Optical switch with low-phase transition temperature based on thin nanocrystalline VOx film
TL;DR: In this article, an optical switch is fabricated by using micromachining technology, which is based on thin nanocrystalline vanadium oxide (VO x ) film, and it consists of four layers: a silicon (Si) substrate layer, a VO x layer, Si 3 N 4 buffer layer, and an aurum (Au) electrode layer.
About: This article is published in Optik.The article was published on 2010-09-01. It has received 16 citations till now. The article focuses on the topics: Optical switch & Extinction ratio.
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TL;DR: In this paper, vanadium oxide thin films were grown by RF magnetron sputtering from a V2O5 target at room temperature, which resulted in different colors, from yellow to black, depending on composition.
52 citations
TL;DR: In this article, a smart uncooled infrared detector with wavelength selectivity in the long-wavelength infrared (LWIR) band is presented, which can enhance the probability of detecting and identifying objects in a scene.
Abstract: -This paper describes the design and modeling of a smart uncooled infrared detector with wavelength selectivity in the long-wavelength infrared (LWIR) band. The objective is to enhance the probability of detecting and identifying objects in a scene. This design takes advantage of the smart properties of vanadium dioxide (VO2): it can switch reversibly from an IR-transparent to an IR-opaque thin film when properly triggered. This optical behavior is exploited here as a smart mirror that can modify the depth of the resonant cavity between the suspended thermistor material and a patterned mirror on the substrate, thereby altering wavelength sensitivity. The thermistor material used in the simulation is vanadium oxide (VOx). The simulation results show that, when VO2 is used in the metallic phase, it reflects IR radiation back to the suspended VOx and enhances IR absorption in the 9.4-10.8-μm band. When the film is switched to the semiconductor phase, it admits most IR radiation, which is then reflected back to the suspended VOχ by a patterned gold thin film under an SiO2 spacer layer. The spacer layer is used to increase the resonant cavity depth underneath the microbolometer pixel. Thus, the peak absorption value is shifted to 8-9.4 μm, creating the second spectral band. The detector is designed with a relatively low thermal conductance of 1.71 X 10-7 W/K to maximize responsivity (Rv) to values as high as 1.27 X 105 W/K and detectivity (D*) to as high as 1.62 x 109 cm-Hz1/2/W, both at 60 Hz. The corresponding thermal time constant is equal to 2.45 ms. Hence, these detectors could be used for 60-Hz frame rate applications. The extrapolated noise equivalent temperature difference is 14 and 16 mK for the 8-9.4- and 9.4-10.8-μm bands, respectively. The calculated absorption coefficients in the two spectral bands were 59% and 65%, respectively.
52 citations
Cites background from "Optical switch with low-phase trans..."
...These features have prompted many groups to use VO at the phase transition for electrooptical switches [26], [27]....
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TL;DR: In this article, the phase transitions of the vanadium oxide films were investigated by the differential scanning calorimetric technique and the sheet resistance of the deposited films was measured by a two-probe method and the data were in the range of 106 to 105 Ω per square.
Abstract: Vanadium oxide thin films were grown on both quartz and Si(111) substrates, utilizing a pulsed RF magnetron sputtering technique at room temperature with the RF powers at 100 W to 700 W. The corresponding thicknesses of the films were increased from 27.5 nm to 243 nm and 21 nm to 211 nm as the RF power was increased from 100 W to 700 W for the quartz and silicon substrates, respectively. X-ray diffraction and field emission scanning electron microscopy were carried out to investigate the phase and surface morphology of the deposited films. The electronic structure and the vanadium oxidation states of the deposited films were investigated thoroughly by X-ray photoelectron spectroscopy. The as-grown films show only stoichiometric vanadium oxide, where vanadium is in V5+ and V4+ states. The phase transitions of the vanadium oxide films were investigated by the differential scanning calorimetric technique. The reversible i.e. smart transition was observed in the region from 337 °C to 343 °C. The average hemispherical infrared emittance of the deposited vanadium oxide films was evaluated by an emissometer in the wavelength range of 3 μm to 30 μm. The sheet resistance of the deposited films was measured by a two-probe method and the data were in the range of 106 to 105 Ω per square. The optical properties of the films, such as solar transmittance, solar reflectance and solar absorptance, as well as optical constants e.g. optical band gap, were also evaluated. Finally, mechanical properties such as the hardness and the Young’s modulus at the microstructural length scale were evaluated by employing a nanoindentation technique with a continuous stiffness mode.
35 citations
TL;DR: In this article, a well defined optical absorption edge was formed when the vanadium oxide (VOx) thin films were annealed using the plasma arc of a fusion splicer, suggesting the formation of crystalline VOx.
Abstract: Fiber optic temperature sensors were fabricated by depositing vanadium oxide thin films on the tips of optical fibers, and by incorporating vanadium oxide materials into the core of optical fibers. It was found that the properties of the initially amorphous vanadium oxide can be controllably converted to those of crystalline VOx compounds via the plasma arc of a fiber fusion splicer. These crystalline VOx compounds can then be over-coated with SiO2, and subsequently fused with another fiber to form an in-line fiber optic sensor. It was found that a well defined optical absorption edge was formed when the vanadium oxide (VOx) thin films were annealed using the plasma arc of a fusion splicer, suggesting the formation of crystalline VOx. Moreover, it was observed that the spectral position of this absorption edge varied with temperature in a reproducible way. The optical fiber devices described in this paper could also be employed for optical switching applications. Based on the spectral position of the band edge and the Raman spectra of the VOx films, deposited on the fiber optic tips, it was found that these annealed VOx films contained a mixture of different phases of vanadium oxide (VOx), in particular V2O5 and VO2. Furthermore, similar in-line optical fiber switches, based only on the insulator to metal phase transitions of VO2, can be fabricated by following the techniques described in this paper.
