Determination of Thermal Parameters of Vanadium Oxide Uncooled Microbolometer Infrared Detector

Vanadium oxide thin films are the potential candidates for uncooled microbolometers due to their high temperature coefficient of resistance (TCR) at room temperature. A 2D array of 10-element test microbolometer without air-gap thermal isolation structure was fabricated with pulsed laser deposited vanadium oxide as IR sensing layer for the first time. Infrared responsivity of the uncooled microbolometer was evaluated in the spectral region 8-15 μm. The device exhibits responsivity of about 12 V/W at 30 Hz chopper frequency for 20 μA bias current. Thermal time constant (τ), Thermal conductance (G) and thermal capacitance (C) are the thermal parameters characterize the performance of the uncooled microbolometer infrared detectors are determined as 15 ms, ～10^-3 W/K and ～3.5 × 10^-5 J/K respectively. The influence of the thermal parameters on the performance of the microbolometer is discussed.     

Monolithic Uncooled 8 × 8 Bolometer Arrays Based on Poly-SiGe Thermistor

This paper presents a monolithic uncooled 8 × 8 bolometer array with polycrystalline silicon-germanium (poly-SiGe) thermistors as active elements. The poly-SiGe films are deposited by ultrahigh vacuum vapor deposition (UHV/CVD) system and the dependence of the temperature coefficient of resistance (TCR) on annealing temperature has been investigated. To decrease the thermal conductance of the bolometer, the poly-SiGe thermistor was formed on a four leg suspended microbridge. The improved porous silicon micromachining techniques described here enable the integration of the bolometer array with the MOS readout circuitry. The measurements and calculations show that the mean responsivity is 1.07 × 10⁴ V/W with an uncorrected uniformity of 10.5% and a thermal response time of 10.5 ms, and the detectivity of 3.75 × 10⁸ cm Hz^1/2/W is achieved at a chopping frequency of 30 Hz and a bias voltage of 5 V.     

High Tc superconducting linear array ir detectors using YBa2Cu3O7-δ thin films

8-element linear array IR detectors based on high Tc superconducting films have been fabricated. The thin films were deposited by magnetron sputtering onZrO ₂ substrates and patterned by standard photolithographic technique forming microbridge structure. An average detectivity of 1.85 × 10⁹ cmHz ^1/2 W^?1 with a variance of less than 20% in the detector-to-detector detectivity of the array has been obtained at the operating temperature of 84K. A bolometric response mechanism has been discussed.     

锰钴镍氧薄膜热敏型多元红外探测器研制

通过光刻和湿化学腐蚀工艺,成功制作出规格为2×8的多元锰钴镍氧薄膜红外探测器件.测试表明,室温下锰钴镍氧薄膜材料负电阻温度系数达-3.8%K-1.10 Hz调制频率和±15 V电压偏置条件下,线列器件典型探测元黑体响应率为107 V/W,探测率为2×107cmHz1/2/W,8元器件响应不均匀度为5.9%.实验结果表明锰钴镍氧薄膜焦平面器件制备的可行性,有可能作为新型室温全波段探测器件得到应用.     

Fabricating Microbolometer Array on Unplanar Readout Integrated Circuit

In this paper, the integration of an experimental 32 × 32 uncooled IR microbolometer array with an unplanar CMOS Readout Integrated Circuit (ROIC) is presented. A vanadium oxide film fabricated by low temperature reactive ion beam sputtering is utilized as thermal-sensitive material in the bolometric detectors Before the integration, the unplanar ROIC for commercial use is first planarized by bisbenzocyclobutene film, then a electroless nickel-plating on ohmic contact areas is accomplished. Finally the bolometer array is fabricated using a micromachining process, which is completely compatible with CMOS technology. Measurements and calculations for the as-fabricated samples show that the responsivity of 1.4 × 10⁴ V/W and the detectivity of 2.1 × 10⁸cmHz^1/2W^?1 and a thermal response time of 10ms are obtained at a pulse bias of IV.     

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.     

Sb2Te3 and Bi2Te3 Thin Films Grown by Room-Temperature MBE

Sb₂Te₃ and Bi₂Te₃ thin films were grown on SiO₂ and BaF₂ substrates at room temperature using molecular beam epitaxy. Metallic layers with thicknesses of 0.2?nm were alternately deposited at room temperature, and the films were subsequently annealed at 250°C for 2?h. x-Ray diffraction and energy-filtered transmission electron microscopy (TEM) combined with high-accuracy energy-dispersive x-ray spectrometry revealed stoichiometric films, grain sizes of less than 500?nm, and a texture. High-quality in-plane thermoelectric properties were obtained for Sb₂Te₃ films at room temperature, i.e., low charge carrier density (2.6?×?10¹⁹?cm^?3), large thermopower (130???V?K^?1), large charge carrier mobility (402?cm²?V^?1?s^?1), and resulting large power factor (29???W?cm^?1?K^?2). Bi₂Te₃ films also showed low charge carrier density (2.7?×?10¹⁹?cm^?3), moderate thermopower (?153???V?K^?1), but very low charge carrier mobility (80?cm²?V^?1?s^?1), yielding low power factor (8???W?cm^?1?K^?2). The low mobilities were attributed to Bi-rich grain boundary phases identified by analytical energy-filtered TEM.     

