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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 March 2025 | Viewed by 5447

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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Further information on MDPI's Special Issue policies can be found here.

Published Papers (7 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 369
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)
►▼ Show Figures

Figure 1

Figure 1
<p>(<b>a</b>) Schematic cross-section of the GaN SBD; (<b>b</b>) SEM top view of the MEMS chip; (<b>c</b>–<b>e</b>) FIB lamella preparation and transfer of the diode lamella into the MEMS microheater element; (<b>f</b>) Multi-physics simulation result of thermal field of the MEMS microheater element at 4 V.</p> Full article ">Figure 2
<p>(<b>a</b>) Forward I–V and (<b>b</b>) high-voltage reverse I–V curves of the fabricated SBD.</p> Full article ">Figure 3
<p>(<b>a</b>) Low-magnification TEM bright-field image of pristine GaN diode; (<b>b</b>) dislocations near the GaN/sapphire interface; (<b>c</b>) extension of dislocations towards anode; (<b>d</b>) STEM image of the pristine diode; (<b>e</b>) HAADF STEM image near the anode; EDS maps of (<b>f</b>) Ga, (<b>g</b>) Au, and (<b>h</b>) Pd.</p> Full article ">Figure 4
<p>Low-magnification TEM cross-section after biasing at (<b>a</b>) 2 V and 85 °C, (<b>b</b>) 3 V and 185 °C, and (<b>c</b>) 4 V and 300 °C; (<b>d</b>) new defect generation near substrate; (<b>e</b>) HAADF image near the damaged Schottky contact; (<b>f</b>) Au, (<b>g</b>) Pd, and (<b>h</b>) Ga EDS maps at 4 V and 300 °C.</p> Full article ">Figure 5
<p>(<b>a</b>) Failure of Schottky contact at 5 V and 455 °C; (<b>b</b>,<b>c</b>) Au/Pd nanocrystallites in the GaN layer; (<b>d</b>) SAED pattern of GaN layer after metal diffusion; (<b>e</b>) HAADF STEM image shows widespread diffusion of metal into GaN; EDS maps of (<b>f</b>) Au, (<b>g</b>) Pd, (<b>h</b>) Ga, (<b>i</b>) N, (<b>j</b>) Al, and (<b>k</b>) O.</p> Full article ">Figure 6
<p>HRTEM images for (<b>a</b>) pristine, (<b>b</b>) 2 V, 85 °C, (<b>c</b>) 3 V, 185 °C, and (<b>d</b>) 4 V, 300 °C. GPA strain maps: in-plane strain maps (ε<sub>xx</sub>) for (<b>e</b>) pristine, (<b>f</b>) 2 V, 85 °C, (<b>g</b>) 3 V, 185 °C, and (<b>h</b>) 4 V, 300 °C. Out-of-plane strain maps (ε<sub>yy</sub>) for (<b>i</b>) pristine, (<b>j</b>) 2 V, 85 °C, (<b>k</b>) 3 V, 185 °C, and (<b>l</b>) 4 V, 300 °C.</p> Full article ">
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 484
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)
►▼ Show Figures

