單光子崩潰二極體陣列之串音現象

Abstract

為了提高偵測效率與影像解析度，我們藉由縮小SPAD彼此之距離來實現高面積填充率的陣列，然而，在近十年中，鄰近的SPAD所引發的串音問題卻愈趨嚴重。在本論文中，我們藉由許多面向如元件結構、元件間距、外加偏壓以及時間上的特性，來探討SPAD陣列中之串音問題。從實驗結果以及擬合曲線中，我們推論出在元件中主導串音的機制為光學串音中的直接路徑。另外，在時間特性的量測中，除了可以證實我們所提出的構想，也為我們提供了串音機制中的一個新的觀點。對於單一元件的特性，我們以恰當的離子佈值濃度分布模擬其崩潰電壓與溫度之關係以及C-V曲線，發現其結果都尚稱吻合。而對於尺寸效應，我們利用二維光計數映像來探討之，從實驗結果與模擬結果中皆發現，PDP的不均勻性是來自於保護環所導致的空乏區電場降低，因此，為了解決此問題，對於元件保護環的部分也提出了一個新的濃度分布，期待在未來SPAD陣列的影像應用能有所貢獻。

To enhance detection efficiency and image resolution, high fill-factor array of single-photon avalanche diodes (SPADs) is applied by shortening the distance between devices. However, crosstalk between adjacent SPADs becomes an issue in this decade. In this thesis, an extensive study on various aspects of crosstalk in a CMOS SPAD array, including device structure, device-to-device distance, bias voltage, and its timing characteristics, is presented. According to the experimental results and a simple model fitting, we deduce that the crosstalk between CMOS SPADs is dominated by direct optical coupling. Timing characteristics of crosstalk support our explanation and provide an additional angle of observation on its mechanism. For single SPADs, by applying a proper doping concentration profile in TCAD simulation, experimental temperature-dependent breakdown voltages and C-V curves are fitted in good consistence. The size effect of photon-detection probability (PDP) is investigated by using 2-D photo-count mapping. The same simulation method and doping profiles tells that the PDP non-uniformity is caused by the guard-ring induced electric field lowering. A doping profile for guard-ring region is proposed to ease this problem. This work is highly valuable for SPAD array design for various imaging applications in the future.