Amorphous silicon and germanium films for uncooled microbolometers

The possibility of using amorphous silicon and germanium films prepared by magnetron sputtering as components in uncooled microbolometers has been analyzed experimentally and results are presented. Amorphous silicon and germanium films having activation energies of 0.135 and 0.2 eV, and resistivities of 50 and 0.4 kΩ·cm, respectively, were fabricated. Pis’ma Zh. Tekh. Fiz. 23, 21–26 (July 12, 1997)     

电容式非制冷红外探测器的设计与热力学特性分析

本文设计了一种基于MEMS工艺的电容式非制冷红外探测,并利用ANSYS对器件的热力学特性进行了分析.使用ANSYS模拟研究了器件温度响应、位移响应与吸收的红外辐射能量的关系,研究了器件结构尺寸对器件性能参数的影响.红外探测器的温度响应和位移响应与吸收的红外辐射能量呈线性关系;随着红外探测器结构尺寸的增加,其温度响应度、位移响应度、热时间常数都随之增加,探测能力增强,但瞬态响应特性降低;当铝膜与氮化硅层的厚度比为0.5～0.6时,器件的位移响应度最大.     

Performance of a long-wave infrared hyperspectral imager using a Sagnac interferometer and an uncooled microbolometer array

Field and laboratory measurements using an interferometer spectrometer based on the Sagnac interferometer using a microbolometer array detector are presented. Remotely obtained signatures collected with this instrument and with a cryogenic IR spectrometer are compared and shown to closely correspond. Ground-to-ground and air-to-ground image products are presented that demonstrate the image quality of the sensor. Signal-to-noise measurements are presented and compared with a simple parametric performance model that predicts the sensor performance. The performance model is used to predict the performance of this technology when equipped with cooled detectors.     

An object detection strategy for uncooled infrared imagery

Abstract

An overall strategy for the very difficult problem of object detection using uncooled infrared (UCIR) sensors is discussed. The UCIR sensors are based on micro-bolometer technology and thus differ significantly from cooled infrared sensors that employ photon-counting detectors. As such, UCIR imagery tends to be very low contrast, since the sensor operates over a broad spectral band; and blurry, because of the long integration times. Ideally, the UCIR imagery would be preprocessed using an appropriate image reconstruction/restoration algorithm. If the sources of image degradation are understood and lend themselves to accurate modelling, the image reconstruction can be solved as an inverse problem. Most often this is not the case and the problem is solved using minimization approaches, such as blind deconvolution. Because image reconstruction/restoration approaches tend to be very throughput intensive, they are rarely performed in a tactical environment. More typically, a detection algorithm is applied directly to the UCIR imagery. In this paper, Local Singular Value Decomposition (LSVD) is evaluated for anomaly detection. LSVD uses local statistics to identify anomalous regions and is very good at identifying local texture differences; it appears to work quite well on UCIR imagery. Target detection results are presented for a simulated data set.     

Optical response of laser-doped silicon carbide for an uncooled midwave infrared detector

An uncooled mid-wave infrared (MWIR) detector is developed by doping an n-type 4H-SiC with Ga using a laser doping technique. 4H-SiC is one of the polytypes of crystalline silicon carbide and a wide bandgap semiconductor. The dopant creates an energy level of 0.30 eV, which was confirmed by optical spectroscopy of the doped sample. This energy level corresponds to the MWIR wavelength of 4.21 μm. The detection mechanism is based on the photoexcitation of electrons by the photons of this wavelength absorbed in the semiconductor. This process modifies the electron density, which changes the refractive index, and, therefore, the reflectance of the semiconductor is also changed. The change in the reflectance, which is the optical response of the detector, can be measured remotely with a laser beam, such as a He-Ne laser. This capability of measuring the detector response remotely makes it a wireless detector. The variation of refractive index was calculated as a function of absorbed irradiance based on the reflectance data for the as-received and doped samples. A distinct change was observed for the refractive index of the doped sample, indicating that the detector is suitable for applications at the 4.21 μm wavelength.     

Heat sensitive property of sputtered titanium oxide thin films for uncooled IR detector application

Titanium oxide (TiO_x) thin films were deposited on thermally grown Si₃N₄-film-coated Si substrates by dc reactive magnetron sputtering. The crystallographic structure, microscopic morphology, electrical resistivity, temperature coefficient of resistance (TCR) and activation energy of the films were proven as functions of the oxygen partial pressure (pO₂) and substrate temperature (T _s ). The mixed valence TiO_x thin films deposited with temperature from 30 to 250 °C in different pO₂ present various electrical properties even though all the samples are amorphous. The TCR and activation energy of the films vary with different pO₂ and T _s . It has been demonstrated that the sputtered TiO_x films are promising heat sensitive materials for uncooled Infrared detector application.     

