Micro&Nano-ZnO Structures Grown By CVD Method And Their Application In Piezoelectric Strain Sensor

ZnO is a II-VI functional semiconductor material with direct wide gap (3.37eV) and wurtzite structure. Its exciton binding energy is very large (60meV) at room temperature, which make it a kind of promising material for the next generation of short-wavelength light emitting diode (LED) and lasing device (LD). In addition, owing to its other excellent properties, such as outstanding piezoelectricity, superior chemical and thermal stability, high transparency, high biocompatibility, wide range of conductivity and it is also a kind of environment friendly and economical material, ZnO shows huge potential in optoelectronics devices and microelectronic devices, especially in the piezoelectric devices based on ZnO micro&nano structure, such as nanogenerators, piezoelectric-gated diodes and piezoelectric field-effect transistors. So to obtain much more novel and excellent piezoelectric devices based on the coupled semiconducting and piezoelectric properties of ZnO has become the research hot spot.In this article, we obtained several kinds of micro&nano-ZnO structrues by an unusual chemical vapor deposition (CVD) method after systematically summing up the fabrication of material and the study of history, the present situation and problems of device technology based on ZnO. Furthermore, a novel flexible piezoelectric strain sensor based on one kind of the micro&nano-ZnO structrues was fabricated by a simple technique. The main contents are summarized as follows:Firstly, we used a CVD system with an upstream growth pattern to grow ZnO microtree structures. A small quartz with two terminals open was chosen as the reaction vessel. We got a lot of ZnO microtree structures at the upstream terminal and some ZnO tetrapod structures at the downstream terminal owing to the backflow effect and temperature change. The morphologies of the two kinds of ZnO structures were investigated by scanning electron microscopy (SEM). SEM images showed that there were some smaller flower structures among the microtree structures, it laid the foundation of growing microball structures in the following experiment.Secondly, by adjusting the experimental conditions we got ZnO micro-wire-ball structures and ZnO micro-thornyball structures. A small quartz with only one terminal open was chosen as the reaction vessel this time. Then we changed the supplying of oxygen. In the end we got ZnO micro-ball structures. The morphologies of the two kinds of ZnO structures were investigated by scanning electron microscopy (SEM). SEM images clearly showed the ZnO micro-thorny ball structures were neat and uniform, and when a certain number of micro-thorny balls got together the entirety became elastic. So the ZnO micro-thorny ball structures were suitable for the fabrication of the piezoelectric sensor.At the end, we fabricated a novel flexible piezoelectric strain sensor based on the ZnO micro-thorny ball structures. The characterization of the sensor was test by semiconductor characterization system (Keithey4200). The sensor is highly sensitive to an applied stress and has a high on-off ratio (-60). The sensor is expected to have potential applications in detection of external mechanical force, as well as electromechanical switch.