-chip. These measures would simplify overall system design, reduce parts count and interface, improve reliability, and reduce cost; and they would meet requirements of systems destined for use in space exploration missions. In this work, the performance of a recently-developed MEMS voltage-controlled oscillator was evaluated under a wide temperature range. Operation of this new commercial-off-the-shelf (COTS) device was also assessed under thermal cycling to address some operational conditions of the space environmen

Hammoud, Ahmad

Patterson, Richard

NASA Technical Reports Server

 1 
December  2009 
 
NASA Electronic Parts and Packaging Program 
 
Evaluation of a Programmable Voltage-Controlled MEMS Oscillator, 
Type SiT3701, Over a Wide Temperature Range 
 
Richard Patterson, NASA Glenn Research Center 
Ahmad Hammoud, ASRC Corporation / NASA GRC 
 
Scope 
 
Semiconductor chips based on MEMS (Micro-Electro-Mechanical Systems) technology, such as 
sensors, transducers, and actuators, are becoming widely used in today’s electronics due to their high 
performance, low power consumption, tolerance to shock and vibration, and immunity to electro-
static discharge.  In addition, the MEMS fabrication process allows for the miniaturization of 
individual chips as well as the integration of various electronic circuits into one module, such as 
system-on-a-chip. These measures would simplify overall system design, reduce parts count and 
interface, improve reliability, and reduce cost; and they would meet requirements of systems destined 
for use in space exploration missions.  In this work, the performance of a recently-developed MEMS 
voltage-controlled oscillator was evaluated under a wide temperature range.  Operation of this new 
commercial-off-the-shelf (COTS) device was also assessed under thermal cycling to address some 
operational conditions of the space environment. 
 
Test Procedure 
 
The device investigated in this work comprised of a SiTime Corporation SiT3701 MEMS voltage-
controlled oscillator (VCO).  This programmable device combined a highly robust and reliable 
MEMS resonator with advance analog circuits to provide a flexible and programmable solution for 
clock synchronization applications [1].   It provided a 0.5% linear pull range, representing significant 
improvement over the 5% - 10% linearity offered by quartz-based VCO’s.  This enhancement allows 
system designers to simplify the clock synchronization algorithm, improve system lock time and 
provide better system stability [1].  Some of the manufacturer’s specifications for this MEMS VCO 
are shown in Table I [1]. 
 
Table I.  Specifications of SiT3701 MEMS voltage-controlled oscillator [1]. 
 
Parameter Symbol SiT3701AI-32-25A-
80.00000 
Supply Voltage (V) Vdd 2.25 to 2.75 
Supply Current (mA) Idd 8 to 10 
Programmed Frequency (MHz) f 80 
Control Voltage (V) Vin 0 to 1.75 
Duty Cycle (%) D 40 to 60 
Rise/Fall Time (ns) Tr, Tf 1 to 2 
Operating Temperature (°C) T(oper) -40 to +85 
Package  4-pin Plastic SMD 
Lot Number  5032F 
The oscillator chip was examined for operation between -180 °C and +85 °C.  Performance 
characterization was obtained in terms of output frequency and supply current at specific test 
https://ntrs.nasa.gov/search.jsp?R=20130013124 2019-08-31T00:56:04+00:00Z
 2 
temperatures.  The duty cycle of the output signal along with its rise and fall time characteristics were 
also recorded.  All of these properties were also obtained as a function of the input “control” voltage 
(Vin).  During these tests, a temperature rate of change of 10 °C per minute was used, and a soak 
time of at least 20 minutes was allowed at every test temperature.  Restart operation capability of the 
device under extreme temperatures was also investigated.  In addition, the effects of thermal cycling 
under a wide temperature range on the operation of this part were determined.  The device was 
exposed to a total of 12 cycles between -180 °C and +85 °C.  Following cycling, measurements were 
then performed at the test temperatures of +22, -180, and +85 °C at selected Vin values.  Figure 1 
shows the circuit board populated with the MEMS VCO chip along with a couple of filter capacitors. 
 
 
Figure 1.  Oscillator chip and filter capacitors mounted on circuit board. 
 
