Simulation model development and verification for high voltage GaN HEMT in cascode structure

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.

This paper reports a detailed analysis of the performance and stability of E-mode GaN HEMTs under soft and hard switching conditions. We developed a novel on-wafer setup that controls the overlapping between the gate and drain pulses and, simultaneously, senses the current at the source. This allowed us to plot the instantaneous power, the switching I-V locus and evaluate the switching losses on wafer level. The dynamic on-resistance RDS,ON is evaluated during hard and soft switching at room temperature and high temperature. The results demonstrate that (i) the properties of the buffer impact on dynamic-Ron, in soft- and hard-switching; devices with non-optimized buffer have stronger dynamic-Ron under hard switching; (ii) Ron-increase under hard switching is not strongly influenced by switching (power) losses; (iii) results indicate that a higher dynamic-Ron in hard switching is correlated to a wider switching locus. The proposed testing approach can be used as a screening tool to evaluate - in one single measurement - the switching losses, the dynamic-Ron and the impact of hard-switching on wafer level.

Background: The upsurge in the field of radio frequency power electronics has led to the involvement of wide bandgap semiconductor materials because of their potential characteristics in achieving high breakdown voltage, output power density, and frequency. III-V group materials of the periodic table have proven to be the best candidates for achieving this goal. Among all the available combinations of group III-V semiconductor materials, gallium nitride (GaN), having a band gap of 3.4eV, has gradually started gaining the confidence to become the next-generation material to fulfill these requirements. Objective: Considering the various advantages provided by GaN, it is widely used in AlGaN/GaN HEMTs (High Electron Mobility Transistors) as their fundamental materials. This work aimed to review the structure, operation, and polarization mechanisms influencing the HEMT device, different types of GaN HEMT, and the various process technologies for developing the device. Methods: Various available methods to obtain an enhancement type GaN HEMT are discussed in the study. It also covers the recent developments and various techniques to improve the performance and device linearity of GaN HEMT. Conclusion: Despite the advantages and continuous improvement exhibited by the GaN HEMT technology, it faces several reliability issues, leading to degradation of device performance. In this study, we review various reliability issues and ways to mitigate them. Moreover, several application domains are also discussed, where GaN HEMTs have proven their capability. It also focuses on reviewing and compiling the various aspects related to the GaN HEMT, thus providing all necessary information.

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.

The single event effect (SEE) and the total ionizing dose (TID) effect of a commercial enhancement mode gallium nitride (GaN) high electron nobility transistor (HEMT) with p-type gate structure and cascode structure are studied by using the radiation of heavy ions and <sup>60</sup>Co gamma in this paper. The safe operating areas ofSEE, the sensitive parameters degradation of TID effect and the SEE and TID characteristics of GaN HEMT device are respectively presented. The experimental results show that the SEE and TID effect have less influence on the p-type gate GaN device. The linear energy transfer (LET) threshold of the single event Burnout effect (SEB) is higher than 37 MeV·cm<sup>2</sup>/mg and the failure threshold of TID effect is above 1M rad (Si) for p-type gate GaN device. However, the GaN HEMT device with cascode structure is much more sensitive to SEE and TID effect than p-type gate GaN device. Under heavy ions at LET of 22 MeV·cm<sup>2</sup>/mg and a cumulative dose of 200 krad (Si), the SEB phenomenon and parameters-degradation of cascode-type GaN HEMT are respectively observed. Besides, the circuit structure of the cascode-type GaN HEMT device is analyzed by using metallographic microscope imaging and focused ions beam technology. It reveals the possible reason why it is sensitive to SEB and TID for cascode-type GaN HEMT. These results show that the extra carriers caused by heavy ion radiation can tunnel the Schottky barrier formed by gate metal and AlGaN layer, leading to a large source-drain current in GaN HEMT device. Meanwhile, it is shown that the metal oxide semiconductor field-effect transistor in cascode circuit for TP90H180PS GaN HEMT may be the main reason why the cascode-type GaN HEMT is sensitive to TID.

