GaN HEMT Research Articles

Investigation of Interlayer Dielectric in BaTiO3/III‐Nitride Transistors

In this study, the impact of varying the thickness of the Al2O3 interlayer dielectric on the electrical characteristics of BaTiO3/III‐nitride transistors is investigated. In the findings, it is revealed that a minimum thickness of 8 nm for the Al2O3 layer is crucial to maintain high device performance and protect against sputtering‐induced damage during BaTiO3 deposition. The fabricated BaTiO3/Al2O3/AlGaN/GaN high electron mobility transistors exhibit exceptional electrical properties, including a maximum current density of 700 mA mm−1, an on‐resistance of 5 Ω mm, an ION/IOFF ratio of 107, a subthreshold slope of 119 mV dec−1, and significantly reduced gate leakage current. The devices with the optimal 8 nm Al2O3 thickness demonstrates excellent agreement between theoretical and experimental values for effective mobility, achieving a value of 1188 cm2 V−1·s at a 2D electron gas density of 1013 cm−2. Furthermore, in the study, it is confirmed that increasing the Al2O3 thickness also improves the quality of interface charge density, as evidenced by the results obtained from capacitance–voltage measurements. In these findings, the critical role of controlling the Al2O3 thickness in optimizing the electrical characteristics and overall performance of BaTiO3/III‐nitride transistors are highlighted.

Design of a wideband, highly efficient FPA using an asymmetrical open-circuit coupled-lines-based filtering matching network

This study introduces a novel approach to designing a broadband, highly efficient filtering power amplifier (FPA) characterized by unique integrated filtering capabilities. Central to the proposed technique is the utilization of an asymmetrical open-circuit coupled-lines bandpass filter (BPF), serving dual functions as both an input matching network and an output matching network. Notably, this filter design not only enhances the bandpass filtering response but also significantly improves second harmonic rejection performance. To validate this methodology, a broadband FPA is implemented, employing the Cree 10 W GaN HEMT. The proposed FPA, operating between 2.0–3.0 GHz, achieves a peak drain efficiency of 45.9 %-73.26 %, corresponding to a peak output power of 38.5–41.95 dBm at saturation. This marks a notable efficiency enhancement compared to recent research findings. It is believed that the FPA solution is custom-tailored to meet the demanding requirements of modern base stations, striking the balance between improved power-efficiency and good filtering performance.

An improved small‐signal model for GaN HEMTs devices

AbstractAn improved small‐signal model applied to GaN‐based devices is presented in this article. The extrinsic elements of the equivalent circuit topology are extracted using the test structures and the cut‐off method. In order to obtain a good agreement between model simulations and measurements, distributed capacitive effects are taken into account. In addition, an inductance Lds is introduced based on the conventional intrinsic equivalent circuit topology. Good agreement between the modeled and measured S‐parameters is obtained for GaN HEMTs with a gate width of 2 × 100 μm (number of gate fingers × unit gate width) in the frequency range of 0.5–40 GHz.

Exploring the impact of AlGaN barrier thickness and temperature on normally-on GaN HEMT performance

We study varying barrier thicknesses in GaN/AlGaN HEMTs as well as the effect of temperature fluctuation on device functionality theoretically. Structures A, B, C, D, and E are designed each with barrier thickness 16 nm, 19 nm, 22 nm, 25 nm, and 28 nm respectively. The impact of barrier thickness on the surface barrier height, strain relaxation and 2DEG concentration is explained including GaN HEMT’s drain and transfer properties. At elevated temperatures, the polar-optical phonon dispersion is the predominant process. Yet, at lower temperatures, the interface-roughness (IFR) and alloy disorder dispersion both satisfactorily account for the calculated mobilities.

