Editorial

3 pages, 192 KiB

Open AccessEditorial

Editorial for the Special Issue on Wide Bandgap Based Devices: Design, Fabrication and Applications

by Farid Medjdoub

Micromachines 2021, 12(1), 83; https://doi.org/10.3390/mi12010083 - 15 Jan 2021

Viewed by 1544

Emerging wide bandgap (WBG) semiconductors hold the potential to advance the global industry in the same way that, more than 50 years ago, the invention of the silicon (Si) chip enabled the modern computer era [...] Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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13 pages, 5970 KiB

Open AccessArticle

A GaN HEMT Amplifier Design for Phased Array Radars and 5G New Radios

by Dawid Kuchta, Daniel Gryglewski and Wojciech Wojtasiak

Micromachines 2020, 11(4), 398; https://doi.org/10.3390/mi11040398 - 10 Apr 2020

Cited by 15 | Viewed by 5884

Abstract

Power amplifiers applied in modern active electronically scanned array (AESA) radars and 5G radios should have similar features, especially in terms of phase distortion, which dramatically affects the spectral regrowth and, moreover, they are difficult to be compensated by predistortion algorithms. This paper [...] Read more.

Power amplifiers applied in modern active electronically scanned array (AESA) radars and 5G radios should have similar features, especially in terms of phase distortion, which dramatically affects the spectral regrowth and, moreover, they are difficult to be compensated by predistortion algorithms. This paper presents a GaN-based power amplifier design with a reduced level of transmittance distortions, varying in time, without significantly worsening other key features such as output power, efficiency and gain. The test amplifier with GaN-on-Si high electron mobility transistors (HEMT) NPT2018 from MACOM provides more than 17 W of output power at the 62% PAE over a 1.0 GHz to 1.1 GHz frequency range. By applying a proposed design approach, it was possible to decrease phase changes on test pulses from 0.5° to 0.2° and amplitude variation from 0.8 dB to 0.2 dB during the pulse width of 40 µs and 40% duty cycle. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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10 pages, 4889 KiB

Open AccessArticle

Compact 20-W GaN Internally Matched Power Amplifier for 2.5 GHz to 6 GHz Jammer Systems

by Min-Pyo Lee, Seil Kim, Sung-June Hong and Dong-Wook Kim

Micromachines 2020, 11(4), 375; https://doi.org/10.3390/mi11040375 - 02 Apr 2020

Cited by 13 | Viewed by 4586

Abstract

In this paper, we demonstrate a compact 20-W GaN internally matched power amplifier for 2.5 to 6 GHz jammer systems which uses a high dielectric constant substrate, single-layer capacitors, and shunt/series resistors for low-Q matching and low-frequency stabilization. A GaN high-electron-mobility transistor (HEMT) [...] Read more.

In this paper, we demonstrate a compact 20-W GaN internally matched power amplifier for 2.5 to 6 GHz jammer systems which uses a high dielectric constant substrate, single-layer capacitors, and shunt/series resistors for low-Q matching and low-frequency stabilization. A GaN high-electron-mobility transistor (HEMT) CGH60030D bare die from Wolfspeed was used as an active device, and input/output matching circuits were implemented on two different substrates using a thin-film process, relative dielectric constants of which were 9.8 and 40, respectively. A series resistor of 2.1 Ω was chosen to minimize the high-frequency loss and obtain a flat gain response. For the output matching circuit, double λ/4 shorted stubs were used to supply the drain current and reduce the output impedance variation of the transistor between the low-frequency and high-frequency regions, which also made wideband matching feasible. Single-layer capacitors effectively helped reduce the size of the matching circuit. The fabricated GaN internally matched power amplifier showed a linear gain of about 10.2 dB, and had an output power of 43.3–43.9 dBm (21.4–24.5 W), a power-added efficiency of 33.4–49.7% and a power gain of 6.2–8.3 dB at the continuous-wave output power condition, from 2.5 to 6 GHz. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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8 pages, 2070 KiB

Open AccessArticle

Self-Aligned Hierarchical ZnO Nanorod/NiO Nanosheet Arrays for High Photon Extraction Efficiency of GaN-Based Photonic Emitter

by Won-Seok Lee, Soon-Hwan Kwon, Hee-Jung Choi, Kwang-Gyun Im, Hannah Lee, Semi Oh and Kyoung-Kook Kim

Micromachines 2020, 11(4), 346; https://doi.org/10.3390/mi11040346 - 26 Mar 2020

Cited by 4 | Viewed by 2491

Abstract

Advancements in nanotechnology have facilitated the increased use of ZnO nanostructures. In particular, hierarchical and core–shell nanostructures, providing a graded refractive index change, have recently been applied to enhance the photon extraction efficiency of photonic emitters. In this study, we demonstrate self-aligned hierarchical [...] Read more.

