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This paper reports a normally-off high voltage hybrid Al2O 3/GaN gate-recessed MOSFET fabricated on silicon substrate. The normally off operation was implemented by digital gate recess using an oxidation and wet etching based AlGaN barrier remove technique. The Al2O 3/GaN MOSFET features a true normally off operation with a threshold voltage of 2 V extracted by the linear extrapolation of the transfer curve. The three terminal off-state breakdown voltage is 1650 V for the device with 30 μm gate-drain distance with floating Si substrate. The breakdown voltage is limited to 1000 V when the Si substrate is grounded. The on-resistance is 7.0 mΩ.cm2 for the device with 30 μm gate-drain distance and the power figure of merit is 388 MW/cm2. The small signal RF performance of the normally-off GaN MOSFET is also evaluated. © 2014 IEEE.

The gate forward leakage current in AlGaN/GaN high electron mobility transistors (HEMTs) is investigated. It is shown that the current which originated from the forward biased Schottky-gate contributed to the gate forward leakage current. Therefore, a fluorine-plasma surface treatment is presented to induce the negative ions into the AlGaN layer which results in a higher metal - semiconductor barrier. Consequently, the gate forward leakage current shrinks. Experimental results confirm that the gate forward leakage current is decreased by one order magnitude lower than that of HEMT device without plasma treatment. In addition, the DC characteristics of the HEMT device with plasma treatment have been studied. © 2013 Chinese Institute of Electronics.

The gate forward leakage current in AlGaN/GaN high electron mobility transistors (HEMTs) is investigated. It is shown that the current which originated from the forward biased Schottky-gate contributed to the gate forward leakage current. Therefore, a fluorine-plasma surface treatment is presented to induce the negative ions into the AlGaN layer which results in a higher metal - semiconductor barrier. Consequently, the gate forward leakage current shrinks. Experimental results confirm that the gate forward leakage current is decreased by one order magnitude lower than that of HEMT device without plasma treatment. In addition, the DC characteristics of the HEMT device with plasma treatment have been studied. © 2013 Chinese Institute of Electronics.

The gate forward leakage current in AlGaN/GaN high electron mobility transistors (HEMTs) is investigated. It is shown that the current which originated from the forward biased Schottky-gate contributed to the gate forward leakage current. Therefore, a fluorine-plasma surface treatment is presented to induce the negative ions into the AlGaN layer which results in a higher metal - semiconductor barrier. Consequently, the gate forward leakage current shrinks. Experimental results confirm that the gate forward leakage current is decreased by one order magnitude lower than that of HEMT device without plasma treatment. In addition, the DC characteristics of the HEMT device with plasma treatment have been studied. © 2013 Chinese Institute of Electronics.

In this letter, enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistors (HEMTs) were demonstrated based on lateral scaling of the 2-D electron gas channel using nanochannel array (NCA) structure. The NCA structure consists of multiple parallel channels with nanoscale width defined by electron-beam lithography and dry etching. Because of the improved gate control from the channel sidewalls and partially relaxed piezoelectric polarization, the fabricated 2 μm-gate-length NCA-HEMT with a nanochannel width of 64 nm showed a threshold voltage of + 0.6 V and a higher extrinsic transconductance of 123 mS/mm, compared to-1.6 V and 106 mS/mm for the conventional HEMT with μ m-scale channel width. The scaling of threshold voltages, peak transconductance, and gate leakage as a function of the nanochannel width were investigated. Small-signal RF performance of NCA-HEMTs were characterized for the first time and compared with those of conventional HEMTs. © 2012 IEEE.

In this letter, we present the deployment of Schottky source/drain (SSD) in InAlN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) for off-state breakdown voltage improvement. The improved breakdown voltage relies on the suppression of electron injection into the buffer under the Schottky source contact. A V BD of 460 V is obtained in an SSD MISHEMT with an L GD = 10 μm, at a 170% improvement compared with that of the control MISHEMT featuring ohmic source/drain. Despite the SSD contacts, an SSD MISHEMT with a gate length of 1 μm exhibits a respectable drain current density of 416 mA/mm and a transconductance of 113 mS/mm. © 2011 IEEE.

AlGaN/GaN MOS-HEMTs on a silicon platform were realized using a CMOS-compatible gold-free process. Process modules commonly used in CMOS were used, including gate stack formation, etching modules, etc. R on of 3 mΩ.cm 2 was obtained. Breakdown voltage V BR of 800 V was achieved, the highest for L GD below 10 μm for AlGaN/GaN/Si MOS-HEMTs fabricated using a gold-free process. The devices could be generally useful for cost-competitive power switching circuits with supply voltage in the range of several hundred volts. © 2012 IEEE.

