GaN HEMT Power Research Articles

H-Bridge Derived Topology for Dynamic On-Resistance Evaluation in Power GaN HEMTs

Gallium nitride high electron mobility transistors outperform Silicon devices due to their excellent physical properties. However, being an immature technology, it exhibits dynamic <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R_{\text{ds}, \text{on}}$</tex-math></inline-formula> ). This causes increased conduction loss and leads to reduced operating efficiency. To evaluate the dynamic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R_{\text{ds}, \text{on}}$</tex-math></inline-formula> of the device, a measurement circuit is required. In literature, a standardized double pulse test is widely used for the measurement of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R_{\text{ds}, \text{on}}$</tex-math></inline-formula> . However, due to the uncontrolled <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> -state time and inability to independently adjust, the test conditions result in restricted measurement. This article proposes a measurement circuit of the device in power electronics operations. The circuit uses an H-Bridge-derived topology with capacitive storage to enable forward and reverse conduction mode measurement of the device. In all the modes, the circuit allows measurement from the first switching cycle and independent control over the testing conditions by using a hysteresis current control. The proposed measurement circuit is validated using simulation and experimentation. Finally, analytical efficiency compared with the state-of-the-art measurement circuits is provided.

Development of Diamond Device-Level Heat Spreader for the Advancement of GaN HEMT Power and RF Electronics

Development of Diamond Device-Level Heat Spreader for the Advancement of GaN HEMT Power and RF Electronics

GaN on Engineered Bulk Silicon Power Integration Platform With Avalanche Capability Enabled by Built-in Si PN Junctions

A GaN on engineered bulk silicon (GaN-on-EBUS) power IC platform featuring an industry-standard 200-V GaN power HEMT epi-structure has been recently demonstrated, showing effective isolation and crosstalk suppression between the high-side (HS) and low-side (LS) GaN transistors in half-bridge configuration. In this work, we scale up the vertical breakdown voltage (BV) of the GaN film on the EBUS substrate to be over 600 V. Meanwhile, the built-in back-to-back PN junctions along the trench created in the Si substrate are employed to provide an overvoltage-protection scheme through their intrinsic avalanche capability for the overlaying GaN half-bridge circuit.

(Invited) Advances in High Power, High Voltage, Reliable GaN Products for Multi Kilo-Watt Power Conversion Applications.