Amorphous silicon as hydrogen glass

The hydrogen in hydrogenated amorphous silicon (a-Si: H) makes it behave like a hydrogen glass. Above a temperatureT _E, which is analogous to the glass transition temperature, the hydrogen is able to move more freely than belowT _E. This motion of hydrogen is believed to be responsible for the observed thermal and light induced metastabilities in a Si: H. However, the changes in the microstructure of the bonded hydrogen upon thermal quenching are found to influence the electronic properties of a-Si: H, in a manner, which is different from light soaking. Our studies suggest that the light soaking changes the potential fluctuations in lithium doped a-Si: H, whereas the thermal quenching does not.     

Amorphous silicon twin photodiode structure for differential current measurements

In this paper we present a new amorphous silicon structure called “twin photodiode” constituted by two p–i–n series connected photodiodes biased at the same reverse voltage. The structure takes advantage of the differential current measurement to reveal very small variations of photocurrent in a large background current signal. The removal of the background allows us to increase the dynamic range of the input signal and the sensitivity of the detection system. In addition, the differential approach allows us to reduce the common mode signal due to the effect of temperature variations and instability of light source intensity.We have fabricated several twin structures for detection of ultraviolet radiation with different geometries utilizing a four mask-step process. Experimental results have demonstrated the ability of our structure to detect differential currents three orders of magnitude lower than the current of each sensor. The achieved common mode rejection ratio keeps constant with reverse bias voltage and increases with increasing wavelengths, varying from 30 dB nm at 254 nm to 42 dB at 365 nm.     

Amorphous silicon exhibits a glass transition

Amorphous silicon is a semiconductor with a lower density than the metallic silicon liquid. It is widely believed that the amorphous-liquid transition is a first-order melting transition. In contrast to this, recent computer simulations and the experimental observation of pressure-induced amorphization of nanoporous silicon have revived the idea of an underlying liquid-liquid phase transition implying the existence of a low-density liquid and its glass transition to the amorphous solid. Here we demonstrate that during irradiation with high-energy heavy ions amorphous silicon deforms plastically in the same way as conventional glasses. This behaviour provides experimental evidence for the existence of the low-density liquid. The glass transition temperature for a timescale of 10 picoseconds is estimated to be about 1,000 K. Our results support the idea of liquid polymorphism as a general phenomenon in tetrahedral networks.     

Amorphous silicon coatings with silver nanoparticles

We describe a plasma-ion sputtering technology for obtaining amorphous silicon coatings containing dispersed silver nanoparticles with average dimensions of 20–30 nm. Results of X-ray diffraction and electron-microscopic investigations of these coatings are presented, and a possible mechanism of silver nano-particle formation from 2- to 3-nm-sized nanoclusters is considered.     

Electrical and optical properties of reactive sputtered TiO x thin films for uncooled IR detector applications

Nanostructured titanium oxide (nano-TiO _x ) thin films for uncooled IR detectors were fabricated by dc reactive magnetron sputtering and post-deposition annealed in oxygen atmosphere. The crystalline structure and surface morphology were characterized by glancing incidence X-ray diffraction (GIXRD) and field emission scanning microscopy. The results of GIXRD measurements indicate that TiO _x thin film deposited at room temperature is amorphous. A mixture of anatase and rutile nanocrystalline structure phase were present in oxygen annealed TiO _x thin film. A weak absorption peak around 438 cm^?1 corresponding to Ti–O stretching vibration is observed by Fourier transform infrared spectroscopy with annealed TiO _x thin film. The X-ray photoelectron spectra reveals Ti³⁺ and Ti⁴⁺ ions are coexisting in TiO _x films. The optical spectra of the films indicate that the optical absorption edge of the nano-TiO _x film exhibits a red shift compared to the as-deposited film. Furthermore, compared to bulk TiO _x , a blue shift was observed in both of the deposited and annealed films due to quantum size effect. The dependence of resistivity on temperature reveals both the absolute value of temperature coefficient of resistivity (TCR) and activation energy of TiO _x thin film increase significantly after annealing in oxygen.     

