Soogine Chong

Bio: Soogine Chong is an academic researcher from Samsung. The author has contributed to research in topics: High-electron-mobility transistor & Transient (oscillation). The author has an hindex of 3, co-authored 7 publications receiving 117 citations.

Impact of Channel Hot Electrons on Current Collapse in AlGaN/GaN HEMTs

Abstract: This letter studies the current collapse phenomenon during switching in p-GaN gate AlGaN/GaN high-electron-mobility transistors. It is found that channel hot electrons play a major role in increasing the current collapse and that adding a field plate significantly reduces the effect. By stressing the device with OFF-state pulses of 100 μs× 10 μs with a VGS rise/fall time of 10 ns at Vdc 400 V, compared to the ON-resistance before stress, the ON-resistance was 78 times larger after stress without field plates. With a field plate, it was only 1.8 times larger.

Source-Connected p-GaN Gate HEMTs for Increased Threshold Voltage

Abstract: A pathway to increase the threshold voltage $(V_{\rm TH})$ of p-GaN gate high-electron-mobility transistors (HEMTs) is presented. The hole depletion width in the p-GaN layer at the gate interface is one of the key controlling factors of $V_{\rm TH}$ in p-GaN gate HEMTs. In order to increase the depletion width, we devise a new device structure of p-GaN gate HEMT having a source-connected p-GaN bridge. We demonstrate that a bridged p-GaN gate HEMT structure increases the $V_{\rm TH}$ from 0.93 to 2.44 V.

High threshold voltage p-GaN gate power devices on 200 mm Si

Abstract: In this paper, we present high threshold voltage, low on-resistance, and high speed GaN-HEMT devices using a p-GaN layer in the gate stack. There are three novel features - first, for the first time, p-GaN gate HEMTs were fabricated on a 200-mm GaN on Si substrate using a Au-free fully CMOS-compatible process. Second, good electrical characteristics, including a threshold voltage of higher than 2.8 V, a low gate leakage current, no hysteresis, and fast switching, were obtained by employing a p-GaN and W gate stack. Finally, TO-220 packaged p-GaN gate HEMT devices, which can sustain a gate bias of up to 20 V, were demonstrated. Such properties indicate that our p-GaN HEMT devices are compatible with the conventional gate drivers for Si power devices.

Estimation of Short Circuit Capability of GaN HEMTs Using Transient Measurement

Abstract: Wafer level transient voltage measurement (WLTVM) to estimate the short circuit capability of AlGaN/GaN HEMT devices is suggested. Two groups of samples with similar DC and switching properties but different short circuit capabilities of 4-7 and $>{10}\mu \text{s}$ were evaluated. The extracted junction temperature and the measured saturation/linear current under repeated short circuit stresses suggest that the short circuit failure is attributed to the degradation in the drift region. The WLTVM could measure the transient potential change along the drift region during short circuit condition. The sample with lower short-circuit survivability showed a faster propagation of the high field traveling from the gate to the drain. The time the high electric field reaches the drain coincides with the time of the short circuit failure. In addition to providing the insight into the short circuit failure mechanism, wafer-level method can provide a quick and non-destructive evaluation of the short circuit capability before packaging devices.

Transient Measurement of GaN HEMT Drift Region Potential in the High Power State

Abstract: This work reports the transient measurement of the AlGaN/GaN high electron-mobility transistor (HEMT) drift region potential in the high power state during switching. The effect of high power stress has been reported by device characterization after stress or during high power DC stress at voltages below the operating voltages to avoid device failure. However, transient measurement during high power stress is challenging, since the device can sustain the high power stress only for a few $\mu \text{s}$ before failure occurs. In this work, a test structure with voltage probe inserted in the drift region between the gate and the drain is used to perform real-time measurement of the drift region potential during the high power state at operating voltages. It is found that the high electric field formed at the gate side during the off-state stress propagates towards the drain side within a few $\mu \text{s}$ . The propagation speed of this high electric field increased with increase in drain voltage. It is proposed that trapping of hot channel electrons is causing this effect, and dynamic on-resistance measurement suggests that the traps are 0.44 eV below the conduction band.

GaN-based power devices: Physics, reliability, and perspectives

Abstract: Over the last decade, gallium nitride (GaN) has emerged as an excellent material for the fabrication of power devices. Among the semiconductors for which power devices are already available in the market, GaN has the widest energy gap, the largest critical field, and the highest saturation velocity, thus representing an excellent material for the fabrication of high-speed/high-voltage components. The presence of spontaneous and piezoelectric polarization allows us to create a two-dimensional electron gas, with high mobility and large channel density, in the absence of any doping, thanks to the use of AlGaN/GaN heterostructures. This contributes to minimize resistive losses; at the same time, for GaN transistors, switching losses are very low, thanks to the small parasitic capacitances and switching charges. Device scaling and monolithic integration enable a high-frequency operation, with consequent advantages in terms of miniaturization. For high power/high-voltage operation, vertical device architectures are being proposed and investigated, and three-dimensional structures—fin-shaped, trench-structured, nanowire-based—are demonstrating great potential. Contrary to Si, GaN is a relatively young material: trapping and degradation processes must be understood and described in detail, with the aim of optimizing device stability and reliability. This Tutorial describes the physics, technology, and reliability of GaN-based power devices: in the first part of the article, starting from a discussion of the main properties of the material, the characteristics of lateral and vertical GaN transistors are discussed in detail to provide guidance in this complex and interesting field. The second part of the paper focuses on trapping and reliability aspects: the physical origin of traps in GaN and the main degradation mechanisms are discussed in detail. The wide set of referenced papers and the insight into the most relevant aspects gives the reader a comprehensive overview on the present and next-generation GaN electronics.