A boundary-temperature-controlled epitaxy, where the growth temperature of InN is controlled at its maximum, is used to obtain high-electronmobility InN layers on sapphire substrates by molecular beam epitaxy. The Hall-effect measurement shows a recorded electron mobility of 3280 cm 2 V -1 s -1 and a residual electron concentration of 1.47 × 10 17 cm -3 at room temperature. The enhanced electron mobility and reduced residual electron concentration are mainly due to the reduction of threading dislocation density. The obtained Hall mobilities are in good agreement with the theoretical modelling by the ensemble Monte Carlo simulation. © 2012 The Japan Society of Applied Physics.

In this report, we present a study on the exploitation of nanostructure-thin film interfaces. Here, the objective is to utilize such interfaces for developing nanostructures for advanced sensing devices, while using state-of-the-art microelectronic technology that enables batch production. In this context, growth of ZnO nanostructures on the GaN/AlGaN heterostructure layers was studied. A fabrication process, based on a hydrothermal growth method, was used for preparing the interfaces of nanostructured thin film. Samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and obtained results suggested near epitaxial quality of the hetero-interface. Field-effect transistors (FETs) based on ZnO nanorods/GaN heterostructures were fabricated and tested in a controlled gas environment. Thus, it was demonstrated that nanostructures could be exploited in unconventional ways by employing them in scalable and batch-producible conventional semiconductor devices. © 2011 Elsevier Ltd. All rights reserved.

A boundary-temperature-controlled epitaxy, where the growth temperature of InN is controlled at its maximum, is used to obtain high-electronmobility InN layers on sapphire substrates by molecular beam epitaxy. The Hall-effect measurement shows a recorded electron mobility of 3280 cm 2 V -1 s -1 and a residual electron concentration of 1.47 × 10 17 cm -3 at room temperature. The enhanced electron mobility and reduced residual electron concentration are mainly due to the reduction of threading dislocation density. The obtained Hall mobilities are in good agreement with the theoretical modelling by the ensemble Monte Carlo simulation. © 2012 The Japan Society of Applied Physics.

In this report, we present a study on the exploitation of nanostructure-thin film interfaces. Here, the objective is to utilize such interfaces for developing nanostructures for advanced sensing devices, while using state-of-the-art microelectronic technology that enables batch production. In this context, growth of ZnO nanostructures on the GaN/AlGaN heterostructure layers was studied. A fabrication process, based on a hydrothermal growth method, was used for preparing the interfaces of nanostructured thin film. Samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and obtained results suggested near epitaxial quality of the hetero-interface. Field-effect transistors (FETs) based on ZnO nanorods/GaN heterostructures were fabricated and tested in a controlled gas environment. Thus, it was demonstrated that nanostructures could be exploited in unconventional ways by employing them in scalable and batch-producible conventional semiconductor devices. © 2011 Elsevier Ltd. All rights reserved.

A boundary-temperature-controlled epitaxy, where the growth temperature of InN is controlled at its maximum, is used to obtain high-electronmobility InN layers on sapphire substrates by molecular beam epitaxy. The Hall-effect measurement shows a recorded electron mobility of 3280 cm 2 V -1 s -1 and a residual electron concentration of 1.47 × 10 17 cm -3 at room temperature. The enhanced electron mobility and reduced residual electron concentration are mainly due to the reduction of threading dislocation density. The obtained Hall mobilities are in good agreement with the theoretical modelling by the ensemble Monte Carlo simulation. © 2012 The Japan Society of Applied Physics.

In this report, we present a study on the exploitation of nanostructure-thin film interfaces. Here, the objective is to utilize such interfaces for developing nanostructures for advanced sensing devices, while using state-of-the-art microelectronic technology that enables batch production. In this context, growth of ZnO nanostructures on the GaN/AlGaN heterostructure layers was studied. A fabrication process, based on a hydrothermal growth method, was used for preparing the interfaces of nanostructured thin film. Samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and obtained results suggested near epitaxial quality of the hetero-interface. Field-effect transistors (FETs) based on ZnO nanorods/GaN heterostructures were fabricated and tested in a controlled gas environment. Thus, it was demonstrated that nanostructures could be exploited in unconventional ways by employing them in scalable and batch-producible conventional semiconductor devices. © 2011 Elsevier Ltd. All rights reserved.

