金氧半電容元件在反轉區光感應特性及其光敏感度之提升

Photosensing Characteristic of MOS Devices in Inversion Region and Enhancement of Sensitivity

楊彰臺(Chang-Tai Yang)

指導教授 ： 胡振國

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201600655

摘要

本篇論文主要探討氧化層厚度介於23埃到29埃之超薄氧化層p型、超薄氧化層n型以及氧化層厚度大於40埃之薄氧化層p型矽基板金氧半電容元件之周邊相關電流及照光反應。在論文的第二章，探討超薄氧化層p型以及超薄氧化層n型矽基板金氧半電容元件的暗電流以及照光反應，可以得知p型矽基板的暗電流及光電流都會隨著氧化層的厚度增加而增加；n型矽基板的暗電流則因受穿隧效應影響而隨氧化層厚度增加而減少，並且光電流對氧化層厚度有一轉折處，此電流最低點的氧化層厚度會受到光照強度而影響。由過去的文獻以及本篇的模擬結果顯示，p型矽基板金氧半電容元件是受到蕭基位障的調變而影響；而n型矽基板不僅受到氧化層壓降影響，亦可用蕭基效應以及金屬-絕緣體-半導體公式做推論。在論文的第三章，利用側邊擴散電流的影響，探討指叉狀電極的特性。藉由在相同長度之下、不同的電極數量，可以發現當電極距離越遠，暗電流會越大。其原因推測是因為當兩電極距離漸進時，電極邊緣的電子濃度會下降，因此使得電流減少。但在光照之下，電極邊緣的電子濃度都很高，當電極距離為60微米到10微米之間，其受到電極距離的影響不大，因此電極數量為主導使得電流會上升。然而當電極極度靠近約為5微米時，電極邊緣的電子濃度會因彼此影響分散而減少，使電流下降。論文的第四章，使用薄氧化層p型金氧半電容元件，利用額外加偏壓使其氧化層崩潰，探討此種元件對光之敏感度。我們發現，原先在第二章超薄氧化層結構的元件之電流會進入深空乏區而飽和，但薄氧化層的元件在崩潰前並不會飽和。崩潰後的薄氧化層元件電流會迅速進入飽和區，因空乏區在氧化層崩潰處變深，使得電子的移動受到改變，同時也有更多電子進入空乏區，進而造成整體電流值上升。在照光之下，當電壓從累積區進入空乏區時，電流會有一個凸起，我們利用光伏打效應作為此現象的理論基礎。此外，此種崩潰的光二極體，其對光的敏感度極高。

關鍵字

超薄氧化層 ； 金氧半元件 ； 側邊擴散電流 ； 蕭基位障調變 ； 金氧半光二極體

並列摘要

In this thesis, the currents and illumination effect of MOS(p) and MOS(n) with ultrathin oxide, i.e. oxide thickness from 23 Å to 29 Å, along with MOS(p) with thin oxide, oxide thickness over 40 Å, are investigated. In chapter 2, by demonstrating the currents of MOS(p) and MOS(n) with and without illumination, the relationships between currents and oxide thickness are as followed: both the dark current and light currents of MOS(p) increases as the oxide thickness increases; on the other hand, the dark current of MOS(n) decreases as the oxide thickness increases and the light currents will have a minimum, which depends on the light intensity. From the previous works and the simulation of this work show that MOS(p) is influenced by Schottky barrier height modulation, while MOS(n) is controlled by the oxide electric field and may be deduced by Schottky Emission and Metal-Insulator-Semiconductor models.
In chapter 3, by using the effect of lateral diffusion current, we discuss the characteristics of finger electrode. By having different gate electrode number under same length, it is shown that the dark current will increase as the electrode distance increases. It is speculated that the lateral electron concentration will decrease as the electrode distance decreases, which causes the current to decrease. On the contrary, under illumination, the lateral electron concentration is high. It will not affect the current when the electrode distances are ranging from 60μm to 10μm. The electrode number will dominate and cause the light current to increase. However, when the electrode distance is extremely small, i.e. 5μm, the lateral electron concentration will be shared and then decreases, which causes the light current to decrease.
In chapter 4, MOS(p) with thin oxide thickness over 40 Å and having external voltage pulse to make the oxide breakdown is investigated. It is observed that the currents of MOS(p) with thin oxide will not saturate until it breakdown while MOS(p) with ultrathin oxide will get into deep depletion region and saturates. Thin oxide MOS(p) after breakdown will saturate in very small voltage, which is because the inversion layer at oxide breakdown point is deeper than origin. The electron movement is changed by this phenomenon and more electrons are induced into inversion layer, which causes the current increases. Under illumination, there is a hump of the current when the voltage is between accumulation and depletion region, and we use photovoltaic effect to explain the mechanism. Furthermore, this breakdown device has extremely high sensitivity.

並列關鍵字

ultrathin oxide ； MOS devices ； lateral diffusion current ； Schottky barrier height modulation ； MOS photodiode

參考文獻

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