ETTC'2003 - SEE

∆ T dét. (°C/g)
10
1
0,1
0,01
CO 2
air
100 µm : slope = -1,77
300 µm : slope = -1,86
500 µm : slope = -1,99
1E-3
1E-5 1E-4
a ( m 2 .s -1 )
Figure 10: Sensor sensitivity ∆T vs. heater temperature rise.
det.
S 0 (°C / g)
1000
100
10
1
0,1
1 10
p (bar)
∆T = 183 °C
100 µm
300 µm
500 µm
- - - - n = 2
Figure 11: Sensor sensitivity ∆T vs. nitrogen pressure.
det.
Since the sensitivity of these sensors is proportional
to the differential temperature ∆Tdet, the acceleration
range where the response is linear is necessarily limited
because a linear response including high accelerations
should lead to a differential temperature ∆Tdet higher than
the heater temperature rise ∆T : it is obviously impossible
and we assume that an infinite acceleration should give
the equality ∆Tdet = ∆T. Therefore, we have defined a
sensitivity S0 for the linear response range and it is this
sensitivity which is studied afterwards.
The sensor is placed in an hermetic chamber, a hole
is made in the TO16 and a manometer controls the gas
pressure. The gas is nitrogen and its pressure ranges from
1 to 30 bars. Figure 11 presents the sensor sensitivity S0 for
the linear response range . In low pressure range, the
curve
slope n is close to 2 in a log-log scale so, the
sensitivities are proportional to the square of the gas
pressure in good accordance with the model based on the
Grashof number. For higher pressure, a deviation of the
square law is observed and different optimum pressures
are obtained according to the distance heater/detectors.
The best sensitivity S0 is 168°C/g, the same order than the
heater temperature rise, for a distance heater/detectors of
300 µm and a pressure of 25 bars.
4.6. Linearity and bandwidth
With air at atmospheric pressure, measurements in a
centrifuge have shown that the sensor has a good linearity
for a range about 0-3g and a 3dB-bandwidth of 20 Hz is
measured by applying a sinusoidal acceleration [12].
F. Mailly et Al. ETTC 2003
He
5. Conclusion
A micromachined thermal accelerometer without proof
mass has been manufactured using the techniques of
micromachining silicon and its sensitivity has been
proven to be proportional to the Grashof number.
References
[1]
U. A. Dauderstädt, P.H.S. de Vries, R. Hiratsuka, P.M. Sarro, Silicon
accelerometer based on thermopiles, Sens. Actuators A 46-47 (1995) 201-
204.
[2] U. A. Dauderstädt, P.H.S. de Vries, R. Hiratsuka, J.G. Korvink, P.M.
Sarro, H. Baltes and S. Middelhoek, Simulation aspects of a thermal
accelerometer, Sens. Actuators A 55 (1996) 3-6.
[3] U. A. Dauderstädt,
P.M. Sarro and P.J. French, Temperature
dependence
and drift of a thermal accelerometer, Sens. Actuators A 66
(1998) 244-249.
[4] R. Dao, D.E. Morgan, H.H. Kries, D.M. Bachelder, Convective
accelerometer and inclinometer, US Patent n° 5,581,034 (1996).
[5] V. Milanovic, E. Bowen, M. E. Zaghloul, N. H. Tea , J. S. Suehle,
B.
Payne,
and M. Gaitan, Micromachined convective accelerometers in
standard integrated
circuits technology, Appl. Phys. Lett. 76 (4) (2000)
508-510.
[6] V. Milanovic, E. Bowen, N. Tea , J. Suehle, B. Payne, M. Zaghloul,
and M. Gaitan, Convection-based Accelerometer and Tilt Sensor
Implemented
in Standard CMOS, International Mechanical Engineering
and Exposition, MEMS Symposia, Anaheim, CA, (1998) 627-630.
[7] A.M. Leung, J. Jones, E. Czyzewska, J. Chen
and B. Woods,
Micromachined
accelerometer based on convection heat transfer, MEMS
98 (1998) 627-630.
[8] A.M. Leung,
J. Jones, E. Czyzewska, J. Chen, M. Pascal,
Micromachined
accelerometer with no proof mass, Technical Digest of
Int. Electron Device Meeting (IEDM97), (1997) 899-902.
[9]
S. Billat, H. Glosch, M. Kunze, F. Hedrich, J. Frech, J. Auber, H.
Sandmaier, W. Wimmer and W. Lang, Micromachined inclinometer with
high sensitivity and very good stability, Sens. Actuators A 97-98 (2002)
125-130.
[10]
X.B. Luo, Y.J. Yang, F. Zheng, Z.X. Li and Z.Y. Guo, An optimized
micromachined convective accelerometer with no proof mass, J.
Michromech. Microeng. 11 (2001) 504-508.
[11] X.B. Luo, Z.X. Li, Z.Y. Guo and Y.J. Yang, Study on linearity
of a
micromachined
convective accelerometer, Microelectronic Engineering
65 (2003) 87-101.
[12] F. Mailly, A. Giani,
A. Martinez, R. Bonnot, P. Temple-Boyer and A.
Boyer,
Micromachined thermal accelerometer, Sens. Actuators A 103 (3)
(2003), p. 359-363.
[13] F. Mailly, A. Martinez, A. Giani, F. Pascal-Delannoy and A. Boyer,
Design
of a micromachined thermal accelerometer : thermal simulation
and experimental results, Microelectronics Journal 34 (4), p. 275-280.
[14] F. Mailly, Etude et réalisation de microcapteurs thermiques :
anémomètre
et accéléromètre thermique, Ph.D. Thesis, Université
Montpellier
II, France (2002).
[15] P. Temple-Boyer, C. Rossi, E Saint-Etienne, and E. Scheid, Residual
stress in low pressure chemical vapor deposition
SiNx films deposited
from
silane and ammonia, J. Vac. Sci. Technol. A 16(4) (1998) 2003-
2007.
[16] A Giani, F. Mailly,
F. Pascal-Delannoy, A. Foucaran, and A. Boyer,
Investigation
of Pt/Ti bilayer on SiNx/Si substrates for thermal sensor
applications, J. Vac. Sci. Technol. A 20 (1) (2002) 112-116.
[17] F. Mailly, A. Giani, R. Bonnot, P. Temple-Boyer, F. Pascal-
Delannoy,
A. Foucaran and A. Boyer, Anemometer with hot platinum thin
film, Sens. Actuators A 94 (2001) 32-38.
[18] R. Dao, Thermal accelerometers Temperature Compensation,
MEMSIC
Application note (2002), www.memsic.com.
4