Changwook Jung

Using a full band description of electronic bandstructure, the Landauer approach to diffusive transport is mathematically related to the solution of the Boltzmann transport equation, and expressions for the thermoelectric parameters in both formalisms are presented. Quantum mechanical and semiclassical techniques to obtain from a full description of the bandstructure, E(k), the density of modes in the Landauer approach or the transport distribution in the Boltzmann solution are compared and ther

The question of what fraction of the total heat flow is transported by phonons with different mean-free-paths is addressed using a Landauer approach with a full dispersion description of phonons to evaluate the thermal conductivities of bulk and thin film silicon. For bulk Si, the results reproduce those of a recent molecular dynamic treatment showing that about 50% of the heat conduction is carried by phonons with a mean-free-path greater than about 1 μm. For the in-plane thermal conductivity o

Traditional transparent conducting materials such as ITO are expensive, brittle, and inflexible. Although alternatives like networks of carbon nanotubes, polycrystalline graphene, and metallic nanowires have been proposed, the transparency-conductivity trade-off of these materials makes them inappropriate for broad range of applications. In this paper, we show that the conductivity of polycrystalline graphene is limited by high resistance grain boundaries. We demonstrate that a composite based o

Using a full dispersion description of phonons, the thermal conductivities of bulk Si and Bi2Te3 are evaluated using a Landauer approach and related to the conventional approach based on the Boltzmann transport equation. A procedure to extract a well-defined average phonon mean-free-path from the measured thermal conductivity and given phonon-dispersion is presented. The extracted mean-free-path has strong physical significance and differs greatly from simple estimates. The use of simplified dis

We present machine learning models for the prediction of thermal and mechanical properties of polymers based on the graph convolutional network (GCN). GCN-based models provide reliable prediction performances for the glass transition temperature (<i>T</i> _g), melting temperature (<i>T</i> _m), density (ρ), and elastic modulus (<i>E</i>) with substantial dependence on the dataset, which is the best for <i>T</i> _g (<i>R</i> ² ∼ 0.9) and worst for <i>E</i>

There is a growing consensus that the physics-based model needs to be coupled with machine learning (ML) model relying on data or vice versa in order to fully exploit their combined strengths to address scientific or engineering problems that cannot be solved separately. We propose several methodologies of bridging technology computer-aided design (TCAD) simulation and artificial intelligence (AI) with its application to the tasks for which traditional TCAD faces challenges in terms of simulatio

The question of what bandstructure produces the best thermoelectric device performance is revisited from a Landauer perspective. We find that a delta-function transport distribution function (TDF) results in operation at the Mahan-Sofo upper limit for the thermoelectric figure-of-merit, ZT. We show, however, the Mahan-Sofo upper limit itself depends on the bandwidth (BW) of the dispersion, and therefore, a finite BW dispersion produces a higher ZT when the lattice thermal conductivity is finite.

The DC current-voltage characteristics of an n-channel silicon MOSFET with an effective gate length of about 60 nm are analyzed and interpreted in terms of scattering theory. The experimental results are found to be consistent with the predictions of scattering theory - the drain current is closer to the ballistic limit under high drain bias than under low drain bias, and the on-current in strong inversion is limited by a small portion of the channel near the source. The question of how the low-

An advanced bottom electrode contact (BEC) was successfully developed for reliable high-density 256Mb phase-change random access memory (PRAM) using a ring-type contact scheme. This advanced ring-type BEC was prepared by depositing very thin TiN films inside a contact hole, after which core dielectrics were uniformly filled into the TiN-deposited contact hole. Using this novel contact scheme, it was possible to reduce reset current while maintaining a low set resistance and a uniform cell distri

Thin aluminum oxide (Al 2 O 3 ) films were grown by the plasma-assisted atomic layer controlled deposition (PAALD) method using Dimethylethylamine alane [(CH 3 ) 2 (C 2 H 5 )N:AlH 3 ] (DMEAA). Al was deposited by the PAALD method, then the Al films were oxidized into Al 2 O 3 by plasma oxidation in the same chamber without breaking the vacuum. Al 2 O 3 thin films of 15 nm thickness were prepared by repetition of this process. Thus prepared Al 2 O 3 thin films exhibited a refractive index of 1.68

For devices beyond the 14nm node, it is important to investigate performance boosters such as high mobility channels. Although pure Ge offers a higher hole mobility than Si, conventional problems like surface passivation and its integration with Si makes SiGe alloy with low Ge mole fraction a viable option. The significance of alloy scattering, however, has been widely debated [1-3], so the accurate modeling of alloy scattering in SiGe channel has become an important issue to predict the perform

Substantial reduction of thermal conductance (Kph) was recently reported for air gap heterostructures (AGHs) in which two bulk layers were connected by low-density nanopillars. We analyze Kph using a full phonon dispersion and including important phonon scattering. We find a transition from ballistic at low temperatures to quasi-ballistic transport near room temperature and explain the slow roll-off in Kph that occurs near room temperature. We show that the density of nanopillars deduced from th