互補式金氧半元件之射頻特性研究

Abstract

本論文針對互補式金氧半主動元件之射頻特性進行模型化與分析。以MOSFET元件的完整小訊號模型所推導的y-參數在本論文中被呈現出來。與已往的文獻比較，我們所推導出來的y-參數更為完整。而此一完整的y-參數模型將可應用於高頻系統的模擬，同時，亦可當作MOSFET元件的高頻參數萃取之用。此外，本論文提出一套分析MOSFET元件高頻行為的物理模型，稱之為four blocks method。在本模型中，我們觀察到閘極與汲極網路不僅具有功率消耗的特性，同時還有阻抗不匹配所造成的功率損耗。而其基底網路亦被發現為一回授網路，主動網路為放大的功能。 MOSFET的射頻特性如截止頻率、最大震盪頻率、功率增益與穩定度亦在本論文中詳加討論。雖然本論文採用0.13□m、0.18□m與0.35□m的MOSFET元件進行分析，但對其高頻特性的研究更勝於技術的開發。本論文亦首度提出穩定度頻寬的概念，藉由此一概念，MOSFET元件的穩定度分析更為清楚。元件的佈局與高頻指標的關係亦被廣泛討論。藉由本論文的研究可發現，最佳化的佈局方式將使得0.13微米與0.18微米的MOSFET分別具有86GHz與65GHz的高截止頻率。同時，本論文亦研究了不同的佈局方式所呈現出的二階效應。 基於製程的相容性，低成本與高轉導特性的諸多考量，我們亦在本論文中提出基底動態臨界電壓MOSFET(B-DTMOS)的三種操作模式於射頻領域的應用。於我們的研究中，觀察到B-DTMOS在moderate與over-drive操作模式下具有高輸出能力，高頻寬良好的穩定度與高轉導對電流比的好處。此外，本論文並模型化B-DTMOS的表面電壓與通道電流。我們所推得的模型將可應用在以B-DTMOS為主的電路模擬中。

This dissertation presents original research on modeling and analyzing the performance of CMOS technology based devices for RF applications. Y-parameters of MOSFET with complete small-signal equivalent circuit were derived in order to implement in the RF circuit simulation. The developed analytic y-parameters of MOSFET are beneficial for parameter extraction, and also are useful for the simulation of large system. Further, small-signal equivalent circuit of MOSFET including intrinsic and extrinsic parts is divided into four blocks. They are, input, active, substrate and output networks. By the use of quasi-static approximation, the gate resistance reveals not only the power dissipation but also the power loss due to the impedance mismatch. Similarly, drain resistance also serves as the power dissipation and loss due to impedance mismatching. Additionally, thesubstrate network is found to be the in-series feedback network in the first time, and intrinsic part of MOSFET is the main active network for amplification. RF properties of MOSFET were examined in detail by considering the cut-off frequency, maximum oscillation frequency, power gain and stability. Test structures of MOSFET in this dissertation include the technology nodes of 0.13□um, 0.18□um and 0.35□um CMOS technologies. Even this thesis addresses the up-to-date technologies; the discussion is not restricted to the development of advance technologies. Instead, general analysis was performed. Bandwidth of RF stability of MOSFET is proposed to investigate the stability of MOSFET. It is found that the bandwidth of MOSFET to be potentially unstable is higher when the gate length is reduced. RF figures-of-merit of MOSFET with finger gate structure was discussed. By selecting optimal layout structure, 86GHz and 65GHz of cut-off frequencies of 0.13□m and 0.18□m nMOSFET can be achieved. Secondary effects induced by finger gate structure also examined in this thesis. Bulk dynamic threshold voltage MOSFET (B-DTMOS) under various operation modes are proposed and analyzed because of its attractive benefits, that is, technology compatibility, cost efficiency and outstanding transconductance. The surface potential of B-DTMOS was derived according Poisson’s equation and charge sheet approximation. It is found that the surface potential of B-DTMOS kept minimal changes under the input bias below threshold voltage. While the input bias higher than threshold voltage, the surface potential decreased dramatically because of the shielding of channel charges. Channel current due to MOSFET action of B-DTMOS was derived according to the drift-diffusion equations, and then verified with two-dimensional device simulation. Excellent accuracy was obtained. Additional to the static properties, high-frequency characteristics of B-DTMOS was studied. Exceed 100GHz of fT of B-DTMOS under moderate mode was extrapolated, and nearly 220GHz of fT of B-DTMOS under over-drive mode was extrapolated. Our results show that B-DTMOS exhibits high bandwidth by compensating its current gain. Besides, B-DTMOS exhibits high driving capability, better stability, and high transconductance to drain current ratio. Addressed results present that B-DTMOS is potential for the use of designing 10GHz upper applications, especially for the amplifier design.