Bolometric Applications Research Articles

Characterization of platinum and titanium thermistors for terahertz antenna-coupled bolometer applications

Microbolometer is a radiation detector for infrared (IR) and terahertz (THz) waves. The temperature coefficient of resistance (TCR) of the thermistor is a vital factor, as the responsivity is proportional and noise equivalent power (NEP) is inversely proportional to it. The narrow-width effect on TCR and resistivity on two different substrates (SiO2/Si and SiNX/SiO2/Si) for platinum (Pt) and titanium (Ti) thermistor with various design width (DW) = 0.1–5 μm are investigated. Increased resistivity and reduced TCR of the devices with the decreased line width, is observed commonly for both metal and fitted with empirical formulae, which hold well for different substrates. It is evident from electron backscatter diffraction (EBSD) results showing reduced average grain size form Ti film to Ti nanowire (DW = 0.1 μm), that the reduced TCR is not dependent on crystal orientation or phase variation of material but can be correlated with reduced grain size due to reduction of width. The optimum value considering design requirement, thermistor of DW = 0.1 μm and 0.2 μm is used further for the fabrication of microbolometers. It is found that the device with DW = 0.1 μm of Ti thermistor has ∼1.5 times higher electrical responsivity (376 V/W) at maximum allowable current than that with DW = 0.2 μm (254 V/W), which is also ∼11 times higher than device with DW = 0.1 μm of Pt thermistor.

Enhanced bolometric properties of nickel oxide thin films for infrared image sensor applications by substitutional incorporation of Li

This study aims to investigate the influence of substitutionally incorporated Li on sensing performance of nickel oxide films for bolometer applications by comparing Ni1-xO and (LiyNi1-y)1-xO films. From the results of structural analysis, it was confirmed that the film deposited from Li0.2Ni0.8O target contained Li which substitutionally occupies the Ni cation site while maintaining a cubic NiO structure. The substitutionally incorporated Li in nickel oxide can serve as an acceptor providing a hole carrier, like as a structural defect. However, in contrast to the structural defect, the substitutional incorporation of Li made it possible to increase the number of hole carriers in nickel oxide film while maintaining excellent film quality. In addition, the contact resistance with electrode was greatly reduced as a result of the substitutionally incorporated Li. These changes in structural and electrical properties lead to a significant reduction of 1/f noise arisen from the (LiyNi1-y)1-xO film. As a result, the sensing performance of the (LiyNi1-y)1-xO film as evaluated using the (αH/n)1/2/|β| value was nearly 10 times better than that of the Ni1-xO film. Consequently, it can be concluded that the substitutional incorporation of Li can significantly improve the sensing performance of nickel oxide films for bolometer applications.

Graphene oxide reduction by solid-state laser irradiation for bolometric applications

We present a method for reduced graphene oxide (GO) patterning on the surface of GO film by a 445 nm solid-state laser with the adjustable fluence from 0.2–20 kJ cm−2. We demonstrate that the optimal argon concentration in air to obtain good quality reduced GO films is 90%. Varying the laser irradiation energy density allows controlling the resistance and IG/ID and IG/I2D ratios of Raman peak intensities. As a result, we demonstrate the possibility of forming of conductive patterns with a sheet resistance of 189 Ohm/□ and ∼1 μm film thickness by a local reduction of the GO. The fabricated structures reveal excellent bolometric response with a high speed and sensitivity to the radiation in the visible wavelength region.

The effect of bismuth on the structure, magnetic and electric properties of Co2MnO4 spinel multiferroic

Mixed Co2Mn1−xBixO4 (x = 0, x = 0.05 and x = 0.1) samples were prepared by the sol–gel method using the citric acid route and characterized by various techniques. The X-ray diffraction (XRD) and Raman spectroscopic analyses confirmed the formation of inverse spinel cubic structure with Fd3‾m space group. The introduction of Bismuth (Bi) into Co2MnO4 did not modify the ferrimagnetic character of the parent compound Co2MnO4, whereas the field-cooled magnetizations MFC and the Curie temperature Tc decreased when increasing the Bi content. The electrical properties showed an activation energy (Ea) increase caused by the decrease of the double-exchange interaction following the substitution of Mn3+ by Bi3+. Eventually, the temperature coefficient of resistance (TCR) shows significant values for all samples can be investigated also as good candidates for bolometer applications.

