An investigation of using micromachined silicon diaphragms in high temperature pressure sensors

Ren, Juan (2012). An investigation of using micromachined silicon diaphragms in high temperature pressure sensors. University of Birmingham. Ph.D.

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Abstract

Micromachined silicon diaphragms have been widely used as sensing elements in standard pressure sensors. However, at elevated temperature, the pressurized silicon diaphragms may suffer from the plastic deformation or creep. Therefore, this project is to investigate the possibility of using silicon diaphragms in high temperature pressure sensors.

A series of experiments were performed to investigate the effect of size, temperature and ion implantation on the mechanical behaviour of the micromachined silicon diaphragms. The test structures were annealed under the atmospheric pressure at a temperature of 600°C, 800°C and 900°C, respectively. The surface profiles of the diaphragms were measured with respect to the anneal time. Based on the experimental results, the suggestions of the design of the silicon diaphragms for the high temperature pressure sensors were given. Moreover, the onset of the plastic deformation was predicted by the theory of the critical resolved shear stress. The predicted behaviour was in good agreement with the experimental observation for the heavily-boron-doped silicon diaphragms. Finally, the constitutive equations were implemented in Comsol Multiphysics to simulate the evolution of the diaphragm deformation in the initial anneal stage. The model successfully predicted the deflections for the diaphragms with a radius from 0.5mm to 2.0mm at 900°C.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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