Stepping toward standard methods of small-signal parameter extraction for HBT's

An improved BET small-signal parameter extraction procedure is presented in which all the equivalent circuit elements are extracted analytically witho ut reference to numerical optimization. Approximations required for simplif ied formulae used in the extraction routine are revised, and it is shown th at the present method has a wide range of applicability, which makes it app ropriate for GaAs- and InP-based single and double HBT's. Additionally, a n ew method is developed to extract the total delay time of HBT's at low freq uencies, without the need to measure h(21) at very high frequencies and/or extrapolate it with -20 dB/dec roll-off. The existing methods of finding th e forward transit time are also modified to improve the accuracy of this pa rameter and its components. The present technique of parameter extraction a nd delay time analysis is applied to an InGaP/GaAs DEBT and it is shown tha t: 1) variations of all the extracted parameters are physically justifiable ; 2) the agreement between the measured and simulated S- and Z-parameters i n the entire range of frequency is excellent; and 3) an optimization step f ollowing the analytical extraction procedure is not necessary. Therefore, w e believe that the present technique can be used as a standard extraction r outine applicable to various types of HBT's.