Investigation of electron beam lithography effects on metal–insulator transition behavior of vanadium dioxide

Vanadium dioxide (VO2) shows metal–insulator phase transition at nearly 68 °C. This metal–insulator transition (MIT) in VO2 leads to a significant change in near-infrared transmittance and an abrupt change in the resistivity of VO2. Due to these characteristics, VO2 plays an important role on optic and electronic devices, such as thermochromic windows, meta-materials with tunable frequency, uncooled bolometers and switching devices. In this work, VO2 thin films were fabricated by reactive direct current magnetron sputtering in O2/Ar atmosphere on sapphire substrates without any further post annealing processes. The effect of sputtering parameters on optical characteristics and structural properties of grown thin films was investigated by SEM, XRD, Raman and UV/VIS spectrophotometer measurements. Patterning process of VO2 thin films was realized by e-beam lithography technique to monitor the temperature dependent electrical characterization. Electrical properties of VO2 samples were characterized using microprobe station in a vacuum system. MIT with hysteresis behavior was observed for the unpatterned square samples at around 68 °C. By four orders of magnitude of resistivity change was measured for the deposited VO2 thin films at transition temperature. After e-beam lithography process, substantial results in patterned VO2 thin films were observed. In this stage, for patterned VO2 thin films as stripes, the change in resistivity of VO2 was reduced by a factor of 10. As a consequence of electrical resistivity measurements, MIT temperature was shifted from 68 °C to 50 °C. The influence of e-beam process on the properties of VO2 thin films and the mechanism of the effects are discussed. The presented results contribute to the achievement of VO2 based thermochromic windows and bolometer applications.

Resistivity, I–V characteristics and Hall effect in Dy0.5(Sr1-xCax)0.5MnO3 manganites

Dy0.5(Sr1-xCax)0.5MnO3 (x=0 and x=0.3) manganites were synthesized using sol-gel method. Both samples exhibited an insulating behavior in the whole temperature range. Even the application of 5T magnetic fields does not change this state. Conduction mechanisms were also investigated. The I–V characteristics of both samples present Ohmic behavior at minor voltages. Magnetoresistance and electroresistance were also studied. The thermal variation of Hall resistivity of Dy0.5Sr0.5MnO3 was determined in cooling down and warming up processes revealing electron-like type of charge carriers. Temperature coefficient of resistance shows significant values for both systems making them good candidates for bolometer applications.

Structural, magnetic, magnetocaloric and electrical studies of Dy0.5(Sr1−xCax)0.5MnO3 manganites

Based on sol-gel method, the Dy0.5(Sr1−xCax)0.5MnO3 (x=0 and 0.3) manganites were synthesized. Orthorhombic distortion was presented in both samples via X-ray diffraction patterns with Pnma as a space group. Magnetic measurements of both systems illustrate anomalies at around TN(Mn)∼27K for the x=0 sample and 40K for x=0.3, showing antiferromagnetic coupling among Mn-spins. Then, the AC magnetic susceptibility of these systems was investigated to demonstrate the existence of spin glass state. In order to check if these samples can be good candidates for magnetic refrigeration, relative cooling power was determined depicting that the sample with a Ca content x=0.3 can be useful for magnetic refrigeration at cryogenic temperatures with about 133.89J/kg under a magnetic field of 5T. The experimental magnetic entropy change was then treated via Landau theory showing a big discrepancy between the measured and the theoretical magnetic entropy change under 1 and 5T. The antiferromagnetic behavior, which is governed by the super exchange interactions, describes also the insulating character, thus, we discussed the electrical properties and examined the conduction mechanisms. Based on Hall effect measurements, charge careers type was determined to be electron for both samples. Eventually, both systems can be investigated also as good candidates for bolometer applications.

