射頻金氧半電晶體小訊號等效電路模型參數萃取方法建立以應用於各種偏壓與幾何結構

Abstract

在本論文中，發展了小訊號等效電路模型及其所對應的參數萃取方法，以應用於射頻互補式金氧半場效電晶體電路模擬上。本研究涵蓋雙埠三端點與四埠四端點的射頻金氧半電晶體。前者即三端點共源組態射頻金氧半電晶體是在電路設計上最為廣泛使用的元件，為了符合雙埠射頻量測系統，其測試元件佈局必須設計成源極與基極連接在一起並接地的雙埠組態結構。事實上，在射頻電路設計中，源極與基極並非總是連接在一起，此傳統的雙埠測試元件將無法得到完整的四端點金氧半電晶體的特點，也無法代表正確之高頻特性。為了解決此關鍵的問題，本研究設計四埠四端點的射頻金氧半電晶體，並利用0.13um互補式金氧半場效電晶體製程研製出來探討元件高頻特性及模型的發展。 本論文中，首先介紹了雙埠與多埠散射參數(S參數)的基本原理，然後，對於雙埠三端點的元件，分別詳盡探討在不同的偏壓條件與幾何結構上的小訊號電路與其所對應的參數萃取方法。基於雙埠三端元件已做的工作上，適時地改良其小訊號電路以相對應於四埠四端點的元件架構，並建立四埠四端點的去寄生效應方法與參數的萃取流程等基本的研究工作。 最後，在不同偏壓下所提出的小訊號等效電路分別透過模擬做更廣泛的驗證，驗證其模型的準確性以可靠地應用在超過40GHz的寬頻範圍，以及不同的偏壓條件如線性區與飽和區。更重要地，所建立的等效電路模型其本身的參數值充分表現出良好的可伸縮性，可預測於固定指叉寬度下變化閘極長度與閘極指叉數目之效應。在各種頻率、偏壓下的準確性和元件幾何參數之可伸縮性，可有效提昇高頻電路的模擬的準確性，以及輔助射頻互補式金氧半場效電晶體積體電路設計。

Small signal equivalent circuit models and the corresponding parameter extraction methods have been developed in this thesis for RF CMOS circuit simulation. Both two-port 3-terminal (3T) and four-port 4-terminal (4T) RF MOSFETs are covered in this work. The former one – 3T MOSFETs with a common source topology is a conventional one widely used in RF circuits, and the test-key layout is arranged in a two-port configuration with a common ground for source and body tied together to fit the two-port RF measurement system. In fact, source and body terminals are not always connected together in the practice of RF circuit design, the traditional two-port test-key cannot capture a whole spectrum of 4T MOSFET’s features and cannot adequately represent 4T MOSFET’s characteristics over high frequencies. To solve this critical problem, the latter one – four-port 4T RF MOSFETs are designed and fabricated in 0.13um RF CMOS process for high frequency characterization and model development in this work. In this thesis, the basic principles of two-port and multi-port scattering parameters (S-parameters) will be reviewed in the first place. Then, the small signal equivalent circuits and parameter extraction methods developed for two-port 3T device under various biases and geometries will be discussed in detail. Based on what have been done for two-port 3T MOSFET, a modified equivalent circuit relevant to four-port 4T test structures, and the corresponding fundamental works, such as de-embedding method and parameter extraction flow have been carried out. Finally, an extensive verification has been performed on the proposed small signal equivalent circuit models through simulation under various biases. The model accuracy is certified over a broad frequency up to 40GHz and various bias conditions – linear and saturation. More importantly, the model parameters of the developed equivalent circuit models manifest themselves a promisingly good scalability over various geometries in MOSFETs, such as gate lengths and gate finger numbers under a specified finger width. The accuracy over frequencies and biases and scalability over device geometries is useful to improve accuracy of high frequency circuit simulation and facilitate RF CMOS integrated circuit development.