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Objectives: Oral squamous cell carcinoma (OSCC) is often diagnosed with cervical lymph node metastasis. Mesenchymal stem cells (MSCs) and interleukin‐6 (IL‐6) signalling are considered to play important roles in promoting tumour malignancy. The detailed biological interaction of MSCs and IL‐6 and the subsequent effect on OSCC metastasis remain largely unclear. This study aimed to determine the effects and molecular mechanism of MSCs‐derived IL‐6 on tumour invasion and metastasis. Subjects and Methods: The effects of MSC‐derived IL‐6 and tocilizumab on the proliferation, mobility, and epithelial‐mesenchymal transition (EMT) of OSCC cells and potential pathways were detected in vitro. In addition, a murine xenograft model was generated to verify the biological mechanism in vivo. Results: The results showed that the expression of MSCs and EMT‐related signals was increased in poorly differentiated OSCC tissues. MSCs released a higher level of IL‐6 and promoted the proliferation, invasion, and metastasis of OSCC cells and solid neoplasms, which were activated by the downstream molecules JAK and STAT3. Conclusions: The results indicated that MSCs‐derived IL‐6‐promoted tumour invasion and metastasis via JAK–STAT3 signalling. Blockade of this pathway by tocilizumab may be a potential treatment to improve the prognosis and survival rate of patients with OSCC. [ABSTRACT FROM AUTHOR]

The hot-electron-related reliability is an important issue for GaN power devices under harsh operation condition or environment. These high-energy electrons can scatter toward the device surface or buffer layer, introducing newly generated traps/defects and resulting in the degradation of dynamic ON-resistance (RON). This work investigates the dynamic characteristics in active-passivation p-GaN gate HEMTs (AP-HEMTs) after hot-electron stress (HES). Unlike the dielectric passivation whose dynamic RON performance is often reported to severely worsen as hot-electron-induced defects/traps accumulate, the active passivation is found to have a superior robustness against hot-electron stress. In this study, after an HES of 30 min with VD = 200 V and IS = 10 mA/mm, the dynamic RON/static RON of a conventional HEMT increases dramatically from 3.63 to 9.35 for VDS-OFF = 650 V, whereas that of AP-HEMT only shows a slight increase from 1.51 to 1.85. Two mechanisms have been experimentally proved for the improved hot-electron robustness in AP-HEMT. (i) The mobile holes in active passivation layer can effectively screen the preexisting and/or newly generated surface defects/traps from affecting the 2DEG channel. (ii) The recovery of buffer trapping is accelerated by hole injection from gate and active passivation. [ABSTRACT FROM AUTHOR]

PbSn solders are used in semiconductor devices for aerospace or military purposes with high levels of reliability requirements. Microalloying has been widely adopted to improve the reliability for Pb-free solders, but its application in PbSn solders is scarce. In this article, the optimization of PbSn solder reliability with Ge microalloying was investigated using both experimental and calculation methods. Intermetallic compounds (IMC) growth and morphologies evolution during reliability tests were considered to be the main factors of device failure. Through first-principle calculation, the growth mechanism of interfacial Ni3Sn4 was discussed, including the formation of vacancies, the Ni-vacancies exchange diffusion and the dominant Ni diffusion along the [1 0 0] direction. The doping of Ge in the cell increased the exchange energy barrier and thus inhibited the IMC development and coarsening trend. In three reliability tests, only 0.013 wt% Ge microalloying in Pb60Sn40 was able to reduce IMC thickness by an increment of 22.6~38.7%. The proposed Ge microalloying method in traditional PbSn solder could yield a prospective candidate for highly reliable applications. [ABSTRACT FROM AUTHOR]

A thermal-based acoustic vector sensor consisting of three heated wires can detect acoustic particle velocity instead of pressure. This paper proposes an analytical model for calculating the temperature distribution and acoustic-caused temperature perturbation of the sensor with a three-hot-wire configuration. In this model, the nonlinear effect caused by non-uniform thermal conductivity is considered. The nonlinear effects will not only affect the temperature of the three hot wires, but also the frequency response of the sensor. Based on the stationary temperature distribution calculated by the nonlinear model, we correct the heat diffusion coefficient in the acoustic perturbation model. The nonlinear stationary model and the corrected perturbation model are found to be in good agreement with the numerical results. Furthermore, we design a chip to measure the temperature distribution of the three heated wires and compare the sensitivity of the sensor with the corrected model. The experimental results can verify the proposed model. This study provides a theoretical basis for sensor performance optimization. [ABSTRACT FROM AUTHOR]

