The rapid development of the RF power electronics requires the introduction of wide bandgap material due to its potential in high output power density, high operation voltage and high input impedance GaN-based RF power devices have made substantial progresses in the last decade This paper attempts to review the latest developments of the GaN HEMT technologies, including material growth, processing technologies, device epitaxial structures and MMIC designs, to achieve the state-of-the-art microwave and millimeter-wave performance The reliability and manufacturing challenges are also discussed

GaN-Based RF Power Devices and Amplifiers

A wide variety of semiconductor devices are used in wireless power amplifiers. The RF performance and other attributes of cellphone RF power amplifiers using Si and GaAs based technologies are reviewed and compared.

RF power amplifiers for wireless communications

Gallium nitride (GaN) power devices are an emerging technology that have only recently become available commercially. This new technology enables the design of converters at higher frequencies and efficiencies than those achievable with conventional Si devices. This paper reviews the characteristics and commercial status of both vertical and lateral GaN power devices, providing the background necessary to understand the significance of these recent developments. In addition, the challenges encountered in GaN-based converter design are considered, such as the consequences of faster switching on gate driver design and board layout. Other issues include the unique reverse conduction behavior, dynamic $R_{\mathrm {{ds}},\mathrm {{on}}}$ , breakdown mechanisms, thermal design, device availability, and reliability qualification. This review will help prepare the reader to effectively design GaN-based converters, as these devices become increasingly available on a commercial scale.

Review of Commercial GaN Power Devices and GaN-Based Converter Design Challenges

A dry etching method for etching an aluminum (Al) based layer for effectively combatting the after-corrosion in accordance with three aspects. In the first aspect, while a resist mask and chlorine based gas as known per se are used, S 2 F 2 is used during etching of the barrier metal layer. In this manner, residual chlorine in a carbonaceous polymer as a sidewall protection material or a resist mask is replaced by fluorine, whilst sulfur yielded from S 2 F 2 under conditions of discharge dissociation is deposited to provide for sidewall protection effects. In the second aspect, a SiO 2 mask and an S 2 Cl 2 etching gas are used. Since the sidewall protection material is solely sulfur yielded from S 2 Cl 2 , it becomes possible to avoid the effects of the residual chlorine. In the third aspect, an neutral Ar beam is irradiated at a suitable stage in the etching process for increasing the resistance of the SiO 2 mask against reducing compounds contained in an etching gas for the layer of the aluminum-based material. By irradiation of the neutral beam, a reduction-resistant layer is produced on the surface of the SiO 2 mask to render it possible to reduce the mask thickness without producing problems such as increased step differences on the wafer surface.

Dry etching method

Failure modes and mechanisms of AlGaN/GaN high-electron-mobility transistors are reviewed. Data from three de-accelerated tests are presented, which demonstrate a close correlation between failure modes and bias point. Maximum degradation was found in "semi-on" conditions, close to the maximum of hot-electron generation which was detected with the aid of electroluminescence (EL) measurements. This suggests a contribution of hot-electron effects to device degradation, at least at moderate drain bias (VDS 30-50 V), new failure mechanisms are triggered, which induce an increase of gate leakage current. The latter is possibly related with the inverse piezoelectric effect leading to defect generation due to strain relaxation, and/or to localized permanent breakdown of the AlGaN barrier layer. Results are compared with literature data throughout the text.

Reliability of GaN High-Electron-Mobility Transistors: State of the Art and Perspectives

A high electron mobility transistor (HEMT) logic is described. Ring oscillators with enhancement-mode switching and depletion-mode load HEMTs with a 1.7 µm-gate length have been fabricated to assess logic performance capability. Switching delays down to 56.5 ps at room temperature and down to 17.1 ps at liquid nitrogen temperature have been obtained. The switching delay of 17.1 ps is the lowest of all the semiconductor logic technologies reported thus far.

https://iopscience.iop.org/article/10.1143/JJAP.20.L598/pdf

High Electron Mobility Transistor Logic

Selective dry etching of GaAs to AlxGa1-xAs (x=0.3) using an etching gas composed of CCl2F2 and helium was studied. Etching was carried out at gas composition ratios of PCCl2F2 /PHe above 0.25, total pressures of 0.5 to 5.0 Pa, and power densities of 0.18 to 0.53 W/cm2. A high selectivity ratio exceeding 200 and a clean etch profile were obtained at a gas composition ratio of PCCl2F2 /PHe=1 operated at 5 Pa and 0.18 W/cm2. The etched profile of GaAs under the above conditions exhibited a nearly vertical-wall character.

https://iopscience.iop.org/article/10.1143/JJAP.20.L847/pdf

Selective Dry Etching of AlGaAs-GaAs Heterojunction

AlGaN/GaN high electron mobility transistors (HEMTs) have been developed for current-collapse-free operation at high drain bias voltages The newly designed single-chip GaN HEMT amplifier for W-CDMA base station applications achieves a record CW output power of 150 W with a high power-added efficiency (PAE) of 54% at 21 GHz The amplifier, combined with a digital pre-distortion (DPD) system, also demonstrates a state of the art efficiency of 40% with an adjacent channel leakage power ratio (ACLR) of less than -50 dBc for 4-carrier W-CDMA signals and reaches the saturated peak power level of 174 W with a drain supply voltage of 63 V We prove for the first time that the AlGaN/GaN HEMT amplifier can completely fulfills the W-CDMA system requirement

A 174 W high-efficiency GaN HEMT power amplifier for W-CDMA base station applications

In this paper, a current status and future technologies of high-power GaN HEMTs was described. First, commercialization roadmap was shown with output power and efficiency status. Power electronics benchmark was also introduced. Reliability improvement technologies were addressed with recent issues such as drift phenomena. Then, future requirements for expanding GaN electronics market were shown with some recent device developments. Novel E-mode recessed GaN-HEMT has been developed using the triple cap layer structure. High-k insulated gate HEMTs using Ta2O5 were also developed. Finally, we described the next generation GaN HEMTs for millimeter-wave applications. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High performance and high reliability AlGaN/GaN HEMTs

We demonstrate high voltage HFET operation with suppression of gm dispersion and current collapse using an n-type thin GaN cap layer combined with SiN passivation and a recessed ohmic structure Polarization-induced surface charge was controlled Off state and on-state breakdown voltages were 140 V and 70 V We obtained power HFETs with high CW operation voltage of 35 V without any heat sinking method

Kazukiyo Joshin

Papers

High Electron Mobility Transistor Logic

Selective Dry Etching of AlGaAs-GaAs Heterojunction

A 174 W high-efficiency GaN HEMT power amplifier for W-CDMA base station applications

High performance and high reliability AlGaN/GaN HEMTs

Surface-charge controlled AlGaN/GaN-power HFET without current collapse and gm dispersion