Analysis of device parameters for pnp-type AlGaAs/GaAs HBTsincluding high-injection using new direct parameter extraction

Device parameters of the small-signal T equivalent circuit for pnp-type AlGaAs/GaAs heterojunction bipolar transistors (HBTs) are obtained using a new direct parameter extraction technique. These parameters are analyzed not only under the low-current conditions but also under high-current conditions so as to understand the RF-performance fall-off after base pushout occurs. In this analysis, the intrinsic and extrinsic small-signal parameters which affect RF performance are directly determined using several steps without numerical optimization in order to properly analyze device parameters. The T equivalent circuit model determined by the method shows excellent agreement with the mean errors of 3.5-6.9% under both low-and high-current conditions. The analysis showed that the intrinsic transit time, which is the sum of the base transit time (τ_b) and the collector depletion layer transit time (τ_c), small-signal emitter resistance (r_e), small-signal base resistance (r_b) and collector-base capacitance (C_BC) all increase under high-current conditions. In addition, we found that the intrinsic transit time is the dominant parameter for the fall-off of the cut-off frequency (f_t) under high-current conditions, and there is little effect of r_b and C_BC in the fall-off of the maximum oscillation frequency (f_max) under high-current conditions. Judging from these results, device parameters are successfully obtained under a wide current range by a new parameter extraction technique and circuit modeling for HBTs under a wide current range can be achieved using the small-signal T-equivalent circuit     

Transistor equivalent circuits

This paper surveys the history of the electric-circuit representation of the transistor over the past fifty years. During the first two decades after the transistor was announced in 1948, primary emphasis was on small-signal equivalent circuits, which could be used for linear-circuit analysis and design. In addition, parameters of many of these equivalent circuits for the bipolar junction transistor, which are described, were related to the physical construction of the device. Approximately two-thirds of the paper is devoted to this period, when the writer personally contributed to this effort. By the beginning of the third decade, transistor circuits had became more complex, and circuit analysis was carried out with the help of digital computers. Interest then shifted away from small-signal equivalent circuits to “models” for computer-aided circuit design (CACD). This transition, including the models used in the widely used CACD program SPICE, is described. MOS transistors are treated only briefly; by the time MOS transistors became commercially viable devices, emphasis then also had shifted to “models” for CACD. In conclusion, the writer notes that there is still hope for us aficionados of small-signal equivalent circuits; new types of transistors are still being characterized in this manner     

A new charge-control model for single- and double-heterojunctionbipolar transistors

A new charge-control relation is derived for heterojunction bipolar transistors. The relation is valid for arbitrary doping density profiles and for all levels of injection in the base. It is applicable to both single- and double-heterojunction transistors. The model is an improvement over another recently proposed charge-control model that was valid only for constant doping density and low injection in the base. Large- and small-signal equivalent circuit models are also presented for heterojunction bipolar transistors. Comparisons with numerical and experimental data show excellent agreement     

SiGe HBT非准静态小信号等效电路的参数提取

提出了一种硅锗异质结双极型晶体管（SiGe HBT）非准静态效应的小信号等效电路模型的参数提取方法。整个参数提取过程建立在由非准态效应的小信号等效电路推导出的一系列泰勒级数解析公式并结合参数直接法,该方法依赖于测量的S参数,不使用任何的数值优化法,参数提取结果使用CAD仿真验证。结果表明该参数提取方法简单易行,较为精确,该方法能够用到不同工艺SiGe HBT参数提取。     