A new design approach of Rat-Race coupler based compact GaN HEMT power amplifier towards flat high efficiency over broadband

This paper presents a high efficiency Rat-Race Coupler based compact GaN HEMT power amplifier (PA) design over broadband for high power transmitter in wireless communication. The rat-race coupler integrated PA Compact design is proposed for the first time as per author best knowledge. The design methodology used a higher order two open stubs and a rat-race coupler (RRC) at input/output sections to control harmonics impedances. The RRC is used to enhance the i/o power, and efficiency over broadband, which provides a good insertion loss, and consumes the least power and non-crucial impedance bandwidth for the normalized frequency band of interest. As a proof of concept, a PA is fabricated using a monolithic microwave integrated circuit (MMIC) 0.15 µm gallium nitride high electron mobility transistor (GaN HEMT) process. The measured result shows that the designed PA achieves a flat power added efficiency (PAE) of 65 % − 74 %, output power (Pout) of 44.8 dBm − 46 dBm, and drain efficiency (DE) of 72 % − 85 %, over a record wide frequency of 1.8 GHz − 3.6 GHz, which is the highest one among all reported harmonic tuned PAs.

Analysis of the Influence of Temperature on Stress Waves of Cascode GaN HEMT

Analysis of the Influence of Temperature on Stress Waves of Cascode GaN HEMT

A compact Non-Quasi-Static small-signal model for GaN HEMT

In this work, we introduce a compact Non-Quasi-Static (NQS) model for the long-channel Gallium nitride high-mobility field effect transistor based on charge-based EPFL (École Polytechnique fédérale de Lausanne) HEMT model implemented in Verilog-AMS modeling language. The proposed model has been validated for the low-frequency (quasi-static) operating region as well as high frequencies up to sub-terahertz. This model has been derived from the analytical solution of the drift–diffusion and continuity equations based on physically valid assumptions. Polynomial approximation was used to make the model design-oriented and compatible with conventional circuit simulators for designing microwave circuits. Intrinsic trans-admittance parameters, obtained from the model for two devices with channel lengths of 1μm and 10μm has been validated with TCAD simulation results. Besides, the scattering parameters for the GaN HEMT equivalent circuit, have been validated with TCAD simulations and with our previous work, which already validated with experimental data. These results confirm the effectiveness of the proposed compact model for circuit simulations.

Robust Ku-Band GaN Low-Noise Amplifier MMIC

This paper employs the 0.2 μm ETRI GaN HEMT process on SiC to develop a Ku-band GaN low-noise amplifier monolithic microwave integrated circuit (MMIC) characterized by high-input power robustness for radar transceiver modules. A source degeneration inductor is employed to obtain the proposed amplifier’s stable operation and the compromised impedance trajectory of the maximum available gain and minimum noise figure. The analysis results show simultaneous gain and noise impedance matching, achieved using only a small number of passive elements. Furthermore, the proposed low-noise amplifier MMIC secures a linear gain of 21.3−22.6 dB, an input return loss of 19.6−21.4 dB, and a noise figure of 1.7−1.8 dB in the 15–16 GHz frequency range. It also exhibits an input 1 dB compression point of 0.4−1.5 dBm in the single-tone power test, and an input third-order intercept point of 5.8−10.1 dBm within the 15−16 GHz frequency range in the two-tone intermodulation distortion test.

Raman Spectroscopy Analysis for Precise Channel Temperature Estimation in AlGaN/GaN HEMT Devices

In recent years, high-electron-mobility GaN HEMTs have demonstrated significant advancements in applications such as power converters and RF amplifiers. Nevertheless, their thermal reliability poses a notable challenge, placing constraints on their power-handling capacities. This study employs micro-Raman spectroscopy to evaluate the localized self-heating-induced channel temperature. The channel temperature, determined using the single phonon modes of GaN HEMT (E2(H) & A1(LO)), exhibits discrepancies and does not align with device temperature values calculated using the SiC phonon peak near the GaN channel. However, by employing both phonon modes of GaN to decouple the combined effects of joule heating and the thermoelastic effect, accurate channel temperature values are obtained, matching well with those obtained from the SiC phonon peak. The agreement between calculated temperatures from phonon modes and those obtained by heating the device from the back side enhances the credibility of the proposed method.

