Research On Basic Theory And Key Technologies Of MEMS Acceleration Sensor Based On Acousto-optic Effect

MEMS acceleration sensors are important sensors for inertial applications, whichhave the advances of small bulk, low cost, high precision, and integratable. They are notonly applied in the military fields of inertial navigation, guided weapons, and intelligentsystems, but also in the commercial fields of cars, medical devices, and consumerelectronics. MEMS acceleration sensors with noval principles and structures havealways been an important branch in the field of MEMS acceleration sensors research.In this paper, a noval MEMS acceleration sensor based on the acousto-optic effectwas improved. By utilizing the Raman-Nath acousto-optic diffraction, the sensitivity ofnoval acousto-optic MEMS acceleration sensors was obviously higher than that of thetraditional SAW acceleration sensor. The researches about the theory, the design, thefabrication, and the detecting were performed. In detail, the recursive asymptoticmethod （RAM） model and coupling of modes （COM） model were studied to discuss thepropagation of the SAW in the multilayered piezoelectric structures and in the ST-cutquartz wafer respectively; the key technologies for the design of the SAW resonatorwhich satisfied Raman-Nath acousto-optic diffraction condition, and the compatibalemachining of the three-demensional bulk micromachining of the ST-cut quartz waferwith the fabrication and patterning of the multilayered films were broken through; theexperimental prototype Ⅰa ndⅡ were fabricated and detected. The sensitivities,linearities and resolutions the prototypes were obtained respectively.The main contributions of this work are listed as following:①The research status of different kinds of MEMS acceleration sensors werefirstly studied. And then the micro acceleration sensors based on acoustic principleswere reviewed in detail. Motivated by the above observation, the stratagem of theMEMS acceleration sensor based on the acousto-optic effect were taken out. Theresearch objectives and contents of this work were developed respectively.②The basic structure and operation principle of the sensor were introduced. Themacro model was established and the lecture experiment is presented. By calculating thepropagation of SAW in the multilayed piezoelectric structures using the RAM method,It was fund that the multilayed piezoelectric structures, like ZnO-SiO2-Si structure, werenot suitable for the proposed noval acousto-optic acceleration sensor. The ST-cut quartzwafer was chosen as the substrate, and the sensitivity was calculated as60¹50KHz/g depending on the used diffraction light beams.③The structure of the SAW resonantor which satisfied Raman-Nathacousto-optic diffraction condition was simulated and optimized by using COM methodand P matix method. The single mode optic waveguide was designed by effective indexmethod, the TE0mode waveguide polarizer and the waveguide reflector were alsodesigned. The cantilever beam structure was designed and simulated by COMSOLsoftware, its reliability was demonstrated.④Based on the MEMS fabrication platform in the lab, the fabrication process andthe photoetching mask layout were designed, the compatibale machining of thethree-demensional bulk micromachining of the ST-cut quartz wafer with the fabricationand patterning of the multilayered films were broken through, and the experimentalprototype was fabricated. The typical process was obtained.⑤The loop-locked positive feedback oscillation circuit was designed and theSAW oscillator was fabricated; and then the detecting platform was formed which couldbe turned by different degrees. The realationships between the outputted photo-beatfrequency and the inputted acceleration of experimental prototype Ⅰ and Ⅱweredetected. The sensitivities of8.32kHz/g and16.29kHz/g, linearities of2.2%and2.3%,resolutions of5.6×10^-4g and4.7×10^-4g were obtained respectively.