Advancements in nanotechnology have facilitated the increased use of ZnO nanostructures. In particular, hierarchical and core–shell nanostructures, providing a graded refractive index change, have recently been applied to enhance the photon extraction efficiency of photonic emitters. In this study, we demonstrate self-aligned hierarchical ZnO nanorod (ZNR)/NiO nanosheet arrays on a conventional photonic emitter (C-emitter) with a wavelength of 430 nm. These hierarchical nanostructures were synthesized through a two-step hydrothermal process at low temperature, and their optical output power was approximately 17% higher than that of ZNR arrays on a C-emitter and two times higher than that of a C-emitter. These results are due to the graded index change in refractive index from the GaN layer inside the device toward the outside as well as decreases in the total internal reflection and Fresnel reflection of the photonic emitter. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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13 pages, 2704 KiB

Open AccessArticle

Effect of the Ammonium Tungsten Precursor Solution with the Modification of Glycerol on Wide Band Gap WO₃ Thin Film and Its Electrochromic Properties

by Jinxiang Liu, Guanguang Zhang, Kaiyue Guo, Dong Guo, Muyang Shi, Honglong Ning, Tian Qiu, Junlong Chen, Xiao Fu, Rihui Yao and Junbiao Peng

Micromachines 2020, 11(3), 311; https://doi.org/10.3390/mi11030311 - 16 Mar 2020

Cited by 16 | Viewed by 3086

Abstract

Tungsten trioxide (WO₃) is a wide band gap semiconductor material, which is commonly not only used, but also investigated as a significant electrochromic layer in electrochromic devices. WO₃ films have been prepared by inorganic and sol-gel free ammonium tungstate ((NH [...] Read more.

Tungsten trioxide (WO₃) is a wide band gap semiconductor material, which is commonly not only used, but also investigated as a significant electrochromic layer in electrochromic devices. WO₃ films have been prepared by inorganic and sol-gel free ammonium tungstate ((NH₄)₂WO₄), with the modification of glycerol using the spin coating technique. The surface tension, the contact angle and the dynamic viscosity of the precursor solutions demonstrated that the sample solution with a 25% volume fraction of glycerol was optimal, which was equipped to facilitate the growth of WO₃ films. The thermal gravimetric and differential scanning calorimetry (TG-DSC) analysis represented that the optimal sample solution transformed into the WO₃ range from 220 °C to 300 °C, and the transformation of the phase structure of WO₃ was taken above 300 °C. Fourier transform infrared spectroscopy (FT-IR) spectra analysis indicated that the composition within the film was WO₃ above the 300 °C annealing temperature, and the component content of WO₃ was increased with the increase in the annealing temperature. The X-ray diffraction (XRD) pattern revealed that WO₃ films were available for the formation of the cubic and monoclinic crystal structure at 400 °C, and were preferential for growing monoclinic WO₃ when annealed at 500 °C. Atomic force microscope (AFM) images showed that WO₃ films prepared using ammonium tungstate with modification of the glycerol possessed less rough surface roughness in comparison with the sol-gel-prepared films. An ultraviolet spectrophotometer (UV) demonstrated that the sample solution which had been annealed at 400 °C obtained a high electrochromic modulation ability roughly 40% at 700 nm wavelength, as well as the optical band gap (E_g) of the WO₃ films ranged from 3.48 eV to 3.37 eV with the annealing temperature increasing. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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10 pages, 2664 KiB

Open AccessArticle

Silver Nanorings Fabricated by Glycerol-Based Cosolvent Polyol Method

by Zhihang Li, Dong Guo, Peng Xiao, Junlong Chen, Honglong Ning, Yiping Wang, Xu Zhang, Xiao Fu, Rihui Yao and Junbiao Peng

Micromachines 2020, 11(3), 236; https://doi.org/10.3390/mi11030236 - 25 Feb 2020

Cited by 4 | Viewed by 2271

Abstract

The urgent demand for transparent flexible electrodes applied in wide bandgap devices has promoted the development of new materials. Silver nanoring (AgNR), known as a special structure of silver nanowire (AgNW), exhibits attractive potential in the field of wearable electronics. In this work, [...] Read more.

