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Study Of Thermal Conductivity Of Thin Films By Experimental Measurement And Molecular Dynamics Simulation

Posted on:2008-02-02Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z X HuangFull Text:PDF
GTID:1118360218953577Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
Thin films are widely used in microelectronic devices. Thermal conductivities (TCs) of thin films considerably differ from bulk material ones due to microstructure and boundary effects. Study of thermal conductivities of them is important for optimizing the thermal management and thermal design. The existing commercial instruments for thermal property measurement can not be used to measure thermal property of thin films of thickness under 1 micron for the time being. Experimental measurement technology and molecular dynamics simulation (MDS) are the topics of the microscale heat transfer at present.A transient thermal reflectance (TTR) measurement system is set up after a study of the existing methods used to TC measurement of thin films. The system is verified by the measurements of thermal grown (TG) SiO2 thin films. The measured TCs of SiO2 made by sputtering and LPCVD are less that those of TG SiO2. The possible reason for that is the difference between their microstructure. ZnO thin films with thicknesses from 80-276nm prepared by sol-gel method are measured by the TTR system. The obtained TCs decrease with the decreasing thicknesses. The possible reasons are the grain boundary effect and the microstructure effect, the latter is dominating one from the analysis.To study TCs of the very thin films, molecular dynamics simulation (MDS) is utilized. A calculation based on solid argon shown that whether the momentum is conserved or not when using NEMDS does not influence the results. The TCs of SiO2 and ZnO of thicknesses from 2-9 nm are obtained by MDS. An obvious size effect is observed. Through MDS, we find thermal conductivity of crystal thin films have different temperature dependence with that of bulk materials, the temperature for maximum thermal conductivity varied with the thicknesses of thin films.The main findings by MDS and experimental measurements of this thesis including: 1. Thermal conductivity of 42nm amorphous SiO2 thin film equals to that of bulk materials from experimental mensurement, thermal conductivity of 4nm amorphous SiO2 from MDS shows that it changed, when the thickness decreases to 2nm, thermal conductivity will be 67.5% of the bulk one. 2. From MDS, The different temperature dependences between crystal SiO2 thin film and bulk materials are found, in some temperature range, thermal conductivities of thin film increase with the increasing temperature, but the bulk ones have a reverse trend. 3. Thermal conductivities of 80-276nm ZnO thin films measured by the TTR system decrease with the decreasing thicknesses, I ascribe the trend to the different microstructures from perfect bulk ZnO crystal. From MDS, the same temperature dependence of ZnO crystal thin film as that of crystal SiO2 thin films is found. These findings will help to improve thermal management and design of microelectronic devices and micro sensors.
Keywords/Search Tags:Thin Film, Thermal conductivity, Laser Measurement, Molecular Dynamic Simulations
PDF Full Text Request
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