Pyroelectric properties of arrayed BaTiO3 system thick film for uncooled IR detector

The Sr and Ca added to BaTiO₃ in order to shift transition temperature near room temperature. The donor (Yb₂O₃) and acceptor (MnCO₃) impurities were added to the (Ba,Sr,Ca)TiO₃ powder for the improvement of structural and electrical properties. The (Ba,Sr,Ca)TiO₃ powder was made by sol-gel method and the thick films were fabricated by screen-printing. We fabricated array type thick films. The 1 mm × 3 mm array thick films were arranged 2 × 8. Relative dielectric constant and dielectric loss of Yb₂O₃ 0.1 mol% doped (Ba,Sr,Ca)TiO₃ array thick film were 1068 and 2.8%, respectively at Curie temperature, 44 °C. Pyroelectric coefficient and F.M.D* showed 21.7 × 10⁻⁹ C/cm² K and 3.2 × 10⁻⁹ C cm/J, respectively.     

IR spectroscopic study of hydrogenated silicon layers

Proton-implanted (100) KEF-4.5 (phosphorus-doped) silicon wafers 460 μm in thickness have been studied by IR spectroscopy in an on-axis geometry. The implantation process has been run at increased proton energies and current densities to rather high implant doses, up to 7.1 × 10¹⁷ H⁺/cm². The results are used to identify the structure of chemical bonds in the hydrogen centers produced by the implantation and subsequent annealing at 550°C. We show that the assignment of absorption bands to particular Si-H _x (x = 1–3) bonds must take into account the substrate temperature during the implantation process and the annealing temperature.     

Amorphous hydrogenated silicon films prepared from a glowdischarge

From a detailed study of electrical and optical properties of amorphous hydrogenated silicon prepared from a mixture of 10% silane and 90% hydrogen, it is shown that the properties of the films compare favourably with the best reported results on those prepared from 100% silane.     

用于微测辐射热探测器的纳米VO2薄膜

用离子束溅射和后退火工艺制备了一种适用于微测辐射热探测器热敏材料的新型纳米结构二氧化钒(VO2)薄膜材料,薄膜具有平均粒度8 nm,在半导体相区具有电阻温度系数(TCR)为-7%/K,性能高于传统的VO2材料(平均粒度为1-2μm,在半导体相区具有TCR约为-2%/K).基于纳米结构的VO2薄膜材料的器件比基于传统的VO2薄膜材料具有更高的性能,而两者的噪声基本相当.     

A protein microbolometer for focal plane arrays

 Conventional forward-looking infrared (FLIR) devices made of a cooled platinum silicide, cooled mercury-cadmium-telluride, or indium antimonide are costly, in part, because they require an initial cool-down period and need additional power for a cooling pump. Using proteins and DNAs in an uncooled microbolometer will significantly improve the performance of the current technology. Received: 23 October 1998 / Reviewed and accepted: 7 December 1998     

Amorphous ferroelectric thin film capacitive device for hydrogen detection

Hydrogen is a promising alternative energy source for next generation automobile engines that meet the concern of energy shortage and global environmental pollution. Hydrogen detection is an important associated technology to be developed. The recently developed amorphous ferroelectric thin film capacitive gas sensors with a largely improved sensitivity to hydrogen show a great potential for this associated technology. This review presents an overall picture of amorphous ferroelectric thin film hydrogen gas sensors. It focuses on the correlation among processing, microstructural evolution and electrical properties of amorphous ferroelectric thin films. An attempt is made to detail the hydrogen sensitivity and transient response of various prototype capacitive devices with respect to the quality of the films and the hydrogen kinetic processes in the Pd/ferroelectric heterostructure. Recent advances on the hydrogen interface-blocking model for amorphous ferroelectric gas sensors are also described.     

Thermal drift compensation method for microbolometer thermal cameras

We propose a new method of compensation for drifts in thermal cameras using a filter in place of a shutter. The latter method requires periodically closing the camera, thus causing the images to appear frozen frequently. Our technique of replacing the shutter with a filter eliminates this frozen image problem. In this paper we discuss the principles of the new method and present the obtained results.     

Amorphous and nanocrystalline silicon growth on carbon nanotube substrates

In this study, smooth and conformal hydrogenated silicon thin films are examined and analyzed on various multi-walled carbon nanotube (MWCNT) substrates. The films are deposited using radio-frequency plasma-enhanced chemical vapor deposition with He dilution and parameters that are heavily in the γ regime. It is proposed that high-energy plasmas with limited penetration depth can induce crystallization to occur on MWCNT substrates of varying active surface areas. The samples presented exhibit properties that are promising for energy applications, including photovoltaics and lithium-ion batteries and have been studied using scanning electron microscopy, Raman spectroscopy, X-ray diffraction, UV-Vis spectrophotometry, four-point probe measurements, and Fourier transform infrared spectroscopy.