A Temperature Dependent Scalable Large Signal InP/InGaAs DHBT Model

Modern radio frequency and mixed signal circuit design has increasingly relied on compound semiconductor devices to push operating frequencies deep into millimeter-wave range. InP/InGaAs/InP heterojunction bipolar transistors are capable of achieving both a unity current gain frequency (fT) and maximum frequency of oscillation (fMAX) in excess of 300GHz as well as high linearity and good thermal performance, making them a prime technology for ultra-high speed and mixed signal circuit design [1,2]. Designing precision circuits with these devices has been problematic, however, due to the lack of accurate large signal DHBT device models. The industry standard VBIC model, for example, was developed for older silicon bipolar technology and does not completely model the physics of modern HBT devices. Effects stemming from the heterostructure nature of both junctions are poorly modeled in the VBIC model, which leads to poor large signal modeling of III-V devices. To design new higher speed circuits an accurate model is needed, one that is capable of modeling large signal nonlinear device characteristics. Several models that are specifically based on modern HBT devices (AgilentHBT, HiCUM and UIUC SDD2) have been developed in an attempt to give a more accurate large signal modeling and more reliable circuit designs. The UIUC SDD2 (Symbolically Defined Device) model has been shown to be especially good at modeling large signal characteristics for both individual devices and complex circuits [3]. The SDD’s strength is its ability to model carrier velocity modulation in the collector, current blocking of the base-collector junction, and self-induced thermal effects. The model however lacks emitter scalability and temperature dependence, limiting circuit designs to the use of only one size of device at one operating temperature. A temperature dependent, scalable large signal DHBT model that is based on the UIUC SDD model is being developed and is the focus of this work. This new SDD2 model is currently capable of providing accurate DC, RF, and large signal modeling over emitter sizes from 0.5 X 3.0 um2 to 0.5 X 5.2 um2. The model, when compared with the VBIC model extracted and issued by the device manufacture, is shown to be far superior in modeling all aspects (DC, RF, and nonlinear large signal) of the device.