During the last few years, thermopiles have come increasingly under the spotlight of commercial infrared sensing. This growing interest has motivated us to write an overview of micromachined thermopiles. The first part deals with the Seebeck effect and discusses the most important physical parameters with their interactions. We also describe the main noise sources and give a derivation of the figures of merit and their relevance for thermopile detectors. In the second part, a number of material systems, techniques and micromachined structures are discussed on the basis of different examples. We explain the motivation behind miniaturized thermopile detectors and give a functional explanation of physical interrelations. Finally, different applications are presented and discussed in terms of their future potential.

http://iopscience.iop.org/article/10.1088/0957-0233/18/7/R01/pdf

Review of micromachined thermopiles for infrared detection

New micro and sensor systems are being rapidly developed for their application in all technology events in future. The energy consumption of systems incorporated the latest technical advances decreases permanently to the range of only /spl mu/W. For the applications in this low power range (a few 10 /spl mu/W), DTS has developed a new self-sufficient power supply the low power thermoelectric generator. Whereas earlier with the help of MOS processing techniques manufactured thermoelectric generators reached only a /spl mu/W-output, it was now possible to open up the /spl mu/W-performance range on the basis of high effective thermoelectric compound semiconductor thin films, prepared by physical vapour deposition on polyimid substrates. The LPTG of DTS is a small compact thermoelectric device, full hybrid compatible with micro electronic and micro matched systems. Essential information about the LPTG device properties are given.

Low power thermoelectric generator-self-sufficient energy supply for micro systems

Well-known for its promising luminescence properties, porous Si (PS) appeared also during last 5 years as a new thermal insulating material. Indeed, its extremely low thermal conductivity (TC) values (0.1–2 W m −1  K −1 ) allow to use PS for efficient thermal isolation in microdevices and microsystems as new alternative to usually used micromachined Si structures such as thin membranes or cantilever beams. In this paper, the state of art upon the study of thermal properties of PS is reviewed. In particular, TC measurement methods, the nature of such low TC values as well as influence of the PS nanoscale morphology on its TC are discussed. Numerous technological aspects to form thick and mechanically stable PS layers are described. Finally, some thermal microdevices using PS-based thermal isolation and realized in different research laboratories over the world are presented.

Thermal isolation in microsystems with porous silicon

The design, fabrication, and application of microthermal sensors are presented in this work. The working principle of the microthermal sensor is thermistor, using platinum as the sensing material. A new mesh-membrane structure is presented. This design can reduce the etching time and still provide stiff-enough suspension. The fabrication of the mesh-membrane is timesaving and wastes less material because the back-side etching processes are avoided. The fabricated thermal sensor has flat surface, a sensitivity of 3.263 8CrmW, and a response time of less than 5 ms. In addition, one-wire type thermal flow sensors based on this kind of microthermal sensor are designed and fabricated. For the flow velocity higher than 1.5 mrs, the sensitivity of the flow sensor operating in the constant-voltage mode is . y1r2 . y1r2 above 0.01433 mA mrs , with power consumption of 14.56 mW, and is above 7.98 mV mrs in the constant-current mode, with power consumption of 45.10 mW. q 2000 Elsevier Science S.A. All rights reserved.

/pdf/the-development-and-application-of-microthermal-sensors-with-5ccddpctov.pdf

The development and application of microthermal sensors with a mesh-membrane supporting structure

Bismuth telluride films were deposited by coevaporation at various Te/Bi flux ratios to optimize their resistivity and their Seebeck coefficients for use in a thin film Peltier heat pump. Bismuth telluride films deposited at a flux ratio of Te/Bi=2.3 were found to possess optimal characteristics. Using these coatings, microintegrated Peltier heat pumps were fabricated on micromachined oxide bridges using standard semiconductor patterning and etching techniques. Chrome–gold and bismuth telluride metallizations were used to form the thermoelectric junctions. A maximum heat pumping rate of −30 μW was achieved by the device when operating in the cooling mode. A temperature reduction of 1.5 °C was attained, with an initial thermal response time in the cooling mode of 10 ms/°C.

Optimization of Bi2Te3 thin films for microintegrated Peltier heat pumps

Thermoelectric properties of materials are essentially based on the thermoelectrical figure of merit Z=S 2 σ/K, where S is the thermoelectrical power, σ the electrical conductivity and K the thermal conductivity. Narrow-bandgap semiconductors Bi 2 Te 3 (n), Sb 2 Te 3 (p) layered onto amorphous substrates using the molecular beam technique are investigated. These materials present the highest values of Z. Following the previous work on these materials, the variations in mobility μ and carrier density n as a function of film thickness are performed. It is found that μ and n tend to constant values when the film thickness is higher than 6000 A. We also undertook the study of the thermoelectric properties of Bi x Sb 2-x Te 3 alloys as a function of the bismuth concentration x. The optimal value of S was obtained at x=0.1. The improvement of S in comparison with that of Sb 2 Te 3 results in the reduction in antisite defects or the carrier compensation. Thermopile and pressure sensors based on [Bi 0.1 Sb 1.9 Te 3 (p)-Bi 2 Te 3 (n)] are constructed. These [p-n] active junctions constitute the sensitive elements of both the thermopiles and the vacuum gauges. In comparison with the [Bi-Sb] couple, an improvement in the sensitivity by a factor 2.8±0.2 was achieved. Thermal simulation based on COSMOS/M software confirmed the experimental findings.

F. Tcheliebou

Papers

Improvement of thermal sensors based on Bi2Te3, Sb2Te3 and Bi0.1Sb1.9Te3