An epitaxial emitter-cap SiGe-base bipolar technology optimized forliquid-nitrogen temperature operation

We give the first demonstration that a properly designed silicon bipolar technology can achieve faster unloaded circuit speed at liquid-nitrogen temperature than at room temperature. Transistors were fabricated using a reduced-temperature process employing an in situ arsenic-doped polysilicon emitter contact, a lightly phosphorus-doped epitaxial emitter-cap layer, and a graded SiGe base. At 84 K, transistors have a current gain of 500, with a cutoff frequency of 61 GHz, and a maximum oscillation frequency of 50 GHz. ECL circuits switch at a record 21.9 ps at 84 K, 3.5-ps faster than at room temperature. Circuits which were optimized for low-power operation achieve a minimum power-delay product of 61 fJ (41.3 ps at 1.47 mW), nearly a factor of two smaller than the best achieved to date at 84 K. The unprecedented performance of these transistors suggests that SiGe-base bipolar technology is a promising candidate for cryogenic applications requiring the fastest possible devices together with the processing maturity and integration level achievable with silicon fabrication     

Linearity and power characteristics of SiGe HBTs at high temperatures for RF applications

In this paper, the power gain, power-added efficiency (PAE) and linearity of power SiGe heterojunction-bipolar transistors at various temperatures have been presented. The power characteristics were measured using a two-tone load-pull system. For transistors biased with fixed base voltage, the small-signal power gain and PAE of the devices increase with increasing temperature at low base voltages, while they decrease at high base voltages. Besides, the linearity is improved at high temperature for all voltage biases. However, for devices with fixed collector current, the small-signal power gain, PAE, and linearity are nearly unchanged with temperature. The temperature dependence of power and linearity characteristics can be understood by analyzing the cutoff frequency, the collector current, Kirk effect and nonlinearities of transconductance at different temperatures.     

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.     

Forward transit delay in In0.53Ga0.47Asheterojunction bipolar transistors with nonequilibrium electrontransport

The authors measured the microwave performance of high speed InP/In_0.53Ga_0.47As heterojunction bipolar transistors in the temperature range 55 K⩽T⩽340 K. The extrinsic unity current gain cutoff frequency is 130 GHz at 340 K, increasing to 300 GHz at 55 K. The intrinsic emitter-collector forward delay decreases with decreasing temperature from 0.5 ps at 340 K to a saturated value of 0.28 ps for ⩽150 K. Such behavior may be explained only by the presence of nonequilibrium electron transport in the base and collector of the device     

Base profile design for high-performance operation of bipolartransistors at liquid-nitrogen temperature

Measurements of thin epitaxial-base polysilicon-emitter n-p-n transistors with increasing base doping show the effects of bandgap narrowing, mobility changes, and carrier freezeout. At room temperature the collector current at low injection is proportional to the integrated base charge, independent of the impurity distribution. At temperatures below 150 K, however, minority injection is dominated by the peak base doping because of the greater effectiveness of bandgap narrowing. When the peak doping in the base approaches 10¹⁹ cm^-3, the bandgap difference between emitter and base is sufficiently small that the current gain no longer monotonically decreases with lower temperature but instead shows a maximum as low as 180 K. The device design window appears limited at the low-current end by increased base-emitter leakage due to tunneling and by resistance control at the high-current end. Using the measured DC characteristics, circuit delay calculations are made to estimate the performance of an emitter-coupled logic ring oscillator at room and liquid-nitrogen temperatures. It is shown that if the base doping can be raised to 10¹⁹ cm^-3 while keeping the base thickness constant, the minimum delay at liquid-nitrogen temperature can approach the delay of optimized devices at room temperature     

多晶硅发射极晶体管的低温频率特性研究

本文考虑低温下半导体中载流子冻析效应和浅能级杂质的陷阱效应等因素,分析了多晶硅发射极晶体管的低温频率特性。研究表明,受载流子冻析效应的影响,基区电阻在低温下随温度下降接近于指数上升,使晶体管的频率性能变环;而由于浅能级杂质的陷阱效应,低温下基区和发射区渡越时间变长,截止频率下降。这些因素在低温器件设计中应予重视。     

Simulation and design of InAlAs/InGaAs pnp heterojunction bipolartransistors

The performance capabilities of InP-based pnp heterojunction bipolar transistors (HBT's) have been investigated using a drift-diffusion transport model based on a commercial numerical simulator. The low hole mobility in the base is found to limit the current gain and the base transit time, which limits the device's cutoff frequency. The high electron majority carrier mobility in the n⁺ InGaAs base allows a reduction in the base doping and width while maintaining an adequately low base resistance. As a result, high current gain (>300) and power gain (>40 dB) are found to be possible at microwave frequencies. A cutoff frequency as high as 23 GHz and a maximum frequency of oscillation as high as 34 GHz are found to be possible without base grading. Comparison is made with the available, reported experimental results and good agreement is found. The analysis indicates that high-performance pnp InP-based HBT's are feasible, but that optimization of the transistor's multilayer structure is different than for the npn device     

