The design and analysis method of a MOEMS accelerometer consisting of a grating interferometry cavity and a micromachined sensing chip is presented in this paper. The grating interferometeric cavity is composed of a frequency-stabilized laser source, a diffraction grating, and a mirror ,to realize a subnanometer resolution. With an ultrasensitive micromachined chip, the MOEMS accelerometer can finally achieve a few ug resolution. This paper combines the geometrical optics and nano optics design methods to simulate the whole system, analyses how the divergence angle, grating constant and the length of the interferometeric cavity influence the ultimate sensitivity. A new set of MOEMS accelerometer is proposed, the theoretical analysis shows that the acceleration sensitivity can achieve 1200 v/g, and the resolution remains 1.3ug.
MOEMS accelerometers bring together the advantages of both optical measurement and MEMS technique. It has higher resolution than traditional accelerometers and can be widely implemented in more application fields. Packaging is an important step for MOEMS accelerometers in their fabrication process. It can maintain the high parallelism of the upper surface of the proof mass and the grating, so that it helps to improve the temperature stability of accelerometers. In addition, it can reduce the effect of the external temperature on the sensitive structures, thereby reducing the changes of the zero drift and scale factor by temperature. Since the accelerometers measures the acceleration which involves the stress and strain of the springs, the thermal stress introduced during the packaging process will have significant side impacts on the device performance and life, etc. In this paper, we establish a finite element method (FEM) model of the MOEMS accelerometer which contains package and sensitive structure based on grating interferometry cavity. The FEM model considers the thermal coupling of sensitive structure and adhesive, adhesive and package substrate. Based on it, the influence of the thermal stress of the material of the adhesive and the substrate are studied. The results show that a good match between the coefficient of the thermal expansion (CTE) of the substrate and sensitive structure material and a reduced elastic modulus as well as the increase of thickness of the adhesive can effectively diminish the thermal stress. Besides, well designed packaging can help to reduce the zero drift and scale factor drift to minimum.