kumar presentation

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-Micro-Heater Designs Using COMSOLTM for Gas

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Presented By

Velmathi .G, Ramshanker .N and Mohan .S

Department of Instrumentation and Applied

[email protected]

Presented at the COMSOL Conference 2010 India
http://www.comsol.com/conf_cd_2011_in


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Integrated micro structure of a Gassensor

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as sensors are e ev ces w c e erm ne e n orma onabout the gas present and its concentration in an ambient gasatmosphere.

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Miniaturized gas sensors with a low power consumption forthe detection of various ases such as CO LPG and H is ver

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essential for a wide range of applications.

e cro- ea er s e ma n componen n gas sensors omake the sensing layer more sensitive and selective. Which isalso a most power consuming part in gas sensors.

Hence perfect design and fabrication of Micro-heater is anim ortant as ect.


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-which can attain a temperature of 300oC - 400oC due to joule

heating, when sufficient voltage is applied across them. r x y

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The design of micro-heaters is optimized for

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low power consumption

low thermal mass

enhanced thermal isolation from the surroundings


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-The Plane plate with central

Double spiral Hone comb r x y

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S-shape Fan shape Meander


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Electro Thermal Mathematical modeling of

In Joule heating, the temperature increases due to theresistive heating from the electric current.

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The electric potential V is the solution variable in theConductive Media DC application mode.

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of the magnitude of the electric current density J.

Current density, in turn, is proportional to the electric field,

In our Simulations we assume the temperature andpotential gradients in the z-direction (perpendicular to the

ea er p ane are sma n compar son o e gra en s n x-y plane. There by reducing the problems to twodimensions. This is a reasonable assumption given the

much smaller than the length or width.


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temperature Taccording to:

where 0 is the conductivity at the reference temperature T0. is the,

varies with temperature. A typical value for platinum copper is 0.00385 per oC


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The coefficient of proportionality is the electric resistivity= 1/ which is also the reci rocal of the tem erature- r x y

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dependent electric conductivity = (T). Combining thesefacts gives the fully coupled relation.

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The equations have been solved under Dirichlet, Neumann,and mixed boundary conditions numerically using theFinite Element Method (FEM) when the Electro-Thermalmodule is selected in COMSOL .


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The optimized meshing for the simulation isdetermined b erformin an inde endent

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grid study to minimize the modeling error.

When the chan e in the solution betweensubsequent stages of meshing refinement is

considered to be ne li ible, the lower but

still sufficient, mesh resolution is kept.


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Material properties of layers used in the MEMS micro-Heater structure

Material (Si) (SixNy) (SiO2) (Pt)

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Thermal Conductivity (W/mK) 157 22 1.4 73

Youngs Modulus (GPa) 190 290 73 170

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. . . .

Thermal expansion (1/K) 2.33e-6 2.33e-6 0.55e-6 8.9e-6

Density (kg/m3) 2.32e3 3.1e3 2.2e3 2.145e4

Heat Capacity (J/kgoC) 700 600-800 730 130


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Square plate with center hole

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Double Spiral Shape

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Honey Comb structure

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S-Shape structure

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Fan shape

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FABRICATION PROCESS STEPS

(1) Thermally grown SiO2 on Si Substrate (2) Si3N4 deposition on top side (3) Pt heater

deposition (4) Si3N4 deposition over Pt heater (5) contact pad open (6) back side window open

(7) Backside etching using TMAH

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Photograph of Gold

wire bonded, packedmicro-heater


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SL.N Heater pattern Power consumptionO

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1. Double Spiral 9.56

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. an ape .

3. S-Shape 17.50

4. Meander pattern 20.00

5. Honeycomb 140.63

6. Square with centerhole

787.50


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So taking (R= W i+1 / W i) as an important variable

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and tested for its heating profile

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SEM image of FabricatedMicro-heater

Image of Fabricated Micro-heater inSurface Profilometer

TMAH etched Membrane


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Gold Wire Bonded Heater

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Thermal Imaging

The ThermaCAM P65 delivers unmatched temperature measurement accuracy. A

thermal sensitivit of 0.08C results in clear noise-free ima es 320 x 240 ixels .A low thermal sensitivity not only offers you the possibility to see the smallest oftemperature changes. It also means you get crisp, very detailed high-resolutionimages which cannot be obtained by less sensitive cameras.

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How it Works?

The FLIR P65 uses an advanced, highly-sensitive detector for non-contact scanningacross wide areas. Camera controls and software make it easy to quickly scan foremissivit and ob ect temperature differencesdifferences that can si nal trouble in

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building envelopes and infrastructure

FLIR thermal image @ 0.06V applied

voltage. ThermaCAM P65ThermaCAM P65


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Thermal analysis of M icro-heater

Practical Data

Resistance-temperature dependence for the determination of temperature (RT)

R sensor =Ro(1+T)

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Where T = T sensor T amb

Ro is the sensor resistance in ohms at T = T amb,

erma mage

0.06V applied voltage.

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is Temperature coefficient of resistance (TCR) in oC-1

voltage temperature

0.020074 50.66

0.029974 101.32

0.040104 172.24

0.04976 253.29

0.060008 377.12

0.070045 506.58

0.079998 628.16 COMSOL simulated


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The authors are thankful to NPMASS for fundingthis activity and Ministry of Communication and

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Information Technology for providing the funds for

setting up Center of Excellence in Nanoelectronicsac y a c.


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