Photoacoustic elastic bending method: Study of the silicon membranes

Photoacoustic (PA) amplitude and phase spectra vs the modulation frequency of the excitation optical beam were measured and analyzed by PA elastic bending method. The PA spectra were measured in a frequency range (from 20 to 20000 Hz), for different thicknesses of Si rectangular membranes (from 10 to 100 μm).. The elastic characteristics of the Si chip with square membranes were described by the theory of thin elastic plate, i.e. as an elastic simply supported rectangular plate. The PA signals (sum of the thermodiffusion, thermoelastic and electronic deformation components) were calculated and compared with the experimental ones. These results showed that the PA elastic bending spectra are convenient for investigation the characteristics of micromechanical membraines. The PA elastic bending spectra of the optically driven micro-opto-electro-mechanical systems (MOEMS) enable, for example, to investigate the different electronic and thermal transport characteristics or technological processes in MEMS fabrications, etc.