Research On Fabrication And Performance Of Microchannel Heat Sink With Integrated Temperature Sensors

With the development of microelectronics technology,transistors in an integrated circuit(IC)keep scaling down.The heat flux concomitantly rises up due to the shrinking dimension,and severe hot spots are formed.The problem of thermally induced failure gradually becomes a bottleneck restricting the further development of microelectronic technology.Therefore,thermal management is particularly important today.Compared with the conventional thermal management technologies,the micro-channel based heat sink has outstanding heat dissipation performance.Unfortunately,most of these studies do not look into the detail of micro-channel heat sink,and the understanding of such a device is quite limited.This is mainly because few tools or methods are available for directly monitoring details inside the micro-channel.The discrete temperature sensors can only be placed at the inlet and outlet of the heat sink,while the infrared(IR)camera can only take the temperature distribution images of the heat sink surface.Neither of these methods can provide the details inside the micro-channels.In addition,some researches are based on simulation,where the conclusion can only be some non-proven hypothesis.In order to overcome these limitations,a microfluidic channel based heat sink with integrated temperature sensors is proposed in this paper.The thin-film(Ti/Pt/Cr/Au)temperature sensors are fabricated together with the micro-channel heat sink,which realizes the high-spatial-resolution monitoring of the temperature inside the microchannels.Benefiting from the high sensitivity and accuracy of these integrated sensors,the temperature profile along the micro-channel is extracted,and even small temperature perturbations can be observed.The specific work and results are shown as follow:(1)A multi-layer(Ti/Pt/Cr/Au)resistive temperature sensor is proposed and investigated to precisely measure the temperature characteristic in microchannel heat sink.The Ti/Pt/Cr/Au sensor is fabricated by a dc sputtering method,vacuum coating technology and a lift-off process.The thermal annealing test is conducted in the temperature range of 200?-800? for obtaining an appropriate propriety of the multilayer.The measured results of the as-deposited sheet resistivity indicate that 400? is the appropriate annealing temperature for the Ti/Pt/Cr/Au layer.Redistribution of structural imperfections and recrystallization promote the multi-layer sensor has better physical characteristics(interface rearrangement,stress annihilation,adhesion promotion).Moreover,the temperature coefficient of resistance(TCR)of the sensors is investigated through VPF-100-FTIR Cryostat.(2)Then,we design and fabricate the micro channels and the simulated heater.The microchannel chip and sensors-based chip are aligned and die-to-die bonded using benzocyclobutene(BCB)epoxy by FINEPLACER sigma Semi-Automated Sub-Micron Bonder.The as-fabricated device including thin-film temperature sensors,micro channels and simulated theater is mounted and wire-bonded on a customized printed circuit board(PCB).A thermal testing system is built up for real-time measurement.The simulated heater is driven by a direct-circuit(DC)power source,while the coolant(deionized water)flow rate is controlled by an injection pump.All the sensors are connected to the customized data acquisition system(KEITHLEY-2000 multimeter),and a LabVIEW program is developed for automatic measurement and data process.The resistance changes of the sensors are acquired one by one with a time step of 50 ms,and are then transmitted to PC for temperature conversion,display and storage.An infrared(IR)camera monitors the surface temperature of power IC in real time.(3)Based on the testing system,we investigate the performance of the temperature sensors and microchannel heat sink under different flow rate and different input power.The excellent stability and sensitivity of the Ti/Pt/Cr/Au thin-film temperature sensor and testing system are verified.The resolution of the sensors is better than 0.05 °C.Results show that the microchannel heat sink have excellent heat dissipation capability,and the temperature decreases over 40? when the flow rate is 100ml/h.In particular,the slope of the temperature distribution trend in the micro-channel from inlet to outlet is related to the heating power and independent of the flow rate.Such temperature non-uniformity may bring problems for power IC and the micro-channel based heat sink should be designed and optimized for minimizing such temperature non-uniformity.The experimental results match well with simulation results and can be used to directly verify the modeling results,helping to build a convincing simulation model.A worth noting case is the bubble effect.When gas bubbles are mixed into the cooling liquid and flow through the micro channel,the heat sink suffers a sudden temperature change.The micro bubble may slightly affect the temperature,while the large bubble can last for as long as 20 s with temperature increase of 15?.Furthermore,as the temperature increases,the temperature fluctuation is more obvious.The cause of the phenomenon is possibly the decreasing of air solubility in water when the temperature rises.The capability of the Ti/Pt/Cr/Au thin-film temperature sensor detecting these details is both meaningful to the power IC and microchannel heat sink.