Silicon-germanium Heterojunction Bipolar Transistors Research Articles

Pulsed microwave characterization of an SiGe heterojunction bipolar transistor

This paper presents the first pulsed characterization of a silicon-germanium (SiGe) heterojunction bipolar transistor (HBT). Comparison is made of the SiGe HBT's performance to that of a Si bipolar junction transistor fabricated using the same mask set. Measurements made over a 400-/spl mu/s pulse show how device self-heating dramatically affects the microwave-frequency response of the devices. Using pulse-profiled S-parameters to find the intrinsic base resistance r/sub /spl pi// and base-collector capacitance C/sub jc/, plots reveal how these two elements significantly vary over the length of the pulse. The results emphasize the need for accurate characterization of microwave Si-based devices in pulsed applications.

Silicon-germanium

The strong points of compound and single element semiconductors are united in a new type of transistor, silicon-germanium heterojunction bipolar transistor (Si-Ge HBT). The device is the offshoot of bandgap engineering and the manufacturing economics of silicon. Silicon-germanium is a new material used in making microchips for less expensive, high-performance communications tools. Low energy consumption and processing at ultra-high speeds make silicon-germanium transistors a treasure for many people in microelectronics. Silicon-germanium is a critical breakthrough in an anxiety-laden field. Practitioners fear that traditional silicon technology is nearing its physical limits. Higher speeds cannot be attained without miniaturization to a point at which the devices no longer function.

Selective and non-selective growth of self-aligned SiGe HBT structures by LPCVD epitaxy

Silicon-germanium (SiGe) heterojunction bipolar transistors (HBT) have become increasingly important for high speed applications. Novel device structures are often required to fully exploit the advantages from incorporation of a heterojunction. In this work, a growth technique is described which uses both selective and non-selective growth of Si and SiGe to produce an advanced SiGe HBT structure. The surface morphology of the material grown is examined using Nomarski contrast optical microscopy and scanning electron microscopy (SEM), and the surface of the epitaxial areas appears smooth with a low defect density. The growth surface is reasonably planar, as needed for further device processing, which suggests the required thicknesses of both selective and non-selective epitaxy were achieved. The Ge and B profiles of the material are measured using secondary ion mass spectroscopy (SIMS), and the layer thicknesses are found to meet the device specification. The crystallinity and defects in the material are examined by transmission electron microscopy (TEM). The material produced is shown to be suitable for fabrication into the proposed device.

A 60-dB gain, 55-dB dynamic range, 10-Gb/s broad-band SiGe HBT limiting amplifier

A limiting amplifier IC implemented in a silicon-germanium (SiGe) heterojunction bipolar transistor technology for low-cost 10-Gb/s applications is described. The IC employs 20 dB gain limiting cells, input overload protection, split analog-digital grounds, and on-chip isolation interface with transmission lines. A gain enhancement technique has been developed for a parallel-feedback limiting cell. The limiting amplifier sensitivity is less than 3.5 mV/sub pp/ at BER=10/sup -9/ with 2-V/sub pp/ maximum input (55-dB dynamic range). The total gain is over 60 dB, and S/sub 21/ bandwidth exceeds 15 GHz at 10-mV/sub pp/ input. Parameters S/sub 11/ and S/sub 22/ are better than -10 dB in the 10-GHz frequency range. The AM to PM conversion is less than 5 ps across input dynamic range. The output differential voltage can be set from 0.2 to 2 V/sub pp/ with IC power dissipation from 250 mW to 1.1 W. The chip area is 1.2/spl times/2.6 mm/sup 2/. A 10-Gb/s optical receiver, built with the packaged limiting amplifier, demonstrated -19.6-dBm sensitivity. The IC can be used in 10-Gb/s fiber-optic receivers requiring high sensitivity and wide input dynamic range.

