SiGe technology: application to wireless digital communications

Abstract

Heterojunction bipolar technology using SiGe expitaxial base grown by ultra high vaccumlchemical vapor deposition (UHVEVD) offers very high performance and very low cost for the production of wireless communication high frequency ICs. This paper reports on the status of SiGe HBT development and compares it with existing Si and GaAs technologies.New systems in wireless digital communications require high performance, low cost RF components operating from 800 MHz to 2500 MHz. The main challenge for semiconductor manufacturers is the development of highly integrated, low power consumption, low voltage, surface mount transceiver integrated circuits manufacturable at very low cost in large volume (> several million/year) for hand held telephones.The existing semiconductor process performance and cost suggest homojunction silicon ICs will dominate the 800 to 1000 MHz market while GaAs ICs might conquer a substantial portion of the 1700 to 2500 MHz (and later on the 5700 to 5800 MHZ) marked1 1 where GaAs performance advantages offset its higher cost. The emergence of productionready very hgh performance silicon ermanium heterojunction bipolar IC pcocessesfi1 [31 tailored for low voltage, low power consumption RF and mixed signal applications modifies the initial market split between silicon and GaAs technology and allows for a silicon based technology to address existing wireless communication applications as well as the 5700 to 5800 MHz ISM band future requirements. This paper presents the performance capability of the SiGe HBT technology, compares it with existing silicon and GaAs technology and demonstrates its performance/cost advantage for the development and manufacturing of wireless communications RF ICs.94CH3351-4/94/0000-01$01.00 0 1994 IEEE Heterojunction bipolar transistors off er considerable leverage over conventional homojunction transistors mainly due to higher emitter injection efficiency and lower base transit time. Although the feasibility of HBTs has been well demonstrated in Ill4 semiconductor system (AIGaAdGaAs), achieving Si HBT posed a significant problem until the first SiGe HBT is reported in 198d41, followed by a 75 GHz F device in MO[~] and a 117 GHz transistor in 1 9 9 3 h The SiGe HBT principle is to use "bandgap engineering" in the silicon material system by introducing a small amount of Ge (smaller bandgap) into the Si BJT and selectively tailor the properties of the transistor. Figure 1 shows the band diagram of a graded-bandgap SiGe HBT. The smaller base bandgap increases electron injection into the base (thus dramatically increasing beta) which in turn allows for a more heavily doped base (thus decreasing the base resistance RB). In addition, the graded Ge content in the base region induces a dint field in the base which decreases the base transit time (thus increases the transition frequency FT).The net result is S i e HBT's transition frequency FT and maximum oscillation frequency Fmax are typically twice larger than their Si BJT counterparts (for 0.5 micron emitter geometry) and the ...