Thermal conduction phenomena in nanostructured semiconductor devices and materials [electronic resource]
Keywords: Mechanical Engineering

Thermal phenomena have become very important in a variety of nanostructured semiconductor devices and materials. The reduced dimensions and large interface densities lead to complex thermal phenomena which do not occur in bulk materials and larger devices. Successful designs of high-performance semiconductor devices, including phase change memory (PCM) and high electron mobility transistors (HEMT), rely on the accurate thermal characterization of thin film materials and improved understanding of nanoscale energy transport physics. This thesis addresses nanoscale thermal transport problems relevant for three promising electronics technologies. The first part of this work investigates thermal conduction phenomena in phase change memory. A combination of frequency-domain electrical thermometry and suspended microstructure design are used to measure the in- and out-of-plane thermal conductivities of thin-film Ge2Sb2Te5 in the amorphous and crystalline phases. The preferential grain orientation and mixed phase distribution lead to a reduced in-plane thermal conductivity that is 60% -- 80% of the out-of-plane value. Anisotropic heat conduction benefits PCM devices by reducing the programming current and mitigating the thermal disturbance to adjacent cells. A fully coupled electrothermal simulation unveils the detailed transient phase distribution during a programming operation, enabling more efficient structural designs for multilevel memory operation. This research extends the thermal characterization and modeling techniques to diamond-based high electron mobility transistors. The high thermal conductivity of the diamond provides superior thermal performance and allows for up to 10x higher power density. Nanoheaters down to 50 nm wide are patterned by electron-beam lithography in order to measure the thermal resistance experienced by the single transistor channel, the multi-gate configuration, and the device package. The thermal resistance data reveals the critical role of thermal interface between the GaN device layer and the diamond substrate. This work established a criterion for the diamond technology to be viable in HEMT applications. Specifically, the thermal interface resistance needs to be less than 30 m2K/GW. The lengthscales of thermal conduction studied in this research are further scaled down to a few nanometers in the final portion of this work. This work measures the thermal properties of the mirror material for extreme ultra-violet (EUV) lithography as the next-generation semiconductor manufacturing technology. The thermal transport across the interfaces of drastically different materials, such as the Mo/Si multilayers (2.8 nm / 4.1 nm), is important in the performance and reliability of the EUV mirrors. This work demonstrates strong anisotropy in the thermal conductivities of the multilayers, where the in-plane conductivity is 13 times higher than the out-of-plane value, owing to the high density of metal-semiconductor interfaces. This research reveals that thermal conduction in such periodic multilayer composites is largely determined by the nonequilibrium electron-phonon physics. A new model indicates that two additional mechanisms -- quasi-ballistic phonon transport normal to the metal film and inelastic electron-interface scattering -- can also impact conduction in metal-dielectric multilayers with period below 10 nm, the critical length scale for the EUV mirrors.