I. A. Khrebtov

Modeling and performance of vanadium–oxide transition edge microbolometers

The performance of a VO2 thin-film microbolometer has been investigated. The device is operated within 35°C<T<60°C, in the hysteretic metal-insulator transition region. An algebraic hysteresis model has been used to model the resistance-temperature characteristic of the sensor. It accurately describes the resistance versus temperature characteristics of the material. Employing this model, and in conjunction with established bolometer theory, the responsivity of a VO2 film is calculated and compared with experimental data. Superior performance of the device is achievable under conditions of single pulse incident radiation where the operating point remains on the major hysteresis loop. This results in a pronounced responsivity peak within the center of the metal-insulator transition. Continuous periodic excitation, in contrast, leads to a steadily decreasing and much lower sensitivity at higher temperature, due to the formation of minor hysteresis loops and the loop accommodation process.

Sensitive high‐Tc transition edge bolometer on a micromachined silicon membrane

Superconducting transition edge bolometers on micromachined silicon membranes have been fabricated. The optical response is 580 V/W at a time constant of 0.4 ms. The detectivity D* is 3.8×109 (cm Hz1/2 W−1) at a temperature of 84.5 K and within the frequency regime 100<f<300 Hz. This is one of the fastest composite type bolometers ever reported. Upon thermal optimization, this type of detector should be competitive with state‐of‐the‐art quantum detectors.

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.

Vanadium oxide films with improved characteristics for ir microbolometric matrices

Vanadium oxide (VOx) films intended for use in uncooled IR microbolometric matrices were deposited by reactive magnetron sputtering on silicon substrates. Optimum deposition conditions were determined, which provide for the obtaining of films possessing a current 1/f noise level 3–10 times lower, extended dynamic range, and increased working temperature interval. It was found that the 1/f noise level of the VOx films depends on the VO2 phase content and grain size. It is suggested that the observed 1/f noise is caused by the martensite transformation characteristic of the semiconductor-metal phase transition in VO2.

Figures of merit and optimization of a VO 2 microbolometer with strong electrothermal feedback

The influence of electrothermal feedback and hysteresis on the operation conditions, noise, and performance of a VO2 transition-edge microbolometer has been evaluated. The material undergoes a first-order semiconductor-to-metal phase transition (SMT) within the temperature range 40<T<70 °C. Due to electrothermal feedback, all device parameters, including the required heat-sink temperature, output voltage and current response, response time, linear dynamic range, responsivity, noise, and detectivity, display complex and nonlinear variations with temperature, electrical biasing conditions, input radiation levels, and hysteresis width. In the constant-current mode, the device responsivity extends over a broad temperature range, but under constant-voltage operation it is sharply localized and restricted to the SMT center. Film quality, as represented by the transition and the hysteresis width and the flicker noise magnitude, crucially affects device performance. In the weak hysteretic case and at low 1/f noise levels, the device detectivity improves substantially in both operation modes. The spectral range of the device is largely determined by the optical absorptivity of the VO2 film. For operation within the SMT, it extends well into the far IR wavelength region of the atmospheric window, but is substantially smaller for operation in the semiconducting region.

Noise, bolometric performance and aging of thin high Tc superconducting films on silicon membranes

An experimental study regarding the noise properties of thin superconducting films of composition GdBa2Cu3O7−x on silicon membranes is reported. Noise measurements that include a determination of the Hooge parameter αH as a function of resistance have been carried out at temperatures 78 K 200 K most likely is assigned to an increasing interaction and charge fluctuations between the metallic overlayer and the semiconducting silicon membrane material beneath. The magnetron sputtered epitaxial GdBa2Cu3O7−x films consistently revealed Hooge parameters αH <0.04 near the transition temperature, representing the smallest values ever reported for high Tc-films on silicon substrates. Based on these data, the achievable bolometric detectivity D* of superconducting transition edge microbolometers has been calculated. The model calculations fully confirm recent experimental data obtained for various degrees of thermal isolation.

Nonlinearity and electrothermal feedback of high Tc transition edge bolometers

The effects of electrothermal feedback on the performance of a micromachined superconducting high Tc transition edge bolometer, over a temperature range 85–95 K, have been investigated. The system behaves nonlinearly, due to the variation of the resistance-temperature coefficient β with temperature. Optimum operating points of constant current mode (CCM) and constant voltage mode (CVM) modes vary with temperature and biasing conditions. In CCM, effective response time τeff varies little with temperature. The optimum output signal of CVM occurs at approximately 3–5 K lower temperature within the tail region, where β is maximum. The biasing voltage also displays a maximum, above which the bolometric performance degrades. The CCM exhibits a comparatively limited linear dynamic range. Negative thermal feedback causes a decrease of τeff of up to 2 orders of magnitude in CVM. CCM requires precise thermal stabilization at midtransition. Noise in both modes is limited by the 1/f contribution. Maximum D* values ar...

Calculational modelling of the main characteristics of an uncooled linear microbolometer array

This paper describes a technique for calculating the main characteristics of an uncooled linear microbolometer array. It presents the results of the calculations that were carried out, discusses them, and compares them with the experimental values. It shows that a detectivity of about 10 9 cm Hz 1/2/W can be achieved in microbolometers with a detector area of 46×46 µm at a frequency of 10 Hz and that they can be used as a basis for creating a linear 64-element array of a scanning thermal viewer with frame rate of as much as 1.6 Hz having NETD=0.06 K.

Comparative investigations of the bolometric properties of thin film structures based on vanadium dioxide and amorphous hydrated silicon

A choice of sensitive element material for uncooled microbolometric array dependents on the ultimate array parameters to a great extent. This paper presents the results of studies of sandwich and planar bolometric structures based on aSi:H and VO2 films accordingly. The aSi:H films were fabricated by plasmachemical vapor-phase deposition and VO2 films were prepared by reactive magnetron ion-plasma sputtering. Sandwich structures with area 100 X 100 micrometers have a resistance of 20 k(Omega) and temperature coefficient of resistance (TCR) of approximately equals 2%/K at 25 degree(s)C. Planar structures with operating section dimensions of 100 X 70 micrometers have TCR of 2.9%/K at the same resistance. The methods of contact noise reduction are found for both type structures. Sandwiches constructed to act as an optical cavity absorb 80% of radiation at 8 micrometers wavelength. It is shown that the planar structures absorption of 50 - 80% can be reached in the 8.5 - 10 micrometers band.

Antenna-coupled microbolometers

This paper analyzes the development trends of devices and processes for fabricating antenna-coupled microbolometers for the IR, submillimeter, and millimeter ranges. Depending on the problem to be solved, these thermal detectors can be self-contained or can be built into linear or two-dimensional arrays and can operate at temperatures of 300, 78, and 4 K. The temperature determines the choice of material of the thin-film heat-sensitive element—metal, semiconductor, high-temperature or classical superconductor. The planar antennas used in these detectors provide efficient reception of radiation in the specified spectral range. The achievable parameters and examples of the use of antenna-coupled microbolometers are discussed.