Density dependence of the room temperature thermal conductivity of atomic layer deposition-grown amorphous alumina (Al2O3)

Abstract

We report on the thermal conductivity of atomic layer deposition-grown amorphous alumina thin films as a function of atomic density. Using time domain thermoreflectance, we measure the thermal conductivity of the thin alumina films at room temperature. The thermal conductivities vary ∼35% for a nearly 15% change in atomic density and are substrate independent. No density dependence of the longitudinal sound speeds is observed with picosecond acoustics. The density dependence of the thermal conductivity agrees well with a minimum limit to thermal conductivity model that is modified with a differential effective-medium approximation.

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

“…319 The reported thermal conductivities for poly-crystalline 254,320 and amorphous [57][58][59]321 Al 2 O 3 of 16-33 and 0.7-2.6 W/mK, respectively, are also comparable to the previously discussed lower range reported for AlN and amorphous SiO 2 (see Table VIII Regarding HfO 2 , we are unaware of any reports of thermal conductivity for single-crystal hafnia. Investigations of bulk ceramic or sputter deposited thin film poly-crystalline hafnia doped/stabilized with yttria for thermal barrier coating applications have reported relatively low thermal conductivities of 1.5-2.0 W/mK.…”

“…44,45 For such devices, knowledge of properties such as Young's modulus and film stress are critical for predicting the flexure and resonance frequencies of bridged and cantilevered switches and sensors, [46][47][48][49] stretched transistor device performance, 50,51 buckling failures in nanopatterned structures, 52,53 and macroscale buckling and nanoscale wrinkling effects for stiff high-k films deposited on compliant polymeric substrates. 54,55 Unfortunately, only a limited number of studies have reported on the thermal [56][57][58][59] and mechanical 42,[60][61][62][63][64][65][66] properties of ALD highk dielectric materials, and the numerous reviews [2][3][4][5][6][7][8] of high-k dielectrics have focused primarily on the electronic structure and interfacial properties of high-k dielectrics from a CMOS device perspective. To the authors' knowledge, a clear correspondence between thermal/mechanical and electrical/optical properties for ALD high-k dielectrics has yet to be established.…”

“…The former was determined via both mechanical profilometry as well as picosecond acoustics, the details of which have been described thoroughly elsewhere. 58 For the latter, the heat capacity reported for bulk high-k dielectrics were utilized and scaled by the density as measured via NRA-RBS. 149,150 As will be discussed later, this assumption was justified based on the mass density of the high-k films approaching the bulk crystalline values.…”

“…Thermal conductivity.-The out-of-plane thermal conductivity and interfacial thermal resistance between the ALD high-k dielectrics and the Si substrate was determined via TDTR measurements that have been previously described. 58,146 Briefly, an aluminum film with nominal thickness of 80 nm was first deposited on the ALD high-k dielectrics via E-beam evaporation. The samples were then exposed to a short (<1 ps) pulsed optical beam from an oscillating Ti:sapphire laser operating at a repetition rate of 80 MHz centered at a wavelength of 800 nm.…”

Low‐Temperature Mullite Formation in Ternary Oxide Coatings Deposited by ALD for High‐Temperature Applications

“…The estimated ratio was calculated by using the individual compound growth per cycle, for Al 2 O 3 and SiO 2 of 1.7 and 0.6 Å per cycle, respectively, and an average of already reported film densities. [52][53][54] It was assumed that the whole opaline structure was homogeneously infiltrated, for further details refer to the Supporting Information.…”