| 摘要: | 隨著先進製程的蓬勃發展，矽基板矽鍺異質接面雙極性電晶體的電流增益截止頻率已發展至350 GHz，而較低的製作成本、低溫環境的適應性、與金氧半場效電晶體的高整合性以及可將數位和類比電路整合於同一基板的優點使得矽鍺異質接面雙極性電晶體更有吸引力。由於基極厚度的持續變薄使其在高頻特性上獲得大幅的提升，因此矽鍺異質接面雙極性電晶體已被廣泛的建議並使用於無線收發電路。為了達到這些目標，一個準確的等效電路模型以及詳細的元件特性分析對電路設計者而言是非常重要的。 為了要找出最佳的元件佈局，我們研究了三個擁有相同集極面積與不同接點結構的0.18微米矽鍺異質接面雙極性電晶體的高頻與功率特性。並利用大訊號VBIC等效電路模型萃取出之成分來做傳輸延遲時間分析。經由分析矽鍺異質接面雙極性電晶體的傳輸延遲時間，我們可以得到一個具有較高電流增益截止頻率的元件佈局。這個最佳元件佈局也可產生最高的功率輸出，在操作頻率為2.4 GHz時，其最大輸出功率為6.4 dBm且轉換效率為40 %。 在此論文中我們也量測了矽鍺異質接面雙極性電晶體在不同溫度下的直流與微波特性，與溫度相關的直流、高頻與功率特性在此有詳盡的分析，利用分析傳輸延遲時間，我們可以發現矽鍺異質接面雙極性電晶體藉由縮短基極與射極傳輸延遲時間來得到較高在低溫時的電流增益截止頻率。此外，在高電壓型態元件中，當高注入效應產生時在射極-基極接面的價帶不連續面會產生一個寄生的導電帶能障，這個寄生的能障會縮小元件的電流增益與電流增益截止頻率並限制電流-電壓曲線的寬度，尤其是在低溫環境中，因此，所量測到的輸出功率、轉換效率與線性度都會隨著降溫明顯的下降，但此寄生能障效應不會在高速型態元件中產生，所以可以在低溫環境中發揮較佳的功率特性。 在這個研究中，我們也探討矽鍺異質接面雙極性電晶體在常溫與低溫環境中的低頻雜訊特性，經由比較高速與高電壓型態元件的1/f雜訊，高速元件中的高射極參雜會產生較高的雜質濃度並增加射極電流的1/f雜訊，此外，在高電壓型態元件中的寄生能障效應也會影響1/f雜訊，由於寄生能障效應在射極-基極接面產生大量的載子累積也產生了額外的基極複合電流，此複合電流提高了元件的低頻雜訊。 With the technological advances, the Si-based SiGe HBTs was already developed to over 350 GHz. The low cost of fabrication, high integration with CMOS process and the possibility of placing both analog and digital circuits on the same chip so as to improve the overall performance made SiGe BiCMOS technology attractive. The thin out of base layer improves the speed of HBTs significantly and hence the SiGe BiCMOS technologies have been widely recommended and used in wireless front-end transceiver for its high integration level, low cost, and good adaptability with cooling. To achieve these goals, the accurate device model and detailed device characteristics are important for the circuit designers. In order to find out the optimal layout for rf properties, we investigated the high-frequency and power properties of three 0.18 um SiGe HBTs with different contact configurations and the same emitter area. The large-signal VBIC model is used to extract the equivalent components for the transit delay time analysis. By using the analysis of transit delay time for SiGe HBTs, we can obtain an optimal contact configuration layout to achieve higher cutoff frequency. Furthermore, regarding the maximum output power, the SiGe HBT with optimal layout provides highest of 6.4 dBm maximum output power and a PAE of 40 % at 2.4 GHz. We also measured the dc and rf characteristic for npn SiGe HBTs with various temperatures. Detailed analyses of temperature-dependent on dc, high-frequency parameters, and power performances are presented. By analyzing the emitter-collector transit time, the temperature-dependent of cutoff frequency was characterized at different functionalities of SiGe HBTs to explain the improvement in fT with reducing the base and collector transit delay time at cryogenic temperature. Furthermore, in SiGe HBTs without SIC, the valance band discontinuity at base-collector heterojunction induces a parasitic conduction band barrier at the onset of high-injection effect. This parasitic conduction band barrier reduces the current gain and cutoff frequency and limit the broad of dc I-V curve significantly especially at cryogenic temperatures. Therefore, the measured output power, power-added efficiency and linearity at 2.4 GHz decrease significantly with decreasing operation temperatures. This heterojunction barrier effect in SiGe HBT with SIC is negligible and thus the device achieves better power performance at cryogenic temperatures compared with that in a SiGe HBT without SIC. In this study, we investigated the low-frequency noise in SiGe HBTs at room and cryogenic temperatures. By comparing the magnitude of 1/f noise of the SiGe HBTs with and without SIC, we show that the impurities at the collector produced by the incomplete activation of the implanted ions cause an increase in the collector current 1/f noise spectrum. Thus, SiGe HBT with SIC exhibits higher collector noise current spectra due to the inactive ions in the collector. Furthermore, the HBE on SiGe HBT without SIC also influences the 1/f noise property at the onset of high-injection effect. The 1/f noise degrades due to the increasing of recombination base current which produced by the accumulation of carriers at the CB junction. |
