International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 10 - Oct 2013
Design Of Temperature Sensors For
Enviromental Applications
Ashish 1 , Kumari Nidhi Gupta2, Dr. T. Shanmuganantham 3
1,2
3
Student, Department Of Electronics Engineering
Assistant Professor, Department Of Electronics Engineering
Pondicherry University, Puducherry , India
Abstract—
MEMS sensors have been widely used in
automobiles, airplanes, submarines, and biomedical devices.
For some applications such as aerospace and underground
oil exploration, sensors which can endure extremely high
temperature are required. In this paper, the design and
simulation of temperature sensor for high-temperature
applications is proposed. The sensor is an array of bimorph
cantilevers whose deflections are sensed by application of
temperature . The cantilevers are initially thermally annealed
to relax the film stresses. With change in materials of
bimorph, overall sensitivity also changes.
Keywords—MEMS, Cantilever, Bimorph, Displacement.
I.INTRODUCTION
The Temperature sensor works on the principle
that deflection occurs due to an applied
temperature on the bimorph[1]. The aim of this
work is to model, compare and analyze the
different performance parameters like deflection,
voltage output and sensitivity[2].
A bimorph is created by stacking two materials
with different coefficients of thermal expansion
(CTE)[3]. As temperature increases, the material
with the higher CTE will expand to a greater
extent, and cause the structure to deflect. To
generate large deflection, a metal is commonly
used for the top layer, and a dielectric for the
bottom[4].
II. SENSOR DESIGN METHODOLOGY
The measurement and control of temperature is
important in many areas including industry,
domestic environment & medicine. Different
methods are used for measurements of
temperature using different principles as-RTD
,Thermocouple, Bimorph. Here we have used
Bimorph material for temperature sensing. A
bimorph is created by stacking two materials
with differing coefficients of thermal expansion .
As temperature increases, the material with the
higher CTE will expand to a greater extent, and
ISSN: 2231-5381
cause the structure to deflect. The temperature
coefficient of resistance is a measure of the
thermal sensitivity of resistors and is defined as
the ratio of resistance change versus temperature
variation to resistance value. Mathematically it is
represented as
Rt = R ref × (1    T ) . . . . . .(1)
Where R is measured value of resistance at
temperature T , R ref is measured value of
resistance at reference value of temperature ,  is
temperature coefficient of resistance and T is
change in temperature.
In present case temperature gradient is subjected
to cantilever beam which results deflection. The
pressure equivalent of temperature of atmosphere
is taken into consideration.
The deflection of beam is given by relation as
(1  v )
2
  3 
 L / t  . . . . . .(2)
E
Where v is the poisson’s Ratio ,E is the Young’s
Modulus, L is beam length ,t is thickness of
cantilever and  is stress/pressure.
III. DESIGN AND MODEL
The Temperature sensor model is drawn using the
3D Builder module of the IntelliSuite Software. In
this paper we discussed two different structures of
Temperature sensors with
1.Gold as sensing layer.
2.Aluminium/Titanium as sensing layer
In first design Gold is used as sensing layer
and Silicon Oxide as dielectric layer. Because of
thermal mismatch in the processing, the beams
are naturally deflected at room temperature. The
thicknesses of these layers and their respective
coefficient of thermal expansion will determine
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International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 10 - Oct 2013
the amount
temperature.
of
deflection
at
a
YOUNG
MODULUS
(µm)
specific
POISSON
RATIO
DENSITY
( gm/cc)
(GPa)
Substrate
100×50×5
Silicon
170
0.26
2.32
Dielectric
50×20×1
Silicon
Oxide
73
0.17
2.2
Sensing
Layer
50×20×1
Gold
74.48
0.42
19.32
Figure.1 Temperature Sensor Model-1
In second design Aluminum is used as sensing
layer and Titanium layer is underneath the
sensing layer. The thickness and materials
should be selected so that the beams will be flat
at the maximum desired operating temperature.
