ScAl Nitride sensor for high temperature applicationsVersatily of scandium in various applications. 5 times higre pietzoelectric cofficient by adding 43% Sc in Al Mityride.
Industrial demand for higher temperature piezoelectric sensors is increasing for the control of automobiles, aircrafts and turbine engines, and the monitoring of furnaces and reactor systems. It is generally known that piezoelectric materials with a higher Curie temperature possess a lower piezoelectric coefficient. The study result of the relationship between the maximum use temperature and the piezoelectric coefficient d33 shows that piezoelectric materials with a higher maximum use temperature possess a lower piezoelectric coefficient d33. For example, the Curie temperature and piezoelectric coefficient d33 of lead zirconium titanate (PZT), which is widely used in many electronic devices, are 250°C and 410 pCIN, respectively. The maximum use temperature and d33 of aluminum nitride (AIN), which is one of the typical high temperature piezoelectric materials, are 1150°C and 5.5 pCIN[3]. It is difficult to achieve a good balance between a high maximum use temperature and a large piezoelectricity in materials.
Sc(x)Al(l-x)N thin films exhibited a large piezoelectric coefficient d33. The films were prepared by dual co-sputtering. When the Sc concentration was 43%, the film exhibited a peak d33 of 24.6 pCIN, which is the highest reported to date for nitride semiconductors. This film also exhibited the potential of high temperature durability by showing no deterioration after approximately 1,000°C heat treatment. As one of its possible applications, SAW devices on 6H-SiC substrate were fabricated and evaluated. The results showed promising properties in the GHz range.
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