Research On Lamb Type Surface Acoustic Wave Passive Wireless Temperature Sensors

Surface acoustic wave(saw) resonators are widely studied because it is low cost,easy to fabricate and stable. Rayleigh wave propagates in traditional saw resonator,Aluminum nitride(Al N) is widely used as piezoelectric film in which the speed of Rayleigh wave is between 5000 m/s and 6000 m/s. With the development of antenna’s miniaturization, the working frequency of devices are raised to GHz. Under the condition of not changing the speed of the surface acoustic wave, the line width of the interdigital electrode must be reduced to raise the working frequency, this will complicate the process, so it is important to change the mode of the surface acoustic wave to improve the speed to raise the working frequency of the devices.Firstly, the thesis use COMSOL to simulate and design the Rayleigh wave resonator and Lamb wave resonator respectively, the structure of the Rayleigh wave resonator is: the thick of the silicon is 200 μm, the thick of the Al N is 1.44 μm, the thick of the interdigital electrode is 200 nm, and it’s wavelengh is 16 μm, and through simulation the resonance frequency of the Rayleigh wave resonator is found to be306.08 MHz. The structure of the Lamb wave resonator is: the thick of the silicon is 25μm, the thick of the Al N is 1.44 μm, the thick of the interdigital electrode is 200 nm,and it’s wavelengh is 16 μm. Through simulation it is found that there are seven mode waves propagate in the resonator, the resonance frequency of each mode is 297.8 MHz,398.8 MHz, 448.2 MHz, 500.4 MHz, 531.34 MHz, 584.6 MHz and 615.23 MHz.Then, surface wave acoustic resonators are made through lithography、corrosion and e-beam evaporation. Silicon and silicon dioxide are corroded to make Lamb wave resonator, and when silicon is corroded, silicon dioxide is used as protection mask, on the other hand, silica gel is used to protect the Al N, and then the Lamb wave resonator is made. Silicon and silicon dioxide don’t need to be corroded to make Rayleigh wave resonator.Finally, the thesis use vector nerwork analyzer to test the surface acoustic wave devices. It shows that the Rayleigh wave resonator’ resonance frequency is 305.15 MHz,the resonance frequency of each mode in Lamb wave resonator is 294.63 MHz, 294.63 MHz, 398.125 MHz, 435.625 MHz, 482 MHz, 531.625 MHz, 570 MHz, 613.625 MHz,the result is well agree with the simulation. And then this two resonators is used assensors to test the temperature, and the temperature- frequency of each sensor is get,the result show that the resonance frequency of each sensor decreases while the temperature raises. The sensitivity to temperature of Rayleigh wave sensor is test to be10.77 KHz/℃, the sensitivity to temperature of each mode in Lamb wave sensor is test to be 10.92 KHz/℃, 13.69 KHz/℃, 15.86 KHz/℃, 16.37 KHz/℃, 18.04 KHz/℃, 20.1KHz/℃ and 21.46 KHz/℃. The thesis also use the mode with the highest sensitivity and the highest speed in Lamb wave resonator to test the the temperature wirelessly, the sensitivity to temperature is 19.15 KHz/℃.