A Micromachined Piezoresistive Accelerometer With Axially Deformed Tiny Beams

A micromachined piezoresistive accelerometer with axially deformed tiny beamsBy Huang Shusen Directed by Professor Wang Yuelin and Professor Li XinxinIn this thesis, a novel micromachined piezoresistive accelerometer with axially deformed tiny beams has been proposed and developed, which bear both higher sensitivity and natural resonant frequency.Micromachining technology, MEMS devices and their applications are surveyed in Chapter 1. The development of micromachined accelerometer is also summarized.In Chapter 2, the operation scheme of a micromachined piezoresistive accelerometer with axially deformed tiny beams is studied in details. The sensor chip consists of a central sppport beam, a proof mass, two mass legs and two tiny beams. Due to the specially designed structure of the proof mass and the mass legs, the tiny beams can be axially stretched or compressed. A theoretical model is created to show that, due to the three-beam-structure and the axial deformation of the tiny beams, the sensor's sensitivity and resonant frequency are both much improved. FEM simulation is also used to verify the analytic results.In Chapter 3, a figure of merit, S2, is used for geometric optimization of the sensor. This design rule is for design of sensors of various measure-ranges based on the optimized results. The design rule can be used for design of the accelerometers with l-25000g range.Attribute to SOI wafer and deep reactive ion etching technology used, the fabrication process of the sensor is easy to control. A preliminary packaging technology is also described in Chapter 4.At last, based on the design rule, sensors of 2.5g range are fabricated and the static and dynamic properties are tested. Measure results show that the piezoresistive accelerometer is with sensitivity of 104.4V/5V/g and resonant frequency of 1115HZ. These agree well with design.