Gallium Nitride has been proven to be a superior material system for high performance, reliable, high power transistors enabling high efficiency in power conversion applications [1,2]. In this paper we highlight some recent advances in GaN technology which expand the capabilities and applications of GaN power switches.Transphorm, Inc, is a pioneer and leader in GaN power electronics with a wide product portfolio of products spanning <100W to >10kW applications with JEDEC and AEC-Q101 qualified products including qualified 650V and 900V products (Fig. 1), as well as demonstrated 1200V devices in development. Transphorm’s vertical integration allows for control over device design, GaN epitaxial growth, and device fabrication resulting in industry leading performance and reliability.Transphorm’s breadth of volume production applications from 45 W through 10 kW is in part due to its impressive Failure in Time (FIT) rate of < 0.3 failures per billion hours is based on Field Reliability Data collected over 40 billion hours.[3]Transphorm’s normally-off devices are built by combining a state-of-the-art high voltage (HV) GaN HEMT with a low voltage (LV) Silicon MOSFET into a cascode GaN FET configuration to offer superior reliability, performance, and ease of use. The LV Si MOSFET features low gate charge and high threshold voltage which makes for a very easy to drive switch with a large gate voltage drive margin and the HV GaN HEMT offers high performance due to the superior material and transport properties of GaN combining the best of both materials.The latest GenV 15 mΩ 650V SuperGaN® FET (TP65H015G5WS) is the lowest Ron packaged GaN FET in the market enabling >10kW output powers with a single switch [4]. Inductive switching waveforms in a half-bridge at 400 V/65 A for the SuperGaN FET and SiC MOSFET were compared (Fig. 2) and the GaN device delivered current and voltage switching speeds of 4 kA/μs and 60 kV/μs which is about 2x faster than that of the SiC MOSFET, resulting in a 50% reduction in switching loss.To assess the performance of the SuperGaN FET vs similarly rated SiC MOSFETs and SiC JFETs, the devices were configured into a 240V:400V boost converter operating at 70kHz (Fig. 3). The GaN FET based boost converter was able to operate up to 12kW of output power with a maximum junction temperature of just 139 oC while the SIC MOSFET and JFET boost converters were limited 11kW and 9.2kW respectively due to junction temperature reaching 165oC. At 9.2Wk output power, the SuperGaN FET power loss was 38% and 21% lower than the loss in the SiC JFET and SiC MOSFET respectively. This combination of lower temperature and higher output power demonstrates the importance of the high efficiency of the SuperGaN FET.The unparalleled efficiency of Transphorm’s SuperGaN FETs has enabled to the development of unique products such as a 3KVA datacenter UPS released by and industry leading supplier, which is the smallest, lightest, and most powerful 3KA datacenter UPS on the market with 93.3% peak efficiency and 2.5x higher power density which enabled the form factor to shrink form a 2U to 1U enclosure.Until recently, commercial GaN power electronic devices have only available up to 650V with Transphorm’s qualified 900V GaN FET (TP90H050WS) device being the exception. We have recently announced a breakthrough in GaN technology with the demonstration of a 1200V, 70mΩ lateral GaN FET in a TO-247 packageThe 1200V GaN FET achieved > 99% peak efficiency in a 450V:900V synchronous boost converter operating at 50kHz which is similar to the peak efficiency of our 650V Gen IV and Gen V products. Additionally, the 1200V GaN FET achieved higher efficiency than a similarly rated state-of-the-art 1200V SIC MOSFET in a 900V:450V buck converter at 100kHz and 5.5kW (Fig 4) demonstrating GaN can excel in 1200V applications [5].[1] Y.F. Wu, J. Gritters, L. Shen, R.P. Smith, J. McKay, R. Barr, R. Birkhahn, “Performance and robustness of first generation 600-V GaN-on-Si power transistors”, The 1st IEEE Workshop on Wide Bandgap Power Devices and Applications, 6-10, Oct, 2013.[2] Parikh, Y.F. Wu, L.K. Shen, "Commercialization of High 600V GaN-on-Silicon Power Devices", Materials Science Forum, Vols. 778-780, pp. 1174-1179, October 2014. [3] https://www.transphormusa.com/en/gan-technology/#quality-reliability [4] C. J. Neufeld, Y.-F. Wu, S. Wienecke, R.P. Smith, Y. Huang, M. Kamiyama, J. Ikeda, T. Hosoda,B. Swenson and R. Birkhahn, “650V/780A GaN Power HEMT Enabling 10kW-Class High-efficiency Power Conversion”, IEEE 8th Workshop on Wide Bandgap Power Devices and Applications, 7-11 Nov. 2021.[5] Gupta, et al. IEEE International Symposium on Power Semiconductor Devices 2022 (accepted for publication) Figure 1

Compact Modeling of Nonideal Trapping/Detrapping Processes in GaN Power Devices

Compact modeling of charge trapping processes in GaN transistors is of fundamental importance for advanced circuit design. The goal of this article is to propose a methodology for modeling the dynamic characteristics of GaN power HEMTs in the realistic case where trapping/detrapping kinetics are described by stretched exponentials, contrary to ideal pure exponentials, thus significantly improving the state of the art. The analysis is based on: 1) an accurate methodology for describing stretched-exponential transients and extracting the related parameters and 2) a novel compact modeling approach, where the stretched exponential behavior is reproduced via multiple <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> networks, whose parameters are specifically tuned based on the results of 1). The developed compact model is then used to simulate the transient performance of the HEMT devices as a function of duty cycle and frequency, thus providing insight on the impact of traps during the realistic switching operation.

