Abstractc‐Axis oriented aluminum nitride (AlN) thin films are successfully prepared on amorphous polyimide films by radiofrequency magnetron reactive sputtering at room temperature. Structural analysis shows that the AlN films have a wurtzite structure and consist of c‐axis oriented columnar grains about 100 nm wide. The full width at half maximum of the X‐ray diffraction rocking curves and piezoelectric coefficient d33 of the AlN films are 8.3° and 0.56 pC N–1, respectively. The AlN films exhibit a piezoelectric response over a wide temperature range, from –196 to 300 °C, and can measure pressure within a wide range, from pulse waves of hundreds of pascals to 40 MPa. Moreover, the sensitivity of the AlN films increases with the number of times it was folded, suggesting that we can control the sensitivity of the AlN films by changing the geometric form. These results were achieved by a combination of preparing the oriented AlN thin films on polyimide films, and sandwiching the AlN and polymer films between top and bottom electrodes, such as Pt/AlN/polyimide/Pt. They are thin (less than 10 μm), self powered, adaptable to complex contours, and available in a variety of configurations. Although AlN is a piezoelectric ceramic, the AlN films are flexible and excellent in mechanical shock resistance.

Aluminum nitride (AlN) thin films were prepared on Inconel 600 superalloy diaphragms by rf magnetron sputtering for the first time to our knowledge. The crystal structure of the AlN films is hexagonal, and the c-axis of the AlN films orients perpendicular to the diaphragm surfaces. The full-width at half-maximum (FWHM) of the X-ray rocking curves of the AlN films is 5.7°, and the piezoelectric constants d33 and d31 are 2.0 and 0.7 pC/N, respectively. We have investigated the influence of the diaphragm structure on the piezoelectric response to pressure of the AlN films. The AlN films sensitively generate electric charges to pressure changes, and the generated charges show an excellent linearity with increasing pressure. The AlN films indicate a high sensitivity of 723 pC/N. The sensitivity of the AlN films agrees with the result calculated using a method in which the electroelastic energy is differentiated from the voltage in AlN films for unimorph circular diaphragms.

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Aluminum nitride (AlN) is a promising Acoustic Emission (AE) sensor element for high-temperature environments such as gas turbines and other plants because AlN maintains its piezoelectricity up to 1200°C. Highly c-axis-oriented AlN thin-film sensor elements were prepared on silicon single crystals by rf magnetron sputtering. Both ordinary-temperature AE sensors and high-temperature AE sensors have been developed using these elements. In this paper, to study effects of d33 and thickness of AlN elements on sensor sensitivity, AlN elements with d33 from 2 to 7 pm/V and thickness from 3 to 9 /m were prepared. It is confirmed that the AE sensor sensitivity increased with d33 and thickness of AlN elements. The sensitivity of the high-temperature AE sensor was also improved by a design of the sensor structure. The sensor characteristics were evaluated at elevated temperatures from 200 to 600°C. It was confirmed that the AE sensor works well at 600°C and does not deteriorate.

Yukari Morofuji ＊ , Non-member C-axis-oriented zinc oxide (ZnO) thin films were prepared on Inconel substrates by rf magnetron sputtering technique. The ZnO film characteristics were evaluated under pressures of 10.0 to 300.0 MPa and frequencies of 0.1 to 30 Hz at room temperature. The deviation from the linearity of charges with pressures for the ZnO films was within 0.52 % of a full scale at 300.0 MPa, which indicated a good linearity between 10.0 and 300.0 MPa. Furthermore the ZnO films were evaluated under combustion pressure in a single-piston 90 cc engine rotating at 1900 rpm. The waveform of the ZnO films was similar to those of a commercial sensor. It is demonstrated that the ZnO films have a good possibility as combustion pressure sensor elements.