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Micromachines
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RF and Power Electronic Devices and Applications
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RF and Power Electronic Devices and Applications

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D：Materials and Processing".

Deadline for manuscript submissions: 31 October 2025 | Viewed by 8121

Special Issue Editors

Dr. Yuqi Wei

E-Mail Website
Guest Editor
State Key Lab of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Interests: Semiconductor characterization, active gate driver; high-frequency power converter
Special Issues, Collections and Topics in MDPI journals
Dr. Hao Lu

E-Mail Website
Guest Editor Assistant
State Key Discipline Laboratory of Wide Bandgap Semiconductor Technology, School of Microelectronics, Xidian University, Xi’an 710071, China
Interests: wide-bandgap semiconductor device; GaN HEMT; RF and mmWave devices; high-frequency applications

Special Issue Information

Dear Colleagues,

The advent of 5G and beyond 5G (B5G) wireless networks is revolutionizing connectivity, enabling faster speeds and significantly enhancing the quality of life through applications like smart cities, autonomous vehicles, and the Internet of Things (IoT). Concurrently, electric vehicles (EVs) are capturing an increasing share of the market, promising a more efficient and sustainable future by reducing carbon emissions and reliance on fossil fuels. These advancements create substantial demands for high-performance semiconductor devices, particularly in the fields of RF and power electronics, where wide-bandgap (WBG) devices are playing a crucial role in achieving superior efficiency and reliability.

This Special Issue aims to gather cutting-edge developments in novel RF and power electronics devices and their applications. We welcome contributions covering, but not limited to, the following topics:

Wide-bandgap devices (GaN, Ga2O3, AlN, etc.) and applications;

High-frequency RF/mmWave device and applications;

Advanced device processing;

Device reliability;

Device characterization;

Gate driver design for semiconductors;

WBG-based power converters.

We invite researchers and industry experts to submit their latest findings and reviews to contribute to the advancement of this dynamic field.

Dr. Yuqi Wei
Dr. Hao Lu
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • gallium nitride HEMT
  • power electronics
  • RF and mmWave device
  • power converter

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Published Papers (8 papers)

