GaN HEMT Research Articles

A fully integrated half-bridge driver circuit in All-GaN GAN-IC technology

To unlock the full potential of fast switching GaN technology, monolithic integration of power circuit is crucial. GaN-IC ensures a fast efficient switching operation by reducing the parasitic inductance of interconnections significantly. In this paper, we demonstrate a monolithically integrated half-bridge power switch with its corresponding driving stage and the protection circuits that is realized by using our GAN-on-SOI technology. A low gate threshold voltage along with a low gate overdrive makes the driving of a GaN HEMT difficult. An optimized gate driver design is important to fully utilize a GaN power switch. This is also crucial for overall system efficiency, robustness, and EMI performance. Along with the design description this paper discusses the challenges and the design considerations of the GaN power IC.

Mechanical-electrical synergy damage effect on GaN HEMT under high-power microwave

Mechanical-electrical synergy damage effect on GaN HEMT under high-power microwave

Large-signal behavior modeling of GaN HEMTs using SSA augmented ELM algorithm

Large-signal behavior modeling of GaN HEMTs using SSA augmented ELM algorithm

A Thorough Evaluation of GaN HEMT Degradation under Realistic Power Amplifier Operation

In this paper, we experimentally investigate the effects of degradation observed on 0.15-µm GaN HEMT devices when operating under realistic power amplifier conditions. The latter will be applied to the devices under test (DUT) by exploiting a low-frequency load-pull characterization technique that provides information consistent with RF operation, with the advantage of revealing electrical quantities not directly detectable at high frequency. Quantities such as the resistive gate current, play a fundamental role in the analysis of technology reliability. The experiments will be carried out on DUTs of the same periphery considering two different power amplifier operations: a saturated class-AB condition, that emphasizes the degradation effects produced by high temperatures due to power dissipation, and a class-E condition, that enhances the effects of high electric fields. The experiments will be carried out at 30 °C and 100 °C, and the results will be compared to evaluate how a specific RF condition can impact on the device degradation. Such a kind of comparison, to the authors’ knowledge, has never been carried out and represents the main novelty of the present study.

N-Polar GaN HEMTs in a High-Uniformity 100-mm Wafer Process With 43.6% Power-Added Efficiency and 2 W/mm at 94 GHz

We report the fabrication of N-polar GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) with a power-added efficiency (PAE) of 43.7% from an 8-V supply measured by load pull at 94 GHz. The devices are fabricated on 100-mm SiC substrates and exhibit excellent uniformity, constituting the first report on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$</tex-math> </inline-formula> -band power performance across a 100-mm N-polar GaN sample. Compared with the available efficiency of N-polar GaN on SiC at 94 GHz, the devices presented here demonstrate among the highest PAE performance, while delivering a power density of 2 W/mm, competitive with highly scaled, and previously reported both Ga and N-polar devices using an 8-V power supply.

Исследование тепловых характеристик беспроволочной интеграции мощных СВЧ кристаллов

This paper presents the results of thermal analysis evaluation of two assembly techniques for high power microwave applications: conventional integration on metal carrier using solder preform and flip-chip mounting using Au-Sn system for SLID bonding as an interconnect layer to dielectric substrate. A high power GaN HEMT on SiC substrate with fabrication technology of 0.15 μm and total gate width 1.2 mm are used. The results of the flip-chip approach showed a 7.2% reduction in the overall thermal resistance of the assembly compared to conventional integration approach. Dependences of individual circuit elements on thermal parameters are determinated. Electrical equivalent circuit of thermal models of investigated constructions are obtained.

A new bandwidth-extended harmonic-tuned Class-E/F3 power amplifier based on continuous mode design philosophy

For Class-E/F3 power amplifiers (PAs) working in the radio frequency (RF) band, the freedom of broadband design is limited because the original design space is a single point. In this paper, a new bandwidth-extended Class-E/F3 PA is proposed, which is based on finite harmonic tuning and continuous mode design philosophy. In the theoretical derivation, the high-efficiency frequency domain equations are solved in conjunction with the inherent conditions of the transistor, resulting in a waveform cluster that can expand the design space while keeping the efficiency constant. This approach eliminates the need for tedious circuit derivation and is able to allow greater design freedom. With the extended Class-E/F3 design space, a broadband PA using GaN HEMT CGH40010F operating in the bandwidth of 1.9–3.3 GHz is designed and tested. The experimental results show that the designed PA demonstrates 65% to 74.8% drain efficiency (DE) and 40.1 to 41.7dBm output power over the target bandwidth.

