Microhotplate Temperature Sensor Calibration and BIST

In this paper we describe a novel long-term microhotplate temperature sensor calibration technique suitable for Built-In Self Test (BIST). The microhotplate thermal resistance (thermal efficiency) and the thermal voltage from an integrated platinum-rhodium thermocouple were calibrated against a freshly calibrated four-wire polysilicon microhotplate-heater temperature sensor (heater) that is not stable over long periods of time when exposed to higher temperatures. To stress the microhotplate, its temperature was raised to around 400 °C and held there for days. The heater was then recalibrated as a temperature sensor, and microhotplate temperature measurements were made based on the fresh calibration of the heater, the first calibration of the heater, the microhotplate thermal resistance, and the thermocouple voltage. This procedure was repeated 10 times over a period of 80 days. The results show that the heater calibration drifted substantially during the period of the test while the microhotplate thermal resistance and the thermocouple-voltage remained stable to within about plus or minus 1 °C over the same period. Therefore, the combination of a microhotplate heater-temperature sensor and either the microhotplate thermal resistance or an integrated thin film platinum-rhodium thermocouple can be used to provide a stable, calibrated, microhotplate-temperature sensor, and the combination of the three sensor is suitable for implementing BIST functionality. Alternatively, if a stable microhotplate-heater temperature sensor is available, such as a properly annealed platinum heater-temperature sensor, then the thermal resistance of the microhotplate and the electrical resistance of the platinum heater will be sufficient to implement BIST. It is also shown that aluminum- and polysilicon-based temperature sensors, which are not stable enough for measuring high microhotplate temperatures (>220 °C) without impractically frequent recalibration, can be used to measure the silicon substrate temperature if never exposed to temperatures above about 220 °C.     

Experimental Investigation of the Thermal Impedance of Interstitial Material at a Junction

Using a quasi-steady-state T-type probe, experimental evidence of the different behavior of the thermal impedance of a junction with different interstitial material (interposer) was presented. In the T-type probe, a short hot wire serves both as a heater and a thermometer, which is subjected to an alternating current, and a thermally infinite long test wire is attached to the midpoint of the hot wire with an interposer. The thermal impedance of the interposer was introduced, which was taken to be the product of the steady-state thermal resistance and a complex ratio function. A complete expression for the thermal impedance of the interposer was derived, and the effects of the radiation heat loss as well as the deviation of the contact junction position were theoretically estimated. A microscale Pt wire with two interposers was measured, including solidified platinum black and Apiezon N vacuum grease. Experimental results showed that the platinum black contact with high thermal effusivity served as a negative thermal impedance, while a positive thermal impedance was observed for the Apiezon N contact. The obtained thermal impedance of the Apiezon N contact could be equivalent to its thermal resistance, which was verified by measuring the thermal conductivity of a Cu wire using the steady-state T-type probe.     

Thermal Response of Transparent Silver Nanowire/PEDOT:PSS Film Heaters

Thermal response behavior of transparent silver nanowire/PEDOT:PSS film heaters are intensively studied for manipulating heating temperature, response time, and power consumption. Influences of substrate heat capacity, heat transfer coefficient between air and heater, sheet resistance and dimension of Ag nanowire film, on the thermal response are investigated from thermodynamic analysis. Suggestion is given for practical applications that if other parameters are fixed, Ag nanowire coverage can be utilized as an effective parameter to adjust the thermal response. The heat transfer coefficient plays opposite roles on thermal response speed and achievable steady temperature. A value of ≈32 W m^?2 K^?1 is obtained from transient process analysis after correcting it by considering heater resistance variation during heating tests. Guidance of designing heaters with a given response time is provided by forming Ag nanowire film with a suitable sheet resistance on substrate of appropriate material and a certain thickness. Thermal response tests of designed Ag heaters are performed to show higher heating temperature, shorter response time, and lower power consumption (179 °C cm² W^?1) than ITO/FTO heaters, as well as homogeneous temperature distribution and stability for repeated use. Potential applications of the Ag heaters in window defogging, sensing and thermochromism are manifested.     