TABLE-2
Dimension & Material Property of Model-2
LAYERS
DIMENSION
(µm)
MATERIAL
MATERIAL PROPERTY
YOUNG
MODULUS
POISSON
RATIO
DENSITY
( gm/cc)
(GPa)
Substrate
100×100×10
Silicon
170
0.26
2.32
Dielectric
50×20×0.5
Sio2
PECVD_ECR
61
0.24
2.1
Sensing
Layer
50×20×0.1
Titanium
115
0.3
4.51
50×20×0.3
Aluminium
70
0.36
2.7
Figure.2 Temperature Sensor Model-2
TABLE-3
Sensitivity Analysis of Temperature Sensor
IV. RESULTS AND DISCUSSION
The fabrication process and associated packaging
are the main steps. The fabrication starts with a
low-resistivity silicon wafer. A wet oxide film is
thermally grown at the wafer to about 1.0 µm and
then patterned with a buffered oxide etch
.Subsequently, a layer of Gold is deposited on
the wafer for sensing purpose for first design as
stated in Table-1 and a layer of Aluminium/
Titanium for the second design as depicted in
Table-2. With almost same dimension, sensitivity
is calculated as ratio of output displacement to
that of input temperature as explained in Table3.
Input
Tempe rature
Existing Mode l
Proposed Model
(ᴼC)
Displacement
(µm)
Se nsitivity (m/ᴼC)
Displacement
(µm)
Se nsitivity (m/ᴼC)
10
1.02487
1.02487 e-7
1.37522
1.37522 e-7
20
2.07024
1.03512 e-7
2.77046
1.38523 e-7
30
3.11055
1.03685 e-7
4.18896
1.39632 e-7
40
4.14663
1.03665 e-7
5.95692
1.48923 e-7
50
5.19199
1.03839 e-7
7.83333
1.56662 e-7
60
6.23039
1.03839 e-7
9.49944
1.58324 e-7
TABLE-1
Dimension & Material Property of Model-1
LAYERS
DIMENSION
MATERIAL
ISSN: 2231-5381
MATERIAL PROPERTY
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International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 10 - Oct 2013
SIMULATION RESULTS
Sensitivity Analysis of Model 2
1.6
Sensitivity(10E
-7/C
)
1. 55
1.5
1. 45
1.4
1. 35
10
Fig.3
15
20
25
30
35
40
Temperat ure(C)
45
50
55
60
Model-1 (10 ºC)
V.CONCLUSION
Fig.4
The effect of cantilever geometry, materials and
dimensions on the sensitivity of a temperature
sensor has been analyzed using INTELLISUITE
as finite element based tool. The sensitivity
analysis for different temperature ranges presents
an idea to utilize a Silicon wafer area in an
optimum manner, when designing cantilever type
temperature sensors for different temperature
ranges. From the analysis it is observed that
Al/Ti metal shows better sensitivity than Gold as
sensing layer.
Model-1 (60ºC )
REFERENCES
[1] .Sean Scott, Farshid Sadeghi, and Dimitrios Peroulis “An InherentlyRobust MEMS Temperature Sensor for Wireless Health Monitoring of
Ball and Rolling Element Bearings”, Proceedings of IEEE Conference on
Sensors, New Zealand ,vol.3, May 2009.
Fig. 5 Model-2 (10ºC )
[2]. Aaron P. Gerratt, Sarah Bergbreiter, “Microfabrication of compliant
all-polymer MEMS thermal actuators”, Sensors and Actuators : Physical
Journal September 2011.
[3]. Sean Scott, Joseph Katz, Farshid Sadeghi, and Dimitrios Peroulis,
Member, “Highly Reliable MEMS Temperature Sensors for 275ºC
Applications—Part 2:Creep and Cycling Performance”, Journal of
Micromechanical System vol.no. 22, February 2013.
[4].David Schmidt and Yingzi Lin “ Design of a Flexible MEMS
Pressure and Temperature Sensing Film”, International Workshop on
Advanced Smart Materials and Smart Structures Technology 2011,
Dalian, China.
Fig.6
Model-2 (50ºC)
Sensitivity Analysis of Model 1
1.6
S
e
n
sitivity(1
0
E
-7
/C
)
1.55
1.5
1.45
1.4
1.35
10
15
20
25
30
35
40
Temperature(C)
ISSN: 2231-5381
45
50
55
60
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International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 10 - Oct 2013
ISSN: 2231-5381
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