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Researchers developed digital micro fluidiccooling system to solve the problem causedby non uniform thermal distribution.

Here we use microlitre to nanolitre sizeddroplets to move independently along thesubstrate and there by cool the chip.Here we use liquid metal droplets to create

an adaptive thermal interface

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PASSIVE COOLINGIt include thermalconduction, naturalconvection,radiationVery highperformance andlow expensive

Eg: Heat pipes andThermosyphons

ACTIVE COOLINGIt requires externalpower

It use externalcomponents such asforced convectiondevice ,pumped loopsand refrigerators

It is of two typesAdaptive andnonadaptive

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Fan based coolingMacro fluidic based coolingMEMS based coolingRefrigeration based coolingMicro fluidics based system

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The first micro fluidic cooling device wasthe microchanel heat sinkThis is based on the principle of Newton's law

of coolingdQ/dt=hA (Tb-Tf)

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Micro fluidic operations can be reduced to aset of basic discrete operations ,allowing ahierarchical cell based design approach.

The absence of permanently etchedstructures allows a completelyreconfigurable systemGiven a 2D array of actuating electrodes ,

the device can manipulate liquid dropletslaterally in any arbitrary path with externalpumps and valves.

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Electro wetting baseddroplet actuation

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A digital micro fluidic device achieves dropletmotion through the electro wetting effect .Applying a potential to an underlying electrode

controls a droplets ability to wet the surface .Applying this electric field increases the dropletsurface energy and therefore the droplet wets thesurface. This result in a decrease in the contact

angle ,causing the droplet to spread in to theelectrode. Placing a droplet on top of the array of electrode initiates lateral motion.

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Flow through adaptive cooling , would useaqueous droplets continuously dispensedfrom an actively cooled reservoir and

transported over an ICs surface .The droplet would transfer, store and carryheat away from the IC substrate back to thecooling reservoir .

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The device detects a hotspot over a cell ,theelectrode in the cell is turned off , causingthe droplet to relax and subsequently come

into contact with the top plate.This reduces thermal resistance between thehotspot and the heat sink by several ordersof magnitude , and can then pass more

efficiently from the hotspot to the heat sink

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Temperature drop of ahotspot when a mercurydroplet in oil or a waterdroplet in oil passes over itwith and without a viabeneath the droplet

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Temperature drop for thehot spot versus heat fluxdensity

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Faster coolingHigh efficiencyCooling rates match with chip thermal profile

Avoid the problem caused by nonuniformthermal profile .Easy hot spot cooling .

Reconfigurable system

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We have demonstrated the feasibility of usingthe concept of digital micro fluidics forapplications in chip cooling . Several challengersremain , however , before adaptive spot coolingis possible in a real system. These include scalingthe platforms physical dimensions to transitionfrom microlitre to nanolitre size droplets,exploring alternative liquids to achieve even

higher thermal conductivities, and implementingalternative dielectric materials to insulate theelectrodes from the droplet in order to achieveeven faster droplet transport speeds.

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Design and test of computers , IEEEDigital object identifierPublished : 2008

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