Test Results 
 
Temperature Effects 
 
The output waveform of the MEMS voltage-controlled oscillator at room temperature is shown in 
Figure 2, and the VCO output frequency at various control voltages is shown as a function of 
temperature in Figure 3.  Below -180 °C the oscillator became unstable.  Between -100 °C and -180 
°C, control of frequency was unreliable.  Figure 4 shows frequency vs. control voltage at various 
temperatures.  Figure 4 indicates that temperature has some effect on frequency, namely that between 
+85 °C and -50 °C for a decrease in temperature there is a decrease in frequency.  Figure 5 shows that 
as temperature decreased from -50 °C to -100 °C for a given control voltage there was an increase in 
frequency.   It is important to note that this industrial-grade device was only specified to - 40 °C as 
the low end of operating temperature.  In addition, the anomalies exhibited in the frequency response 
at the test temperature below - 100 °C were transitory in nature as recovery took place upon exposing 
the device to temperatures warmer than -100 °C. 
 
 
 
Figure 2.  Output waveform of the MEMS VCO.  (Horiz: 20 ns/div; Vert: 0.5 V/div) 
 3 
 
Temperature (°C)
-200 -150 -100 -50 0 50 100
F
re
q
u
e
n
c
y
 (
k
H
z
)
79960
80000
80040
80080
80120
80160
Vin =
0.75 V
1.25 V
1.75 V
0 V
1.5 V
0.5 V
1.0 V
0.25 V
 
 
Figure 3.  Oscillator frequency versus temperature for various control voltages. 
 
 
 
Input Voltage, Vin (V)
0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75
F
re
q
u
e
n
c
y
 (
k
H
z
)
79995
79996
79997
79998
79999
80000
80001
80002
80003
Temperature
-100 °C
+85 °C
+22 °C
0 °C
-50 °C
 
 
 
Figure 4.  Oscillator frequency as a function of control voltage at various temperatures. 
 
 
 4 
Temperature  ( °C )
-100 -50 0 50 100
F
re
q
u
e
n
c
y
  
(k
H
z
)
F
re
q
u
e
n
c
y
  
(k
H
z
)
79995
79996
79997
79998
79999
80000
80001
80002
80003
Vcontrol  = 1.75 V
Vcontrol  = 0.75 V
Vcontrol  = 0 V
 
 
Figure 5.  Oscillator frequency as a function of temperature for three control voltages. 
 
The duty cycle of the MEMS VCO output signal did not display any significant change over the test 
temperature range as its value retained a value around 55 % throughout the test temperature range 
between -180 °C and +85 °C, as shown in Figure 6. 
 
Temperature (°C)
-200 -150 -100 -50 0 50 100
D
u
ty
 C
y
c
le
 (
%
)
0
20
40
60
80
100
 
 
 
Figure 6.  Duty cycle of the VCO output versus temperature. 
 
The rise and fall times of the output signal underwent very slight variation with temperature. While 
both of these characteristics were steady between -50 °C and +85 °C, their values experienced similar 
trivial fluctuation as temperature was set to below -50 °C.  Figure 7 displays these characteristics as a 
function of the test temperature. 
 
 5 
Temperature (°C)
-200 -150 -100 -50 0 50 100
T
im
e
 (
n
s
)
0
2
4
6
8
10
Fall Time
Rise Time
 
 
 
Figure 7.  Rise and fall times of output signal versus temperature. 
 
Similar to the rise and fall times, the supply current of the MEMS voltage-controlled oscillator 
exhibited no dependency on temperature in the range of -50 °C to +85 °C as it sustained a constant 
value of about 10 mA, as shown in Figure 8.  At temperatures below -50 °C, the current initially 
decreased very slightly but began to increase as temperature was decreased further.  The onset of the 
current increase seemed to develop at about -110 °C; reaching a value of about 13.75 mA at the 
extreme cryogenic temperature of -180 °C. 
 
 
Temperature (°C)
-200 -150 -100 -50 0 50 100
S
u
p
p
ly
 C
u
rr
e
n
t 
(m
A
)
0
5
10
15
20
 
 
 
Figure 8.  VCO supply current as a function of temperature. 
 
 6 
Re-Start at Extreme Temperatures 
 
Restart capability of this SiT3701 MEMS voltage-controlled oscillator was investigated at the 
extreme test temperatures at which stable operation was maintained, i.e. -180 °C and 85 °C.  The 
oscillator chip was allowed to soak separately at those two temperatures, with electrical power off for 
at least 20 minutes.  Power was then applied to the circuit, and measurements of the oscillator’s 
output waveform characteristics and frequency were recorded.  The voltage-controlled oscillator 
circuit was able to operate successfully at either of the two extreme temperatures and the results 
obtained were similar to those obtained earlier at these respective temperatures. 
 
