A simple method for the thermal resistance measurement of AlGaAs/GaAs heterojunction bipolar transistors

Abstract

A novel electrical method to accurately measure the thermal resistance of heterojunction bipolar transistors (HBT's) is presented. The keg advantage of the method is its simplicity, because it requires only the measurement of the device DC output characteristics at two different temperatures. In this brief, the measurement technique is illustrated, applied to multifinger HBT's and compared with other methods

Electrical measurement of the junction temperature and thermal resistance of HBTs

“…The transistor is rated to give about 1.25 W of RF power in band with a collector efficiency around 60%. The method was applied in two different bias regions and was confronted with the technique proposed by Marsh [1] and Bovolon [2]. Measurements were also made to confirm the validity of the assumption that equi-points correspond to equithermal points.…”

“…Using the classical definition for th, we can write the following equations for point A in (2) (3) 1 The variation of with V (basewidth modulation) is usually negligible when base doping is high, as is usually the case for HBT devices. 2 For the same average dissipated power.…”

“…2 This relationship can be linear as in [2], or almost linear (within 10% of a straight line) as in [3]. However, and , can be assumed to be univocal functions of only.…”

“…Moreover, the behavior of the thermal resistance with temperature and power dissipation is important to characterize the electro-thermal models used in PA design. Most of the proposed techniques to derive the junction temperature and thermal resistance of HBTs from electrical measurements are based on pulsed or dc measurements and exploit the thermal dependence of the current gain , the base-emitter voltage , or the base current [1], [2] (and references therein). Direct techniques [1] derive the junction temperature for a certain bias condition, whereas indirect techniques make use of a previously calculated to obtain the junction temperature.…”

“…The distinction is not important if the behavior of with junction temperature and dissipated power is known, but can become relevant when estimating the junction temperature using an obtained at a different junction temperature or dissipation condition. Moreover, indirect techniques such as [2] rely on a linearization of the or characteristics around a certain operating condition. As the reported variations of with case temperature can deviate from a straight line up to 10% [3], small increments of the case temperature might be necessary during the measurement, thus involving greater errors.…”