Structural and electrical properties of fiber textured and epitaxial molybdenum thin films prepared by magnetron sputter epitaxy

TL;DR

This study investigates how growth temperature affects the structural and electrical properties of molybdenum thin films grown on different aluminum nitride substrates, aiming to optimize their use in acoustic resonators.

Contribution

It provides a systematic analysis of the relationship between growth temperature, crystallinity, and electrical resistivity of Mo films on fiber-textured and epitaxial AlN substrates.

Findings

Mo grown at 700°C on epitaxial AlN shows low resistivity and high crystal quality.

Resistivity decreases with increasing growth temperature due to larger grain size.

Fiber-textured Mo has higher resistivity than epitaxial Mo due to more high-angle grain boundaries.

Abstract

Molybdenum (Mo) due to its optimal structural, physical, and acoustic properties find application as electrode material in aluminum scandium nitride (AlScN) and aluminum nitride (AlN) based bulk acoustic wave (BAW) resonators. Epitaxial Mo thin films exhibiting low resistivity can improve the performance of the BAW resonator by enhancing both the electromechanical coupling coefficient and quality factor. In this study, we systematically vary the growth temperature of Mo grown on fiber-textured and epitaxial wurtzite-aluminum nitride (AlN) to study the changes in structural and electrical properties of the Mo films. Results show that Mo grown at 700{\deg}C on epitaxial AlN exhibit low surface roughness, large average grain diameter, low resistivity, and high crystal quality. XRD pole figure and phi-scan reveal that irrespective of the growth temperature, Mo is fiber textured on fiber-textured AlN, and has three rotational domains on epitaxial AlN. The study shows that the resistivity of Mo reduces with increasing growth temperature, which we relate to increasing average grain diameter. Additionally, we show that fiber-textured Mo has more high angle grain boundaries resulting in consistently higher resistivity than its epitaxial equivalent.