VO2-Based Infrared Microbolometer Array

V0₂-based thin film materials on silicon substrates are fabricated by ion beam sputtering and a post-annealing which is different from the conventional fabricating method. An infrared linear microbolometer array with 128 pixels is prepared using as-deposited vanadium dioxide thin films. Optical and electrical properties for V0₂-based microbolometer array are tested.     

Investigation of the electrical transport mechanism in VOx thin films

Vanadium oxide VO₂ is a material that transforms from semiconductor to a metal state at a temperature of 67 °C. This phase transformation is accompanied by a dramatic change in its electrical and optical properties. Therefore, vanadium oxide thin films are most attractive for switching applications. Non-stoichiometric thin films of VO_x, including VO₂, also present such thermal response.This paper presents the optical and electrical properties of vanadium oxide thin films deposited by vacuum thermal evaporation of a metal vanadium with follows oxidation. We have studied the electro-physical behavior of these films during their phase transition. It was shown that the electrical transport mechanism of the obtained vanadium oxide films differ in low and high electrical fields. In low electrical fields, conductivity is obtained by the Schottky transport mechanism, whereas in high electrical fields, conductivity ranges from Ohmic, for medium fields, to Poole-Frenkel for higher fields. Also, FTIR and near IR reflectance characteristics of the obtained films are presented.     

Novel pulsed-laser-deposition—VO<Subscript>2</Subscript> thin films for ultrafast applications

VO₂ thin films deposited on fused quartz substrates were successfully fabricated by the pulsed-laser-deposition (PLD) technique. The obtained samples were examined by microscopy and x-ray diffraction (XRD). The films show a fast, passive thermochromic effect of semiconductor-to-metal phase transition (PT) with a characteristic hysterisis at ∼68°C. The thermochromic effect was measured as resistivity, optical transmission, and reflection versus temperature. Under pulsed laser excitation, an optically induced ultrafast PT of VO₂ thin film was observed. Using the degenerate-four-wave-mixing (DFWM) technique, it was found that excited state dynamics is responsible for the induced lattice reorientation polarization, which results in the ultrafast PT.     

二氧化钒薄膜的退火组分变化及光学特性研究

为得到高纯度的VO2薄膜,对其制备参数进行了探索。VO2薄膜用磁控溅射法制备。对不同条件下制备的VO2薄膜用X射线电子能谱仪(XPS)测试,并通过拟合来得到3,4,5价钒在薄膜中所占的比例。为提高4价钒的含量对薄膜进行了退火处理,分析了退火对氧化钒薄膜中4价钒含量的影响。结果表明,VO2薄膜对10.6μm激光的透过率从60℃时的74%变到78℃时的11.93%,发生了相变。     

调整VO2薄膜相变特性和TCR的制备及辐照方法

采用不同的真空还原时间、真空退火温度和衬底制备出了VO2薄膜,并对制备出的薄膜进行电子辐照.通过测试辐照前后的VO2薄膜相变电学性能及低温半导体相电阻温度系数(TCR),表明不同的制备工艺和不同注量的电子辐照可明显改变VO2薄膜相变过程中电学性能,提高薄膜的电阻温度系数.对影响VO2热致相变薄膜电学性能及电阻温度系数的因素进行了讨论.     

用于红外激光防护的VO2薄膜的研究进展

二氧化钒（VO2）薄膜由于具有优异的热致变色性能已成为激光防护材料领域的研究热点.本文综述了国内外VO2薄膜的研究进展,对VO2薄膜的主要制备方法、用于红外激光防护的原理及防护波段进行了探讨,并总结了用VO2薄膜实现激光防护所面临的问题.     

Insulator-to-metal phase transformation of VO2 films upon femtosecond laser excitation

Light-induced insulator-to-metal phase transition of vanadium dioxide films was studied by ultrafast optical pump-probe spectroscopy. The transient optical reflection measurement shows that both heating and laser illumination contribute to the phase transition of VO₂. Within 10⁻¹¹–10⁻⁹ sec, these two mechanisms are competitive. Excited-state dynamics were found to be strongly dependent on the concentration of structural defects and the pump laser power as well. Comparison of the transient reflection of VO₂ films deposited on different substrates suggests that the excitonic-controlled light-induced insulator-to-metal phase transition in VO₂ proceeded through an intermediate state. The transient reflection measurement of VO₂ in metallic phase shows a three-stage relaxation process. A polaron excitation model is introduced to describe the dynamical process for metallic VO₂.     

