Issues important for the manufacturing of GaAlAs/GaAs heterojunction bipolar transistors (HBTs) and their prospects for application in various areas are discussed. The microwave and digital performance status of HBTs is reviewed. Extrapolated values of maximum frequency of oscillation above 200 GHz and frequency divider operation at 26.9 GHz are reported. Key prospects for further device development are highlighted. >

GaAlAs/GaAs heterojunction bipolar transistors. Issues and prospects for application

A novel parameter extraction formalism for the evaluation of heterojunction bipolar transistor (HBT) device physics is presented. The technique uses analytically derived expressions for direct calculation of the HBT T-model equivalent circuit element values in terms of the measured S-parameters. All elements are directly calculated with the exception of the emitter leg of the T-model. This approach avoids errors due to uncertainty in fitting to large, overdetermined equivalent circuits, and does not require the use of test structures and extra measurement steps to evaluate parasitics. Detailed bias-dependent results for the directly calculated circuit elements are presented. An analysis of the short circuit current gain that separates the transit times and RC products and allows evaluation of their individual contribution to the measured f/sub T/ and significance in limiting the HBT's high-frequency performance is reported. >

Evaluation of the factors determining HBT high-frequency performance by direct analysis of S-parameter data

A physical, yet simple, small-signal equivalent circuit for the heterojunction bipolar transistor (HBT) is proposed. This circuit was established by analyzing in detail the physical operation of the HBT. The model verification was carried out by comparison of the measured and simulated S- and Z-parameters for both passive (reverse-biased) and active bias conditions. A feature of this model is that it uses a direct extraction method to determine the parasitic elements, in particular, the parasitic capacitances. The excellent agreement between the measured and simulated parameters was verified all over the frequency range from 0.25 to 75 GHz.

A physical, yet simple, small-signal equivalent circuit for the heterojunction bipolar transistor

An accurate and broadband method for the direct extraction of heterojunction bipolar transistor (HBT) small-signal model parameters is presented in this paper. This method differs from previous ones by extracting the equivalent-circuit parameters without using special test structures or global numerical optimization techniques. The main advantage of this method is that a unique and physically meaningful set of intrinsic parameters is extracted from the measured S-parameters for the whole frequency range of operation. The extraction procedure uses a set of closed-form expressions derived without any approximation. An equivalent circuit for the HBT under a forward-bias condition is proposed for extraction of access resistances and parasitic inductances. An experimental validation on a GaInP/GaAs HBT device with a 2/spl times/25 /spl mu/m emitter was carried out, and excellent results were obtained up to 30 GHz. The calculated data-fitting residual error for three different bias points over 1-30 GHz was less then 2%.

Direct parameter-extraction method for HBT small-signal model

An extraction technique for determining the small-signal equivalent circuit model of an InP/GaInAs heterojunction bipolar transistor is presented. The equivalent circuit includes the extrinsic base collector capacitance and extrinsic base resistance. It is clearly indicated which elements are uniquely determined, and which elements are estimated. >

Extraction of the InP/GaInAs heterojunction bipolar transistor small-signal equivalent circuit

The authors describe a novel, direct technique for determining the small-signal equivalent circuit of a heterojunction bipolar transistor (HBT). The parasitic elements are largely determined from measurements of test structures, reducing the number of elements determined from measurements of the transistor. The intrinsic circuit elements are evaluated from y-parameter data, which are DC-embedded from the known parasitics. The equivalent-circuit elements are uniquely determined at any frequency. The validity of this technique is confirmed by showing the frequency independence of the extracted circuit elements. The equivalent circuit models the HBT s-parameters over a wide range of collector currents. Throughout the entire 1-18-GHz frequency range, the computed s-parameters agree very well with the experimental data. >

Direct extraction of the AlGaAs/GaAs heterojunction bipolar transistor small-signal equivalent circuit

A technique for determining the small-signal equivalent-circuit model of an AIGaAs/GaAs heterojunction bipolar transistor (HBT) is presented. Most of the parasitic ele- ments are independently extracted from measurements of test structures. The intrinsic elements are calculated from y-parameter data, which are de-embedded from the previously determined parasitics. The agreement between the measured and model-produced data is excellent over the frequency range of 1 to 18 GHz. I. INTRODUCTION CCURATE, physically based equivalent circuits are A very useful for designing devices with reduced par- asitics and optimized performance. Although numerical optimization is often used to fit the model-generated s-parameters to the measured s-parameters, the resulting element values depend on the starting values and may be nonphysical. This uncertainty in the element values has been addressed by several authors. A new de-embedding method for determining the FET model was proposed by Dambrine et al. ( 11. Trew et al. (2) described a parameter extraction technique for an HBT that makes use of the emitter-to-collector time delay to constrain the element values used in optimization. We propose a new technique for determining the small-signal equivalent circuit of an HBT. With this technique, most of the parasitics are first obtained from measurements of test structures and those remaining are determined from measurements of the tran-

http://ieeexplore.ieee.org/iel1/16/2732/00083724.pdf

Direct Extraction of the AlGaAs/GaAs Heterojunction Bipolar Transis tor Small- S ig nal Equivalent Circuit

An analytical solution for the minority carrier concentration to the 2-D diffusion equation in the base of a mesa-structure bipolar transistor is derived. The solution is especially applicable for AlGaAs/GaAs heterojunction bipolar transistors for which the extrinsic base surface has a high surface recombination velocity if the surface is not passivated. The different components of the base current are determined from the derived 2-D minority carrier concentration in the base. The major components to the base current include: surface recombination at the extrinsic base surface, at the base ohmic contact and bulk recombination in the base. The relative importance of each component is discussed as a function of the extrinsic base length, emitter length and base doping. The effects of quasielectric field in the base and the passivation on the extrinsic base region are also evaluated. The results indicate that as base doping is increased, the current gain is limited by bulk recombination, independent of the details of the device geometry.

Theoretical comparison of base bulk recombination current and surface recombination current of a mesa AlGaAs/GaAs heterojunction bipolar transistor

Graded AlGaAs/GaAs heterojunction bipolar transistors with and without a base quasi-electric field are fabricated to investigate the various components of base current. The experimental results demonstrate that the base current for devices with extrinsic base surface passivation is dominated by base-emitter space-charge recombination current, rather than base bulk recombination current. Both a simple theoretical calculation and SEDAN (semiconductor device analysis) simulations are used to support this finding. SEDAN simulations also indicate strong effects of hole barrier lowering which reduces device current gain when the current gain approaches values of 1000 and when the maximum aluminum composition in the AlGaAs emitter is >

Current gain of graded AlGaAs/GaAs heterojunction bipolar transistors with and without a base quasi-electric field

Various expressions for the emitter-collector transit time of a heterojunction bipolar transistor (HBT) can be found in the literature. It is not obvious whether the product of the emitter contact resistance and the base-emitter capacitance should be included in the emitter-collector transit time expression. This paper theoretically demonstrates that the above product does not appear in the transit time expression. Additional physical insights observed from the derived transit time expression and comparison to a similar expression for homojunction bipolar transistors will be discussed.

D. Costa

Papers

Direct extraction of the AlGaAs/GaAs heterojunction bipolar transistor small-signal equivalent circuit

Direct Extraction of the AlGaAs/GaAs Heterojunction Bipolar Transis tor Small- S ig nal Equivalent Circuit

Theoretical comparison of base bulk recombination current and surface recombination current of a mesa AlGaAs/GaAs heterojunction bipolar transistor

Current gain of graded AlGaAs/GaAs heterojunction bipolar transistors with and without a base quasi-electric field

Derivation of the emitter-collector transit time of heterojunction bipolar transistors