Two-dimensional analysis of high injection effects in AlGaAs/GaAs HBTs with semi-insulating external collectors

Two-dimensional simulations of AlGaAs/GaAs HBTs with various collector structures were performed. The introduction of a semi-insulating external collector improves cutoff frequency f_T in the low current region because the base-collector capacitance decreases. However, it leads to an earlier fall of f_T in the high current region, because a high injection effect is enhanced. This high injection effect has two features: (1) expansion of the collector depletion layer is remarkable near the interface between the intrinsic collector and the semi-insulating external collector, resulting in a longer transit time in this region; and (2) the effective channel in the intrinsic collector becomes narrow by introducing the semi-insulating external collector and so the effective current density there becomes high, leading to an earlier appearance of the high injection situation. It is shown that to minimize these unfavourable high injection effects, the semi-insulating layer should be slightly away from the intrinsic collector region so that it may not affect electron transport in the intrinsic collector region.     

A New Analytical Method for Robust Extraction of the Small-Signal Equivalent Circuit for SiGe HBTs Operating at Cryogenic Temperatures

We present a new analytical direct parameter-extraction methodology for obtaining the small-signal equivalent circuit of HBTs. It is applied to cryogenically operated SiGe HBTs as a means to allow circuit design of SiGe HBT low-noise amplifiers for cooled radio astronomy applications. We split the transistor into an intrinsic transistor (IT) piece modeled as a Pi-topology, and the quasi-intrinsic transistor (QIT), obtained from the IT after that the base resistance (R_b) has been removed. The relations between Z-Y-parameters of the IT and QIT are then established, allowing us to propose a new methodology for determining R_b. The present extraction method differs from previous studies in that each of the model elements are obtained from exact equations that do not require any approximations, numerical optimization, or post-processing. The validity of this new extraction methodology is demonstrated by applying it to third-generation SiGe HBTs operating at liquid-nitrogen temperature (77 K) across the frequency range of 2-22 GHz.     

Optimization of characteristics related to the emitter-base junction in self-aligned SEG SiGe HBTs and their application in 72-GHz-static/92-GHz-dynamic frequency dividers

Characteristics related to the emitter-base junction of self-aligned selective-epitaxial-growth SiGe heterojunction bipolar transistors (HBTs) were optimized for use with a highly-doped base. The thickness of the Si-cap layer affected both the emitter-base junction concentration and space-charge width, so the dc and ac characteristics of the SiGe HBTs were in turn dependent on this thickness. With a 4/spl times/10/sup 19/-cm/sup -3/ boron-doped base, a 131-GHz cutoff frequency and ECL gate-delay time of 5.4 ps were achieved for the optimized SiGe HBTs. A static frequency divider with a maximum operating frequency of 72.2 GHz and a dynamic frequency divider with a maximum operating frequency of 92.4 GHz were developed for optical-fiber link and millimeter-wave communication systems of the future.     

Emitter injection and collector current ideality in abrupt heterojunction AlInAs/GaInAs HBTs

We investigated the electron injection process for high-speed N-p-n AlInAs/GaInAs HBTs by measuring collector and base currents as a function of base-emitter voltage with collector-base voltage equal to zero (Gummel plots) at temperatures from 77 to 300 K. We compared the measured collector current with calculations based on electron injection from emitter to base by tunneling through the conduction band spike and thermionic emission over it, using a modified version of the thermionic-field emission theory developed by Crowell and Rideout. Good agreement was obtained between the experimental collector current ideality factor and tunneling-thermionic emission theory for all temperatures and currents. This is an improvement over drift-diffusion and thermionic emission models, which have been used for HBTs but which do not correctly describe the experimentally observed temperature and current dependence of the ideality of the collector current. The tunneling-thermionic emission model explains the increase in collector current ideality factor that occurs as the transistor is biased at high collector current density (J_C 10⁵ A cm⁻²), which is the regime of operation in which f_T is maximized and a low ideality factor is most important. The model also explains the experimentally observed variation of h_FE with ln I_C. Thus the tunneling-thermionic emission model is a useful aid in the design of the epitaxial structure for high-frequency HBTs.     

