An integrated SAW voltage sensor

An integrated SAW (surface acoustic wave) voltage sensor is presented, based on the SAW oscillator system, with features such as high sensitivity, broad measuring range, high input impedance, and direct voltage-to-frequency conversion. The dual oscillator system possesses the additional advantage of temperature compensation. The piezoelectric zinc oxide layer is not only used for the excitation and detection of surface acoustic waves, but also as a very thin dielectric (approximately 18 μm). As a result, the generation of high electric fields by low voltages enables the design of high-sensitivity sensors. The sensor shows a short-term stability of 2 Hz at an operating frequency of 72 MHz and a drift of about 100 Hz/hr. The sensitivity for DC signals is 60 Hz/V. Frequency modulation of the output signal in response of an AC input has been detected for frequencies up to 50 Hz. An important technological step is the application of a passivation layer on top of the zinc oxide layer. Two passivating materials and processes have been examined