Review—Investigation and Review of the Thermal, Mechanical, Electrical, Optical, and Structural Properties of Atomic Layer Deposited High-k Dielectrics: Beryllium Oxide, Aluminum Oxide, Hafnium Oxide, and Aluminum Nitride

Abstract

Atomic layer deposited (ALD) high-dielectric-constant (high-k) materials have found extensive applications in a variety of electronic, optical, optoelectronic, and photovoltaic devices. While electrical, optical, and interfacial properties have been the primary consideration for such devices, thermal and mechanical properties are becoming an additional key consideration for many new and emerging applications of ALD high-k materials in electromechanical, energy storage, and organic light emitting diode devices. Unfortunately, a clear correspondence between thermal/mechanical and electrical/optical properties in ALD high-k materials has yet to be established, and a detailed comparison to conventional silicon-based dielectrics to facilitate optimal material selection is also lacking. In this regard, we have conducted a comprehensive investigation and review of the thermal, mechanical, electrical, optical, and structural properties for a series of prevalent and emerging ALD high-k materials including aluminum oxide (Al2O3), aluminum nitride (AlN), hafnium oxide (HfO2), and beryllium oxide (BeO). For comparison, more established silicon-based dielectrics were also examined, including thermally grown silicon dioxide (SiO2) and plasma-enhanced chemically vapor deposited hydrogenated silicon nitride (SiN:H). We find that in addition to exhibiting high values of dielectric permittivity and electrical resistance that exceed those of SiO2 and SiN:H, the ALD high-k materials exhibit equally exceptional thermal and mechanical properties with coefficients of thermal expansion ≤ 6 × 10−6 /°C, thermal conductivites (κ) of 3–15 W/m K, and Young's modulus and hardness values exceeding 200 and 25 GPa, respectively. In many cases, the observed extreme thermal/mechanical properties correlate with the presence of crystallinity in the ALD high-k films. In contrast, some of the electrical and optical properties correlate more strongly with the percentage of ionic vs. covalent bonds present in the high-k film. Overall, the ALD high-k dielectrics investigated concurrently exhibit compelling thermal/mechanical and electrical/optical properties.