InGaP/GaAs HBT線性度改善與InP DHBT製作與特性分析

Linearity Improvement of InGaP/GaAs HBTs and Characterization of InP-based Type-I/II HBTs

王則閔(Che-ming Wang)

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(2007年)

摘要

在1957年異質接面雙載子電晶體設計概念在貝爾實驗室被提出，利用異質接面能帶差來提高雙載子電晶體的射極注入效應；在1980年代隨著MOCVD與MBE長晶技術逐漸成熟，砷化鎵與磷化銦異質接面雙載子電晶體成功製作與應用。近年來隨著無線通訊快速的發展，異質接面雙載子電晶體也被廣泛應用在功率放大器。但電晶體的非線性效應影響到電路輸出特性，四個主要的異質接面雙載子電晶體的非線性因子在本文中被討論，同時也分析大訊號輸入時，非線性特性的表現。另外在磷化銦異質接面雙載子電晶體研究方面，因磷化銦異質接面雙載子電晶體是目前世界最快速的電晶體，將其兩種形態(type-I 與type-II)的材料特性與能帶圖分析與比較。藉由了解目前磷化銦異質接面雙載子電晶體的截止頻率相對最大震盪頻率、崩潰電壓、集極厚度與集極電流密度的關係，可以對高速電晶體結構設計上有進一步的幫助。
在第二章中，提出非均勻的集極摻雜來改善元件線性度與高頻特性，此設計是利用一薄層高摻雜濃度至於均勻的集極區域中，薄層高摻雜的濃度與厚度由模擬來求得最佳化，並藉由薄層高摻雜層來侷限集極的空乏厚度，因而達到有效改善非線性基極集極電容改變量，從模擬可觀察出非線性基極集極電容改變率由1.6降低至1.1，此外非均勻的集極摻雜設計也同時延遲元件Kirk 效應，提高最大輸出電流2倍，同時有效提高元件的高頻特性、功率輸出與改善線性度特性。
在第三章中，利用上一章所設計的非均勻集極摻雜製作砷化鎵異質接面雙載子電晶體並量測與分析。在直流特性上，因為相同的射極與基極決定了雙載子電晶體的直流特性，所以在集極中加入一薄層高摻雜濃度並不影響直流特性，且非均勻集極摻雜電晶體的操作電流密度比傳統均勻摻雜設計高2倍。在高頻截止頻率特性因延遲Kirk effect而有明顯的改善 12 GHz，並保持相似的最大震盪頻率。在電容量測方面，包含了反偏下電容的變化與不同電流下電容改變，非均勻的集極摻雜元件有效控制空乏厚度減少非線性電容的產生，而在電流操作下，因為Kirk effect改善而展延了完全空乏的基極集極電容區域，因而達到改善線性度的要求。在1.8 GHz功率與線性度量測上，最高飽和功率輸出藉由延遲Kirk effect提升最大電流密度而改善2.2 dBm，此外線性度量測發現OIP3有10 dB的改善。此非均勻的集極摻雜設計在異質接面雙載子電晶體不但可以改善線性度特性,同時也能增加最大輸出功率。
在第四章中，主要研究高速次微米磷化銦/砷化鎵銦異質接面雙載子電晶體製作技術。次微米元件是利用電子束顯影技術製作，有別於一邊傳統利用深紫外光曝光製作。單根射極0.6 × 12 μm2的磷化銦/砷化鎵銦元件被製作與量測，在直流特性上，集極電流密度666 kA/cm2時有最大的電流增益28.4，崩潰電壓大於5 V。在高頻特性上，最高截止頻率與最大震盪頻率分別為230 GHz與135 GHz。在29 GHz的功率量測上，線性增益為7.6 dB，最大功率輸出為14.3 dBm，最大功率效益為34%，本實驗磷化銦/砷化鎵銦元件在29 GHz操作頻率下，是目前單位面積下可輸出最大功率的元件。
在最後一章中，則利用鋁化鎵銦-磷化銦射極來改善傳統type-II的磷化銦/砷化鎵銻電晶體在低電流下低增益現象，此設計可有效降低電子堆積在射極基極接面，增加電子通過並降低表面復合電流。直流特性顯示此結構在低電流時擁有高增益，在電流密度1.78

關鍵字

線性度 ； 磷化銦 ； 砷化鎵 ； 異質接面雙載子電晶體

並列摘要

Heterojunction Bipolar Transistors (HBTs) proposed to improve the emitter efficiency by base-emitter (BE) heterojunction in 1958s. The GaAs-based and InP-based HBTs were implemented as the material growth techniques of MOCVD and MBE became mature in 1980s. In recent, the HBTs are widly applicated in the power amplifier of wireless communication system. The nonlinear characteristic of HBTs is an important point that affects power performance of circuit design. The four major sources of HBTs nonlinearity and the large-signal swing related nonlinear factors are discussed. InP-based HBTs achieved record high speed results and are currently the most promising technologies for achieving Terahertz (THz) operation. The energy band and relation material of the type-I and type-II of InP-based HBTs are studied. And the correlation between cutoff frequency (fT), maximum oscillation frequency (fMAX), collector thickness, breakdown voltage, collector current density is compared and analyzed.
In the chapter 2, a non-uniform collector doping design is studied by employing a thin high-doping layer inside the low doping collector. The collector doping design limits collector depletion and electric field at the thin-high doping layer. The ratio of maximum to minimum values of CBC with uniform and non-uniform collector doping are 1.6 and 1.1. This collector design results in the re-distribution of the electric fields in the collector to delay the onset of Kirk effect and thus improve the current handling capability, fT, output power, and linearity characteristics.
In the chapter 3, a non-uniform collector doping design of GaAs HBTs by employing a thin high-doping layer inside the low doping collector are fabricated and analyzed. The identical emitter and base epi-layer structures shows the similar results in dc characteristics except the negligible reduction in breakdown voltage. The fT of non-uniform collector increases 12 GHz compared to convention HBT (HBT-A) by delay onset of Kirk effect. The power performance and linearity characteristic show the improvement of 2.2 dB in saturation output power and 10 dB in OIP3 at frequency 1.8 GHz. The HBTs (HBT-B and HBT-C) with a thin high-doping layer in the collector demonstrate the improved cutoff frequency, linearity and output power characteristics compared with a conventional HBT.
In the chapter 4, a submicrometer 0.6×12 μm2 InP/InGaAs DHBTs by E-bean lithography is fabricated and measured. The current gain is 28.4 at JC = 666 kA/cm and the common-emitter breakdown voltage exceeds 5 V. The fT and fMAX of the InP/InGaAs DHBT are 230 GHz and 135 GHz, respectively. The saturation output power of 14.3 dBm and the maximum output power density of 3.7 mW/µm2 are measured at Ka-band with load-pull system matching to maximize the output power. This is the highest output power density obtained with submicrometer DHBTs at 29 GHz every reported for on-wafer load-pull measurement using InP/InGaAs DHBT technology.
Finally, in the chapter 5, the InAlAs-InP composite emitter could effectively reduce electron pile-up at the InP/GaAsSb base-emitter junction and improve current gain. The current gain (

並列關鍵字

type-II ； type-I ； collector ； linearity ； InP ； GaAs ； HBT

參考文獻

[28] J. W. Lai,W. Hafez, and M. Feng, " Vertical Scaling of type I InP HBT with fT >500GHz," International Journal of High Speed Electronics and Systems, vol. 14, , pp. 625-631, 2004.

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