Embedding impedance approximations in the analysis of SIS mixers

The adequacy of three approximations to J.R. Tucker's (1979) quantum theory of mixers is examined. They are: (i) the usual three-frequency approximation, which assumes a sinusoidal local oscillator (LO) voltage at the junction and a short-circuit at all frequencies above the upper sideband; (ii) a five-frequency approximation, which allows two LO voltage harmonics and five small-signal sidebands; and (iii) a quasi five-frequency approximation in which five small-signal sidebands are allowed, but the LO voltage is assumed sinusoidal. These are compared with a full harmonic-Newton solution of Tucker's equations, including eight LO harmonics and their corresponding sidebands, for realistic SIS (superconductor-insulator-superconductor) mixer circuits. It is shown that the accuracy of the three approximations depends strongly on the value of ωR_NC for the SIS junctions used. For ωR_NC values in the range 0.5-10, the range of most practical interest, the quasi five-frequency approximation is a considerable improvement over the three-frequency approximation, giving results very close to those of the eight-harmonic solution, and should be suitable for much design work     

Si/Si1-xGex heterojunction bipolartransistors with high breakdown voltage

Heterojunction bipolar transistors are desirable for microwave applications because a low base resistance can be achieved yielding high maximum frequency of oscillation. Here we report Si/Si_1-xGe _x heterojunction bipolar transistors with high breakdown voltages and excellent small-signal microwave characteristics. The transistors structures were grown by molecular beam epitaxy and fabricated by a double-mesa process. Measured f_T and f_max were 10 and 22 GHz, respectively, for transistors with BV_CBO of 40 V     

Direct measurement of base drift field in bipolar transistors

The authors have developed a method to measure an effective base drift field and the base transit-time reduction factor of bipolar transistors, by measuring the excess phase of the base transport factor. This technique relies on measuring small-signal characteristics of the transistor at a low frequency and following the phase of the transconductance at the frequency approaching and exceeding the unit current gain frequency (f_T). With this technique, the authors verify that the effective drift inside the base of Si bipolar transistors decreases with increased base implantation energy and thermal treatment. Such directly measured drift-dependent base transport provides additional insight for optimizing processing used in bipolar technology development     

Design tradeoffs for improved V/sub CE(sat/) versus ICof bipolar transistors under forced gain conditions

Based on the quasi-saturation analysis of bipolar transistors and using numerical simulation, it is shown in this paper that the quasi-saturation performance of transistors under forced gain conditions can be improved by increasing the base-Gummel number if the emitter diffusion is also simultaneously altered to keep the active region current gain h_FEO constant. It is further shown that for a given h_FEO, if the ratio of h_FEO to the forced current gain β_f is below 10, the quasi-saturation performance of the transistors will be poor compared to those with h_FEO/β_f⩾10. Design curves obtained using numerical simulation are also presented to choose the quasi-saturation current limit of the transistors as a function of breakdown voltage and for different reach-through collector structures     

A New Extraction Technique for the Complete Small-Signal Equivalent-Circuit Model of InGaP/GaAs HBT Including Base Contact Impedance and AC Current Crowding Effect

In this paper, both ac current crowding and base contact impedance are considered and included in the T-type small-signal equivalent circuit of InGaP/GaAs heterojunction bipolar transistors. The ac current crowding effect and base contact impedance are modeled as a parallel$RC$circuit, respectively. Devices parameters of the equivalent circuit are obtained by a new parameters extraction technique. The technique is to directly analyze the two-port parameters of multibias conditions (cutoff-bias, open-collector, and active-bias modes). The parallel capacitances ($C_B$and$C_ bi$), base resistances ($R_B$and$R_ bi$), and base inductance$(L_B)$are especially determined under the active-bias mode without numerical optimization. In addition, the small-signal equivalent circuits of cutoff-bias and open-collector modes are directly derived from the active-bias mode circuit for consistency. By considering base contact impedance and intrinsic base impedance effects in the presented small-signal equivalent circuit, the calculated$S$-parameters agree well with the measured$S$-parameters. The observed difference in the slope for the unilateral power gain$(U)$versus frequency at high frequency is mainly attributed to the ac emitter current crowding effect and well modeled in this study.     

