Electroacoustical measurements of silicon microphones on wafer scale

A new method for the electroacoustic characterization of small-sized silicon microphones is described. Using closed-field acoustical measurements, it is demonstrated how a precise device characterization can be carried out directly on wafer-scale, thereby eliminating the need to separate and mount each microphone. The performance of the setup is illustrated by measurements on piezoelectric and condenser microphones. Accurate measurements of the frequency response can be performed between 100 Hz and 15 kHz. The determination of the total harmonic distortion of the condenser microphones has been done for SPL (SPL=sound pressure level) from 95 to 125 dB and of the piezoelectric microphones for SPL from 110 to 127 dB, respectively. Furthermore, the A-weighted noise voltage of the microphones can be measured easily. Regarding size, 2- to 4-in. wafers may be used and the minimum measurable chip area is about 1.5 mm(2). An almost complete characterization of a microphone, including the different measurements mentioned above, can be carried out within a few minutes. By measuring several microphones on several wafers, important information, such as yield and reproducibility, can be obtained. Additionally, statistical calculations on sensitivity, equivalent noise level, etc, can be performed. (C) 1997 Acoustical Society of America.