VOx Microbolometer Research Articles

Evaluation of characteristics in VOx microbolometer fabricated by MOD on Si3N4/SiO2 membrane

AbstractVOx thin films were fabricated on Si3N4/SiO2/Si substrates by firing precursor films, which were fabricated by metal‐organic decomposition (MOD), with a reduced pressure. Resistance‐temperature (R‐T) characteristics of the films indicating the phase transition from metal to insulator with about 4 orders of resistance change specified with VO2 (M) were obtained. Furthermore, the films fabricated with a firing temperature of 580‐600°C had temperature coefficient of resistance (TCR) of −2.8 to −2.9 %/K at room temperature. After fabricating VOx microbolometers with 40 × 10 μm2 using the films on Si3N4/SiO2/Si substrates, Si with a thickness of about 340 μm was etched using Deep‐RIE and XeF2 vapor etching from the backside of the substrate. Then, the VOx microbolometer was completed on Si3N4/SiO2 membrane. The VOx microbolometer on Si3N4/SiO2 membrane had a high DC sensitivity of 2310 W−1, which was about 15 times higher than that of the microbolometer on the Si3N4/SiO2/Si substrate.

Low‐noise readout circuit for thermo‐electrical cooler‐less uncooled microbolometer infrared imager

A low-noise analogue frontend readout circuit is presented for VOx microbolometer infrared imager without thermo-electrical cooler. A modified differential mirror structure with substrate temperature and self-heating effect compensation ability is used, targeting below 40 mK noise equivalent temperature difference (NETD) with 17 μm pixel pitch. Noise characteristics are investigated to give an optimal trade-off approach to reach lower NETD at same power consumption compared with traditional readout structures.

Investigated performance of uncooled tantalum-doped VOx floating-type microbolometers

Various tantalum (Ta)-doped vanadium oxide (VOx:Ta) films with various Ta doping contents were deposited on the Si substrates as the sensitive layer of the floating-type microbolometers using a magnetron radio frequency (RF) co-sputtering system. The vanadium (V) target and the tantalum pentoxide (Ta2O5) target were used to deposit the VOx:Ta films. To improve the microbolometer responsivity by effectively reducing the thermal loss from the Si substrates, the floating-type microbolometers were fabricated using bulk micromachining technique. From the X-ray photoelectron spectroscopy (XPS) spectra, except the V2O5 and V6O13, the lower oxygen state of VOx films, such as VO2 and V2O3, were also obtained by doping Ta into the VOx films. Consequently, compared with the VO2 microbolometers, the VOx:Ta microbolometers could operate at a higher operating temperature range. The temperature coefficient of resistance (TCR) and the resistivity of the VOx:Ta (Ta content of 7.63%) films measured by four point probe measurement in heating system were −3.47%/K and 9.32Ω-cm, respectively. The Ta-doped VOx microbolometer revealed a higher responsivity of 341kV/W compared with 106kV/W of the undoped VOx microbolometer.

Fabrication and Evaluation of Thin-Film Spiral-Antenna-Coupled VOx Microbolometer by Metal–Organic Decomposition

A VOx microbolometer coupled with thin-film spiral antenna was fabricated on a fused-quartz substrate by metal–organic decomposition (MOD). The size of the bolometer was 1 ×52 µm2, and the antenna was designed for operating at 75–110 GHz. The DC sensitivity and responsivity of the bolometer were 540 W-1 and 124 V/W at the bias current of 0.5 mA under the irradiation of a 94 GHz electromagnetic wave, respectively. These values were over one order higher than those of the Bi microbolometer, which is conventionally utilized as a detector in terahertz and infrared regions. The antenna-coupled VOx microbolometer with a high responsivity was realized by MOD.

Nanostructured vanadium oxide thin film with high TCR at room temperature for microbolometer

In order to obtain high quality of thermal sensitive material, VOx thin film of high temperature coefficient of resistance (TCR) of 6.5%/K at room temperature has been deposited by reactive ion beam sputtering and post annealing method. AFM and XRD measurements indicate that the VOx thin film with nanostructured crystalline is composed of VO2 and V2O3. The nanostructured VOx microbolometer has been designed and fabricated. The measurement of the film system with TiN absorbing layer indicates that it has about 92% infrared absorption in the range of 8–14μm. The performance of this bolometer, comparing with that of bolometer with common VOx, has a better result. At 20Hz frequency and 10μA bias current, the bolometer with high TCR has reached detectivity of 1.0×109cmHz1/2/W. It also indicates that this nanostructured VOx thin film has not only a higher TCR but also a lower noise than common VOx thin film without annealing.

Infrared Detectors for the Future

In the paper, fundamental and technological issues associated with the development and exploitation of the most advanced infrared detector technologies are discussed. In this class of detectors both photon and thermal detectors are considered. Special attention is directed to HgCdTe ternary alloys on silicon, type-II superlattices, uncooled thermal bolometers, and novel uncooled micromechanical cantilever detectors. Despite serious competition from alternative technologies and slower progress than expected, HgCdTe is unlikely to be seriously challenged for high-performance applications, applications requiring multispectral capability and fast response. However, the nonuniformity is a serious problem in the case of LWIR and VLWIR HgCdTe detectors. In this context, it is predicted that type-II superlattice system seems to be an alternative to HgCdTe in long wavelength spectral region. In well established uncooled imaging, VOx microbolometer arrays are clearly the most used technology. In spite of successful commercialization of uncooled microbolometers, the infrared community is still searching for a platform for thermal imagers that combine aordability, convenience of operation, and excellent performance. Recent advances in microelectromechanical systems have led to the development of uncooled IR detectors operating as micromechanical thermal detectors. Between them the most important are biomaterial microcantilevers.