An apparatus for noncontact measurement of thermal conductivity by thermal radiation heating

Thermal radiation calorimetry was applied to measure the thermal conductivity of insulating solid specimens. We consider the system in which a disk-shaped specimen and a flat heater are mounted in a vacuum chamber with the specimen heated on one face by irradiation. A temperature difference between two faces was observed at elevated temperatures under steady-state conditions. An apparatus was developed using a thin graphite sheet as the heater element. Disk-shaped Pyrex glass and Pyroceram specimens, whose surfaces were blackened with colloidal graphite, were used in the measurements. Noncontact temperature measurement was performed using pyrometers and a thermocouple set in the gap between the heater and the specimen. Deviations of the estimated thermal conductivities from the recommended values were about 5% in the temperature range 250 to 800°C. Paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

Experimental study on the double-evaporator thermosiphon for cooling HTS (high temperature superconductor) system

A cryogenic thermosiphons is an efficient heat transfer device between a cryocooler and a thermal load that is to be cooled. This paper presents an idea of thermosiphon which contains two vertically-separated evaporators. This unique configuration of the thermosiphon is suitable for the purpose of cooling simultaneously two superconducting bearings of the HTS (high temperature superconducting) flywheel system at the same temperature. A so-called double-evaporator thermosiphon was designed, fabricated and tested using nitrogen as the working fluid under sub-atmospheric pressure condition. The interior thermal condition of the double-evaporator thermosiphon was examined in detail during its cool-down process according to the internal thermal states. The double-evaporator thermosiphon has operated successfully at steady-state operation under sub-atmospheric pressure. At the heat flow of 10.6 W, the total temperature difference of the thermosiphon was only 1.59 K and the temperature difference between the evaporators was 0.64 K. The temperature difference of two evaporators is attributed to the conductive thermal resistance of the adiabatic section between the evaporators. The method to reduce this temperature difference has been investigated and presented in this paper. The proper area selection of condenser, evaporator 1, and evaporator 2 was studied by using thermal resistance model to optimize the performance of a thermosiphon. The superior heat transfer characteristic of the double-evaporator thermosiphon without involving any cryogenic pump can be a great potential advantage for cooling HTS bulk modules that are separated vertically.     

Effect of jet length and ambient temperature on the performance of a two-phase jet impingement heat sink refrigeration system

The jet impingement heat sink integrated with a compact oil-free R-134a vapor compression refrigeration system introduced in a previous work (Oliveira and Barbosa, 2017) is now further evaluated in terms of the influence of the compressor piston stroke, applied thermal load, orifice-to-heater distance (jet length) and ambient (hot end) temperature. The proposed heat sink is a compact active thermal solution for concentrated heat loads because it integrates the evaporator and the expansion device into a single unit, making use of a single two-phase impinging jet as the cooling mechanism. The present analysis is based on the coefficient of performance and other steady-state heat transfer parameters associated with the impinging jet (heat transfer coefficient and heater surface temperature). A reduction of the jet length promoted a more vigorous splattering of the jet on the heated surface, enhancing the droplet breakup, which in turn reduced significantly the critical heat flux. An increase of the hot reservoir temperature increased the jet impingement heat transfer coefficient.     

Heat conduction across monolayer and few-layer graphenes

We report the thermal conductance G of Au/Ti/graphene/SiO(2) interfaces (graphene layers 1 ≤ n ≤ 10) typical of graphene transistor contacts. We find G ≈ 25 MW m(-2) K(-1) at room temperature, four times smaller than the thermal conductance of a Au/Ti/SiO(2) interface, even when n = 1. We attribute this reduction to the thermal resistance of Au/Ti/graphene and graphene/SiO(2) interfaces acting in series. The temperature dependence of G from 50 ≤ T ≤ 500 K also indicates that heat is predominantly carried by phonons through these interfaces. Our findings suggest that metal contacts can limit not only electrical transport but also thermal dissipation from submicrometer graphene devices.     

