Collector-base junction avalanche multiplication effects inadvanced UHV/CVD SiGe HBTs

The collector-base junction avalanche multiplication factor (M-1) in SiGe HBTs is investigated using a new technique better tolerant to self-heating and collector-base leakage. The new technique provides higher accuracy at low current densities and enables M-1 to be measured at high current densities typically used in circuits. Comparisons with identically processed silicon control devices show that M-1 is not inadvertently increased by the incorporation of SiGe, despite its smaller bandgap. With cooling, M-1 first increases, and then saturates when T<117 K. A 2.3 V critical reverse CB voltage at which base current reversal occurs is observed down to 83 K, which is sufficiently high for today's bipolar and BiCMOS logic applications     

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.     

Characterization and modeling of avalanche multiplication in HBTs

The accurate modeling of weak avalanche breakdown of HBTs in compact bipolar transistor models for circuit simulation is presented. Based on various device electrical characteristics that are grouped into three classes, a modified VBIC avalanche multiplication model is proposed. By simply replacing one constant avalanche model parameter with current linear dependence, the new model predicts well broad behaviors of breakdown from weak avalanche up into high level injections.     

Avalanche multiplication and pinch-in models for simulating electrical instability effects in SiGe HBTs

The onset of impact ionization-induced instabilities limits the operative range of SiGe hetero-junction bipolar transistors. Based on referential Monte Carlo simulation results, a critical review of major models for the avalanche multiplication factor (M) is presented, and a new analytical model is proposed and successfully verified by measurements. The novel M formulation has been incorporated in a two-dimensional theoretical model describing bipolar transistor operation under pinch-in conditions/above the open-base breakdown voltage BV_CEO. The physical mechanisms leading to electrical instability are addressed, and closed form analytical relations defining the onset of instability under forced-I_E conditions are derived. The proposed model defines the limits of the Safe Operating Area (SOA) related to impact ionization, enabling the reliable usage of HBTs above BV_CEO.     

40 GHz 7.9 mW low-power frequency divider IC using self-alignedselective-epitaxial-growth SiGe HBTs

A low-power current-mode-logic frequency divider integrated circuit (IC) that operated at 40 GHz with a power consumption of 7.9 mW per master-slave flip-flop was fabricated using 0.2 μm self-aligned selective-epitaxial-growth SiGe heterojunction bipolar transistors. This IC also operated at 35 GHz from a supply voltage of -2.2 V. To the authors' knowledge this IC consumes the least power of any for operation in the millimetre-waveband that have appeared to date     

An analysis of base bias current effect on SiGe HBTs

The anomalous dip in scattering parameter S/sub 11/ of SiGe heterojunction bipolar transistors (HBTs) is explained quantitatively for the first time. Our results show that for SiGe HBTs, the input impedance can be represented by a "shifted" series RC circuit at low frequencies and a "shifted" parallel RC circuit at high frequencies very accurately. The appearance of the anomalous dip of S/sub 11/ in a Smith chart is caused by this inherent ambivalent characteristic of the input impedance. In addition, it is found that under constant collector-emitter voltage (V/sub CE/), an increase of base current (which corresponds to a decrease of base-emitter resistance (r/sub /spl pi//) and an increase of transconductance (g/sub m/)) enhances the anomalous dip, which can be explained by our proposed theory.     

Optimization of SiGe HBTs for operation at high current densities

A comprehensive investigation of the impact of Ge profile shape as well as the scaling of collector and base doping profiles on high-injection heterojunction barrier effects in SiGe HBTs has been conducted over the -73-85°C temperature range. The onset of Kirk effect at high current densities is shown to expose the Si/SiGe heterojunction in the collector-base space charge region, thereby inducing a conduction band barrier which negatively impacts the collector and base currents as well as the dynamic response, leading to a premature roll-off in both β and f_T. In light of this, careful profile optimization is critical for emerging SiGe HBT circuit applications, since they typically operate at high current densities to realize maximum performance. We first explore the experimental consequences and electrical signature of these barrier effects over the 200-358 K temperature range for a variety of Ge profiles from an advanced UHV/CVD SiGe HBT technology. We then use extensive simulations which were calibrated to measured results to explore the sensitivity of these barrier effects to both the Ge profile shape and collector profile design, and hence investigate the optimum profile design points as a function of vertical scaling     

Leakage current mechanisms in SiGe HBTs fabricated using selectiveand nonselective epitaxy

