Compact Test Structure to Measure All Thermophysical Properties for the In-Plane Figure of Merit ZT of Thin Films

Abstract

This paper reports a versatile thermophysical test structure to measure all material properties contributing to the in-plane thermoelectric figure of merit $ZT=S^2T\kappa ^{-1} \rho ^{-1}$ from a single thin film sample of only about 0.5 mm$^2$. These properties are the Seebeck coefficient S of the sample against aluminum (Al), its thermal conductivity $\kappa$ , and its resistivity $\rho$. The thermal membrane-based test structure is produced using standard thin film deposition and structuring processes followed by silicon micromachining. It can be used to characterize thin films deposited at high temperature, such as doped polycrystalline silicon (poly-Si), as well as films deposited at low temperature, e.g., sputtered metals. We present the measurement of all components of the ZT of low-pressure, chemical vapor-deposited n- and p-doped poly-Si thin films in the temperature range from 300 K to 380 K. Values of 1.46 × 10⁻² and 0.95 × 10⁻² were found at room temperature (RT) for the ZT of n- and p-doped poly-Si films, respectively. Furthermore, the test structure was used to extract $\rho$ and $\kappa$ of a sputtered aluminum film in the same temperature range. The respective RT values are 48.7 × 10⁻⁹ $\Omega {\hbox{m}}$ and 154 W m⁻¹ K⁻¹.