Tuning Characteristics of AlN-Based Piezoelectric Micromachined Ultrasonic Transducers Using DC Bias Voltage

In this article, we investigate the effects of dc bias voltage on characteristics for Aluminum Nitride (AlN)-based piezoelectric micromachined ultrasonic transducers (PMUTs). As dc bias voltage is applied to the AlN piezoelectric layer, it would produce controllable stress leading to the variation of device response. When the bias voltage is adjusted between -30 to 30 V, experimental results show distinguishable improvement in the characteristics of PMUTs. First, characteristics, such as the resonance frequency, the -3 dB bandwidth (BW), and the quality factor vary almost linearly with respect to the bias voltage. Second, the temperature drift of the resonant frequency is experimentally demonstrated to be compensated through dc bias voltage. Third, the ring-down time decreases by more than 3.03% compared to non-biased condition. Fourth, the biased PMUTs can cover an effective frequency range of 4.66 kHz through technology like frequency-hopping spread spectrum (FHSS), which is an increment of 370.71%, compared to an effective frequency range of only 0.99 kHz at non-biased conditions. This provides more potential applications, such as ultrasonic communication. This proposed dc bias voltage approach has demonstrated a cost-effective method to compensate for the temperature drift, reduce the ring-down time, and expand the effective frequency range of PMUTs. The dc-biased AlN PMUTs can be widely used in ultrasonic communication, range-finders, and relative high temperature applications.