Kiegészítés - Bíró Ferenc eloadása -micro-pellistor

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Optimisation of Low Dissipation Micro-hotplates:

Thermo-mechanical Design and Characterisation

Ferenc Bíró^1,2

Csaba Dücső¹, Zoltán Hajnal¹, Andrea Edit Pap¹, István Bársony¹

1 Institute of Technical Physics and Matrials Science - MFA ,

2University of Pannonia, Hungary

7/2 Nanocatalytic gas sensors

Aims:

• Development of integrable micro-hotplate

• Low power consumption, (<30mW at >500°C)

• Thermo-mechanical stability over extended lifetime ( >5 years)

• CMOS compatible process

Optimisation of Low Dissipation Micro-hotplates Thermo-mechanical Design and Characterisation 10/2

Means:

• FEM modeling

• Selection of appropriate structural materials

• Functional testing and verification

Materials & Methods:

• n-type Si, <100> wafer

• Standard CMOS processes

• TiO_x/Pt: DC magnetron sputtering

• Filament patterned by lift-off

• Cavity etching from back side by Deep Reactive Ion Etching (DRIE)

• Porous alumina (catalyst support) by electrochemical anodisation of Al layer on top of the hotplate

Layer structures Layer thicknesses are given in nm.

Type A B C D E

SiO₂ Thermally

grown

100 100 100 1000 1000

SiO₂

CVD 100 100 100 - -

Si₃N₄

LPCVD 200 200 - - -

TiO_x/ Pt

15 / 270

15/

270 15/

270 15/

270 15/

270 Si₃N₄

LPCVD - - 200 200 150

SiO₂

CVD 300 300 300 300 300

Porous alumina

1400 Plate Diam.

100 µm 1400 Bridge Structure of alternative

membranes investigated

7/4 Nanocatalytic gas sensors

Thermo-mechanical FEM Simulation

Optical view of two hotplates for the targeted pellistor.

Membrane diameter: 300 µm Chip size: 1×1 mm². Optimisation of Low Dissipation Micro-hotplates Thermo-mechanical Design and Characterisation 10/4

• Structures analyzed by COMSOL Multiphysics®

• Considered physical effects & parameters

• Bottom surface of membrane:

Natural convective cooling

in horizontal back plan, parameterized by Cooling area/perimeter

• Top surface of membrane:

Natural convective cooling in horizontal plan, parameterized by Cooling area/perimeter.

• Filament:

Embedded in SiO2-Si3N4

Joule heating

Temperature dependent TCR

•Cavity:

Filled with air

• Side surfaces:

Kept at 25 °C

400×400 µm area were considered

• Multilayer:

Temperature dependent thermal and electrical properties

Heat transfer between layers and Si cube

Mechanical stress

Simplified geometry of the full- membrane sensor models.

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Characterisation of Micro-heaters

Applied structures:

• 10×10mm²square membranes and wafers.

Average residual stress calculated from wafers curvature using Stoney equation.

• Wafer curvature measured by Makyoh topography.

1. Residual Mechanical Stress Measurement

Layer structure

Parameters of

Si wafer Parameters of layer structures E_s

[GPa] υ_s [s.d.] d_s

[µm] d_f [nm] R

[m] σ_f [MPa]

C 130 0,28 370 700 -30,6 -192

D 130 0,28 370 1200 25,6 133

E 130 0,28 370 1150 21,5 166











 +

⋅ ⋅

−

⋅

= ⋅

pre post f s

s s

s d R R

d

E 1 1

) 1 ( 6

2

σ υ Results

• Residual stress below 200MPa

• Membrane:

Type C compressive, flat Type D, E, tensile, bumpy

• C selected for operational device SiO2Thermal

100nm

SiO2CVD 100nm

TiOx/Pt 15/270nm

Si3N4LPCVD 200nm

SiO2CVD 300nm

Porous-Al2O3

1400nm

7/6 Nanocatalytic gas sensors

Characterisation vs. Modelling of Micro-heaters

2. Thermal characterisation

▻ C.

