Abstract
Single crystal silicon (SCS) diaphragms are widely used as pressure sensitive elements in micromachined pressure sensors. However, for harsh environments applications, pure silicon diaphragms are hardly used because of the deterioration of SCS in both electrical and mechanical properties. To survive at the elevated temperature, the silicon structures must work in combination with other advanced materials, such as silicon carbide (SiC) or silicon on insulator (SOI), for improved performance and reduced cost. Hence, in order to extend the operating temperatures of existing SCS microstructures, this work investigates the mechanical behavior of pressurized SCS diaphragms at high temperatures. A model was developed to predict the plastic deformation of SCS diaphragms and was verified by the experiments. The evolution of the deformation was obtained by studying the surface profiles at different anneal stages. The slow continuous deformation was considered as creep for the diaphragms with a radius of 2.5 mm at 600 °C. The occurrence of plastic deformation was successfully predicted by the model and was observed at the operating temperature of 800 °C and 900 °C, respectively.
Highlights
Single crystal silicon (SCS) is an excellent material for sensor applications because of its good mechanical properties, high purity and crystalline perfection [1]
Traditional silicon sensors are incapable of working in high-temperature environments due to the deterioration in both electrical and mechanical properties
The results suggest that the higher the operating temperature and the larger the diaphragm that the higher the operating temperature and the larger the diaphragm radius, the more likely the radius, the more likely the plastic deformation is
Summary
Single crystal silicon (SCS) is an excellent material for sensor applications because of its good mechanical properties, high purity and crystalline perfection [1]. The magnitude of the pressure is normally determined by measuring the resultant strain or displacement of the diaphragm, which requires the diaphragms to work in the small deflection range under moderate pressure for a better linearity It is well-known that SCS is a temperature-sensitive material and exhibits no plasticity or creep at normal temperature. The conventional SCS-based sensors are free from hysteresis [2] These diaphragms can be shaped with high precision with the aid of the advanced silicon micromachining technology. The creep properties for Si have previously been investigated using the uniaxial compression test and the four-point bending test [15,16,17,18] When it comes to the silicon microstructures, it is found that the plastic behavior relates to the specimen size, the specimen orientation and the fabrication routes [19,20,21]. Based on the evolution of the measured profiles, the size effect and the temperature effect on the diaphragm behavior are discussed
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