Dominant Energy Carrier Transitions and Thermal Anisotropy in Epitaxial Iridium Thin Films

Abstract

High aspect ratio metal nanostructures are commonly found in a broad range of applications such as electronic compute structures and sensing. The self-heating and elevated temperatures in these structures, however, pose a significant bottleneck to both the reliability and clock frequencies of modern electronic devices. Any notable progress in energy efficiency and speed requires fundamental and tunable thermal transport mechanisms in nanostructured metals. In this work, time-domain thermoreflectance is used to expose cross-plane quasi-ballistic transport in epitaxially grown metallic Ir(001) interposed between Al and MgO(001). Thermal conductivities ranges from roughly 65 (96 in-plane) to 119 (122 in-plane) W m −1 K −1 for 25.5-133.0 nm films, respectively. Further, low defects afforded by epitaxial growth are suspected to allow the observation of electron-phonon coupling effects in sub-20 nm metals with traditionally electron-mediated thermal transport. Via combined electro-thermal measurements and phenomenological modeling, the transition is revealed between three modes of cross-plane heat conduction across different thicknesses and an interplay among them: electron dominant, phonon dominant, and electron-phonon energy conversion dominant. The results substantiate unexplored modes of heat transport in nanostructured metals, the insights of which can be used to develop electro-thermal solutions for a host of modern microelectronic devices and sensing structures.

High Thermal Conductivity of Submicrometer Aluminum Nitride Thin Films Sputter-Deposited at Low Temperature

“…A schematic of the AlN film specimens measured in this work is displayed in Figure d, consisting of an aluminum (Al) optothermal transducer, the AlN film, and a Si(111) or c-Al 2 O 3 substrate. Thermal properties were determined by TDTR (Section S5 in the Supporting Information), an optical pump–probe technique described extensively in our prior works. − In TDTR, an ultrafast laser is used to both induce (pump) and monitor (probe) modulated heating on the surface of the sample as a function of pump–probe time delay. The thermal conductivity and thermal boundary conductances are then determined by fitting the intensity of the ratio (− V in / V out ) signal of the reflected probe laser to a three-dimensional (3D) heat diffusion model for a multilayer stack of materials.…”

“…The thermal conductivity of the AlN films was measured with time-domain thermoreflectance (TDTR), an optical pump–probe method used extensively to determine the thermal properties of nanoscopic materials. − Knife-edge measurements of the focused spot sizes provided 1/ e 2 beam radii of 5.36 ± 0.1 and 3.19 ± 0.05 for the pump and probe, respectively. Additionally, a pump modulation frequency of 10 MHz and total emitted power of 12.5 mW were applied.…”

Non-volatile electrically programmable integrated photonics with a 5-bit operation

“…The thermal conductivity of our lms was measured with time-domain thermore ectance (TDTR) 43,44 . TDTR uses ultrafast modulated laser heating through the absorption of a thin metallic transducer layer (70 nm Pt).…”

Non-volatile electrically programmable integrated photonics with a 5-bit operation

“…The thermal conductivity of our films was measured with time-domain thermoreflectance (TDTR) 47 , 48 . TDTR uses ultrafast modulated laser heating through the absorption of a thin metallic transducer layer (70 nm Pt).…”