In this article, integrated AlGaN/GaN cantilevers on (111) silicon substrate are fabricated and characterized. The process started with AlGaN/GaN HEMTs fabrication followed by a series of dry-etch-only MEMS process. To characterize the residual stress distribution, Micro-Raman spectroscopy is used and the residual stress in suspended GaN cantilever is found ∼ 90% lower after releasing. A type of micro-bending test is used to characterize the piezoresponse of AlGaN/GaN HEMT on the GaN cantilever. An output current modulation greater than 20% can be observed when the cantilever is vertically downward deflected ∼ 30 μm. © (2011) Trans Tech Publications.

The variations in surface potential and the Schottky barrier height ΦB in fluorine-plasma-treated AlxGa1-xN/GaN heterotructures are systematically studied by x-ray photoelectron spectroscopy (XPS), giving insights into the mechanisms underlying the strong threshold voltage shift in AlxGa1-xN/GaN HEMTs by the F plasma treatment technology. It is found that the treatment resulted in a fluorinated surface containing masses of AlF3, with the surface potential of Al0.25Ga0.75N/GaN heterostructure increased by ~0.38 eV during the first 60 seconds of the treatment. Annealing at 400 °C in N2 ambient for 10 minutes does not affect the surface potential, but results in quick reduction of AlF3, consistent with the relative poor thermal stability of AlF3 reported in literature. ΦB between Ni and F-plasma-treated Al0.25Ga0.75N surface was extrapolated from the shift in Ga 2p3/2 core-level and exhibits a small increase of 0.20 eV. The enhanced ΦB is much smaller than the positive shift in Vth observed from HEMTs fabricated with the same treatment conditions, suggesting that the primary factor responsible for the conversion from depletion-mode to enhancement-mode AlxGa1-xN/GaN by F plasma treatment is not the surface modifications, but rather the negative fixed charges carried by F ions in AlxGa1-xN/GaN heterostructures. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In this article, Gallium nitride (GaN) cantilevers integrated with AlGaN/GaN high electron mobility transistors (HEMTs) are fabricated with a GaN-on-silicon platform, which is fully compatible with the standard HEMTs fabrication process. A type of micro-bending test was used to characterize the piezoresponse of AlGaN/GaN HEMT on the GaN cantilever. The modulation capability of the AlGaN/GaN heterostructures under different gate bias voltages for either high sensitivity or large output signals was demonstrated. A pulsed vibration measurement technique was used to evaluate the Young's modulus of the suspended GaN cantilevers, yielding a Young's modulus of ∼293 GPa.

A manipulation system utilizing the properties of two-dimensional electron gas (2DEG) at the interface of AlGaN/GaN and dielectrophoresis (DEP) was investigated in this study. At an applied frequency ranging from 100 kHz to 1 MHz and a potential of 20 vpeak to peak, the positive and negative DEP of the microspheres were reported for the first time by the Fluorine ion patterned and parylene covered 2DEG. In addition, by simply switching the applied frequency between 100 kHz and 500 kHz, the microspheres could come onto or get off from 2DEG region of AlGaN/GaN surface. Thus, a promising sensing scheme was proposed by combining the manipulation with sensing properties of 2DEG. This manipulation system based on 2DEG will bring much benefit to sensor applications. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

GaN based heterojunction devices, especially in the form of AlGaN/GaN high electron mobility transistors (HEMTs), are capable of delivering high-frequency power amplifiers and power switches with performances far superior than those offered by the mainstream silicon technology and other advanced semiconductor technologies. Rapid progress has been made in material growth and device processing technologies during the last decade. Meanwhile, there remain technical challenges to overcome. For example, unlike the silicon MOSFET technology, in which the devices' threshold voltage can be locally adjusted in the processing stage by ion implantation, the threshold voltage of conventional Cplane Ga-face AlGaN/GaN high electron mobility transistors (HEMTs) is mainly determined in the material growth stage, and exhibit large negative values due to the strong spontaneous and piezoelectric polarization effect, even without any intentional doping. A robust approach to modulating the local potential and local carrier concentration in AlGaN/GaN HEMTs was developed based on the fluorine plasma ion implantation technology. The most significant development based on this technology is the demonstration of self-aligned enhancement-mode (or normally-off) AlGaN/GaN HEMTs with low on-resistance. The stability of fluorine ions in III-nitride is of great importance to applications since it will ultimately determine the E-mode HEMTs' reliability. This paper attempts to address the stability of fluorine ions in III-nitride materials and devices based on a series of experimental and theoretical studies. © 2011 SPIE.