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Research

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13 pages, 6135 KiB  
Article
Electrothermal Failure Physics of GaN Schottky Diodes Under High-Temperature Forward Biasing
by Nahid Sultan Al-Mamun, Yuxin Du, Jianan Song, Rongming Chu and Aman Haque
Micromachines 2025, 16(3), 242; https://doi.org/10.3390/mi16030242 - 20 Feb 2025
Viewed by 684
Abstract
The reliability of GaN-based devices operating under high temperatures is crucial for their application in extreme environments. To identify the fundamental mechanisms behind high-temperature degradation, we investigated GaN-on-sapphire Schottky barrier diodes (SBDs) under simultaneous heating and electrical biasing. We observed the degradation mechanisms [...] Read more.
The reliability of GaN-based devices operating under high temperatures is crucial for their application in extreme environments. To identify the fundamental mechanisms behind high-temperature degradation, we investigated GaN-on-sapphire Schottky barrier diodes (SBDs) under simultaneous heating and electrical biasing. We observed the degradation mechanisms in situ inside a transmission electron microscope (TEM) using a custom-fabricated chip for simultaneous thermal and electrical control. The pristine device exhibited a high density of extended defects, primarily due to lattice mismatch and thermal expansion differences between the GaN and sapphire. TEM and STEM imaging, coupled with energy-dispersive X-ray spectroscopy (EDS), revealed the progressive degradation of the diode with increasing bias and temperature. At higher bias levels (4–5 V) and elevated temperatures (300–455 °C), the interdiffusion and alloying of the Au/Pd Schottky metal stack with GaN, along with defect generation near the interface, resulted in Schottky contact failure and catastrophic device degradation. A geometric phase analysis further identified strain localization and lattice distortions induced by thermal and electrical stresses, which facilitated diffusion pathways for rapid metal atom migration. These findings highlight that defect-mediated electrothermal degradation and interfacial chemical reactions are critical elements in the high-temperature failure physics of GaN Schottky diodes. Full article
(This article belongs to the Special Issue RF and Power Electronic Devices and Applications)
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13 pages, 3537 KiB  
Article
Compact SPICE Model for TeraFET Resonant Detectors
by Xueqing Liu, Yuhui Zhang, Trond Ytterdal and Michael Shur
Micromachines 2025, 16(2), 152; https://doi.org/10.3390/mi16020152 - 28 Jan 2025
Viewed by 588
Abstract
This paper presents an improved compact model for TeraFETs employing a nonlinear transmission line approach to describe the non-uniform carrier density oscillations and electron inertia effects in the TeraFET channels. By calculating the equivalent components for each segment of the channel—conductance, capacitance, and [...] Read more.
This paper presents an improved compact model for TeraFETs employing a nonlinear transmission line approach to describe the non-uniform carrier density oscillations and electron inertia effects in the TeraFET channels. By calculating the equivalent components for each segment of the channel—conductance, capacitance, and inductance—based on the voltages at the segment’s nodes, our model accommodates non-uniform variations along the channel. We validate the efficacy of this approach by comparing terahertz (THz) response simulations with experimental data and MOSA1 and EKV TeraFET SPICE models, analytical theories, and Multiphysics simulations. Full article
(This article belongs to the Special Issue RF and Power Electronic Devices and Applications)
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9 pages, 3838 KiB  
Article
Novel Bidirectional ESD Circuit for GaN HEMT
by Pengfei Zhang, Cheng Yang, Jingyu Shen, Xiaorong Luo, Gaoqiang Deng, Shuxiang Sun, Yuxi Wei and Jie Wei
Micromachines 2025, 16(2), 129; https://doi.org/10.3390/mi16020129 - 23 Jan 2025
Viewed by 738
Abstract
In this paper, the ESD protection circuit for p-GaN gate HEMTs with bidirectional clamp is proposed and investigated. ESD clamp circuits consist of several forward diodes in serials and a reverse diode. During the ESD pulse, a discharging channel in the proposed ESD [...] Read more.
In this paper, the ESD protection circuit for p-GaN gate HEMTs with bidirectional clamp is proposed and investigated. ESD clamp circuits consist of several forward diodes in serials and a reverse diode. During the ESD pulse, a discharging channel in the proposed ESD clamp is built and the gate to source voltage for p-GaN HEMTs is clamped at safety value. Based on the experimental verification, the proposed ESD clamps have bidirectional protection functionality by being triggered by a required voltage and exhibit a high secondary breakdown current in both forward and reverse transient ESD events. Meanwhile, the proposed ESD clamp circuit can decrease the power loss in a static state. Full article
(This article belongs to the Special Issue RF and Power Electronic Devices and Applications)
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13 pages, 5049 KiB  
Article
Quantum Channel Extreme Bandgap AlGaN HEMT
by Michael Shur, Grigory Simin, Kamal Hussain, Abdullah Mamun, M. V. S. Chandrashekhar and Asif Khan
Micromachines 2024, 15(11), 1384; https://doi.org/10.3390/mi15111384 - 15 Nov 2024
