Jeremy A. Rowlette

Thermal Boundary Resistance Measurements for Phase-Change Memory Devices

Thermal interfaces play a key role in determining the programming energy of phase-change memory (PCM) devices. This letter reports the picosecond thermoreflectance measurements of thermal boundary resistance (TBR) at TiN/GST and Al/TiN interfaces, as well as the intrinsic thermal conductivity measurements of fcc GST between 30°C and 325°C. The TiN/GST TBR decreases with temperature from ~26 to ~18 m2·K/GW, and the Al/TiN ranges from ~7 to 2.4 m2·K/GW. A TBR of 10 m2·K/GW is equivalent in thermal resistance to ~192 nm of TiN. The fcc GST conductivity increases with temperature between ~0.44 and 0.59 W/m/K. A detailed understanding of TBR is essential for optimizing the PCM technology.

Thermal Properties of Ultrathin Hafnium Oxide Gate Dielectric Films

Thin-film HfO2 is a promising gate dielectric material that will influence thermal conduction in modern transistors. This letter reports the temperature dependence of the intrinsic thermal conductivity and interface resistances of 56-200-Aring-thick HfO2 films. A picosecond pump-probe thermoreflectance technique yields room-temperature intrinsic thermal conductivity values between 0.49 and 0.95 W/(mmiddotK). The intrinsic thermal conductivity and interface resistance depend strongly on the film-thickness-dependent microstructure.

Fully Coupled Nonequilibrium Electron–Phonon Transport in Nanometer-Scale Silicon FETs

Heat conduction from transistors and interconnects is a critical design consideration for computing below the 20-nm milestone. This paper reviews detailed heat generation and transport mechanisms in silicon devices with a focus on the nonequilibrium behavior of electrons and phonons. Fully coupled and self-consistent ballistic phonon and electron simulations are developed in order to examine the departure from equilibrium within the phonon system and its relevance for properly simulating the electrical behavior of devices. We illustrate the manner in which nanoscale-transport phenomena are critically important for a broad variety of low-dimensional silicon-based devices, including FinFETs and depleted substrate transistors.

Thermal conduction in lattice–matched superlattices of InGaAs/InAlAs

Understanding the relative importance of interface scattering and phonon-phonon interactions on thermal transport in superlattices (SLs) is essential for the simulation of practical devices, such as quantum cascade lasers (QCLs). While several studies have looked at the dependence of the thermal conductivity of SLs on period thickness, few have systematically examined the effect of varying material thickness ratio. Here, we study through-plane thermal conduction in lattice-matched In0.53Ga0.47As/In0.52Al0.48As SLs grown by metalorganic chemical vapor deposition as a function of SL period thickness (4.2 to 8.4 nm) and layer thickness ratio (1:3 to 3:1). Conductivities are measured using time-domain thermoreflectance and vary between 1.21 and 2.31 W m−1 K−1. By studying the trends of the thermal conductivities for large SL periods, we estimate the bulk conductivities of In0.53Ga0.47As and In0.52Al0.48As to be approximately 5 W m−1 K−1 and 1 W m−1 K−1, respectively, the latter being an order of magnitude low...

Temperature-Dependent Thermal Properties of Phase-Change Memory Electrode Materials

The programming current required to switch a phase-change memory cell depends upon the thermal resistances in the device. In many designs, significant heat loss occurs through the electrode. This letter investigates the thermal properties of a multilayer electrode stack. This material offers greater thermal resistance than single-material electrodes due to the presence of multiple thermal boundary resistances (TBRs), reducing heat loss from the device and potentially lowering the programming current. Picosecond time-domain thermoreflectance interrogates the temperature-dependent thermal conductivity of three as-deposited and postannealed electrode materials: carbon, titanium nitride, and tungsten nitride. These data are used to extract the temperature-dependent, as-deposited, and postannealed TBR in two multilayer electrode stacks: carbon-titanium nitride and tungsten-tungsten nitride. The C-TiN stacks demonstrate an as-deposited TBR of 4.9 m2K/GW, increasing to 11.9 m2K/GW postanneal. The W-WNx stacks demonstrate an as-deposited TBR of 3.9 m2K/GW, decreasing to 3.6 m2 K/GW postanneal. These resistances are equivalent to electrode films with thickness on the order of tens of nanometers.

Joule Heating under Quasi-Ballistic Transport Conditions in Bulk and Strained Silicon Devices

We use Monte Carlo simulations to examine self-heating in ultra-short silicon devices when quasiballistic transport conditions dominate. The generated phonon spectrum in strained silicon is found to be different from bulk silicon at low electric fields, but essentially the same under high fields. Joule heat dissipation in ultra-short devices occurs almost entirely in their drain region, since transport across the channel is quasiballistic. The results of this work can be used to gauge the electro-thermal performance of ultra-scaled device geometries.

Thermal phenomena in deeply scaled MOSFETs

Thermal phenomena are having an increasing influence on drive and leakage currents in modern transistors. This trend is accelerated for confined-geometry devices, which include thermally-resistive interfaces and materials with low thermal conductivity (e.g. SiO2, Si 1-xGex). This paper summarizes the nanotransistor thermal design challenges and reviews the latest advancements in electro-thermal modeling

Electro-Thermal Transport in Silicon and Carbon Nanotube Devices

This work examines electro-thermal transport in silicon devices and in single-wall carbon nanotubes (SWNTs). Non-local transport is found to strongly affect heat generation in quasi-ballistic silicon devices. Under such conditions, Joule heat is mainly dissipated in the drain region, and increasing power densities may lead to phonon non-equilibrium. Significant current degradation is observed in suspended SWNTs, which is attributed to the presence of hot optical phonons and to a decrease in thermal conductivity (as ∼ 1/T) at high temperature (T) under self-heating. The high temperature thermal conductivity can then be extracted by using the high bias characteristics of suspended SWNTs.