一种低噪声SiGe微波单片放大电路

介绍了一种利用SiGe技术制作的低噪声SiGe微波单片放大电路(MMIC)。该电路以达林顿结构的形式级联,由两个异质结双极型晶体管(HBT)和4个电阻组成;HBT采用准自对准结构,其SiGe基区为非选择性外延。在1 GHz频率下,电路噪声为1.59 dB,功率增益为14.3 dB,输入驻波比为1.6,输出驻波比为2.0。     

TiSi2在微波低噪声SiGe HBT中的应用

通过在SiGe HBT外基区和多晶发射极上制作TiSi2,从而使器件的高频噪声系数得到进一步降低.以PD=200mW的SiGe HBT为例,采用TiSi2工艺的噪声系数典型值为F=1.6dB@1.1GHz,明显低于无TiSi2工艺SiGe HBT的2.0dB@1.1GHz,且频率越高,二者差别越大.     

New collector undercut technique using a SiN sidewall for low basecontact resistance in InP/InGaAs SHBTs

A new collector undercut process using SiN protection sidewall has been developed for high speed InP/InGaAs single heterojunction bipolar transistors (HBTs). The HBTs fabricated using the technique have a larger base contact area, resulting in a smaller DC current gain and smaller base contact resistance than HBTs fabricated using a conventional undercut process while maintaining low C_bc. Due to the reduced base contact resistance, the maximum oscillation frequency (f_max) has been enhanced from 162 GHz to 208 GHz. This result clearly shows the effectiveness of this technique for high-speed HBT process, especially for the HBTs with a thick collector layer, and narrow base metal width     

Small-signal performance and modeling of sub-50 nm nMOSFETs with fT above 460-GHz

We have fabricated and tested the performance of sub-50 nm gate nMOSFETs to assess their suitability for mixed signal applications in the super high frequency (SHF) band, i.e. 3–30 GHz. For a 30 nm × 40 μm × 2 device, we found f_T = 465 GHz at V_ds = 2 V, V_g = 0.67 V, which is the highest cut-off frequency reported for a MOSFET produced on bulk silicon substrate so far. However, our measurements of f_max and noise figure indicate that parasitics impose limitations on SHF operation. We also present a high frequency ac model appropriate to sub-50 nm gate length nanotransistors, which incorporates the effects of the parasitics. The model accurately accounts for measurements of the S- and Y-parameters in the frequency range from 1 to 50 GHz.     

Self-aligned SiGe NPN transistors with 285 GHz f/sub MAX/ and 207 GHz f/sub T/ in a manufacturable technology

This paper reports on SiGe NPN HBTs with unity gain cutoff frequency (f_T) of 207 GHz and an f_MAX extrapolated from Mason's unilateral gain of 285 GHz. f_MAX extrapolated from maximum available gain is 194 GHz. Transistors sized 0.12×2.5 μm² have these characteristics at a linear current of 1.0 mA/μm (8.3 mA/μm²). Smaller transistors (0.12×0.5 μm²) have an f_T of 180 GHz at 800 μA current. The devices have a pinched base sheet resistance of 2.5 kΩ/sq. and an open-base breakdown voltage BV_CEO of 1.7 V. The improved performance is a result of a new self-aligned device structure that minimizes parasitic resistance and capacitance without affecting f_T at small lateral dimensions     

MBE-grown Si/SiGe HBTs with high β, fT,and fmax

Si/SiGe heterojunction bipolar transistors (HBTs) were fabricated by growing the complete layer structure with molecular beam epitaxy (MBE). The typical base doping of 2×10¹⁹ cm^-3 largely exceeded the emitter impurity level and led to sheet resistances of about 1 kΩ/□. The devices exhibited a 500-V Early voltage and a maximum room-temperature current gain of 550, rising to 13000 at 77 K. Devices built on buried-layer substrates had an f_max of 40 GHz. The transit frequency reached 42 GHz     

Analytical modelling of current gain and frequency characteristics under high injection levels in Si/SiGe heterojunction bipolar transistors at 77 and 300 K

This paper reports an analytical modelling of current gain and frequency characteristics in Si/SiGe heterojunction bipolar transistors (HBTs) at 77 and 300 K. Important transistor parameters, such as current gain, transconductance, cutoff frequency and maximum oscillation frequency are calculated as a function of Ge concentration in the base under different injection levels. The main physical mechanisms for the current and cutoff frequency rolloff at high injection levels are also analyzed. It shows that the high-level injection effect is more pronounced in the SiGe HBTs as a result of the increasing minority carrier concentration in the base and the Ge concentration and distribution will have a decisive influence of device performance. The results may provide a basis for the design of low temperature operation SiGe HBTs.     

