Two-Phase Vapor Chambers with Micropillar Evaporators: A New Approach to Remove Heat from Future High-Performance Chips

Abstract

High power densities lead to thermal hot spots in modern processors. These power densities are expected to reach kW/cm 2 scale in future high-performance chips and this increase may significantly degrade performance and reliability, if not handled efficiently. Using two-phase vapor chambers (VCs) with micropillar wick evaporators is an emerging technique that removes heat through the evaporation process of a coolant and has the potential to remove high heat fluxes. In this cooling system, the coolant is supplied passively to the micropillar wick via capillary pumping, eliminating the need for an external pump and ensuring stable thinfilm flow. Evaluation of such an emerging cooling technique on realistic chip power densities and micropillar geometries necessitates accurate and fast thermal models. Although multiphysics simulators based on either finite-element or finitevolume methods are highly accurate, they have long design and simulation times. This paper introduces a novel compact thermal model capable of simulating two-phase vapor chambers with micropillar wick evaporators. In comparison to COMSOL, our model shows a competitively low error of 1.25 • C and a 214x speedup. We also present a comparison of the cooling performance of different cooling techniques such as a conventional heat sink, liquid cooling via microchannels, hybrid cooling using thermoelectric coolers and liquid cooling via microchannels, and two-phase VCs with micropillar wick evaporators for the first time. Based on our observations, twophase VCs and microchannel-based two-phase cooling show better cooling performance for hot spot power densities of less than 1500 W/cm 2 , while hybrid cooling achieves lower hot spot temperature and thermal gradients for hot spot power densities between 1500 and 2000 W/cm 2 .

Neural network-based cooling design for high-performance processors

“…Micropillar wick evaporator is one type of evaporator that is particularly interesting because it uses thin-film evaporation to provide high HTC ( Vaartstra. et al., 2019 ; Yuan et al., 2019a ; 2019b ). The HTC and dry-out heat flux of the micropillar wick evaporator are mainly determined by the micropillar geometry (height, diameter, and pitch).…”

“…The cooling performance and cooling power of these potential solutions vary significantly based on the cooling parameters (such as liquid flow velocity, evaporator design, TEC current, etc.) ( Yuan et al., 2019a ; 2019b ). The selection of the cooling technologies and the cooling parameters also needs to consider the chip architecture, chip size, and floorplan, as well as the power profiles of the applications running on the given chip.…”

“…Dry-out heat flux is the thermal limit of a two-phase device. If the hot spot power density of the chip is higher than the dry-out heat flux, the coolant will no longer remain in the two-phase state and possibly cause overheating and damage to the chip ( Vaartstra et al., 2019 ; Yuan et al., 2019a ; 2019b ). Therefore, a higher dry-out heat flux means more heat can be removed before the coolant dries out.…”

“…However, these tools require significant efforts to construct system-specific models. Such tools also incur long simulation times as well as large memory requirements (e.g., simulating an -scale chip takes from hours to multiple days and easily requires tens of GBs of memory) ( Yuan et al., 2019a ; 2019b ; Kaplan et al., 2017 ). Compact thermal modeling has been designed to tackle the long design and simulation time problem ( Pedram and Nazarian, 2006 ; Skadron et al., 2003 ).…”

A Learning-Based Thermal Simulation Framework for Emerging Two-Phase Cooling Technologies

“…The reason for this accuracy loss is that these correlations are derived from various prototypes with different microchannel height, width, shape, and mass flow velocity values, and they are not sufficiently modular for application to any other microchannel structures and flow velocities. Yuan et al introduced a CTM for two-phase VCs with micropillar wick evaporators [17], [18]. The HTC values of micropillar wick geometries are extracted from a finite element model and stored in a lookup table.…”