太赫兹波段二氧化钒薄膜的研究进展

Recent Progress on Vanadium Dioxide Thin Film at Terahertz Range

在68℃附近,二氧化钒薄膜就能实现低温半导体相和高温金属相之间的一级可逆相变,相变时二氧化钒薄膜的太赫兹透过率和反射率等都会发生急剧的变化。更为重要的是,除了加热之外,其他激励方式,如光照、电场、太赫兹场等也能使二氧化钒薄膜发生相变。这一独特、优异的半导体-金属相变性能使得二氧化钒薄膜在太赫兹开关、调制器等领域具有巨大的应用前景。因此,二氧化钒薄膜已成为太赫兹材料与功能器件方面的一个研究热点。研究工作主要集中在二氧化钒薄膜的制备方法、相变性能及在太赫兹器件领域的应用三个方面。探究制备高质量二氧化钒薄膜的方法是其获得优异的相变性能及应用的前提条件。在太赫兹波段,二氧化钒薄膜的常用制备方法有脉冲激光沉积法、磁控溅射法及溶胶-凝胶法。脉冲激光沉积法是最早用来研究太赫兹波段二氧化钒薄膜相变性能的薄膜制备方法,该法制备的薄膜质量高、相变性能好。磁控溅射法制备二氧化钒薄膜时,主要采用在氩气/氧气混合气氛下溅射金属钒靶的反应磁控溅射法。然而,利用反应溅射法时,二氧化钒薄膜的成膜条件范围很窄(尤其是氧流量比),不利于薄膜结构及性能的优化。为此,研究者们探索利用二氧化钒陶瓷材料作为溅射靶材来制备二氧化钒薄膜。尽管脉冲激光沉积法和溅射法被广泛应用于制备二氧化钒薄膜,但所需设备复杂且成本高。相比之下,溶胶-凝胶法设备简单、成本低且易于实现掺杂和成分控制,但薄膜附着性差。二氧化钒薄膜的相变性能研究主要包括不同的相变激励方式及相变性能的优化提高两个方面。二氧化钒薄膜的热致相变简单易控,但响应时间长;而光致及电致相变响应快,但实现相变的条件要求高,且调制幅度较小。二氧化钒薄膜相变性能的提高一直颇受关注,优化工艺条件、掺杂及制作超材料结构是目前常用的方法。在应用方面,二氧化钒薄膜主要是被用来制作太赫兹开关和太赫兹线偏振器、可调频滤波器、频率选择表面器及吸收器等太赫兹调制器。本文对近年来太赫兹波段二氧化钒薄膜的制备方法、相变性能以及在太赫兹方面的应用进展进行了综述。

The reversible semiconductor-metal phase transition of vanadium dioxide thin films can be induced by heating at^68℃,accompanied by a giant and abrupt change of terahertz transmission.Moreover,the semiconductor-metal phase transition of vanadium dioxide thin film can be triggered not only by heating but also by optical excitation,electric field,terahertz field,etc.Owing to its excellent phase transition characteristics,vanadium dioxide thin film can be used in a wide variety of applications such as terahertz switching,terahertz modulator.As a result,vanadium dioxide thin film has been a hot topic in functional materials and devices at terahertz range.The researches mainly focus on the preparation me-thods,the phase transition properties and the applications of vanadium dioxide thin films at terahertz frequency range.Exploring a simple and controllable thin film preparation method plays an important role in improving the semiconductor-mental transition properties and the application of vanadium dioxide.The methods mainly include pulsed laser deposition,magnetron sputtering and sol-gel method.Pulsed laser deposition can prepare high-quality vanadium dioxide films and was firstly used to investigate the semiconductor-metal transition pro-perties of vanadium dioxide thin film at terahertz range.Reactive magnetron sputtering technique from a metal vanadium target in Ar/O 2 atmosphere is often used to deposit vanadium dioxide thin films.However,in order to prepare a vanadium dioxide phase,reactive sputtering requires a narrow range of experimental conditions,especially for the O 2 flow ratio,which is unfavorable for improving the structure and the property.Hence,magnetron sputtering from a VO 2 ceramic target is exploited to prepare vanadium dioxide thin film.Although both pulsed laser deposition and magnetron sputtering are widely used to prepare vanadium dioxide film,they have disadvantages of complex equipment and high cost.Sol-gel me-thod,as compared to pulsed laser deposition and magnetron sputtering,has advantages of simple equipment,small cost and easily doping.Study on semiconductor-mental transition properties of vanadium dioxide includes different triggering stimulus and performance optimization.Phase transition induced by heating is easy to be controlled,but it undergoes a long response time.For phase transition triggered by light and voltage,the case is on the contrary.Presently,not only improving the process conditions and doping but also designing the metamaterial has been utilized to improving the phase transition performance of vanadium dioxide film.Due to these unique phase transition properties,vanadium dioxide films have been intensively exploited in many potential applications such as terahertz switching elements,switchable linear polarizer,tunable filter,frequency selective surface and absorber.This review summarizes the preparation methods of vanadium dioxide thin film in recent years,the semiconductor-metal phase transition properties and its applications at terahertz frequency range.