The Effect of Self-Heating on the Measurement of a Temperature Change Using a Bolometric Detector

Even when care is taken to lower as much as possible the Joule power dissipated in a bolometric detector, the self-heating effect is far from being negligible. Consequently, in the steady state, it is of crucial importance to carefully distinguish the cell temperature, the bolometer temperature and the temperature of the part of the helium film which covers it. In the light of these results, when a bolometer is used to measure a small change in a thermal heat flux, the fundamental question concerns the exact definition of the quantity measured by the detector. To illustrate this problem we have considered the amplitude measurement of the third sound temperature oscillation. When the bolometer is operated from a current source, a detailed analysis of the different heat fluxes involved in the problem, provides a relation between the quantity usually measured in the experiments, and the real amplitude of the third sound temperature oscillation: Clearly these two values are noticeably different. Experimental measurements performed at 0.3 K support very well our analysis. Finally we show that a constant temperature bolometer appears much more suited to this kind of measurements.     

A bolometric detector built into the diamond bulk

Since diamond can be used as both the substrate and the active medium in electronic devices, it is very important to obtain information concerning the temperature variations in the immediate vicinity of active elements and the conditions of heat removal from such elements. This task is solved by a bolometer built into a diamond plate, which is capable of measuring temperature increments induced by laser pulses in the diamond or in the diamond-supported surface structures. The bolometer, representing a buried graphitized layer formed by helium ion implantation with subsequent annealing, has a characteristic response time of ∼10 ns.     

Dynamical Theory of a High-Temperature Superconductor Photo-Thermoelectrical Bolometer

In this paper, we develop a dynamic theory starting from the basic heat balance equation for a high-temperature superconductor (HTSC) photothermoelectrical bolometer. We include dynamics via a small infrared sinusoidal signal incident on the sensitive area of the bolometer. The sensitive area of the bolometer is considered to be approximately mm × mm, with a film thickness in the micron range. This area is a thermoelectrical junction between an HTSC—for example, YBCO—and a high thermoelectic figure of merit material—for example, BiSb—grown on a substrate—for example, Yttria stabilized zirconia (YSZ). The two legs of the thermocouple are connected in a parallel geometry. Heat is transferred by direct conductance to the substrate underneath as well as toward the cold end of the thermojunction—that is, Peltier heat in the plane of the substrate—is also taken into account. It is found that if the bolometer is operated under a voltage bias condition, there is substantial improvement in the response time and the responsivity of the bolometer. This appears to be due to the photothermoelectrical operation superimposed on the normally used photoelectrical operation.     

Electron-Phonon Coupling in Bolometers Used for Cryogenic Particle Detection

Superconducting transition-edge sensors have been used extensively in cryogenic particle detectors, either as thermometers for microcalorimetry or as bolometers for the detection of the prompt phonons resulting from a particle decay in a single crystal absorber. Bolometer action depends upon the energy coupling of the prompt phonons to the bolometer electrons. A study has been made of the electron-phonon coupling for a series of Au-Ti bolometers on a Si substrate and of the use of these bolometers for prompt phonon detection below 1 K. The electron-phonon coupling was found to be proportional to the normalized resistance (R/R _n) of the bolometer; R is the bolometer resistance and R _n is the normal resistance. When extrapolated to R/R _n = 1, this coupling was consistent with /VT ³ = 3 × 10⁹ Wm^–3K^–4 where is the thermal conductance from the bolometer electrons to the Si phonons and V and T are the volume and transition temperature of the bolometer. The response of the bolometers to heat pulses generated by a thin film heater on the opposite face of a Si single crystal were similar to that generally seen above 1 K, apart from a delay time constant that varied from 0.5 to 1.3 µs as the transition temperature decreased from 600 to 200 mK. This delay time constant is attributed to the thermal equilibrium time of normal regions of the bolometer.     

Surface Event Rejection of the EDELWEISS Cryogenic Germanium Detectors Based on NbSi Thin Film Sensors

Near-surface-events are a major limitation to the performance of cryogenic massive germanium heat and ionisation detectors for dark matter search, due to their incomplete charge collection. We present here a powerful method of surface event identification based on the transient heat signal of a Ge bolometer, equipped with two NbSi high impedance thin film sensors. Calibration runs using electrons and low energy gamma particles from a ¹⁰⁹Cd source show highly effective surface event rejection down to the heat threshold energy. Neutron and gamma source calibrations were realised to get information on the fiducial volume of the Ge absorber. First results from low background data taking are discussed.     