On the accuracy of direct extraction of the heterojunction-bipolar-transistor equivalent-circuit model parameters C/sub /spl pi//, C/sub BC/, and R/sub E/

Several basic small-signal equivalent-circuit models for bipolar transistors lead to simple analytical expressions for the model parameters in terms of measured values. This paper investigates the accuracy of these expressions for real transistors by applying the direct extraction equations to more complicated small-signal models. The extraction of the base/collector capacitance, base/emitter capacitance, and emitter resistance are considered. Analytically derived trends are illustrated using measurements on small-area high-speed InP/GaAsSb/InP double heterojunction bipolar transistors.     

Numerical analysis and interpretation of the small-signalminority-carrier transport in bipolar devices

A simple and efficient one-dimensional numerical technique is presented that determines the small-signal minority-carrier transport in the quasineutral regions of bipolar devices, such as diodes and transistors, under sinusoidal excitation. The technique is applied to study small-signal properties of p-n junction diodes and bipolar transistors. Examples treated include the frequency dependence of transistor current gain, the diffusion capacitance of a quasineutral base or emitter, and base-layer carrier propagation delay     

Temperature dependence of InGaP/GaAs heterojunction bipolartransistor DC and small-signal behavior

This work describes the temperature dependence of the DC and small-signal performance of InGaP/GaAs heterojunction bipolar transistors (HBT's) with different collector thicknesses. Detailed analyses of the small-signal performance and the temperature dependence of both DC and high-frequency parameters are presented. An HBT delay-time analysis is also presented and justified empirically. In addition, the factors causing the decrease in f_T with temperature are described, and the variations in collector resistance and collector drift velocity with temperature are determined     

Analytical current-voltage relations for compact SiGe HBT models.I. The “idealized” HBT

Based on the generalized integral charge control relation (GICCR), analytical current-voltage relations for “true” SiGe heterojunction bipolar transistors (HBTs) are derived, which are well suited for compact physically based transistor models. For this, the weighted minority charge in the collector, which proved to be of dominating influence at high current densities, is calculated from simple physical expressions. They contain the operating point as well as physical and technological parameters. The model equations, which serve as a basis for a new physically based compact SiGe HBT model called SIGEM, are verified up to high current densities by numerical device simulations. It is shown that not only the static behavior but also the small-signal parameters y₂₁ and y₂₂, which are more sensitive to potential model errors, are well described even far within the high-current region. In this first part of the paper, the work is restricted to HBTs with idealized and simplified doping profile. In the second part [2] it is shown how these equations can also he applied to HBTs with modified, more practical doping profiles and how the model parameters can be extracted     

RF figures-of-merit for process optimization

Today, transistor y-parameters are routinely being measured for the determination of the current-gain cut-off frequency f/sub T/ and the maximum oscillation frequency f/sub max/. In this paper, it is shown that a much wider use of y-parameter measurements can be made for the RF characterization of transistors. A method is presented to determine the small-signal behavior of actual RF circuit-blocks from the measurements of the y-parameters of the individual circuit components. This is applied to define additional RF figures-of-merit for basic building blocks of analogue and digital RF circuits. No equivalent transistor circuit or compact-model parameters are needed, which is important for giving quick feedback to process developers. This approach is illustrated on three basic RF circuit blocks using bipolar transistors.     

The use of base ballasting to prevent the collapse of current gainin AlGaAs/GaAs heterojunction bipolar transistors

We propose the use of base-ballasting resistance to guarantee absolute thermal stability in AlGaAs/GaAs heterojunction bipolar transistors (HBTs). Base-ballasted HBTs are fabricated and the measured I-V, regression and S-factor characteristics are discussed. We present a numerical model which elucidates the reasons why the base-ballasting scheme is helpful to HBTs but is damaging to silicon bipolar transistors. We compare measured small-signal and large-signal performances of unballasted, emitter-ballasted, and base-ballasted HBTs     

SiGe HBT小信号等效电路的参数直接提取

提出了一种求解硅锗异质结双极型晶体管(SiGe HBT)小信号等效电路模型的参数直接提取方法.整个提取过程使用由小信号等效电路推导出的一系列解析表达式,不使用任何数值优化方法.参数提取结果使用ADS软件仿真验证.结果表明,该方法简单易行,较为精确.     

