Development of nano-sheet heat flow control unit with heat phonon transmission spectroscopy

Abstract

The severe heat issues prevalent in semiconductor nano-devices restrict their maximum operating speed. As these devices are constructed with nano-scale thinner materials, the Thermal Boundary Resistance (TBR) between distinct materials significantly contributes to the overall thermal resistance. Consequently, the interface is often a significant hurdle in achieving efficient thermal management. Despite needing a detailed microscopic understanding to address these thermal management challenges, current experimental approaches have yielded limited insights through frequency- and polarization-integrated boundary resistance values. In my dissertation, I introduce a novel research platform to overcome heat dissipation issues in nano-devices. Building upon the preliminary investigations by Hua et al., I have developed an experimental platform to measure the acoustic phonon transmission coefficient spectrum across nano-thick interface layers. Utilizing the Heat Phonon Transmission Spectroscopy (HPTS), I have determined the phonon transmission spectra at metal-semiconductor interfaces. This is complemented by structural and chemical analyses using Transmission Electron Microscopy (TEM) and Energy-Dispersive Spectroscopy (EDS). The resulting transmission data, linked to the spectral heat flux at the interface, offers a more comprehensive understanding of the thermal properties of interfaces by highlighting polarization- and frequency-dependent phonon transport. For example, I have successfully shown that spectral thermal functionalities, such as phonon low-pass filters and mode converters, can be implemented in nanometer-thick interface layers. These layers include amorphous & chemically graded layers, crystalline & chemically graded layers, oxidized layers, and graphene inserts; all formed between Al and various semiconductors (GaAs, Ge, Si). Through the HPTS, which enables the acquisition of spectrally-resolved scattering rates by transforming the phonon transmission coefficients, I have elucidated the mechanisms underlying these thermal functionalities. Moreover, this also gives a chance to investigating the Boson peak behavior in amorphous materials, crucial for understanding the fundamental heat flow phenomena.