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.
Numerical and experimental modeling of the characteristics (sensitivity, constant time, noise properties) of high-<i>T<sub>c</sub></i> transition edge superconducting bolometers, operating in the various modes with an electrothermal feedback, are carried
out: the mode with constant bias current, i.e. passive positive electrothermal feedback, the mode with constant bias
voltage, i.e. passive negative electrothermal feedback and the mode with active electronic negative electrothermal
feedback . It is shown, that in the modes with negative electrothermal feedback it is possible essentially to reduce
constant time of bolometers till 5-15 of times in at some prize of the noise equivalent power on high frequencies. The
estimation of influence of various noise components on a performance of the bolometers, operating with positive or
negative electrothermal feedbacks, is carried out at the variation of bolometer parameters.
This paper presents the structure and technology of 65- elements linear array of membrane type microbolometers, and the research results of its properties. DC biased microbolometers with VO<SUB>x</SUB> thermosensitive layer have detectivity of 5x10<SUP>7</SUP> cm/Hz<SUP>1/2</SUP>W at 12.5 Hz at 12.5 Hz frequency, and response time of 3 ms. The ways of improvement of developed linear array sensitivity are planed.
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 VO<SUB>2</SUB> films accordingly. The aSi:H films were fabricated by plasmachemical vapor-phase deposition and VO<SUB>2</SUB> 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.
The results of experimental and theoretical investigations of the noise properties of high-Tc superconducting films and bolometers are reported. YBaCuO and GdBaCuO films produced by magnetron and laser deposition on various substrates were studied. The effect of various noise components on the noise equivalent power (NEP) of different bolometers is considered. Structural, noise and critical current properties were investigated. Using the laser ablation YBaCuO films with very low noise Hooge's parameter close to 2 X 10<SUP>-4</SUP> was obtained. Experimental data are discussed on basis of the modern excess low frequency l/f models. Besides, the noise measurements of antenna YBaCuO microbolometers on NdGaO<SUB>3</SUB> substrate and GdBaCuO bolometers on Si-membrane are reported. The NEP equals 1.2 X 10<SUP>-11</SUP> W/Hz<SUP>1/2</SUP> at response time of 0.3 microsecond(s) for microbolometer and D* equals 3.8 X 10<SUP>9</SUP> cmHz<SUP>1/2</SUP>W<SUP>-1</SUP> at response time of 0.45 ms for bolometer on Si-membrane were reached. NEP of the bolometers is limited by only the phonon noise.
An infrared detector system based on high-T<SUB>c</SUB> superconducting (HTS) membrane bolometer is reported. Superconducting transition-edge bolometer has been manufactured by silicon micromachining using an epitaxial GdBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-x</SUB> film on an epitaxial yttria- stabilized zirconia buffer layer on silicon. The active area of the element is 0.85 X 0.85 mm<SUP>2</SUP>. The membrane thickness is 1 micrometers , those of the buffer layer and HTS films are 50 nm. The detectivity of bolometer, D<SUP>*</SUP>, is 3.8 X 10<SUP>9</SUP> cm Hz<SUP>1/2</SUP> W<SUP>-1</SUP> at 84.5 K and within the frequency regime 100 < f < 300 Hz. The optical response is 580 V/W at time constant 0.4 ms. This is one of the fastest composite type HTS-bolometer ever reported. The bolometer is mounted on a metal N<SUB>2</SUB>-liquid cryostat, which fits the preamplifier. With the volume of N<SUB>2</SUB>-reservoir being 0.1 liter, the cryostat holds nitrogen for about 8 hours. Using only wire heater with constant current, the temperature stability of about 0.03 K/h is achieved. The detector system can be used in IR- Fourier spectroscopy at wavelengths longer than the typical operating range of semiconductor detectors (wavelength greater than about 20 micrometers ).
The experimental investigation of the influence of electric field on luminescence of thin liquid crystal layers are presented. It is shown that the observed luminescence quenching is nearsurface phenomena dye to the exiton nature of liquid crystal luminescence.