The Investigation of Dynamic, Power and Noise Characteristics on SiGe Heterojunction Bipolar Transistors

• Main Authors: Meng-wei Hsieh, 謝孟緯
• Other Authors: Yi-jen Chan
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/zq454b

博士 === 國立中央大學 === 電機工程研究所 === 96 === 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.