Comparative study of annealing and gold dopant effect on DC sputtered vanadium oxide films for bolometer applications

Vanadium oxide (VOx) thin film has been widely used for IR detectors and it is one of the promising materials for THz detectors due to its high temperature coefficient of resistance (TCR) values. VOx films with proper TCR values have also high resistance and it restricts bolometer performance especially for uncooled bolometers. To overcome this problem, deposition at elevated temperatures or annealing approach has been accepted and used but gold co-deposition approach has been proposed recently. In this study, vanadium oxide films were fabricated on high resistivity silicon substrates by reactive direct current magnetron sputtering in different O2/Ar atmosphere at room temperature. We investigated influence of oxygen partial pressure during deposition process and fabricated VOx thin films with sufficient TCR values for bolometer applications. In order to decrease resistivity of the deposited films, post annealing and gold doping approaches were performed separately. Effect of both post annealing process and gold doping process on structural and electrical properties of VOx thin films deposited at room temperature were investigated and detailed comparison between these methods were presented. We obtained the best possible approach to obtain optimum conditions for the highly reproducible VOx thin films which have the best resistivity and suitable TCR value for bolometer applications.

Realization of a helix-based perfect absorber for IR spectral range using the direct laser write technique

We report the design and fabrication of perfect absorber metasurfaces for infrared spectral range using the direct laser writing technique. The metasurface structures have a helix-based architecture, which has advantages in comparison to traditional planar architectures, but is difficult to fabricate due to complex shapes and the sub-micrometer size of 3D helices comprising them. This challenge was addressed by fabricating dielectric templates of structures using the femtosecond direct laser write technique, which provides spatial resolution close to 100~nm, and subsequently metalizes the templates using gold sputtering. Optical characterization of the fabricated samples reveals resonant absorption in excess of 80\% in the wavelength range of $6-11\,\mu$m in accordance with theoretical expectations. Similar structures may find applications in bolometers, narrow-band thermal detectors and emitters, and infrared energy harvesting devices.

Structural, magnetic and electrical transport properties in electron-doped La0.85Hf0.15MnO3 epitaxial film

Using a pulsed laser deposition method, the electron-doped La0.85Hf0.15MnO3 (LHMO) film with the thickness of 90 nm was epitaxially grown on LaAlO3 (001) single crystal substrate. The structural, magnetic and electrical transport properties of the film have been studied comprehensively. The X-ray diffraction patterns confirm that LHMO film is of single phase, good quality and c axis orientation. The film undergoes a ferromagnetic-like ordering to paramagnetic states at TC=280 K. Moreover, a spin glass behavior observed in the film may be attributed to the strain effects. Using the percolation theory, we have analyzed the resistivity data ρ (T) of the film and given an excellent fit in the whole temperature range. Particularly, large temperature coefficient of resistance of 11.27% K− 1 has been discovered near sub-room-temperature, indicating that LHMO film could be useful for bolometric applications.

Silver/zinc oxide self-assembled nanostructured bolometer

Temperature coefficient of resistance (TCR) is the main figure of merit for bolometric detectors. Reports show that zinc oxide can have TCR values higher than vanadium oxide (VOx) and amorphous silicon (a-Si), which are the most common materials used in bolometric applications, however its high resistivity makes it difficult to match it to read-out electronics. In this work, self-assembled nanostructures of Silver/Zinc oxide (Ag/ZnO) have been fabricated as well as their electrical and optical properties were measured as function of the Ag/ZnO concentration ratio. It was found that the nanostructures with the highest ZnO concentration exhibited a temperature coefficient of resistance as high as −11.8%K−1 near room temperature. Moreover, the TCR values and conductivity of the material can be tuned with the Ag/ZnO concentration ratio. This tuning flexibility allows this material to be better matched to read-out integrated circuits.

Domain Reengineering of the [011]‐Poled PMN–0.35PT Single Crystals for Dielectric Bolometer Arrays

The domain configuration was reengineered with a modified poling procedure for the [011]‐poled single‐domain PMN–0.35PT crystals located at the morphotropic phase boundary. As a consequence, the dielectric constant εr at room temperature was significantly enhanced by more than 10 times to about 18 000, extremely higher than the reported (1 − x)Pb(Mg1/3Nb2/3)O3‐xPbTiO3 ferroelectric crystals. Besides, the decreasing rate of the dielectric constant (dεr/dT) was about 300/K with a temperature coefficient (α) of 1.7%/K, comparable to the BST materials for dielectric bolometer applications. The ferroelectric phase transition behavior was investigated to establish the poling procedure and a thermal hysteresis of about 25°C was indicated across the room temperature for the orthorhombic–tetragonal phase transition, which contributed to the revolution of the domain pattern.

