Sensitive materials are the core components of high-temperature thin-film sensors. Their chemical and electrical stability have a great influence on piezoelectric rings vibration sensor whether thin-film sensors can be used in harsh environments. The kinds of sensitive materials, the microstructure of the sensitive material has own crystal structure, and the properties of free carriers are carried out the coefficient sensitivity of the fabricated thin-film sensor. In general, the alloy film strain gauge has the lowest gauge factor, followed by a thin film strain gauge made of piezo ceramic material, and the highest piezoelectric ceramic disc transducer is a semiconductor thin film strain gauge.
coefficient sensitivity
The higher strain coefficient of the high temperature has thin film strain gauge, the higher coefficient of the high temperature PZT material piezoelectric sensor is thin film thermocouple, and the higher temperature coefficient of resistance is the thin film RTD, the higher sensitivity and the easier the measurement signal, but the sensitivity of the high temperature thin film sensor is made of different sensitive piezo materials .The coefficients vary widely. The high-temperature thin-film strain gauges are made of high-temperature alloys generally have a strain coefficient of 1 to 3, while the ordinary strain gauges of piezo ceramic have a slightly higher strain coefficient of 3 to 9, but they are comparable to those of semiconductor-doped strain gauges ( 100 to 200) .which is still not high enough. The coefficient of a thin film thermocouple is made of an alloy is low,the seebeck coefficient of a thin film thermocouple is made of piezo ceramic is slightly high.
Performance of high temperature
Sensitive materials bear the task of generating signals and can tolerate limited temperatures. When the temperature exceeds a certain temperature of ultrasonic piezoelectric ceramic transducer, the phase change or even crack the sensitive piezo material occurs, which affects the electrical performance and eventually leads to the failure of the thin film sensor. At present, the alloy can withstand temperatures of 1 100 °C, and piezo ceramics can withstand temperatures of 1 500 °C. In the high-temperature applications (such as high temperature areas of aeroengines), the temperature has exceeded 1700 °C. Nowadays, high-temperature thin-film sensors can no longer withstand to select piezo materials and processes that are more resistant to high temperatures and can withstand higher temperatures sensor.
Manufacturing process of sensitive piezo material
Piezoelectric ceramic sensorsare sensitive materials and have the characteristics of high temperature resistance and oxidation resistance. The initial state is liquid. After light curing or thermosetting at a temperature of about 90 °C to about 100 °C, the temperature is about 300 °C to 600 °C. Cross-linking is carried out, and the precursor piezo ceramic is finally pyrolyzed at a temperature of about 1 000 °C. Precursor piezoceramics work stably at temperatures above 1 400 °C but shrink during cross-linking and pyrolysis, typically shrinking by about 30%. Adding fillers can reduce shrinkage. There are mature processes for fabricating body parts using precursor piezoelectric disk vibration sensor, but there are few reports on their thin film patterning processes. There is no report on the patterning process of PDC thin films on nickel-base alloys. Therefore, the use of piezo ceramics for the fabrication is high-temperature thin film sensors requires the resolution of shrinkage.it is problems and patterning process problems. Choosing the right material can improve the sensitivity coefficient of the high-temperature thin film sensor. The sensitivity coefficient of the high-temperature thin film sensor can also be improved by changing the composition of the sensitive material by doping multi-layer sensitive materials.
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