Modeling, Simulation And Analysis Of Semiconductor Devices: Research On High Power LED Devices And Semiconductor Piezoresistive Devices

This thesis of my work is mainly about the simulation and analysis of semi-conductor devices which contains two part:(1) The first is the solution of techniques of the modeling, simulation and thermal analysis of high-power light-emitting diodes (LED); the second part is composed by model-ing study and simulation of organic semi-conductor piezo-resistance devices.In the first part:Surrounding structure-model-heat dissipation problems in high-power LED system, we established systematical method of device analysis for high-power LEDs and built a related tool of parameterized finite-element analysis.Our study contains:(1) Theoretical analysis on heat dissipation of high-power LED and pri-mary study on factors of heat transfer in LED system; (2) based on material analysis method (ex-perimental), we investigate several factors impacting LED’s heat dissipation and establish a solution for structure analysis and parameter extraction from macro-scope to micro-scope; (3) for thermal analysis of high-power LED device, we customized and made second development on the related open-source FEM software and designed a parameterization thermal simulation package with other open-source tools; (4) we analyze a real commercial high-power LED device by using fore-men-tioned method and tools. The total study are listed below:1. Theoretical analysis of high-power LED’s thermal problems. After investigation of paper references, based on the elementary knowledge of high-power LED’s package technology, we made a general theoretical analysis for the heat dissipation of LED device. Based on the theory of thermal resistance network, we analyze the impact on the device heat dissipation of those inter-facial factors. The analysis shows that the main joule conduit is constructed of several interfaces which affect the total heat conduction much. Once inter-facial defects block the main joule conduit, the total thermal resistance, tending to the part with higher thermal resistance, will grow higher.2. Solution of structure analysis and parameter extraction. By applying micro-analysis method, we established a systematical solution for device analysis from non-destructive analysis to destructive analysis. Based on this solution, we analyze a series of high-power LED devices and extract related parameters and material information, then we compare the similarities and differences of their processes. As result, we recognize that bonding interface in LED device highly impact the total thermal resistance. We have observed many defects existed in the AuSn soldering interface which may cause increasing of total thermal resis- tance. As this experimental results, we extract related parameter for FEM simulation.3. Development of Parameterized FEM simulation solution. By studying and comparing the open-source FEM tools and the commercial counterpart, we choose and expand the open-source software to do parameterized FEM analysis. We did second development for GMSH to simplify establishing parameterized models of the high-power LED device. Then we cus-tomize GetDP for adapting that parameterized model and processing transient thermal analy-sis. Combining other open-source like Python language and GNU Make, we designed a pa-rameterization program package for FEM simulation with file interface and controlled the solving flow. We have made a whole package as a parameterization FEM solution for high-power LED’s thermal analysis. The numerical problems (stability, accuracy and conver-gence) and impact of physical parameters on the iteration process are varified in this study by calculating simplified models. The result indicates that the optimized iteration method is more efficient with numerical stability, accuracy and convergence.4. Study of parameterization FEM simulation for a high-power LED device. Based on the theory of the first part, the experiments of the second part and the tools of the third part, we study the thermal problem of a flip-chip high-power LED with complicated structure by pa-rameterization FEM method. The conclusions are:(1) The geometric size of gold bump has limited effect on the total heat dissipation; (2) The defects in AuSn soldering interface may cause rising of the junction temperature at higher input power (about 4w); (3) We study im-pact of the exterior heat sink fin’s number on the total heat dissipation under two different device/exterior sink interface:one is metal solder bonding, the other is silicone grease bonding, in result, the more fins (48) will cause junction temperature reducing about 10 de-grees to less fins (12).The second part:we study the organic semiconductors that used in piezoresistance devices.The experimental data (nano-indentation instrument) shows a current-saturated effect on the piezo-resistance film device. We extend the Miller-Abrahams model on this case and build current-strain(stress) curve. The electrical and mechanic factors are both concerned in our study. The work contains:1. Building physical model. Based on Miller-Abrahams model and reasonable assumption of inter-facial carrier-transfer behaviors, we get a current formula containing the saturation effect. The asymptotic behavior of the formula suggests two different carrier transfer mechanics. When the pressure goes up, the inter-facial charge injection is restricted, which affect the carrier distribution beside and causes the current growth and finally the current saturation.2. Characterization of the mechanical properties of the device film. Introduce mechanic test of the device film and convert the current-stress data to current-strain data, from which we the non-linear mechanic properties of film is only a part of reasons for the current saturation.3. Numerical simulation. We use Monte Carlo method to simulate the carrier transfer behavior in the film and get the current-strain curve. Under a higher ex-voltage, energy disorder will not impact the linear relation between strain and log current.4. Fitting. Using fore-mentioned equation, we fit the experimental data and found that the the-ory matches well.