激光激励微型硅悬臂梁的振动特性研究

本文用光学探测方法研究了半导体硅悬臂梁的振动问题；运用基于外差干涉原理的实验装置得到了悬臂梁在激光激励下的振动响应（振动振幅和相位随调制激光频率的变化）；采用等离子波和热弹性波的数学模型，对悬臂梁的振动进行了理论分析；可看到实验与理论模拟结果吻合很好，同时通过分析可得振动相位与调制激光频率的平方根之间有线性关系。关键词词: 光学探测, 硅悬臂梁，振动. 

STUDY ON THE VIBRATION SILICON CANTILEVERS UNDER LASER EXCITATION

Microcantilevers were used widely in physical, chemical, biological and mechanical system as sensors to detect the tiny change of environment. The resonance frequency and Q-factor were usual output quantities during detection. So the study of vibration characteristics of cantilever under different excitation was very important for its uses. In this paper the vibration of silicon cantilever, subjected to a uniform laser excitation on one surface, was investigated experimentally and theoretically. The spectrum analyzer was used to obtain the spectrum response curve of cantilevers. The result showed that the resonance frequency obtained from experimental measurement agreed very well with that obtained from theoretical calculation. To measure the cantilever deflection, an optical experimental apparatus called thermoelastic microscopy, which was based on the principle of heterodyne interferometer, was used to obtain the amplitude and phase of the cantilever deflection under different frequencies of excitation laser. Theoretically, the thermal wave model, along with plasma wave model, was adopted to simulate the vibration of silicon cantilever under optical excitation. The thermal wave model was widely used to describe the change of sample temperature in the physical process during laser operation, while the plasma wave was the specific characterization of semiconducting samples under strong laser excitation, and the plasma wave model was used to describe the change of excess carrier density in sample. These two models were used together here to study the cantilever vibration. The expressions of excess carrier density and temperature of cantilever were obtained. Also the curves of amplitude and the phase of silicon cantilever deflection versus modulation frequency were calculated. The good agreement between measurements and simulations was observed from the results. From linear fitting analysis we obtained a linear relationship between the vibration phase and the square root of modulation frequency. This conclusion was the same as the result from other authors.