Abstract
In most MEMS devices, the moving micro-structures are surrounded by air which significantly affects their dynamics behaviors. The correct prediction of the squeeze-film air damping ratio is essential in MEMS (Micro-Electro-Mechanical System) devices design. In the paper, a static test is proposed to measure the squeeze-film air damping ratios of capacitive MEMS accelerometer under different pressures. The unsealed chip of capacitive accelerometer is placed in vacuum extraction equipment and an open loop circuit is developed to apply step signal in the test. By charging the pressure and measuring the overshoot Mp and the settling time ts from the time response of the system, the damping ratio ξ under different pressures can be calculated. Finite element method (FEM) based on the modified Reynolds equation is utilized to simulate the transient response of the micro-structure. Good correlation between experiment and FEM analysis is obtained. The proposed static test in this paper provides a new method to more easily measure the dynamic performances of micro-structures under various pressures.
Highlights
With the development of micro fabrication, Micro-Electro-Mechanical-System (MEMS) devices such as MEMS sensors, MEMS actuators and micro optical devices are widely used in aviation, aerospace, biomedicine and so on
The proposed static test in this paper provides a new method to more measure the dynamic performances of micro-structures under various pressures
The most notable characteristic of MEMS devices is that their structures are a few microns in size and separated by micron-sized gaps which are filled with fluid
Summary
With the development of micro fabrication, Micro-Electro-Mechanical-System (MEMS) devices such as MEMS sensors, MEMS actuators and micro optical devices are widely used in aviation, aerospace, biomedicine and so on. The performance or the quality factor of MEMS devices is largely determined by the squeezed film air damping. To avoid air damping, using a vacuum packaging to enable MEMS devices working in low-pressure environment is a feasible way. Zelong Zhou et al [10] used the lava pipe model to obtain the velocity of air flow to modify the conventional Reynolds equation to investigate the dynamic behaviors of thick perforated plate. Vacuum packaging and perforated plate have been proved to be useful method to reduce squeeze film damping in MEMS devices. A static test based on an open loop circuit is presented to measure the squeeze film damping ratio of a capacitive MEMS accelerometer with a 2 μm air gap under different air pressures. There is good agreement between experimental result and finite element analysis
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