Hiroto Kasai

NANO-STRUCTURED TWO-PHASE HEAT SPREADER FOR COOLING ULTRA-HIGH HEAT FLUX SOURCES

A two-phase heat spreader has been developed for cooling high heat flux sources in high-power lasers, high-intensity light-emitting diodes, and semiconductor power devices. The heat spreader targets the passive cooling of heat sources with fluxes greater than 5 W/mm2 without requiring any active power consumption for the thermal solution. The prototype vapor chamber consists of an evaporator plate, a condenser plate and an adiabatic section, with water as the phase-change fluid. The custom-designed high heat flux source is composed of a platinum resistive heating pattern and a temperature sensor on an aluminum nitride substrate which is soldered to the outside of the evaporator. Experiments were performed with several different microstructures as evaporator surfaces under varying heat loads. The first microstructure investigated, a screen mesh, dissipated 2 W/mm2 of heat load but with an unacceptably high evaporator temperature. A sintered copper powder microstructure with particles of 50 μm mean diameter supported 8.5 W/mm2 without dryout. Four sets of particle diameters and different thicknesses for the sintered copper powder evaporators were tested. Additionally, some of the sintered structures were coated with multi-walled carbon nanotubes (CNT) that were rendered hydrophilic. Such nano-structured evaporators successfully showed a further reduction in thermal resistance of the vapor chamber.Copyright

High-performance blazed GxLTM device for large-area laser projector

A blazed GxL device is described that has high optical efficiency (>70% for RGB lasers), and high contrast ratio (> 10,000:1), and that is highly reliable when used in a large-area laser projection system. The key features were a robust design and precise stress control technology to maintain a uniform shape (bow and tilt) of more than 6,000 ribbons, a 0.25-μm CMOS compatible fabrication processing and planarization techniques to reduce fluctuation of the ribbons, and a reliable Al-Cu reflective film that provided protection against a high-power laser. No degradation in characteristics of the GxL device was observed after operating a 5,000- lumen projector for 2,000 hours and conducting 2,000 temperature cycling tests at -20°C and +80°C. Consequently, the worlds largest laser projection screen with a size of 2005 inches (10 m × 50 m) and 6 million pixels (1,080 × 5,760) was demonstrated at the 2005 World Exposition in Aichi, Japan.

A two-phase heat spreader for cooling high heat flux sources

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/mm2 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/mm2, but at unacceptably high evaporator temperatures. For sintered copper powder with a 50 µm particle diameter, a heat load of 8.5 W/mm2 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.

Nanometer-Order Control of MEMS Ribbons for Blazed Grating Light Valves

The performance of grating light valve (GLV™) chips can be increased by optimizing their ribbon structures [ 1]. A GLV is a one-dimensional light modulator using diffraction that can be applied to a high definition display by scanning the second dimension. We applied blazed GLV, which diffracts in only one direction [ 2], and achieved a jump in contrast from 3000:1 to 10000:1. Moreover, we achieved a 55 to 70% improvement in optical efficiency due to nanometer-order control of blazed GLV ribbon. These technologies were applied to the 2005-inch theater system “ GxL™ Laser Dream Theater” [ 3, 4].

Blazed GxL™ device for laser dream theatre at the Aichi expo 2005

Abstract A blazed GxL™ device is described as having high optical efficiency (> 70% for RGB lasers), and high contrast ratio (> 10,000:1), and that is highly reliable when used in a large‐area laser projection system. It has a robust design and precise stress control technology to maintain a uniform shape (bow and tilt) of more than 6,000 ribbons, a 0.25‐μm CMOS compatible fabrication processing and planarization techniques to reduce fluctuation of the ribbons, and a reliable Al‐Cu reflective film that provided protection against a high‐power laser. No degradation in characteristics of the GxL device is observed after operating a 5,000‐ lumen projector for 2,000 hours and conducting 2,000 temperature cycling tests at ‐20°C and +80°C. At the 2005 World Exposition in Aichi, Japan the worlds largest laser projection screen with a size of 2005 inches (10 m × 50 m) and 6 million pixels (1,080 × 5,760) was demonstrated.