Si/SiGe epitaxial-base transistors. I. Materials, physics, andcircuits

A detailed review of SiGe epitaxial base technology is presented, which chronicles the progression of research from materials deposition through device and integration demonstrations, culminating in the first SiGe integrated circuit application. In part I of this paper, the requirements and processes for high-quality SiGe film preparation are discussed, with emphasis on fundamental principles. A detailed overview of SiGe HBT device design and implications for circuit applications is then presented     

Scaling and technological limitations of 1/f noise and oscillator phase noise in SiGe HBTs

This paper examines the impact of SiGe HBT scaling on 1/f noise and phase noise of oscillators and frequency synthesizers. The increase of transistor speed with scaling is shown to significantly increase the sensitivity of oscillation frequency to 1/f noise and, thus, degrade close-in phase noise, but decrease the sensitivity of oscillation frequency to base current shot noise and base resistance thermal noises. The results show that corner offset frequency defined by the intersect of the 1/f³ and 1/f² phase noise has little to do with the traditional 1/f corner frequency. The relative importance of individual noise sources in determining phase noise is examined as a function of technology scaling, device sizing, and oscillation frequency. The collector current shot noise and base resistance noise are shown to set the fundamental limits of phase noise reduction. A methodology to identify the maximum tolerable 1/f K factor is established and demonstrated for the HBTs used     

The early history of IBM's SiGe mixed signal technology

The history of Silicon Germanium (SiGe) at IBM is a story of persistence. The program began with an idea to replace a conventional implantation step, used in every silicon semiconductor bipolar process, by growing an in-situ doped alloy (SiGe). Many people thought the idea was of value only for a few exotic niche “research” applications. This is a story about how a small group of people persuaded a large digital computer manufacturer to invest in a new unproven technology for telecommunication applications in a field which the company knew little about. It is a success story, as SiGe technology has now become the only BiCMOS technology in development in IBM and is in the roadmaps of every major telecommunication company     

Heterojunction bipolar transistors using Si-Ge alloys

Advanced epitaxial growth techniques permit the use of pseudomorphic Si_1-xGe_x alloys in silicon technology. The smaller bandgap of these alloys allows for a variety of novel band-engineered structures that promise to enhance silicon-based technology significantly. The authors discuss the growth and properties of pseudomorphic Si_1-xGe_x structures and then focus on their applications, especially the Si_1-xGe_x -base heterojunction bipolar transistor (HBT). They show that HBTs in the Si_1-xGe_x system allow for the decoupling of current gain and intrinsic base resistance. Such devices can be made by using a variety of techniques, including molecular-beam epitaxy and chemical vapor deposition. The authors describe the evolution of fabrication schemes for such HBTs and describe the DC and AC results obtained. They show that optimally designed HBTs coupled with advanced bipolar structures can provide performance leverage     

High-mobility modulation-doped SiGe-channel p-MOSFETs

A novel subsurface SiGe-channel p-MOSFET is demonstrated in which modulation doping is used to control the threshold voltage without degrading the channel mobility. A novel device design consisting of a graded SiGe channel, an n⁺ polysilicon gate, and p⁺ modulation doping is used. A boron-doped layer is located underneath the graded and undoped SiGe channel to minimize process sensitivity and maximize transconductance. Low-field hole mobilities of 220 cm²/V-s at 300 K and 980 cm²/V-s at 82 K were achieved in functional submicrometer p-MOSFETs     

Substrate current based avalanche multiplication measurement in 120 GHz SiGe HBTs

A new substrate current-based technique for measuring the avalanche multiplication factor (M - 1) in high-speed SiGe heterojunction bipolar transistors (HBTs) is proposed. The technique enables M - 1 measurement at high operating current densities required for high-speed operation, where conventional techniques fail because of self-heating. Using the proposed technique, M - 1 was measured up to 10 mA//spl mu/m/sup 2/ on SiGe HBTs featuring 120 GHz peak f/sub T/ which occurs at J/sub C/ about 7 mA//spl mu/m/sup 2/. Implications for circuit applications are also discussed.     

An 11 GHz 3-V SiGe voltage controlled oscillator with integratedresonator

A 10.5- to 11-GHz fully monolithic voltage controlled oscillator circuit implemented in a standard SiGe bipolar technology is presented. An oscillator phase noise of -78 to -87 dBc/Hz is achieved at 100-kHz offset. The tuning range is close to 5% with an on-chip varactor-tuned resonator and for a control voltage of 0 to 3 V. The circuit draws less than 8 mA from a 3-V supply including the reference branch bias current     

Selective epitaxy base transistor (SEBT)

A bipolar transistor using selective epitaxy for base formation in a double-poly self-aligned structure is presented. The intrinsic base was formed by a selective-epitaxial deposition in place of ion implantation. Such epitaxial base processes are capable of achieving a narrow intrinsic base sheet resistance R_bi and base-emitter diffusion capacitance c_be compared to advanced ion-implanted processes. A selective epitaxial base can be simply introduced in advanced double-poly self-aligned processes compared to a nonselective epitaxial layer     

Microwave transformers, inductors and transmission linesimplemented in an Si/SiGe HBT process

Experimental results are presented on microwave inductors, transformers, and transmission lines fabricated in an Si/SiGe heterojunction-bipolar-transistor process with standard metallization and a thick polyimide dielectric. Microstrip transmission lines with characteristic impedances from 44 to 73 Ω, Q's from 10 to 14, and insertion losses from 0.11 to 0.16 dB/mm at 10 GHz are presented. Conventional planar inductors with inductances from 0.5 to 15 nH and with peak Q's up to 22 are presented. Lateral transformers with a maximum available gain of better than -5 dB and a measured coupling coefficient (k) of 0.6 at 5.5 GHz and 0.4 up to 12.5 GHz are also discussed     

RF linearity characteristics of SiGe HBTs

Two-tone intermodulation in ultrahigh vacuum/chemical vapor deposition SiGe heterojunction bipolar transistors (HBTs) were analyzed using a Volterra-series-based approach that completely distinguishes individual nonlinearities. Avalanche multiplication and collector-base (CB) capacitance were shown to be the dominant nonlinearities in a single-stage common emitter amplifier. At a given I_c an optimum V_ce exists for a maximum third-order intercept point (IIP3). The IIP3 is limited by the avalanche multiplication nonlinearity at low I_c, and limited by the C_CB nonlinearity at high I_c. The decrease of the avalanche multiplication rate at high I_c is beneficial to linearity in SiGe HBTs. The IIP3 is sensitive to the biasing condition because of strong dependence of the avalanche multiplication current and CB capacitance on I_c and V_ce. The load dependence of linearity was attributed to the feedback through the CB capacitance and the avalanche multiplication in the CB junction. Implications on the optimization of the transistor biasing condition and transistor structure for improved linearity are also discussed