Novel double channel reverse conducting GaN HEMT with an integrated MOS-channel diode

A novel normally-off double channel reverse conducting (DCRC) HEMT with an integrated MOS-channel diode (MCD) is proposed and investigated by TCAD simulation. The proposed structure has two features: one is double heterojunctions to form dual 2DEG channels named the 1st path and the 2nd path for reverse conduction, and the other is the MCD forming by the trench source metal, source dielectric, and GaN. At the initial reverse conduction stage, the MCD acts as a switch to control the 1st path which would be turned on prior to the 2nd path. Because of the introduction of the 1st path, the DCRC-HEMT has an additional reverse conducting channel to help enhance the reverse conduction performance. Compared with the conventional HEMT (Conv. HEMT), the DCRC-HEMT can obtain a low reverse turn-on voltage (V RT) and its V RT is independent of the gate–source bias (V GS) at the same time. The DCRC-HEMT achieves the V RT of 0.62 V, which is 59.7% and 75.9% lower than that of the Conv. HEMT at V GS = 0 V and −1 V, respectively. In addition, the forward conduction capability and blocking characteristics almost remain unchanged. In the end, the key fabrication flows of DCRC-HEMT are presented.

Polarization independent grating in a GaN-on-sapphire photonic integrated circuit.

In this work, we report the realization of a polarization-insensitive grating coupler, single-mode waveguide, and ring resonator in the GaN-on-sapphire platform. We provide a detailed demonstration of the material characterization, device simulation, and experimental results. We achieve a grating coupler efficiency of -5.2 dB/coupler with a 1 dB and 3 dB bandwidth of 40 nm and 80 nm, respectively. We measure a single-mode waveguide loss of -6 dB/cm. The losses measured here are the lowest in a GaN-on-sapphire photonic circuit. This demonstration provides opportunities for the development of on-chip linear and non-linear optical processes using the GaN-on-sapphire platform. To the best of our knowledge, this is the first demonstration of an integrated photonic device using a GaN HEMT stack with 2D electron gas.

Equivalent circuit model of GaN high electron mobility transistor with consideration of non-ideal effects using genetic algorithm

This work proposes a semi-physical equivalent circuit model for GaN-based high electron mobility transistors (GaN HEMTs), taking into account the non-ideal effects of both the current source and resistance–capacitance components. The current source model is built based on both device operation and multiple model interfaces setup for important non-ideal effects, such as self-heating effects, channel length modulation, short channel effects, and so on. Moreover, according to the improved Meyer capacitance model with fringe capacitances, the non-linear capacitances of the GaN HEMT are modeled with a dependence on the bias voltages and gate geometry. The extraction of the model parameters is implemented accurately and efficiently in MATLAB through a genetic algorithm. Moreover, the capacitance model is established to be mathematically simple and Simulation Program with Integrated Circuit Emphasis (SPICE)-compatible for the design of GaN-based integrated circuits (ICs). The static and dynamic characteristics of GaN ICs were simulated and found to be in excellent agreement with the experimental results, validating that the established and well-packaged equivalent circuit model can be of great help to GaN HEMT development and IC design.

A continuous Class‐EF power amplifier based on the general continuous mode design theory

SummaryContinuous mode provides better bandwidth performance and constant efficiency by offering greater design flexibility in fundamental and harmonics. However, this mode is mainly applicable to limited classes of power amplifiers (PAs) (such as Class‐F, Class‐J, and their derived types). In view of this problem, this paper proposes a general design theory for high‐efficiency broadband continuous PAs, which can easily extend any waveform of PAs to obtain the continuous impedance space. In theoretical analysis, first, the high‐efficiency equations are analyzed from the perspective of frequency domain. Furthermore, combining time domain constraints, a general continuous mode analysis and solution theory is presented. The theory is applied to the bandwidth expansion of Class‐EF PAs, resulting in a new continuous Class‐EF (C‐EF) mode that maintains constant efficiency while offering greater broadband design freedom. The proposed theory is verified by fabricating a C‐EF PA using GaN HEMT CGH40010F, which demonstrated output power (Pout) ranging from 39.5 to 41.2 dBm and drain efficiency (DE) of 69.5% to 79.2% in the frequency range of 2.5–3.6 GHz.

Investigation of variable field plate length in GaN HEMT on SiC substrate for MMIC applications

This work intends to improve the GaN HEMT device breakdown voltage, by uniformly distributing peak electric field using field plate engineering technique. A peak electric field reduction is observed by adding field plate at the gate end along with remolding the distribution of electric field linearly. The device breakdown voltage is improved by gradual decrease in electric field is observed. To analyze the OFF-state breakdown voltage, the gate field plate of various lengths is used and optimum size is calculated for GaN HEMTs. A breakdown voltage of 350 V is prominently observed in the simulation results. Moreover, the obtained results show a good substantiation with experimental data. The DC Characteristics and AC characteristics of the proposed structure exhibit an enhanced performance than the existing structures, justifying the GaN field plated HEMT as to be a promising solution for Microwave monolithic Integrated Circuit applications.

