GaN MOSHEMTs and MISHEMTs: A comprehensive review of device physics, materials innovation, and technological pathways in power and RF electronics

Wide bandgap electronics made from nitrides (e.g., Gallium Nitride (GaN)) and oxides (e.g., Gallium Oxide (Ga2O3)) are currently under development due to their potential to create some of the most advanced RF and power electronic devices in the world. However, the thermal response of these devices under applied electric fields can create large power densities (RF and power electronics) that must be understood. For many of these devices, the electrothermal response plays a strong role in both the acceptable operation or long-term failure and reliability of the devices. Thus, tools that can help elucidate these responses and provide a method to help design better devices is of critical need for this field.In this talk we will discuss advancements in thermal characterization techniques that have allowed new insights into electrothermal behavior in GaN and Ga2O3 materials and devices. Specifically, a focus on the role of device architecture and material processing will be addressed. For GaN and Ga2O3 RF and power electronics, the role of thermal interfaces in the heat dissipation of both lateral and vertical device architectures will be discussed. We will cover aspects of semiconductor-semiconductor as well as metal-semiconductor interfaces and their roles in device thermal management. A highlight will be the use of plasma activated bonding to provide ultralow thermal resistance interfaces that allow for heterogenous integration of nitrides and oxides with high thermal conductivity substrates. Finally, we will discuss the implications of these effects on device behavior through experiments and modeling.

We are studying the development of space-flight compatible room-temperature electronics for the Lynx x-ray microcalorimeter (LXM) of the Lynx mission. The baseline readout technique for the LXM is microwave SQUID multiplexing. The key modules at room temperature are the RF electronics module and the digital electronics and event processor (DEEP). The RF module functions as frequency converters and mainly consists of local oscillators and I/Q mixers. The DEEP performs demultiplexing and event processing, and mainly consists of field-programmable gate arrays, ADCs, and DACs. We designed the RF electronics and DEEP to be flight ready, and estimated the power, size, and mass of those modules. There are two boxes each for the RF electronics and DEEP for segmentation, and the sizes of the boxes are 13 in: × 13 in: × 9 in: for the RF electronics and 15.5 in: × 11.5 in: × 9.5 in: for the DEEP. The estimated masses are 25.1 kg∕box for the RF electronics box and 24.1 kg∕box for the DEEP box. The maximum operating power for the RF electronics is 141 W or 70.5 W∕box, and for the DEEP box is 615 W or 308 W∕box. The overall power for those modules is 756 W. We describe the detail of the designs as well as the approaches to the estimation of resources, sizes, masses, and powers.

Efficient thermal management is crucial for maintaining the performance, reliability, and longevity of power electronics systems, especially as power densities increase with advancements in semiconductor technologies. This paper explores various heat dissipation techniques, including passive, active, and hybrid cooling methods, while addressing the challenges of thermal management, such as high power density, material limitations, and cost-performance trade-offs. Additionally, it delves into heat sink design optimization, advanced cooling technologies, and the impact of thermal management on system reliability and performance. Finally, the paper examines future trends in heat dissipation, highlighting innovations in materials, designs, and sustainable cooling solutions to meet the evolving demands of power electronics.

In this work we proposea novel design for an enhancement-modegallium nitride (GaN) high-electron-mobility transistor (HEMT) thatachieves normally off operation along with increased drive currentand improved breakdown voltage. The device uses an undoped aluminumnitride (AlN) buffer layer to boost breakdown strength. By etchingthe AlN buffer into a fin-like shape under the gate, a two-dimensionalhole gas (2DHG) forms at the GaN/AlN interface. This 2DHG locallydepletes the two-dimensional electron gas (2DEG) under the gate, therebyconverting the transistor to enhancement-mode. Silvaco ATLAS TechnologyComputer-Aided Design (TCAD) simulations have been performed and calibratedwith experimental data, to validate the effectiveness of the proposedstructure. The results demonstrate a positive threshold voltage ofabout +2.3 V, ∼6× increase in maximum drain current, and∼2.4× increase in breakdown voltage compared to a conventionalPE-HEMT. The influence of key design parameters (AlN fin depth, length,and polarization scaling) on the device performance is analyzed indetail. An AC analysis was also conducted, revealing that the proposeddevice achieves a 1.4× improvement in cutoff frequency (fT) and a 1.2× increase in maximum oscillationfrequency (fmax) compared to the conventionalPE-HEMT. The proposed GaN MOS-HEMT shows promising features for next-generationhigh-power and RF electronics which offers a reliable normally offoperation with enhanced current drive and high voltage capability.

This work demonstrates a novel approach featuring low-temperature 300°C 5 mins thermal oxidation of the AlN/gate metal interface performed prior to ohmic contact formation to eliminate thermal degradation of contacts. Compared to standard non-oxidized Schottky device, this optimized flow delivers an order-of-magnitude reduction in gate leakage current, alongside a 16.4% increase in peak transconductance (g<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m,max</inf>) and a 7.3% enhancement in maximum drain current (I<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DMAX</inf>). Comparative C-V analysis showed minimal capacitance variation but revealed a slight negative threshold voltage shift with increasing temperature. This highly effective, equipment-shared approach is promising for next-generation high-performance GaN power and RF electronics.

