• Shchepetov, Andrey
• Grigoras, Kestutis
• Tappura, Kirsi
• Ahopelto, Jouni
• Prunnila, Mika
• Gomès, Séverine
• Timofeev, Andrey
• Varpula, Aapo
• Renahy, David
• Hassel, Juha

Abstract

Thermoelectric devices consisting of a thermocouple or thermopile can be used as efficient detectors in various applications. Thermoelectric detectors themselves do not require external power to operate. This eliminates noise sources associated with electric current. This leaves thermal fluctuation and Johnson-Nyquist noises as the dominating ones. In frequencies well below thermal cut-off the internal noise-equivalent power of a thermoelectric detector is given by [1]NEP = NEPth[ 1+ 1/(ZeffT) ]1/2, (1)with NEPth=(4kBT2G)1/2, the NEP of the thermal fluctuation noise, kB, Boltzmann’s constant, T, the absolute temperature, G, the total thermal conductance between the detector hot junction(s) and the surroundings (including phonons and other thermal channels), ZeffT = S2T/(GR), the detector effective thermoelectric figure of merit, S, the total Seebeck coefficient of the thermocouple(s), and R, the total electric resistance of the thermocouple(s). In specific geometries and material parameter values ZeffT coincides with the text-book expression of the thermoelectric figure of merit ZT [1]. Equation (1) shows that when ZeffT>1, the internal noise is dominated by the fundamental NEPth only. Therefore, silicon nanomembranes [1–3] are attractive materials for thermoelectric detectors as they possess the relatively high power factor of silicon and their thermal conductivity can be reduced up to two orders of magnitude from the bulk value. We present thermoelectric thermal detectors based on silicon nanomembranes and demonstrate their use in scanning thermal microscopy. The devices have a built in heater that allows the device (Fig.) and material performance, and the SThM tip –device interaction to be characterized. When equipped with an optical absorber, this kind of detector can be optimized of infrared sensing as well [5]. We discuss also these applications.

Topics

• impedance spectroscopy
• Silicon
• thermal conductivity
• microscopy