The Investigation Of The Dual Surface Acoustic Device Based On LGS

Surface acoustic wave devices have the characteristics of small size,high frequency selectivity and good repeatability.The SAW sensor which is an important branch of surface acoustic wave devices has the advantages of fast response speed,high sensitivity and strong performance,it can be applied in high temperature and complicated harsh environment.Therefore,it is applied in aerospace,traffic transportation,energy extraction and other fields abroad.The main factor that affects whether SAW sensors can be applied to high temperature environments is the choice of piezoelectric substrate materials.Therefore,this paper uses a new kind of piezoelectric material whose name is langasite(LGS)with excellent piezoelectric properties as the piezoelectric substrate to produce the SAW sensor.In order to study the characteristics of SAW sensor based on LGS,this paper designs a single resonator SAW sensor according to the related theory of SAW device.The designed interdigital width is 4?m,the pitch is 8?m,the duty ratio is 1: 1,the logarithm of IDT is 50,the acoustic aperture is 100?,the interdigital gap is 12 ?m,the number of reflection grids is 300.The LGS with different Euler angle(0°,138.5°,26.6°),(0°,138.5°,56.6°),(0°,138.5°,71.6°),(0°,138.5°,86.6°)(0°,138.5°,116.6°)could be used as the piezoelectric substrate of the SAW sensor with a single resonator,through the microelectronics process to complete preparation of the device with electrode thickness of 100 nm,after testing found that five different devices have a strong resonant peak,their resonant frequencies are 168.289 MHz,164.325 MHz,160.000 MHz,150.275 MHz,162.426 MHz respectively.The SAW resonator of the LGS with the Euler angle(0°,138.5°,26.6°)has the highest resonant frequency,maximum sound velocity and the highest electromechanical coupling coefficient.The SAW resonator of the LGS of Euler angle(0°,138.5°,86.6°)has the greatest quality factor and highest first order,second order frequency temperature coefficient.In this paper,five sensors with different Euler angles were tested for temperature and the maximum test temperature was 450°C.The test results show that the resonant frequency of the SAW sensor with Euler angle(0°,138.5°,26.6°)with the increase of temperature is decreasing.The resonant frequency of the SAW sensor of Euler angle(0°,138.5°,56.6°),(0°,138.5°,71.6°),(0°,138.5°,86.6°),(0°,138.5°,116.6°)increases first andthen decreases with the increase of the temperature,and their frequency and temperature relations are quadratic function curves.The exchange temperatures(Tex)of the sensor of five kinds of Euler angle which are calculated by the quadratic function fitting are-22°C,183°C,249°C,390°C,204°C,their quality factor(Q)and electromechanical coupling coefficient(K2)with the increasing of temperature firstly increased and then reduced.Because the relationship of frequency and temperature of the single-resonator SAW sensor based on LGS is quadratic function,which leads to it as a temperature sensor can only achieve a small temperature range of the test.In order to solve this problem,this paper presents the SAW temperature sensor of dual resonators with a novel structure based on the LGS sensors of five kinds of Euler angles.The dual SAW devices with angle of 30°,45°,60° and 90° are prepared by microelectronic process.The dual SAW device have two obvious characteristic peaks.In this paper,the dual SAW devices with different angels are tested for temperature testing.The maximum test temperature is 450°C,and the frequency and temperature characteristics of the device are quadratic function fitting calculated.The maximum error between the calculated temperature of the dual SAW devices with different angles wich are 30°,45°,60°,90° respectively and the actual temperature are6.7°C,5.4° C,3.2°C,4.5°C,respectively.In addition,the temperature resolution of the dual SAW device is related to the difference in the transition temperature of the two resonators.The greater the difference,the higher the temperature resolution of the device.The feasibility of the dual SAW device in temperature testing is verified by comparing the dual SAW temperature sensor whose angle is 60° with the thermocouple temperature in the course of the testing of temperature.It can realize the measurement of the larger temperature range without considering the second order frequency temperature coefficient of the LGS material.