Figure 1

Figure 1
<p>Schematic of a TeraFET under THz radiation and the equivalent circuit of the TeraFET multi-segment compact model. In contrast to previous models, the Drude inductance is a function of the voltage at the nodes of each segment.</p> Full article ">Figure 2
<p>Profile of <span class="html-italic">L<sub>drude</sub></span> variation for a TeraFET with 90 nm channel length using EKV 50-segment model with varying <span class="html-italic">L<sub>drude</sub></span>.</p> Full article ">Figure 3
<p>Schematic of a 90 nm FDSOI MOSFET TCAD model (<b>a</b>) and comparison of IV characteristics between the TCAD model and both the single-channel and multi-segment MOSA1 SPICE models: (<b>b</b>) output characteristics and (<b>c</b>) transfer characteristics.</p> Full article ">Figure 4
<p>Comparison of simulated THz response using the TeraFET SPICE models and measured THz response for NMOSFETs [<a href="#B39-micromachines-16-00152" class="html-bibr">39</a>] with (<b>a</b>) 80 nm channel length and (<b>b</b>) 180 nm channel length.</p> Full article ">Figure 5
<p>Comparison of THz response between the analytical theory, COMSOL simulation, 50-segment SPICE models with uniform <span class="html-italic">L<sub>drude</sub></span> or varying <span class="html-italic">L<sub>drude</sub></span> for TeraFETs with (<b>a</b>) 90 nm channel length and 0.4 m<sup>2</sup>/Vs mobility, (<b>b</b>) 45 nm channel length and 0.4 m<sup>2</sup>/Vs mobility, (<b>c</b>) 20 nm channel length and 0.4 m<sup>2</sup>/Vs mobility, and (<b>d</b>) 20 nm channel length and 0.1 m<sup>2</sup>/Vs mobility.</p> Full article ">Figure 6
<p>Profile of drift velocity for 90 nm MOSFET (<span class="html-italic">µ</span> = 0.4 m<sup>2</sup>/Vs) under THz radiation: (<b>a</b>) COMSOL simulation, (<b>b</b>) MOSA1 50-segment model with varying <span class="html-italic">L<sub>drude</sub></span>, (<b>c</b>) EKV 50-segment model with varying <span class="html-italic">L<sub>drude</sub></span>.</p> Full article ">Figure 7
<p>Profile of electron density in the channel for 90 nm MOSFET (<span class="html-italic">µ</span> = 0.4 m<sup>2</sup>/Vs) under THz radiation: (<b>a</b>) COMSOL simulation, (<b>b</b>) MOSA1 50-segment model with varying <span class="html-italic">L<sub>drude</sub></span>, (<b>c</b>) EKV 50-segment model with varying <span class="html-italic">L<sub>drude</sub></span>.</p> Full article ">Figure 8
<p>Comparison of THz response between the analytical theory (lines), COMSOL simulation (circles), 50-segment SPICE model with constant <span class="html-italic">L<sub>drude</sub></span> (rectangles), and variable <span class="html-italic">L<sub>drude</sub></span> (triangles) for low mobility MOSFET with (<b>a</b>) 45 nm channel length and (<b>b</b>) 90 nm channel length.</p> Full article ">Figure 9
<p>Profile of drift velocity for 90 nm MOSFET (<span class="html-italic">µ</span> = 0.1 m<sup>2</sup>/Vs) under THz radiation: (<b>a</b>) COMSOL simulation, (<b>b</b>) EKV 50-segment model with varying <span class="html-italic">L<sub>drude</sub></span>, and profile of electron density in the channel for 90 nm MOSFET (<span class="html-italic">µ</span> = 0.1 m<sup>2</sup>/Vs) under THz radiation: (<b>c</b>) COMSOL simulation, (<b>d</b>) EKV 50-segment model with varying <span class="html-italic">L<sub>drude</sub></span>.</p> Full article ">Figure 9 Cont.
<p>Profile of drift velocity for 90 nm MOSFET (<span class="html-italic">µ</span> = 0.1 m<sup>2</sup>/Vs) under THz radiation: (<b>a</b>) COMSOL simulation, (<b>b</b>) EKV 50-segment model with varying <span class="html-italic">L<sub>drude</sub></span>, and profile of electron density in the channel for 90 nm MOSFET (<span class="html-italic">µ</span> = 0.1 m<sup>2</sup>/Vs) under THz radiation: (<b>c</b>) COMSOL simulation, (<b>d</b>) EKV 50-segment model with varying <span class="html-italic">L<sub>drude</sub></span>.</p> Full article ">
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 533
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)
►▼ Show Figures