Industrial prospects of Pb1 − x Sn x Te:In with x > 0.3 solid solutions for photodetectors with extended sensitivity spectral range

Photoelectric properties of Pb_{1 ? x} Sn _x Te:In films with composition x > 0.3 in the temperature range from 4.2 to 80 K have been investigated. High sample sensitivity to black-body radiation has been discovered at the temperature of helium, and as the temperature of the radiation source decreases the sensitivity increases, which can be connected with the optical-frequency transition in the short-wavelength infrared and terahertz spectral range. The detectivity value D* = 8.2 × 10¹⁶ cm · Hz^1/2/W corresponding to the NEP = 3.1 × 10^?18 W/Hz^1/2, has been obtained at detector temperature 4.2 K and T _BBR = 15 K.     

Specific features of photoconductivity in thin n-PbTe:Ga epilayers

Photoconductivity and transient processes in thin (0.2–0.3 µm) n-PbTe:Ga epilayers were studied. The films were grown by the hot-wall technique on BaF₂ 〈111〉 substrates. Photoelectric properties of the samples were investigated in the temperature range from 4.2 to 300 K. A GaAs light-emitting diode and miniature incandescent lamp were used as sources of pulsed and continuous infrared radiation, respectively. The most important characteristic of the films is the very wide temperature range of photosensitivity. At an illumination power density of 10^?5 to 10^?4 W/cm², the temperature at which the films become photosensitive T _C is as high as 150 K, which exceeds T _C for thicker films (2–3 µm) and high-resistivity single crystals of n-PbTe:Ga by 40 and 70 K, respectively. An analysis of the transient behavior of photoconductivity shows that photoexcited carriers are uniformly distributed over the volume of the thin films. A barrier for recombination of nonequilibrium charge carriers was estimated for slow relaxation processes.     

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.     

Room Temperature Bolometric Applications Using Manganese Oxide Thin Films

We report the optical responses of magnetic manganese oxide La_2/3Ca_1/3MnO_δ thin films at room temperature. The voltage responses to a He-Ne laser at the wavelength of 0.63 μm and incident infrared (IR) power at the wavelength of 8-14 μm were measured. The measured signals were attributably to a bolometric response due to the heating of the sample by radiation. We report the optical responses in La_2/3Ca_1/3MnO_δ thin films as a function of chopping frequency and bias current. The noise behavior around room temperature was also discussed. It is suggested that perovskite manganese oxide thin films are suitable candidates for uncooled optical detectors.     

Crystallization behavior and ferroelectric properties of PbTiO<Subscript>3</Subscript>/Ba<Subscript>0.85</Subscript>Sr<Subscript>0.15</Subscript>TiO<Subscript>3</Subscript>/PbTiO<Subscript>3</Subscript> sandwich thin film on Pt/Ti/SiO<Subscript>2</Subscript>/Si substrates

A PbTiO₃/Ba_0.85Sr_0.15TiO₃/PbTiO₃ (PT/BST15/PT) sandwich thin film has been prepared on Pt/Ti/SiO₂/Si substrates by an improved sol-gel technique. It is found that such films under rapid thermal annealing at 700°C crystallize more favorably with the addition of a PbTiO₃ layer. They possess a pure, perovskite-phase structure with a random orientation. The polarization-electric field (P-E) hysteresis loop and current-voltage (I-V) characteristic curves reveal that a PT/BST15/PT film exhibits good ferroelectricity at room temperature. However, no sharp peak, only a weak maximum, is observed in the curves of the dielectric constant versus temperature. The dielectric constant, loss tangent, leakage current density at 20 kV/cm, remnant polarization, and coercive field of the PT/BST15/PT film are 438, 0.025, 1.3 × 10⁻⁶ Acm⁻², 2.46 μCcm⁻², and 41 kVcm⁻¹, respectively, at 25°C and 10 kHz. The PT/BST15/PT film is a candidate material for high sensitivity elements for uncooled, infrared, focal plane arrays (UFPAs) to be used at near ambient temperature.     

