{"id":5202,"date":"2012-07-18T22:29:05","date_gmt":"2012-07-18T22:29:05","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2012\/?p=5202"},"modified":"2012-07-18T22:29:05","modified_gmt":"2012-07-18T22:29:05","slug":"a-virtual-source-based-transport-model-for-gan-based-hemts-including-non-linear-access-region-behavior-and-self-heating","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2012\/a-virtual-source-based-transport-model-for-gan-based-hemts-including-non-linear-access-region-behavior-and-self-heating\/","title":{"rendered":"A Virtual-source-based Transport Model for GaN based HEMTs including Non-linear Access Region Behavior and Self-heating"},"content":{"rendered":"

Compact models for GaN based HEMTs describing the voltage-dependent terminal currents are essential for circuit simulations.\u00a0 In this work, we extend the virtual-source (VS)-based transport model [1<\/a>] <\/sup> originally developed for Si MOSFETs to GaN based HEMTs along with models for non-linear access regions and device self-heating. The model is suitable for quasi-ballistic or fully ballistic short channel devices typically used for RF and mixed-signal applications. The model has been implemented in Verilog-A language.<\/p>\n

Access region behavior is analyzed by measuring I-Vs of TLM structures that represent those transistor access regions. Velocity versus field plot obtained from the I-Vs is shown in Figure 1. The velocity undergoes quasi-saturation at a field of about 5 KV\/cm, which is lower than in [2<\/a>] <\/sup>. The quasi-saturation is attributed to velocity saturation and self-heating. Access regions are modeled as non-linear resistors to capture this effect. The intrinsic transistor region is modeled using the VS model including self-heating in the channel. The developed model is compared against DC measurements of a short channel RF HEMT. The device has a gate length of 105 nm, access region lengths of 0.5 \u00b5m, and device structure as reported in [3<\/a>] <\/sup>. DC characteristics obtained from the model and measurements are shown in Figure 2. The model gives a good match to the measurements, as Figure 2 shows. Results show that the access regions rather than the intrinsic channel region limit the maximum current in output characteristics. Access regions also cause reduction of transconductance (gm<\/sub>) with gate voltage after reaching a peak value. The compact model captures these effects well.\u00a0 The gm<\/sub> estimated from the model along with gate capacitances would enable estimation of fT<\/sub> and make projections for future scaling of GaN based HEMTs.<\/p>\n\n\t\t