An investigation of the spatial location of proton-induced traps in SiGe HBTs

The effects of 46 MeV proton irradiation induced trap generation and its impact on the electrical characteristics of silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) from an advanced ultrahigh vacuum/chemical vapor deposition (UHV/CVD) SiGe BiCMOS technology are examined and discussed for the first time. At proton fluences as high as 10/sup 14/ p/cm/sup 2/ the peak current gain of the devices degraded by less than 8% compared to the pre-irradiated samples. The maximum oscillation frequency and cutoff frequency of the SiGe HBTs showed only minor degradation after 10/sup 14/ p/cm/sup 2/. Calibration of 2-D device simulation (MEDICI) to measured data in both forward and inverse modes of operation was used to infer the spatial location of the proton-induced traps. Traps in the collector-base space charge region appear as generation/recombination (G/R) centers in the inverse emitter-base region and are the result of displacement damage. Traps at the emitter-base spacer oxide interface appear as G/R centers in the forward emitter-base space charge region and are the result of ionization damage. Taken together, these results suggest that UHV/CVD SiGe HBT technology is robust to proton fluences at least as high as 10/sup 13/ p/cm/sup 2/ without radiation hardening.

Device design and circuit modeling issues in ultrahigh vacuum/chemical vapor deposition SiGe heterojunction bipolar transistors

We discuss the physical basis, experimental results, and compact circuit modeling issues associated with neutral base recombination, germanium-ramp effects, and high-injection heterojunction barrier effects in graded-base, silicon-germanium heterojunction bipolar transistors. All three phenomena depend strongly on Ge profile shape and temperature, and are unaccounted for in conventional silicon bipolar transistor compact models such as SPICE.

SiGe HBT technology: a new contender for Si-based RF and microwave circuit applications

The silicon-germanium heterojunction bipolar transistor (SiGe HBT) is the first practical bandgap-engineered device to be realized in silicon. SiGe HBT technology combines transistor performance competitive with III-V technologies with the processing maturity, integration levels, yield, and hence, cost commonly associated with conventional Si fabrication. In the ten-and-one-half years since the first demonstration of a functional transistor, SiGe HBT technology has emerged from the research laboratory, entered manufacturing on 200-mm wafers, and is poised to enter the commercial RF and microwave market. State-of-the-art SiGe HBT's can deliver: (1) f/sub T/ in excess of 50 GHz; (2) f/sub max/ in excess of 70 GHz; (3) minimum noise figure below 0.7 dB at 2.0 GHz; (4) 1/f noise corner frequencies below 500 Hz; (5) cryogenic operation; (6) excellent radiation hardness; (7) competitive power amplifiers; and (8) reliability comparable to Si. A host of record-setting digital, analog, RF, and microwave circuits have been demonstrated in the past several years using SiGe HBT's, and recent work on passives and transmission lines on Si suggest a migratory path to Si-based monolithic microwave integrated circuits (MMIC's) is possible. The combination of SiGe HBT's with advanced Si CMOS to form an SiGe BiCMOS technology represents a unique opportunity for Si-based RF system-on-a-chip solutions. This paper reviews state-of-the-art SiGe HBT technology and assesses its potential for current and future RF and microwave systems.

Base-profile optimization for minimum noise figure in advanced UHV/CVD SiGe HBT's

We investigate the base-profile design issues associated with optimizing ultrahigh vacuum/chemical vapor deposition (UHV/CVD) silicon-germanium (SiGe) heterojunction bipolar transistors (HBT's) for minimum broad-band noise. Using the simulator for cryogenic research and SiGe bipolar device optimization (SCORPIO), the impact of Ge profile, base doping level, and base thickness on minimum noise figure (NF/sub min/) are quantitatively examined across the -55/spl deg/C-125/spl deg/C temperature range. We introduce a novel Ge profile for optimum NF/sub min/, which allows independent control of current gain (/spl beta/) and achieves maximum f/sub T/ while maintaining thermodynamic stability. Simulations show that this profile can achieve a /spl beta/ of /spl sim/200, a peak f/sub T/>50 GHz, a peak f/sub max/>60 GHz, and an NF/sub min/ 70 GHz, and a peak f/sub max/>90 GHz. These 300-K performance values improve as the temperature is reduced.