This paper presents a novel structure for compact dual- band balun design. The proposed structure is based on modified Marchand (with the fourth port shorted). To achieve the desired dual- band operation, two additional open-ended stubs are added to the two balanced ports of the modified Marchand balun. Explicit design equations are then derived using even-odd mode analysis. Finally, to verify the design concept, a microstrip balun operating at 0.9/2GHz are fabricated on Duroid RO3210 printed circuit board. Measurement results are in good agreement with the theoretical predictions.

In this article, Gallium nitride (GaN) cantilevers integrated with AlGaN/GaN high electron mobility transistors (HEMTs) are fabricated with a GaN-on-silicon platform, which is fully compatible with the standard HEMTs fabrication process. A type of micro-bending test was used to characterize the piezoresponse of AlGaN/GaN HEMT on the GaN cantilever. The modulation capability of the AlGaN/GaN heterostructures under different gate bias voltages for either high sensitivity or large output signals was demonstrated. A pulsed vibration measurement technique was used to evaluate the Young's modulus of the suspended GaN cantilevers, yielding a Young's modulus of ∼293 GPa.

A manipulation system utilizing the properties of two-dimensional electron gas (2DEG) at the interface of AlGaN/GaN and dielectrophoresis (DEP) was investigated in this study. At an applied frequency ranging from 100 kHz to 1 MHz and a potential of 20 vpeak to peak, the positive and negative DEP of the microspheres were reported for the first time by the Fluorine ion patterned and parylene covered 2DEG. In addition, by simply switching the applied frequency between 100 kHz and 500 kHz, the microspheres could come onto or get off from 2DEG region of AlGaN/GaN surface. Thus, a promising sensing scheme was proposed by combining the manipulation with sensing properties of 2DEG. This manipulation system based on 2DEG will bring much benefit to sensor applications. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

This paper presents a novel structure for compact dual- band balun design. The proposed structure is based on modified Marchand (with the fourth port shorted). To achieve the desired dual- band operation, two additional open-ended stubs are added to the two balanced ports of the modified Marchand balun. Explicit design equations are then derived using even-odd mode analysis. Finally, to verify the design concept, a microstrip balun operating at 0.9/2GHz are fabricated on Duroid RO3210 printed circuit board. Measurement results are in good agreement with the theoretical predictions.

This paper presents a novel structure for the implementation of compact dual-band balun for multiple-band antenna application. Two stubs tapped to the two balanced ports in a conventional Marchand balun configuration facilitate the dual-band operation. Explicit design equations are derived using even-odd mode analysis. To verify the design concept, a microstrip balun operating at 0.9/2 GHz is fabricated on printed circuit boards. Measurement results are in good agreement with the theoretical predictions. © 2011 IEEE.

In this article, Gallium nitride (GaN) cantilevers integrated with AlGaN/GaN high electron mobility transistors (HEMTs) are fabricated with a GaN-on-silicon platform, which is fully compatible with the standard HEMTs fabrication process. A type of micro-bending test was used to characterize the piezoresponse of AlGaN/GaN HEMT on the GaN cantilever. The modulation capability of the AlGaN/GaN heterostructures under different gate bias voltages for either high sensitivity or large output signals was demonstrated. A pulsed vibration measurement technique was used to evaluate the Young's modulus of the suspended GaN cantilevers, yielding a Young's modulus of ∼293 GPa.

GaN based heterojunction devices, especially in the form of AlGaN/GaN high electron mobility transistors (HEMTs), are capable of delivering high-frequency power amplifiers and power switches with performances far superior than those offered by the mainstream silicon technology and other advanced semiconductor technologies. Rapid progress has been made in material growth and device processing technologies during the last decade. Meanwhile, there remain technical challenges to overcome. For example, unlike the silicon MOSFET technology, in which the devices' threshold voltage can be locally adjusted in the processing stage by ion implantation, the threshold voltage of conventional Cplane Ga-face AlGaN/GaN high electron mobility transistors (HEMTs) is mainly determined in the material growth stage, and exhibit large negative values due to the strong spontaneous and piezoelectric polarization effect, even without any intentional doping. A robust approach to modulating the local potential and local carrier concentration in AlGaN/GaN HEMTs was developed based on the fluorine plasma ion implantation technology. The most significant development based on this technology is the demonstration of self-aligned enhancement-mode (or normally-off) AlGaN/GaN HEMTs with low on-resistance. The stability of fluorine ions in III-nitride is of great importance to applications since it will ultimately determine the E-mode HEMTs' reliability. This paper attempts to address the stability of fluorine ions in III-nitride materials and devices based on a series of experimental and theoretical studies. © 2011 SPIE.