Global climate change and the energy crisis pose severe challenges to sustainable development, driving the urgent need for innovative carbon-neutral technological pathways. Among various potential solutions, photocatalytic CO2 reduction technology attracts significant attention for its ability to directly utilize solar energy to convert CO2 into high-value-added fuels and chemicals. However, in practical application environments, the low concentration of CO2 and the pronounced inhibitory effect of oxygen on the catalytic reaction have long constrained the scalable development of this technology. This review systematically elaborates on the latest significant advancements in the field of photocatalytic CO2 reduction under close-to-realistic conditions (containing 0.04% or 15% CO2 and 5%-20% O2 under simulated solar light), focusing on three main technological directions: integrated CO2 capture and conversion, CO2-preferential microenvironment engineering, and O2-assisted CO2 reduction mechanisms. These interconnected research pathways have collectively driven a paradigm shift in the field from "passively avoiding oxygen interference" to "actively harnessing oxygen synergy." This progress has preliminarily overcome key bottlenecks such as low conversion efficiency of dilute CO2, intense competitive oxygen reduction reactions, and high energy consumption for product separation. These advancements provide the way for distributed carbon-neutral technologies and shifting CO2 utilization from idealized systems toward real-world applications.

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

This research article provides an in-depth examination of the operational principles, structural intricacies, material innovations, and electrical behavior of High Electron Mobility Transistors (HEMTs). Emphasizing their essential role in high-frequency and power electronics, this review explores the underlying physics of heterostructure formation, analyzes advanced material systems such as InP and GaN, and introduces the velocity-electric field (V–E) characteristics as a crucial performance metric. The inclusion of novel materials and fabrication strategies has propelled HEMTs into diverse application domains, from RF amplifiers to satellite communication systems. This study aims to serve as a foundational reference for researchers and engineers working in advanced electronic device design.

This special edition presents the results of the exploration of properties and sphere of applications of cutting-edge engineering materials, providing a comprehensive understanding of their role in the development of various engineering fields. The compilation will serve as a valuable resource for researchers and engineers seeking to stay at the forefront of developments in applied material science, and we hope that it will inspire their further exploration and innovation.

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The microwave (MW) dielectric permittivity of gallium oxide (β-Ga2O3) fundamentally determines its interaction with an electromagnetic wave in bulk power. Yet, there is a lack of experimental data due to limitations of high-temperature MW dielectric measurements and the large uncertainty under variable-temperature conditions. Herein, we develop a deep potential (DP) based on density functional theory (DFT) results and apply deep potential molecular dynamics (DPMD) for accurately predicting temperature-dependent MW dielectric permittivity of β-Ga2O3. The predicted energies and forces by DP demonstrate excellent agreement with DFT results, and DPMD successfully simulates systems up to 1280 atoms with quantum precision over nanosecond scales. Overall, the real part of the MW dielectric permittivity decreases with rising frequency, but the dielectric loss increases. The MW dielectric permittivity gradually increases as the temperature increases, which is closely related to the reduced dielectric relaxation time and increased static and high-frequency dielectric constants. Besides, the oxygen vacancy defects significantly reduce the relaxation time; however, augmenting the defect concentration will cause a slight rise in relaxation time. The electron localization function analysis reveals that more free electrons and low localization of electrons produced by high defect concentrations facilitate the increased relaxation time. This study provides an alternative route to investigate the temperature-dependent MW permittivity of β-Ga2O3, which attains prime importance for its potential applications in RF and power electronics.

