Book Description

Achieving complex integrated circuits and devices, through miniaturization into the nanoscale, increasingly relies on understanding the thermal properties of the materials used in these components. Conductors at the nanoscale have properties that differ substantially from their bulk or thin film counterparts. Nanostructured gold, for example, is currently being used in a wide range of applications, including interconnects, solar cells, flexible screens, detection of cancerous cells, and energy storage. Thermal management on the nanoscale has posed significant industry challenges that directly impact the maximum current and power, speed, reliability, and lifetime of devices where so-called self-heating is a factor. General factors at reduced scale include increasing resistivity, reduction in thermal conductivity (kappa), and the desired increasing device density per unit area. Despite the prominent role of metallic nanostructures in current and future technologies, large gaps exist in understanding the influence of "size effects" on thermal characteristics at small dimensions. Prior work attempted to simulate the thermal characteristics of nanoscale materials to account for these size effects, but often fall short due to the lack of experimental verification needed for informing and testing the models based, primarily, on the Boltzmann transport equation. This dissertation focuses on development and test of a method used to generate direct experimental data on thermal conductivity for nanofilms and nanowires. The approach is applied to gold with thickness dimensions of 50 and 100 nm. The lateral dimensions studied range from 74 nm to 720 nm, thereby spanning the micro to nano regimes. The main components of this research are the fabrication and measurement methodology for direct studies of thermal conductivity at the nanoscale. Both design and data analysis rely on extensive finite element analysis simulations. The experimental results include an observed decrease in thermal conductivity as film thickness is reduced, for any lateral dimension studied. At large lateral width, corresponding to the microscale, thermal conductivity values are 280 and 200 W/mK for thicknesses of 100 and 50 nm, respectively. These are to be compared with the accepted value of 317 W/mK for thermal conductivity of bulk gold. In addition, as the latter is reduced, for either thickness, a characteristic decrease is observed beginning at ~300 nm width. For the smallest nanowire investigated, 50 nm in thickness and 74 nm in width, a value of thermal conductivity = 56 W/mK is obtained. The trends obtained are supported by data available in the literature. The decrease in thermal conductivity with diminishing size are also consistent with theoretical calculations for gold, thereby validating the reported Boltzmann transport equation approach.