Self-Heating and Trapping Effects in GaN HEMT Models

Self-Heating and Trapping Effects in GaN HEMT Models

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Self-Heating and Trapping Effects in GaN HEMT Models

Source: SPICE Model

Original Author: Ruo Ming

The rapid adoption of Gallium Nitride (GaN) technology in 5G base stations, satellite communications, and other applications has raised the bar for transistor modeling. In particular, the latest version of ADS supports ASM-HEMT 101.4 and MVSG_CMC 3.2.0 GaN HEMT models. For device modeling engineers, accurately extracting the model parameters for these two effects is often a challenge. Today, we will introduce how to extract the Self-heating and Trapping effect model parameters using the GaN HEMT model parameter extraction package in IC-CAP.

Standard Model of GaN Devices

Through the validation and selection of industry GaN models, the Compact Model Coalition (CMC) has chosen ASM-HEMT and MVSG_CMC as the standard models for GaN devices.
ASM-HEMT is a computationally efficient, surface-potential-based current and charge model that considers various secondary device effects, including Self-heating and Trapping effects.
Self-Heating and Trapping Effects in GaN HEMT Models
MVSG_CMC (MIT Virtual Source GaNFET Compact Model Coalition) is a charge-based model with multiple field-effect current and charge models available. It also includes Leakage, Noise, Self-heating, and Trapping effects.
Both models provide simulations of GaN device behavior, suitable for accurate simulations in both frequency and time domains. They both use R-C networks with thermal resistance and thermal capacitance to simulate Self-heating effects. Both also provide parameter selections for various Trapping scenarios, including the latest version of the R-C network model, which includes variable drain-lag and gate-lag.

Self-Heating Model Parameter Extraction

The increased power density of GaN devices leads to self-heating concentrated in smaller areas, reducing mobility, increasing signal delay, and potentially shortening device lifespan. Using IC-CAP to extract self-heating parameters is similar for both ASM-HEMT and MVSG_CMC GaN HEMT models.
Under static and pulsed excitation, modeling the thermal resistance RTH0 using the drain current Id as a function of the drain voltage Vd and gate voltage Vg is effective. First, the static Id-Vd curve at room temperature provides a baseline. Then, applying short Id pulses while keeping Vd0 and Vg0 at 0V minimizes Trapping and Self-heating, thus providing response curves at different temperatures. Overlaying the static curve with the pulse curve yields the same intersection point for Id. Calculating and plotting the relationship between power and temperature, the slope of the curve gives RTH0. The pulsed Id method provides a more direct extraction method than extracting RTH0 solely from DC static characteristics.
Self-Heating and Trapping Effects in GaN HEMT Models

Trapping Model Parameter Extraction

The Trapping effects in GaN devices also severely impact device performance and reliability. Charge capture in the buffer and interface layers reduces the 2DEG channel charge density and dynamic ions, increases dynamic Ron and cut-off voltage, and modulates Id.
Similarly, the parameter extraction methods for ASM-HEMT and MVSG_CMC are similar, even though there are differences in the implementation of the R-C networks between the models. Trapping parameter extraction is performed after DC, IV, Thermal, and S-parameter extraction. Gate-lag Trapping parameters are extracted first, as they affect the initial response and overall behavior of the transistor, only impacting surface trap capture. By analyzing gate-lag behavior, drain-lag Trapping extraction becomes more accurate while affecting both surface and buffer traps.
ASM-HEMT Trapping Model 4 uses two R-C circuits to simulate drain-lag and gate-lag.
Self-Heating and Trapping Effects in GaN HEMT Models
MVSG_CMC Trapping Model 2 uses a similar network, but the physical model is slightly different, considering variations in capture and release times.
Self-Heating and Trapping Effects in GaN HEMT Models
To extract gate-lag parameters, keep Vd constant while pulsing Vg; to extract drain-lag parameters, keep Vg constant while pulsing Vd.
Self-Heating and Trapping Effects in GaN HEMT Models
A typical drain-lag graph of MVSG-CMC illustrates the differences in trap capture and release effects.
References:
  1. https://si2.org/cmc/
  2. How-to-Extract-the-ASM-HEMT-Model-for-GaN-RF-Devices-Including-Thermal-Effects.pdf
  3. Trapping-Extraction-of-GaN-HEMTs.pdf
END
Reprinted content represents the author’s views only
Does not represent the position of the Institute of Semiconductors, Chinese Academy of Sciences
Editor: Renowned Wei Classmate
Responsible Editor: Mu Xin
Submission Email: [email protected]
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Self-Heating and Trapping Effects in GaN HEMT Models

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