Effect of heat link capacity on the energy pulse response of bolometers

A number of applications have been suggested for low temperature bolometers, for which their response to energy pulses should be optimized. When the heat capacity of the thermal link is not negligible, the bolometer response to energy pulses can be calculated by using programs written for analysis of electrical networks. The resulting response is not a single exponential, in agreement with experiments by McCammon et al.³ A satisfactory estimate of the signal-to-noise ratio is obtained by adding a third of the heat capacity of the link to that of the bolometer.     

Effects of elastic anisotropy on the surface stability of thin film/substrate system

The surface stability of thin film/substrate system is an important problem both in the film synthesis and reliability of micro electrical and mechanical system (MEMS). In this work, the elastic anisotropy effect on surface stability of thin film/substrate system was considered. The theoretical analysis indicates that elastic anisotropic influence could play an important role in the surface stability of thin film/substrate system. And the anisotropy effect should be considered both in the thin film synthesis process and its service reliability. In addition, there exists an nondimensional parameter k for cubic crystalline thin film materials in evaluating the anisotropic effect. When k is larger than one unit, the surface stability will be weakened by anisotropic effect; vice versa. The method used in present work could be easy extended to multi-layered thin film/substrate system and help us to consider the elastic anisotropy effect.     

YBCO Thin Film Preparation on Unbuffered Ag Substrate by Resistive Evaporation

It is widely accepted that thin film formation of YBCO on conducting and flexible substrate is one of the keys for further development of advanced devices in the microelectronics. Various fabrication methods such as spray pyrolysis, powder-in-tube processing, dip-coating rolling-assisted biaxially textured substrate, etc., widely used for YBCO thick films (few tens of m) production. However in this work we report for the first time on the preparation of YBCO thin film on unbuffered silver substrate using a simple conventional vacuum system equipped with only one single resistively heated evaporation source. The subsequent heat treatment was carried out under a low oxygen partial pressure and temperature that never exceeded 740° C. A thin film of Ag was first deposited on MgO substrate. A pulverized stoichiometric mixture of Y, Cu, and BaF ₂ was then deposited on this film. The amorphous YBCO film of a 500-nm thickness was obtained after the heat treatment. The results of the film evaluation are presented and discussed.     

聚酰亚胺薄膜与太阳翼基板粘贴技术研究

卫星在轨运行过程中,太阳翼会受到恶劣的低真空、温度等环境因素影响,为了提高太阳翼在轨运行过程中的可靠性,对聚酰亚胺薄膜与太阳翼基板的粘贴技术进行了实验研究。结果表明:对聚酰亚胺薄膜表面进行电晕处理,能够显著地提高其表面粗糙度。聚酰亚胺薄膜与硅橡胶结合力得到大大提高,聚酰亚胺薄膜与基板剥离强度达到8.59N/cm,经过热真空及温度循环实验验证,电晕后的聚酰亚胺薄膜薄膜与基板粘贴牢固可靠,能够适应空间恶劣的环境。电晕技术为聚酰亚胺薄膜与基板的粘贴提供了一种有效的表面处理方法,可以推广至航天器其他舱外部件上使用。     

Voltage-Biased Superconducting Transition-Edge Bolometer with Strong Electrothermal Feedback Operated at 370 mK

We present an experimental study of a composite voltage-biased superconducting bolometer (VSB). The tested VSB consists of a Ti-film superconducting thermometer (T(c) ~375 mK) on a Si substrate suspended by NbTi superconducting leads. A resistor attached to the substrate provides calibrated heat input into the bolometer. The current through the bolometer is measured with a superconducting quantum interference device ammeter. Strong negative electrothermal feedback fixes the bolometer temperature at T(c) and reduces the measured response time from 2.6 s to 13 ms. As predicted, the measured current responsivity of the bolometer is equal to the inverse of the bias voltage. A noise equivalent power of 5 x 10(-17) W/ radicalHz was measured for a thermal conductance G ~ 4.7 x 10(-10) W/K, which is consistent with the expected thermal noise. Excess noise was observed for bias conditions for which the electrothermal feedback strength was close to maximum.     