A manipulation system utilizing the properties of two-dimensional electron gas (2DEG) at the interface of AlGaN/GaN and dielectrophoresis (DEP) was investigated in this study. At an applied frequency ranging from 100 kHz to 1 MHz and a potential of 20 vpeak to peak, the positive and negative DEP of the microspheres were reported for the first time by the Fluorine ion patterned and parylene covered 2DEG. In addition, by simply switching the applied frequency between 100 kHz and 500 kHz, the microspheres could come onto or get off from 2DEG region of AlGaN/GaN surface. Thus, a promising sensing scheme was proposed by combining the manipulation with sensing properties of 2DEG. This manipulation system based on 2DEG will bring much benefit to sensor applications. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

This paper presents a novel structure for compact dual- band balun design. The proposed structure is based on modified Marchand (with the fourth port shorted). To achieve the desired dual- band operation, two additional open-ended stubs are added to the two balanced ports of the modified Marchand balun. Explicit design equations are then derived using even-odd mode analysis. Finally, to verify the design concept, a microstrip balun operating at 0.9/2GHz are fabricated on Duroid RO3210 printed circuit board. Measurement results are in good agreement with the theoretical predictions.

This paper presents a novel structure for the implementation of compact dual-band balun for multiple-band antenna application. Two stubs tapped to the two balanced ports in a conventional Marchand balun configuration facilitate the dual-band operation. Explicit design equations are derived using even-odd mode analysis. To verify the design concept, a microstrip balun operating at 0.9/2 GHz is fabricated on printed circuit boards. Measurement results are in good agreement with the theoretical predictions. © 2011 IEEE.

Enhancement-mode (E-mode) AlGaN/GaN heterojunction field effect transistors (HFETs) with a nominal gate length of 0.35 μm are fabricated on a SiC substrate by fluorine plasma ion implantation without the use of gate recess. The threshold voltage is measured to be +0.2 V by linear extrapolation from the transfer characteristics. The E-mode device exhibits a saturation drain current density of 735 mA/mm at a gate bias of 4 V, a peak transconductance of 269 mS/mm, a current-gain cutoff frequency fT of 39 GHz, and a maximum oscillation frequency fmax of 91 GHz. At 18 GHz, the fabricated E-mode device exhibits a maximum output power density of 3.65 W/mm, a linear gain of 11.6 dB, and a peak power-added efficiency of 42%. This is the first report of the large-signal performance of AlGaN/GaN E-mode HFETs in the Ku-band. © 2006 IEEE.

Self-protected GaN power devices were realized using AlGaN/GaN-on-Si platform, where two built-in intelligent functions were demonstrated for "Smart Discrete" applications. First, an AlGaN/GaN normally-off high electron mobility transistor (HEMT) with reverse drain blocking capability was realized, featuring a Schottky contact controlled drain barrier. Compared to the Schottky drain structures, the new design exhibits only a 0.55 V onset voltage in the forward biased "ON" state, while effectively blocks the reverse current conduction. The device fabrication is also free of extra photomask and process steps. Second, an AlGaN/GaN lateral field-effect rectifier (L-FER) with intrinsic "ON" state current limiting capability was fabricated, featuring a depletion-mode (D-mode) Schottky controlled depletion-mode channel extension (length of LD) beyond the ohmic contact at the cathode electrode, where the on-state current of the new rectifiers are self-limited at 4.59 kA/cm2 (LD = 1.3 μm) and 3.56 kA/cm2 (L D = 1.9 μm) at room temperature. The current limiting level shows a negative temperature coefficient (TC) that is desirable for thermal stability.

GaN "Smart Discrete" power devices were realized using the AlGaN/GaN-on-Si platform, where two built-in intelligent self-protection functions were demonstrated. First, an AlGaN/GaN normally-off high electron mobility transistor (HEMT) with reverse drain blocking capability was realized, featuring a Schottky contact controlled drain barrier. Compared to the Schottky drain structures, the new design exhibits only a 0.55 V onset voltage in the forward biased "ON" state, while effectively blocks the reverse current conduction. The device fabrication is also free of extra photomask and process steps. Second, an AlGaN/GaN lateral field-effect rectifier (L-FER) with intrinsic "ON" state current limiting capability was fabricated, featuring a Schottky controlled depletion- mode (D-mode) channel extension (length of LD) beyond the ohmic contact at the cathode electrode, where the on-state current of the new rectifiers are self-limited at 4.59 kA/cm 2 (LD = 1.3 μm) and 3.56 kA/cm2 (L D = 1.9 μm) at room temperature. The current limiting level shows a negative temperature coefficient (TC) that is desirable for thermal stability. ©2010 IEEE.