Investigation of DC and RF characteristics of spacer layer thickness engineered recessed gate and field‐plated III‐nitride nano‐HEMT on β‐Ga2O3 substrate

AbstractIn this work, a field plated recessed gate III‐nitride HEMT on β‐Ga2O3 substrate is proposed using AlN spacer between AlGaN and GaN layers. The two‐dimensional electron gas (2DEG) transport characteristics, input/output, and RF characteristics of the proposed HEMT with AlN spacer layer of different thickness (1, 2, 3, 4, and 5 nm) are numerically simulated and compared with HEMT without spacer layer. The 2DEG, which is created at the junction of AlGaN/GaN, plays a crucial role in the operation of GaN HEMTs. With the help of AlN as spacer layer between AlGaN and GaN, an augmented 2DEG concentration is accomplished owing to its large conduction band offset, high polarization effect, and higher barrier. Additionally, the inclusion of AlN spacer layer shifts the 2DEG density away from interface, resulting minimized interface scattering which results into greater mobility. The HEMT exhibited a mobility of 1261 cm2/Vs, threshold voltage of −0.45 V, drain current of 1.12 A/mm, breakdown voltage of 149 V, and excellent RF characteristics, that is, cut‐off frequency (maximum oscillation frequency) of 384 GHz (546 GHz) using 2‐nm AlN spacer layer. The proposed III‐nitride HEMT on β‐Ga2O3 substrate with 2‐nm AlN spacer can be used for RF/microwave and high‐power nanoelectronics applications.

Effect of Field Plate on Device Performance of Wide Bandgap HEMT

Background: Devices with field plates have gained much popularity in high power and high voltage applications. The work done in this paper is related to designing and studying the different DC and RF characteristics of a field plated GaN HEMT. The results obtained were compared with that of non-field plated GaN HEMT. This comparison and study reported the effect of field plate on device performance. Methods: A GaN HEMT device with and without a field plate was designed and simulated in the SILVACO ATLAS TCAD tool. The performance of both the devices was compared in terms of the exhibited DC and RF characteristics in order to study the effect of the field plate on the device. We have also studied the variation in the cut-off frequency and maximum frequency of both the field plate and without field plate GaN HEMT with respect to gate-source voltage. We have further investigated the device performance by varying the length of the field plate from 0 to 2.5 μm. Results: The study reflects the advantageous feature of GaN HEMT with field plate by exhibiting high breakdown voltage of 292 V in comparison to GaN HEMT without field plate which exhibits a breakdown voltage of 98 V. As a result of using field plate in the GaN HEMT structure, a rise in the Cgs and Cgd capacitances are witnessed. This in turn affects the other RF characteristics of the GaN HEMT with field plate even though the GaN HEMT with and without field plate exhibits nearly same DC characteristics. The field plated GaN HEMT exhibits a reduced cut-off frequency and maximum frequency of 7 GHz and 20 GHz, respectively, in comparison to the GaN HEMT without field plate’s cut-off frequency and maximum frequency of 10 GHz and 25 GHz, respectively. Conclusion: The study reports that using a field plate helps in enhancing the breakdown voltage but at the cost of reduced frequency performance. We have compared our proposed field plated device with different non-field plated devices and concluded that our device exhibits much higher breakdown voltage in spite of reduced device dimension. With the attainment of higher breakdown voltage our proposed GaN HEMT device can be used for high power applications. From the study, it is reported that while increasing the length of the field plate the breakdown voltage also increases. For a particular set of device dimensions, an optimum field plate length provides the highest breakdown voltage but increasing the length of the field plate beyond the optimum value results in reduction in breakdown voltage.

A Review of High-Speed GaN Power Modules: State of the Art, Challenges, and Solutions

Wide bandgap (WBG) devices are a desirable choice for high-density energy conversion systems. In high-speed hard-switching applications, voltage overshoot across device terminals, oscillations at gate loop and Electro-magnetic Interference (EMI) becomes harder to mitigate and overall system reliability is reduced. To address the key challenges and harness the benefits offered by these latest generations of devices, improved and advanced packaging structures are required, as packaging technology often has a critical impact on module performance and reliability. This paper summarizes the design procedure for power modules, essential parts, and available materials for the fabrication of a power module package. Moreover, it provides a review of commercially available gallium nitride based high electron mobility transistors (GaN HEMTs) and state-of-the-art module packaging technologies adopted for them with a focus on module layout, module integration trends, and identifying their impacts on the GaN HEMT’s performance. Through this review, the paper also discusses major challenges faced by designers with GaN HEMTs in power electronics applications and their potential solutions, which is critical for the mainstream adoptions of GaN HEMTs and defining the future technology roadmap.