A new model for bipolar transistors at high current

A model for current gain and cutoff frequency falloff at high currents for bipolar transistors is proposed. The model is based on considering that the vertical and lateral base widening occur simultaneously for a typical bipolar transistor. The results of this model successfully fit Pisces-2B simulation results     

Implementation of reduced turn-on voltage InGaP HBTs using graded GaInAsN base regions

InGaP/GaInAsN double heterojunction bipolar transistors (HBTs) with compositionally graded bases are presented which exhibit superior dc and radio frequency performance. Reducing the average base layer energy gap and optimizing the emitter-base (e-b) and base-collector (b-c) heterojunctions leads to a 100-mV reduction in the turn-on voltage compared to a baseline InGaP/GaAs process. Simultaneously grading the base layer energy band-gap results in over a 66% improvement in the dc current gain and up to a 35% increase in the unity gain cutoff frequency. DC current gains as high as 250 and cutoff frequencies of 70 GHz are demonstrated. In addition, the InGaP/GaInAsN DHBT structure significantly reduces the common emitter offset and knee voltages, as well as improves the dc current gain temperature stability relative to standard InGaP/GaAs HBTs.     

MOSFET behavior and circuit considerations for analog applications at 77 K

We present an investigation into the behavior of silicon MOS transistors and analog circuits operated at liquid-nitrogen temperature (LNT). Simple scaling rules are used to predict the LNT performance of CMOS operational amplifier circuits designed for room-temperature operation. Measurements show that unity gain frequency and slew rate can be improved by the same amount as the mobility increase with no loss of stability if bias currents are properly controlled. We also show that room-temperature CMOS amplifier circuits can be redesigned for 77-K operation by reducing channel widths and compensation capacitor area, giving performance equal in most respects to that of unscaled circuits at room temperature. However, 1/f noise is degraded by such redesign. Similar considerations of NMOS amplifiers show that such circuits do not benefit greatly from operation at liquid-nitrogen temperature. To aid in studying the temperature dependence of the sheet resistance of diffused resistors, a computer program was developed based on available models for bulk mobility and carrier freeze-out. Accurate predictions require a temperature dependence for lattice scattering that differs from previously reported values.     

A physics-based, analytical heterojunction bipolar transistormodel, including thermal and high-current effects

A detailed, analytical model for predicting the DC and high-frequency performance of AlGaAs/GaAs graded heterojunction bipolar transistors (HBTs) is presented. The model is developed based on the relevant device physics, such as current-induced base pushout and thermal effects. The current gain, cutoff frequency, and maximum frequency versus the collector current density, which is a function of the applied voltage as well as the corresponding temperature in the HBT, are calculated. The results suggest that the conventional HBT model, which assumes the HBT temperature is the same as that of the ambient, can overestimate the three figures of merit considerably when the collector current density is high. Furthermore, it is shown that the present model correctly explains such experimentally observed HBT high-current behavior as the rapid falloff of the current gain and cutoff frequency. The model predictions compare favorably with the results obtained from a model which solves numerically the Poisson and continuity equations coupled with the lattice heat equation     

Optimization of silicon bipolar transistors for high current gainat low temperatures

Bipolar transistors designed specifically for operation at liquid-nitrogen (LN₂) temperature are discussed. It is found that for high-gain LN₂ bipolar transistors, the emitter concentration should be around 5×10¹⁸ cm^-3. Compensating impurities in the base should be kept to minimum. Test bipolar transistors with polysilicon emitter contacts were fabricated using these criteria. The devices show very little current degradation between room temperature and 77 k. Polysilicon emitter contacts are also shown to be somewhat more effective at lower temperatures     

低温多晶硅发射极晶体管电流增益和截止频率的解析模型

本文综合考虑了多晶硅发射极的载流子输运障碍,界面氧化物遂穿、晶粒间界杂质分凝和界面能带弯曲等因素,以及禁带变窄效应、低温下载流子冻析效应和浅能能补偿杂质隐阱效应,建立了低温多晶硅发射极晶体管电流增益和截止频率的解析模型,对电流增益和截止频率的温度关系进行了理论分析并与３００Ｋ和７７Ｋ下的实测结果进行了比较。     

Improving the characteristics of InAlAs/InGaAs heterojunction bipolar transistors by employing thin base and collector layers

InAlAs/InGaAs heterojunction bipolar transistors with thin base and collector layers are fabricated. The maximum value of current gain cutoff frequency is as high as 96 GHz. It is shown that thinning of the base and collector is very effective not only for reducing the base and collector transit times but also for suppressing the space charge effect in the collector.<>     