Development and characterization of Au-Cu seal ring for lead free packaging of MEMS devices

Seal rings are developed for packaging of circular openings of sensors and the fluidic flow based Micro Electro Mechanical Systems. Lead free technique based on isothermal solidification is used in this course of study. Thick film Au and high purity Cu substrates have been used during the development practice. Indium is used as the interlayer metal. Interconnections of high thermal and mechanical stabilities are fabricated for variable process parameters. The effects of temperature, pressure and reaction time on the ultimate tensile strength (UTS) and ultimate shear strength (USS) are presented and reported in this paper. The thermal stabilities of the specimen seal rings are obtained in the 700-900 K temperature range. Effect of ageing for various cycles and shelf life in different environments are discussed.     

Bench for high-temperature material testing and its application in metallurgy of refractory intermetallides

A simple laboratory technological bench (low-inertial high-temperature electric furnace) with a resistance plane heater based on SiC is produced. The bench makes it possible to carry out the spatial isothermal thermal treatment of samples with a volume of up to 8 cm³, which are placed in the heater, with a controlled thermal cycle at temperatures of up to 2400°C within the inertial gas flow, including their hardening at the final stage of the process at a rate of up to 20°C/s. The photography and the video filming of the sample under test together with optical pyrometric control of its temperature can be carried out by means of a removable quartz or sapphire body of a reactor. Possible fields of application of the bench and the experimental technological and materials science problems are considered. Examples of the comparative investigation of the chemical compatibility of intermetal refractory alloy TiAl-Nb with crucible oxygen-free special ceramics AlN and BN during melting, superheating, fixed isochronous-isothermal holding of the melt at 1670°C, and its abrupt crystallization within test cymbiform crucibles in high-purity Ar are presented.     

Heat and mass transfer under frosting conditions

The effect of frost formation on heat transfer between a test cylinder and its gaseous environment was studied experimentally. The main parameters discussed in the paper are: the total heat flux, the steady-state convective heat transfer coefficient, and the mass of frost adhering to the test cylinder. The emphasis of the paper is on the thermal conducivity of frost. The data indicate that the diffusion mechanisms of moisture transfer within the frost layer causes the frost density and thermal conductivity to increase with time. Frost thermal conductivity is a function of the local temperature and average density. The can be used by designers of low temperature systems with uninsulated surfaces.     

Thermal Conductivity and Thermal Boundary Resistances of ALD Al$$_{}$$O$$_{3}$$3 Films on Si and Sapphire

On Si and sapphire substrates, 6–45 nm thick films of atomic layer-deposited Al\(_{2}\)O\(_{3}\) were grown. The thermal conductivity of ALD films has been determined from a linear relation between film thickness and thermal resistance measured by the 3\(\omega \) method. ALD films on Si and sapphire showed almost same thermal conductivity in the temperature range of 50–350 K. Residual thermal resistance was also obtained by extrapolation of the linear fit and was modeled as a sum of the thermal boundary resistances at heater–film and film–substrate interfaces. The total thermal resistance addenda for films on sapphire was close to independently measured thermal boundary resistance of heater–sapphire interface. From the result, it was deduced that the thermal boundary resistance at ALD Al\(_{2}\)O\(_{3}\)–sapphire interface was much lower than that of heater–film. By contrast, the films on Si showed significantly larger thermal boundary resistance than films on sapphire. Data of \(< 30\) nm films on Si were excluded because an AC coupling of electrical heating voltage to semiconductive Si complicated the relation between 3\(\omega \) voltage and temperature.     

Singularities of Realization of Film Boiling on Wire Heaters. Organic Liquids

The singularities of realization of the mode of film boiling on wire heaters are investigated in a wide range of organic liquids. Carbon tetrachloride and various alcohols (C1–C5) are used for investigation. It is demonstrated that chemical reactions accompanied by gas liberation proceed in the cavity of film boiling, which are caused by the thermal decomposition (pyrolysis) of the original substance. The kinetics of chemical gas liberation are studied, and the composition of reaction products is determined as a function of the heater and liquid temperature and of the heater material. It is demonstrated that the gas liberation in subcooled liquids at high heater temperatures is fully defined by the chemical processes. It is found that, in the case of a short heating element and in liquids subcooled to the saturation temperature, the heat transfer in the film mode occurs in the form of a self-oscillatory process with the oscillation amplitude of the heater temperature of 350–400°C. The mechanism of the emergence of such oscillation is suggested.     