Figure 1

Figure 1
<p>Clamp1: (<b>a</b>) schematic structure, (<b>b</b>) PCB layout and picture; Clamp2: (<b>c</b>) schematic structure, (<b>d</b>) PCB layout and picture.</p> Full article ">Figure 2
<p>(<b>a</b>) Positive TLP <span class="html-italic">I–V</span> characteristics of clamp1; (<b>b</b>) positive leakage current characteristics of clamp1.</p> Full article ">Figure 3
<p>Test result for clamp2: positive TLP <span class="html-italic">I–V</span> characteristics with different <span class="html-italic">R</span><sub>2</sub> values (<b>a</b>) linear-scale and (<b>b</b>) log-scale; (<b>c</b>) <span class="html-italic">V</span><sub>Tri</sub>; (<b>d</b>) positive TLP <span class="html-italic">I–V</span> characteristics with different number of forward diodes.</p> Full article ">Figure 4
<p>Positive leakage current characteristics of clamp2 with different <span class="html-italic">R</span><sub>2</sub> values.</p> Full article ">Figure 5
<p>Schematic structure and test board pictures of (<b>a</b>) resistive ESD circuit and (<b>b</b>) clamp2 with gate-source shorted p-GaN HEMT as equivalent diode; comparison of test results of: (<b>c</b>) positive TLP <span class="html-italic">I–V</span> and (<b>d</b>) positive leakage current characteristics with different ESD circuit.</p> Full article ">Figure 6
<p>Reverse TLP <span class="html-italic">I–V</span> characteristics of clamp2.</p> Full article ">Figure 7
<p>Switch characteristics of protected HEMT with or without the proposed ESD clamp2: (<b>a</b>) schematic structure; (<b>b</b>) test board pictures; (<b>c</b>) test result for gate voltage of mainHEMT (<span class="html-italic">V</span><sub>G</sub>); (<b>d</b>) test result for drain voltage of mainHEMT (<span class="html-italic">V</span><sub>D</sub>).</p> Full article ">
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 906
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)
►▼ Show Figures

Figure 1

Figure 1
<p>Conventional (<b>a</b>) and QC-HEMT (<b>b</b>) designs. QC-HEMT in (<b>b</b>) can have GaN or AlGaN channel (GaN channel is shown).</p> Full article ">Figure 2
<p>Conduction energy band diagrams of conventional HEMT (<b>a</b>) and QC-HEMTs (<b>b</b>,<b>c</b>) with different channel-barrier configurations, as shown in <a href="#micromachines-15-01384-t001" class="html-table">Table 1</a> below. VG and VTTH are the gate and threshold voltages correspondingly. The EBG HEMT in (<b>d</b>) is included for comparison with experimental data discussed later in this paper.</p> Full article ">Figure 3
<p>Conduction band Ec profile (<b>a</b>) and electron density profile (<b>b</b>) at V<sub>G</sub> ≈ V<sub>TH</sub> for the QC-HEMT with a 500 Å thick GaN channel between the 25%-Al top and back barriers. For comparison, (<b>b</b>) also shows the electron density profile for the conventional HEMT at V<sub>G</sub> ≈ V<sub>TH</sub>.</p> Full article ">Figure 4
<p>Dependencies of the ground state energy <span class="html-italic">E</span><sub>0</sub> above the bottom of the conduction band on the sheet carrier concentration <span class="html-italic">n<sub>S</sub></span> for the conventional HEMT and the QC-HEMT with a 2 nm thick channel.</p> Full article ">Figure 5
<p>The 2DEG volume electron density as a function of n<sub>s</sub> in conventional and QC HEMTs.</p> Full article ">Figure 6
<p>(<b>a</b>) Expected mobility increase in a QC HEMT; (<b>b</b>) experimentally observed mobility increase in double heterostructure (DH) HEMT.</p> Full article ">Figure 7
<p>Schematic cross-section (<b>a</b>) and reciprocal space mapping of the epilayer structure (<b>b</b>) of Al<sub>0.64</sub>Ga<sub>0.36</sub>N channel insulated-gate <span class="html-italic">E<sub>BG</sub></span> HEMT [<a href="#B38-micromachines-15-01384" class="html-bibr">38</a>,<a href="#B39-micromachines-15-01384" class="html-bibr">39</a>].</p> Full article ">Figure 8
<p>EBG HEMT breakdown current-voltage characteristics [<a href="#B1-micromachines-15-01384" class="html-bibr">1</a>].</p> Full article ">Figure 9
<p>EBG HEMT drain current I<sub>D</sub> (V<sub>D</sub>) (<b>a</b>), transfer ID (VG), and transconductance g<sub>m</sub> (V<sub>G</sub>) (<b>b</b>) characteristics [<a href="#B39-micromachines-15-01384" class="html-bibr">39</a>].</p> Full article ">Figure 10
<p>Triangular QW profile used in MATLAB calculations of the ground state energy <span class="html-italic">E</span><sub>1</sub>. The barrier height at the Al<sub>0.87</sub>Ga<sub>0.13</sub>N/Al<sub>0.64</sub>Ga<sub>0.36</sub>N barrier/channel interface, <span class="html-italic">V<sub>B</sub></span> = 0.72 eV, electric field in the channel <span class="html-italic">F<sub>CH</sub></span> = 0.5 MV/cm, electron effective mass in the channel, <span class="html-italic">m<sub>EF</sub></span> = 0.34 <span class="html-italic">m</span><sub>0</sub>.</p> Full article ">Figure 11
<p>Barrier reduction for energetic electrons: (<b>a</b>) effective barrier height versus kinetic energy of electrons for effective mass ratio in the QC-HEMT studied in this paper and (<b>b</b>) effective barrier height versus kinetic energy of electrons for all mass ratios for AlN/GaN system.</p> Full article ">
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 829
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)
►▼ Show Figures

