A sampling scheme for three-phase high switching frequency and speed converter

In this paper, we present a new technique to unify and intensify the magnetic fields that results in higher performance of Anisotropic Magneto-Resistive (AMR) current sensors and consequently develop a closed loop controller for 100W synchronous GaN buck converter at 1MHz. The closed loop operation of high switching frequency converters at high power has always been a big challenge due to lack of access to current information. The proposed method that also intensifies the magnetic fields through the sensor, significantly improves the bandwidth limits, and reduces electromagnetic interference (EMI) on AMR sensors, making them applicable for high switching frequency and high current power electronics converters. After verifying uniform distribution concept through simulation, we also implemented a prototype of AMR current sensors onto Printed Circuit Board (PCB) for verification of the concept at high frequency converter. We then present the design procedure and associated challenges of an integrated analogue peak current controller for creating the closed loop operation of a GaN buck converter at high switching frequency.

The high electron mobility transistor (HEMT) based on Gallium nitride (GaN) is a new power switching device with high switching frequency, high temperature resistance and high voltage resistance, which has aroused wide research interests. However, a key question need to consider is that the breakdown voltage (BV) of the power AlGaN/GaN HEMT is far from the theoretical value. In this paper, the relationship between the breakdown voltage of AlGaN/GaN HEMT and the gate to drain distance (Lgd) and buffer layer thickness (T(buffer)) has been studied in theory. With the TCAD software, the effect of gate to drain distance on the breakdown voltage of AlGaN/GaN HEMT had been demonstrated. Further, after the breakdown voltage saturation, the relationship of breakdown voltage and buffer layer thickness was studied. The results demonstrate that the breakdown voltage of power AlGaN/GaN HEMT increases with the gate to drain distance, but it will be gradually saturate. Then, as the increase of buffer layer thickness, breakdown voltage will rise again. As a result, breakdown voltage of power AlGaN/GaN HEMT increases with the gate to drain distance rise up and is restricted by the thickness of the buffer layer.

This paper will revise, experimentally investigate, and discuss the main application challenges related to gallium nitride power semiconductors in switch-mode power converters. Gallium Nitride (GaN) devices are inherently gaining space in the market. Due to its high switching speed and operational switching frequency, challenges related to the circuit design procedure, passive component selection, thermal management, and experimental testing are currently faced by power electronics engineers. Therefore, the focus of this paper is on low-voltage (<650 V) devices that are used to assemble DC-DC and/or DC-AC converters to, for instance, interconnect PV generation systems in the DC and/or AC grids. The current subjects will be discussed herein: GaN device structure, the advantages and disadvantages of each lateral gallium nitride technology available, design challenges related to electrical layout and thermal management, overvoltages and its implications in the driver signal, and finally, a comprehensive comparison between GaN and Si technology considering the main parameters to increase the converters efficiency.

This paper explains the advantages of using Wide Bandgap (WBG) semiconductor made of Silicon Carbide (SiC) by the characterization of power efficiency and losses of SiC inverter of 15kVA/540V and the analysis of EMI and overshoot of commutation at high switching frequency. The measured power efficiency of inverter can be higher 99%. This inverter also implemented in to electromechanical chain to drive an aeronautic motor (type PMSM). However, faster switching (higher di/dt and dv/dt) of SiC inverter, at higher frequencies, it is necessary to identify the electromagnetic impact (EMI) and the overshoot switching voltage. The experimental results will be shown the interesting of this technology and the impact at high switching frequency.

