Cooling of integrated circuits using droplet-based microfluidics

Abstract

Decreasing feature sizes and increasing package densities are making thermal issues extremely important in IC design. Uneven thermal maps and hot spots in ICs cause physical stress and performance degradation. Many MEMS and microfluidics-based solutions were proposed in the past. We present a cooling method based on high-speed electrowetting manipulation of discrete submicroliter droplets under voltage control with volume flow rates in excess of 10 mL/min. We also propose a flow-rate feedback control where the hot areas get increased supply of droplets without the need for external sensors and electrothermocapillary control where hot areas attract droplets due to thermocapillarity and are returned to their reservoirs by electrowetting resulting in a self-contained and a self-regulated system.

Digitized Heat Transfer Using Electrowetting on Dielectric

“…EWOD can be used for transporting electrically conductive liquid metals and alloys; these fluids typically demonstrate orders of magnitude higher thermal conductivities than non-metallic liquids such as water or oils [7]. Galinstan, 1 an inexpensive eutectic gallium/indium/tin alloy commonly used in modern medical thermometers, has a thermal conductivity 65 times higher than water's.…”

Oscillating nanofluid droplet for micro-cooling

“…Fast and efficient cooling of hot spots has remained a major challenge while designing the latest cooling strategies. In this respect, Digital microfluidics (DMF) [4,5] technology may offer a better alternative for chip cooling as it can efficiently handle discrete droplets of small volume, and provide enhanced process rate due to the high surface to volume ratio [6]. A recent study also shows an enhancement in the cooling efficiency by pulsating DC voltage induced oscillating droplets [7].…”

Characterization of the heat transfer accompanying electrowetting or gravity-induced droplet motion

“…The key application areas driving this interest include lab-on-chip systems, electrowetting-based optics and liquid displays. There has been recent interest in using electrowetting for heat transfer applications [3][4][5]; as an illustration, electrowetting-based microelectronics thermal management (package level as well as site-specific hot spot thermal management) has been the focus of some recent research efforts.…”

“…Only a few studies have reported experimental measurements of the heat transfer performance of electrowetting-based droplet systems. Pamula and Chakrabarty [3] suggested the use of an electrowetting-based digital microfluidic system for cooling hot spots in integrated circuits. They also proposed a dynamic cooling system utilizing thermocapillarity and electrowetting; hot spots on the chip would attract higher flow rates due to thermocapillarity, and this hot fluid would be returned to the reservoir using electrowetting-based pumping.…”

“…Preliminary feasibility calculations by Pamula and Chakrabarty [3] showed that up to 90 W/cm 2 of heat dissipation is possible from an array of droplets flowing on a chip without any area enhancement. Oprins et al [21] modeled the internal flow and heat transfer inside a two-dimensional droplet moving between two plates under electrowetting actuation.…”