All entries for ujwal radhakrishna

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MIT Virtual Source GaNFET – High Voltage (MVSG-HV) Model: A Physics-based Compact Model for HV-GaN HEMTs

• Authors: U. Radhakrishna, T. Imada, T. Palacios, D. Antoniadis
• Sponsorship: Singapore-MIT Alliance for Research and Technology

Compact models of GaN-based high-electron-mobility transistors (HEMTs) are essential for the design of power conversion circuits such as power integrated circuits (ICs), DC-DC convertors, etc.^[1]. In this work, we propose a new physics-based transport and charge model for long-channel GaN HEMTs. The model is based on the concept of virtual source (VS) carrier transport^[2] and is extended to the drift diffusion regime. The model is fully scalable from non-velocity saturation to the velocity saturation regime. In addition, non-linear access regions are modeled as implicit-gated transistors. Self-heating effects and self-consistent charge models are included. The model is implemented in Verilog-A and is validated against state-of-the-art industry devices.

The MVSG-HV intrinsic transistor model extends a previous short-channel GaN field-effect transistor model^[3] that was based on quasi-ballistic transport to the drift-diffusion transport.  Drain-end charge modulation by pinch-off and velocity saturation is achieved smoothly as function of gate length; the resulting current has self-consistent linear- to saturation-region transition. Terminal charges are self-consistently solved by employing current continuity and Ward-Dutton charge partitioning. The access regions are modeled as implicit-gated transistors similar to the intrinsic device. Key differences are that these regions have no physical gate and an implicit-gate-overdrive is linked to the sheet resistance. Figure 1 shows the sub-circuit model along with the structure schematic. DC characteristics obtained from the model and measurements are shown in Figure 2. The model captures physics in different regions of the device and is able to replicate both static and dynamic behavior of experimental devices.



Figure 1: (a) Cross-section schematic of HV GaN HEMTs under study (b) Equivalent circuit implementation of the model that captures the intrinsic transistor and non-linear access region behavior as implicit-gated transistors.



Figure 2: Output, transfer, output conductance, and transfer conductance plots of Lg=3 μm and Lgd= 9.5 μm device. Good agreement has been achieved between the model (curves) and measurement (circles).




1. U. Mishra, L. Shen, T. E. Kazior, and Y-F Wu, “GaN-Based RF Power Devices and Amplifiers,” Proceedings of the IEEE, vol. 96, no. 2, pp. 287-305, Feb. 2008. [↩]
2. A. Khakifirooz, O. Nayfeh, and D. Antoniadis, “A Simple Semiempirical Short-Channel MOSFET Current-Voltage Model Continuous Across All Regions of Operation and Employing Only Physical Parameters,” IEEE Transactions on Electron Devices, vol. 56, pp. 1674-1680, 2009. [↩]
3. U. Radhakrishna, L. Wei, D. S. Lee, T. Palacios, and D. Antoniadis, “Physics-based GaN HEMT transport and charge model: Experimental verification and performance projection,” IEEE International Electron Devices Meeting., pp.13.6.1-13.6.4, 10-13 Dec. 2012. [↩]