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 August 29, 2005 Sintering 2005 – Grenoble page : 1
Objective low temperature High temperature thick-film system thick-film system Resistor Conductor Conductor Dielectric Substrate August 29, 2005 Sintering 2005 – Grenoble page : 2
Issues with low-temperature thick-films � Compatibility of thermal expansion � Dielectric-resistor compatibility � Adhesion � Stability of the resulting circuits August 29, 2005 Sintering 2005 – Grenoble page : 3
3 Temperature Ranges System Firing Temperature 500…550°C 575…650°C 850°C Dielectrics & Resistor Dielectrics Based on V8 glass Based on V6 glass Commercial dielectrics & Du 2041 resistor 85% PbO + 10% B 2 O 3 75% PbO + 10% B 2 O 3 + 5% SiO 2 + 2% Al 2 O 3 + 15% SiO 2 + 2% Al 2 O 3 & ESL 3114 Resistor Austenitic Alumina, & Austenitic & ferritic ferritic steels steels August 29, 2005 Sintering 2005 – Grenoble page : 4
TCE of tested Substrates Alumina Ferritic steel 1.4016 Austenitic steel 1.4435 0 5 10 15 20 (ppm/K) August 29, 2005 Sintering 2005 – Grenoble page : 5
Studied dielectric compositions Deno- glass Filler Grain % filler T f (°C) TCE Substrate Size ( µ mination powder (ppm/K) screen-printed m) V8A40 V8 Al 2 O 3 ~1 40 ~500 ~9 - Steels V8Q40 V8 quartz ~3 40 ~500 ~12 - Steels Al 2 O 3 40 . Steels V6A40 V6 ~1 ~600 ~8 - Steels V6Q50 V6 quartz ~3 50 ~600 ~10-11 (ESL - - - - 850 ~7-8 - Alumina 4916) - Steels +Her GPA (ESL - - - - 850 ~7-8 - Alumina 4916) - Steels +ESL 4924 August 29, 2005 Sintering 2005 – Grenoble page : 6
Dielectrics & resistor Compositions Dielectric composition Resistor composition -400 nm -Firing temperature 500°C August 29, 2005 Sintering 2005 – Grenoble page : 7
Paste preparation Mixing powder SiO 2 , B 2 O 3 , PbO, Al 2 O 3 melting Al 2 O 3 or SiO 2 Milling, sieving of powder glass powder Mixing glass powder Organic vehicle –filler powder Mixing in the tri-cylinder Dielectric paste August 29, 2005 Sintering 2005 – Grenoble page : 8
Screen-printing sequence Basic Resistor Conductor Conductor structure 40 µ m Dielectric Substrate August 29, 2005 Sintering 2005 – Grenoble page : 9
Samples for characterisation � Gauge Factor measurement � TCR measurement Longitudinal resistors Transverse resistors August 29, 2005 Sintering 2005 – Grenoble page : 10
Adhesion & Crack problems � Crack problems � Adhesion Non adherence on non-oxidised substrates Match TCE Oxidation 1h @ 900°C August 29, 2005 Sintering 2005 – Grenoble page : 11
Dissolution of SiO 2 powder in glass SiO 2 particles & low-temp. glass glass + SiO 2 SiO 2 - rich glass � Effect on resistors… V8 glass V6 glass Dissolution 600 °C 625°C Temperature of SiO 2 (10% filled) August 29, 2005 Sintering 2005 – Grenoble page : 12
Results: Alumina & Steel Substrates Low Temperature range 160'000 0 140'000 Sheet Resistance HTCR (ppm/K) -50 120'000 (Ohms) 100'000 -100 80'000 60'000 -150 40'000 20'000 -200 0 500 525 550 500 525 550 Firing Temperature (°C) Firing Temperature (°C) 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 August 29, 2005 Sintering 2005 – Grenoble page : 13
Results: Alumina & Steel Substrates Intermediate Temperature range 45000 75 600°C 40000 Sheet Resistance 575°C 25 35000 TCR (ppm/K) 30000 -25 (Ohms) 25000 -75 20000 15000 -125 575°C 10000 -175 5000 575°C -225 0 Dielectric Firing Temperature (°C) Dielectric Firing Temperature (°C) 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 August 29, 2005 Sintering 2005 – Grenoble page : 14
Results: Alumina & Steel Substrates High Temperature range Dielectric 4924 GPA 98-029 Alumina (alumina) 1.4016 850°C 1.4435 850°C 0 5000 10000 15000 20000 25000 Sheet resistance (Ohms) Dielectric 4924 GPA 98-029 (alumina) 0 50 100 150 200 250 300 TCR (ppm/K) August 29, 2005 Sintering 2005 – Grenoble page : 15
Electrical results Insulting Dielectric Substrate Resistor System Sheet TCR GF Dielectric TCE paste Firing resistance (ppm/K) (ppm/K) Temp.(°C) (kOhms) V8A40 9 1.4016 V8 525 81.0 -158 6 Resistor 1.4435 88.7 -103 - 12 1.4016 550 31.7 -139 6 V8Q40 1.4435 25.9 -41 6 1.4016 26.1 -124 - V6A40 8 ESL 575 3114 1.4435 34.5 73 - 1.4016 24.9 -178 - V6Q50 10-11 600 1.4435 39.8 53 - ~7-8 Alumina Du 2041 850 14.6 39 12.4 Her GPA (+ ESL 4916 as 1.4016 17.6 104 10.6 under-layer on 1.4435 20.7 218 - steel) Alumina 19.9 38 ESL 4924 ~7-8 (+ ESL 4916 as 1.4016 19.3 136 9.9 under-layer on 1.4435 22.2 243 12.1 steel) August 29, 2005 Sintering 2005 – Grenoble page : 16
Gauge factor results Similar gauge factors 1.4435 - V8A40 550°C 1.4435 - V8A40 525°C 1.4435 - V8Q40 500°C Dielectrics 1.4435 - V8A40 525°C 1.4016 - V8A40 550°C Transverse Longitudinal 1.4016 - V8A40 525°C 1.4016 - V8Q40 500°C 1.4016 - V8A40 525°C Alumina 0 2 4 6 8 10 Gauge Factor August 29, 2005 Sintering 2005 – Grenoble page : 17
Conclusions � Dielectric – resistor chemical compatibility � Very low processing temperature achieved � Compatible with wide range of substrates � Matching of thermal expansion is critical August 29, 2005 Sintering 2005 – Grenoble page : 18
CTE range: glass + SiO 2 Little reaction : very wide range of CTE values possible • due to different forms of SiO 2 Fully reacted : OK for alumina, float glass & Ti • August 29, 2005 Sintering 2005 – Grenoble page : 19
Outlook � Fillers: improve stability and reproducibility of dielectrics � Control of TCR of our resistors through additives (CuO, NiO, TiO 2 , Sb 2 O 3 ) � Materials without Pb or precious metals August 29, 2005 Sintering 2005 – Grenoble page : 20
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