Mechanical behavior of laser micro-machined bulk 6H–SiC diaphragms

Mechanical behavior of laser micro-machined monolithic hexagonal silicon carbide (6H–SiC) diaphragms was investigated to determine the effects of laser processing. Square diaphragms with a nominal size of 1.5 mm × 1.5 mm were fabricated from bulk 6H–SiC wafers using a Q-switched Nd:YAG laser operating at a wavelength of 1064 nm, an average power of 0.35W, a pulse repetition rate of 3 kHz, and a pulse width of 100 ns. These parameters were chosen, based on previous experiments, to minimize surface roughness. Analysis of laser-machined diaphragms revealed that the average thickness of a diaphragm was 151 μm which is composed of two layers. One is a soft, black layer with a thickness of about 83 μm consisting of silicon, oxygen, and carbon. The other layer was a hard, virgin SiC layer with a thickness of 68 μm. The diaphragms were subjected to micro-hardness indentation tests to obtain load versus deflection curves. The data was validated using Timoshenko’s analytical model for maximum deflection of a thin plate under concentrated loading with hinged and clamped boundary conditions. Experimental measurements of the deflection were found to be slightly higher than those predicted by the analytical model. The variations in the thickness of the diaphragms, homogeneity of the elastic properties of the laser micro-machined SiC, and possibly inappropriate boundary conditions during testing of the diaphragms chiefly account for the deviations between the experimental results and the analytical model.