Abstract
High power density electronics are severely limited by current thermal management solutions which are unable to dissipate the necessary heat flux while maintaining safe junction temperatures for reliable operation. We designed, fabricated, and experimentally characterized a microfluidic device for ultra-high heat flux dissipation using evaporation from a nanoporous silicon membrane. With ~100 nm diameter pores, the membrane can generate high capillary pressure even with low surface tension fluids such as pentane and R245fa. The suspended ultra-thin membrane structure facilitates efficient liquid transport with minimal viscous pressure losses. We fabricated the membrane in silicon using interference lithography and reactive ion etching and then bonded it to a high permeability silicon microchannel array to create a biporous wick which achieves high capillary pressure with enhanced permeability. The back side consisted of a thin film platinum heater and resistive temperature sensors to emulate the heat dissipation in transistors and measure the temperature, respectively. We experimentally characterized the devices in pure vapor-ambient conditions in an environmental chamber. Accordingly, we demonstrated heat fluxes of 665 ± 74 W/cm2 using pentane over an area of 0.172 mm × 10 mm with a temperature rise of 28.5 ± 1.8 K from the heated substrate to ambient vapor. This heat flux, which is normalized by the evaporation area, is the highest reported to date in the pure evaporation regime, that is, without nucleate boiling. The experimental results are in good agreement with a high fidelity model which captures heat conduction in the suspended membrane structure as well as non-equilibrium and sub-continuum effects at the liquid–vapor interface. This work suggests that evaporative membrane-based approaches can be promising towards realizing an efficient, high flux thermal management strategy over large areas for high-performance electronics.
Highlights
Heat dissipation is a critical bottleneck in a wide range of electronic devices including microprocessors, solar cells, laser diodes and radio frequency (RF) power amplifiers
Gallium nitride (GaN)-based power amplifiers have demonstrated unprecedented RF output power densities due to the excellent electrical properties of GaN; high dissipated power densities lead to elevated electronic junction temperatures and degraded performance and reliability[1,2]
These thermal management challenges arise from the layout and spatial distribution of heat sources which exhibit sub-millimeter hot spots with heat fluxes (q′′) in excess of 1 kW/cm[2] over a planar area of 5–10 mm2 . 4 In the traditional remote cooling paradigm, a power amplifier chip is bonded to a series of solid-state, high conductivity heat spreaders (Cu, CuW, and diamond) with thermal interface materials and cooled by air-cooled heat sinks or liquidcooled plates[5]
Summary
Heat dissipation is a critical bottleneck in a wide range of electronic devices including microprocessors, solar cells, laser diodes and radio frequency (RF) power amplifiers. In many commercial and defense applications, GaN power amplifiers are limited to onetenth of their potential RF output power due primarily to the limitations of existing thermal management technologies[3]. These thermal management challenges arise from the layout and spatial distribution of heat sources which exhibit sub-millimeter hot spots with heat fluxes (q′′) in excess of 1 kW/cm[2] over a planar area of 5–10 mm . To efficiently dissipate high heat fluxes while limiting temperature rise, an embedded cooling solution utilizing phase-change heat transfer is needed in which heat is removed at the chip level rather than at the electronics package level, thereby eliminating the resistance of the thermal spreaders and interface materials[6]. In power amplifier applications, embedded cooling is only possible with dielectric fluids, because the flow of a conducting fluid in close proximity to the transistor induces a magnetic field which disrupts electrical device performance
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