Viewed by 1073
Abstract
An extreme bandgap Al0.64Ga0.36N quantum channel HEMT with Al0.87Ga0.13N top and back barriers, grown by MOCVD on a bulk AlN substrate, demonstrated a critical breakdown field of 11.37 MV/cm—higher than the 9.8 MV/cm expected for [...] Read more.
An extreme bandgap Al0.64Ga0.36N quantum channel HEMT with Al0.87Ga0.13N top and back barriers, grown by MOCVD on a bulk AlN substrate, demonstrated a critical breakdown field of 11.37 MV/cm—higher than the 9.8 MV/cm expected for the channel’s Al0.64Ga0.36N material. We show that the fraction of this increase is due to the quantization of the 2D electron gas. The polarization field maintains electron quantization in the quantum channel even at low sheet densities, in contrast to conventional HEMT designs. An additional increase in the breakdown field is due to quantum-enabled real space transfer of energetic electrons into high-Al barrier layers in high electric fields. These results show the advantages of the quantum channel design for achieving record-high breakdown voltages and allowing for superior power HEMT devices. Full article
(This article belongs to the Special Issue RF and Power Electronic Devices and Applications)
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12 pages, 8350 KiB  
Article
Low Power Emission Pulse Generation Circuit Based on n-Type Amorphous In-Ga-Zn-Oxide Transistors for Active-Matrix Organic Light-Emitting Diode Displays
by Min-Kyu Chang, Ji Hoon Kim and Hyoungsik Nam
Micromachines 2024, 15(11), 1330; https://doi.org/10.3390/mi15111330 - 30 Oct 2024
Viewed by 936
Abstract
This paper presents a low power emission (EM) pulse generation circuit using n-type amorphous In-Ga-Zn-Oxide (a-IGZO) semiconductor thin-film transistors (TFTs). The low power consumption is achieved by avoiding the shoot-through current paths through an optimized inverter circuit. The proposed circuit consists of 12 [...] Read more.
This paper presents a low power emission (EM) pulse generation circuit using n-type amorphous In-Ga-Zn-Oxide (a-IGZO) semiconductor thin-film transistors (TFTs). The low power consumption is achieved by avoiding the shoot-through current paths through an optimized inverter circuit. The proposed circuit consists of 12 TFTs and 2 capacitors including 6 TFTs and 1 capacitor for the inverter circuit to control the pulling-down TFTs. In addition, the wider variance range of the threshold voltage (Vth) from −4 V to 2.5 V is covered by additional 6 TFTs for series-connected two transistor (STT) schemes and two low supply voltages to take into account the negative Vth of depletion-mode TFTs. The simulation of 30 EM circuits is conducted over a 6.1-inch active-matrix organic light-emitting diode display of 120 Hz refresh rate and 3840 × 2160 (UHD) resolution. The power consumption of the EM circuit with the proposed inverter is measured at the low values from 0.836 mW to 0.568 mW over pulse widths from 3 to 2157 horizontal times. It is ensured that the proposed circuit achieves the low power consumption regardless of pulse widths. Full article
(This article belongs to the Special Issue RF and Power Electronic Devices and Applications)
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10 pages, 4510 KiB  
Article
Improved DC and RF Characteristics of GaN-Based Double-Channel HEMTs by Ultra-Thin AlN Back Barrier Layer
by Qian Yu, Chunzhou Shi, Ling Yang, Hao Lu, Meng Zhang, Xu Zou, Mei Wu, Bin Hou, Wenze Gao, Sheng Wu, Xiaohua Ma and Yue Hao
Micromachines 2024, 15(10), 1220; https://doi.org/10.3390/mi15101220 - 30 Sep 2024
Cited by 2 | Viewed by 1279
Abstract
In order to improve the off-state and breakdown characteristics of double-channel GaN HEMTs, an ultra-thin barrier layer was chosen as the second barrier layer. The strongly polarized and ultra-thin AlN sub-barrier and the InAlN sub-barrier are great candidates. In this article, the two [...] Read more.
In order to improve the off-state and breakdown characteristics of double-channel GaN HEMTs, an ultra-thin barrier layer was chosen as the second barrier layer. The strongly polarized and ultra-thin AlN sub-barrier and the InAlN sub-barrier are great candidates. In this article, the two epitaxial structures, AlGaN/GaN/AlN/GaN (sub-AlN) HEMTs and AlGaN/GaN/InAlN/GaN (sub-InAlN) HEMTs, were compared to select a more suitable sub-barrier layer. Through TEM images of the InAlN barrier layer, the segregation of In components can be seen, which decreases the mobility of the second channel. Thus, the sub-AlN HEMTs have a higher output current density and transconductance than those of the sub-InAlN HEMTs. Because the high-quality AlN barrier layer shields the gate leakage current, a 294 V breakdown voltage was achieved by the sub-AlN HEMTs, which is higher than the 121 V of the sub-InAlN HEMTs. The current gain cut-off frequency (fT) and maximum oscillation frequency (fmax) of the sub-AlN HEMTs are higher than that of the sub-InAlN HEMTs from low to high bias voltage. The power-added efficiency (PAE) and output power density (Pout) of the sub-AlN HEMTs are 57% and 11.3 W/mm at 3.6 GHz and 50 V of drain voltage (Vd), respectively. For the sub-InAlN HEMTs, the PAE and Pout are 41.4% and 8.69 W/mm, because of the worse drain lag ratio. Thus, the Pout of the sub-AlN HEMTs is higher than that of the sub-InAlN HEMTs. Full article
(This article belongs to the Special Issue RF and Power Electronic Devices and Applications)
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Review