Terahertz Switching Focuser Based on Thin Film Vanadium Dioxide Zone Plate

In this paper, we propose a switchable focuser device based on a Fresnel zone plate (FZP) structure for terahertz (THz) applications. Each FZP contains seven rings, etched in thin VO₂ film with the designed focal lengths of 50 and 100 mm for 3.7-THz frequency. Temperature-induced VO₂ phase transition leads to the change in dielectric susceptibility of the material, which allows one to switch on and off the focusing properties of the device. The devices were tested with radiation of 3.1 and 3.7 THz emitted by quantum cascade lasers. Experimental results were compared with numerical simulations. In this article, we compare the FZP based on VO₂ films with different properties and show that a thicker VO₂ film reveals higher focusing efficiency, while a thinner one reveals a higher modulation ratio for the peak intensity at the focal point of FZP. We demonstrate experimentally the near-diffraction-limited size of the beam in the focal point of the device. Switching between two phase states of the VO₂ films results in up to the 38-fold change of intensity in the focal point.     

Effect of crystallization of amorphous vanadium dioxide films on the parameters of a semiconductor-metal phase transition

The hysteresis loops of reflectivity and capacitance of amorphous and polycrystalline vanadium dioxide films in the range of a semiconductor-metal phase transition were studied. The morphology of these films was studied by an atomic-force microscope. It is established that the small number (2–3) of temperature cycles suppress the phase transition due to possible diffusion of oxygen from VO₂ clusters into adjacent clusters consisting of the lowest oxides of the Magnelli series. It is shown that the annealing of an amorphous film of vanadium dioxide in oxygen leads to an additional oxidation of low oxides and the formation of VO₂, the formation of a polycrystalline film, and the recovery of the phase transition. The above results and the data obtained by atomic-force microscopy are indicative of the high optical quality of the polycrystalline vanadium dioxide films produced by the annealing of amorphous VO₂ films. The results also show that these films can be used in interferometers and optical limiters.     

Optical transmission in thin films of vanadium compounds

Thin films of five vanadium compounds/composite： （1） VO2（3-fl） （3-fl = 3-Hydroxyflavone）, （2） VO（pbd）： （pbd = 1-Phenyl-l, 3-butadione）, （3） VO（dbm）2 （dbm = Dibenzoylmethane）, （4） VPc （Vanadyl Phthalocyanine） and （5） V2O5-PEPC （V2O5- poly-N-epoxypropylcarbazole composite）, were deposited by the dropcasting method from the solution in benzene. The transmittance-irradiance relationships were investigated and the transmission in the visible spectrum and optical images were obtained as well. It was found that the transmittance of the VO2（3-fl）, VO（pbd）2, VO（dbm）2 and VPc, was practically independent of the irradiance; whereas the transmittance of V2O5-PEPC decreased by 4% for thin and 9% for thick films with an increase of the irradiance.     

Phase Transition VO2 Thin Films for Optical Switches

This paper presents a method to make vanadium dioxide (VO₂) crystallites on silicon substrates by reactive ion beam sputtering. The thickness of the thin film is about 100nm. The phase transition temperature of VO₂ is 65°C. The transmittance of the semiconducting phase VO₂ is about 50% and it is reduced to as low as 3% in metal phase at the infrared wavelenghth spectrum. The extinction ratio of the optical switches is 12dB. and the insertion loss is of 1-2dB. The switching time is about 1ms.     

Metal‐Insulator Transition in ALD VO2 Ultrathin Films and Nanoparticles: Morphological Control

Nanoscale morphology of vanadium dioxide (VO₂) films can be controlled to realize smooth ultrathin (<10 nm) crystalline films or nanoparticles with atomic layer deposition, opening doors to practical VO₂ metal‐insulator transition (MIT) nanoelectronics. The precursor combination, the valence of V, and the density for as‐deposited VO₂ films, as well as the postdeposition crystallization annealing conditions determine whether a continuous thin film or nanoparticle morphology is obtained. It is demonstrated that the films and particles possess both a structural and an electronic transition. The resistivity of ultrathin films changes by more than two orders of magnitude across the MIT, demonstrating their high quality.     

