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

A parameter-extraction approach for the heterojunction bipolar transistor (HBT), which combines the analytical approach and empirical optimization procedure, is developed. The extraction techniques for extrinsic base-collector capacitance and pad parasitics are also included in this approach. The cutoff operation of the HBT's is utilized to extract the values of the pad capacitances. An excellent fit between measured and simulated S-parameters in the frequency range of 50 MHz-36 GHz is obtained over a wide range of bias points.

A semianalytical parameter-extraction procedure for HBT equivalent circuit

The present paper describes a new approach to fabricating high performance HBT's with low base resistance. Their base contact resistance is reduced by using MOMBE selective growth in the extrinsic base region-a key process in the fabrication of high-f/sub max/ AlGaAs/InGaAs and AlGaAs/GaAs HBT's. A p/sup +//p regrown base structure, which consists of a 40-nm-thick graded InGaAs strained layer and a heavily C-doped regrown contact layer, is used for the AlGaAs/InGaAs HBT's to reduce both their base transit time and base resistance, while preventing aluminum oxide incorporation at the regrowth interface. An h/sub fe/ of 93, an f/sub T/ of 102 GHz, and an f/sub max/ of 224 GHz are achieved for a 1.6-/spl mu/m/spl times/4.6-/spl mu/m HBT, together with reduced base push-out effects and improved reliability. AlGaAs/GaAs HBT's with an 80-nm-thick uniform base layer that have high f/sub max/ values ranging from 140-216 GHz are also fabricated using the selective growth technique. These results confirm the high potential of the proposed HBT's, especially for microwave and millimeter-wave applications. >

High-f/sub max/ AlGaAs/InGaAs and AlGaAs/GaAs HBT's with p/sup +//p regrown base contacts

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. >

D.R. Pehlke

Papers

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