15 citations
TL;DR: In this article, vanadium oxide films, deposited on aluminium (Al), titanium (Ti) and tantalum (Ta) metal substrates by pulsed RF magnetron sputtering at a working pressure of 1.5 × 10−2mbar at room temperature are found to display mixed crystalline vanadium dioxide phases.
Abstract: Vanadium oxide films, deposited on aluminium (Al), titanium (Ti) and tantalum (Ta) metal substrates by pulsed RF magnetron sputtering at a working pressure of 1.5 x10−2 mbar at room temperature are found to display mixed crystalline vanadium oxide phases viz., VO2, V2O3, V2O5. The films have been characterized by field-emission scanning electron microscopy, X-ray diffraction, differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy, and their thermo-optical and electrical properties have been investigated. Studies of the deposited films by DSC have revealed a reversible-phase transition found in the temperature range of 45–49 °C.
13 citations
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TL;DR: The effect of uniaxial stress along the c axis on the metal-insulator transition of VO2 has been studied in the form of epitaxial thin films grown on TiO2 (001) and (110) substrates as mentioned in this paper.
Abstract: The effect of uniaxial stress along the c axis on the metal–insulator transition of VO2 has been studied in the form of epitaxial thin films grown on TiO2 (001) and (110) substrates. A large reduction in the transition temperature TMI from 341 K for a single crystal to 300 K has been observed in the film on TiO2 (001) where the c-axis length is compressed owing to an epitaxial stress, while the TMI has been increased to 369 K in the film on TiO2 (110) where the c-axis length is expanded. The correlation between the c-axis length and TMI is suggested: the shorter c-axis length results in the lower TMI.
481 citations
TL;DR: Simulation results suggest that the FS-MOS approach holds considerable promise for being expandable to the port-count values that will be needed in future core-transport lightwave networks.
Abstract: Fiber-optic switches with high port count have emerged as leading candidates for deployment in future optical transport networks, where restoration and provisioning in the optical layer will become increasingly important. This paper reviews the principle and performance of free-space micromachined optical switches (FS-MOS) featuring free-rotating hinged micromirrors. A single-chip FS-MOS that implements the critical function of bridging-essential for restoration in core optical networks is also proposed and demonstrated. The scalability of FS-MOS devices, and the dependence of their insertion losses on mirror-angle, are estimated theoretically. Simulation results suggest that the FS-MOS approach holds considerable promise for being expandable to the port-count values that will be needed in future core-transport lightwave networks.
326 citations
TL;DR: In this paper, the parameters of reactive pulsed laser deposition were successfully optimized for fabrication of vanadium dioxide thin films, and the structural properties of the deposited films were analyzed by x-ray diffraction, while their semiconductor-to-metal phase transitions were studied by electrical resistivity using the four-point technique and infrared transmittance from room temperature up to 100'°C.
Abstract: The parameters of reactive pulsed laser deposition were successfully optimized for fabrication of vanadium dioxide thin films. It is observed that the O2 concentration in Ar gas and the total deposition pressure are critical in stabilizing the single VO2 phase. Thermochromic VO2 and V1−xWxO2 (x=0.014) thin films were synthesized on various substrates (silicon, quartz, and sapphire) at 5% of O2/Ar ratio gas and total pressure of 90 mTorr. The structural properties of the deposited films were analyzed by x-ray diffraction, while their semiconductor-to-metal phase transitions were studied by electrical resistivity using the four-point technique and infrared transmittance from room temperature up to 100 °C. The observed transition temperature was about 36 °C for W-doped VO2 compared to 68 °C for VO2 films. This transition temperature was then lowered by about 22.85 °C per 1 at. % of W added. The temperature coefficient of resistance was about 1.78%/°C for VO2 and about 1.90%/°C for W-doped VO2. Using the pump...
101 citations
TL;DR: In this article, the authors have successfully fabricated two types of 1 × 2 optical switch devices, namely, all-optical switch (VO2/quartz) and electro-optically switch ( VO2/TiO2/ITO/glass) based on the semiconductor-to-metallic phase transition characteristic of vanadium dioxide (VO 2) smart coatings.
Abstract: We have successfully fabricated two types of 1 × 2 optical switch devices, namely, all-optical switch (VO2/quartz) and electro-optical switch (VO2/TiO2/ITO/glass) based on the semiconductor-to-metallic phase transition characteristic of vanadium dioxide (VO2) smart coatings. The VO2 active layer, the TiO2 buffer layer and the ITO transparent conductive electrode used in these devices were achieved by reactive pulsed laser deposition. The optical switching of the fabricated devices was investigated at λ = 1.55 µm. The semiconductor (on) to metallic (off) phase transition was controlled by photo-excitation of VO2 in the case of the all-optical switch and by an external electric field applied between the ITO and the VO2 layer in the case of the electro-optical switch. The extinction ratio (on/off) is found to be much higher for the all-optical switch than for the electro-optical switch. For the all-optical switch, extinction ratios of about 22 and 12 dB are obtained in the transmission and reflection modes, respectively. In the case of the electro-optical switch, the extinction ratio is about 12 dB in the transmission mode and 5 dB in the reflection mode. Finally, to explain our optical switching results, we propose a simple model based on the energy band diagram of VO2 in which the charge density increases under an external excitation (either photo-excitation or an electrical field), and then induces the semiconductor-to-metallic phase transition in the VO2 active layer.
91 citations
TL;DR: In this article, anti-reflection coating on a thermochromic VO 2 film has been studied by means of the RF sputtering and is proposed as a possible solution for the enhancement of luminous transmittance of thermophromic film.
90 citations