GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> A. INTEGRATED COMPONENTS <s> The electrical characteristics of Ni and Ti Schottky barriers on n-Al0.15Ga0.85N on SiC were investigated. We report that the barrier height for Ni on n-Al0.15Ga0.85N was about 1.26 eV and about 1 eV or less for Ti. These barrier heights are about 0.3–0.4 eV larger than those for Ni and Ti on n-GaN, which are in good agreement with Schottky model predictions. <s> BIB001 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> A. INTEGRATED COMPONENTS <s> This work was partly supported by Conselho Nacional ::: de Pesquisas (CNPq, Brazil) under Contract No. 200541/ ::: 99-4. <s> BIB002 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> A. INTEGRATED COMPONENTS <s> Fabrication and characterization of AlGaN/GaN HEMT inverters and ring oscillators utilizing integrated en- hancement/depletion-mode (E/D-mode) AlGaN/GaN HEMTs are presented. The core technique is a CF4 plasma treatment that can effectively convert a D-mode AlGaN/GaN heterostructure to an E-mode heterostructure. A significant advantage of the plasma-treated E-mode HEMTs is that the gate current is reduced in both reverse- and forward-bias regions due to the effectively enhanced barrier height induced by the negatively charged fluo- rine ions in the AlGaN barrier. As a result, the input voltage swing is expanded by about 1 V for the E-mode HEMT, enabling conve- nient input/output logic level matching for multistage logic circuits such as ring oscillators. The fabricated 17-stage direct-coupled field-effect transistor logic ring oscillator using the 1-µm-gate technology can operate properly at a larger supply voltage of 3.5 V, and a minimum propagation delay of 130 ps/stage is achieved. Index Terms—AlGaN/GaN, depletion mode (D-mode), direct- coupled field-effect transistor (FET) logic (DCFL), enhance- ment/depletion (E/D) inverter, enhancement mode (E-mode), fluorine ions, gate current, HEMT, plasma treatment, post-gate rapid thermal annealing (RTA), ring oscillator. <s> BIB003 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> A. INTEGRATED COMPONENTS <s> A high electron mobility transistor (HEMT)-compatible power lateral field-effect rectifier (L-FER) with low turn-on voltage is demonstrated using the same fabrication process as that for normally off AlGaN∕GaN HEMT, providing a low-cost solution for GaN power integrated circuits. The power rectifier features a Schottky-gate-controlled two-dimensional electron gas channel between the cathode and anode. By tying up the Schottky gate and anode together, the forward turn-on voltage of the rectifier is determined by the threshold voltage of the channel instead of the Schottky barrier. The L-FER with a drift length of 10μm features a forward turn-on voltage of 0.63V at a current density of 100A∕cm2. This device also exhibits a reverse breakdown voltage (BV) of 390V at a current level of 1mA∕mm and a specific on resistance (RON,sp) of 1.4mΩcm2, yielding a figure of merit (BV2∕RON,sp) of 108MW∕cm2. The excellent device performance, coupled with the lateral device structure and process compatibility with AlGaN∕GaN... <s> BIB004 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> A. INTEGRATED COMPONENTS <s> We report high breakdown combined with low on-resistance results on AlGaN/GaN/AlGaN double heterostructure devices (DHFET) grown on 4 inch Silicon substrates. On two fingers devices with gate-drain distance (LGD) of 8 μm we measured a breakdown voltage (VBD) of 650 V and an on-resistance (Ron) of 7.2 Ω·mm. We also demonstrated that increasing the buffer thickness and etching deep into the AlGaN buffer layer improve both buffer and device breakdown. Moreover, we have also achieved a high breakdown voltage (580 V) for smaller LGD (5 μm) combined with the lowest reported on-resistance (6 Ω·mm) for this voltage range. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) <s> BIB005 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> A. INTEGRATED COMPONENTS <s> We demonstrate a single-chip switch-mode boost converter that features a monolithically integrated lateral field-effect rectifier (L-FER) and a normally off transistor switch. The circuit was fabricated on a standard AlGaN/GaN HEMT epitaxial wafer grown with GaN-on-Si technology. The fabricated rectifier with a drift length of 15 mum exhibits a breakdown voltage of 470 V, a turn-on voltage of 0.58 V, and a specific on-resistance of 2.04 mOmegaldrcm2. The L-FER exhibits no reverse recovery current associated with the turn-off transient because of its unipolar nature. A prototype of GaN-based boost converter that includes monolithically integrated rectifiers and transistors is demonstrated using conventional GaN-on-Si wafers for the first time to prove the feasibility of the GaN-based power IC technology. <s> BIB006 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> A. INTEGRATED COMPONENTS <s> Nitrogen ion-implanted AlGaN/GaN high electron mobility transistor structures showed an isolation blocking voltage of 900 V with a