A Cost-Effective 5-W GaN HEMT Power Amplifier for Sub-6-GHz 5G Wireless Communications

A Cost-Effective 5-W GaN HEMT Power Amplifier for Sub-6-GHz 5G Wireless Communications

Design of High-Power High-Efficiency Broadband GaN HEMT Power Amplifier for S Band Applications using Load-Pull Technique

This work reveals the design for broadband high-power high-efficiency GaN HEMT power amplifier, operating in the frequency band ranging from 2.15 GHz to 2.65 GHz. The proposed structure is implemented using Cree GaN HEMT CGH40010 transistor. The high-power and high-efficiency performances over the broadband bandwidth are achieved using the load-pull technique. The proposed power amplifier is unconditionally stable over the entire operating frequency band. With the neatly designed matching circuits, the introduced power amplifier shows an excellent input/output matching. The simulated results show a flat power gain of 15 dB with an output 1-dB compression point of 14 dB. In terms of largesignal performance, the proposed amplifier reaches a saturated output power of 41.3 dBm (~13.6 Watts) with a PAE of 64% and a drain efficiency of 72%. The proposed design achieves an excellent linearity with an output third order two-tone intercept point TOI of 48 dBm.

Stability of wireless power transfer using gamma-ray irradiated GaN power HEMTs

In this work, we have demonstrated the wireless power transfer (WPT) system based on the pristine and irradiated E-mode GaN devices. The GaN device has been irradiated up to the 100 kGy dose under the γ-ray irradiation, showing the improved electrical characteristic, such as the drain current increase (~8.34%) and gate current decrease (~−7.79%). An off-state drain induced instability measurement shows the robust performance in pristine and irradiated GaN device. Noted that the irradiated device exhibits less ΔVTH, suggesting the device instability has been improved. Moreover, the wireless power transfer efficiency was evaluated by utilizing different load (20 Ω ~ 120 Ω) at VDS = 50 V and VGS = 4 V. The results indicate that the transfer efficiency of WPT by implementing the pristine and irradiated GaN device are similar. Furthermore, the output power of WPT using the irradiated GaN device becomes higher, which is mainly due to the improved drain current in irradiated GaN power devices.

Reliability and failure analysis in power GaN-HEMTs during S-band pulsed-RF operating

This paper reports a reliability study on two technologies of AlGaN/GaN high-electron mobility transistors (AlGaN/GaN HEMTs) (Device “A” and Device “B”). A failure analysis study is conducted on devices stressed under real operating conditions for radar applications. The devices underwent pulsed-RF long ageing tests and after 11,000 h show a degradation in RF and DC performances (Drop of drain current and RF output power, pinch-off shift, decrease of the maximum of transconductance, lateral translation of transconductance, and increase of gate-lag and drain-lag). Hot electron effects are supposed to be the origin of the observed degradations and trapping phenomena within the passivation or GaN layers. Photon emission microscopy (PEM), Optical Beam Induced Resistance Change (OBIRCH), Electron Beam Induced Current (EBIC) measurements concur with this hypothesis. The three techniques reveal a non-uniform response and an inhomogeneous distribution along the gate fingers, in addition to the presence of some localized spots localized on the gate edge either on the drain side or on the source side. Spectral PEM analysis of these spots identifies a native defect that could be related to crystallographic defects such as dislocations or impurities. Atom probe tomography (APT) analysis on the two technologies of AlGaN/GaN HEMTs supports this hypothesis. APT results show the presence of some chemical impurities like carbon and oxygen. These impurities are in relatively significant concentrations in device “A” which could explain the high level of gate-lag and drain-lag in this device compared to device “B”.

Design of bandwidth‐enhanced power amplifier based on class‐EF modes

AbstractThis article describes a methodology for designing broadband high‐efficiency GaN HEMT power amplifier (PA) which is suitable for base stations and modern wireless communication based on the Class‐EF mode. To achieve both efficiency enhancement and bandwidth extension for the PA, the load‐pull technique is employed to acquire the optimum impedance regions of the second harmonic. Especially, considering the influences of the harmonic control network on the accuracy of obtaining the fundamental impedance, the load‐pull technique is performed to obtain the optimal fundamental impedance again after the harmonic control circuit is determined. In addition, the theory of multiple frequencies matching is also employed to manipulate six desired fundamental frequency points concurrently. Based on the proposed theory, the Class‐EF PA prototype is designed and fabricated. The measurement results exhibits a drain efficiency (DE) of 60%–75% in the range of 2.1–3.6 GHz while having an output power of 38–40.5 dBm and gain of larger than 8 dB.