Nonlinear Capacitance Compensation Method for Integrating a Metal–Semiconductor–Metal Varactor with a Gallium Nitride High Electron Mobility Transistor Power Amplifier

A nonlinear capacitance compensation technique is presented in this paper to enhance the linearity of a power amplifier (PA) in the GaN process. The method involves placing an MSM varactor device alongside the GaN HEMT device, which works as the amplifying unit such that the overall capacitance observed at the amplifier input is constant, thus improving linearity. This approach is a reliable and straightforward way to improve PA linearity in the GaN process. The proof-of-concept prototype in this study involves the fabrication of a PA device using a standard GaN HEMT process, which successfully integrates the proposed compensation technique and demonstrates excellent compatibility with existing processes. The prototype has a saturation output power of 18 dBm, a peak power-added efficiency of 51.8%, and a small signal gain of 15.5 dB at 1 GHz. The measured AM–PM distortion at the 5 dB compression point is reduced by more than 50% compared to that of an uncompensated device. Furthermore, the results of third-order intermodulation distortion demonstrate the effectiveness of the linearity enhancement concept, with values improved by more than 5 dB in the linear region compared to those of the uncompensated device. All of the results demonstrate the potential utility of this design approach for wireless communication applications.

Highly Reliable Short-Circuit Protection Circuits for Gallium Nitride High-Electron-Mobility Transistors

This paper presents a circuit for detecting and protecting against short circuits in E-mode gallium nitride high-electron-mobility transistors (GaN HEMTs) and analyzes the protection performance of the circuit. GaN HEMTs possess fast switching characteristics that enable high efficiency and power density in power conversion devices. However, these characteristics also pose challenges in protecting against short circuits and overcurrent situations. The proposed method detects short-circuit events by monitoring an instantaneous drop in the DC bus voltage of a circuit with GaN HEMTs applied and uses a bandpass filter to prevent the malfunction of the short-circuit protection circuit during normal switching and ensure highly reliable operation. Using this method, the short-circuit detection time of E-mode GaN HEMTs can be reduced to 257 ns, successfully protecting the device without malfunctions even in severe short-circuit situations occurring at high DC link voltages.

A high-performance terahertz detector based on a graded channel GaN high-electron-mobility transistor with a recessed gate

A novel recessed gate graded AlGaN high-electron-mobility transistor (RGGA HEMT) for high-sensitivity terahertz (THz) detectors is reported, which exhibits significant potential for high-sensitivity THz detectors, and consequently. The simulation results indicate the exceptional field-effect factor of the proposed RGGA HEMT, which is largely attributed to the three-dimensional electron gas generated by the graded AlGaN barrier layer and the subsequent enhancement of channel conductance. The responsivity and noise equivalent power reach 58mA/W and 43pW/Hz respectively at 227GHz by utilizing a technical computer-aided design platform. As compared to conventional structure GaN HEMT experimental data, the current responsivity is improved by 2.64 times, and the NEP is reduced by 43.4%. The unprecedented improvement in detection performance renders the RGGA HEMT a highly promising approach for future THz real-time single-pixel imaging applications at room temperature.

Design of Inner Matching Three-Stage High-Power Doherty Power Amplifier Based on GaN HEMT Model.

This paper introduces the structure and characteristics of an internal-matching high-power Doherty power amplifier based on GaN HEMT devices with 0.25 μm process platforms from the Nanjing Electronic Devices Institute. Through parameter extraction and load-pull testing of the model transistor, an EE_HEMT model for the 1.2 mm gate-width GaN HEMT device was established. This model serves as the foundation for designing a high-power three-stage Doherty power amplifier. The amplifier achieved a saturated power gain exceeding 9 dB in continuous wave mode, with a saturated power output of 49.7 dBm. The drain efficiency was greater than 65% at 2.6 GHz. At 9 dB power back-off point, corresponding to an output power of 40.5 dBm, the drain efficiency remained above 55%. The performance of the amplifier remains consistent within the 2.55-2.62 GHz frequency range. The measured power, efficiency, and gain of the designed Doherty power amplifier align closely with the simulation results based on the EE_HEMT model, validating the accuracy of the established model. Furthermore, the in-band matching design reduces the size and weight of the amplifier. The amplifier maintains normal operation even after high and low-temperature testing, demonstrating its reliability. In conjunction with DPD (digital pre-distortion) for the modulated signal test, the amplifier exhibits extremely high linearity (ACLR < -50.93 dBc). This Doherty power amplifier holds potential applications in modern wireless communication scenarios.