leakage current at 1 μA/mm across an implanted isolation-gap of 10 μm between two Ohmic pads. The effect of implanted gap distance (1.7, 5, or 10 μm) between two Ohmic contact pads was evaluated. The isolation current density was determined to be solely dependent on the applied field between the contact pads. A model using a combination of resistive current and Poole–Frenkel current is consistent with the experimental data. The resistance of the isolation implantation region significantly decreased after the sample was annealed at temperatures above 600 °C. <s> BIB007 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> A. INTEGRATED COMPONENTS <s> We demonstrate high-voltage depletion-mode and enhancement-mode (E-mode) AlGaN/GaN high-electron-mobility transistors (HEMTs) on a GaN-on-silicon-on-insulator (SOI) platform. The GaN-on-SOI wafer features GaN epilayers grown by metal-organic chemical vapor deposition on a p-type (111) Si SOI substrate with a p-type (100) Si handle wafer. Micro-Raman spectroscopy significantly reveals reduced stress in the GaN epilayers, which is a result expected from the compliant SOI substrate. E-mode HEMTs fabricated by fluorine plasma implantation technique deliver high on/off current ratio (108-109), large breakdown voltage (1471 V with floating substrate), and low on-resistance (3.92 mΩ·cm2). <s> BIB008 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> A. INTEGRATED COMPONENTS <s> In this letter, we present AlGaN/GaN lateral Schottky barrier diodes on silicon with recessed anodes and dual field plates. A low specific ON-resistance $R_{{\rm ON, SP}}$ (5.12 $\text{m}\Omega \cdot \textrm {cm}^{2}$ ), a low turn-ON voltage ( 1.9 kV) were simultaneously achieved in devices with a 25- $\mu \text{m}$ anode/cathode distance, resulting in a power figure-of-merit BV $^{2}$ / $R_{{\rm ON, SP}}$ of 727 $\textrm {MW}\,\cdot \, \textrm {cm}^{-2}$ . The record high BV of 1.9 kV is attributed to the dual field-plate structure. <s> BIB009 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> A. INTEGRATED COMPONENTS <s> An AlGaN/GaN-on-Si lateral power diode with recessed metal/Al2O3/III-nitride (MIS)-gated ohmic anode for improved forward conduction and reverse blocking has been realized. The low onset voltage of $\sim 0.6$ V with good uniformity for the fabricated 189 devices is obtained. In comparison with the conventional Schottky diode the specific ON-resistance ( $R_{\mathrm {\mathbf {\mathrm{{\scriptscriptstyle ON}},SP}}})$ was reduced by 51% in a device with anode-to-cathode spacing ( $L_{\mathrm {\mathbf {AC}}})$ of 5 $\mu \text{m}$ . The incorporation of high- $k$ dielectric in the recessed gate region enabling two-order lower reverse leakage comparing with the conventional device, leading to a high breakdown voltage over 1.1 kV at leakage current as low as 10 $\mu \text{A}$ /mm in device with $L_{\mathrm {\mathbf {AC}}}=20~\mu \text{m}$ . The strong reverse blocking over 600 V was still achieved at 150 °C. The proposed diode is compatible with GaN normally $\mathbf {\mathrm{{\scriptstyle OFF}}}$ MIS high-electron-mobility transistors, revealing its potential for highly efficient GaN-on-Si power ICs. <s> BIB010 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> A. INTEGRATED COMPONENTS <s> Monolithic integration of a half bridge on the same GaN-on-Si wafer is very challenging because the devices share a common conductive Si substrate. In this letter, we propose to use GaN-on-SOI (silicon-on-insulator) to isolate the devices by trench etching through the GaN/Si(111) layers and stopping in the SiO2 buried layer. By well-controlled epitaxy and device fabrication, high-performance 200 V enhancement-mode (e-mode) p-GaN high electron mobility transistors with a gate width of 36 mm are achieved. This letter demonstrates that by using GaN-on-SOI in combination with trench isolation, it is very promising to monolithically integrate GaN power systems on the same wafer to reduce the parasitic inductance and die size. <s> BIB011 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> A. INTEGRATED COMPONENTS <s> This paper presents the design of a gate driver, monolithically integrated with power p-gate Gallium Nitride High Electron Mobility Transistor (p-GaN HEMT). It is implemented by an enhancement mode GaN-on-SOI (Silicon on Insulator) technology. Circuit-level simulations considering parasitic components in the integrated circuit (IC) verify the switching operation at 10 MHz, 50 V of off-state V DS and 10 A of on-state I D . GaN-HEMT model has been calibrated by experimental results. The simulation results shows that the proposed gate driver realizes 3.8/ 3.4 ns of turn on/ turn off time, which are 89.0/ 78.9% smaller than a discrete gate driver. <s> BIB012 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> A. INTEGRATED COMPONENTS <s> Power integration is essential for the fully utilization of advanced GaN devices in power conversion applications due to the reduced parasitic inductance, low on-state resistance, and high-temperature operation. This