A physics-based compact device model for GaN HEMT power devices

This paper reports a high-performance microwave receiver protector (RP) based on a single gallium nitride (GaN) high electron mobility transistor (HEMT) at an operation frequency of 30 to 3000 MHz. The HEMT-based RP exhibits multi features: high power compression, constant output power, tunable threshold power level, and insensitivity to frequency variation. With a low drain voltage (Vds) of 3 V, constant output power of 9.9 dBm was acquired for input power over its threshold power of 3.2 dBm. Power compression of 13.3 dB was achieved at the input power of Pin = 20 dBm. In addition, adjustable threshold power level Pth could be obtained by merely tuning drain voltage. Transducer gain measurement results were employed to explain the occurrence of output power saturation. Relatively higher Pth was linked to wider gate voltage swing which extended the linear region of the Pout-Pin characteristic. In addition, the GaN HEMT’s power compression capability shows great immunity to frequency variation, which is promising for protecting sensitive receiver components at both low and high frequencies. Finally, the phase shift of the GaN HEMT RP at high input power was measured and analyzed by the nonlinear behaviors of input capacitance Cgs.

Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs) are thermally limited much below the electrical capability of the devices. The unique challenge of a GaN HEMT is its ultra-high heat flux at the micro-scale gate fingers, which cannot be effectively and adequately addressed by conventional packaging and thermal management systems and lead to a large junction-to-ambient thermal resistance. A novel thermal interface material (TIM) that offers unique heat spreading, CTE compliance and ultra-high thermal performance was developed. The new TIM enables attaching GaN die directly onto a copper carrier. The heat spreading feature of the TIM can effectively dissipate heat near junction and greatly reduce the maximum heat flux, which leads to smaller temperature difference across each layer underneath of the TIM. A preliminary demonstration of the technology on a GaN-on-Silicon device shows 50% higher heat dissipation capability, compared to the state-of-the-art pin fin cold plate liquid cooling, while maintaining the device junction temperature at 150°C.

The self-heating effect has long been a persistent issue for high electron mobility transistors based on gallium nitride due to their inherently poor heat dissipation capability. Although a wide variety of thermal management solutions has to date been proposed, the problem of the extremely non-uniform heat dissipation at the micrometer scale is still challenging. It has recently been demonstrated, however, that the performance of gallium nitride high electron mobility transistors can be substantially improved by the introduction of various heat-spreading elements based on graphene, boron nitride or diamond. In this paper, using numerical simulation, we carried out a design optimization procedure for a normally-off gallium nitride high electron mobility transistor containing both graphene and cubic boron nitride layers. First, a screening experiment based on a very economical Plackett-Burman design was performed in order to find the most critical geometric parameters that influence the dc characteristics. After that, a full two-level factorial experiment consisting of three factors was implemented and an optimized parameter set was yielded. By applying this set, the output power was increased by 11.35%. The combination of the most significant parameters does not include any factors related to the heat-spreading layers. Keywords: gallium nitride, high electron mobility transistor, optimization, Plackett-Burman design, screening experiment, self-heating.

A low noise amplifier (LNA) is the first active stage in a receiver, which plays a key role in the entire receiver. In this paper, LNAs with three different kinds of devices - enhancement mode (E-mode) Gallium Arsenide (GaAs) pseudomorphic high electron mobility transistor (PHEMT), depletion mode (D-mode) Gallium Nitride (GaN) high electron mobility transistor HEMT, and Silicon-On-Insulator (SOI) CMOS- are designed, simulated, analyzed and compared. For a fair comparison, the LNAs of the same circuit topology are built up with noiseless matching components, and their performances are compared in the terms of both important specifications and a universal Figure of Merits (FOM). The simulation results show that: the LNA with using E-mode GaAs PHEMT achieves the lowest noise figure (NF) of 0.51 dB while the SOI-CMOS gets the best FOM of among the three devices. To our limited knowledge, this paper is one of few attempts to compare devices' capabilities in building up wide bandwidth LNAs with resistor feedback networks.