Thermo-Sensitive Ba0.64Sr0.36TiO3 Thin Film Capacitors for Dielectric Type Uncooled Infrared Sensors

Ba_0.64Sr_0.36TiO₃ (BST) thin films are prepared on Pt/Ti/SiO₂/Si₃N₄/SiO₂/Si substrates by a sol-gel method. Thermo-sensitive BST thin film capacitors with a Metal-Ferroelectrics-Metal (M-F(BST)-M) structure are fabricated as the active elements of dielectric type uncooled infrared sensors. XRD are employed to analyze the crystallographic structures of the films. AFM observations reveal a smooth and dense surface of the films with an average grain size of about 35 nm. Rapid temperature annealing (RTA) process is a very efficient way to improve crystallization quality. The preferable annealing temperature is 800°C for 1 min. The butterfly shaped C-V curves of the capacitors indicate the films have a ferroelectric nature. The dielectric constant and dielectric loss of the films at 100 kHz are 450 and 0.038, respectively. At 25°C, where the thermo-sensitive capacitors work, the temperature coefficient of dielectric constant (TCD) is about 5.9 %/°C. These results indicate that the capacitors with sol-gel derived BST thin films are promising to develop dielectric type uncooled infrared sensors.     

Reactive Ion Beams Sputtering of Vanadium Oxides Films for Uncooled Microbolometer

Vanadium oxides thin films for uncooled bolometric detectors have been fabricated on Si₃N₄-film-coated Si substrates by low temperature reactive ion beam sputtering in a controlled oxygen atmosphere. The typical growth temperature is kept at 200°C during sputtering, which is compatible with the post-CMOS technology. The as-deposited film exhibits sheet resistance and temperature coefficient resistant of 32 kΩ and ?0.025 K^?1 at room temperature, respectively.     

Injection photodiode based on an n-CdS/p-CdTe heterostructure

The possibility of developing injection photodiodes with a tunable/reconfigurable? photosensitivity spectrum in the spectral range of 500–800 nm based on an n-CdS/p-CdTe heterostructure is shown. It is established that such a structure in the short-wavelength region λ = 500 nm has the highest spectral sensitivity S _λ ≈ 3 A/W in the forward direction at a bias voltage of V = +120 mV and S _λ ≈ 2 A/W in the reverse direction at a bias voltage of V = ?120 mV. The integrated sensitivity of the device is S _int = 2 400 A/lm under illumination with white light E = 3 × 10^?2 lx, at a bias voltage of V = +4.6 V, and temperature of T = 293 K. Upon illumination with the monochromatic light of an LG-75 laser with the wavelength λ = 625 nm, S _int = ?1400 A/W (illumination power P = 18 × 10^?6 W/cm², bias voltage V = +4.6 V, and temperature T = 293 K). High values of S _λ and S _int provide the highly efficient transformation of light energy into electrical energy at low illumination levels (P < 18 × 10^?6 W/cm²).     

Properties of V–Ce mixed-oxide thin films deposited by RF magnetron sputtering

Thin films of vanadium cerium mixed oxides are good counter-electrodes for electrochromic devices because of their passive optical behavior and very good charge capacity. We deposited thin films of V–Ce mixed oxides on glass substrates by RF magnetron sputtering under argon at room temperature using different power settings. The targets were pressed into pellets of a powder mixture of V₂O₅ and CeO₂ at molar ratios of 2:1, 1:1, and 1:2. For a molar ratio of 2:1, the resulting crystalline film comprised an orthorhombic CeVO₃ phase and the average grain size was 89 nm. For molar ratios of 1:1 and 1:2, the resulting films were completely amorphous in nature. Scanning electron microscopy images and energy-dispersive X-ray spectroscopy data confirmed these results. The optical properties of the films were studied using UV-Vis-NIR spectrophotometry. The transmittance and indirect allowed bandgap for the films increased with the RF power, corresponding to a blue shift of the UV cutoff. The average transmittance increased from 60.9% to 85.3% as the amount of CeO₂ in the target material increased. The optical bandgap also increased from 1.94 to 2.34 eV with increasing CeO₂ content for films prepared at 200 W. Photoacoustic amplitude (PA) spectra were recorded in the range 300–1000 nm. The optical bandgap was calculated from wavelength-dependent normalized PA data and values were in good agreement with those obtained from UV-Vis-NIR data. The thermal diffusivity calculated for the films increased with deposition power. For thin films deposited at 200 W, values of 53.556×10⁻⁸, 1.069×10⁻⁸, and 0.2198×10⁻⁸ m²/s were obtained for 2:1, 1:1, and 1:2 V₂O₅/CeO₂, respectively.     