paper presents a GaN-based monolithic integration design with optimized gate drivers for high-temperature DC?DC converters. Four different gate drivers are experimentally evaluated for integration with boost converters based on enhancement (E)-mode AlGaN/GaN metal?insulator?semiconductor heterojunction-field-effect-transistors (MIS-HFETs). The optimized gate driver, consisting of DCFL (Direct-Coupled FET Logic) inverters and a buffer amplifier, can operate over a wide temperature range (from 25??C to 250??C). Furthermore, a 100?kHz, 5?V/11?V (V IN/V OUT) boost converter prototype with the proposed monolithic integration design was built and found to operate successfully under high temperatures (HTs) up to 250??C. These results validate the advantages of GaN-based monolithic integration techniques in achieving HT, high power density, and high efficiency power converters. <s> BIB013 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> A. INTEGRATED COMPONENTS <s> In this letter, we demonstrate high-performance lateral GaN power Schottky barrier diodes based on a novel multi-channel tri-gate architecture. A significant reduction in ON-resistance ( ${R}_{ \mathrm{\scriptscriptstyle ON}}$ ) of 50%, down to $7.2 \pm 0.4~\Omega \cdot {\mathrm {mm}}$ , along with a much smaller forward voltage ( ${V}_{\mathrm {F}}$ ) of 1.57 ± 0.06 V, were achieved with multiple 2DEG channels (multi-channels) formed by periodic AlGaN/GaN heterostructures. We used a tri-anode structure to form Schottky contact to the multi-channels through the fin sidewalls, leading to a small turn- ON voltage ( ${V}_{ \mathrm{\scriptscriptstyle ON}}$ ) of 0.67 ± 0.04 V. To simultaneously control the multi-channels and effectively spread the electric field in OFF state, a tri-gate structure was integrated in the anode, resulting in an ultra-low leakage current ( ${I}_{\mathrm {R}}$ ) of ~1 nA/mm at −600 V and a high breakdown voltage ( ${V}_{\mathrm {BR}}$ ) of −900 V at $1~\mu$ A/mm with grounded substrate. In addition, the devices presented promising switching performance, due to the small product of ${R}_{ \mathrm{\scriptscriptstyle ON}}$ and reverse charge ( ${Q}$ ), thanks to the optimized tri-gate geometry, and high effective mobility ( $\mu _{\mathrm {e}}$ ) of 2063 ± 123 cm2 $\cdot $ V−1s−1 despite the small fin width ( ${w}$ ) of 50 nm. Our approach combines in a unique way the excellent electrostatic control of the tri-gate structure with the high conductivity of multi-channels, offering a promising platform for future advances in GaN power devices. <s> BIB014
The smart power IC platforms can be categorized in terms of gate dielectric structure and normally-OFF technology. With the proposal of every normally-OFF technology, a novel platform can be formed based the integration of normally-ON and normally-OFF devices. Fig. 13 illustrates the schematic of smart power IC platforms using gate recess BIB013 , fluorineion implantation BIB003 or p-type cap layer BIB012 technology. The isolation is formed by deep mesa or ion-implantation to remove the 2DEG channel between devices. Mesa depth values up to 500 nm are reported BIB005 to reduce leakage current among devices. However, deep trench makes interconnection more difficult and brings extra surface traps. Implantation isolation uses high energy ions (Ar, F, H, He, N, O) to destroy or deplete the 2DEG channel BIB002 , BIB007 , which can provide flat device surface and is beneficial for lateral metal interconnection. The GaN-on-SOI (Silicon-on-Insulator, SOI) approach has been reported in BIB008 , BIB011 . The devices are isolated by trench etching until the buried SiO 2 layer and refilling deposition of SiO 2 passivation in the trenches as shown in Fig. 13(c) . Especially Interuniversity Microelectronics Center (IMEC) has launched their 200-nm GaN-on-SOI platform and provides Multi-Project Wafer (MPW) runs for power devices and smart power ICs. Diodes are essential devices to provide high voltage single direction blocking state in power ICs, and also can be used as voltage level shifter which takes advantage of its forward voltage drop. Most common is the Schottky barrier diode (SBD) which is formed by deposition Ni-based metal on AlGaN or GaN surface BIB001 , BIB009 as shown in Fig. 14(a) . Chen et al. BIB004 firstly introduces the Lateral Field Effect Rectifiers (L-FERs) which uses a Schottky-gate-controlled 2DEG channel between anode and cathode. The lateral device structure and process compatibility with AlGaN/GaN HEMT make the L-FER a well-qualified candidate in smart power IC platform BIB006 , BIB010 as shown in Fig. 14(b) . In Fig. 14(c) the tri-gate Schottky diodes are based on the tri-anode structure with Schottky contact to the multi-channels through the fin sidewalls to obtain lower turn-on voltage BIB014 . It also exhibits great potential in working with normally-OFF AlGaN/GaN FIGURE 14. Schematic structure of (a) a typical Schottky barrier diode BIB009 , (b) a L-FER with a normally-OFF HEMT BIB004 and (c) a tri-gated Schottky barrier diode BIB014 .