128元非致冷氧化钒红外探测器的制作

采用新工艺在氮化硅衬底上制备了室温时电阻温度系数为 - 0 .0 2 1K-1的氧化钒薄膜 ,以此为基础 ,利用光刻和反应离子刻蚀工艺在硅衬底上制作了 12 8元氧化钒红外探测器 .为了降低探测器敏感元与衬底间的热导 ,设计制作了自支撑的微桥结构阵列 .测试结果显示探测器的响应率和探测率在 8～ 12 μm的长波红外波段处分别达到10 4V/W和 2× 10 8cmHz1/ 2 W-1.     

SnO_(2)缓冲层对VO_(2)薄膜微观结构与相变性能的影响北大核心

利用电子束蒸发法在Si衬底上制备了不同厚度的SnO_(2)缓冲层,并使用磁控溅射法制备出上层氧化钒薄膜,研究了SnO_(2)缓冲层厚度对于氧化钒薄膜微观结构、相组成以及相变性能的影响。结果表明,引入具有四方金红石结构的SnO_(2)缓冲层后,上层氧化钒薄膜的结晶性变好,随着SnO_(2)缓冲层厚度的增加,沉积的氧化钒薄膜中V^(4+)含量逐渐提高,氧化钒薄膜的平均晶粒尺寸增大,成膜质量变好;相变锐度有所降低,热滞回线宽度减小。这些结果表示SnO_(2)缓冲层的引入有利于在硅衬底上生长高质量且相变性能优越的VO_(2)薄膜。     

Micromachined Uncooled IR Bolometer Linear Array Using VO2 Thin Films

Mixed vanadium oxide thin films, as VO₂ for the main composition are materials for uncooled microbolometer due to their high temperature coefficient of resistance (TCR) at room temperature. This paper describes the design and fabrication of 8-element linear array IR uncooled microbolometers using the films and micromachining technology. The characteristics of the array is investigated in the spectral region of 8–12 μm. The fabricated detectors exhibit responsivity of up to 10 KV/W, typical detectivity of 1.89×10⁸ cmHz^1/2/W, and thermal time constant of 11 ms, at 296 K and at a frequency of 30 Hz. Furthermore, The uncorrected response uniformity of the linear array bolometers is less than 20%.     

Tailoring Vanadium Dioxide Film Orientation Using Nanosheets: a Combined Microscopy,Diffraction, Transport,and Soft X‐Ray in Transmission Study

Vanadium dioxide (VO₂) is a much‐discussed material for oxide electronics and neuromorphic computing applications. Here, heteroepitaxy of VO₂ is realized on top of oxide nanosheets that cover either the amorphous silicon dioxide surfaces of Si substrates or X‐ray transparent silicon nitride membranes. The out‐of‐plane orientation of the VO₂ thin films is controlled at will between (011)_M1/(110)_R and (?402)_M1/(002)_R by coating the bulk substrates with Ti_0.87O₂ and NbWO₆ nanosheets, respectively, prior to VO₂ growth. Temperature‐dependent X‐ray diffraction and automated crystal orientation mapping in microprobe transmission electron microscope mode (ACOM‐TEM) characterize the high phase purity, the crystallographic and orientational properties of the VO₂ films. Transport measurements and soft X‐ray absorption in transmission are used to probe the VO₂ metal–insulator transition, showing results of a quality equal to those from epitaxial films on bulk single‐crystal substrates. Successful local manipulation of two different VO₂ orientations on a single substrate is demonstrated using VO₂ grown on lithographically patterned lines of Ti_0.87O₂ and NbWO₆ nanosheets investigated by electron backscatter diffraction. Finally, the excellent suitability of these nanosheet‐templated VO₂ films for advanced lensless imaging of the metal–insulator transition using coherent soft X‐rays is discussed.     

