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A two-phase heat spreader has been developed for cooling high heat flux sources in high-power lasers, high-intensity light-emitting diodes (LEDs), and semiconductor power devices. The heat spreader uses a passive mechanism to cool heat sources with fluxes as high as 5 W/mm 2 without requiring any active power consumption for the thermal solution. The prototype is similar to a vapor chamber in which water is injected into an evacuated, air-tight shell. The shell consists of an evaporator plate, a condenser plate and an adiabatic section. The heat source is made from aluminum nitride, patterned with platinum.The heat source contains a temperature sensor and is soldered to a copper substrate that serves as the evaporator. Tests were performed with several different evaporator microstructures at different heat loads. A screen mesh was able to dissipate heat loads of 2 W/mm 2 , but at unacceptably high evaporator temperatures. For sintered copper powder with a 50 Pm particle diameter, a heat load of 8.5 W/mm 2 was supported, without the occurrence of dryout. A sintered copper powder surface coated with multi-walled carbon nanotubes (CNT) that were rendered hydrophilic showed a lowered thermal resistance for the device. KEYWORDS: heat spreader, two-phase, high heat flux, carbon nanotube, sintered copper NOMENCLATURE A cross-sectional area, m 2 d mesh wire diameter, m p D particle diameter, m g D channel depth, m h heat transfer coefficient, W/m 2 K K permeability, m 2 L length, m m mass flux, kg/s P ǻ pressure differential, Pa con Q condensation heat, W eff r effective pore radius, m t thickness, m T ' temperature differential, K W mesh opening, m g W channel width, m Greek symbols H porosity P viscosity, Pa s U mass density, kg/m 3 V surface tension coefficient, N/m

The rapid development of microfluidic technology has increased the demand for the integration of driving circuits in the microfluidic devices. We have proposed a novel on-chip electroosmotic (EOF) micropump integrated with a high-voltage (HV) generator. The HV (49.8 V) generator is based on a Dickson charge pump, which is fabricated on a silicon-on-insulator (SOI) substrate by the standard CMOS process, and the isolation is achieved by MEMS post-processed deep trench isolation. The size of the 49.8 V generator is 425×353 µ m 2 . The HV required for the successful operation of the micropump was generated by the integrated driving circuit with a low-voltage power supply. The maximum flow velocity and flow rate of the proposed EOF micropump were measured as 137 µ m/s and 167 nL/min, respectively when it was driven by the integrated 49.8 V generator. The efficiency of the micropump is demonstrated by comparing it with the previously reported micropumps. The proposed integration technique is reliable and effective, and potentially boosts the practical applications of lab-on-chip devices.