Noise in SiGe HBT RF Technology: Physics, Modeling, and Circuit Implications

This paper presents an overview of the physics, modeling, and circuit implications of RF broad-band noise, low-frequency noise, and oscillator phase noise in SiGe heterojunction bipolar transistor (HBT) RF technology. The ability to simultaneously achieve high cutoff frequency (f/sub T/), low base resistance (r/sub b/), and high current gain (/spl beta/) using Si processing underlies the low levels of low-frequency 1/f noise, RF noise, and phase noise of SiGe HBTs. We first examine the RF noise sources in SiGe HBTs and the RF noise parameters as a function of SiGe profile design, transistor biasing, sizing, and operating frequency, and then show a low-noise amplifier design example to bridge the gap between device and circuit level understandings. We then examine the low-frequency noise in SiGe HBTs and develop a methodology to determine the highest tolerable low-frequency 1/f noise for a given RF application. The upconversion of 1/f noise, base resistance thermal noise, and shot noises to phase noise is examined using circuit simulations, which show that the phase noise corner frequency in SiGe HBT oscillators is typically much smaller than the 1/f corner frequency measured under dc biasing. The implications of SiGe profile design, transistor sizing, biasing, and technology scaling are examined for all three types of noises.     

500 GHz cutoff frequency SiGe HBTs

A current gain cutoff frequency f_T of 508 GHz is reported for a SiGe heterojunction bipolar transistor (HBT) operating at 40 K. This 63% increase over the 311 GHz value measured at room temperature results from the overall decrease of the transit and charging times. Two HBTs are compared to highlight the importance of the topology of the HBT to reach maximum performances.     

An X-band high-power amplifier using SiGe/Si HBT and lumped passivecomponents

We report the design and fabrication of a compact microwave monolithic integrated circuit (MMIC) amplifier, which demonstrates high output power at X-Band. A single-stage power amplifier is demonstrated, with a double-mesa type SiGe/Si HBT as the active device and spiral inductors and MIM capacitors as lumped passive components. At 8.4 GHz, a linear gain of 8.7 dB, an output power at peak efficiency of 23 dBm, and a saturated output power P_sat of 25 dBm, are measured. To our knowledge, this is the first MMIC X-Band power amplifier using SiGe/Si HBTs     

Submicron scaling of HBTs

The variation of heterojunction bipolar transistor (HBT) bandwidth with scaling is reviewed. High bandwidths are obtained by thinning the base and collector layers, increasing emitter current density, decreasing emitter contact resistivity, and reducing the emitter and collector junction widths. In mesa HBTs, minimum dimensions required for the base contact impose a minimum width for the collector junction, frustrating device scaling. Narrow collector junctions can be obtained by using substrate transfer or collector-undercut processes or, if contact resistivity is greatly reduced, by reducing the width of the base ohmic contacts in a mesa structure. HBTs with submicron collector junctions exhibit extremely high f_max and high gains in mm-wave ICs. Transferred-substrate HBTs have obtained 21 dB unilateral power gain at 100 GHz. If extrapolated at -20 dB/decade, the power gain cutoff frequency f_max is 1.1 THz. f_max will be less than 1 THz if unmodeled electron transport physics produce a >20 dB/decade variation in power gain at frequencies above 110 GHz. Transferred-substrate HBTs have obtained 295 GHz f_T. The substrate transfer process provides microstrip interconnects on a low-ϵ_r polymer dielectric with a electroplated gold ground plane. Important wiring parasitics, including wiring capacitance, and ground via inductance are substantially reduced. Demonstrated ICs include lumped and distributed amplifiers with bandwidths to 85 GHz and per-stage gain-bandwidth products over 400 GHz, and master-slave latches operating at 75 GHz     