Hot Resistance Temperature Method (HRTM) Filament temperature calculated by measured resistance

and TCR of Pt filament. 0

0

1 R T R T

H

HP +

−

=

α

Optimisation of Low Dissipation Micro-hotplates Thermo-mechanical Design and Characterisation 10/6

▻ B.

Micro Melting Point Measurement(MMPM)

• Compounds of definite melting points selected to cover temperature range between 212 and 884°C

• Sharp solid-liquid phase transformation

• Small grains dropped on the hotplate by glycerol based suspension

• Phase transformation observed by optical microscopy

▻ A.

FEM simulation (current ramp)

biro.ferenc@ttk.mta.hu membrane

0 5 10 15 20 25 30 35 40 45 50 55 0

200 400 600 800 1000 1200 1400

AgNO₃ KNO₃

Pb(NO₃)₂

CuCl₂+2H₂O V₂O₅ Na₂SO₄

Temperature /O C

Power / mW

Temperature measured by melting point of salts.

Average temperature of Pt, calculated by COMSOL.

Maximum temperature of Pt, calculated by COMSOL.

Average temperature of Pt, calculated from the resistivity.

• FEM calculated average temperature

Temperature measured by MMPM

• FEM model is correct for design

• MMPM is effective for calibration.

• HRTM method gives lower average temperature

• Huge differences between the average temperature and the hottest point of the filament as calculated by FEM⇨

to be verified by high resolution IR camera

Temperature vs. Power relationship determined by different methods and calculated by FEM

2. Thermal characterisation

coincidence Results

7/8 Nanocatalytic gas sensors

Charactrisation of Micro-heaters

Method:

• Hotplates powered by square wave current.

• Voltage-, current waveforms measured by DSO.

2 3 4 5 6 7

0 100 200 300 400 500 600

Temperature /O C

Time / ms Rise time of micropellistors:

A : t

90%=2.3ms B : t_90%=2.2ms C : t_90%=2.3ms

3. Dynamic properties: Response time

Optimisation of Low Dissipation Micro-hotplates Thermo-mechanical Design and Characterisation 10/8

Results:

• Quick response time (~2.3ms,t₉₀), for all types investigated.

• No significant difference between various structures.

Rise time of microheaters, driven by square wave current. Input power is 23mW in all cases.

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Charactrisation of Micro-heaters

Test conditions:

• Devices powered by square wave current pulses.

Input power amplitude is constant 30mW, D=20%, T=1s.

4. Dynamic properties: Accelerated Life Time Test

Results:

• No membrane crack was observed.

• Resistance changing in time.

• Failure: electromigration in the filament.

Optical micrograph of degraded Pt filament after 8.7×10⁵ temperature cycles.

Resistance of micro-heaters of hotplate vs. time.

0 200000 400000 600000 800000 1000000 350

355 360 365 370 375 380

Device close to the end of its life.

Operation conditions:

Heating power = 30 mW Period time = 1 sec Duty cycle = 20 %

Resistance / Ohm

Time / sec Device1, type A Device2, type A 30mW

0 Pin

t D=20%

1 sec

7/10 Nanocatalytic gas sensors

Conclusions

• Thermo-mechanical properties of alternative membrane designs were modeled by COMSOL code and

• Tested experimentally in terms of temperature vs. power, response time and long-term stability. FEM results are verified.

• The selected full-membrane type structure reaches 700^oC at 30mW.

23.3^oC/mW !

• The full membrane is stable, can stand cycling between room temperature and 700^oC for minimum 8×10⁵periods.

• Quick response time with porous catalyst support layer.

• Improvement of filament characteristics is necessary

Acknowledgements

This work was partially supported by

Hungarian National Development Agency grant TÁMOP-4.2.2/B-10/1-2010-0025.

and

Tateyama Kagaku Industries Co. Ltd., Japan.

Optimisation of Low Dissipation Micro-hotplates Thermo-mechanical Design and Characterisation 10/10

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Thank you for your attention