Figure 1

Figure 1
<p>The basic structure of the proposed EM pulse generation circuit (12T2C).</p> Full article ">Figure 2
<p>Timing diagrams for the proposed EM pulse generation circuit. (<b>a</b>) Even multiple pulse width of a horizontal time (4 horizontal times) where CLKE is equivalent to CLKB. (<b>b</b>) Odd multiple pulse width of a horizontal time (5 horizontal times) where CLKE is synchronized to CLK. The operation consists of (1) Pulling-Up, (2) Capacitive-Coupling, (3) Holding, and (4) Pulling-Down periods.</p> Full article ">Figure 3
<p>The four-phase operational sequence of the proposed EM circuit. (<b>a</b>) Pulling-Up, (<b>b</b>) Capacitive-Coupling, (<b>c</b>) Holding, (<b>d</b>) Pulling-Down. Blue line, light blue arrow, and pink arrow represent turned-off TFT, charging, and discharging, respectively.</p> Full article ">Figure 4
<p>Internal inverter circuits for QB[n] generation. (<b>a</b>) Previous circuit with the shoot-through current path of one horizontal time regardless of the pulse width [<a href="#B33-micromachines-15-01330" class="html-bibr">33</a>], (<b>b</b>) Proposed circuit without any shoot-through current paths.</p> Full article ">Figure 5
<p>EM pulse generation circuit with depletion mode prevention structures.</p> Full article ">Figure 6
<p>Transfer curve of a n-Type a-IGZO TFT model for simulation.</p> Full article ">Figure 7
<p>Overall configuration of proposed EM pulse generation circuits.</p> Full article ">Figure 8
<p>Simulated waveforms of signals, outputs, and internal nodes. (<b>a</b>) For the even multiple short pulse width of 4 horizontal times, (<b>b</b>) For the odd multiple short pulse width of 3 horizontal times, (<b>c</b>) For the even multiple long pulse width of 2156 horizontal times, (<b>d</b>) For the odd multiple long pulse width of 2157 horizontal times.</p> Full article ">Figure 9
<p>Robustness of the proposed EM circuit over <math display="inline"><semantics> <msub> <mi>V</mi> <mrow> <mi>t</mi> <mi>h</mi> </mrow> </msub> </semantics></math>. The proposed circuit keeps the stable operation over the range of <math display="inline"><semantics> <msub> <mi>V</mi> <mrow> <mi>t</mi> <mi>h</mi> </mrow> </msub> </semantics></math> from <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>4.0</mn> </mrow> </semantics></math> V to <math display="inline"><semantics> <mrow> <mn>2.5</mn> </mrow> </semantics></math> V.</p> Full article ">Figure 10
<p>Rising and falling transitions of EM[n] pulses depending on <math display="inline"><semantics> <msub> <mi>C</mi> <mn>1</mn> </msub> </semantics></math> and <math display="inline"><semantics> <msub> <mi>C</mi> <mn>2</mn> </msub> </semantics></math>. Consequently, the transition characteristics are independent of <math display="inline"><semantics> <msub> <mi>C</mi> <mn>1</mn> </msub> </semantics></math> and <math display="inline"><semantics> <msub> <mi>C</mi> <mn>2</mn> </msub> </semantics></math>.</p> Full article ">Figure 11
<p>Estimated power consumption over the <math display="inline"><semantics> <msub> <mi>V</mi> <mrow> <mi>t</mi> <mi>h</mi> </mrow> </msub> </semantics></math> variation from −4.0 V to 2.5 V for 30 stages and the pulse width of 2157 horizontal times.</p> Full article ">Figure 12
<p>Estimated power consumption over the <math display="inline"><semantics> <msub> <mi>V</mi> <mrow> <mi>t</mi> <mi>h</mi> </mrow> </msub> </semantics></math> variation from <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>4.0</mn> </mrow> </semantics></math> V to 2.5 V for 30 stages and the pulse width of 2157 horizontal times.</p> Full article ">Figure 13
<p>Layout design of the proposed EM pulse generation circuit.</p> Full article ">
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 1136
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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Figure 1

