Ultrasound-transducer using membrane resonators realized with bipolar IC technology

We investigate the generation and detection of ultrasound for proximity sensing using micromachined resonant membrane structures. The silicon membranes are fabricated with industrial bipolar IC technology followed by an anisotropic etching step. Electrothermal excitation and piezoresistive detection of ultrasound are technologically promising because of their compatibility with industrial IC technology. The efficiency of the electrothermal excitation and sound generation is investigated as a function of the membrane thickness in the case of initial compressive stress. A slight buckling of the membranes clearly improves the efficiency of thermal excitation. We demonstrate the on-chip piezoresistive detection of vibrations and ultrasound using a Wheatstone bridge arrangement. Using two identical membranes with electrothermal excitation and piezoresistive detection an ultrasound-barrier for short distances has been realized. The use of industrial IC technology allows the co-integration of signal conditioning circuitry.