RESUMO
The research on the stable thermoelectric properties and contact interface of high-precision thin-film thermocouples lags far behind the demand. In this study, a zinc-rich Al-doped ZnO (AZO) thin film was fabricated, in which the carriers were mainly donated by the Al dopant, and the oxygen defects migrated together, forming cage defects. Then, an indium tin oxide (ITO)/AZO thin-film thermocouple was prepared. It had a special temperature-dependent voltage curve due to the effects of cage defects on the thermoelectric properties of the AZO thin film and interfacial electron diffusion. When the zinc atoms in the cage defects were excited after annealing, a linear relationship between the temperature and voltage was obtained. The Seebeck coefficient of the thermocouple was constant at 168 µV K-1 over the entire measured temperature range. In addition, the calculated error of the thermocouple was lower than 1% from 50 °C to 500 °C, showing good repeatability. These results showed that defect engineering could effectively be used to improve the temperature range stability of thermoelectric materials and optimize the precision of thin-film thermocouples.
RESUMO
In recent years, thermoelectric (TE) devices have been used in several refrigeration applications and have gained attention for energy generation. To continue the development of devices with higher efficiency, it is necessary not only to characterize their materials but also to optimize device parameters (e.g., thermal contacts). One attempt to increase the efficiency at the device level consists of the replacement of the typical ceramic layers in TE modules by metallic plates, which have higher thermal conductivity. However, this alternative device design requires the use of a very thin electrical insulating layer between the metallic strips that connect the TE legs and the outer external layers, which introduces an additional thermal resistance. Impedance spectroscopy has been proved to be useful to achieve a detailed characterization of TE modules, being even capable to determine the internal thermal contact resistances of the device. For this reason, we use here the impedance method to analyze the device physics of these TE modules with outer metallic plates. We show for the first time that the impedance technique is able to quantify the thermal contact resistances between the metallic strips and the outer layers, which is very challenging for other techniques. Finally, we discuss from our analysis the prospects of using TE modules with external metallic plates.
RESUMO
Electrical four-terminal sensing at (sub-)micrometer scales enables the characterization of key electromagnetic properties within the semiconductor industry, including materials' resistivity, Hall mobility/carrier density, and magnetoresistance. However, as devices' critical dimensions continue to shrink, significant over/underestimation of properties due to a by-product Joule heating of the probed volume becomes increasingly common. Here, we demonstrate how self-heating effects can be quantified and compensated for via 3ω signals to yield zero-current transfer resistance. Under further assumptions, these signals can be used to characterize selected thermal properties of the probed volume, such as the temperature coefficient of resistance and/or the Seebeck coefficient.