Figure 1
<p>Schematic diagram of the epitaxial layer structure of (<b>a</b>) AlGaN/GaN/AlN/GaN and (<b>b</b>) AlGaN/GaN/InAlN/GaN.</p> Full article ">Figure 2
<p>The energy-dispersive X-ray spectroscopy mapping images of In, Al, and Ga element distribution.</p> Full article ">Figure 3
<p>(<b>a</b>) CV and (<b>b</b>) electron concentration distribution of the AlGaN/GaN/InAlN/GaN and AlGaN/GaN/AlN/GaN HEMTs.</p> Full article ">Figure 4
<p>The energy band diagram and electron concentration distributions of the (<b>a</b>) sub-AlN HEMTs and (<b>b</b>) sub-InAlN HEMTs.</p> Full article ">Figure 5
<p>The contact resistance (<span class="html-italic">R</span><sub>c</sub>) and block resistance (<span class="html-italic">R</span><sub>sheet</sub>) of the sub-InAlN/sub-AlN HEMTs tested from the transmission line model (TLM).</p> Full article ">Figure 6
<p>The transfer curve of (<b>a</b>) AlGaN/GaN/AlN/GaN and (<b>b</b>) AlGaN/GaN/InAlN/GaN HEMTs.</p> Full article ">Figure 7
<p>The mobility curve of AlGaN/GaN/InAlN/GaN and AlGaN/GaN/AlN/GaN HEMTs extracted from the transfer curve.</p> Full article ">Figure 8
<p>(<b>a</b>) The output curve of the sub-AlN/sub-InAlN HEMTs. (<b>b</b>) The breakdown characteristics of the sub-AlN/sub-InAlN HEMTs.</p> Full article ">Figure 9
<p>The <span class="html-italic">f</span><sub>max</sub> and <span class="html-italic">f</span><sub>T</sub> of (<b>a</b>) the sub-InAlN and (<b>b</b>) sub-AlN HEMTs at a <span class="html-italic">V</span><sub>d</sub> of 10 V.</p> Full article ">Figure 10
<p>(<b>a</b>) The <span class="html-italic">f</span><sub>max</sub> of the sub-InAlN/sub-AlN HEMTs versus <span class="html-italic">V</span><sub>d</sub>. (<b>b</b>) The <span class="html-italic">f</span><sub>T</sub> of the sub-InAlN/sub-AlN HEMTs versus <span class="html-italic">V</span><sub>g</sub>.</p> Full article ">Figure 11
<p>(<b>a</b>) The drain lag ratio (DRL) of the sub-AlN/sub-InAlN HEMTs. (<b>b</b>) The DRL versus <span class="html-italic">V</span><sub>DS</sub>. Schematic of AlN barrier suppressing the DRL in (<b>c</b>) sub-AlN HEMTs compared with the (<b>d</b>) sub-InAlN HEMTs.</p> Full article ">Figure 12
<p>The load-pull measurement for the (<b>a</b>) sub-AlN and (<b>b</b>) sub-InAlN HEMTs at 3.6 GHz with 50 V of <span class="html-italic">V</span><sub>d</sub>.</p> Full article ">