Due to their superior material properties, wide bandgap (WBG) semiconductors enable the application of power electronics at higher temperature operation, higher frequencies, and higher efficiencies compared to silicon (Si). However, the commonly-used aluminum wire bonding as topside interconnection technology prevents WBG semiconductors from reaching their full potential, due to inherent parasitic inductances, large size, heat dissipation, and reliability issues of wire bonding technology. Therefore, this article presents a comprehensive review of topside interconnection technologies of WBG semiconductor power devices and modules. First, the challenges and driving factors for the interconnection of WBG semiconductor dies are discussed. Second, for each widely commercially used WBG semiconductor, i.e., silicon carbide and gallium nitride, technical details and innovative features of state-of-the-art interconnection techniques in packages are reviewed. Then, the majority of existing topside interconnection materials for WBG semiconductors are categorized and compared, followed by a discussion of their advantages, challenges, and failure modes. Based on this elaborate discussion, potential future directions of the interconnection technology development are given. It is concluded that the superior performance of WBG semiconductors can be obtained by combining novel materials with innovative designs for the topside interconnections.

Wide-bandgap power semiconductor devices offer enormous energy efficiency gains in a wide range of potential applications. As silicon-based semiconductors are fast approaching their performance limits for high power requirements, wide-bandgap semiconductors such as gallium nitride (GaN) and silicon carbide (SiC) with their superior electrical properties are likely candidates to replace silicon in the near future. Along with higher blocking voltages wide-bandgap semiconductors offer breakthrough relative circuit performance enabling low losses, high switching frequencies, and high temperature operation. ARPA-E’s SWITCHES program, started in 2014, set out to catalyze the development of vertical GaN devices using innovations in materials and device architectures to achieve three key aggressive targets: 1200V breakdown voltage (BV), 100A single-die diode and transistor current, and a packaged device cost of no more than ȼ10/A. The program is drawing to a close by the end of 2017 and while no individual project has yet to achieve all the targets of the program, they have made tremendous advances and technical breakthroughs in vertical device architecture and materials development. GaN crystals have been grown by the ammonothermal technique and 2-inch GaN wafers have been fabricated from them. Near theoretical, high-voltage (1700-4000V) and high current (up to 400A pulsed) vertical GaN diodes have been demonstrated along with innovative vertical GaN transistor structures capable of high voltage (800-1500V) and low RON (0.36-2.6 mΩ-cm2). The challenge of selective area doping, needed in order to move to higher voltage transistor devices has been identified. Furthermore, a roadmap has been developed that will allow high voltage/current vertical GaN devices to reach ȼ5/A to ȼ7/A, realizing functional cost parity with high voltage silicon power transistors.

MOSFETs built using wide band gap (WBG) materials offer numerous benefits to power electronic circuits. These benefits are quite apparent in applications requiring breakdown voltages ≥ 600V, where Silicon IGBTs are typically used due to their combination of high breakdown voltage and low conduction losses. Compared to Silicon IGBTs, WBG MOSFETs offer very short turn-ON and turn-OFF times, which reduce switching losses and enable significantly higher switching frequencies. This paper explores the application of WBG MOSFETs to motor drives, where higher switching frequencies reduce motor losses and torque ripple and allow higher control bandwidth, thus enabling greater output frequencies needed to operate motors at higher speeds. Specifically, two-level voltage source inverters utilizing Silicon Carbide (SiC) MOSFETs are constructed to operate a 1 HP induction motor. Experimental results are presented which show that the short turn-ON and turn-OFF transients as well as high switching frequencies lead to increased shaft voltage and conducted ground currents. Mitigation techniques are implemented and evaluated, including clamp-on ferrites and an open-end winding drive implementation. The shaft voltage and ground currents are found to be best suppressed in an open-end winding drive utilizing clamp-on ferrites.

Increasing the power density of PV inverters have been of great interest in the PV industry. With a smaller and lighter inverter, the installation cost can be greatly reduced, making solar energy more affordable. To improve the power density of PV inverters, a new internal parallel converter has been proposed in the literature and prototyped. This paper presents the key design considerations of the Gallium Nitride (GaN) based power stage as the high switching frequency (HSF) module in the modularized prototype. Two issues have been addressed in detail, i.e. the sizing of film capacitor based flying capacitor (FC) and design of GaN power board. A current stress based sizing has been investigated for FC indicating that the volume of the FC bank is dominated by the current stress instead of the switching frequency. Furthermore, design of the GaN power board based on insulated metal substrate (IMS) board has been discussed in detail. In addition to improved thermal performance, the metal substrate can serve as a shielding layer and help reducing the power loop parasitic inductance. Experimental results have confirmed that the designed GaN HSF module can safely operate under full power.

