Center for Sustainable Future Technologies @POLITO, Istituto Italiano di Tecnologia, C.so Trento 21, 10129 Torino, Italy.
Department of Applied Science and Technology, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Turin, Italy.
Sci Rep. 2017 Feb 6;7:41957. doi: 10.1038/srep41957.
Vanadium doped ZnO (VZO) thin films were grown by RF magnetron sputtering, starting from a ZnO:V ceramic target. The crystal structure, chemical composition, electric and piezoelectric properties of the films were investigated either on the as-grown thin films or after a post-deposition rapid thermal annealing (RTA) treatment performed at 600 °C for different lengths of time (1 and 5 min) in an oxygen atmosphere. Substitutional doping of Zn with V and V ions strongly deteriorated the hexagonal wurtzite ZnO structure of the as-grown thin films due to lattice distortion. The resulting slight amorphization led to a poor piezoelectric response and higher resistivity. After the RTA treatment, strong c-axis oriented VZO thin films were obtained, together with a partial conversion of the starting V ions into V. The improvement of the crystal structure and the stronger polarity of both V - O and V - O chemical bonds, together with the corresponding easier rotation under the application of an external electric field, positively affected the piezoelectric response and increased conductivity. This was confirmed by closed-loop butterfly piezoelectric curves, by a maximum d piezoelectric coefficient of 85 pm·V, and also by ferroelectric switching domains with a well-defined polarization hysteresis curve, featuring a residual polarization of 12.5 μC∙cm.
掺钒氧化锌（VZO）薄膜采用射频磁控溅射法，以 ZnO:V 陶瓷靶材为原料生长而成。无论是在生长的薄膜上，还是在 600°C 下于氧气中进行不同时间（1 和 5 分钟）的后沉积快速热退火（RTA）处理后，都研究了薄膜的晶体结构、化学成分、电学和压电性能。V 离子和 V 取代 Zn 掺杂严重破坏了生长薄膜的六方纤锌矿 ZnO 结构，这是由于晶格畸变。由此导致的轻微非晶化导致压电响应较差和电阻率较高。经过 RTA 处理后，获得了强 c 轴取向的 VZO 薄膜，同时部分起始 V 离子转化为 V。晶体结构的改善和 V-O 和 V-O 化学键的更强极性，以及在外电场作用下更容易旋转，对压电响应和导电性产生了积极影响。这一点从闭环蝴蝶型压电曲线得到了证实，其 d33 压电系数最大值为 85pm·V，而且还从具有明确极化滞后曲线的铁电畴得到了证实，其剩余极化强度为 12.5μC·cm。
