A NEW UNIAXIAL ACCELEROMETER IN SILICON BASED ON THE PIEZOJUNCTION EFFECT

A uniaxial accelerometer with virtually no cross-sensitivity is realized using a combination of micromachining techniques and the piezojunction effect in bipolar transistors. The piezojunction phenomenon quantifies the changes in transistor characteristics under mechanical stress. Experiments revealed a linear relationship between VBE change and stress in the base-emitter junction. This approach enables the performance of stress measurements at lower power consumption. Selective etching techniques are used to micromachine a seismic mass in the center of the chip, which is suspended by four beams. The realization of high resonant frequencies in every axis was emphasized. By using an electrical cross-coupling technique of the four piezojunction transistors, transverse sensitivity can be reduced to less than 1%. The accelerometers have been developed for airborne and robotic applications and measure less than 4 mm multiplied by 4 mm. They are designed for an acceleration range between 1 and 100 g, depending on the processing parameters, and a resolution of better than four decades.