A SiGe HBT having an $f_{max}$ (maximum oscillation frequency) higher than $f_τ$ (cut off frequency) has been fabricated using a production chemical vapor deposition (CVD) reactor which allows $SiH_2Cl_2$-based Si collector epi-growth at high growth-rate as well as $SiH_4$-based SiGe base epi-growth at low growth-rate. Transistor design together with process integration was focused on lowering the extrinsic base resistance and the collector-base capacitance. To this purpose, a $TiSi_2$ layer with a sheet resistance of 1.3Ω/sq was used as a base electrode and a selectively implanted collector (SIC) was utilized. For base layer, an undoped-Si (300Å)/p-SiGe(200Å, $N_A = 4.4 \times 10^{18} cm^{-3}$, linearly-graded Ge composition from 0 to 0.19)/undoped-$Si_{0.81}Ge_{0.19}$ (110Å)/undoped-Si (300Å) multilayer was deposited on a LOCOS (LOCal Oxidation of Silicon)-patterned wafer. In order to form the emitter-base junction and to activate the As dopants in the polysilicon-emitter, rapid thermal anneal (RTA) at 900℃ for 20 sec was performed only one time so that outdiffusion of the boron in the base could be suppressed. The collector and base currents are shown nearly ideal. We obtained an $f_τ$ of 37GHz which is near the theoretical limit imposed by $BV_{CEO}$, and an $f_{max}$ of 42GHz. The base resistance and the collector-base capacitance extracted from measured S-parameters have a value of 37Ω and 27.2 fF, respectively.
Using an RP (Reduced Pressure) CVD-grown SiGe-base HBT and a resonator consisting of a chip varactor and a microstrip line inductor, a COB (Chip-On-Board)-type 2.4GHz voltage-controlled oscillator (VCO) for wireless local loop (WLL) application has been demonstrated. The fabricated VCO chip size is 10 mm × 14 mm. At a supply voltage voltage of 5V, power dissipation was 28mW. Using an HP 8563 spectrum analyzer, a center frequency of 2.4GHz and a tuning band of 87MHz with variation of ±0.5dBm over the tuning band, and a phase noise of -110dBc/Hz (at 1MHz off the carrier) were obtained.