Body: Newly emerged wide bandgap semiconductor (WBG) β-Ga2O3 has been extensively researched for power electronics, RF electronics and optoelectronics due to its large bandgap of 4.7- 4.9 eV and high breakdown field of ~ 8 MV/cm. Due to the absence of p-type Ga2O3, most of demonstrated β-Ga2O3 devices are unipolar devices such as high electron mobility transistors (HEMTs) and Schottky barrier diodes. To overcome this limitation, other p-type materials, such as GaN and NiO, have been investigated to produce Ga2O3 based p-n heterojunctions. Among these p-type materials, p-GaN has attracted especial interests since GaN is also a WBG semiconductor and has a clear crystallographic relationship to β-Ga2O3 for epitaxial growth. In addition, both β-Ga2O3 and GaN can be produced in the industrial standard tools, i.e., the metalorganic chemical vapor deposition (MOCVD). The growth of high-quality GaN on Ga2O3 by MOCVD has been recently reported. β-Ga2O3/GaN p-n heterojunction via mechanically exfoliation also showed decent rectifying behaviors. However, the breakdown capability of the β-Ga2O3 based p-n heterojunctions is still far from expectations due to the lack of effective edge terminations. Here we design and simulate mesa based edge terminations for the vertical β-Ga2O3/GaN p-n heterojunctions using SILVACO TCAD simulator. The model was first calibrated by the experimental results, including the conduction and valance band offsets of the heterojunction and electrical properties. The device structure consisted of n+-Ga2O3 n-contact layer, 5 µm unintentionally doped (UID) β-Ga2O3 drift layer and 500 nm p-GaN layer. The ideal breakdown voltage (BV) of the heterojunction was 1.37 kV, while the BV of the reference device without effect mesa edge termination dropped dramatically to 300 V due to the electric field crowding at the device edge. Therefore, it is critical to design and optimize the mesa edge termination to improve the BV of the β-Ga2O3/GaN p-n heterojunctions. Three mesa edge termination structures were investigated in this work: beveled mesa, step mesa, and deeply-etched mesa. The beveled mesa angle θ is the key parameter in determining the device BV. When θ was varied from 15° to 90°, the highest BV of 1224 V was obtained for θ =15°. For the step mesa edge termination, the width (W), depth (D), and the number of steps define the mesa structure. It was found that the BV of the devices increased with increasing number of steps. The combination of (W, D) values of (0.5,0.5) and (0.5,1.0) and (1.0,1,0) was investigated, where all the values are in µm. The highest value was obtained for W = 0.5µm, D = 1.0µm and the number of steps = 5. Smaller W and larger D led to better BV. The electric field distributions of devices with different mesa edge terminations were compared at –300V. Without effect mesa edge termination, the peak electric field at the junction edge was ~ 4.2 MV/cm. By incorporating the mesa edge termination techniques, the electric field crowding at the device edge was mitigated, and the peak electric fields were reduced to 1.8 MV/cm and 2.4 MV/cm for the beveled and step mesa edge terminations, respectively. For the deeply-etched mesa structure, it was found that a more uniform electric field distribution was observed when the mesa depth was increased from 0.5,1.0, 2.0, to 3.0 µm, where the peak electric fields were decreased from 2.1, 1.8 ,1.5 to 1.2 MV/cm, respectively. In summary, this work presents a comprehensive design and optimization of mesa edge terminations for the wide bandgap vertical β-Ga2O3/GaN p-n heterojunctions, which is first of its kind. Three mesa structures were explored, including beveled mesa, step mesa and deeply-etched mesa. It was found that these mesa edge terminations can alleviate the electric field crowding at the junction edge and increase the device BV. This work can provide critical guidance for the development of high-performance β-Ga2O3 based bipolar high voltage and high power devices.

Summary form only given. The scaling of CMOS technology has led to phenomenal growth in transistor density and performance during the last three decades. However, starting at 90nm CMOS node, the industry started to experience significant barriers in achieving historical transistor performance gains through traditional dimensional scaling. Fortunately, the industry has responded positively to this challenge by implementing many innovations in device structure and materials to overcome traditional scaling barriers. Intel has been at the forefront in addressing these challenges by successfully driving transistor innovations from research phase to mainstream CMOS manufacturing. Implementation of uniaxial strained-silicon transistors at the 90nm node and the recently announced HiK+Metal Gate transistors for the 45nm node are two excellent examples of major innovations which have demonstrated dramatic performance enhancement. After a brief review highlighting the dramatic performance benefits demonstrated with uniaxial strained silicon technology, I will describe process details and present significant performance gains achieved with HiK+Metal Gate transistor technology for 45nm CMOS node. Finally, I will discuss the role of increasing power density and transistor parasitics in limiting future CMOS transistor scaling and describe potential new transistor structure and material innovations required to meet performance/power/density improvements beyond 45nm CMOS node. The convergence of new transistor structure and materials will be critical for successfully scaling CMOS transistors through next decade.

Fabrication of binder-free mixed sulphide/PANI nanocomposite based electrode for supercapacitor application

The synergy between biology and electronics has revolutionized the material science and biological science world and have been emerged as a new field of science known as bioelectronics. The fabrication of novel bioelectronic devices integrates the estates of materials as well as biology and will bridge the gap between these two branches. The design and development of bioelectronic devices such as bio-actuators, biofuel cells, and biosensors will open new horizons and prospects in the fields of electronics, biology, medicine, health care, forensic, environmental protection, etc. Among the nanomaterials, carbon-based nanomaterials have the bourgeoning power to act as an interface material in bioelectronic devices. The intriguing chattels of graphene, the allotropic form of carbon have emerged as an innovative and elegant nano-biosensing interface material in recent times. The unique characteristics of graphene such as excellent electrical conductivity, mechanical strength, and larger surface area, brand this material as an auspicious contender in diverse application fields like biosensors, energy storage, and hydrogen storage devices. The striking and brilliant assets of graphene-based nanomaterials have surfaced the assembly of novel bioelectronic devices with amended analytical performances. The biological recognition processes as well as sensing studies can be achieved with a lower detection limit and with a high degree of accuracy by integrating the graphene-based materials. The present chapter will be comprised of structure, synthesis, characterization, and excellent properties of graphene-based interface materials with their promising applications in the fields of bioelectronics and will focus on the future projections of graphene-based bioelectronic interfaces.