The urgent demand for transparent flexible electrodes applied in wide bandgap devices has promoted the development of new materials. Silver nanoring (AgNR), known as a special structure of silver nanowire (AgNW), exhibits attractive potential in the field of wearable electronics. In this work, an environmentally friendly glycerol-based cosolvent polyol method was investigated. The Taguchi design was utilized to ascertain the factors that affect the yield and ring diameter of AgNRs. Structural characterization showed that AgNR seeds grew at a certain angle during the early nucleation period. The results indicated that the yield and ring diameter of AgNRs were significantly affected by the ratio of cosolvent. Besides, the ring diameter of AgNRs was also tightly related to the concentration of polyvinylpyrrolidone (PVP). The difference of reducibility between glycerol, water, and ethylene glycol leads to the selective growth of (111) plane and is probably the main reason AgNRs are formed. As a result, AgNRs with a ring diameter range from 7.17 to 42.94 μm were synthesized, and the quantity was increased significantly under the optimal level of factors. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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11 pages, 6017 KiB

Open AccessArticle

Gallium Nitride (GaN) High-Electron-Mobility Transistors with Thick Copper Metallization Featuring a Power Density of 8.2 W/mm for Ka-Band Applications

by Y. C. Lin, S. H. Chen, P. H. Lee, K. H. Lai, T. J. Huang, Edward Y. Chang and Heng-Tung Hsu

Micromachines 2020, 11(2), 222; https://doi.org/10.3390/mi11020222 - 21 Feb 2020

Cited by 19 | Viewed by 5226

Abstract

Copper-metallized gallium nitride (GaN) high-electron-mobility transistors (HEMTs) using a Ti/Pt/Ti diffusion barrier layer are fabricated and characterized for Ka-band applications. With a thick copper metallization layer of 6.8 μm adopted, the device exhibited a high output power density of 8.2 W/mm and a [...] Read more.

Copper-metallized gallium nitride (GaN) high-electron-mobility transistors (HEMTs) using a Ti/Pt/Ti diffusion barrier layer are fabricated and characterized for Ka-band applications. With a thick copper metallization layer of 6.8 μm adopted, the device exhibited a high output power density of 8.2 W/mm and a power-added efficiency (PAE) of 26% at 38 GHz. Such superior performance is mainly attributed to the substantial reduction of the source and drain resistance of the device. In addition to improvement in the Radio Frequency (RF) performance, the successful integration of the thick copper metallization in the device technology further reduces the manufacturing cost, making it extremely promising for future fifth-generation mobile communication system applications at millimeter-wave frequencies. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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10 pages, 1982 KiB

Open AccessArticle

Investigation of Recessed Gate AlGaN/GaN MIS-HEMTs with Double AlGaN Barrier Designs toward an Enhancement-Mode Characteristic

by Tian-Li Wu, Shun-Wei Tang and Hong-Jia Jiang

Micromachines 2020, 11(2), 163; https://doi.org/10.3390/mi11020163 - 03 Feb 2020

Cited by 16 | Viewed by 4369

Abstract

In this work, recessed gate AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with double AlGaN barrier designs are fabricated and investigated. Two different recessed depths are designed, leading to a 5 nm and a 3 nm remaining bottom AlGaN barrier under the gate region, and [...] Read more.

In this work, recessed gate AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with double AlGaN barrier designs are fabricated and investigated. Two different recessed depths are designed, leading to a 5 nm and a 3 nm remaining bottom AlGaN barrier under the gate region, and two different Al% (15% and 20%) in the bottom AlGaN barriers are designed. First of all, a double hump trans-conductance (g_m)–gate voltage (V_G) characteristic is observed in a recessed gate AlGaN/GaN MIS-HEMT with a 5 nm remaining bottom Al_0.2Ga_0.8N barrier under the gate region. Secondly, a physical model is proposed to explain this double channel characteristic by means of a formation of a top channel below the gate dielectric under a positive V_G. Finally, the impacts of Al% content (15% and 20%) in the bottom AlGaN barrier and 5 nm/3 nm remaining bottom AlGaN barriers under the gate region are studied in detail, indicating that lowering Al% content in the bottom can increase the threshold voltage (V_TH) toward an enhancement-mode characteristic. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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22 pages, 12466 KiB

Open AccessArticle

Design and Implementation of a GaN-Based Three-Phase Active Power Filter

by Chao-Tsung Ma and Zhen-Huang Gu

Micromachines 2020, 11(2), 134; https://doi.org/10.3390/mi11020134 - 24 Jan 2020

Cited by 8 | Viewed by 2545

Abstract

Renewable energy (RE)-based power generation systems and modern manufacturing facilities utilize a wide variety of power converters based on high-frequency power electronic devices and complex switching technologies. This has resulted in a noticeable degradation in the power quality (PQ) of power systems. To [...] Read more.