A GaN-HEMT Compact Model Including Dynamic RDSon Effect for Power Electronics Converters

In order to model GaN-HEMT switching transients and determine power losses, a compact model including dynamic RDSon effect is proposed herein. The model includes mathematical equations to represent device static and capacitance-voltage characteristics, and a behavioural voltage source, which includes multiple RC units to represent different time constants for trapping and detrapping effect from 100 ns to 100 s range. All the required parameters in the model can be obtained by fitting method using a datasheet or experimental characterisation results. The model is then implemented into our developed virtual prototyping software, where the device compact model is co-simulated with a parasitic inductance physical model to obtain the switching waveform. As model order reduction is applied in our software to resolve physical model, the device switching current and voltage waveform can be obtained in the range of minutes. By comparison with experimental measurements, the model is validated to accurately represent device switching transients as well as their spectrum in frequency domain until 100 MHz. In terms of dynamic RDSon value, the mismatch between the model and experimental results is within 10% under different power converter operation conditions in terms of switching frequencies and duty cycles, so designers can use this model to accurately obtain GaN-HEMT power losses due to trapping and detrapping effects for power electronics converters.

Analysis and modeling of OFF-state hysteretic losses in GaN power HEMTs

We present a detailed analysis of large-signal Sawyer–Tower measurements on a power GaN HEMT device in OFF-state. The measurements show hysteresis which results in an energy loss dissipated as heat in the range of sub-μJ’s. We model this important phenomenon in this paper using a previously calibrated model of the same device. We propose two models, one with linear Effective Series Resistance (ESR) and another using non-linear ESR (NLESR). It is found that to model the non-linear profile of hysteretic curve from Sawyer–Tower measurements, non-linear ESR and output capacitance are needed. The similarities and differences between these two models have been explained in detail. While linear ESR is shown to be a simple model for modeling the hysteretic losses, non-linear ESR and output capacitance model the dynamics of charge imbalance that occurs during the charging and discharging processes more accurately. A detailed analysis based on recent literature suggests that 2DEG electron trapping by acceptor type traps in the underlying buffer layers are the primary cause of this charge imbalance.

True Breakdown Voltage and Overvoltage Margin of GaN Power HEMTs in Hard Switching

This work studies the dynamic breakdown voltage (BV) and overvoltage margin of a 650-V-rated commercial GaN power HEMT in hard switching. The dynamic BV measured in the hard switching circuits is over 1.4 kV, being 450 V higher than the static BV measured in the quasi-static I-V sweep. The device can survive at least 1 million hard-switching overvoltage pulses with 1.33 kV peak overvoltage (~95% dynamic BV). Recoverable device parametric shifts are observed after the 1-million pulses, featuring small reductions in threshold voltage and on-resistance. These shifts are different from the ones after the hard-switching pulses without overvoltage and are attributable to the trapping of the holes produced in impact ionization. These results suggest that the BV and overvoltage margin of GaN HEMTs in practical power switching can be significantly underestimated using the static BV.

An Independently Biased 3-stacked GaN HEMT Power Amplifier for Next-Generation Wireless Communication Systems

An Independently Biased 3-stacked GaN HEMT Power Amplifier for Next-Generation Wireless Communication Systems

A novel on-wafer approach to test the stability of GaN-based devices in hard switching conditions: Study of hot-electron effects

In this work, a novel system to investigate the stability of GaN-based HEMT devices is presented and used to investigate hot-electron effects. The developed system is used to study the impact of hard switching on the dynamic on-resistance of such devices. In particular, we were able to obtain (on-wafer level) a very fast turn-ON commutation with dVDS/dt ≈ 10 V/ns (representative of realistic conditions) thanks to the low parasitics at the drain node. As a result, a realistic performance assessment of the dynamic stress of GaN power HEMTs is now available on wafer level, thus shortening the technology development loop. By intentionally tuning the capacitance at the drain node we can accurately control the amount of energy/charge released during each hard switching event, thus being able to evaluate the impact of increasing stress conditions on the devices. The results indicate that even if the hard-switching lasts few nanoseconds, it significantly impacts the dynamic RDSON: we conclude that hot-electron trapping can occur in ns-time scale.