SiGe heterojunction bipolar transistors (HBTs) have been fabricated using selective epitaxy for the Si collector, followed in the same growth step by nonselective epitaxy for the p⁺ SiGe base and n-Si emitter cap. DC electrical characteristics are compared with cross-section TEM images to identify the mechanisms and origins of leakage currents associated with the epitaxy in two different types of transistor. In the first type, the polysilicon emitter is smaller than the collector active area, so that the extrinsic base implant penetrates into the single-crystal Si and SiGe around the perimeter of the emitter and the polycrystalline Si and SiGe extrinsic base. In these transistors, the Gummel plots are near-ideal and there is no evidence of emitter/collector leakage. In the second type, the collector active area is smaller than the polysilicon emitter, so the extrinsic base implant only penetrates into the polysilicon extrinsic base. In these transistors, the leakage currents observed depend on the base doping level. In transistors with a low doped base, emitter/collector and emitter/base leakage is observed, whereas in transistors with a high doped base only emitter/base leakage is observed. The emitter/collector leakage is explained by punch through of the base caused by thinning of the SiGe base at the emitter perimeter. The emitter/base leakage is shown to be due to a Poole-Frenkel mechanism and is explained by penetration of the emitter/base depletion region into the p⁺ polysilicon extrinsic base at the emitter periphery. Variable collector/base reverse leakage currents are observed and a variety of mechanisms are observed, including Shockley-Read-Hall recombination, trap assisted tunneling, Poole-Frenkel and band to band tunneling. These results are explained by the presence of polysilicon grains on the sidewalls of the field oxide at the collector perimeter     

Self-heating in multi-emitter SiGe HBTs

High power bipolar transistors often have multiple emitters, to achieve high currents, and efficient use of the whole emitter area. The emitters experience high current densities and are self-heated above the ambient temperature, leading to concerns about thermal run-away and damage to the device. Here we use a multi-emitter SiGe HBT, with multiple emitter contacts, to examine the temperature distribution in the emitters in such devices. We have measured the temperature increase in different emitters by biasing one emitter at a time and using the other base–emitter junctions as thermometers. We show that use of a selectively implanted collector does not alter the temperature increase or thermal coupling between the emitters.     

Analysis of temperature dependence of linearity for SiGe HBTs in the avalanche region using Volterra series

In this paper, linearity characteristic of silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) at different temperatures in the avalanche regime is investigated by the Volterra approach incorporating with a physics-based breakdown network for the first time. Third-order intermodulation distortion (IMD₃) decreases with increasing temperature in the impact ionization region due to lower nonlinear contributions from individual nonlinearity according to the Volterra analysis results. Calculated gain, output power, and efficiency of SiGe HBTs are in good agreement with measurement results in the avalanche region. This analysis with respect to temperature can benefit the reliability study of linearity for SiGe HBTs in the avalanche regime.     

Parasitic energy barriers in SiGe HBTs

Parasitic energy barriers can easily be introduced during processing. Measurements and calculations of experimental n-p-n HBTs (heterojunction bipolar transistors) are presented, showing that a parasitic conduction-band barrier at the base-collector junction reduces the collector current and the cutoff frequency. A simple analytical model explains the f_T degradation, caused by the reduction of the collector current and a pileup of minority carriers in the base. With the model the effective height and width of the barrier can also be derived from the measured collector current enhancement factor I_C(SiGe)/I_C(Si)     

A model for dark current and multiplication in HgCdTe avalanche photodiodes

In this paper we report the calculated results of the dark current and multiplication factor in MBE grown HgCdTe avalanche photodiodes with separate absorption and multiplication (SAM-APD). The device architecture used for this analysis comprises the following layers: p⁺ contact, p junction, n⁻ multiplication, n charge sheet, n⁻ absorber, and n⁺ contact. Various leakage current mechanisms are considered and the generation-recombination term is found to be the dominant one for this device structure. However, experimental reverse bias I-V characteristics reported earlier by T. de Lyon et al. shows a large deviation from ideality, which can not be explained in terms of bulk leakage current mechanism. To explain the large difference between experimental and theoretical data we consider that the dominant generation-recombination current is multiplied through impact ionization process. To validate this assumption, multiplication is calculated as a function of reverse bias. Electric field profile is obtained and the multiplication is computed using the ionization coefficients and avalanche gain equations. Breakdown voltage is found to be 85 V for room temperature operation in agreement with available data in the literature. The theoretical I-V curves considering multiplication are compared with the experimental ones and a close agreement is found which validate this model.     

基于SiGe HBT工艺的GNSS接收机混频器设计

针对目前国内RFIC发展比较滞后的现状,设计了3款应用于GNSS接收机的基于0.5 μm SiGe HBT工艺的混频器(Ⅰ、Ⅱ、Ⅲ),并采用针对混频器的优良指数FOM(figure-of-merit)对这3个混频器进行结构和综合性能比较.3款混频器的供电电压为3.3 V,本振LO输入功率为-10 dBm,其消耗总电流、转换增益、噪声系数、1 dB增益压缩点依次为:Ⅰ)8.7 mA,15 dB,4.1 dB,-17 dBm;Ⅱ)8.4 mA ,10 dB,4.6 dB,-10 dBm;Ⅲ)5.4 mA,11 dB,4.9 dB,-10 dBm.而3款混频器的FOM分别为-57.8、-56.6、-54.3,表明混频器Ⅲ的综合性能最佳,混频器Ⅱ次之,最后为混频器Ⅰ.     

