Silicon-germanium heterojunction bipolar transistors (SiGe HBTs) show enormous potential in RF and sub-mm-wave applications due to its excellent capability to deliver high fT and fmax (up to several hundreds of GHz). In the high-frequency region, both vertical and lateral non-quasi-static (NQS) effects are visible. The lateral NQS (LNQS) effect or AC current crowding is caused due to finite delay in the lateral hole transport within the internal base region, while the vertical NQS effect originates from the delayed response of excess minority charge within the device. The LNQS effect is modeled using a single-pole RC network in the state-of-the-art HICUM model. Such a model is not useful in large-signal transient operation.

In this seminar we present a modified physics-based two-section model that accurately captures the lateral non-quasi-static effect in SiGe HBTs. A methodology is proposed to include the DC emitter current crowding effect in the existing two-section model framework. The proposed two-section model is implemented in Verilog-A. Results of the large signal transient and small-signal AC simulations are compared with the numerical device simulation data. The proposed model is observed to perform better than all the existing models. We also present a two-RC model to predict the LNQS effect. This model uses a new methodology to implement the internal base impedance of the device using two-RC network. The proposed model is implemented in Verilog A. The small-signal AC and the large-signal transient simulations show that the two-RC model yields higher accuracy compared with those of the state-of-the-art model and the π-model. As a follow-up, a 3-RC model is also derived and the results appear to validate the generic nature of the modeling technique.