InGaP HBT元件的特性與模型分析

Characterization and modeling of InGaP HBT

湯文斌(Wen-Bin Tang)

指導教授 ： 辛裕明

國立中央大學/資訊電機學院/電機工程學系/博士(2006年)

摘要

在此論文中，主要研究以砷化鎵為基礎的異質接面雙載子電晶體的小訊號等效電路模型、 雜訊特性、溫度特性、功率特性與元件佈局效應對其特性的影響。第二章主要討論此電晶體的小訊號等效電路模型的建構及其等效電路模型參數的擷取方法。小訊號等效電路模型加入了兩項電容，其中一個電容用來描述介於基極接觸電極與基極磊晶層之間的介面層(interfacial layer)所產生的電容效應，另一個電容用來描述因為高頻交流訊號所產生的射極交流電流密集化效應(ac emitter current crowing effect)。由於加入了兩項電容，新的等效電路模型參數的擷取方法將於第二章討論。此新發展的小訊號等效電路模型所模擬出的S參數不但與量測結果吻合，更可說明在較高頻率時，元件的單向功率增益(unilateral power gain)並非依照 -20dB/decade的斜率下降的原因。
第三章主要研究元件的雜訊特性。雜訊特性的研究分成低頻雜訊、高頻雜訊及雜訊等效電路三方面。低頻雜訊被考慮成1/f 雜訊；高頻雜訊的討論則著眼於高頻雜訊參數對偏壓與元件佈局效應的影響。同時藉由已知的內在雜訊源及小訊號等效電路模型，雜訊等效電路模型可被建立。
元件尺寸不但影響雜訊特性，也影響射頻與功率特性。尤其是基極接觸電極面積大小直接影響基極電阻及基集極間的電容大小，因此對最大振盪頻率、輸出功率及線性度等有顯著影響。元件尺寸效應將於第四章中討論。此外，利用新的元件佈局及離子佈植方式來降低基集極間的電容大小的方法也被應用於射極在上(Emitter-up)及集極在上(Collector-up )之異質接面雙載子電晶體上，其特性亦於第四章中討論。
藉由變溫系統量測結果，異質接面雙載子電晶體的溫度特性將於第五章中討論，其中包括了直流與交流特性討論。利用不同迴火(annealing)條件，元件溫度特性會被改變的現象也於此章節討論。同時利用 Kirk-effect及分析電子遷移暫態時間(transit time)，電子飽和速度及電子遷移暫態時間各項組成對溫度的變化亦於第五章中討論。
第六章為本文總結及未來研究方向之討論。

關鍵字

小訊號等效電路模型 ； 雜訊 ； 溫度 ； 砷化鎵 ； 電晶體

並列摘要

In this study, the characteristics of GaAs based HBTs are studied by using small-signal equivalent and DC measurement which includes the dc current gain, the electron saturation velocity, and the temperature dependence effect. The new small-signal equivalent circuit model and the new extraction techniques are proposed to include the base impedance effects which describe the base contact impedance and the ac emitter current crowding. Although these base impedance effects (capacitance elements) are usually neglected for typical HBTs, they must be considered in some situations such as higher base resistance and higher frequency. It will be described in the Chapter 2 that the high frequency performance of HBTs can not be predicted well without incorporating these capacitance into small-signal equivalent circuit.
The noise behavior of InGaP/GaAs HBTs is discussed in Chapter 3 by using a RF noise model and the general linear noisy two-port theory. Low frequencies are usually considered as 1/f noise; and high frequency (HF) noise parameters are in terms of four noise parameters. These HF noise parameters can be predicted by using the noisy two-port circuit if the small-signal equivalent circuits are known. The analytical procedure of HF noise by using the small-signal equivalent circuit as well as the intrinsic noise model is presented.
However, the design issues and tradeoffs associated with geometrical layout of a given HBT technology have not been investigated in detail. Therefore, we attempt to study this geometrical layout in a specific InGaP/GaAs HBT technology by addressing how the device geometry optimizes a given RF performance metric. In Chapter 4, we focus on the frequency response and power performance on the base contact width dependence.
In addition, the CBC has a direct impact on the RF performance and should be minimized. Reducing the CBC to improve the performance of emitter-up HBT by ion implantation process and novel layout will be presented. Compared with the emitter-up HBT, the performance of collector-up HBTs is also presented.
Three issues about temperature dependence are studied: base-emitter turn on voltage, current gains stabilization and RF performances. With the study on temperature dependence effect of the parameters of HBTs, the effective saturation velocity can also be obtained which is discussed in Chapter 5. It is found that the trend of dc current gain versus temperature is different from the annealing conditions, and this is also described in Chapter 5.
Finally, a conclusion and future work are presented in Chapter 6.

並列關鍵字

small signal equivalent circuit model ； temperature ； noise ； GaAs ； HBT

參考文獻

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