Perspective Material and Applications of Uncooled Metal Bolometers

A new method is proposed to compare the sensitivity of uncooled metal bolometers. This method allows us to conduct a comparative analysis for the sensitivity of uncooled bolometers with metal and metal alloy resistive elements. The experiments showed a twofold superiority in the sensitivity of the TiNi alloy-based bolometer with a resistive element less than $10~\Omega $ in resistance over the identical bolometers based on technologically applicable metals due to improved electrophysical properties. The Ti50.5Ni49.5 bolometer developed to measure the total solar radiation has a higher sensitivity, a higher measuring efficiency, a smaller weight, and size compared with a serial CMP-11 pyranometer, as well as the best environmental protection. The highly sensitive uncooled metal bolometers are shown to be used as an integral part of the optical absorption gas analyzer to provide the control of background mercury vapors in the atmosphere.

Broadband Anti-Reflective Coating Based on Plasmonic Nanocomposite.

We report on the fabrication, the characterization, and the optical simulation of a gold–silica nanocomposite and present its integration into a broadband anti-reflective coating (ARC) for a silicon substrate. The two-layer ARC consists of a nanocomposite (randomly distributed gold cluster in a silica matrix) and a pure silica film. We capitalize on the large refractive index of the composite to impose an abrupt phase change at the interface of the coating to diminish the light reflection from the substrate through the ultrathin nanocoating. The average reflectivity of the silicon can be reduced by such a coating to less than 0.1% in the entire visible spectrum. We experimentally and numerically prove that percolated nanocomposites with an overall thickness of 20 nm can provide anti-reflectivity up to near infrared (NIR). The ARC bandwidth can be shifted more than 500 nm and broadened to cover even the NIR wavelength by changing the volume filling fraction of the gold clusters. The angular sensitivity of thin ultrathin antireflective coating is negligible up to 60°. The present ARC could find applications in thermo-photovoltaics and bolometers.

Room temperature, very sensitive thermometer using a doubly clamped microelectromechanical beam resonator for bolometer applications

We propose a room temperature, all electrical driving and detecting, very sensitive thermometer structure using a microelectromechanical (MEMS) resonator for bolometer applications. We have fabricated a GaAs doubly clamped MEMS beam resonator whose oscillation can be excited and detected by the piezoelectric effect. When a heating power is applied to a NiCr film deposited on the MEMS beam surface, internal thermal stress is generated in the beam, leading to a reduction in the resonance frequency. The present device detects the shift in the resonance frequency caused by heating and works as a very sensitive thermometer. When the resonator was driven by a voltage slightly below the threshold for the nonlinear, hysteretic oscillation, the thermometer showed a voltage responsivity of about 3300 V/W, while keeping a low noise spectral density of about 60 nV/Hz1/2, demonstrating a noise equivalent power of <20 pW/Hz1/2 even at room temperature. The observed effect can be used for realizing high-sensitivity terahertz bolometers for room-temperature operation.

Structural, electronic and magnetic properties of Sm0.55Sr0.45−xAgxMnO3 (0.00 ≤ x ≤ 0.10) system

We have synthesized the single phase polycrystalline sample of silver doped disordered Sm0.55Sr0.45−xAgxMnO3 using the conventional solid state method. They have been investigated by X-ray diffraction for phase evolution and their Rietveld refined X-ray diffraction pattern indicates an increase in lattice parameters and unit cell volume with Ag doping. The magnetization analysis shows the presence of a first order paramagnetic to ferromagnetic transition; the transition temperature and amount of thermal hysteresis decreases on Ag doping. The transport, magneto-transport results indicates decrease in metal to insulator transition, drastic increase in resistance and temperature coefficient of resistance (TCR %) with nearly unaffected colossal magnetoresistance effect which indicates that at least a part of silver is incorporated in the lattice. Scanning electron micrographs indicate that silver has also increased the grain growth sharpness and thus decrease the effect of grain boundary scattering. The significant value of TCR of ∼43% of our samples indicates their applied nature for bolometric application.