Transistor and circuit design for 100-200-GHz ICs

Compared to SiGe, InP HBTs offer superior electron transport properties but inferior scaling and parasitic reduction. Figures of merit for mixed-signal ICs are developed and HBT scaling laws introduced. Device and circuit results are summarized, including a simultaneous 450 GHz f/sub /spl tau// and 490 GHz f/sub max/ DHBT, 172-GHz amplifiers with 8.3-dBm output power and 4.5-dB associated power gain, and 150-GHz static frequency dividers (a digital circuit figure-of-merit for a device technology). To compete with advanced 100-nm SiGe processes, InP HBTs must be similarly scaled and high process yields are imperative. Described are several process modules in development: these include an emitter-base dielectric sidewall spacer for increased yield, a collector pedestal implant for reduced extrinsic C/sub cb/, and emitter junction regrowth for reduced base and emitter resistances.     

DC characteristics and stability behaviour of high-speed Si/SiGe HBTs with undoped SiGe spacer between base and collector

The quality of MBE-grown Si/SiGe heterojunction bipolar transistors (HBTs) was improved by inserting a well-defined undoped SiGe layer between the neutral base and the collector. The DC characteristics and the long-term stability of these non-selfaligned devices proved to be excellent, and the transit frequency reached 33 GHz (V/sub CB/=1 V). Those features are essential preconditions for future application in high-speed ICs.<>     

SiGe HBT低频噪声PSPICE模拟分析

对SiGe HBT低频噪声的各噪声源进行了较全面的分析,据此建立了SPICE噪声等效电路模型,进一步用PSPICE软件对SiGe HBT的低频噪声特性进行了仿真模拟.研究了频率、基极电阻、工作电流和温度等因素对低频噪声的影响.模拟结果表明,相较于Si BJT和GaAs HBT,SiGe HBT具有更好的低频噪声特性;在低频范围内,可通过减小基极电阻、减小工作电流密度或减小发射极面积、降低器件的工作温度等措施来有效改善SiGe HBT的低频噪声特性.所得结果对SiGe HBT的设计和应用有重要意义.     

SiGe HBT and BiCMOS technologies for optical transmission and wireless communication systems

Technologies for a self-aligned SiGe heterojunction bipolar transistor (HBT) and SiGe HBTs with CMOS transistors (SiGe BiCMOS) have been developed for use in optical transmission and wireless communication systems. n-Si cap/SiGe-base multilayer fabricated by selective epitaxial growth (SEG) was used to obtain both high-speed and low-power performance for the SiGe HBTs. The process except the SEG is almost completely compatible with well-established Si bipolar-CMOS technology, and the SiGe HBT and BiCMOS were fabricated on a 200-mm wafer line. High-quality passive elements, i.e., high-precision poly-Si resistors, a high-Q varactor, an MIM capacitor, and high-Q spiral inductors have also been developed to meet the demand for integration of the sophisticated functions. A cutoff frequency of 130 GHz, a maximum oscillation frequency of 180 GHz, and an ECL gate-delay time of 5.3 ps have been demonstrated for the SiGe HBTs. An IC chipset for 40-Gb/s optical-fiber links, a single-chip 10-Gb/s transceiver large-scale IC (LSI), a 5.8-GHz electronic toll collection transceiver IC, and other practical circuits have been implemented by applying the SiGe HBT or BiCMOS technique.     

SiGe HBT噪声的研究进展

噪声对RF电路设计非常关键,故需要对SiGe HBT噪声特性进行深入研究。根据器件的高频噪声模型,指出了影响SiGe HBT高频噪声参数的主要因素,论述了优化设计的具体方法;举例说明尺寸缩小使得高频噪声性能已经达到了GaAs pHEMT的水平,fT达到了375 GHz。分析了SiGe HBT低频噪声的机理和模型及其与几何尺寸的关系,指出用fC/fT表达低频噪声性能更合适;举例说明小尺寸效应使得SiGe HBT的低频噪声偏离了1/f噪声形式。