Devices based on wide bandgap (WBG) semiconductors like silicon carbide (SiC), gallium nitride (GaN), and gallium oxide (Ga2O3) are ideal for high-power electronics in harsh environments. Among the WBG semiconductors, ultrawide bandgap (UWBG) β-phase gallium oxide (Ga2O3), EG ≈ 4.8 eV, is emerging as a replacement for the current commercially available wide bandgap (WBG) power electronics due to its generational improvements in performance and manufacturing cost [1]. Ga2O3 has a high theoretical breakdown electrical field of 8 MV/cm which in turn gives its Baliga’s figure of merit for power devices that is larger than other WBG materials. The availability of high-quality Ga2O3 substrates produced from melt-grown bulk single crystals also facilitates the development of vertical power devices.In the current stage, the vertical Schottky barrier diode (SBD) with Ga2O3 can have an improved current spreading effect when compared to power diode devices from Si, SiC, and GaN. Especially, the Ga2O3 is expected to surpass the trade-off relationship between breakdown voltage (BV) and on resistance (Ron,sp) that other materials have [2]. Nevertheless, the Ga2O3 vertical SBD still cannot achieve the theoretical breakdown electric field. One of the key topics for WBG semiconductors application is a structure for improved electrical management such as field rings, junction termination extension, and field plates to reduce the leakage current in the reverse bias state.Here, we investigate the characteristics of Ga2O3 SBDs with and without mesa structure in extreme environments at high and low temperature. Conventional and mesa Ga2O3 SBDs were fabricated on the halide vapor phase epitaxy (HVPE) grown β-Ga2O3 (001). A Sn-doped substrate with 61016 cm-3 was used for the HVPE growth. In the SBD with mesa structure, the circular mesa with a diameter of 162 μm and a depth of 500 nm was formed around anode electrodes. The Ti/Au metal stack on the back side of the substrate acted as a cathode and the anode electrode deposited Ni/Au/Pt layers. After the fabrication process, current-voltage (I-V) measurements were performed on the SBDs between -5 V and 1 V. From the results, the values of Ron,sp at 0.7 V are 46.4 Ω•cm2 and 46.2 Ω•cm2 in conventional and mesa SBDs, respectively. And additionally, the leakage current at -5 V is reduced by approximately 44.3% in the mesa structure. To obtain the Schottky barrier height (SBH) from I-V and capacitance-voltage (C-V) measurements, the C-V was observed in the range of -5 V to 0.5 V at 100 kHz. The SBH values from I-V and C-V measurements, the mesa SBDs have 1% - 5% larger SBH compared to the conventional structure, and it could be related to lower leakage current. Moreover, the depletion depths of conventional and mesa SBDs were 52.2 nm and 57.8 nm, respectively, from C-V measurements. For considering the electrical characteristics in extreme temperatures, the I-V measurements of both SBDs structure will be measured between 75 K to 525 K. From an initial low temperature measurement series, we determine a Richardson constant of 49 A/cm2 comparable to what has been reported by other groups. Furthermore, we will extend the study by performing deep-level transient spectroscopy (DLTS) to understand the defect information in Ga2O3.

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.