Electrical conduction and transmission electron microscopy studies of CdSe0.8Te0.2 thin films

Electrical resistance of CdSe_0.8Te_0.2 thin films were found to be dependent on various film parameters such as substrate temperature, film thickness, deposition rate and post-deposition heat treatment in different environments. A decrease in film resistivity was observed for thicker films and for those heat treated in vacuum. Films deposited at higher substrate temperatures and faster rates showed an increase in film resistivity. A spectrum of activation energies was observed in the films which fell within either of the activation energies observed in CdSe or CdTe films. Films heated in an oxygen environment showed an increase in film resistivity with a different activation energy. Transmission electron microscopy (TEM) of the films showed an improvement in crystallinity with increasing film thickness and substrate temperature, and a reduction in crystallinity with increasing deposition rate.     

Operation of a Wideband Terahertz Superconducting Bolometer Responding to Quantum Cascade Laser Pulses

We make use of a niobium film to produce a micrometric vacuum-bridge superconducting bolometer responding to THz frequency. The bolometer works anywhere in the temperature range 2–7?K, which can be easily reached in helium bath cryostats or closed-cycle cryocoolers. In this work the bolometer is mounted on a pulse tube refrigerator and operated to measure the equivalent noise power (NEP) and the response to fast (μs) terahertz pulses. The NEP above 100?Hz equals that measured in a liquid helium cryostat showing that potential drawbacks related to the use of a pulse tube refrigerator (like mechanical and thermal oscillations, electromagnetic interference, noise) are irrelevant. At low frequency, instead, the pulse tube expansion-compression cycles originate lines at 1?Hz and harmonics in the noise spectrum. The bolometer was illuminated with THz single pulses coming either from a Quantum Cascade Laser operating at liquid nitrogen temperature or from a frequency-multiplied electronic oscillator. The response of the bolometer to the single pulses show that the device can track signals with a rise time as fast as about 450?ns.     

Heat diffusion in normal4He and3He thin films

We report measurements of heat diffusion at the surface of a glass substrate coated by normal⁴He and³He thin films. As the normal Helium film is grown, we observe for both isotopes that the diffusion of heat is strongly altered. Clearly a new diffusive channel is associated to the presence of the normal film itself, and for an³He film thickness of 7a.l. two distinct characteristic diffusion times are measured. The shorter time is characteristic of the diffusion of heat in the bare substrate while the longer one is associated to the diffusive process taking place in the normal adsorbed film. Considering the two diffusive channels as independent, we are able to obtain the diffusive contribution of the normal He film. The analysis of these data leads us to propose the picture of phonons traveling in the film with a wavevector parallel to the substrate plane. The existence of this independent diffusive mode, with a characteristic time larger than that of the substrate, is supported by the very slow decrease at long times of the measured temperature deviation for the coated substrate.     

Ellipsometric studies of microscopic surface roughness of CdS thin films

Analysis of changes in surface roughness of CdS thin films with preparation temperature was carried out using variable angle spectroscopic ellipsometry (VASE). The films studied were prepared by spray pyrolysis technique, in the substrate temperature range 200–360°C. The VASE measurements were carried out in the visible region below the band gap (E _g=2·4eV) of CdS so as to reduce absorption by the film. The thickness of the films was in the range 500–600 nm. Bruggeman’s effective medium theory was used for analysis of the surface roughness of the film. The roughness of the film had a high value (∼ 65 nm) for films prepared at low temperature (200°C) and decreased with increase in substrate temperature. This reached minimum value (∼ 27 nm) in the temperature range 280–300°C. Thereafter roughness increased slowly with temperature. The growth rate of the films was calculated for different temperature ranges. It was found that the deposition rate decreases with the increase in substrate temperature and have an optimum value at 300°C. Above this temperature deposition rate decreased sharply. The scanning electron micrograph (SEM) of the film also showed that the film prepared at 280–300°C had very smooth surface texture.     

Nonlinearity of the transduction of a laser pulse by a fine-wire bolometer

The normalized efficiencies of transduction of the instantaneous power of optical radiation by a bolometer as a function of the average incident energy per unit length and the nonuniformity of its distribution are determined on the basis of the solution of the heat balance equation averaged over the length of the bolometer when the absorption efficiency factor, the temperature coefficient of resistance, and the specific heat of the material depend linearly on the temperature. Calculations are carried out for platinum bolometers and a radiation wavelength of 10.6 m. The amplitude distortions of the recorded signal do not exceed +20%.Translated from Izmeritel'naya Tekhnika, No. 10, pp. 33–35, October, 1993.     

