以四埠散射參數量測射頻金氧半電晶體特性並製作其高頻等效電路模型

Abstract

先進的互補金氧半製程使得射頻金氧半電晶體成為製造快速成長的無線通訊產品的候選者之一，以金氧半電晶體設計無線通訊電路，將有希望把無線通訊系統中的前端射頻模組、基頻電路、數位處理電路三部分整合在單一晶片中，如此不但可降低生產成本，也增加了通訊產品的可攜性。然而以金氧半電晶體設計射頻電路具有一定的挑戰性，因為元件內部會產生複雜的訊號耦合，特別是基板的部分，因此提供可以準確預測元件高頻特性的元件模型供電路設計者使用，是當前的要務。傳統雙埠量測方式並無法有效的完整探測四端點金氧半電晶體特性，通常必須將金氧半電晶體設定為共源組態，將源極和基板連接在一起並接地，以配合雙埠量測系統，如此將無法量測源極與基板之間的訊號耦合效應，也無法將汲極與基板間的耦合效應從汲極的輸出特性中分離。本論文提出並實現了以四埠散射參數在晶量測金氧半電晶體的量測方式。 在本論文中，首先重新整理基本的單埠散射參數原理，並將其觀念延伸至多埠的應用，另外也簡介了本研究所使用的四埠參數量測系統及其校正的原理。 接著提出了四埠量測所使用的在晶量測結構，包括了去除量測結構本身寄生效應的傀儡結構，並發展了去除量測結構寄生效應的方法。利用這些四埠測試結構，實現了以四埠參數量測射頻電晶體的構想，一次的四埠參數量測，即可獲得電晶體操作在共源、共閘、共汲的高頻特性。 此外本論文也提出了具有合理基板電容電阻寄生元件的金氧半電晶體小訊號等效電路模型，並根據四埠量測所得的金氧半電晶體高頻特性，發展粹取小訊號等效電路模型中各元件參數值之方法，實驗中並粹取了不同尺寸的金氧半電晶體等效電路模型中的相關參數，粹取得隨元件尺寸縮小放大的模型參數。 最後，將小訊號等效墊路模型以及根據四埠量測資料粹取出的電路參數以電路模擬軟體模擬其輸出特性，並將此模擬特性與實際量測的高頻特性比較，在100MHz到20GHz的量測頻率範圍內，獲得優良的模擬結果。

With superior advancement of CMOS technologies, RF MOSFET’s have become an important candidate for the rapid growing wireless communication applications. Communication applications base on COMS technologies are potential to integrate the RF front end, base-band and DSP module together on a single chip, which not only improve the production cost but also the portability of modern communication applications. However, designing RF circuit base on CMOS devices is a challenge since the complex signal coupling inside the device, especially the substrate coupling effect. Therefore, establishing a model accurately predicts the RF behaviors of CMOS devices is an urgent mission. The traditional two-port characterization method is inefficient to investigate the detail RF behavior of a four terminal MOSFET. The MOSFET is a device with four terminals and will be always arranged in two-port common source configuration with its source and body grounded to fit the traditional two-port measurement system. Tying the source and body together will result in some consequences that the coupling path between the source and body will not be able to be characterized and the coupling between drain and body will not be able to separated from the output characteristics either. In this thesis, the four-port S-parameter measurement was proposed and demonstrated for the usage of on-wafer characterization of RF MOSFET’s. First of all, the basic principles of one-port scattering parameter were reviewed and were extended for multi-port application. The four-port system was also introduced including the calibration methodology. Next, the four-port test structures for characterizing RF MOSFET’s including dummy structures were proposed. The corresponding de-embedding method was also developed. With the proposed test structures and MOSFET device, the RF characteristics of the MOSFET configured in common source, common gate, and common drain mode was characterized at one four-port measurement procedure. Then, small-signal equivalent circuits with reasonable substrate R-C network for device in different operation mode were proposed and discussed. Extraction methods of the components in these equivalent circuits according to the four-port measurement data were deduced in detail. The extractions of the components for devices in different dimensions were also demonstrated, good scalability of the extracted values with the device dimensions was observed. Finally, the output characteristics of the proposed small-signal equivalent circuits were simulated according to the components extracted from the four-port measurement. The simulated results were compared with the measurement data; good agreement of the Y-parameters from 100MHz to 20GHz was obtained, which suggest the feasibility of applying four-port on-wafer measurement for characterizing RF MOSFET’s.