The on-resistance and its temperature dependence of the high electron mobility transistor (HEMT)-compatible lateral field-effect rectifier (L-FER) are investigated. Three types of transfer length method (TLM) patterns are utilized to extract the temperature-dependent electrical parameters of the resistance model. The technique presented in this paper delivers a direct and simple methodology for the investigation of the temperature dependence of the on-resistance in the L-FER. The simulated output characteristics of the L-FER are in good agreement with the experimental results. © 2006 IEEE.

An AlGaN/GaN lateral field-effect recti. er with intrinsic ON-state current limiting capability is demonstrated by adding a Schottky contact metal (length of L-D) beyond the ohmic contact region at the cathode electrode. The onset of the current limiting function is self-activated when the voltage drop across the two-dimensional gas (2DEG) channel under the Schottky contact reaches the pinch-off voltage of the as-grown AlGaN/GaN heterojunction. With L-D = 2 mu m and a drift region length of 7 mu m, the proposed lateral recti. er exhibited an ON-state current that was self-limited at 1.56 kA/cm(2), while achieving a reverse breakdown voltage of 347 V at a 1mA/mm leakage current.

Normally-off operation AlGaN/GaN high electron mobility transistors have been developed utilising a fluorine-based treatment technique combined with a metal-oxide-semiconductor gate architecture. Threshold voltage as high as 5.1 V was achieved by using an 16 nm-thick Al2O3 gate oxide film. Additionally, the device performed a drain current density of 500 mA/mm and a peak transconductance of 100 mS/mm, which are comparable to the conventional normally-on devices.

A high-voltage normally-off AlGaN/GaN hybrid-gate HEMT (HG-HEMT) with high current-density and low on-resistance on Si substrate is fabricated. The proposed device features a hybrid-gate consisting of a short E-mode gate and a long D-mode gate. In the off-state, the short E-mode gate confirms the normally-off operation, while the D-mode gate can clamp the channel potential at a low drain voltage, which delivers high blocking capability. In the on-state, the short E-mode channel and the D-mode channel providing lower channel resistance facilitate high on-current or low on-resistance. Therefore, the HG-HEMT achieves a high breakdown voltage and low on-resistance simultaneously. Compared with the conventional device, the HG-HEMT is shown to deliver comparable breakdown voltage while featuring 62% lower on-resistance.

One to the thermal mismatch between GaN and Si, GaN grown on Si at elevated temperatures (∼1100 ° C) usually exhibits large internal residual stress. Therefore, the characterization of residual stress in GaN on Si substrate is of particular importance. In this work, a type of reliable bent-beam strain sensor was used to estimate residual stress in suspended GaN microstructures. The device was modeled by finite element method (FEM) and was fabricated by a dry-etch-only deep-releasing technique featuring a combination of anisotropic and isotropic Si etching. Results were analyzed and an averaged residual stress value of ∼ 575 ± 5 MPa was estimated for the GaN sample used in this work. ©2010 IEEE.

Owing to superior physical properties such as high electron saturation velocity and high electric breakdown field, GaN-based high electron mobility transistors (HEMTs) are capable of delivering superior performance in microwave amplifiers, high power switches, and high temperature integrated circuits (ICs). Compared to the conventional D-mode HEMTs with negative threshold voltages, enhancement-mode (E-mode) or normally-off HEMTs are desirable in these applications, for reduced circuit design complexity and fail-safe operation. Fluorine plasma treatment has been used to fabricate E-mode HEMTs [1], and is a robust process for the channel threshold voltage modulation. However, there is no standard equipment for this process and various groups have reported a wide range of process parameters [1-4]. In this work, we demonstrate the self-aligned enhancement-mode AlGaN/GaN HEMTs fabricated with a standard fluorine ion implantation. Ion implantation is widely used in semiconductor industry with well-controlled dose and precise implantation profile. © 2010 IEEE.