Effects of Thermal Cycling 
 
The effects of thermal cycling on the performance of this MEMS VCO were investigated by 
subjecting the SiT3701 oscillator chip to a total of 12 cycles between -180 °C and +85 °C at a 
temperature rate of 10 °C/minute and a soak time of 20 minutes at the extreme temperatures.  
Measurements on the characteristics of the oscillator circuit were then taken at the three temperatures 
of +22, +85, and -180 °C.  A comparison of the output frequency as a function of control voltage at 
these temperatures for pre- and post-cycling conditions is shown in Figure 9.  It can be clearly seen 
that the post-cycling frequency/voltage curves at any given temperature were nearly the same as 
those obtained prior to cycling.  Similar results were obtained for the output signal characteristics as 
well as the circuit’s supply current.  Table II lists post-cycling data of these characteristics along with 
those obtained prior to cycling.  These results indicate that this MEMS VCO oscillator did not 
undergo any significant changes in its operational characteristics due to this limited cycling.  The 
thermal cycling also appeared to have no effect on the structural integrity of the device as no 
packaging damage was noted upon inspection. 
 
Table II.  Pre- and post-cycling characteristics of the oscillator with Vin = 1 V. 
 
T(°C) Cycling f (kHz) Duty cycle (%) Trise (ns) Tfall (ns) IS (mA) 
+22 
pre 79999.508 55.5 3.46 3.90 10.08 
post 79999.618 50.1 3.47 3.84 10.13 
-180 
pre 79974.377 52.9 3.81 4.06 13.75 
post 79974.657 50.9 3.63 3.88 13.71 
+85 
pre 80000.062 55.1 3.56 3.99 10.26 
post 79999.791 51.0 3.46 4.0 10.43 
 7 
Input Voltage, Vin (V)
0.0 0.5 1.0 1.5 2.0 2.5
F
re
q
u
e
n
c
y
 (
k
H
z
)
79960
79970
79980
79990
80000
80010
T= +85 °C
T= -180 °C
T= 22 °C
 
 
Pre-cycling 
 
 
Input Voltage, Vin (V)
0.0 0.5 1.0 1.5 2.0 2.5
F
re
q
u
e
n
c
y
 (
k
H
z
)
79960
79970
79980
79990
80000
80010
T= +85 °C
T= -180 °C
T= 22 °C
 
 
Post-cycling 
 
Figure 9.  Output frequency for pre- and post-cycling as a function of control voltage. 
 8 
Conclusions 
 
The performance of a recently-developed MEMS voltage-controlled oscillator was evaluated under a 
wide temperature range.  The effects of thermal cycling on the operation of this SiT3701 oscillator 
chip and restart capability at extreme temperatures, which are typical of space operational 
requirements, were also investigated. The oscillator was characterized in terms of its output 
frequency stability, output signal rise and fall times, duty cycle, and supply current at various control 
voltages.  As temperature was decreased from +85 °C to -50 °C, there was some decrease in 
frequency.  As temperature changed from -50 °C to -100 °C, frequency increased.  Below -100 °C 
operation became unreliable, and below -180 °C, the oscillator became unstable.  It should be noted 
that the device was only specified to - 40 °C as the low end of operating temperature.  The anomalies 
that occurred below -100 °C were only temporary as recovery took place upon applying test 
temperatures of -100 °C or warmer.  The SiT3701 MEMS voltage-controlled oscillator was also able 
to re-start at both -180 °C and +85 °C, and it exhibited no change in performance due to the thermal 
cycling.  In addition, no physical damage was observed in the packaging material due to extreme 
temperature exposure and thermal cycling.  Temperature had some effect on frequency; therefore use 
of the device will depend upon frequency stability requirements. 
 
References 
 
[1]. SiTime Corporation “SiT3701 Smallest Programmable VCMO Voltage controlled MEMS 
Oscillator - Preliminary Information”, Data Sheet, Rev. #1.3, March 2009,  
http://www.sitime.com. 
 
Acknowledgements 
 
This work was performed under the NASA Glenn Research Center GESS-2 Contract # 
NNC06BA07B.  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”. 


Evaluation of a Programmable Voltage-Controlled MEMS Oscillator, Type SiT3701, Over a Wide Temperature Range

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server