Air-Coupled Piezoelectric Micromachining Ultrasonic Transducer Based on low-Cost and Large Remnant Polarization PZT Thin Film

Due to the development of integrated circuits, control and driving circuits for large element phased arrays have been cheaper and tidier. Therefore, several applications of air-coupled ultrasonic transducer array were published such as ultrasonic haptic feedback and acoustic hologram. However, current air-coupled ultrasonic transducers were bulky. It prevented the commercialization of these applications. Hence, the piezoelectric micromachining ultrasonic transducer (pMUT) was proposed to replace conventional ultrasound transducers. Currently, PZT thin film is the most convincing piezoelectric layer for pMUT. Nevertheless, the existing PZT fabrication methods were either too expensive or required rare metal material. Therefore, in this study, a cost-effective and reliable PZT thin film fabrication method was proposed. Through depositing a commercial sol-gel solution as a seed layer followed by the radio frequency sputtering, a PZT thin film with remnant polarization of 113.35 (μC/cm
²
) and coercive field of 211.6 (kV/cm) was demonstrated. Besides, two sets of pMUTs made by sol-gel and the proposed method were fabricated to examine the output acoustic pressure. As a result, the pMUT made by the proposed thin film deposition method could generate 0.764 Pa/V at 3cm above it.