Development of low-temperature thick-film materials for - - PowerPoint PPT Presentation

page : 1 Sintering 2005 – Grenoble August 29, 2005

Development of low-temperature thick-film materials for piezoresistive sensors

• C. Jacq, T. Maeder, S. Menot-Vionnet, and P. Ryser

EPFL - LPM Lausanne, Switzerland lpmwww.epfl.ch

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Objective High temperature thick-film system low temperature thick-film system

Substrate Dielectric Resistor

Conductor Conductor

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Issues with low-temperature thick-films

Compatibility of thermal expansion Dielectric-resistor compatibility Adhesion Stability of the resulting circuits

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3 Temperature Ranges

75% PbO + 10% B2O3 + 15% SiO2 + 2% Al2O3

System Firing Temperature

575…650°C 500…550°C 850°C Austenitic & ferritic steels Commercial dielectrics & Du 2041 resistor

85% PbO + 10% B2O3 + 5% SiO2 + 2% Al2O3

Dielectrics Based on V6 glass Dielectrics & Resistor Based on V8 glass Alumina, Austenitic & ferritic steels & ESL 3114 Resistor

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TCE of tested Substrates

5 10 15 20

Austenitic steel 1.4435 Ferritic steel 1.4016 Alumina

(ppm/K)

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Studied dielectric compositions

• Steels

~12 ~500

40

~3

quartz

V8 V8Q40 ~7-8 ~7-8 ~10-11 ~8 ~9

TCE (ppm/K)

• ~3

~1 ~1

Grain Size (µ m)

• Alumina
• Steels

850

• (ESL

4916) +ESL 4924

• Alumina
• Steels

850

• (ESL

4916) +Her GPA

• Steels

~600

50 quartz

V6 V6Q50

. Steels

~600

40 Al2O3

V6 V6A40

• Steels

~500

40 Al2O3

V8 V8A40

Substrate screen-printed Tf (°C) % filler powder Filler glass Deno- mination

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Dielectrics & resistor Compositions

Dielectric composition Resistor composition

• 400 nm
• Firing temperature 500°C

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Paste preparation

Mixing powder SiO2, B2O3, PbO, Al2O3 Milling, sieving of glass powder Mixing glass powder –filler powder Al2O3 or SiO2 powder Organic vehicle Mixing in the tri-cylinder Dielectric paste melting

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Screen-printing sequence

Substrate Dielectric Resistor

Conductor Conductor

Basic structure

40µm

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Samples for characterisation

TCR measurement Gauge Factor measurement

Longitudinal resistors Transverse resistors

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Adhesion & Crack problems

Non adherence on non-oxidised substrates

Adhesion Crack problems Oxidation 1h @ 900°C Match TCE

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Dissolution of SiO2 powder in glass

Effect on resistors…

glass + SiO2 SiO2 - rich glass SiO2 particles & low-temp. glass

625°C 600 °C Dissolution Temperature

• f SiO2 (10% filled)

V6 glass V8 glass

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Results: Alumina & Steel Substrates

Low Temperature range

Alumina V8 glass + 40% alumina on 1.4016 V8 glass + 40% alumina on 1.4435 V8 glass + 40% quartz on 1.4016 V8 glass + 40% quartz on 1.4435

20'000 40'000 60'000 80'000 100'000 120'000 140'000 160'000 500 525 550

Firing Temperature (°C) Sheet Resistance (Ohms)

• 200
• 150
• 100
• 50

500 525 550

Firing Temperature (°C) HTCR (ppm/K)

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Intermediate Temperature range

5000 10000 15000 20000 25000 30000 35000 40000 45000

Dielectric Firing Temperature (°C)

Sheet Resistance (Ohms)

Alumina V6 glass + 40% alumina on 1.4016 V6 glass + 40% alumina on 1.4435 V6 glass + 50% quartz on 1.4016 V6 glass + 50% quartz on 1.4435

• 225
• 175
• 125
• 75
• 25

25 75

Dielectric Firing Temperature (°C)

TCR (ppm/K)

575°C 600°C 575°C 575°C

Results: Alumina & Steel Substrates

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High Temperature range

Alumina 1.4016 850°C 1.4435 850°C

5000 10000 15000 20000 25000 (alumina) GPA 98-029 4924

Dielectric

Sheet resistance (Ohms)

50 100 150 200 250 300 (alumina) GPA 98-029 4924

Dielectric

TCR (ppm/K)

Results: Alumina & Steel Substrates

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6

• 41

25.9 1.4435 6

• 139

31.7

550

1.4016

12 V8Q40

• 103

88.7 1.4435 6

• 158

81.0

525 V8 Resistor

1.4016

9 V8A40

• 124

26.1

575 ESL 3114

1.4016

8 V6A40

• 178

24.9

600

1.4016

10-11 V6Q50

10.6 104 17.6 1.4016

• 218

20.7 1.4435 38 19.9 Alumina

~7-8

ESL 4924 (+ ESL 4916 as under-layer on steel)

9.9 136 19.3 1.4016 1.4435 Alumina 1.4435 1.4435

Substrate

Her GPA (+ ESL 4916 as under-layer on steel)

Insulting Dielectric

850

System Firing Temp.(°C)

Du 2041

Resistor paste

~7-8

Dielectric TCE (ppm/K)

12.1 243 22.2 12.4 39 14.6

• 53

39.8

• 73

34.5

GF TCR (ppm/K) Sheet resistance (kOhms)

Electrical results

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2 4 6 8 10 Alumina 1.4016 - V8A40 525°C 1.4016 - V8Q40 500°C 1.4016 - V8A40 525°C 1.4016 - V8A40 550°C 1.4435 - V8A40 525°C 1.4435 - V8Q40 500°C 1.4435 - V8A40 525°C 1.4435 - V8A40 550°C

Dielectrics

Gauge Factor

Transverse Longitudinal

Gauge factor results

Similar gauge factors

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Conclusions

Dielectric – resistor chemical compatibility Very low processing temperature achieved Compatible with wide range of substrates Matching of thermal expansion is critical

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CTE range: glass + SiO2

• Little reaction: very wide range of CTE values possible

due to different forms of SiO2

• Fully reacted: OK for alumina, float glass & Ti

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Outlook

Fillers: improve stability and

reproducibility of dielectrics

Control of TCR of our resistors through

additives (CuO, NiO, TiO2, Sb2O3)

Materials without Pb or precious metals