Fabrication and characterization of back-incident optically immersed bolometer based on Mn–Co–Ni–O thin films for infrared detection

Optically immersed detectors with high index of refraction lenses were an effective technique to improve the performance of thermistor bolometer for infrared detection. In this paper we described the design and fabrication of back-incident optically immersed bolometer with germanium hemispherical lens using the Mn1.56Co0.96Ni0.48O4 thin films prepared by chemical solution deposition method on amorphous Al2O3 substrate. The characteristics of back-incident immersed bolometer operated at room temperature were investigated. It was found that the performance of the detector was significantly enhanced by the use of germanium hemispherical lens. The fabricated bolometer exhibited noise equivalent temperature of 1.56×10−7K/Hz1/2, responsivity of 3.2×103V/W, and detectivity of approximate 9.2×108cmHz1/2/W at 30Hz. The thermal time constant of 7.3ms was about one third of the non-immersion ones. Field of view of ±35° and optical immersion gain of up to 14 times were also obtained. The results demonstrated that the feasibility of back-incident optically immersed bolometer could be used to uncooled infrared bolometric applications.

Uncooled bolometer based on Mn1.56Co0.96Ni0.48O4 thin films for infrared detection and thermal imaging

Polycrystalline films of Mn1.56Co0.96Ni0.48O4 (MCN) were evaluated for uncooled bolometric applications grown by chemical solution deposition on amorphous Al2O3 substrate. The microstructural characterizations showed that the films were of excellent crystallization and compact surface morphology. Electrical results showed that the temperature coefficient of resistance reached −3.8%/K at 295 K. Low excess noise (normalized Hooge parameter αH/n of 7.6 × 10−28 m3) was achieved owing to the good epitaxial quality of the prepared films. Infrared bolometers were fabricated to evaluate the performance on infrared detection. It exhibited a noise equivalent temperature as low as 2.1 × 10−7 K/Hz1/2, responsivity of 330 V/W, detectivity of 0.6 × 108 cm Hz1/2/W, and noise equivalent power of 3.7 × 10−10 W/Hz1/2 at 30 Hz. The feasibility of the MCN films was demonstrated to be used for uncooled bolometric applications by thermal imaging. One can expect to get a responsivity of about 1 × 103 V/W and detectivity higher than 6 × 108 cm Hz1/2/W at 30 Hz for thermally isolated MCN film bolometer. The results of MCN showed its great potentiality for future room-temperature detection.

Thickness Dependence Study of Electron Beam Evaporated LBMO Manganite Thin Films for Bolometer Applications

La0.7Ba0.3MnO3 (LBMO) thin films with different thicknesses were deposited on Si substrates using an electron beam evaporation technique for bolometer applications. To evaluate the influence of the thickness on their structural, compositional, morphological, and electrical properties, the LBMO thin films were characterized by x-ray diffraction (XRD), energy-dispersive spectroscopy, atomic force microscopy, and a four-probe method. XRD measurements showed that the crystal quality of the LBMO films improved with increasing thickness. The surface morphology revealed that the grain size and surface roughness of the films increased with increasing thickness. The resistivity increased with increasing thickness of the film. The temperature coefficient of resistance of the LBMO films decreased from 5.15%/K to 4.12%/K with increase of the film thickness from 20 nm to 100 nm.

Instant one step synthesis of crystalline nano V2O5 by solution combustion method showing enhanced negative temperature coefficient of resistance

A single phase of orthorhombic nano-vanadium pentoxide (V2O5) is produced using a one pot synthesis method of solution combustion process. The yellow-orange colored powder of V2O5 is obtained instantaneously by this method and has elliptical to spherical like morphology of its platelets. A majority of these particles are in the size range of less than 200nm. As revealed by SAED this simple method of synthesis yields a highly crystalline product with monocrystalline and polycrystalline particles of V2O5 existing in the same matrix. The product shows a negative temperature coefficient of resistance (TCR) value of −3.2%°C−1 and a low hysteresis effect with temperature width of 5°C in response to temperature variations. Such characteristics demonstrate that preparation of V2O5 by this facile method renders it a promising candidate for bolometric applications.