Active Flexible Strain Sensor Based on Single ZnO Micro/Nanowire
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Active Flexible Strain Sensor Based on Single ZnO Micro/Nanowire Pei Lin1, Yan Cui1, Xiaoqin Yan1, Zheng Zhang1, Peng Wang1 and Yue Zhang 1, 2* 1
State Key Laboratory for Advanced Metals and Materials, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China. 2 Key Laboratory of New Energy Materials and Technologies, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China. ABSTRACT A facile and cost-effective fabrication approach of active strain sensor based on individual ZnO micro/nanowire was demonstrated. By connecting a ZnO micro/nanowire along polar growth direction with two Ag electrodes on flexible polystyrene (PS) substrate, the fabricated strain sensor was obtained as a typical M-S-M structure. The I-V characteristic of the device was highly sensitive to the strain caused by the obvious change of Schottky barrier height (SBH). Furthermore, both of the symmetric and asymmetric changes of the SBH at the source and drain were observed during device testing process. The respective contribution of piezoresistance effect and the piezoelectric effect to the change of SBHs were also systematically investigated. INTRODUCTION Due to the simultaneous possession of piezoelectric and semiconducting properties, onedimensional ZnO nanomaterial is recognized as one of the scientifically most intriguing and technologically highly promising building blocks for the future electromechanical and optoelectronic devices with enhanced performance [1-2]. Compared with other metal oxide semiconductors, the robust and precisely size-tunable synthesis methods of ZnO provide multi experimental feasibilities in large scale device integration [3]. So far, a series of electronic devices based on ZnO have been realized, including field-effect transistors (FET), light-emitting diode (LED), piezoelectric diode and biosensors [4-7]. Moreover, taking advantage of the straininduced piezoelectric polarization to boost the performance of the photoelectronic devices has also been demonstrated [8-10]. As the development of electronics is moving toward more personal, portable and flexible, a burgeoning field of human-machine interaction has attracted intensive research [2, 11]. The realization of such human-machine communication relies to a large degree on the integration of sensor networks or sensor arrays. Therefore, fabrication of stain or force sensor with the merits of low cost, high-sensitivity and easy integration is essential [12]. Generally, the strain sensors with Ohmic contacts are fabricated based on the piezoresistance effect [13]. Nevertheless, Prof. Zhong Lin Wang’s group demonstrated that devices with nonsymmetrical Schottky contacts possess improved sensitivity because the current passing through the Schottky contact is exponentially-related with the barrier height, especially under reverse-bias conductions [14-16]. When the ZnO is mechanically deformed, strain-induced piezoelectric polarization could tune the barrier heig
