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 ¼ S 2 Tj À1 q À1 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 j , and its resistivity q. 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 9 10 À2 and 0.95 9 10 À2 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 q and j of a sputtered aluminum film in the same temperature range. The respective RT values are 48.7 9 10 À9 Xm and 154 W m À1 K À1 .

Measurements of thermal conductivity and the coefficient of thermal expansion for polysilicon thin films by using double-clamped beams

“…As can be seen in equation (7), when time t is plotted as the X-axis and the transient electrical resistance R(t) is plotted as the Y-axis, time constant τ can be estimated from the exponential fitting curve of R(t). By measuring transient electrical resistances of two double-clamped beams with different lengths l 1 and l 2 , τ 1 and τ 2 are obtained and parameter γ is then calculated from equation (5). By substituting the value of γ into equation ( 9), thermal conductivity of polysilicon thin film can be calculated by…”

“…Steady-state methods have been used to measure the thermal conductivity of thin films. The test structure is generally composed of a heater and several temperature sensors (thermocouple [3] or thermistor [4][5][6]). The heater serves as a heat source and heated by a dc current, whereas the temperature sensors capture the temperature profile across the sample film.…”