UCSD HBT SmartSpice Model Released!

SmartSpice now supports a hetrojunction bipolar transistor (HBT) model developed by the UCSD High Speed Devices Group in collaboration with a number of industrial partners [1]. The model has been available for evaluation in the form of a dynamic library for the past year. The model equations are based on a derivative of the standard SPICE Gummel-Poon model, however this model is not backward compatible with the GP model.

The HBT model supports self-heating. The temperature of the device is a function of the power dissipated in the non-energy storage elements of the device and two model parameters (RTH and CTH). The collector current equation of the standard GP model is replaced by a more complex formulation to take into account the potential spike that can occur at the base-emitter or base-collector junction of HBTs. The HBT model supports splitting of the base and collector resistances into intrinsic and extrinsic components. Avalanche breakdown of the base-collector junction is modeled using a voltage dependent current source. Capacitances and storage times are calculated from the charge stored in the junctions as a function of collector current and junction voltages. The depletion capacitance takes into account the fact that the capacitance frequency limits at some minimum value, reached when lightly doped layers are depleted.

The HBT device is a 5 terminal device. The first four terminals are the standard collector, base, emitter and substrate of a bipolar transistor. The fifth node is an external temperature node and can be used to represent an external heat-sink or to model thermal interactions between devices. To indicate to SmartSpice that a HBT model is to be used, use "LEVEL = 20" in the .MODEL statement.

Figure 1. Ic versus Vc plot, illustrating the effect of self-heating.

 

References

[1] "HBT Model Equations", http://hbt.ucsd.edu