Research Of Capillary Surface On Materials For Integrated Circuits Cooling

With the increasing development of science and technology and the actual needs of modern industries,the chip technology advances towards high integration and miniaturization.This has caused the heat flux generated by the chip to increase significantly in recent years and there are local hot spots on the surface of the chip where the heat fluxes exceeds 1000 W/cm2.As traditional cooling methods are increasingly difficult to meet the cooling needs of high-performance chips,improving cooling efficiency and developing new cooling technologies have become critically important issues.Typically,the devices for cooling high-heat-flux chips are based on water-vapor phase transition,so the performance of these cooling devices strongly depends on a capillary material used for quick liquid spreading and evaporation.In this thesis,a femtosecond laser nano/micro fabrication technology is used to create two novel capillary surface structures on a silicon material.The first surface structure is a two-dimensional array of micropillars with a height of 60 ?m and period of 90 ?m.On the one hand,the capillary surface structure can make the liquid isotropically diffuse(ie,uniform spreading to the surroundings);on the other hand,the black silicon has high absorption optical characteristics,which can enhance the cooling effect through thermal radiation.The second created capillary surface structure is an array of parallel microgrooves with a depth of 50 ?m and period of 100 ?m.The material with a two-dimensional micropillar array surface structure has better wetting performance and optical properties.Absorption of light is significantly enhanced as compared to an untreated silicon surface,reaching about 94% in a wavelength range between 200 and 1100 nm.Due to high absorptance the laser-treated sample appears pitch black.The water contact angle was measured to be close to 0° for both created materials,demonstrating their superhydrophilic wetting properties.For the chip cooling device,the liquid spreading dynamics and evaporation in capillary surface structures are major functionalities of the capillary materials used for cooling.In order to study these two functionalities of silicon materials,the spreading and evaporation of water as a function of time at various temperatures were studied using a high speed camera.The experimental results at room temperature reveal h ? t2,h ? t,h ? t1/2,h ? t1/3and other capillary flow stages,where h is the liquid spreadingdistance and t is time.However,for the two silicon materials,the time scales of these stages are different.This thesis also found that stratification occurred at the front of the liquid flow,including the precursor front and the main front.The maximum speed of capillary flow is measured to be 37 cm/s and 16 cm/s on the array of parallel microgrooves and array of micropillars,respectively.When the surface temperature of the material rises,the liquid quickly spreads over the surface and then quickly evaporates.The liquid evaporation takes away a large amount of heat from the material surface,cause the surface temperature to drop.Through a comparative analysis of data between different temperatures,this thesis find that as the temperature increases,the capillary force of the created materials increases(that is,the spreading distance increases).The materials prepared in this thesis retained good superhydrophilic performance and evaporation function throughout the entire research time period of 18 months.In summary,the silicon material prepared in this thesis is of great significance for solving the cooling problem of integrated circuits with high heat flux.