基于SiGe HBT工艺的GNSS接收机混频器设计

针对目前国内RFIC发展比较滞后的现状,设计了3款应用于GNSS接收机的基于0．5μm SiGe HBT工艺的混频器（Ⅰ、Ⅱ、Ⅲ）,并采用针对混频器的优良指数FOM（figure—of-merit）对这3个混频器进行结构和综合性能比较。3款混频器的供电电压为3-3V,本振LO输入功率为-10dBm,其消耗总电流、转换增益、噪声系数、1dB增益压缩点依次为：Ⅰ）8．7mA,15dB,4．1dB,-17dBm;Ⅱ）8．4mA,10dB,4．6dB,-10dBm;Ⅲ）5．4mA,11dB,4．9dB,-10dBm。而3款混频器的FOM分别为-57．8、-56．6、-54．3,表明混频器Ⅲ的综合性能最佳,混频器Ⅱ次之,最后为混频器Ⅰ。     

120 nm SiGe BiCMOS 90~100 GHz低噪声放大器

基于IBM8HP 120 nm SiGe BiCMOS工艺,分析了晶体管的最小噪声系数和最大可用增益特性。采用两级Cascode放大器级联结构,研制出一种频带为90~100 GHz的低噪声放大器(LNA)。详细分析了Cascode放大器潜在的自激可能性,采用串联小电阻的方式消除不稳定性。与电磁仿真软件Sonnet联合仿真,结果表明,在频带内,放大器的输入反射系数S11<-18 dB,输出反射系数S22<-12 dB;在94 GHz处,噪声系数为8 dB,增益为14.75 dB,输出1 dB压缩点功率为-7.9 dBm;在1.8 V供电电压下,整个电路的功耗为14.42 mW。该放大器具有低噪声、低功耗的特点。     

Low-level avalanche multiplication in IGFET's

Results are presented for both theoretical and experimental analyses of low-level avalanche multiplication in an insulated gate field-effect transistor (IGFET). The theoretical model is derived from the ionization integral using a linear field approximation for the electric field at the drain. Experimental multiplication factors are determined by measuring channel and substrate currents. The model is shown to lead to reasonable agreement with data in the range of multiplication factors defined by (Mn- 1) less than unity.     

5.2 GHz SiGe HBT upconverter using active-inductor LC current mirror

A compact 5.2 GHz upconversion micromixer using the 0.35 /spl mu/m SiGe HBT technology is demonstrated. A bandpass and area-saving LC current mirror using the active inductor is incorporated to increase the conversion gain. The demonstrated upconverter has conversion gain of -3.5 dB, OP/sub 1dB/ of -10 dBm, and OIP/sub 3/ of 0 dBm.     

Temperature dependence of avalanche multiplication in InP-based HBTs with InGaAs/InP composite collector: device characterization and physics model

Recent efforts are being focused on improving the breakdown of InP-based heterojunction bipolar transistors (HBTs) towards high-power applications. A fundamental understanding of the temperature dependence of breakdown and its physics mechanism in these devices is important. In this work, a detailed characterization of temperature-dependent collector breakdown behavior in InP DHBTs (DHBTs) with an InGaAs/InP composite collector is carried out. A physics model for the prediction of temperature-dependent breakdown in lnP/InGaAs composite collector is developed. We found that, although the variation of impact ionization coefficient due to the change of temperature may affect the device breakdown, the temperature-dependence of breakdown in the lnGaAs/InP composite collector could be significantly affected by the carrier transport in the InGaAs region. As temperature is increased, the increase in the contribution of InGaAs layer to the junction breakdown due to the reduction of electron energy relaxation length could be the root cause of the reduction of junction breakdown voltage. Good agreement between the physics model and experimental data demonstrate the validities of the proposed physics model to predict the temperature dependent breakdown characteristics for InP DHBTs.     

Band-to-band tunneling in vertically scaled SiGe:C HBTs

A nonideal base current component with negative differential resistance is observed at low injection on Gummel characteristics of high-speed SiGe:C bipolar transistors. The temperature dependence of this effect and the influence of emitter-base engineering on its magnitude are described. The results point to band-to-band tunneling in the emitter-base junction as the physical origin of this phenomenon.     

On the operation configuration of SiGe HBTs based on power gain analysis

The power gain difference, under different device stability conditions, between common-emitter (CE) and common-base (CB) bipolar junction transistors (BJT) is analyzed comprehensively. The analysis reveals that the CB configuration offers higher maximum available power gain than the CE configuration in the device's high operation frequency range, while the inverse relation holds in the very low frequency range. In the intermediate frequency range, the base resistance value, mainly affected by the base doping concentration, determines which configuration offers higher maximum stable power gain (MSG). These analyses have explicit implications on the operation configurations of SiGe heterojunction bipolar transistors (HBTs). Employing a typical doping profile of Si bipolar junction transistors with a trapezoidal Ge profile in SiGe HBTs usually results in a larger base resistance than the emitter resistance. For these devices, the CE configuration exhibits higher MSG than the CB configuration. Employing a higher base doping concentration than the emitter with a box-type Ge profile considerably reduces the base resistance and thus favors the CB configuration for power amplification in this frequency range. The analysis are quantitatively verified with simulation and measurement results from SiGe HBTs of representative Ge and base doping profiles.