Harmonic Included CSWPL Model for Broadband PA Design Based on GaN HEMTs

Harmonic Included CSWPL Model for Broadband PA Design Based on GaN HEMTs

Short-Circuit Failure Modes and Mechanism Investigation of Ohmic-Gate GaN HEMT

Short-Circuit Failure Modes and Mechanism Investigation of Ohmic-Gate GaN HEMT

Temperature Nonmonotonic Behavior of GaN HEMTs Kink Effect Caused by Trap-Assisted Impact Ionization

Temperature Nonmonotonic Behavior of GaN HEMTs Kink Effect Caused by Trap-Assisted Impact Ionization

Microwave and Millimeter-Wave GaN HEMTs: Impact of Epitaxial Structure on Short-Channel Effects, Electron Trapping, and Reliability

Microwave and Millimeter-Wave GaN HEMTs: Impact of Epitaxial Structure on Short-Channel Effects, Electron Trapping, and Reliability

A 3-D Integrated Power Module of GaN HEMTs Based on Silver Sintering Processes

A 3-D Integrated Power Module of GaN HEMTs Based on Silver Sintering Processes

Degradation of electrical performance and radiation damage mechanism of cascode GaN HEMT with 80 MeV proton

In this paper, proton irradiations on Cascode GaN HEMT power device with an energy of 80 MeV and fluences of 2 × 1011 p/cm2 and 6 × 1011 p/cm2 have been carried out, where the threshold voltages drifted negatively by 20.55% and 28.17%, respectively. After two months of room temperature annealing, the threshold voltages recovered 0.22 V and 0.27 V, respectively. The ionizing deposition energy (IEL) was simulated by using Monte Carlo software and TCAD, it the results showed that the value of IEL in Si MOSFET is 5 ∼ 6 orders higher than that in GaN HEMT, while the value of the non-ionizing energy loss (NIEL) is one order higher than that in GaN HEMT. It means that the proton irradiation on the Cascode depleted GaN HEMT is more prone to produce displacement damage. As a large number of electrons and holes pairs were existed on the incident path of Si MOSFET under the proton irradiation, the produced electron will be captured by the gate oxide traps at the SiO2/Si interface, and the holes be captured by the defects generated in displacement damage, resulting in the accumulation of oxide trapped charges. Then, the electrical performance of Si MOSFET degrades seriously, thereby affecting the performance of the entire device. The studies will be helpful for the radiation hardening of Cascode GaN HEMT.

Optimization of 150 nm GaN HEMT for Ku-band applications using field plate engineering

This work presents a systematic study to achieve the best result of having high breakdown voltage with high-frequency operation for a 150 nm GaN HEMT device (fabricated) using different field plate engineering techniques. The device breakdown voltage, cut-off frequency and maximum frequency should be high for high power and high frequency applications. The conventional device has a lower breakdown voltage but good cut-off and maximum frequency ranges. Field plate engineering has been done for breakdown improvement. However, the device's frequency operation is hampered by the typical source and gate field plate. As a result, an Air bridge source connected field plate and floating gate field plate architectures are explored and investigated. The best outcome is obtained with air bridge source connected field plate with VBOff = 100 V maintaining the cut-off frequency and maximum frequency at 29.8 GHz and 50.3 GHz respectively which is suitable for high power and high frequency applications.