Ultrasonic sensing device with ZnO piezoelectric nanorods by selectively electrospraying method

• The structure of piezoelectric ZnO nanorods was patterned selectively.
• The electrospraying electric field of 533–800 V/mm was determined.
• The uniformities of the electrosprayed ZnO seed layer were related with the electrospraying times.
• Piezoelectric ZnO nanorods with high aspect ratio of 10–16 were obtained.
• The scalable sensing device arrays were packaged to measure the underwater ultrasonic waves.

In this study, electrospraying method and hydrothermal process were utilized to fabricate the piezoelectric zinc oxide (ZnO) nanorods. The optimum growing parameters were studied. The electric field around 533–800 V/mm was determined to electrospray ZnO seed layer selectively on Au/chromium/silicon substrates. And the coverage rate of the ZnO seed layers can be controlled. Piezoelectric ZnO nanorods with height of 3–5 μm (aspect ratio from 10 to 16) were obtained. The ZnO nanorods were packaged in arrays of 1 × 1, 2 × 2, 3 × 3, 4 × 4 and 5 × 5 to characterize their piezoelectric properties. We used X-ray diffraction (XRD), photoluminescence (PL) and field emission scanning electron microscopy (FE-SEM) to analyze the morphology and luminescence of ZnO nanorods. For the sensing test, the lower electrode is platinum (Pt) deposited by sputtering that forms Schottky contact with ZnO nanorods, and the upper one is Au. Then they were packaged to measure the underwater ultrasonic waves. With the signals provided by ultrasonic probe, the relation between average voltage output and the force output can be obtained as a function of the various frequencies and distances.