Dependence on temperature and energy of the heteroepitaxy of small metallic nanoclusters

Deposition at different energies and temperatures of small metallic nanoclusters on metallic substrates is studied by molecular-dynamics simulations. Small-, Co/Cu(001), and large-misfit, Cu/Au(001) and Au/Cu(001), systems are considered. The rise in temperature improves the epitaxial order, although its effect is smaller in large-misfit systems. Thus, by increasing this parameter, non-epitaxial clusters can turn their structure into epitaxial in the case of Co/Cu(001), into aligned in Cu/Au(001), and into layered in Au/Cu(001). Therefore, the characteristics of the alignment are determined by the properties of the material. In addition, the influence of the initial structure is more marked in Co and Cu clusters, since they can reproduce locally other phases. Epitaxy can also be improved if the deposition energy is increased, although the deposited cluster loses its original shape progressively. Its effect is different depending mainly on the degree of misfit. An increase in energy (of up to 0.75 eV/atom) produces similar effects, but more noticeable, as a rise in temperature.     

Characterization of a silicon thermal gas-flow sensor with porous silicon thermal isolation

In this paper, the results of full characterization of a micromachined-silicon thermal gas flow sensor will be presented. The sensor is composed of two series of thermocouples on the right and left side of a polysilicon resistor, used as heater. The resistor and the hot contacts of the thermocouples lie on a thick porous silicon layer, which assures local thermal isolation, while the thermopile cold contacts lie on bulk silicon. Gas flow is parallel to the surface of the sensor and perpendicular to the resistor, which is heated at constant temperature. The power of the heater is stabilized by an external circuit, which provides a feedback current to compensate changes in the resistance of the heater under flow. Characterization of the sensor both under static conditions and under flow of different gases will be presented. The sensor shows high sensitivity [of the order of 175 /spl times/ 10/sup -3/ mV/(m/s)/sup 1/2/ per thermocouple] and very rapid response, below 1 ms, which makes it appropriate for use both under laminar and under turbulent flows.     

Parametric study of solidification of PCM around a cylinder for ice-bank applications

This paper presents the results of a numerical parametric study of the solidification of a phase change material (PCM) around a cylinder carrying a heat-transfer fluid (HTF) inside. A pure conduction model is used for the PCM and tube wall, the finite volume method is used together with the interface immobilization technique for treating the phase-change process. The convection problem inside the tube is solved by an energy balance with a Nusselt number value, obtained from the steady-state values for constant wall heat-flux conditions. The effects of the HTF entry temperature, the initial PCM temperature and the thermal conductivity of the tube material on the evolution of the solidification front are studied. Results for the temperature distribution during the process, phase-change interface velocity and thermal energy stored in the system are also presented.     

Improved OCXO's oven using active thermal insulation

This paper shows how it is possible to improve the performance of thermal enclosures by using a compensating system the principle of which has been described by F. Walls a few years ago (41st AFCS, 1987). It is shown that because of the thermal network between the outside temperature, the temperature sensor and the device to be regulated, the latter may undergo residual temperature variations which reduce the overall thermal efficiency of the oven. This paper shows how thermal transfer functions can be measured by using an experimental setup in which the node temperatures are measured by thermal sensors. By identifying the thermal response of the nodes with the theoretical transfer function under external temperature or heater excitation, the components of the equivalent R-C network can be determined. By knowing these thermal transfer functions, it is then possible to make use of a compensating system which can eliminate the parasitic static as well as dynamic thermal effects. Validating measurements and experimental results are presented which show the strong improvement achieved by this compensating system with respect to the conventional approach     