An average power tracking (APT) Doherty power amplifier (PA) is analyzed in terms of its biasing voltage condition, efficiency, and output power. And the drain and gate bias voltages are optimized for operation at different output power conditions. The Doherty power amplifier is designed using 45 W gallium nitride (GaN) high electron mobility transistors (HEMT) for the carrier and peaking cells at 1.94 GHz. The bias voltages are controlled for each average power level(42.9 dBm, 39.9 dBm, 37 dBm). The measured drain efficiencies and gains are 53.2%, 12.8 dB at 42.9 dBm and 54.3%, 11.2 dB at 39.9 dBm and 53.4%, 9.1 dB at 37 dBm for a 10 MHz LTE signal with a 6.5 dB PAPR. This result demonstrates that the Doherty PA can be reconfigured for different average output powers using the bias voltage control method.

In this paper, Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT) based S-band power amplifier design, simulation, fabrication, assembly and RF testing have been discussed. This power amplifier is capable of giving an output power ~8 watts in 3.3–3.5 GHz frequency range with a PAE greater than 90 %.

In this paper, a new three-level boost (TLB) converter built with Gallium Nitride (GaN) high electron mobility transistors (HEMTs) and Silicon Carbide (SiC) Schottky diodes is presented. The proposed converter has a continuous input current, wide gain range, reduced voltage stress (compared to other TLB converters in literature), and a common ground. The reduction of voltage stress on the power switches enables the utilization of transistors with less rated voltage, hence, the efficiency is enhanced. The operation of this converter at wide range of modulation index values is discussed. The proposed converter is a good candidate for applications that require a universal input such as renewable energy systems, and fuel cell vehicles. The experimental results verify the theoretical analysis and the feasibility of the proposed topology.

With the increased power density of gallium nitride (GaN) high electron mobility transistors (HEMTs), effective cooling is required to eliminate the self-heating effect. Incorporating diamond into GaN HEMT is an alternative way to dissipate the heat generated from the active region. In this review, the four main approaches for the integration of diamond and GaN are briefly reviewed, including bonding the GaN wafer and diamond wafer together, depositing diamond as a heat-dissipation layer on the GaN epitaxial layer or HEMTs, and the epitaxial growth of GaN on the diamond substrate. Due to the large lattice mismatch and thermal mismatch, as well as the crystal structure differences between diamond and GaN, all above works face some problems and challenges. Moreover, the review is focused on the state-of-art of polycrystalline or nanocrystalline diamond (NCD) passivation layers on the topside of GaN HEMTs, including the nucleation and growth of the diamond on GaN HEMTs, structure and interface analysis, and thermal characterization, as well as electrical performance of GaN HEMTs after diamond film growth. Upon comparing three different nucleation methods of diamond on GaN, electrostatic seeding is the most commonly used pretreatment method to enhance the nucleation density. NCDs are usually grown at lower temperatures (600–800 °C) on GaN HEMTs, and the methods of “gate after growth” and selective area growth are emphasized. The influence of interface quality on the heat dissipation of capped diamond on GaN is analyzed. We consider that effectively reducing the thermal boundary resistance, improving the regional quality at the interface, and optimizing the stress–strain state are needed to improve the heat-spreading performance and stability of GaN HEMTs. NCD-capped GaN HEMTs exhibit more than a 20% lower operating temperature, and the current density is also improved, which shows good application potential. Furthermore, the existing problems and challenges have also been discussed. The nucleation and growth characteristics of diamond itself and the integration of diamond and GaN HEMT are discussed together, which can more completely explain the thermal diffusion effect of diamond for GaN HEMT and the corresponding technical problems.

Dynamic ON-resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {on}}{)}$ </tex-math></inline-formula> or threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}{)}$ </tex-math></inline-formula> instability caused by charge trapping is one of the most crucial reliability concerns of some gallium nitride (GaN) high-electron mobility transistors (HEMTs). It has been unclear if this issue can be resolved using an alternative GaN device architecture. This work answers this question by characterizing, for the first time, 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">${R} _{\text {ON}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> stability of an industrial vertical GaN transistor-NexGen’s 1200-V/70- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega $ </tex-math></inline-formula> fin-channel junction-gate field-effect transistor (JFET), fabricated on 100-mm bulk GaN substrates. A circuit setup is deployed for the in situ measurement of 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">${R}_{\text {on}}$ </tex-math></inline-formula> under steady-state switching. The longer term stability of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {on}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> is tested under the prolonged stress of negative gate bias and high drain bias. The vertical GaN JFET shows nearly no <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {on}}$ </tex-math></inline-formula> or <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> shift in these tests, which could be attributed to the low defect density of the GaN-on-GaN homoepitaxial growth, the absence of electric field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}$ </tex-math></inline-formula> -field) crowding near the surface, and the minimal charge trapping in the native junction gate. These results present a critical milestone for vertical GaN devices toward power electronics applications.

