We propose two kinds of stacked materials that effectively yield low drain off-state leakage current, high off-state breakdown voltage and low current collapse simultaneously in AlGaN/GaN HEMT. The two kinds of stacked materials, which is NiOX/SiNX and Al2O3/SiNX respectively, act as gate dielectric layer and passivation layer for the devices. The NiOX and Al2O3 are prepared through depositing Ni and Al thin film by electron beam evaporation and then annealing in O2 ambient by rapid thermal processing. The SiNX is deposited by plasma-enhanced chemical vapor deposition. Compared to the single SiNX layer, the NiOX/SiNX stack layer and Al2O3/SiNX stack layer can distinctly reduce the drain off-state leakage current of devices. Meanwhile, high off-state breakdown voltage is also achieved. The off-state breakdown voltage in the devices with NiOX/SiNX stack layer and Al2O3/SiNX stack layer are 52% and 36% higher than that of the devices with single SiNX layer respectively. Especially, the current collapse under 200 V stress bias is reduced by 90% and 58% in the devices with NiOX/SiNX stack layer and Al2O3/SiNX stack layer compare to the devices with single SiNX layer respectively.

Breakdown Enhancement and Current Collapse Suppression in AlGaN/GaN HEMT by NiO X /SiN X and Al 2 O 3 /SiN X as Gate Dielectric Layer and Passivation Layer

Reverse blocking p-GaN gate AlGaN/GaN HEMTs with hybrid p-GaN ohmic drain

The design of a continuous broadband Doherty power amplifier (DPA) based on an X‐parameter model is presented in this work. The broadband load‐pull X‐parameter model is extracted at both the package plane and current generate plane of the device under test. The model cannot only predict the fundamental and harmonic nonlinear behavioral accurately, but also find the optimal output power and drain efficiency (DE) region of the Smith chart precisely, thereby assisting DPA design. A 10‐W gallium nitride packaged transistor from Wolfspeed is utilized in this design. The fabricated DPA reached a saturation output power of 44.3 dBm, with a saturation DE over 68% and a 6 dB output power back‐off efficiency over 51% in the frequency range of 1.1–1.8 GHz, verifying experimentally the effectiveness of the proposed design methodology.

Application of X‐parameter model of gallium nitride device for a continuous broadband Doherty power amplifier design

This work focuses on the equivalent‐circuit modeling of microwave field‐effect transistors. Although the purely direct approach allows obtaining a good prediction accuracy in a straightforward way without the need of any optimization, optimization algorithms are often used to achieve an improved accuracy at the cost of a higher modeling complexity. The pros and cons of empowering the direct approach with optimization algorithms are discussed by focusing the analysis on a 1000‐μm periphery gallium nitride high‐electron‐mobility transistor on silicon carbide substrate. The comparison between the two different approaches is performed through an extensive analysis of the frequency‐dependent behavior of the small‐signal characteristics.

Equivalent‐circuit extraction for gallium nitride electron devices: Direct versus optimization‐empowered approaches

A comparative study on the accuracy of small-signal equivalent circuit modeling for large gate periphery GaN HEMT with different source to drain length and gate width

Traditional lumped small signal equivalent circuit models of AlGaN/GaN metal oxide semiconductor high electron mobility transistors (MOS-HEMTs) are made up of constant valued circuit elements. Such models are unable to capture the high frequency behavior (above 20 GHz) of the device. In this work, a modified small signal equivalent circuit model of AlGaN/GaN MOS-HEMTs is presented. The key feature of the proposed model is that the values of the different circuit elements in the model are considered to be frequency dependent in nature and not constants. The frequency dependent value of each circuit element is mathematically represented using polynomial functions where the coefficients of the functions are determined via a least-square curve fitting approach. This frequency dependent attribute of the circuit element values ensures that the proposed model is very accurate at high frequencies without sacrificing the compactness of the model topology. The accuracy of the proposed model has been verified up to 50 GHz using experimentally measured Y-parameters of AlGaN/GaN MOS-HEMTs having a different gate dielectric and gate length.

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Generalized Frequency Dependent Small Signal Model for High Frequency Analysis of AlGaN/GaN MOS-HEMTs

For the purpose of reducing current collapse, we have studied a special structure of an AIGaN/GaN HEMT, in which an isolated p-GaN layer is located in the gate-drain access region. An addition of an isolated p-GaN layer resulted in significant suppression in current collapse by 98 %, as compared to the conventional HEMT. It was also found that current collapse was more effectively suppressed when the p-GaN region was located closer to the gate.

Reduced Current Collapse in AIGaN/GaN HEMTs with p-GaN Layer in Gate-Drain Access Region

In this paper, a technique to develop small signal circuit (SSC) models of AlGaN/GaN high electron mobility transistors (HEMTs) using dependent current sources is presented. In this technique, experimentally measured broadband Y-parameters of AlGaN/GaN HEMTs are mathematically modeled as a sum of pole-residue terms. By representing each pole-residue term as a dependent current source, it is possible to develop an accurate SSC models for HEMTs which otherwise may not be possible using passive resistive-inductive-capacitive elements. The accuracy of the proposed SSC model is validated against the conventional SSC model using a 2nd, 3rd and 4th order rational function representation of the admittance branches of AlGaN/GaN HEMTs. Therefore, the proposed SSC model turns out to be highly robust in nature and can take care of any form of the transfer functions of the admittance branches between the gate, drain, and source terminal of an AlGaN/GaN HEMT.

https://ieeexplore.ieee.org/ielx7/6245494/6423298/09896132.pdf

Takashi Ozawa

Papers

Generalized Frequency Dependent Small Signal Model for High Frequency Analysis of AlGaN/GaN MOS-HEMTs

Reduced Current Collapse in AIGaN/GaN HEMTs with p-GaN Layer in Gate-Drain Access Region

An Accurate Approach to Develop Small Signal Circuit Models for AlGaN/GaN HEMTs Using Rational Functions and Dependent Current Sources