The drive inverter represents a central component of an electric vehicle (EV) drive train, being responsible for the DC/AC power conversion between the battery and the electrical machine. In this context, novel converter topologies adopting modern 600/650V wide bandgap (WBG) semiconductor devices will play a crucial role in improving the performance of next-generation drive inverters. In fact, WBG devices theoretically allow to achieve both higher inverter power density and higher conversion efficiency with respect to conventional silicon (Si) IGBT based solutions. Even though silicon carbide (SiC) devices are already well established in the automotive industry, high-voltage gallium nitride (GaN) devices are rapidly entering the market, promising higher theoretical performance but featuring a lower degree of maturity. As a consequence, it is currently not clear which semiconductor technology is most suited for future EV drive inverters. Therefore, this paper aims to address this gap providing a comparative performance evaluation of state-of-the-art SiC and GaN 600/650V active switches. In particular, a novel figure-of-merit (FOM) representing the minimum theoretical semiconductor losses under hard-switching operation is introduced. Remarkably, this FOM enables a fair and accurate performance comparison among semiconductor devices, allowing to clearly determine the best performing technology for a given set of application-specific conditions. The results of the comparative assessment show that currently available SiC and GaN active switch technologies can outperform each other depending on the semiconductor operating temperature and the converter switching frequency.

The expansion of the electric vehicle market is driving the request for efficient and reliable power electronic systems for electric energy conversion and processing. The efficiency, size, and cost of a power system is strongly related to the performance of power semiconductor devices, where massive industrial investments and intense research efforts are being devoted to new wide bandgap (WBG) semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN). The electrical and thermal properties of SiC and GaN enable the fabrication of semiconductor power devices with performance well beyond the limits of silicon. However, a massive migration of the power electronics industry towards WBG materials can be obtained only once the corresponding fabrication technology reaches a sufficient maturity and a competitive cost. In this paper, we present a perspective of power electronics based on WBG semiconductors, from fundamental material characteristics of SiC and GaN to their potential impacts on the power semiconductor device market. Some application cases are also presented, with specific benchmarks against a corresponding implementation realized with silicon devices, focusing on both achievable performance and system cost.

On paper, Gallium nitride (GaN) transistor promises exceptional performance when used in converters operating at high switching frequency; nonetheless, reduction in their performance when used in real circuits have been observed. Previous experiments show that tested GaN transistors can display excessive loss of up to three times their predicted values under certain test conditions. This paper evaluates power losses in GaN transistors when used in class Φ 2 resonant soft-switching inverter topologies at MHz frequencies. Thermometric loss calibration technique is used to calculate the power losses. To gain better insight, experiments are set up to subdivide these losses into two components, one associated with on-state transistors and one associated with off-state transistors. Two GaN devices from two different companies were selected for the study. Further, a control study with a silicon (Si) transistor is also done to confirm the validity of the test method, and to compare the performance of GaN transistors to an existing Si transistor. The following paper presents the loss separation method, and the resulting loss breakdown for the tested devices. The tested operating frequency ranges from 3.39 MHz to 27.12 MHz.

In this report we present the switching measurements on large area AlGaN/GaN HEMT devices with high breakdown voltage achieved with the help of multiple field plates. AlGaN/GaN high electron mobility transistors have shown potential advantages over Si and SiC based transistors for high power switching. The very high electron mobility in the AlGaN/GaN HEMT system combined with the high density of polarization induced 2D electron concentration yield a very low on-resistance and high switching frequency. Also the high band gap energy of AlGaN/GaN system results in a high critical electric field. Hence it is possible to have high voltage power switches capable of operating at high frequencies (~100MHz). However there are some difficulties, which have prevented the achievement of very high breakdown voltages at high frequency operation