Design of multioctave power amplifier using multi‐harmonic bilateral pull technique

AbstractIn this letter, the design, implementation and measurements of a multioctave bandwidth high‐efficiency GaN HEMT power amplifier (PA) based on a novel systematic design methodology are presented. To achieve bandwidth expansion while maintaining a high level of efficiency, the multi‐harmonic bilateral pull technique has been employed to acquire the optimum fundamental and second harmonic impedance regions. Especially, the impedance region of the second harmonic is analyzed to conclude that the second harmonic impedance can be expanded to a resistive‐reactive with complex load impedances. Therefore, multioctave bandwidth can be achieved by combining low‐pass lumped circuit (LC) matching network. For experimental verification, the wideband PA is achieved with a 10‐W GaN device. The measurement results manifest that the implemented PA has a drain efficiency (DE) of 54% to 71% and a saturated output power of 38.2 to 42.3 dBm for the entire intended frequency range between 0.5 to 3.1 GHz with a relative bandwidth of 144.4%, while providing a gain larger than 8.2 dB. Measurement results confirm the theoretical findings.

High‐efficiency broadband GaN HEMT power amplifier based on harmonic‐tuned matching approach

High‐efficiency broadband GaN HEMT power amplifier based on harmonic‐tuned matching approach

Insights into the off-state breakdown mechanisms in power GaN HEMTs

We analyze the off-state, three-terminal, lateral breakdown in AlGaN/GaN HEMTs for power switching applications by comparing two-dimensional numerical device simulations with experimental data from device structures with different gate-to-drain spacing and with either undoped or Carbon-doped GaN buffer layer. Our simulations reproduce the different breakdown-voltage dependence on the gate-drain-spacing exhibited by the two types of device and attribute the breakdown to: i) a combination of gate electron injection and source-drain punch-through in the undoped HEMTs; and ii) avalanche generation triggered by gate electron injection in the C-doped HEMTs.

Failure mechanisms of enhancement mode GaN power HEMTs operated in short circuit

The paper reports the results of a study based on experimental data and finite element simulations about the failure mechanism of 650 V p-doped GaN power HEMT operated in short circuit condition. The study focuses on the failure observed during the short circuit of these devices when the test voltage is larger than 350 V. In this failure mode, the energy involved is quite low and the time to failure is <1 μs. Simulation results show that in these test conditions a very high-power density is dissipated in a critical region of the device and it is intensified by a significant current focalization which has been proved by experimental observations. It is demonstrated that the temperature in the critical region can reach the maximum allowable temperature for a GaN/AlGaN structure.

Investigation of the aging of power GaN HEMT under operational switching conditions, impact on the power converters efficiency

This paper investigates the aging of a 650 V, 30 A GaN HEMT power transistor under operational switching conditions. The switching stress respects the Safe Operation Area (SOA) of the tested transistor. The aging campaign lasted 1008 h and was carried out through a developed switching application with high power efficiency. The global aging results show the degradation of five parameters: drain current ID, on-state resistance RDS(ON), transconductance gm, gate leakage current IGSS, and threshold voltage VTH. The major causes that affect the reliability of the GaN HEMT are hard switching, long time of test and high intensity of the stress. The existence of trapped charge in the gate-drain access region after aging is demonstrated using pulsed measurements. The effects of this degradation on power converters are studied by modeling the static characteristics of the aged GaN HEMT using an accurate method based on the Levenberg-Marquardt Algorithm. The accuracy and consistent convergence of the developed SPICE model provide a good way to investigate the reliability of GaN HEMTs by a simulation approach.