Renewable energy (RE)-based power generation systems and modern manufacturing facilities utilize a wide variety of power converters based on high-frequency power electronic devices and complex switching technologies. This has resulted in a noticeable degradation in the power quality (PQ) of power systems. To solve the aforementioned problem, advanced active power filters (APFs) with improved system performance and properly designed switching devices and control algorithms can provide a promising solution because an APF can compensate for voltage sag, harmonic currents, current imbalance, and active and reactive powers individually or simultaneously. This paper demonstrates, for the first time, the detailed design procedure and performance of a digitally controlled 2 kVA three-phase shunt APF system using gallium nitride (GaN) high electron mobility transistors (HEMTs). The designed digital control scheme consists of three type II controllers with a digital signal processor (DSP) as the control core. Using the proposed APF and control algorithms, fast and accurate compensation for harmonics, imbalance, and reactive power is achieved in both simulation and hardware tests, demonstrating the feasibility and effectiveness of the proposed system. Moreover, GaN HEMTs allow the system to achieve up to 97.2% efficiency. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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9 pages, 3035 KiB

Open AccessArticle

Vertical Leakage in GaN-on-Si Stacks Investigated by a Buffer Decomposition Experiment

by Alaleh Tajalli, Matteo Borga, Matteo Meneghini, Carlo De Santi, Davide Benazzi, Sven Besendörfer, Roland Püsche, Joff Derluyn, Stefan Degroote, Marianne Germain, Riad Kabouche, Idriss Abid, Elke Meissner, Enrico Zanoni, Farid Medjdoub and Gaudenzio Meneghesso

Micromachines 2020, 11(1), 101; https://doi.org/10.3390/mi11010101 - 17 Jan 2020

Cited by 3 | Viewed by 5570

Abstract

We investigated the origin of vertical leakage and breakdown in GaN-on-Si epitaxial structures. In order to understand the role of the nucleation layer, AlGaN buffer, and C-doped GaN, we designed a sequential growth experiment. Specifically, we analyzed three different structures grown on silicon [...] Read more.

We investigated the origin of vertical leakage and breakdown in GaN-on-Si epitaxial structures. In order to understand the role of the nucleation layer, AlGaN buffer, and C-doped GaN, we designed a sequential growth experiment. Specifically, we analyzed three different structures grown on silicon substrates: AlN/Si, AlGaN/AlN/Si, C:GaN/AlGaN/AlN/Si. The results demonstrate that: (i) the AlN layer grown on silicon has a breakdown field of 3.25 MV/cm, which further decreases with temperature. This value is much lower than that of highly-crystalline AlN, and the difference can be ascribed to the high density of vertical leakage paths like V-pits or threading dislocations. (ii) the AlN/Si structures show negative charge trapping, due to the injection of electrons from silicon to deep traps in AlN. (iii) adding AlGaN on top of AlN significantly reduces the defect density, thus resulting in a more uniform sample-to-sample leakage. (iv) a substantial increase in breakdown voltage is obtained only in the C:GaN/AlGaN/AlN/Si structure, that allows it to reach V_BD > 800 V. (v) remarkably, during a vertical I–V sweep, the C:GaN/AlGaN/AlN/Si stack shows evidence for positive charge trapping. Holes from C:GaN are trapped at the GaN/AlGaN interface, thus bringing a positive charge storage in the buffer. For the first time, the results summarized in this paper clarify the contribution of each buffer layer to vertical leakage and breakdown. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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11 pages, 9260 KiB

Open AccessArticle

Physical-Based Simulation of the GaN-Based Grooved-Anode Planar Gunn Diode

by Ying Wang, Liu-An Li, Jin-Ping Ao and Yue Hao

Micromachines 2020, 11(1), 97; https://doi.org/10.3390/mi11010097 - 16 Jan 2020

Cited by 3 | Viewed by 2339

Abstract

In this paper, a novel gallium nitride (GaN)-based heterostructure Gunn diode is proposed for the first time to enhance the output characteristics of Gunn oscillation waveforms. A well-designed grooved anode contact is adopted to separate the long-channel diode into two short-channel diodes in [...] Read more.