Improved Thermoelectric Performance of Free-Standing PEDOT:PSS/Bi2Te3 Films with Low Thermal Conductivity

Free-standing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT: PSS)/Bi₂Te₃ thermoelectric (TE) composite films have been successfully prepared by a simple physical mixing method with different contents of Bi₂Te₃. x-Ray diffraction (XRD) and scanning electron microscopy were used to analyze the phase composition and microstructure of the composite films. Their TE performance from 100 K to 300 K was systematically investigated. The maximum electrical conductivity of the composite polymer film reached up to 421 S/cm when the film contained 10 wt.% Bi₂Te₃, corresponding to the highest power factor of 9.9 μW/m/K², while their Seebeck coefficient fluctuated smoothly in a tiny range (14.2 μV/K to 18.6 μV/K). In addition, a relatively low thermal conductivity of 0.07 ± 0.02 W/m/K has been obtained. The maximum figure of merit of the composite reached up to 0.04 at room temperature, which is a relatively high value in the organic TE field.     

Post-annealing Effect on Microstructures and Thermoelectric Properties of Bi0.45Sb1.55Te3 Thin Films Deposited by Co-sputtering

p-Type Bi_0.45Sb_1.55Te₃ thermoelectric (TE) thin films have been prepared at room temperature by a magnetron cosputtering process. The effect of postannealing on the microstructure and TE properties of Bi_0.45Sb_1.55Te₃ films has been investigated in the temperature range from room temperature to 350°C. x-Ray diffraction analysis shows that the annealed films have polycrystalline rhombohedral crystal structure, and the average grain size increases from 36?nm to 64?nm with increasing annealing temperature from room temperature to 350°C. Electron probe microanalysis shows that annealing above 250°C can cause Te reevaporation, which induces porous thin films and dramatically affects electrical transport properties of the thin films. TE properties of the films have been investigated at room temperature. The hole concentration shows a trend from descent to ascent and has a minimum value at the annealing temperature of 200°C, while the Seebeck coefficient shows an opposite trend and a maximum value of 245?μV?K^?1. The electrical resistivity monotonically decreases from 19.8?mΩ?cm to 1.4?mΩ?cm with increasing annealing temperature. Correspondingly, a maximum value of power factor, 27.4?μW?K^?2?cm^?1, was obtained at the annealing temperature of 250°C.     

Improvement on low-temperature deposited HfO2 film and interfacial layer by high-pressure oxygen treatment

In this study, high-pressure oxygen (O₂ and O₂ + UV light) technologies were employed to effectively improve the properties of low-temperature-deposited metal oxide dielectric films and interfacial layer. In this work, 13 nm HfO₂ thin films were deposited by sputtering method at room temperature. Then, the oxygen treatments with a high-pressure of 1500 psi at 150 °C were performed to replace the conventional high temperature annealing. According to the XPS analyses, integration area of the absorption peaks of O-Hf and O-Hf-Si bonding energies apparently raise and the quantity of oxygen in deposited thin films also increases from XPS measurement. In addition, the leakage current density of standard HfO₂ film after O₂ and O₂ + UV light treatments can be improved from 3.12 × 10⁻⁶ A/cm² to 6.27 × 10⁻⁷ and 1.3 × 10⁻⁸ A/cm² at |Vg| = 3 V. The proposed low-temperature and high pressure O₂ or O₂ + UV light treatment for improving high-k dielectric films is applicable for the future flexible electronics.     

Influence of Substrate Temperature on Structural and Thermoelectric Properties of Antimony Telluride Thin Films Fabricated by RF and DC Cosputtering

Antimony and tellurium were deposited on BK7 glass using direct-current magnetron and radiofrequency magnetron cosputtering. Antimony telluride thermoelectric thin films were synthesized with a heated substrate. The effects of substrate temperature on the structure, surface morphology, and thermoelectric properties of the thin films were investigated. X-ray diffraction patterns revealed that the thin films were well crystallized. c-Axis preferred orientation was observed in thin films deposited above 250°C. Scanning electron microscopy images showed hexagonal crystallites and crystal grains of around 500 nm in thin film fabricated at 250°C. Energy-dispersive spectroscopy indicated that a temperature of 250°C resulted in stoichiometric Sb₂Te₃. Sb₂Te₃ thin film deposited at room temperature exhibited the maximum Seebeck coefficient of 190 μV/K and the lowest power factor (PF), S ² σ, of 8.75 × 10⁻⁵ W/mK². When the substrate temperature was 250°C, the PF increased to its highest value of 3.26 × 10⁻³ W/mK². The electrical conductivity and Seebeck coefficient of the thin film were 2.66 × 10⁵ S/m and 113 μV/K, respectively.