Broad Range Tuning of Phase Transition Property in VO2 Through Metal‐Ceramic Nanocomposite Design

Vanadium dioxide (VO₂) is a well‐studied Mott‐insulator because of the very abrupt physical property switching during its semiconductor‐to‐metal transition (SMT) around 341 K (68 °C). In this work, through novel oxide‐metal nanocomposite designs (i.e., Au:VO₂ and Pt:VO₂), a very broad range of SMT temperature tuning from ≈ 323.5 to ≈ 366.7 K has been achieved by varying the metallic secondary phase in the nanocomposites (i.e., Au:VO₂ and Pt:VO₂ thin films, respectively). More surprisingly, the SMT T_c can be further lowered to ≈ 301.8 K (near room temperature) by reducing the Au particle size from 11.7 to 1.7 nm. All the VO₂ nanocomposite thin films maintain superior phase transition performance, i.e., large transition amplitude, very sharp transition, and narrow width of thermal hysteresis. Correspondingly, a twofold variation of the complex dielectric function has been demonstrated in these metal‐VO₂ nanocomposites. The wide range physical property tuning is attributed to the band structure reconstruction at the metal‐VO₂ phase boundaries. This demonstration paved a novel approach for tuning the phase transition property of Mott‐insulating materials to near room temperature transition, which is important for sensors, electrical switches, smart windows, and actuators.     

Linear High-Tc YBa2Cu3O7−δ Superconducting Thin Film Infrared Detectors Coupled with a Cylindrical Microlens Array in Quartz Glass Substrate

Monolithic linear cylindrical microlens array in a quartz glass substrate is fabricated using photolithography and ion beam etching technique, the high-Tc YBa₂Cu₃O_7?δ superconducting thin films are deposited through excimer laser scanning ablation, the superconducting thin films are patterned by photolithographic method and ion beam etching technique, and the hybrid structure of the microlens array component and the superconducting IR detectors has been obtained using an IR glue to cement the microlens component onto the superconducting device. We also investigate the optical response characteristics of the hybrid device in the optical spectral region of 1 ~ 5 μm, as follows. The average optical responsivity $(\overline R )$ of the hybrid device is 1.6×10⁴ V/W, average noise equivalent power $(\overline {NEP} \;)$ is 2.3×10^?12 WHz^?1/2, average detectvity $(\overline {D^ * } )$ is 3.2×10⁹ cmHz^1/2W^?1, and the non-uniformity of detectvity (D*) is not more than 14%. The experimental results show that the performance of the superconducting device is improved notably using a quartz glass refractive microlens array as the incident IR radiation concentrators.     

氮气流量对磁控溅射C掺杂TiO2薄膜光学性能的影响

采用磁控溅射法制备了C掺杂TiO₂薄膜,并研究了氮气引入溅射过程对薄膜光学性能的影响。利用X射线衍射仪、拉曼光谱仪、X射线光电子能谱仪、分光光度计和原子力显微镜分析了不同氮气流量下薄膜的微结构、元素价态、透光性能和表面形貌。结果表明,沉积的薄膜主要是非晶结构,拉曼光谱中存在少量锐钛矿相,且随着氮气流量增大,锐钛矿特征峰强度减弱,意味着晶粒出现细化。当氮气流量增大为4cm³/min时,C掺杂TiO₂薄膜内氮元素含量为3.54%,其光学带隙从3.29eV变化至3.55eV,可见光区的光学透过率明显提高。可见改变氮气流量可实现对C掺杂TiO₂薄膜光学带隙和光吸收率的有效调控。     

N掺杂Cu2O宽光谱吸收材料的实验与计算研究

采用热氧化的方法制备了高择优取向的Cu2O薄膜。并通过离子注入对其进行了不同浓度的N掺杂。吸收谱测试显示高剂量的N掺杂Cu2O薄膜在带隙以下有吸收峰出现。采用第一性原理方法对N掺杂Cu2O的几何、电子结构及光学性质进行了比较系统的研究。计算结果表明,高浓度的N掺杂在Cu2O禁带中引入了一个中间带。价带到中间带的电子跃迁与实验观察到的吸收峰相吻合。实验和计算结果显示N掺杂Cu2O材料在制备宽光谱探测器和中间带太阳电池方面有很大潜能。