In this paper, a novel gallium nitride (GaN)-based heterostructure Gunn diode is proposed for the first time to enhance the output characteristics of Gunn oscillation waveforms. A well-designed grooved anode contact is adopted to separate the long-channel diode into two short-channel diodes in parallel. If the grooved anode contact is positioned in the middle of the device, the output power nearly doubles in the grooved-anode diode compared with the single-channel ones, as does the output frequency. Based on the numerical results, the best output characteristics are obtained at the 2.0-µm symmetrical grooved-anode diode, which produces nearly 5.48 mW of power at the fundamental frequency of 172.81 GHz, with 3.13% efficiency of power conversion. If the grooved anode contact is not positioned in the middle of the diode, the harmonic frequency would be enhanced. The GaN heterostructure grooved-anode Gunn diode has been demonstrated to be an excellent solid-state source of terahertz oscillator. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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10 pages, 4179 KiB

Open AccessArticle

Improving Output Power of InGaN Laser Diode Using Asymmetric In_0.15Ga_0.85N/In_0.02Ga_0.98N Multiple Quantum Wells

by Wenjie Wang, Wuze Xie, Zejia Deng and Mingle Liao

Micromachines 2019, 10(12), 875; https://doi.org/10.3390/mi10120875 - 13 Dec 2019

Cited by 9 | Viewed by 3089

Abstract

Herein, the optical field distribution and electrical property improvements of the InGaN laser diode with an emission wavelength around 416 nm are theoretically investigated by adjusting the relative thickness of the first or last barrier layer in the three In_0.15Ga_0.85 [...] Read more.

Herein, the optical field distribution and electrical property improvements of the InGaN laser diode with an emission wavelength around 416 nm are theoretically investigated by adjusting the relative thickness of the first or last barrier layer in the three In_0.15Ga_0.85N/In_0.02Ga_0.98N quantum wells, which is achieved with the simulation program Crosslight. It was found that the thickness of the first or last InGaN barrier has strong effects on the threshold currents and output powers of the laser diodes. The optimal thickness of the first quantum barrier layer (FQB) and last quantum barrier layer (LQB) were found to be 225 nm and 300 nm, respectively. The thickness of LQB layer predominantly affects the output power compared to that of the FQB layer, and the highest output power achieved 3.87 times that of the reference structure (symmetric quantum well), which is attributed to reduced optical absorption loss as well as the reduced vertical electron leakage current leaking from the quantum wells to the p-type region. Our result proves that an appropriate LQB layer thickness is advantageous for achieving low threshold current and high output power lasers. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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10 pages, 2625 KiB

Open AccessArticle

A Novel GaN Metal-Insulator-Semiconductor High Electron Mobility Transistor Featuring Vertical Gate Structure

by Zhonghao Sun, Huolin Huang, Nan Sun, Pengcheng Tao, Cezhou Zhao and Yung C. Liang

Micromachines 2019, 10(12), 848; https://doi.org/10.3390/mi10120848 - 05 Dec 2019

Cited by 5 | Viewed by 4145

Abstract

A novel structure scheme by transposing the gate channel orientation from a long horizontal one to a short vertical one is proposed and verified by technology computer-aided design (TCAD) simulations to achieve GaN-based normally-off high electron mobility transistors (HEMTs) with reduced on-resistance and [...] Read more.

A novel structure scheme by transposing the gate channel orientation from a long horizontal one to a short vertical one is proposed and verified by technology computer-aided design (TCAD) simulations to achieve GaN-based normally-off high electron mobility transistors (HEMTs) with reduced on-resistance and improved threshold voltage. The proposed devices exhibit high threshold voltage of 3.1 V, high peak transconductance of 213 mS, and much lower on-resistance of 0.53 mΩ·cm² while displaying better off-state characteristics owing to more uniform electric field distribution around the recessed gate edge in comparison to the conventional lateral HEMTs. The proposed scheme provides a new technical approach to realize high-performance normally-off HEMTs. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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9 pages, 2876 KiB

Open AccessArticle

Simulation Study of 4H-SiC Trench Insulated Gate Bipolar Transistor with Low Turn-Off Loss

by Hong-kai Mao, Ying Wang, Xue Wu and Fang-wen Su

Micromachines 2019, 10(12), 815; https://doi.org/10.3390/mi10120815 - 26 Nov 2019

Cited by 4 | Viewed by 3454

Abstract

In this work, an insulated gate bipolar transistor (IGBT) is proposed that introduces a portion of the p-polySi/p-SiC heterojunction on the collector side to reduce the tail current during device turn-offs. By adjusting the doping concentration on both sides of the heterojunction, the [...] Read more.