This letter reports a high-efficiency gallium nitride (GaN) high-electron mobility transistor (HEMT) Doherty power amplifier (DPA) based on the class-E topology for wideband code-division multiple-access (WCDMA) applications. The class-E topology is employed as the carrier and peaking cells of the Doherty configuration. For validations, the proposed DPA is designed and implemented with 25-W GaN HEMTs at 2.14 GHz. For the proposed DPA, the power-added efficiency (PAE) and drain efficiency of 56.1% and 61.2% are achieved at 40 dBm (6-dB backoff power from Psat) for a continuous wave. For a 1-carrier WCDMA signal, the PAE of 44.8% is obtained with an adjacent channel leakage ratio (ACLR) of -31 dBc at 37 dBm, which is an 8.9% improvement over the conventional DPA with an ACLR of -36.4 dBc.

The development of high-quality gallium nitride (GaN) high electron mobility transistors (HEMTs) has provided opportunities for the next generation of high-performance radio frequency and power electronics. Operating devices with smaller length scales at higher voltages result in excessively high channel temperatures, which reduce performance and can have detrimental effects on the device's reliability. The thermal characterization of GaN HEMTs has traditionally been captured from either the top or bottom side of the device. Under this configuration, it has been possible to map the lateral temperature distribution across the device with optical methods such as infrared and Raman thermometry. Due to the presence of the gate metal, however, and often also the addition of a metal air bridge and/or field plate, the temperature of the GaN channel under the gate is typically inferred by numerical simulations. Furthermore, measuring the vertical temperature gradient across multiple epitaxial layers has shown to be challenging. This study proposes a new cross-sectional imaging technique to map the vertical temperature distribution in GaN HEMTs. Combining advanced cross-sectioning processing with the recently developed near bandgap transient thermoreflectance imaging technique, the full transient thermal distribution across a GaN HEMT is achieved. The cross-sectional thermal imaging of the GaN channel is used to study the effects of biasing on the Joule heating profile. Overall, the direct measurement of the GaN channel, capturing both the vertical and lateral gradient, will provide deeper insight into the device's degradation physics and supply further experimental data to validate previously developed electrothermal models.

This paper describes a simple, EM-based approach to accurately predict the frequency behavior of a custom common-gate (CG) Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT) starting from a similar device, but in the most frequently available standard common-source (CS) configuration. The proposed approach exploits electromagnetic (EM) simulations and measured scattering parameters of the reference CS device to represent its extrinsic and intrinsic sections, respectively. Then, the frequency behavior of the CG device is obtained by combining the CS intrinsic section data with the information extracted from the EM simulations of the passive parts of the CG layout. In particular, an 8×130 μm CS GaN HEMT has been adopted as reference device to predict the behavior of an 8×150 μm GaN HEMT in a custom CG configuration. Experimental results confirm the ability of the proposed method to accurately predict the behavior of the custom CG device up to 30 GHz.

본 논문은 GaN(Gallium Nitride) HEMT(High Electron Mobility Transistor) die를 이용하여 S-대역 내부 정합형 전력 증폭기 설계, 제작 그리고 실험 결과에 대해 기술하였다. S-대역 내부 정합형 전력 증폭기를 설계하기 위하여 고유전율을 가지는 기판과 알루미나 기판을 이용하여 입/출력단 정합 회로를 설계 및 제작하였다. 측정 결과로는 펄스 모드로 동작시켰을 때 3 GHz에서 55.4 dBm의 출력 전력, 78 % 드레인 효율 그리고 11 dB의 전력 이득을 얻었다. This paper presents the design, fabrication and measurement results of a S-band internally-matched power amplifier using Gallium Nitride High Electron Mobility Transistor(GaN HEMT) die. In order to fabricate the S-band internally-matched power amplifier, a high dielectric substrate and alumina were used for input/output matching circuits. The measured output power is 55.4 dBm, the drain efficiency is 78 % and the power gain is 11 dB under pulse operation at the frequency of 3 GHz.