Review

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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 640
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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<p>Single-crystal AlN and its epitaxial growth. (<b>a</b>) Graphical illustration of growth process under different growth temperatures [<a href="#B27-micromachines-16-00205" class="html-bibr">27</a>]. Step (1) is Wafer surface cleaning; Step (2) is GaN nucleation layer; Step (3) is GaN growth; Step (4) is AlN growth. This image has been obtained with permission from IEEE Publishing. (<b>b</b>) Schematic using the epitaxial AlN layer as a sputtering template to grow the single-crystal AlN substrate. Adapted from [<a href="#B29-micromachines-16-00205" class="html-bibr">29</a>].</p> Full article ">Figure 2
<p>Properties and preparation of doped AlN. (<b>a</b>) TCF of Sc<sub>x</sub>Al<sub>1−x</sub>N films as a function of Sc concentration (x) [<a href="#B30-micromachines-16-00205" class="html-bibr">30</a>]. This image has been obtained with permission from IEEE Publishing. (<b>b</b>) Method for depositing c-axis zig-zag ScAlN multilayers. Adapted from [<a href="#B56-micromachines-16-00205" class="html-bibr">56</a>].</p> Full article ">Figure 3
<p>The structure of BAW. (<b>a</b>–<b>d</b>) SMR, back silicon etching-type FBAR, lower concave cavity-type FBAR, and upper convex cavity-type FBAR, respectively.</p> Full article ">Figure 4
<p>Fabrication of BAW-SMR. (<b>a</b>) Schematic representation of SMR structures without and with electrode frames. Adapted from [<a href="#B66-micromachines-16-00205" class="html-bibr">66</a>]. (<b>b</b>) Schematic diagram of SMR on acoustic reflector diagram. The bottom electrode cannot be directly accessed by the RF probe and is instead excited by the capacitive coupling effect. Adapted from [<a href="#B64-micromachines-16-00205" class="html-bibr">64</a>].</p> Full article ">Figure 5
<p>The fabrication of BAW-FBAR. (<b>a</b>) Fabrication process of the FBAR device. Adapted from [<a href="#B75-micromachines-16-00205" class="html-bibr">75</a>]. (<b>b</b>) Fabrication of AlScN-based upper mounted cavity-type FBAR. Adapted from [<a href="#B82-micromachines-16-00205" class="html-bibr">82</a>] (<b>c</b>) Wafer bonding and layer transfer techniques. Adapted from [<a href="#B29-micromachines-16-00205" class="html-bibr">29</a>].</p> Full article ">Figure 5 Cont.
<p>The fabrication of BAW-FBAR. (<b>a</b>) Fabrication process of the FBAR device. Adapted from [<a href="#B75-micromachines-16-00205" class="html-bibr">75</a>]. (<b>b</b>) Fabrication of AlScN-based upper mounted cavity-type FBAR. Adapted from [<a href="#B82-micromachines-16-00205" class="html-bibr">82</a>] (<b>c</b>) Wafer bonding and layer transfer techniques. Adapted from [<a href="#B29-micromachines-16-00205" class="html-bibr">29</a>].</p> Full article ">Figure 6
<p>BAW-XBAW resonator. (<b>a</b>) Simplified section view of the XBAR resonator. Adapted from [<a href="#B92-micromachines-16-00205" class="html-bibr">92</a>]. (<b>b</b>) Traditional frequency scaling, simple nth overtone scaling and P3F scaling [<a href="#B89-micromachines-16-00205" class="html-bibr">89</a>]. This image has been obtained with permission from IEEE Publishing.</p> Full article ">Figure 7
<p>Construction and fabrication of HSBRs. Six-mask process flow for fabricating HSBRs. Adapted from [<a href="#B95-micromachines-16-00205" class="html-bibr">95</a>].</p> Full article ">Figure 8
<p>Improvement of HSBR performance. (<b>a</b>) Schematic of the coupled BAW/SAW resonator proposed in [<a href="#B101-micromachines-16-00205" class="html-bibr">101</a>]. (<b>b</b>) The estimation results by FEM (marked stars show the experimental results and phase velocity of the excited mode for Si and GaN substrates) [<a href="#B101-micromachines-16-00205" class="html-bibr">101</a>]. (<b>c</b>) The phase velocity of the excited mode for Si and GaN substrates [<a href="#B101-micromachines-16-00205" class="html-bibr">101</a>]. Images (<b>a</b>–<b>c</b>) have been obtained with permission from IEEE Publishing.</p> Full article ">Figure 9
<p>The measures to expand bandwidth. (<b>a</b>) Ladder filter. (<b>b</b>) lattice filter. (<b>c</b>) ladder-lattice filter [<a href="#B78-micromachines-16-00205" class="html-bibr">78</a>]. (<b>d</b>) Topological structure of the ladder-type FBAR filter circuit. Adapted from [<a href="#B109-micromachines-16-00205" class="html-bibr">109</a>]. (<b>e</b>) The filter topology structure combining BAW and IPD technologies. Adapted from [<a href="#B110-micromachines-16-00205" class="html-bibr">110</a>] (<b>f</b>) Topology of the hybrid B41 BAW filter. Adapted from [<a href="#B111-micromachines-16-00205" class="html-bibr">111</a>] with AlN resonators.</p> Full article ">
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