AlN Surface Acoustic Waves Devices And Their Application For Temperature Sensoring

Surface acoustic waves(SAWs)devices are widely used in electronic devices and communication systems,including resonators,filters,and so forth.SAWs devices are also widely used as sensors,including temperature sensors,pressure sensors,gas sen-sors,and so on.Now,SAWs devices are developing in high frequency and high quality factor(Q)directions.High-frequency SAWS devices could be used to increase the com-munication capacity or enhance the sensitivity of the sensors.High Q SAWs devices would be used in low-noise systems design or to improve the resolution of the sensor.AIN/Sapphire substrate material is one of the ideal materials for making high frequency and high Q SAWs devices.It has many excellent properties for fabricating SAWs de-vices.The SAWs phase velocity is more than 5700 m/s with low propagation loss(0.7 mdB/A)at 1 GHz.The oxidation temperature of AIN is at 900 ? at atmosphere.The crystal quality of substrate material has an important influence on parameters of SAWs devices,such as insertion loss and electromechanical coupling coefficient.At present,high-crystalline AIN films can be grown on Sapphire substrate materials by hydride vapor phase epitaxy(HVPE)with thicknesses higher than 5?m and surface roughness lower than 5 nm.The crystal dislocations density is lower than 108 cm-2.The improve-ment of crystal quality will promote the application of AIN/Sapphire substrate materials in SAWs devices.In this paper,we designed and fabricated one-port SAWs resonators,one-port sur-face phononic crystals(SPCs)resonators and SAWs delay lines on high quality AI-N/Sapphire substrate materials,and achieved the following results:1.According to the structure of one-port SAWs resonator,we designed and fabri-cated a one-port SPCs resonator on AIN/Sapphire substrate material.Unlike one-port SAWs resonator,the one-port SPCs resonator have two resonant modes.According to the results of simulation by finite element analysis,these two resonance modes may be due to the double cavity structure of the one-port SPCs resonator.Since the one-port SPCs resonator exhibits dual resonance modes.We propose a scheme for temperature sensor using difference frequency of this two resonant modes.The temperature sensor s eventual TCF value is-99.30 ppm/?,which is twice more than the TCF value of the one-port SAWs resonator.2.Along the[11-20]AlN/[1-100]Al2O3 and[1-100]AlN/[11-20]A1203 orienta-tions,we designed and fabricated a series of SAWs delay lines.The SAWs Rayleigh mode are systematically studied,including insertion loss,electromechanical coupling coefficient,phase velocity and TCF values.The measured K2 values in both orienta-tions are higher than the calculation results.It is probably due to the thermal expansion mismatch effect between AIN and Sapphire.We discuss the relationship between the SAWs phase velocity,the thermal expansion coefficient and TCF.The results suggest that in a certain crystal orientation,the thermal expansion coefficient is the main factor affecting the TCF values,and the TCF value difference in different directions is mainly due to the SAWs phase velocity difference.3.We proposed a model of AIN/Sapphire anisotropic SAWs double delay line tem-perature sensor.We theoretically studied and calculated the TCF value of the temper-ature sensor.The results show that the AIN/Sapphire anisotropic SAWs double-delay line sensor may be able to achieve highly sensitive in temperature detection by using the difference frequency of the SAWs delay lines in[11-20]A1N/[1-100]Al2O3 and[1-100]AlN/[11-20]Al2O3 orientations.We designed and fabricated a SAWs delay line oscillator with a response center frequency of 352.72 MHz with quality factor of 2841.The experimental conditions for builting the AIN/Sapphire anisotropic SAWs double delay line temperature sensor were obtained.4.Using the finite element analysis method,we simulated and calculated the SAWs phase velocity and group velocity distribution in the[11-20]A1N/[1-100]Al2O3 orien-tation.The simulation results show that the SAWs phase velocity and group velocity have only a little difference in the[11-20]A1N/[1-100]Al2O3 orientation.This shows that the dispersion effect of SAWs is smaller on the AIN/Sapphire substrate material.On the high crystal quality AIN/Sapphire substrate material,we preliminarily designed and fabricated a one-port SAWs resonator with the number Ng =700 of electrodes in the mirror.The quality factor of the one-port SAWs resonator is 10600.