Design And Fabrication Of A Pt Thin Film Micro Heater And Its Boiling Characteristics

With the rapid development of MEMS technology,the application of MEMS-based micro-heaters has become more and more extensive,and the research on micro-heaters becomes more and more important.In this paper,a Pt thin film micro-heater based on MEMS technology is designed.A transient finite element analysis of the temperature field of the micro-heater is carried out.Based on its result,an optimized geometric design of the micro heater and the micro fabrication process are completed.Finally,an experimental setup is estabilished to investigated the boiling heat transfer on the micro heater under pulse-heating.The bubble dynamics in three working fluids: ethanol,degassed water and carbon nano-tube nanofluids are quantitatively studied by using CCD camera and a MATLAB program.The details are as follows:Firstly,a dumbbell-shaped Pt thin film micro heater was specially designed,which was capable of effectively generating heat within a micrometer region.As a result,stable single bubble could be generated on the micro heater.The temperature field of a strip and a dumbbell type micro-heater were simulated by ANSYS.The dumbbell micro-heater had the following advantages: under the same condition,the thermal response time was as short as 15 ms,shortened by 39.6% as compared with that of the strip-shaped micro-heater.The maximum temperature is 3.2% higher than that of the strip-shaped micro-heating.It can effectively concentrate the thermal energy in the very narrow dumbbell region of the micro heater.The simulation results also showed that more than 90% of the heat is transferred to the substrate.Secondly,the process design of Pt thin film micro-heater was carried out,including wet chemical cleaning of the silicon wafer,low pressure chemical deposition of the silicon dioxide,positive photoresist photolithography,sputtering and lift-off of the Pt film,etc.Micro-heater arrays of dumbbell shape were fabricated for experiments.Finally,the Pt thin film micro-heater was processed and studied.The boiling characteristics and bubble dynamics of the micro-heater were studied by changing the type of working fluid and pulse width.The results show that in the same working medium,the diameter change process of bubble generation with the increase of pulse width can be divided into three stages: accelerated growth period,stable growth period and slow change period.And the input power required to initiate boiling as the pulse width increases,the overall diameter of the bubble generated by the same heating time is also relatively small;under the same pulse width,the initial boiling occurs in the carbon nanotube nanofluid working medium The required input power is the largest,and the overall diameter of the generated bubbles is also the largest.Based on the experimental results,a preliminary analysis is made using the relevant theory of surface tension.