An inverse solution for reconstruction of the heat transfer coefficient from the knowledge of two temperature values in a solid substrate

Reconstruction of the heat transfer coefficient from the knowledge of temperature distribution is an inverse problem. The main focus of this study was to develop an inverse model that could be used to determine the heat transfer coefficient associated with a fluid in contact with a solid surface from the knowledge of two measured temperature values (T₁ and T_M) in the solid substrate. The temperature distribution for the inverse problem was numerically generated, for a situation with a known heat transfer coefficient, using an implicit finite-differencing scheme. The solution domain was first discretized in to finite number of small regions and nodes. Conservation of energy was then applied to each of the control volume about the nodal regions. This approach resulted in a set of linear equations that was solved simultaneously. Two nodal temperatures in the substrate, from the direct solution, were then used in the inverse problem to reconstruct the heat transfer coefficient. To solve the inverse problem, the solution domain was divided into two distinct regions (Region I and Region II). Region I contained the solution domain between the two known temperatures (T₁ and T_M), and Region II included the region between T_M and the surface with the convective boundary condition. Again, a finite-differencing scheme was employed to generate a set of linear equations in each region. First, the set of linear equations in Region I was solved simultaneously and the results were then used to reconstruct the nodal temperatures in Region II. The convective surface temperature was then utilized to determine the heat transfer coefficient. A series of numerical experiments were conducted to test the validity of the inverse model. Comparison of the inverse solutions with the direct solutions confirms that the heat transfer coefficient can be reconstructed, with good accuracy, from the knowledge of two temperature points in the solid substrate.     

High mobility organic transistor patterned by the shadow-mask with all structure on a plastic substrate

Pentacene thin film transistors fabricated without photolithographic patterning were fabricated on the plastic substrates. Both the organic/inorganic thin films and metallic electrode were patterned by shifting the position of the shadow-mask which accompanies the substrate throughout the deposition process. By using an optically transparent zirconium oxide (ZrO₂) as a gate insulator and octadecyltrimethoxysilane (OTMS) as an organic molecule for self-assembled monolayer (SAM) to increase the adhesion between the plastic substrate and gate insulator and the mobility with surface treatment, high-performance transistor with field effect mobility 0.66 cm²/V s and I _on/I _off > 10⁵ was formed on the plastic substrate. This technique will be applicable to all structure deposited at low temperature and suitable for an easy process for flexible display.     

Influence of thermal annealing on optical properties and structure of aluminium oxide thin films by filtered cathodic vacuum arc

Optical and structural properties of aluminium oxide thin films are investigated in the annealing temperature range of 200–900 °C. The changes in optical properties and film structure show the great dependence on the temperature. For the film annealed at low temperatures (from 200 °C to 600 °C), the film optical properties, such as transmittance and optical constants, could be improved by thermal annealing with amorphous structure and smooth surface. However, for the film annealed at higher temperature (e.g. 900 °C), the poor performance of optical properties indicates undesirable application for precise use in optics due to significant changes in both structure and surface roughness. At optimum annealing temperature of 600 °C, the transmittance could reach as high as that of substrate and the film possesses better optical constants (refractive index was 1.73 and extinction coefficient was ∼10⁻⁴ at 550 nm) with remaining amorphous structure and smooth surface.     

Measurement of the surface tensions and the interfacial tensions of n-pentane-water and R 113-water systems

The surface and the interfacial tensions of mutually immiscible liquid systems were experimentally studied. The measured systems are n-pentane-water and R 113-water, which are proposed as heat transfer fluids for a direct-contact heat exchanger to be used for geothermal and waste heat recovery plants. The experimental apparatus was constructed based on the principle of the pendant drop method. Measurements were performed in the temperature range from 20 to 150°C. Based on the correlation of the surface and the interfacial tensions, the temperature dependences of the spreading coefficient, the film pressure, and the work of adhesion in each system were calculated.     

热丝CVD系统内衬底温度分布的数值研究

热丝法化学气相沉积金刚石薄膜系统内 ,衬底温度和碳源气体浓度是金刚石薄膜生长最为重要的参数。本文根据传热学基本原理 ,数值模拟了衬底表面辐照度、温度分布 ,讨论了衬底热传导等因素对衬底温度分布的影响 ,探讨了如何改善衬底温度均匀性。结果表明 ,考虑衬底横向热传导后 ,衬底表面温度分布均匀性明显优于基于辐射热平衡得到的温度分布 ,在一定程度上有利于生长大面积薄膜。