ELECTROACOUSTICAL MEASUREMENTS OF SILICON MICROPHONES ON WAFER-SCALE

A new method for the electroacoustic characterization of small-sized s ilicon microphones is described. Using closed-field acoustical measure ments, 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 il lustrated by measurements on piezoelectric and condenser microphones. Accurate measurements of the frequency response can be performed betwe en 100 Hz and 15 kHz. The determination of the total harmonic distorti on of the condenser microphones has been done for SPL (SPL=sound press ure level) from 95 to 125 dB and of the piezoelectric microphones for SPL from 110 to 127 dB, respectively. Furthermore, the A-weighted nois e 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 o ut within a few minutes. By measuring several microphones on several w afers, important information, such as yield and reproducibility, can b e obtained. Additionally, statistical calculations on sensitivity, equ ivalent noise level, etc, can be performed. (C) 1997 Acoustical Societ y of America.