A NEW CONDENSER MICROPHONE WITH A P+ SILICON MEMBRANE

This paper presents the results of investigations which have led to the batch fabrication of a new condenser microphone and the subsequent measurement of its characteristics. With an overall size of 3 x 4 x 0.8 mm3 including an hybrid JFET, the microphone has an integrated back-chamber and is achieved with a very simple IC-compatible process comprising only five photolithography steps. The diaphragm has a thickness of 1-mu-m. It is fabricated with the classical EDP boron etch-stop technique. Frequency responses of the microphone with a bias voltage of 20 V show sensitivities of 3.5 and 0.4 mV/Pa, depending on the fabrication parameters; the corresponding bandwidths are 2.5 and 20 kHz, respectively. Two methods of measurement have been set up in order to determine the built-in tension of heavily boron-doped silicon and have led to the same value of 70 MPa.