在本論文中，我們利用TCAD軟體設計額定崩潰電壓為450V的LDMOSFET，並在導通電阻與崩潰電壓間取得平衡點，使其能兼顧低導通電阻與高崩潰電壓。分析崩潰後元件電流分佈的情形，發現元件從汲極端發生崩潰，電流集中在源極下方的接面處流出源極。
為了使元件更為「強健」，我們必須盡量分散元件崩潰時電流的分佈。我們在汲極下方加入一n型適應層，並觀察其電流分佈改善的情形。通過P型井與磊晶層間接面處的電流，原先幾乎集中在源極下方，加入n型適應層後，元件崩潰的位置改為通道的邊緣，因此部分電流改由通道邊緣流出源極，電流分佈因此較為分散。調整通過源極下方與通道邊緣兩處的電流，使其幾乎相等，則能得到最均勻的電流分佈，元件也最為「強健」。

In this thesis, we use TCAD simulation software to design a 450V LDMOSFET. We adjust the parameters to make the device have not only low turn-on resistance but also high breakdown voltages. Through analyzing the device’s currents’ distribution after it has broken down, we can find out that the breakdown occurs at drain edge. Most of the currents gather at the junction beneath the source contact and then flow out the source.
To make the device more “rugged”, it is important to disperse the device’s breakdown currents as uniform as possible. We add an n-type adaptive layer under drain region to improve the currents’ distribution. Without n-type adaptive layer, most of the device’s currents gather at the junction beneath the source contact. The position where breakdown occurs is shifted from drain edge to channel edge. Thus part of the currents flow through the channel edge then out of the source. And the currents are more dispersed. Adjusting the currents flowing through the junction beneath the source region and the channel edge, when the currents flow through the two regions are almost equal, the currents’ distribution will be most uniform. And we can get the most “rugged” devices.

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