Micro Nano Devices & Systems Lab

Projects

Electro-Thermal Transport in Flexible Electronics

Temperature Distribution in CNT network TFT at High Electric Field

 


Carbon nanotube (CNT) network based thin-film transistors (TFTs) have potential to substantially increase the performance of flexible electronic applications such as displays, e-clothing, pressure-sensitive skin, large-area chemical and biological sensors, flexible and shape-conformable antennae and radar. Our research focuses on developing computational and analytical models to analyze electro-thermal transport in a random percolating network of carbon nanotubes and its composites using the concepts of heat and electron transport physics, and heterogeneous percolation theory. We explore the effect of self-heating in CNT-TFTs using a self-consistent electro-thermal model which provides insights on the challenges and restrictions of these devices for being used in technological applications due to the dominance of contact  resistances at CNT interfaces,  performance variability from one device to other and inability in employing active cooling solutions for high frequency applications. » More Details

 

Thermal Transport in 1-D and 2-D Nanostructures 

Thermal contact resistance at the interface of carbon nanostructures such as carbon nanotube (CNT) or graphene interface with metals and insulators may become bottleneck in heat-removal from the devices employing these structures. We focus on exploring phonon transport in CNTs, graphene and their nano-junctions using atomistic simulation methods such as Molecular Dynamics (MD) and Atomistic Green's Function Method (AGF). We investigate the interlayer thermal interaction of double-wall carbon nanotubes (DWCNTs) using MD simulations and wavelet method. The coupling of the vibration modes and energy exchange between layers of DWCNTs is analyzed through the spatiotemporal profiles of power spectrum. An appropriate understanding of the energy exchange between different layers of tubes will pave the path of the future design of MWCNT based pellets and composites. We study the phonon transport at the interface of graphene and metals using MD and AGF simulations and estimated the contributions of different phonon modes to the in-plane thermal conductivity of metal-supported graphene, frequency dependent transmisison function and thermal bounndary conductance. » More Details

           Thermal/Electronic interactions at interfaces

Thermal Management of Microelectronic Devices

Temperature Profile on ChipRandom       Cyclic              Global

Multiple TECs in Package


This work focuses on two novel techniques for the thermal management of microelectronic processors: power multiplexing and ultra-thin thermoelectric coolers (TECs). Power multiplexing involves dynamical change of the locations of active cores within the chip at fixed time intervals in order to mitigate the spatio-temporal thermal gradients on a chip. Power multiplexing technique helps in reducing the number of hotspots on the chip by facilitating a spatially uniform thermal profile which in turn lowers the maximum temperature on the chip. Our investigation of an electronic package with multi-core processors using a transient thermo-fluidics model shows that the selection of appropriate migration policy and the migration rate can efficiently reduce the spatial non-uniformity and peak temperature on the chip.

The exploration of ultrathin thermoelectric coolers (TECs) on the active side of microelectronic devices for the energy efficient thermal management of hot spots is another thread of this research. Our research analyzes the efficient usage of ultrathin TECs by focusing on important issues such as integration of these devices with electronic package, effect of parasitic contact resistances, utilization of appropriate current pulses and control algorithms. The study extends to analyzing coupled operation of multiple TECs for cooling spatiotemporally varying hot spots in order to maintain the dynamic hot-spot temperature below a threshold. We are currently developing experimental set-up to investigate the operation of embedded TECs using on-chip resistance temperature detectors and thin-film based TECs. » More Details

3D Embedded Interconnects

The increasing levels of integration and high current densities impacts the quality and reliability of interconnects in microelectronics. High operating temperature and high level of thermo-mechanical stresses are primarily responsible for morphological changes in the metallic interconnect lines leading to their early failure. This research addresses the transient thermal behavior of planar and 3D interconnects through both modeling and experimental testing. Development of integrated analysis tool for transient thermal analysis of multiscale interconnects structure is a difficult challenge. We develop a computationally efficient and accurate multi-scale reduced order transient thermal modeling methodology  using a combination of two different approaches: “Progressive Zoom-in” method and “Proper Orthogonal Decomposition (POD)” technique. We demonstrate the capability of this approach in handling several decades of length scale from “package” to “chip components” at a considerably lower computational cost, while maintaining satisfactory accuracy. Additionally, we develop an experimental platform to evaluate rapid transient Joule heating in embedded nanoscale metallic films representing buried on-chip interconnet. Utilizing sub-micron resistance thermometry technique with a spatial resolution of 10 µm and thermal time constant of1µs, we study the effect of rapid transient power input profiles with different amplitudes and frequencies.

      

(a) Optical Image of Interconnect layer. (b) SEM image of the serpentine section of  RTDs fabricated on top of Interconnect layer. (c) Zoomed-in SEM image of the serpentine section of an RTD.

 

Multiscale Modeling of Electrical and Thermal Tranport in GaN High-Electron Mobility Transistors

AlGaN/GaN based high electron mobility transistors (AG-HEMTs) are the strong candidates for the high power and high frequency applications due to the superior properties ofAlGaN/GaN hetero-structure such as high carrier saturation velocity, wide band gap, high breakdown field and thermal conductivity. However, reliability concerns such as performance degradation at elevated temperatures or stresses need to be addressed for the widespread realization of AG-HEMTs. Understanding the underlying details of the thermal transport in the device is going to be an important step towards solving heat dissipation and reliability challenges in these devices. We develop a multi-scale diffuse-ballistic thermal transport model of AG-HEMTs and investigate the hot spot formation and energy transport from hot-spot. Device is studied under both DC and AC operations to understand the heat dissipation effects on device performance under realistic conditions. » More Details