Acoustic dyadic sensors (ADSs) are a new type of acoustic sensor with higher directivity than microphones and acoustic vector sensors, which has great application potential in the fields of sound source localization and noise cancellation. However, the high directivity of an ADS is seriously affected by the mismatches between its sensitive units. In this article, (1) a theoretical model of mixed mismatches was established based on the finite-difference approximation model of uniaxial acoustic particle velocity gradient and its ability to reflect the actual mismatches was proven by the comparison of theoretical and experimental directivity beam patterns of an actual ADS based on MEMS thermal particle velocity sensors. (2) Additionally, a quantitative analysis method based on directivity beam pattern was proposed to easily estimate the specific magnitude of the mismatches, which was proven to be useful for the design of ADSs to estimate the magnitudes of different mismatches of an actual ADS. (3) Moreover, a correction algorithm based on the theoretical model of mixed mismatches and quantitative analysis method was successfully demonstrated to correct several groups of simulated and measured beam patterns with mixed mismatches. [ABSTRACT FROM AUTHOR]

The article presents the discussion on Oral lichen planus (OLP) being a T-cell-mediated chronic inflammatory disease clinically manifested as striated lacy hyperkeratosis. Topics include lymphocytes showing cytotoxicity leading to apoptosis of keratinocytes; and Langerhans cells presenting the MHC class II-associated antigen to CD4+helper T cells secreting large amounts of IL-2 and interferon-c.

Hypoxia is a physiological stress that frequently occurs in solid tissues. Autophagy, a ubiquitous degradation/recycling system in eukaryotic cells, renders cells tolerant to multiple stressors. However, the mechanisms underlying autophagy initiation upon hypoxia remains unclear. Here we show that protein arginine methyltransferase 5 (PRMT5) catalyzes symmetrical dimethylation of the autophagy initiation protein ULK1 at arginine 170 (R170me2s), a modification removed by lysine demethylase 5C (KDM5C). Despite unchanged PRMT5-mediated methylation, low oxygen levels decrease KDM5C activity and cause accumulation of ULK1 R170me2s. Dimethylation of ULK1 promotes autophosphorylation at T180, a prerequisite for ULK1 activation, subsequently causing phosphorylation of Atg13 and Beclin 1, autophagosome formation, mitochondrial clearance and reduced oxygen consumption. Further, expression of a ULK1 R170K mutant impaired cell proliferation under hypoxia. This study identifies an oxygen-sensitive methylation of ULK1 with an important role in hypoxic stress adaptation by promoting autophagy induction. Hypoxia induces mitochondrial clearance and autophagy, although the upstream mechanisms are not well defined. Here, the authors identify that oxygen-sensitive methylation of the key autophagy regulator ULK1 promotes ULK1 activation and subsequent autophagosome formation and mitochondrial clearance. [ABSTRACT FROM AUTHOR]

We extract the electric properties of border traps with long time constant in low-pressure chemical vapor deposition (LPCVD) Si3N4/GaN/AlGaN/GaN metalâ€"insulatorâ€"semiconductor (MIS) structure using quasi-static capacitance voltage method. The energy and depth distribution of the border traps is calculated based on the analysis of energy band diagram and charging dynamic of border traps in the MIS structures. With this method, it is found that LPCVD Si3N4/GaN/AlGaN/GaN MIS structure have a high density of border traps in the order up to 1021 cmâˆ'3 eVâˆ'1 located at energy level between E C,GaN âˆ' 0.04 eV and E C,GaN âˆ' 0.66 eV with distance of 1.0â€"4.2 nm from the Si3N4/GaN interface. Microstructure analysis suggests that the high density of border traps is possibly correlated to the oxygen content at the Si3N4/GaN interface. Meanwhile, the proposed method is also suitable for MIS or metal-oxide-semiconductor structure on other semiconductors, providing another powerful tool to analysis the physical properties of border traps. [ABSTRACT FROM AUTHOR]