Dynamic on -State Resistance Test and Evaluation of GaN Power Devices Under Hard- and Soft-Switching Conditions by Double and Multiple Pulses

Abstract: The dynamic on -state resistance ( R DSON) behavior of commercial GaN devices is very important for a GaN-based converter. Since the zero-voltage switching techniques are popular in high-frequency power conversion, a dynamic R DSON test board integrating both hard- and soft-switching test circuits is built in this study. Two types of commercial GaN devices are tested and compared under hard- and soft-switching conditions by double-pulse and multipulse test modes, respectively. It has been found that their dynamic R DSON exhibit different behaviors depending on the off -state voltage and frequency under hard- and soft-switching conditions due to different device technologies, which should be taken fully into account for GaN-based converter design and loss estimation. In order to simulate the R DSON behavior in a steady-state operating converter, a multipulse measurement has been implemented, the results of which are compared with that of double-pulse test. Furthermore, the primary trapping mechanisms responsible for dynamic R DSON increase under different switching conditions are identified and verified by the numerical device simulation using Silvaco TCAD tool.

An Overview of Normally-Off GaN-Based High Electron Mobility Transistors.

Abstract: Today, the introduction of wide band gap (WBG) semiconductors in power electronics has become mandatory to improve the energy efficiency of devices and modules and to reduce the overall electric power consumption in the world. Due to its excellent properties, gallium nitride (GaN) and related alloys (e.g., AlxGa1−xN) are promising semiconductors for the next generation of high-power and high-frequency devices. However, there are still several technological concerns hindering the complete exploitation of these materials. As an example, high electron mobility transistors (HEMTs) based on AlGaN/GaN heterostructures are inherently normally-on devices. However, normally-off operation is often desired in many power electronics applications. This review paper will give a brief overview on some scientific and technological aspects related to the current normally-off GaN HEMTs technology. A special focus will be put on the p-GaN gate and on the recessed gate hybrid metal insulator semiconductor high electron mobility transistor (MISHEMT), discussing the role of the metal on the p-GaN gate and of the insulator in the recessed MISHEMT region. Finally, the advantages and disadvantages in the processing and performances of the most common technological solutions for normally-off GaN transistors will be summarized.

SiC and GaN devices – wide bandgap is not all the same

Abstract: Silicon carbide (SiC)-diodes have been commercially available since 2001 and various SiC-switches have been launched recently. Parallelly, gallium nitride (GaN) is moving into power electronics and the first low-voltage devices are already on the market. Currently, it seems that GaN-transistors are ideal for high frequency ICs up to 1kV (maybe 2kV) and maximum a few 10A. SiC transistors are better suited for discrete devices or modules blocking 1kV and above and virtually no limit in the current but in that range they will face strong competition from the silicon insulated gate bipolar transistors (IGBTs). SiC and GaN Schottky-diodes would offer a similar performance, hence here it becomes apparent that material cost and quality will finally decide the commercial success of wide bandgap devices. Bulk GaN is still prohibitively expensive, whereas GaN on silicon would offer an unrivalled cost advantage. Devices made from the latter could be even cheaper than silicon devices. However, packaging is already a limiting factor for silicon devices even more so in exploiting the advantage of wide bandgap materials with respect to switching speed and high temperature operation. After all, reliability is a must for any device no matter which material it is made of.

Technology and Reliability of Normally-Off GaN HEMTs with p-Type Gate

Abstract: GaN-based transistors with p-GaN gate are commonly accepted as promising devices for application in power converters, thanks to the positive and stable threshold voltage, the low on-resistance and the high breakdown field. This paper reviews the most recent results on the technology and reliability of these devices by presenting original data. The first part of the paper describes the technological issues related to the development of a p-GaN gate, and the most promising solutions for minimizing the gate leakage current. In the second part of the paper, we describe the most relevant mechanisms that limit the dynamic performance and the reliability of GaN-based normally-off transistors. More specifically, we discuss the following aspects: (i) the trapping effects specific for the p-GaN gate; (ii) the time-dependent breakdown of the p-GaN gate during positive gate stress and the related physics of failure; (iii) the stability of the electrical parameters during operation at high drain voltages. The results presented within this paper provide information on the current status of the performance and reliability of GaN-based E-mode transistors, and on the related technological issues.