AlGaN/GaN high-electron-mobility transistors (HEMTs) for applications in radiation environments has required the exact determination of their radiation hardness. Although bulk GaN is the preferred substrate for the epitaxial growth of GaN and AlGaN, (111) silicon is a possible substrate for HEMT devices. The stability of electrical parameters of enhancement-mode (E-mode) GaN HEMTs under gamma irradiation is an essential characterization for reliability. The present work reports the transfer characteristics degradation of E-mode GaN HEMTs under various total dose irradiation from 5krad up to 60Mrads. This represents the first comprehensive total dose study ranging from a few krads up the tens of Mrads. The measured device-to-device variations within groups of devices are presented. The evolutions of critical DC parameters with accumulated total dose is found to be significant at low doses and saturates at high dose levels. The degradation mechanism is very similar to the reported radiation-induced shallow electron traps that trap and release electrons in the near surface GaN and AlGaN layers. Due to the unique properties including high breakdown voltage, high electron mobility and high thermal stability, wide-bandgap semiconductor power electronic devices, especially Gallium Nitride (GaN) high-electron-mobility transistors (HEMTs), have shown great promise in space, defense and nuclear applications, which often involve radiation-hardened electronics that require high radiation tolerance to fluxes of neutrons or gamma ray of devices. To turn the promising potential of GaN HEMTs into reality, investigations on the influence of irradiation on the device performance and reliability are essential. Many studies have investigated the radiation hardness of group III–nitride compound semiconductor devices under various irradiation types, such as electrons, protons, neutrons, and X-rays and at various total irradiation doses. They generally showed higher radiation tolerance compared with Si because of high displacement energy of GaN, demonstrating the favorability of GaN devices in hard radiation environments. Many studies have investigated the influence of 60Co gamma radiation on the device electrical characteristics. However, they were all focusing on depletion mode (D-mode) devices. Enhancement mode (E-mode) GaN-on-Si transistors have been commercially available for years. Their major advantages over D-mode devices are elimination of negative voltage supply and the enabling of direct-coupled FET logic (DCFL) for digital circuits. They also improve the efficiency of commercial DC-DC converters in various power levels and topologies. A previous work on gamma radiation of E-mode GaN-on-Si HEMTs only reported cumulative total doses of up to 1 Mrads (Si). The present work provides a complete coverage of low-to-high irradiation doses from 5krads up to 60Mrads (Si), for commercially available E-mode GaN HEMTs and the devices are characterized to gauge variations in the critical DC parameters. To the best of the author’s knowledge, the present work is the first to investigate the gamma radiation tolerance of E-mode GaN HEMTs covering such a wide range of total doses. This facilitates the observation of the complete degradation behavior of DC parameters in hard radiation applications of the E-mode GaN HEMTs. The devices were supplied in the form of 0.9mm square passivated die with round solder bumps for contacts. They have a rated continuous drain-to-source voltage VDS of 60V, and a rated continuous drain current ID of 1A. These GaN-on-Si devices were fabricated on Si wafers considering process compatibility and cost. An aluminum nitride (AlN) thin layer was grown on the Si wafer to be a seed layer for the AlGaN/GaN heterostructure. Subsequently, the AlGaN/GaN heterostructure was grown on the AlN layer, with a thin AlGaN layer grown above the highly resistive GaN serving as a strained interface between the GaN and AlGaN crystal layers, allowing the creation of a two-dimensional electron gas (2DEG) filled with abundant free electrons with ultra-high mobility. The gate electrode was processed subsequently forming a depletion region under the gate. As an E-mode transistor, the device is turned on by applying a positive bias to the gate. All the irradiations were conducted at room temperature by 60Co gamma-rays with a flux of 318.5Rads (Si)/s, at the dry-cell panoramic gamma irradiator in the University of Maryland Radiation Facilities. The entire irradiation procedure consists of two parts. The first part is higher-dose irradiation with total doses of up to 60Mrads based on two stages. At the first stage, the devices were irradiated at 10Mrads, while at the second stage, the devices were irradiated for another 50Mrads, with three of them taken out after 25Mrads during the second stage. The second part is lower-dose irradiations with total doses of up to 2Mrads. The temperature throughout the irradiation process was monitored to be below 30°C.

With Gallium Nitride (GaN) device technology for power electronics applications being ramped up for volume production, an increasing amount of research is now focused on the performance of GaN power devices in circuits. In this study, an enhancement mode GaN high electron mobility transistor (HEMT) is switched in a clamped inductive switching configuration with the aim of investigating the source of oscillatory effects observed. These arise as a result of the increased switching speed capability of GaN devices compared to their silicon counterparts. The study identifies the two major mechanisms (Miller capacitance charge and parasitic common source inductance) that can lead to ringing behaviour during turn-off and considers the effect of temperature on the latter. Furthermore, the experimental results are backed by SPICE modelling to evaluate the contribution of different circuit components to oscillations. The study concludes with good design techniques that can suppress the effects discussed.

Compared with silicon, GaN has advantages such as high electron mobility large band gap and high breakdown field strength. Therefore, GaN High Electron Mobility Transistors (HEMT) is resistant to high voltage and high temperature, and GaN HEMT performs well in high-frequency and high-power fields. Enhancement mode GaN HEMT is more suitable for most applications than depletion mode GaN HEMT due to enhancement mode GaN HEMT’s normally-off characteristic. This paper introduces cascode structure GaN HEMT and p-GaN gate structure GaN HEMT, as well as two improved structures, monolithically integrated Si-GaN cascoded FET and Hybrid Drain embedded Gate Injection Transistor, then compares the four structures and analyzes the advantages and disadvantages. Because of the unique advantages of GaN HEMT, many industries that require the use of high-frequency devices or high-power devices are very interested in the application research of GaN HEMT. This paper mainly introduces the research progress of GaN HEMT’s application in the three fields of radio frequency amplifiers, charger circuits, and LiDAR drivers, and the paper summarizes the advantages and current challenges of GaN HEMT, as well as the future of GaN HEMT’s development and application.

