Temperature Dependent Thermal Conductivity and Elastic Properties of a-InGaZnO₄ and a-In₂Ga₂ZnO₇ Thin Films

Amorphous In-Ga-Zn-O is an important oxide semiconductor in advanced display technologies. Despite its importance, little has been reported on the thermal and elastic properties of this material. Here, the temperature dependence of the thermal conductivity, shear modulus, and internal friction of a-InGaZnO₄ and a-In₂Ga₂ZnO₇ films are presented. The thermal conductivity of a-In₂Ga₂ZnO₇, measured from 100 K to room temperature, was found to be larger than that of a-InGaZnO₄ over the entire temperature range. At room temperature the thermal conductivities were 1.9 W/m K and 1.4 W/m K for the a-In₂Ga₂ZnO₇ and a-InGaZnO₄ films, respectively. The shear modulus and internal friction of these films were measured in the temperature range of 340 mK to 65 K. At 4.2 K the shear modulus of the a-InGaZnO₄ and a-In₂Ga₂ZnO₇ films was 44 GPa and 42 GPa, respectively. The internal friction of thin films at each composition exhibited a temperature dependence and magnitude that is in agreement with that observed in all amorphous solids. As the self-heating effect is of concern in the development of amorphous In-Ga-Zn-O based thin film transistors on low thermal conductivity substrates, a thermal model of such a device utilizing a-In₂Ga₂ZnO₇ or a-InGaZnO₄ as the active layer was explored. It was found that the temperature increase of the thin film transistor channel is essentially independent of the thermal conductivity of the active layer.