Hypoxia is a physiological stress that frequently occurs in solid tissues. Autophagy, a ubiquitous degradation/recycling system in eukaryotic cells, renders cells tolerant to multiple stressors. However, the mechanisms underlying autophagy initiation upon hypoxia remains unclear. Here we show that protein arginine methyltransferase 5 (PRMT5) catalyzes symmetrical dimethylation of the autophagy initiation protein ULK1 at arginine 170 (R170me2s), a modification removed by lysine demethylase 5C (KDM5C). Despite unchanged PRMT5-mediated methylation, low oxygen levels decrease KDM5C activity and cause accumulation of ULK1 R170me2s. Dimethylation of ULK1 promotes autophosphorylation at T180, a prerequisite for ULK1 activation, subsequently causing phosphorylation of Atg13 and Beclin 1, autophagosome formation, mitochondrial clearance and reduced oxygen consumption. Further, expression of a ULK1 R170K mutant impaired cell proliferation under hypoxia. This study identifies an oxygen-sensitive methylation of ULK1 with an important role in hypoxic stress adaptation by promoting autophagy induction. Hypoxia induces mitochondrial clearance and autophagy, although the upstream mechanisms are not well defined. Here, the authors identify that oxygen-sensitive methylation of the key autophagy regulator ULK1 promotes ULK1 activation and subsequent autophagosome formation and mitochondrial clearance. [ABSTRACT FROM AUTHOR]

Junction termination extension (JTE) is a mature edge termination structure in Si and SiC power devices, but remains a technical challenge in GaN due to lack of mature selective area doping technique. In this work, GaN vertical p-n diodes with Hydrogen-Modulated Step Graded JTE (HMSG-JTE) are realized by gradually enlarging photolithography windows for hydrogen plasma treatment and controlled thermal diffusion of hydrogen in p-GaN. HMSG-JTE leads to a gradually decreasing hole distribution outwards from the main junction, which laterally spreads the electric field and mitigates the electric field peak under reverse bias. Consequently, the breakdown voltage of vertical GaN p-n diode is successfully boosted from 661 V (with hydrogen-plasma-based edge termination) to 1489 V with HMSG-JTE. [ABSTRACT FROM AUTHOR]

In this letter, we report a quasi-vertical GaN Schottky barrier diode (SBD) fabricated on a hetero-epitaxial layer on silicon with low dislocation density and high carrier mobility. The reduction of dislocation is realized by inserting a thin layer with high density of Ga vacancies to promote the dislocation bending. The dislocation density is ${1.6}\times {10}^{{8}}$ cm−2 with a GaN drift layer thickness of $4.5~\mu \text{m}$. The fabricated prototype GaN SBD delivers a high on/off current ratio of $10^{{10}}$ , a high forward current density of 1.6 kA/cm2@3 V, a low specific on-resistance of 1.1 $\text{m}\Omega \cdot \text {cm}^{{2}}$ , and a low ideality factor of 1.23. [ABSTRACT FROM AUTHOR]

AlGaN/GaN high-electron-mobility transistor (HEMT) based pH sensors have the advantages of fast response and high stability, and can be used in harsh environments. This paper presents a pH sensor based on a planar dual-gate AlGaN/GaN HEMT cascode amplifier, which can increase the pH sensitivity for about 45 times from 45 mV/pH to 2.06 V/pH with linearity of 1.27%. The results indicate that it is possible to improve the pH sensitivity at the origin of detecting instead of the subsequent complex amplifier circuits. The proposed device has also shown the capacity to adjust the sensor’s sensitivity by changing the gate voltage and the resistance values for various pH ranges of different measuring requirements. [ABSTRACT FROM AUTHOR]

