矽基板面內共振的電子光斑干涉術量測

Abstract

商用規格之6吋太陽能電池矽基板的厚度僅200 □m，兼具結構撓性及材料脆性，以模態密度較疏的面內共振特徵可鑑定矽基板的完整性。本研究整合出一套量測薄板面內共振特徵的實驗系統，能夠有效地連續量測矽基板面內共振頻率及模態，包括激振、感測太陽能電池矽基板面內振動的寬頻錐形換能器及電子光斑干涉儀。經數值分析與量測結果比對，確定與所設計之實驗架構近似的模擬分析條件，並發現試片厚度不均會造成電子光斑干涉條紋由厚度較薄處往較厚處偏移。此外，支撐試片的邊界條件對於共振頻率計算值影響甚鉅，試片面內共振分析之正算模型與實際量測條件的差異會導致反算結果不理想。本研究奠定未來可依據面內共振頻率的改變及電子光斑干涉條紋的不連續性，檢測太陽能電池缺陷的可行性。

The crystalline silicon wafers of commercial 6-in photovoltaic cells have the thickness as thin as 200 □m. They have both good flexibility and brittle material property. The in-plane resonance in a thin plate has sparse modal density and can be potentially used to characterize the integrity of a crystalline silicon wafer. This research integrates an experimental system to measure the characteristics of in-plane vibration for a thin plate. Both resonant frequency and mode shapes can be in sequence measured effectively. This system comprises an electronic speckle interferometer for measuring in-plane displacement and a set of broadband conical transducers, which are used to actuate and measure structural vibration. The measuring system was identified through a series of comparisons between experimental and numerical results. The speckle fringes for in-plane resonant modes will drift from the thinner region to the thicker one according to the numerical simulation. In addition, the supporting boundary conditions seriously influence the calculated resonant frequencies. Any deviation between forward calculation model and the real measuring condition will lead to unexpected inverse results of material properties. This study benefits the accomplishment of defect detection in photovoltaic cells based on the variations of in-plane resonant frequencies and speckle fringes caused by material discontinuities.