基于ZnO压电薄膜的柔性MEMS超声波换能器

A Flexible MEMS Ultrasonic Transducer Based on ZnO Piezoelctric Thin Film

该文提出一种柔性的微机电系统（MEMS）超声波器件。该器件由下电极、ZnO薄膜、上电极及聚酰亚胺柔性基底构成。其制作过程简单,采用直流磁控溅射制作上、下电极,反应射频磁控溅射制作氧化锌压电薄膜。薄膜间粘合牢固,可反复弯折。SEM和XRD结果表明,氧化锌薄膜厚度可达4~8μm,具有高度（002）择优取向的柱状晶结构。根据XRD所得的结果计算了薄膜平均晶粒尺寸和内应力大小,结果表明,晶粒尺寸约为22nm,薄膜内压应力约为-1.248 4GPa。利用激光多普勒测得其共振频率约为5MHz。同时,研究发现,较厚的ZnO薄膜使振幅变大,导致振动品质因数（Q）值增加。

This paper presents a kind of flexible ultrasonic transducer, which consists of bottom electrode, ZnO piezoelectric thin film, top electrode and pliable polyimide substrate. The top and bottom electrodes are fabricated by DC magnetron sputtering, and ZnO piezoelectric layer is deposited by the reactive RF magnetron sputtering. The adhesion between layers is robust which makes the device perfectly flexible. SEM and XRD results show that the piezoelectric film exhibits a columnar structure with highly （002） preferred orientation and the film thickness is of 4- 8 μm. The average grain size and mean intrinsic stress levels are calculated from XRD results. The results show that the average grain size is a bout 22 nm, with intrinsic stress of -1. 248 4 GPa. The resonant frequency measured by laser Doppler vibrometer is around 5 MHz. Meanwhile, the investigation shows that the thicker ZnO film has great amplitude, resulting Q value to increase.