A novel gate and passivation dielectric stack consisting of a thin metal-organic chemical vapor deposition (MOCVD) grown in-situ Si3N4 (3 nm) and a thick low-pressure chemical vapor deposition (LPCVD) grown Si3N4 (30 nm) in AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistor (MIS-HEMT) is proposed. The quality of the Si3N4/(Al)GaN interface and the effect on threshold voltage (${V}_{\text {TH}}$) instability and dynamic ${R}_{ \mathrm{\scriptscriptstyle ON}}$ in the MIS-HEMTs with/without the in-situ Si3N4 layer are investigated by high-frequency capacitance-voltage (HFCV), quasi-static (QS) ${C}$ – ${V}$ (QSCV), time-of-fly (TOF) stress/measure, and QS ${I}_{\text {D}}$ – ${V}_{\text {DS}}$ methods. It is founded that the in-situ Si3N4 interfacial layer is effective in improving the dielectric/III-N interface morphology. As a result, better ${V}_{\text {TH}}$ stability and lower ${R} _{ \mathrm{\scriptscriptstyle ON},\text {D}}/{R} _{ \mathrm{\scriptscriptstyle ON},\text {S}}$ ratio are observed in devices with the in-situ Si3N4 interfacial layer due to the reduced density of traps close to the dielectric/III-N interface. Time-dependent dielectric breakdown and Weibull performance further verified that the proposed bilayer gate dielectric stack is a promising structure for the high-reliability power transistors. [ABSTRACT FROM AUTHOR]

In this letter, a distributed network model describing the effects of the border traps and distributed channel resistance on the impedance frequency dispersion of lateral MOS devices is proposed. The proposed model is verified using a gate recessed, normally-off Al2O3/GaN MOSFET structure operating as a MOS diode. The measured frequency-dependent capacitance and conductance curves of the MOS diode over a wide frequency range are found to be in good agreement with the proposed model. According to the intrinsic property of border traps to the ac signal, the proposed model is further modified to get the spatial distribution of border traps. The new insight derived from the impedance dispersion characteristics of lateral MOS devices is critical for quantitative analysis of the quality of III-V lateral MOS structures. [ABSTRACT FROM AUTHOR]

A series of studies are dedicated to research the clinical outcomes of oral leukoplakia (OLK) treated with carbon dioxide laser (CO2 laser); however, the results vary from studies especially related to recurrence and malignant transformation. Hence, we performed this meta-analysis to precisely evaluate the malignant transformation of OLK dealt with CO2 laser and investigate the association between its malignant transformation and kinds of related risk factors, such as gender, clinical classification, long duration of leukoplakia, and degree of epithelial dysplasia and lesion regions. We performed a systematic search of the Cochrane Library, EMBASE, Pubmed, Web of Science, and SCOPUS. Single-arm rate of the overall risk of malignant transformation in OLK treated with CO2 laser was calculated using the Der-Simonian Liard method. We applied subgroup analysis to compare the risk of malignant transformation according to the degree of epithelial dysplasia, clinical type, and region of OLK. Moreover, a pooled odds ratio (OR) is calculated, along with its 95% confidence interval (CI), to compare the risk of malignant transformation according to patients' gender, tobacco, and alcohol consumption. We used the meta package of R software for quantitative data synthesis and analysis. The rate of malignant transformation of OLK treated with carbon dioxide laser ranged from 0 to 15.38% in included studies. The overall rate of malignant transformation of OLK treated with CO2 laser is 4.50% under the random effect model [95% CI 0.0305-0.0659]. A systematic review of observational studies of OLK reported that the estimated overall (mean) malignant transformation rate was 3.5%, with a wide range between 0.13 and 34.0%. Interestingly, our result revealed that it was the male, homogeneous type, no tobacco consumption, and without alcohol-use who had a higher tendency of malignancy after laser surgery. However, this result lack statistically significant data. Generally speaking, whether oral leukoplakia patients underwent laser surgical treatment or not, it may have little effect on malignant transformation. In addition, we strongly advise that it had better not to perform CO2 laser intervention on OLK patients with the following clinical characteristics: homogeneous type, male, no tobacco consumption, and without alcohol-use. Evidence is still lacking in terms of relationship between malignant transformation and risk factors among OLK patients managed with CO2 laser. Thus, these associations should be further investigated. [ABSTRACT FROM AUTHOR]