An AlGaN/GaN lateral field-effect recti. er with intrinsic ON-state current limiting capability is demonstrated by adding a Schottky contact metal (length of L-D) beyond the ohmic contact region at the cathode electrode. The onset of the current limiting function is self-activated when the voltage drop across the two-dimensional gas (2DEG) channel under the Schottky contact reaches the pinch-off voltage of the as-grown AlGaN/GaN heterojunction. With L-D = 2 mu m and a drift region length of 7 mu m, the proposed lateral recti. er exhibited an ON-state current that was self-limited at 1.56 kA/cm(2), while achieving a reverse breakdown voltage of 347 V at a 1mA/mm leakage current.

Normally-off operation AlGaN/GaN high electron mobility transistors have been developed utilising a fluorine-based treatment technique combined with a metal-oxide-semiconductor gate architecture. Threshold voltage as high as 5.1 V was achieved by using an 16 nm-thick Al2O3 gate oxide film. Additionally, the device performed a drain current density of 500 mA/mm and a peak transconductance of 100 mS/mm, which are comparable to the conventional normally-on devices.

A high-voltage normally-off AlGaN/GaN hybrid-gate HEMT (HG-HEMT) with high current-density and low on-resistance on Si substrate is fabricated. The proposed device features a hybrid-gate consisting of a short E-mode gate and a long D-mode gate. In the off-state, the short E-mode gate confirms the normally-off operation, while the D-mode gate can clamp the channel potential at a low drain voltage, which delivers high blocking capability. In the on-state, the short E-mode channel and the D-mode channel providing lower channel resistance facilitate high on-current or low on-resistance. Therefore, the HG-HEMT achieves a high breakdown voltage and low on-resistance simultaneously. Compared with the conventional device, the HG-HEMT is shown to deliver comparable breakdown voltage while featuring 62% lower on-resistance.

The on-resistance and its temperature dependence of the high electron mobility transistor (HEMT)-compatible lateral field-effect rectifier (L-FER) are investigated. Three types of transfer length method (TLM) patterns are utilized to extract the temperature-dependent electrical parameters of the resistance model. The technique presented in this paper delivers a direct and simple methodology for the investigation of the temperature dependence of the on-resistance in the L-FER. The simulated output characteristics of the L-FER are in good agreement with the experimental results. © 2006 IEEE.

The on-resistance and its temperature dependence of the high electron mobility transistor (HEMT)-compatible lateral field-effect rectifier (L-FER) are investigated. Three types of transfer length method (TLM) patterns are utilized to extract the temperature-dependent electrical parameters of the resistance model. The technique presented in this paper delivers a direct and simple methodology for the investigation of the temperature dependence of the on-resistance in the L-FER. The simulated output characteristics of the L-FER are in good agreement with the experimental results. © 2006 IEEE.

An AlGaN/GaN lateral field-effect recti. er with intrinsic ON-state current limiting capability is demonstrated by adding a Schottky contact metal (length of L-D) beyond the ohmic contact region at the cathode electrode. The onset of the current limiting function is self-activated when the voltage drop across the two-dimensional gas (2DEG) channel under the Schottky contact reaches the pinch-off voltage of the as-grown AlGaN/GaN heterojunction. With L-D = 2 mu m and a drift region length of 7 mu m, the proposed lateral recti. er exhibited an ON-state current that was self-limited at 1.56 kA/cm(2), while achieving a reverse breakdown voltage of 347 V at a 1mA/mm leakage current.

A high-voltage normally-off AlGaN/GaN hybrid-gate HEMT (HG-HEMT) with high current-density and low on-resistance on Si substrate is fabricated. The proposed device features a hybrid-gate consisting of a short E-mode gate and a long D-mode gate. In the off-state, the short E-mode gate confirms the normally-off operation, while the D-mode gate can clamp the channel potential at a low drain voltage, which delivers high blocking capability. In the on-state, the short E-mode channel and the D-mode channel providing lower channel resistance facilitate high on-current or low on-resistance. Therefore, the HG-HEMT achieves a high breakdown voltage and low on-resistance simultaneously. Compared with the conventional device, the HG-HEMT is shown to deliver comparable breakdown voltage while featuring 62% lower on-resistance.

Normally-off operation AlGaN/GaN high electron mobility transistors have been developed utilising a fluorine-based treatment technique combined with a metal-oxide-semiconductor gate architecture. Threshold voltage as high as 5.1 V was achieved by using an 16 nm-thick Al2O3 gate oxide film. Additionally, the device performed a drain current density of 500 mA/mm and a peak transconductance of 100 mS/mm, which are comparable to the conventional normally-on devices.