Design of 2.45-GHz High-Efficiency Miniaturized Power Oscillator Using GaN HEMT

This study presents a method for designing a highly efficient miniaturized power oscillator with gallium nitride high electron mobility transistor (GaN HEMT). A harmonic-tuning highly efficient power amplifier (PA) using GaN HEMT is designed firstly by finding optimal fundamental, 2nd and 3rd harmonic load impedances. After the performance of PA meets the requirements, the feedback circuit that is made of a hairpin resonator and a coupler is studied based on the power gain of PA and the required frequency. Both the size of the PA and the feedback circuit should be taken into account to minimize the oscillator at last. Finally, the PA and feedback circuit are combined into a power oscillator. Through this way, the highly efficient miniaturized power oscillator with a size of 2.7*4.9 cm2 fabricated on substrate of FR4 outputs 37.7 dBm power and 72% efficiency at 2.4518 GHz under the bias condition of Vgs = - 3.21V, Vds = 28V, Ids = 25mA.

GaN-Based Matrix Resonant Power Converter for Domestic Induction Heating

Flexible-surface induction cooktops must operate with a variety of induction heating loads with different behavior and power setpoints to be heated simultaneously. In this context, multi-output inverter topologies aim at achieving independent power management while featuring low power-device count and high power density. However, they suffer from limitations when applying classical modulation strategies to ensure soft switching, which is required to reduce transistor losses and achieve efficient operation. In this scenario, wide band-gap devices reduce switching losses, opening a new paradigm in power conversion where soft switching is not mandatory in order to achieve high efficiency. This paper proposes an implementation of a multi-output resonant inverter based on GaN HEMTs and evaluates various modulation strategies in terms of efficiency under different switching modes. The proposed approach is designed and experimentally validated by means of a 2-coil 2000 W prototype implementation.

Ferrite Beads Design to Improve Turn-Off Characteristics of Cascode GaN HEMTs: An Optimum Design Method

In this paper, an optimum ferrite beads design method is proposed to suppress the self-sustained turn-off oscillation of cascode gallium nitride high-electron-mobility transistors (GaN HEMTs). At first, the impacts of gate loop beads and power loop beads on the turn-off oscillation of cascode GaN HEMTs are analyzed. The analysis reveals the weak damping effect of gate loop beads on the turn-off oscillation. Next, an analytical method is proposed to design the power loop beads that can achieve maximum effective damping on the turn-off oscillation. The power loop beads introduce extra stray inductance in the power loop, which can induce high voltage overshoot. To tackle the problem, an optimum design method is proposed so that the power loop beads can suppress the oscillation while mitigating the voltage overshoot. The accuracy of the proposed model is validated by the experimental data in the end.

Micro-Transfer Printing for Heterogeneous Integration of GaN and GaAs HEMTs

Here, we use the micro-transfer printing technique to demonstrate the device-level heterogeneous integration of two solid-state RF device technologies on the same interposer: GaN and GaAs high-electron-mobility transistors. The devices are released from their growth substrate using an epitaxial sacrificial layer while a thin polymer adhesion layer facilitates a strong bond between the target substrate and the compound semiconductor devices, allowing for post-transfer microfabrication processing. Transmission electron microscopy reveals no voids at the device/interposer interface and a polymer adhesion layer thickness of 5 ± 2 nm. No significant degradation in dc electrical characteristics is observed after device transfer for either device technology. Improvement in thermal performance of GaN devices was demonstrated when transferred to a diamond substrate, even with the thin polymer adhesion layer at the device/interposer interface, illustrating a pathway for enhanced thermal management for GaN and other high-output-power density semiconductor technologies. The ability to combine various solid-state technologies at the device level with high density provides an approach to meet next-generation demands for RF and mixed-signal circuits.

Digital Predistortion Linearization of a GaN HEMT Push-Pull Power Amplifier for Cable Applications With High Fractional Bandwidth

This paper presents two linearization strategies for a custom-designed wideband push-pull (PP) power amplifier (PA) for wired communication applications such as, for example, cable TV. Two digital predistortion (DPD) behavioral models are proposed to meet the in-band and out-of-band linearity requirements when efficiently amplifying wideband DOCSIS signals with high fractional bandwidth (FBW). A radiofrequency (RF) DPD linearizer based on a band-pass generalized memory polynomial (BP-GMP) behavioral model and a baseband (BB) I-Q DPD linearizer based on a harmonic distortion GMP (HD-GMP) behavioral model are proposed. Both DPD models take into account the harmonic distortion typical of high FBW amplification. Experimental results will show high efficient and linear amplification of a 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 192 MHz composite DOCSIS signal by properly combining a crest factor reduction (CFR) technique and the proposed DPD strategies.