INTRODUCTIONAccomplishing with the booming market of personal communication services and the fifth generation (5G) mobile systems, the demands for high frequency and high power devices, such as radio frequency (RF) and microwave power amplifiers, becomes the most priority topic required to be dealt with. Considering the intrinsic electric properties, gallium nitride (GaN) is a suitable and important material for high-power device applications. However, there are many inevitable defects formed during epitaxial growth process due to the difference of the thermal expansion coefficient and the lattice constant mismatch between two materials. The reduction of the defect density is known to be the most fundamental way to fabricate high-power, high-efficient GaN electronic devices. In this paper, we proposed a critical technique to adjust the defects density of GaN, which was then introduced to fabricate HEMTs and yielded a well performed device.DEVICE FABRICATIONThe sapphire substrate used in this study was c-plane (0001), and was patterned with specific periodic structure with electron beam lithography in the first. The following wet-etching by using a mixture solution of sulfuric acid (H2SO4) and phosphoric acid (H3PO4) was processed to form the designed structure on the top of sapphire substrate as figure 1(a) and (b) shown. The substrate was then transferred to the epitaxial growth of GaN. The growth began with 3μm-thick insulating GaN as a device buffer layer, and then 30 nm unintentionally doped AlGaN layer doped 18% Aluminum. The as-prepared epi-wafer then processed with sequential procedures including, and the finial structure of HEMT were the same with the illustration of figure 1(c). MATERIAL QUALITY ANALYSIS In order to check the quality of epi-wafer, both Raman spectrum and EPD method were utilized here. We have compared two different regions of the sample, the PSS region and the planar region (without any surface structure). The shift of Raman peak and relative full width at half maximum (FWHM) were recorded and shown in the figure 2. From the figure 2(a), the peak-shift value from the PSS region is lower than planar region, and close to a free standing GaN (568.73 cm-1), which means less stress accumulated within the PSS region. Figure 2(b) shows that the FWHM in PSS region is 2.28, lower than 2.36 in planar region. Both the trends of Raman shift and FWHM are the same, which indicated a solid evidence of good crystal quality within PSS region.The result of EPD method has been observed by SEM, which is shown in figure 3. The dislocation density within the planar region is about 1.06 x 107 cm-2, which is higher than the PSS region (~2.54 x 106 cm-2). This result proves the better crystal quality of PSS region as well as the former two measurements. INFLUENCE OF SURFACE DEFECT DENSITY ON DIRECT CURRENT MEASUREMENT A further HEMT application of the quality-improved sample had been executed. Figure 4 shows the electronic properties of the sample with and without PSS. When the device’s gate is biased from -4V to 1V, the device with PSS exhibits higher drain than the planar one. In figure 4(a), when the gate voltage equal to 1V, the saturation current of the planar sample is 272.2 mA/mm, while the PSS sample is 323.4 mA/mm, about 18.8% increasing. As to the on-resistance (Ron) value, it reduces to 7.7 Ω-mm under very small drain voltage, which is a 65.9% decreasing comparing to the planar sample. The transduction value, which represents the gain of the gate voltage to the current, increases from 78.3 (planar) to 90.5 (PSS) mS/mm, about 15.6% increases. CONCLUSION We demonstrated a method to acquire a better crystal quality of GaN with PSS. The sample has been verified by Raman analysis and the EPD observation, both shown obvious improvement of crystal quality with PSS. The edge defect density has dropped about 1 order. The advance of crystal quality improved the electrical performance of HEMT. We believe that the method will be an effective and efficient technique that is capable to be applied to more semiconductor materials. Acknowledgments This study was supported financially by the Ministry of Science and Technology (MOST), Taiwan, under contract no. MOST 105-2221-E-002-185-MY3. References J.L. Hudgins, G.S. Simin, E. Santi,and M.A. Khan, “An Assessment of Wide Bandgap Semiconductors for Power Devices,” IEEE T POWER ELECTR, vol.18, pp.907-914 (2003).Yuen-Yee Wong ,et al.“The Roles of Threading Dislocations on Electrical Properties of AlGaN/GaN Heterostructure Grown by MBE” J ELECTROCERAM, 157 (7) H746-H749 (2010).Fabio Alessio Marino , et al. ‘’ Effects of Threading Dislocations on AlGaN/GaN High-Electron Mobility Transistors’’ IEEE T POWER ELECTR, VOL. 57, NO. 1, JANUARY (2010). Figure 1