Investigation of the microcantilevers by the photoacoustic elastic bending method

Abstract

The amplitude of the photoacoustic (PA) elastic bending signals vs. the modulation frequency of the excitation optical beam for the chip with Si cantilevers were measured and analyzed. The experimental PA elastic bending signals of the whole micromechanical structure were measured by using special constructed PA cell (the gas-microphone detection technique with transmission configuration). The PA spectra were measured in a frequency range from 20 to 20000 Hz. The signal in the PA cell without optical excitation (noise) was also measured and analyzed. Experimental results show that the PA measuring system (PA cell width electret's microphone and lock-in amplifier) has signal-noise ratio S/N ∼ 30000 at 100 Hz; ∼ 3000 at 1000 Hz; ∼ 5 at 10000 Hz. The correction of the measured signal, in order to remove the coherent electronic noise as a systematic error, was made. The experimental PA elastic bending signals of the cantilever were compared with the experimental PA elastic bending signals of the Si square membranes. These results showed that the PA elastic bending method is convenient for investigation the characteristics of micromechanical structures as microcantilevers.