Owing to superior physical properties such as high electron saturation velocity and high electric breakdown field, GaN-based high electron mobility transistors (HEMTs) are capable of delivering superior performance in microwave amplifiers, high power switches, and high temperature integrated circuits (ICs). Compared to the conventional D-mode HEMTs with negative threshold voltages, enhancement-mode (E-mode) or normally-off HEMTs are desirable in these applications, for reduced circuit design complexity and fail-safe operation. Fluorine plasma treatment has been used to fabricate E-mode HEMTs [1], and is a robust process for the channel threshold voltage modulation. However, there is no standard equipment for this process and various groups have reported a wide range of process parameters [1-4]. In this work, we demonstrate the self-aligned enhancement-mode AlGaN/GaN HEMTs fabricated with a standard fluorine ion implantation. Ion implantation is widely used in semiconductor industry with well-controlled dose and precise implantation profile. © 2010 IEEE.

One to the thermal mismatch between GaN and Si, GaN grown on Si at elevated temperatures (∼1100 ° C) usually exhibits large internal residual stress. Therefore, the characterization of residual stress in GaN on Si substrate is of particular importance. In this work, a type of reliable bent-beam strain sensor was used to estimate residual stress in suspended GaN microstructures. The device was modeled by finite element method (FEM) and was fabricated by a dry-etch-only deep-releasing technique featuring a combination of anisotropic and isotropic Si etching. Results were analyzed and an averaged residual stress value of ∼ 575 ± 5 MPa was estimated for the GaN sample used in this work. ©2010 IEEE.

A zero-bias microwave detector using AlGaN/GaN-based lateral field-effect diode is demonstrated. The diode is compatible with AlGaN/GaN HEMT in fabrication process. Taking advantage of threshold-voltage modulation of fluorine plasma treatment technique, the diode features low turn-on voltage and strong nonlinearity at zero bias thus eliminating DC supplies for the application of zero-bias microwave detection. The diode exhibits good sensitivity from room temperature to 250°C. The peak on-wafer measured sensitivity (βv) of 1027 mV/mW is achieved at 5 GHz at 50°C. The maximum conjugately-matched sensitivity (βv,opt) of 9030 mV/mW is obtained at 2 GHz at 50°C and decreases to 1227 mV/mW at 250°C. At room temperature, the dynamic range as high as 53 and 54 dB at 2 and 5 GHz is observed, respectively, which are the highest values reported so far.

GaN smart power chip technology has been realized using GaN-on-Si HEMT platform, featuring monolithically integrated high-voltage power devices and low-voltage peripheral devices for mixed-signal functional blocks. Two imperative functional blocks for smart power applications with wide-temperature-range stability are demonstrated. The first one is a voltage reference generator, and the second one is a temperature-compensated comparator. These circuits are capable of proper functions within a wide temperature range from room temperature up to 250 °C, illustrating the unique advantage of the wide-bandgap GaN. The voltage reference generator was designed with an AlGaN/GaN HEMT and Schottky diodes, and the devices were operated in the subthreshold regime to obtain low power consumption. The voltage reference generator achieved an average drift of less than 70 ppm/°C and can be used as a reference voltage in various biasing and sensing circuits. The temperature-dependent performance of a conventional comparator is characterized and a new temperature-compensated comparator circuit is proposed. The positive limiting level of the temperature-compensated comparator is less than 450 ppm/°C drift compared to 1350 ppm/°C in the conventional comparator. ©2009 IEEE.

Wide-bandgap GaN-based semiconductor materials are attracting considerable attention as the preferred material for power electronics applications, owning to their superior properties including high breakdown electric-field, high carrier density, high electron mobility and high saturation velocity. In this paper, the technologies for implementing GaN smart power ICs will be introduced based on the large-size, low-cost and highly scalable GaN-on-Si platform. High-voltage power components (normally-off power transistors and HEMT-compatible rectifiers) and low-voltage periphery devices for digital/analog mixed-signal circuits are successfully integrated with the same fabrication process. In particular, key analog functional blocks such as voltage reference generators and comparators are demonstrated using GaN-based technology for the first time. The optimized voltage reference generator achieved less than 70 ppm/°C drift and can be used as a reference voltage m various biasing and sensing circuits. The temperature-dependent performance of a conventional comparator is characterized and a new temperature-compensated comparator circuit is also demonstrated. The positive limiting level of the temperature- compensated comparator is less than 450 ppm/°C drift compared to 1400 ppm/°C in the conventional comparator. ©2009 IEEE.