Heat transport properties of alumina gate insulator films on Ge substrates fabricated by atomic layer deposition

Abstract

Amorphous Al2O3 films deposited by atomic layer deposition (ALD) on Ge substrates are a typical gate insulator dielectric used in Ge channel metal-oxide semiconductor field-effect transistor (MOSFET) devices. As Joule heating in the Ge channel alters the MOSFET performance, the thermal transport properties of ALD-Al2O3 films and interfaces between Al2O3 and Ge have become important characteristics. This study measures the thermal transport properties of Al2O3 films on Ge substrates using the thermo-reflectance method. The thermal conductivity кm of the Al2O3 films and the thermal resistivity of the Al2O3/Ge interface were estimated to be 0.83 W m−1 K−1 and 2.8 × 10−8 m2 K W−1, respectively. A significant reduction from the thermal conductivity of crystalline Al2O3 (46 W m−1 K−1) and the large thermal resistivity of the interface were observed. To understand the thermal transport mechanism in the ALD-Al2O3 film, thermal transport was simulated using phonon-based and diffuson theories. It was found that diffuson theory was better at explaining the relatively low thermal conductivity of ALD-Al2O3. The thermal resistivity of the Al2O3/Ge interface was discussed in comparison with that of SiO2/Si interface. The improved understanding of the thermal transport properties of the ALD-Al2O3/Ge stacking structures is essential to obtain the correct prediction of the electrical performance of the MOSFET devices.