Parameter Extraction Procedure for an Electrothermal

Model Timo Veijola, Mikael Andersson*, and Antti Kallio Helsinki University of Technology, Faculty of Electrical Engineering, Circuit Theory Laboratory, Otakaari 5A, FIN-02150 Espoo, Finland. phone:+358-0-4512293, fax:+358-0-460224, e-mail:[email protected] *Nokia Research Center. P.O. Box 45, FIN-00211 Helsinki, Finland. Abstract| A simple method for transistor DC parameter extraction is presented, where the self-heating of the transistor is taken into account. The thermal behaviour of the transistor is modelled using a single thermal resistance, whose value is extracted simultaneously with the electrical parameters. When pulsed measurements are performed the usage of the thermal resistance, as an e ective thermal resistance, is still justi ed. The method is applied to MESFET parameter extraction. Introduction Pulsed operation of a semiconductor parameter analyzer makes it possible to measure the DC characteristics of a transistor in the high current region. Unfortunately, if the used pulse width is short enough to completely prevent the transistor from heating, there will be additional uncertainties in the measurement results. In practice, pulse widths must be su ciently large, and hence self-heating of the transistor is present in the measurement results. Heating of the transistor junction is a dynamic process that depends on the thermal spreading impedance seen from the junction and on the thermal feedback. A transient simulation that imitates the measurement instrument operation with dynamic electrothermal models [1, 3] can be applied in parameter extraction. However, this requires long transient simulations in every optimization cycle. A proper model for the thermal spreading impedance is needed too. In this paper, a DC parameter extracting procedure for an electrothermal transistor model is discussed where both electrical and thermal parameters are extracted simultaneously. In this procedure, pulsed measurements are imitated by a circuit simulator program. The method presented will increase the accuracy of the extracted model parameters. E ective thermal resistance During the measurement pulse the transistor junction temperature rises towards the value de ned by the thermal resistance of the structure, but due to thermal time constants the temperature will not reach this static value (see Fig. 1). If the amount of thermal