掺钨VO_2薄膜的电致相变特性

采用直流磁控溅射与后退火工艺相结合的方法,在掺氟SnO_2(FTO)导电玻璃基底上制备了高质量的掺钨VO_2薄膜,对薄膜的结构、表面形貌和光电特性进行测试,分析了钨掺杂对其相变性能的影响.结果表明,室温下掺钨VO_2薄膜的阈值电压为4.2 V,观察到阈值电压下约有两个数量级的电流突变.随着温度升高,相变的阈值电压降低,且电流突变幅度减小.当施加8 V电压时,分别在不同温度下测试了掺钨VO_2薄膜的透过率.温度为20和50℃时,掺钨VO_2薄膜相变前后的红外透过率差量分别为23%和27%.与未掺杂的VO_2薄膜相比,掺钨VO_2薄膜具有相变温度低、阈值电压低和电阻率小的特点,在高速光电器件中有广阔的应用前景.

Characteristics of electrically-induced phase transition in tungsten-doped vanadium dioxide film

The phase transition characteristics of tungsten-doped vanadium dioxide film driven by an applied voltage are studied in the paper.A high-quality film is successfully deposited on an FTO (F:SnO₂) transparent conductive glass substrate by direct current magnetron sputtering and post-anneal processing.First of all,an FTO substrate is placed in the chamber of magnetron sputtering system after being cleaned and dried.Then W-doped vanadium film is fabricated on the substrate with V-W alloy target with 1.4% W by mass fraction.In the process of magnetron sputtering,the operating pressure is kept at 3.0×10^-1 Pa,and the operating voltage and current are 400 V and 2 A,respectively.Finally,W-doped VO₂ film with a thickness of about 310 nm is prepared by being annealed at 400℃ in air atmosphere for 2.5 h.In order to explore the crystal structure,element constituents,surface morphology,roughness and photoelectric properties of W-doped vanadium dioxide film,it is respectively characterized by X-ray photoelectron spectroscopy (XPS),X-ray diffraction (XRD),scanning electron microscope (SEM),atomic force microscope (AFM) and semiconductor parameter analyzer.The XPS analysis confirms that there are no other elements except vanadium,oxygen,carbon and tungsten on the surface of W-doped VO₂ film.The XRD patterns illustrate that tungsten-doping exerts an influence on the crystal lattice of VO₂,but the film still prefers the orientation (110).The SEM and AFM images display that the film with low roughness has a compact structure and irregular crystal particles.Tungsten-doping is found to be able to improve the surface morphology of VO₂ thin film significantly.In addition,a remarkable change in electrical resistivity and a narrow thermal hysteresis loop are also obtained in the metal-semiconductor phase transition.Further,the influences of tungsten-doping on the phase transition properties of the film are analyzed.The experiment demonstrates that the threshold voltage at which the phase transition of W-doped VO₂ film occurs is 4.2 V at room temperature when the film is driven by an applied voltage ranging from 0 V to 8 V.It can be observed clearly that the current changes abruptly by two orders of magnitude.As the ambient temperature rises,the threshold voltage of phase transition drops and the current varies slightly.The optical transmittance curves show the distinct differences under applied voltage at different temperatures.It is found that the infrared transmittance difference reaches up to a maximal value of 27% at 50℃ during phase transition,while it increases by only 23% at 20℃ in a wavelength range of 1100-1500 nm.All these outstanding features indicate that W-doped VO₂ film has excellent properties of electrically-induced phase transition. Compared with undoped-VO₂ film,the W-doped VO₂ film is predicated to have a wide range of applications in the high-speed optoelectronic devices due to its advantages of lower phase transition temperature,resistivity and threshold voltage