In this work, an insulated gate bipolar transistor (IGBT) is proposed that introduces a portion of the p-polySi/p-SiC heterojunction on the collector side to reduce the tail current during device turn-offs. By adjusting the doping concentration on both sides of the heterojunction, the turn-off loss is further reduced without sacrificing other characteristics of the device. The electrical characteristics of the device were simulated through the Silvaco ATLAS 2D simulation tool and compared with the traditional structure to verify the design idea. The simulation results show that, compared with the traditional structure, the turn-off loss of the proposed structure was reduced by 58.4%, the breakdown voltage increased by 13.3%, and the forward characteristics sacrificed 8.3%. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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8 pages, 2443 KiB

Open AccessArticle

Electrical Performance and Bias-Stress Stability of Amorphous InGaZnO Thin-Film Transistors with Buried-Channel Layers

by Ying Zhang, Haiting Xie and Chengyuan Dong

Micromachines 2019, 10(11), 779; https://doi.org/10.3390/mi10110779 - 14 Nov 2019

Cited by 7 | Viewed by 4083

Abstract

To improve the electrical performance and bias-stress stability of amorphous InGaZnO thin-film transistors (a-IGZO TFTs), we fabricated and characterized buried-channel devices with multiple-stacked channel layers, i.e., a nitrogen-doped a-IGZO film (front-channel layer), a conventional a-IGZO film (buried-channel layer), and a nitrogen-doped a-IGZO film [...] Read more.

To improve the electrical performance and bias-stress stability of amorphous InGaZnO thin-film transistors (a-IGZO TFTs), we fabricated and characterized buried-channel devices with multiple-stacked channel layers, i.e., a nitrogen-doped a-IGZO film (front-channel layer), a conventional a-IGZO film (buried-channel layer), and a nitrogen-doped a-IGZO film (back-channel layer). The larger field-effect mobility (5.8 cm²V⁻¹s⁻¹), the smaller subthreshold swing value (0.8 V/dec, and the better stability (smaller threshold voltage shifts during bias-stress and light illumination tests) were obtained for the buried-channel device relative to the conventional a-IGZO TFT. The specially designed channel-layer structure resulted in multiple conduction channels and hence large field-effect mobility. The in situ nitrogen-doping caused reductions in both the front-channel interface trap density and the density of deep states in the bulk channel layers, leading to a small subthreshold swing value. The better stability properties may be related to both the reduced trap states by nitrogen-doping and the passivation effect of the nitrogen-doped a-IGZO films at the device back channels. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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11 pages, 5326 KiB

Open AccessArticle

Measurement of Heat Dissipation and Thermal-Stability of Power Modules on DBC Substrates with Various Ceramics by SiC Micro-Heater Chip System and Ag Sinter Joining

by Dongjin Kim, Yasuyuki Yamamoto, Shijo Nagao, Naoki Wakasugi, Chuantong Chen and Katsuaki Suganuma

Micromachines 2019, 10(11), 745; https://doi.org/10.3390/mi10110745 - 31 Oct 2019

Cited by 18 | Viewed by 5057

Abstract

This study introduced the SiC micro-heater chip as a novel thermal evaluation device for next-generation power modules and to evaluate the heat resistant performance of direct bonded copper (DBC) substrate with aluminum nitride (AlN-DBC), aluminum oxide (DBC-Al₂O₃) and silicon [...] Read more.

This study introduced the SiC micro-heater chip as a novel thermal evaluation device for next-generation power modules and to evaluate the heat resistant performance of direct bonded copper (DBC) substrate with aluminum nitride (AlN-DBC), aluminum oxide (DBC-Al₂O₃) and silicon nitride (Si₃N₄-DBC) ceramics middle layer. The SiC micro-heater chips were structurally sound bonded on the two types of DBC substrates by Ag sinter paste and Au wire was used to interconnect the SiC and DBC substrate. The SiC micro-heater chip power modules were fixed on a water-cooling plate by a thermal interface material (TIM), a steady-state thermal resistance measurement and a power cycling test were successfully conducted. As a result, the thermal resistance of the SiC micro-heater chip power modules on the DBC-Al₂O₃ substrate at power over 200 W was about twice higher than DBC-Si₃N₄ and also higher than DBC-AlN. In addition, during the power cycle test, DBC-Al₂O₃ was stopped after 1000 cycles due to Pt heater pattern line was partially broken induced by the excessive rise in thermal resistance, but DBC-Si₃N₄ and DBC-AlN specimens were subjected to more than 20,000 cycles and not noticeable physical failure was found in both of the SiC chip and DBC substrates by a x-ray observation. The results indicated that AlN-DBC can be as an optimization substrate for the best heat dissipation/durability in wide band-gap (WBG) power devices. Our results provide an important index for industries demanding higher power and temperature power electronics. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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8 pages, 2898 KiB