Maximum operating frequency in Si bipolar master-slave toggleflip-flop circuit

This paper presents a propagation-delay equation which is expressed as the influence of the individual device and circuit parameters on the maximum operating frequency of Si bipolar master-slave toggle flip-flop (MS-TFF) circuit with double feedback emitter followers. This equation shows that optimizing the size of individual transistors can enhance the operating speed. Test results show a 10% increase in operating frequency by adopting this design technique. It is also shown that the time constants R_BC_jC, R_B C_D, T_F, R_LCj_C, and R _CCj_C of the upper-level current switch and T_F of the second feedback emitter follower greatly affect the operating speed of circuits using recently developed Si bipolar transistors. The results predicted by the equation are in good agreement with both the experimental ones and SPICE simulations     

Silicon npn bipolar transistors with indium-implanted base regions

In this paper, silicon npn bipolar transistors with indium-implanted base regions are discussed. Polysilicon emitter bipolar transistors are fabricated using a standard 0.5-μm BIC-MOS process flow where the base BF₂ implant is replaced by an indium implant. In indium-implanted transistors, the integrated hole concentration (G_b) in the quasi-neutral base is reduced due to incomplete ionization of indium acceptor states. The novel utilization of this impurity freeze-out effect results in much increased collector currents and common-emitter transistor gains (h_fe) compared to boron-implanted transistors. Also, since indium acceptor states in depletion regions become fully ionized, the spreading of the reverse-biased collector-base junction depletion region into the transistor base (base-width modulation) is minimized. Hence, for indium base bipolar transistor an improved h_fe-V_A product is anticipated. Our first attempt at fabricating bipolar transistors with indium-implanted base regions resulted in devices with greatly increased collector current, impressive gains of h_fe≈1600, excellent collector current saturation characteristics, an Early Voltage of V_A≈10 V, h_fe-V_A product of 16000 (implying an extended device design space), base-emitter breakdown voltages of BV_EBO≈9.6 V, and a cut-off frequency of f_t=17.8 GHz     

Analytical expressions for intermodulation distortion of a MESFET small-signal amplifier using the nonlinear Volterra series

Using the nonlinear Volterra series representation, analytical expressions for the third-order intermodulation distortion power and intercept point for a MESFET small-signal amplifier are derived when its equivalent circuit is bilateral and includes the gate-to-drain capacitance (C_gd) explicitly as a nonlinear element. Previously developed analytical expressions treated C_gd as a linear element or incorporated it as a part of gate-to-source and drain-to-source capacitances (C_gs and C_ds). These new analytical expressions are then compared with experimental data and good agreement is obtained. The analytical expressions are also used to study the variation of intermodulation distortion with input power and frequency, and the effect of the individual nonlinear elements in the MESFET’s equivalent circuit.     

Shifted-frequency internal equivalence

The shifted frequency internal equivalence (SFIE) theorem involving inhomogeneous regions is introduced and proven. For a lossless inhomogeneous region using a vector Green's theorem and potential formulation, it is shown that the frequency-domain electromagnetic field at frequency ω inside the region can be obtained using a set of equivalent volume and surface currents radiating in free space and at the different frequency ω₀. The equivalent currents thus obtained are functions of the two frequencies, electric- and magnetic-volume-type sources of the original problem, material parameters, and the original field phasors at ω, and they only exist inside the region and on its boundary. A direct application of this equivalence is that it can be used to construct an internal equivalence at a shifted frequency for electromagnetic scattering problems if data are needed in a band of frequency. ω₀ can be kept constant while the incident field frequency changes and, as a result, full computation of fields at each different frequency for volume-type equivalent sources can be avoided