Understanding the cryogenic performance of Gal-lium Nitride (GaN) devices is essential for determining their suitability for use in the electrification of large-scale transport such as aircraft, where the power electronics may need to withstand cryogenic temperatures. In this paper we investigate the temperature relationship of the channel on-resistance and gate threshold voltage of various GaN devices, using liquid nitrogen as an inexpensive and effective cryogenic medium. Two cascode-configuration high electron mobility transistors (Cascode HEMT) and two enhancement mode high electron mobility transistors (E-HEMT) devices, each from different manufacturers were selected to ensure a range of technologies were covered. The on-resistance of GaN devices was found to decrease approximately linearly with reducing temperature, until a knee-point is reached whereupon the on-resistance rises. One E-HEMT device did not reach a knee point, indicating the need for further testing at lower temperatures to determine whether, or where such a knee point exists. The device with the lowest normalised on resistance at -196.6°C exhibited 32.8% of its room temperature value, while the device with the highest normalised on resistance showed 89.3% of its room temperature value. It was also found that the gate thresh-old voltage shows temperature dependency. For both Cascode manufacturers, the threshold voltage increased linearly with decreasing temperature. For one of the E-HEMTs the threshold voltage increased non-linearly with decreasing temperature. For the other E-HEMTs the threshold voltage decreased linearly with decreasing temperature. Initial results indicate that GaN devices are compatible with operation in or near cryogenic environments. Further characteristics need investigation to fully confirm suitability. Output characteristics, as well switching rise and fall times may change in cryogenic conditions, potentially affecting suitability.

Gallium nitride high electron mobility transistors (HEMTs) have shown the potential to be highly resistant to radiation damage, making them ideal for use in microwave power amplifiers and DC/DC converters in space-based applications. To investigate the mechanisms of radiation-induced degradation in AlGaN/GaN HEMTs, 2MeV protons were used to simulate the space radiation environment, and to probe the second order effect of inherent material defects on the response the initial material quality was intentionally varied by studying HEMTs on sapphire, Si, and SiC substrates. Irradiation was performed incrementally up to a fluence of 6x1014 cm-2. The Hall mobility and 2DEG density was measured on Van der Pauw structures before irradiation and at each dose. The decrease in mobility can be attributed to increased carrier scattering in the 2DEG as a result of radiation-induced defects while the decrease in sheet carrier density is attributed to screening of the 2DEG from charged trap formation [1]. The magnitude of change in the 2DEG density is the same for all substrate materials (1x1012 cm-2), though the percent change varies due to different initial values. Note that mobility begins to degrade at lower fluence than sheet carrier density. FET I-V analysis indicated increased ON-resistance and decreased saturation current, consistent with the reduced mobility and sheet carrier density observed in the Hall measurements. The off-state leakage current decreased and threshold voltage was shifted slightly positive, again due to the reduced 2DEG density. The trapping mechanisms were further probed using pulsed I-V measurements at varying quiescent bias conditions. While the dynamic ON-resistance degradation under quasistatic conditions was consistent with DC measurements, the degradation under off-state stress conditions initiated at a lower fluence, and a culminated with a 10X higher degradation at the final fluence. This implies that dynamic ON-resistance, a parameter related to charge trapping, is much more sensitive to radiation than DC characteristics and must be considered when evaluating the radiation hardness of HEMT devices. TEM imaging was employed to directly probe the mechanisms suggested by the electrical measurements. Process-induced defects were visible in both reference and irradiated samples, notably an overflow of Au in the metal stack at the gate edge, possibly related to PECVD deposition of passivation layers. In addition a new, radiation-induced void at both edges of the gate in the Ni region of the Ni/Au gate metallization was revealed [2]. EDS line scans indicate that, after radiation, the 20 nm Ni layer diffused up into the Au, and to a lesser extent, into the AlGaN, leaving voids protruding ~300 nm under the gate edges. The mechanism of the void formation shows all features of Ni/Au inter-diffusion through vacancy exchange, known as the Kirkendall effect. The exact process is still under investigation, but the voids result in reduced gate area, which is responsible for the degraded off-state performance. It is particularly rare that such pronounced diffusion occurs at room temperature. Since the voids only occur at the gate edges, an additional electrochemical or strain-induced driving force is likely present. Therefore the role of the SiNx passivation layer, as well as strain, at the gate edge will be factor in this ongoing research. 1. T.J. Anderson, et. Al. IEEE Electron Dev. Lett. 35 (8), 826-828 (2014) 2. A.D. Koehler, et. Al. IEEE Electron Dev. Lett. 35 (10) (2014)