Open AccessArticle

Proton Irradiation Effects on the Time-Dependent Dielectric Breakdown Characteristics of Normally-Off AlGaN/GaN Gate-Recessed Metal-Insulator-Semiconductor Heterostructure Field Effect Transistors

by Dongmin Keum and Hyungtak Kim

Micromachines 2019, 10(11), 723; https://doi.org/10.3390/mi10110723 - 26 Oct 2019

Cited by 1 | Viewed by 2873

Abstract

In this work, we investigated the time-dependent dielectric breakdown (TDDB) characteristics of normally-off AlGaN/GaN gate-recessed metal–insulator–semiconductor (MIS) heterostructure field effect transistors (HFETs) submitted to proton irradiation. TDDB characteristics of normally-off AlGaN/GaN gate-recessed MISHFETs exhibited a gate voltage (V_GS) dependence as [...] Read more.

In this work, we investigated the time-dependent dielectric breakdown (TDDB) characteristics of normally-off AlGaN/GaN gate-recessed metal–insulator–semiconductor (MIS) heterostructure field effect transistors (HFETs) submitted to proton irradiation. TDDB characteristics of normally-off AlGaN/GaN gate-recessed MISHFETs exhibited a gate voltage (V_GS) dependence as expected and showed negligible degradation even after proton irradiation. However, a capture emission time (CET) map and cathodoluminescence (CL) measurements revealed that the MIS structure was degraded with increasing trap states. A technology computer aided design (TCAD) simulation indicated the decrease of the vertical field beneath the gate due to the increase of the trap concentration. Negligible degradation of TDDB can be attributed to this mitigation of the vertical field by proton irradiation. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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10 pages, 6314 KiB

Open AccessArticle

InGaN/GaN Distributed Feedback Laser Diodes with Surface Gratings and Sidewall Gratings

by Zejia Deng, Junze Li, Mingle Liao, Wuze Xie and Siyuan Luo

Micromachines 2019, 10(10), 699; https://doi.org/10.3390/mi10100699 - 14 Oct 2019

Cited by 16 | Viewed by 4066

Abstract

A variety of potential applications such as visible light communications require laser sources with a narrow linewidth and a single wavelength emission in the blue light region. The gallium nitride (GaN)-based distributed feedback laser diode (DFB-LD) is a promising light source that meets [...] Read more.

A variety of potential applications such as visible light communications require laser sources with a narrow linewidth and a single wavelength emission in the blue light region. The gallium nitride (GaN)-based distributed feedback laser diode (DFB-LD) is a promising light source that meets these requirements. Here, we present GaN DFB-LDs that share growth and fabrication processes and have surface gratings and sidewall gratings on the same epitaxial substrate, which makes LDs with different structures comparable. By electrical pulse pumping, single-peak emissions at 398.5 and 399.95 nm with a full width at half maximum (FWHM) of 0.32 and 0.23 nm were achieved, respectively. The surface and sidewall gratings were fabricated alongside the p-contact metal stripe by electrical beam lithography and inductively coupled plasma etching. DFB LDs with 2.5 μm ridge width exhibit a smaller FWHM than those with 5 and 10 μm ridge widths, indicating that the narrow ridge width is favorable for the narrowing of the line width of the DFB LD. The slope efficiency of the DFB LD with sidewall gratings is higher than that of surface grating DFB LDs with the same ridge width and period of gratings. Our experiment may provide a reliable and simple approach for optimizing gratings and GaN DFB-LDs. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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7 pages, 1917 KiB

Open AccessArticle

Improved Output Power of GaN-based VCSEL with Band-Engineered Electron Blocking Layer

by Huiwen Luo, Junze Li and Mo Li

Micromachines 2019, 10(10), 694; https://doi.org/10.3390/mi10100694 - 12 Oct 2019

Cited by 4 | Viewed by 3095

Abstract

The vertical-cavity surface-emitting laser (VCSEL) has unique advantages over the conventional edge-emitting laser and has recently attracted a lot of attention. However, the output power of GaN-based VCSEL is still low due to the large electron leakage caused by the built-in polarization at [...] Read more.