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22 pages, 5677 KiB  
Review
A Review on Micro-Watts All-Digital Frequency Synthesizers
by Venkadasamy Navaneethan, Boon Chiat Terence Teo, Annamalai Arasu Muthukumaraswamy, Xian Yang Lim and Liter Siek
Micromachines 2025, 16(3), 333; https://doi.org/10.3390/mi16030333 - 13 Mar 2025
Viewed by 965
Abstract
This paper reviews recent developments in highly integrated all-digital frequency synthesizers suitable to deploy in low-power internet-of-things (IoT) applications. This review sets low power consumption as a key criterion for exploring the all-digital frequency synthesizer implemented in CMOS fabrication technology. The alignment with [...] Read more.
This paper reviews recent developments in highly integrated all-digital frequency synthesizers suitable to deploy in low-power internet-of-things (IoT) applications. This review sets low power consumption as a key criterion for exploring the all-digital frequency synthesizer implemented in CMOS fabrication technology. The alignment with mainstream CMOS technology offers high-density, comprehensive, robust signal processing capability, making it very suitable for all-digital phase-locked loops to harvest that capacity, and it becomes inevitable. This review includes various divider-less low-power frequency synthesizers, including all-digital phase-locked loops (ADPLL), all-digital frequency-locked loops (ADFLL), and hybrid PLLs. This paper also discusses the latest architectural developments for ADPLLs to lead to low-power implementation, such as DTC-assisted TDC, embedded TDC, and various levels of hybridization in ADPLLs. Full article
(This article belongs to the Special Issue RF and Power Electronic Devices and Applications)
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22 pages, 2998 KiB  
Review
Recent Advances in AlN-Based Acoustic Wave Resonators
by Hao Lu, Xiaorun Hao, Ling Yang, Bin Hou, Meng Zhang, Mei Wu, Jie Dong and Xiaohua Ma
Micromachines 2025, 16(2), 205; https://doi.org/10.3390/mi16020205 - 11 Feb 2025
Viewed by 1216
Abstract
AlN-based bulk acoustic wave (BAW) filters have emerged as crucial components in 5G communication due to their high frequency, wide bandwidth, high power capacity, and compact size. This paper mainly reviews the basic principles and recent research advances of AlN-based BAW resonators, which [...] Read more.
AlN-based bulk acoustic wave (BAW) filters have emerged as crucial components in 5G communication due to their high frequency, wide bandwidth, high power capacity, and compact size. This paper mainly reviews the basic principles and recent research advances of AlN-based BAW resonators, which are the backbone of BAW filters. We begin by summarizing the epitaxial growth of single-crystal, polycrystalline, and doped AlN films, with a focus on single-crystal AlN and ScAlN, which are currently the most popular. The discussion then extends to the structure and fabrication of BAW resonators, including the basic solidly mounted resonator (SMR) and the film bulk acoustic resonator (FBAR). The new Xtended Bulk Acoustic Wave (XBAW) technology is highlighted as an effective method to enhance filter bandwidth. Hybrid SAW/BAW resonators (HSBRs) combine the benefits of BAW and SAW resonators to significantly reduce temperature drift. The paper further explores the application of BAW resonators in ladder and lattice BAW filters, highlighting advancements in their design improvements. The frequency-reconfigurable BAW filter, which broadens the filter’s application range, has garnered substantial attention from researchers. Additionally, optimization algorithms for designing AlN-based BAW filters are outlined to reduce design time and improve efficiency. This work aims to serve as a reference for future research on AlN-based BAW filters and to provide insight for similar device studies. Full article
(This article belongs to the Special Issue RF and Power Electronic Devices and Applications)
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