Improved Si piezo-transistors for mechano-electrical transducers

Piezo-transistors with stresses applied to the emitter region by means of small hard styli for application as mechano-electric transducers have been improved. High signal-to-noise ratios were obtained in gold-doped n-p-n Si planar transistors. New designs for emitter electrodes have been devised which make the fabrication of the transducer units easy. Rather large stressing areas (60-µm diameter) which are surrounded by ring-type emitter electrodes with overlay bonding pads are provided in the central part of the emitter region (90-µm diameter). Signal-to-noise ratios are high and independent of the position of the stylus over the stressing area. By using these transistors mechano-electrical transducer units were fabricated with higher stabilities. It was found that noise decreases with increasing stress. Life-test results of the transducer units are also indicated. The stress dependence of transistors were explained by the combined effects of the stress dependence of the emitter efficiency and the stress dependence of the base transport factor. Gold-doping seemed to enhance the stress dependence of the base transport factor due to a very short minority carrier lifetime.