Hole-spreading effect on upward current gain in n-p-n transistors

The upward current gain and stored charge for future small-sized n-p-n transistors have been studied. Included is the effect of hole spreading from a narrow base region to a wide emitter region, whether buried layer or substrate. When base dimensions are comparable with or shorter than the hole diffusion length in the emitter, the hole current is concentrated near the fringe of the base so that the base current tends to be proportional to the base length instead of the base area. The same tendency appears regarding the stored charge in the emitter. Hence, the scaling down of lateral dimensions gives rise to a decline in the upward current gain and cutoff frequency. The calculations introduced here are in quite fair agreement with the observed base currents in sidewall base contact structure (SICOS) n-p-n transistors, where dimensions for the emitter-base junction are almost the same as for the collector-base junction.     

Submicron InP-InGaAs single heterojunction bipolar transistors with f/sub T/ of 377 GHz

Submicron InP-InGaAs-based single heterojunction bipolar transistors (SHBTs) are fabricated to achieve record-breaking speed performance using an aggressively scaled epitaxial structure coupled with a submicron emitter process. SHBTs with dimensions of 0.35 /spl times/16 /spl mu/m have demonstrated a maximum current gain cutoff frequency f/sub T/ of 377 GHz with a simultaneous maximum power gain cutoff frequency f/sub MAX/ of 230 GHz at the current density Jc of 650 kA/cm/sup 2/. Typical BV/sub CEO/ values exceed 3.7 V.     

High-speed, high-current-gain p-n-p InP/InGaAs heterojunctionbipolar transistors

p-n-p InP/InGaAs heterojunction bipolar transistors (HBTs) are reported for the first time. The transistors, grown by metal organic molecular beam epitaxy (MOMBE), exhibited maximum DC current gain values up to 420 for a base doping level of 4×10¹⁸ cm^-3 . Small-signal measurements on self-aligned transistors with 3-μm×8-μm emitter area indicated the unity gain cutoff frequency value of 10.5 GHz and the inferred maximum frequency of oscillation of 25 GHz. The results clearly demonstrate the feasibility of complementary integrated circuits in the InP material system     

High-gain, high-speed InP/InGaAs double-heterojunction bipolartransistors with a step-graded base-collector heterojunction

We show that by using InP for the emitter and collector layers, and a thin high-doped base layer, it is possible to achieve both a high DC current gain and a high maximum frequency of oscillation. We have fabricated InP/InGaAs double heterojunction bipolar transistors (DHBT's) with cutoff frequencies f_T and f_max of 92 and 95 GHz, respectively, with a DC current gain of over 100. The maximum cutoff frequencies were 107 and 104 GHz     

Co-integration of resonant tunneling and double heterojunctionbipolar transistors on InP

The authors report the first co-integration of resonant tunneling and heterojunction bipolar transistors. Both transistors are produced from a single epitaxial growth by metalorganic molecular beam epitaxy, on InP substrates. The fabrication process yields 9-μm²-emitter resonant tunneling bipolar transistors (RTBTs) operating at room temperature with peak-to-valley current ratios (PVRs) in the common-emitter transistor configuration, exceeding 70, at a resonant peak current density of 10 kA/cm², and a differential current gain at resonance of 19. The breakdown voltage of the In_0.53Ga_0.47As-InP base/collector junction, V_CBO, is 4.2 V, which is sufficient for logic function demonstrations. Co-integrated 9-μm²-emitter double heterojunction bipolar transistors (DHBTs) with low collector/emitter offset voltage, 200 mV, and DC current gain as high as 32 are also obtained. On-wafer S-parameter measurements of the current gain cutoff frequency (f_T) and the maximum frequency of oscillation (f_max) yielded f _T and f_max values of 11 and 21 GHz for the RTBT and 59 and 43 GHz for the HBT, respectively     

RF power characteristics of SiGe HBTs at cryogenic temperatures

This paper investigates the temperature dependence (from 77 to 300 K) of dc, ac, and power characteristics for n-p-n SiGe heterojunction bipolar transistors (HBTs) with and without selectively implanted collector (SIC). In SiGe HBTs without SIC, the valance band discontinuity at the base-collector heterojunction induces a parasitic conduction band barrier while biasing at saturation region and high current operation at cryogenic temperatures. This parasitic conduction band barrier significantly reduces the current gain and cutoff frequency. For transistors biased with fixed collector current, the measured output power, power-added efficiency, and linearity at 2.4 GHz decrease significantly with decreasing operation temperatures. The temperature dependence of output power characteristic is analyzed by Kirk effect, current gain, and cutoff frequency at different temperatures. The parasitic conduction band barrier in SiGe HBTs with SIC is negligible, and thus the device achieves better power performance at cryogenic temperatures compared with that in SiGe HBT without SIC.