A novel thermal sensor concept for flow direction and flow velocity

This paper presents a unified theory for different measurement concepts of a thermal flow sensor. Based on this theory, a new flow sensor concept is derived. The concept allows measuring both direction and velocity of a fluid flow with a heater and an array of temperature sensors. This paper first analyzes the two-dimensional (2-D) forced convection problem with a laminar flow. The two operation modes of a constant heating power and of a constant heater temperature are considered in the analytical model. A novel estimation algorithm was derived for the flow direction. Different methods for velocity measurement were presented: the hot-wire method, the calorimetric method, and the novel average-temperature method. The only geometric parameter of the sensor, the dimensionless position of the sensor array, is optimized based on the analytical results. Furthermore, the paper presents the experimental results of the sensor prototype. In order to verify the analytical model, an array of temperature sensors was used for recording the 2-D temperature profile around the heater. Temperature values are transferred to a computer by a multiplexer. A program running on a personal computer extracts the actual flow velocity and flow direction from the measured temperature data. This paper discusses different evaluation algorithms, which can be used for this sensor. A simple Gaussian estimator was derived for the direction measurement. This estimator provides the same accuracy as the analytical estimator. Velocity results of both the calorimetric concept and the novel average-temperature concept are also presented.     

Proposal of an active composite with embedded sensor

Though advanced composites with embedded actuator materials such as shape memory alloys and piezo ceramics have been developed as active materials, another one by making use of thermal deformation of composites was proposed and an active laminate was prepared as an example by hot-pressing of aluminum plate as material of high coefficient of thermal expansion (CTE), uni-directional carbon fiber reinforced plastics (CFRP) prepreg as low CTE material and electric resistance heater, polymer adhesive film as insulator between them, and copper foils as electrodes. Actuation of this laminate is different from that of bimetal because CTE of the CFRP layer is strongly anisotropic due to directionality of its reinforcement fiber. As CTEs of the CFRP layer and the aluminum plate in the fiber direction are quite different from each other though they are close to each other in the transverse direction, smooth and uni-directional actuation becomes possible. In this study, its fundamental performances such as shape change and output force were observed and evaluated, and after establishment of its fabrication, an optical loss type sensor was formed in the active composite, by embedding multiply pre-notched optical fiber in the CFRP layer and breaking it at the pre-notches under bending, followed by lamination on aluminum plate with adhesive. As the sensing part can be formed inside the matrix without any complicated processes, a robust and low cost sensor is obtained. From the results, it becomes clear that: (1) curvature of the active composite linearly changes as a function of temperature between room temperature and its hot pressing temperature by electric resistance heating of the CFRP layer and cooling, (2) its output force against a fixed punch during heating from room temperature up to around glass transition temperature of the resin phase almost linearly increases with increasing temperature, (3) the multiply pre-notched, embedded and fractured optical fiber works as a sensitive sensor for monitoring the curvature of the active composite.     

Experimental study of thermal condition in a room with hydronic cooling radiant surfaces

This paper presents a new approach for experimental analysis of chilled or heated ceiling systems and its environment (ventilation, windows and thermal loads distribution). The work is aimed at giving a better insight to crucial parameters as the contact thermal resistance, fin effectiveness of ceiling panels, mass flow rate, supply water temperature, thermal load distribution, fenestration and ventilation system effects on the radiant ceiling capacity and comfort conditions. The experimental methodology and its discussion are also presented. A test chamber is adapted in a way to reproduce as good as possible the characteristics of a hospital room with a cooling ceiling system. The convection and radiation heat transfer coefficients to room and losses through the ceiling void are also studied. Experimental data are used to fit the uncertain parameters mentioned and improve the capacity and performance of the ceiling system, but also to evaluate the design of this HVAC system and the applicable control strategies.     

Ultraviolet-nanoimprinted packaged metasurface thermal emitters for infrared CO2 sensing

Abstract

Packaged dual-band metasurface thermal emitters integrated with a resistive membrane heater were manufactured by ultraviolet (UV) nanoimprint lithography followed by monolayer lift-off based on a soluble UV resist, which is mass-producible and cost-effective. The emitters were applied to infrared CO₂ sensing. In this planar Au/Al₂O₃/Au metasurface emitter, orthogonal rectangular Au patches are arrayed alternately and exhibit nearly perfect blackbody emission at 4.26 and 3.95 μm necessary for CO₂ monitoring at the electric power reduced by 31%. The results demonstrate that metasurface infrared thermal emitters are almost ready for commercialization.