The vertical-cavity surface-emitting laser (VCSEL) has unique advantages over the conventional edge-emitting laser and has recently attracted a lot of attention. However, the output power of GaN-based VCSEL is still low due to the large electron leakage caused by the built-in polarization at the heterointerface within the device. In this paper, in order to improve the output power, a new structure of p-type composition-graded Al_xGa_1−xN electron blocking layer (EBL) is proposed in the VCSEL, by replacing the last quantum barrier (LQB) and EBL in the conventional structure. The simulation results show that the proposed EBL in the VCSEL suppresses the leaking electrons remarkably and contributes to a 70.6% increase of the output power, compared with the conventional GaN-based VCSEL. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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8 pages, 7206 KiB

Open AccessArticle

High Lateral Breakdown Voltage in Thin Channel AlGaN/GaN High Electron Mobility Transistors on AlN/Sapphire Templates

by Idriss Abid, Riad Kabouche, Catherine Bougerol, Julien Pernot, Cedric Masante, Remi Comyn, Yvon Cordier and Farid Medjdoub

Micromachines 2019, 10(10), 690; https://doi.org/10.3390/mi10100690 - 12 Oct 2019

Cited by 28 | Viewed by 4007

Abstract

In this paper, we present the fabrication and Direct Current/high voltage characterizations of AlN-based thin and thick channel AlGaN/GaN heterostructures that are regrown by molecular beam epitaxy on AlN/sapphire. A very high lateral breakdown voltage above 10 kV was observed on the thin [...] Read more.

In this paper, we present the fabrication and Direct Current/high voltage characterizations of AlN-based thin and thick channel AlGaN/GaN heterostructures that are regrown by molecular beam epitaxy on AlN/sapphire. A very high lateral breakdown voltage above 10 kV was observed on the thin channel structure for large contact distances. Also, the buffer assessment revealed a remarkable breakdown field of 5 MV/cm for short contact distances, which is far beyond the theoretical limit of the GaN-based material system. The potential interest of the thin channel configuration in AlN-based high electron mobility transistors is confirmed by the much lower breakdown field that is obtained on the thick channel structure. Furthermore, fabricated transistors are fully functional on both structures with low leakage current, low on-resistance, and reduced temperature dependence as measured up to 300 °C. This is attributed to the ultra-wide bandgap AlN buffer, which is extremely promising for high power, high temperature future applications. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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Review

Jump to: Editorial, Research

21 pages, 8089 KiB

Open AccessReview

Vertical GaN-on-GaN Schottky Diodes as α-Particle Radiation Sensors

by Abhinay Sandupatla, Subramaniam Arulkumaran, Ng Geok Ing, Shugo Nitta, John Kennedy and Hiroshi Amano

Micromachines 2020, 11(5), 519; https://doi.org/10.3390/mi11050519 - 20 May 2020

Cited by 17 | Viewed by 4697

Abstract

Among the different semiconductors, GaN provides advantages over Si, SiC and GaAs in radiation hardness, resulting in researchers exploring the development of GaN-based radiation sensors to be used in particle physics, astronomic and nuclear science applications. Several reports have demonstrated the usefulness of [...] Read more.

Among the different semiconductors, GaN provides advantages over Si, SiC and GaAs in radiation hardness, resulting in researchers exploring the development of GaN-based radiation sensors to be used in particle physics, astronomic and nuclear science applications. Several reports have demonstrated the usefulness of GaN as an α-particle detector. Work in developing GaN-based radiation sensors are still evolving and GaN sensors have successfully detected α-particles, neutrons, ultraviolet rays, x-rays, electrons and γ-rays. This review elaborates on the design of a good radiation detector along with the state-of-the-art α-particle detectors using GaN. Successful improvement in the growth of GaN drift layers (DL) with 2 order of magnitude lower in charge carrier density (CCD) (7.6 × 10¹⁴/cm³) on low threading dislocation density (3.1 × 10⁶/cm²) hydride vapor phase epitaxy (HVPE) grown free-standing GaN substrate, which helped ~3 orders of magnitude lower reverse leakage current (I_R) with 3-times increase of reverse breakdown voltages. The highest reverse breakdown voltage of −2400 V was also realized from Schottky barrier diodes (SBDs) on a free-standing GaN substrate with 30 μm DL. The formation of thick depletion width (DW) with low CCD resulted in improving high-energy (5.48 MeV) α-particle detection with the charge collection efficiency (CCE) of 62% even at lower bias voltages (−20 V). The detectors also detected 5.48 MeV α-particle with CCE of 100% from SBDs with 30-μm DL at −750 V. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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