Embedding is a technology which permits to build highly integrated, compact power sections. It also helps to minimise parasitic elements within the power sections, this way facilitating the use of novel, fast switching devices like gallium-nitride (GaN) high electron mobility transistors (HEMTs). This paper deals with required processes and the development of a power section with GaN HEMTs for a three phase drive inverter with a nominal power in the lower kW range; a version with discrete devices has also been built as a benchmark for the embedded solution.

GaN high electron mobility transistors (HEMTs) on SiC substrates are produced for both commercial and defense applications that require high voltage, high power, and high efficiency operation. Although leading GaN HEMT manufacturers have reported excellent RF power characteristics and encouraging reliability, long-term reliability in the space environment remains a major concern due to unknown degradation mechanisms. For the present study, we investigated stressed/degraded RF GaN HEMTs using micro-analytical techniques. Our RF AlGaN-GaN devices grown on SiC substrate had a Ni-Pd-Au Schottky gate length of 0.25 μm, a total gate width of 6 × 150 μm periphery, and a field plate. First, we performed DC bias-temperature stress tests on GaN HEMTs and some GaN HEMTs were thermally stressed as monitor samples. Second, we employed focused ion beam (FIB) to prepare TEM cross sections from degraded and monitor devices for defect analysis using a high resolution TEM. Defects containing highly Pd-enriched features were found at the edge of the drain side of the gate. We present our detailed analysis results including our understanding on the out-diffusion of Pd as a potential degradation mechanism in our RF devices.

The aim of this paper is to improve the understanding of gallium nitride (GaN) high electron mobility transistors (HEMTs) submitted to hard switching operation, with focus on the hot-electron phenomena. This is becoming a hot-topic both for the scientific community and for the industry. The analysis is carried out through a cross-comparison of three different experimental techniques: conventional Pulsed-IV characterization, a novel pulsed-drain current transient (P-DCT) method, and a custom-developed hard switching test protocol. Hard switching analysis was performed through a novel system able to test the device in hard-switching conditions with an unprecedented turn-on slew-rate of 25 V ns−1 on-wafer level. This allows μs to investigate the impact of hard switching in terms of (i) locus trajectory, (ii) dissipated power, and (iii) dynamic increase. Furthermore, the accumulation of switching stress is assessed by repeating the experiment with increasing frequency, from 1 kHz to 100 kHz. The extensive cross-analysis offers a novel insight on the degradation mechanisms occurring in power GaN HEMTs. The results collected within this paper allow: (1) to evaluate the dynamic behavior under both soft- and hard-switching stress, thus differentiating off-state and semi-on-state stress; (2) to pinpoint hot-electrons as the main cause of the current collapse observed in semi-on; (3) by comparing the results obtained from P-DCT and Hard Switching Analysis we demonstrate that the hot-electron trapping is a very fast process which can happen in few ns. The related trapping and de-trapping kinetics are investigated in detail. The results described within this paper provide novel insight on the important role of hot-electrons in the dynamic increase during hard switching operations.

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 investigates the switching performance of a 1.2 kV half-bridge SiC MOSFET module from Sanrex. Unlike in a standard SiC MOSFET module, where the MOSFET and the anti-parallel diode chips are fabricated separately, in the chosen MOSFET module (FCA150XB120), both the MOSFET and the diode are fabricated on a single chip. The device is characterized under both hard and soft switching conditions. For the hard switching characterization, an inductive clamped buck converter is employed, whereas for the soft switching characterization, a resonant half-bridge converter with LC load is used. A comparison of the hard switching loss is performed with the soft switching loss at the same current. This comparison provides insight into the significance of employing an appropriate circuit topology, load and control scheme to reflect the waveforms as in a real application, in order to get a more accurate assessment of the switching losses that will occur. This insight is the main contribution of this paper.

To address the accuracy limitations of the traditional double pulse test (DPT) for measuring switching losses in high-speed gallium nitride (GaN) devices and the slow measurement speed of conventional calorimetric methods, this paper proposes a fast and accurate calorimetric-based method for characterizing GaN switching losses. Compared to DPT, this method allows rapid and faithful measurement of switching losses under both soft- and hard-switching conditions. A testing measurement platform was developed, which confirmed that this method can collect temperature data in 5 minutes or less by characterizing the switching losses of top-side cooled GaN devices. Achieve a measurement error of less than 9% compared to DPT. It can be used as a supplementary method to verify the accuracy of DPT. The combination of the two methods can achieve cross-validation, significantly improving the reliability of GaN device switching loss measurement results.

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.