Vivek Sahu

Hybrid Solid State/Fluidic Cooling for Hot Spot Removal

In this article we describe a novel cooling scheme utilizing a combination of fluidic (single-phase convection and phase change) and solid-state (superlattice cooler) techniques to simultaneously remove high background heat fluxes (∼100 W/cm2) over the entire chip and dissipate ultra high heat fluxes (∼0.5–1 kW/cm2) from multiple localized hot spots. This article focuses on the conceptual design to assess the feasibility of the proposed cooling scheme.

Energy efficient liquid-thermoelectric hybrid cooling for hot-spot removal

We report a study on a liquid-thermoelectric hybrid cooling that allows a multiple larger heat flux (>;600 W/m2) hotspots on a chip that is never achievable with a reasonable pump power for a microchannel with single phase liquid cooling. Thermoelectric effect is realized in this study by embedding to the silicon chip in superlattice microcooler which has been studied in our previous work. We went through an analytic modeling including spreading resistance through the substrate and modeled the fluid dynamic characteristic of microchannel so that we were able to find the pump power and cooling power of superlattice cooler. We also verified the performance with 3D numerical simulation. The results show that the hybrid system allows much higher heat flux for a hotspot while superlattice cooler locates correctly. As an example, if we have a ZT=0.5 material, a 500μm × 500μm hotspot can be maintained at 85°C (ambient 35°C) with around 850W/cm2 while a simple liquid cooling reaches 620W/cm2 for the same 12W/cm2 of overall cooling power.

Infrared Imaging Microscope as an Effective Tool for Measuring Thermal Resistance of Emerging Interface Materials

The reduction of interfacial resistance continues to be a significant challenge in thermal management of semiconductor and other microscale devices. Current state-of-the-art thermal interface materials (TIMs) have resistances in the range of 5–10 mm2 ·K/W. At these values, particularly for the emerging highly nonhomogeneous materials, standard measurement techniques often fail to provide accurate results. This paper describes the use of infrared microscopy for measuring the total thermal resistance across multiple interfaces. The method is capable of measuring samples of wide ranging resistances with thicknesses ranging from 50–250 μm. This steady-state technique has several advantages over other methods, including the elimination of the need for intrusive temperature monitoring devices like thermocouples at the area of interest and the need for a priori knowledge of the specific heat and density of the materials of interest, as in the transient techniques for determining thermal resistances. Results for three different commercially available TIM and uncertainty analysis are presented.Copyright

Experimental investigation of hotspot removal using superlattice cooler

Thermal management of high performance microprocessors is becoming increasingly challenging due to the presence of hotspots. Temperature at the hotspot can be substantially greater than rest of the microprocessor, potentially compromising performance and reliability. In this paper, we have presented a hybrid cooling scheme which combines microfluidic and solidstate cooling techniques. Localized hotspot with heat flux close to 250 W/cm2 has been successfully removed using this hybrid scheme. The effect of ambient temperature, hotspot size, and superlattice cooler electrode location is also studied.

Hybrid solid state/fluidic cooling for hotspot removal

In this paper we describe a novel cooling scheme utilizing a combination of fluidic (single-phase convection and phase change) and solid-state (superlattice cooler) techniques to simultaneously remove high background heat fluxes (~100 W/cm2) over the entire chip and dissipate ultra high heat fluxes (~0.5-1 kW/cm2) from multiple localized hotspots. This paper focuses on the conceptual design to assess the feasibility of the proposed cooling scheme.

Cooling power optimization for hybrid solid-state and liquid cooling in integrated circuit chips with hotspots

We report theoretical investigation and optimization of a hot-spot cooling method. This hybrid scheme contains a liquid cooling microchannel and superlattice hotspot cooler(s). This analysis of the hybrid method aims to solve the potential thermal management challenges for hotspots especially in 3D stacked multichip packaging. The goal is to reduce the overall cooling power and optimize the energy efficiency. Starting with a generic modeling of the superlattice cooler system, the cooling temperature as a function of the superlattice thickness and the driving current is found. The analytic results are then compared with full 3D numerical simulation. The role of spreading thermal resistance in the chip substrate was found to be important. The later part of this report is the integration of the microchannel with the hotspot cooler. The pumping power is modeled based on the microchannel design and fluid properties. The total cooling power, the sum of the electrical power to pump the liquid and the electrical power to drive the superlattice cooler, is found as a function of overall heat dissipation of the chip including hotspot(s). As the goal is to keep the hottest point on the chip below certain threshold (e.g. 85°C), the result shows a dramatic reduction of the required total cooling power, when hybrid cooling scheme - superlattice hotspot cooler in conjunction with microchannel cooler - is used. Above particular analysis is based on the specific microchannel, but this proposed scheme allows us a systematic study to reduce the pump power further.

Experimental Characterization of Hybrid Solid-State and Fluidic Cooling for Thermal Management of Localized Hotspots

A hybrid cooling scheme utilizing superlattice coolers (SLCs) along with microchannel heat sink for thermal management of hotspots is presented. In this paper, we have studied the effect of operating and design parameters on the performance of the SLC. We have also experimentally investigated the effect of interface thermal resistance as well as thermal resistance between the ground electrode and superlattice using two test configurations: one with on-chip microchannels and another with off-chip microchannels. We demonstrated heat removal capability at the localized hotspots of more than over 300 W/cm2.

Computational and Experimental Investigation of Thermal Coupling Between Superlattice Coolers

Thermal coupling between superlattice coolers (SLCs) in an array adversely affects performance of an each individual cooler compared with an isolated device. Here, we have developed an electrothermal model to study this coupling between SLCs and how it is affected by geometric parameters such as separation between the superlattice structure and a ground electrode, and operating parameters such as the convective heat transfer coefficient and the activation current applied for driving the SLC. Complementary to the modeling efforts, we have also experimentally studied thermal coupling between SLCs in a microfabricated array under various conditions. Simulation results are critically compared against the experimental data and yield the conclusions of importance for an optimized design of the hybrid microfluidic SLC cooling scheme for thermal management of multiple clustered hotspots in microprocessors. We have observed more than 60% reduction in cooler performance, when placed within the few characteristic diameters of the ground electrode, due to thermal coupling effect. Thermal properties of the working fluid have even more pronounced effect on the thermal coupling between the coolers.

Hybrid Superlattice Coolers for Dynamic Thermal Management of Microprocessor Hotspots

A hybrid cooling scheme for thermal management of hotspots (300–500 W/cm2 ) in the presence of low background heat flux (100 W/cm2 over 1 cm2 ) is being investigated. It uses superlattice coolers (SLCs) to remove ultra high power density hotspot and microchannel heat sink for lower background heat flux. In this paper, transient response of the SLC for hotspot removal is studied. The effect of contact resistance, chip thickness, and hotspot size on the performance of the hybrid cooling scheme is also investigated.Copyright