Research On Ultra-high Frequency Surface Acoustic Wave Sensor Based On Global Area

Surface acoustic wave（SAW）sensor is sensitive to Surface mass changes,and can realize the sensing of gas,biomolecules,cells and other micro-mass analytes.The mass sensitivity of SAW sensor will increase with the increase of device frequency,but due to the complexity of design and manufacture of high frequency SAW sensor,the operating frequency of SAW micromass sensor is mainly below 1 GHz,and there is still a lot of room for improvement of mass sensor sensitivity.In this paper,based on the mechanism of global sensitivity,a high-frequency SAW micromass sensor is designed to achieve ultra-sensitive humidity sensing.The full work is as follows:（1）The global sensing strategy of SAW was proposed,a two-dimensional simulation model of SAW device was established,and the global sensitive characteristics of SAW sensor were analyzed by using COMSOL simulation platform.Firstly,the simulation comparison between the global sensitivity and the propagation sensitivity of SAW sensors at 400 nm and 800 nm was made to predict the huge advantage of the global sensitivity of SAW sensors at high frequencies.Then,by loading mass load per unit area on different regions of SAW sensor surface,it is concluded that the mass load effect in the electrode region is the cause of global sensitivity.Finally,the physical mechanism of global sensitivity is analyzed with simulation results.（2）Laser direct writing and electron beam exposure were used to fabricate SAW devices with wavelength of 20μm and 800 nm.The mass loads of 0.0966μg·mm^-2were loaded in the acoustic propagation region and the global area of the devices,respectively,and the mass sensing experiments were carried out to verify the results.Experimental results show that the mass sensitivity of 800 nm SAW device is as high as 2590 MHz·mm²·μg^-1,which is about 500 times of that of 20μm SAW device.The experimental results are in good agreement with the simulation results numerically,which verifies the correctness of the simulation work mentioned above and highlights the advantages of global sensitivity at high frequencies.（3）A SAW humidity sensor based on global sensitivity is developed.Humidity sensing was carried out by using zno nanowires as sensing material and modified into the whole domain of SAW sensor.The sensor results show that the sensitivity of the800 nm SAW humidity sensor based on global sensitivity is up to 278 k Hz/%RH,which is about 600 times of the sensitivity of the 20μm SAW humidity sensor.The experimental results of humidity sensor and mass sensor are close,which verifies the advantages and feasibility of the high frequency SAW sensor in global sensitivity.