Design of RF integrated circuits using SiGe bipolar technology

We report on design aspects and the implementation of radio-frequency integrated circuits using TEMIC's SiGe technology. The differences between the device parameters of silicon bipolar junction transistor and silicon germanium heterojunction bipolar transistor technology and their influence on IC design are discussed. Design and measurement results of RFICs, including low noise amplifier, power amplifier, and single-pole, double-throw antenna switch for application in a 1.9 GHz digital enhanced cordless telecommunications RF front end are presented.

Separating the influences of neutral base recombination and avalanche breakdown on base current reduction in SiGe HBT's

A simple experimental procedure is proposed to determine the separate ranges of reverse collector-base bias where neutral base recombination and avalanche breakdown, respectively, dominate base current reduction in silicon germanium heterojunction bipolar transistors (SiGe HBTs) which exhibit significant neutral base recombination.

Experimental verification and numerical application of the thermodynamic approach to high-frequency noise in SiGe HBTs

We present experimental and numerical results on high-frequency noise of Silicon-Germanium heterojunction bipolar transistors (SiGe HBTs) based on small-signal analysis. The minimum noise figure for an SiGe HBT is determined from s-parameter measurements. The approach is verified through comparison with a conventionally measured noise figure and can be used to extract the noise figure from device simulation. By using a two-dimensional device simulation code, we calculate the high-frequency noise figure from the simulated y-parameters. The simulation results are in good agreement with the measured minimum noise figure. We use the model to predict the effect of lateral downscaling on the minimum noise figure.

Operation of SiGe heterojunction bipolar transistors in the liquid-helium temperature regime

We present the first dc measurements of silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) operating in the liquid-helium temperature (LHeT=4.2 K) regime. The current gain of the self-aligned, UHV/CVD-grown SiGe HBT increases monotonically from 110 at 300 K to 1045 at 5.84 K, although parasitic base current leakage limits the useful operating current to above about 1.0 μA at 5.84 K. An aggressively designed base profile (peak N/sub AB//spl ap/8×10/sup 18/ cm/sup -3/) is used to suppress base freeze-out at LHeT (R/sub bi/=18.3 k/spl Omega///spl square/ at 4.48 K). We have also identified a non-ideal minority carrier transport mechanism in the collector current at temperatures below 77 K (I/sub C/ is not proportional to exp(qV/sub BE//kT)) which is unaccounted for in conventional device theory. Preliminary calculations suggest that this phenomenon is due to trap-assisted carrier tunneling from the emitter to the collector through the base potential barrier.

SiGe-HBTs with high f T at moderatecurrentdensities

Silicon-germanium heterojunction bipolar transistors (HBTs) have been developed with regard to high cutoff frequencies within a wide collector current range. Unity current gain frequencies f/sub T/ high as 116 GHz were obtained at a collector current density of 2*10/sup 5/ A/cm/sup 2/. In addition, the FWHM of cutoff frequency f/sub T/ against collector current exceeds one and a half decades. Calculations indicate that the ratio of the collector to emitter area essentially determines the current density range of a high frequency HBT. >

Numerical simulation of SiGe HBT's at cryogenic temperatures

This paper describes SCORPIO, a new one-dimensional, drift-diffusion simulator for modeling silicon-germanium heterojunction bipolar transistors (SiGe HBT's) over a wide temperature range (77-400K). SCORPIO will be used to investigate fundamental low-temperature device physics problems and key device design issues. Comparisons of simulation results with experimental measurements are being used to ensure accurate model calibration

Operation of SiGe bipolar technology at cryogenic temperatures

The recent introduction of silicon-germanium (SiGe) alloys has proven exceptionally promising for achieving excellent bipolar transistor performance at cryogenic temperatures, while maintaining the cost and yield advantages traditionally associated with silicon (Si) manufacturing. In this paper we review the features of silicon-germanium heterojunction bipolar transistors (SiGe HBTs) which make them particularly suitable for cryogenic operation. Using dc and ac experimental results, we also address the issues associated with profile optimization of SiGe HBTs for the cryogenic environment, the potential for cryogenic SiGe BiCMOS technologies, and present new results on liquid-helium temperature operation of SiGe HBTs. We conclude that SiGe HBT technology offers significant leverage for future cryogenic digital, analog and mixed-signal applications requiring the highest levels of performance