Oral lichen planus (OLP) is a chronic mucosal inflammatory disease. The World Health Organization has described it as a potentially malignant condition. The pathogenesis of OLP remains to be fully elucidated, but extensive evidence suggests that immunologic and inflammatory factors have important roles. MicroRNAs (miRs), which are small non-coding RNAs, have been reported to be involved in OLP. In particular, miR-155 is significantly upregulated in patients with OLP. miR-155 has numerous functions and is closely linked to inflammation and immune system regulation. However, in-depth studies of the mechanisms via which miR-155 is involved in OLP are currently insufficient. Considering the close association between miR-155 and immune regulation as well as the importance of immune factors in OLP, the role of miR-155 in the immune system was herein summarized with a focus on OLP. The present review provides a basis for further study of the molecular mechanisms underlying the development and progression of OLP. [ABSTRACT FROM AUTHOR]

A novel early gate dielectric AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) process is reported. With the high-quality Si3N4 dielectric by low-pressure chemical vapor deposition and damage free, self-terminating passivation layer etching at the gate area, the MIS-HEMTs on 150-mm Si substrate demonstrate excellent output performance and good uniformity. The interface trap density between the gate insulator and the barrier layer is as low as $2 \times 10^{{12}}{\mathrm {cm}}^{- {2}}\,\,\cdot \,\,{\mathrm {eV}}^{- {1}}$ extracted by the conductance method. The MIS-HEMT fabricated on the wafer delivers an extremely small gate leakage current of 10−9 mA/mm and a high ${I}_{\mathrm{\scriptscriptstyle {ON}}}/{I}_{{\mathrm{\scriptscriptstyle {OFF}}}}$ ratio of 1011. The subthreshold swing (SS) is around 80 mV/dec, and the saturated output current density is 750 mA/mm. The dynamic on-resistance increases about 42% at a quiescent drain bias of 600 V. The ${V}_{ {th}}$ shift is −0.63 and −0.89 V at a high temperature of 200 °C and negative gate-bias stress of −25 V, respectively, indicating a comparable stability with the state-of-the-art MIS-HEMTs. An excellent threshold voltage and SS uniformity ($ {1} - \sigma /\mu)$ with the value of 94.5% and 95.2% are achieved on the 150-mm wafer. [ABSTRACT FROM AUTHOR]

Fibroblast growth factor receptors (FGFR) play a significant role in both embryonic development and in adults. Upon binding with ligands, FGFR signaling is activated and triggers various downstream signal cascades that are implicated in diverse biological processes. Aberrant regulations of FGFR signaling are detected in numerous cancers. Although FGFR4 was discovered later than other FGFR, information on the involvement of FGFR4 in cancers has significantly increased in recent years. In this review, the recent findings in FGFR4 structure, signaling transduction, physiological function, aberrant regulations, and effects in cancers as well as its potential applications as an anticancer therapeutic target are summarized. [ABSTRACT FROM AUTHOR]

This letter presents the original design of a microelectromechanical systems inertial switch with ultra‐low threshold (∼0.6 g) and great potential for batch manufacturing. The gravity is utilized to narrow the gap between electrodes during operation, defined here as threshold compensation. This lightens the fabrication burden, enabling the device to be made by standard silicon‐on‐glass micromachining without excessive optimization. Finite element analysis has been conducted to demonstrate positive effects of gravity involvement (9.4 μm reduction of the gap) and compliance design of the movable electrodes (multiplied contact time and less than half coefficient of restitution). Fabricated inertial switches have been installed into a vibration system to test fundamental characteristics. Under vibration conditions with amplitude of 0.6 g and frequencies from 25 to 40 Hz, the devices achieve reliable switching with triggering time ranging from 81.2 to 119.3 μs. [ABSTRACT FROM AUTHOR]

Frequency dispersion of the capacitance (C–f) of GaN-based heterostructure are commonly observed at high frequencies. Analytical solutions are derived for frequency dispersion of the heterostructure’s capacitance measured on two concentric-circle Schottky contacts, in form of Bessel function, by modeling a distributed network of heterostructure and solving corresponding circular transmission line functions. Solutions reveal C–f is determined by the Rs of 2-D electron gas (2-DEG). So in reverse, the sheet resistance at a certain carrier density can be extracted from the C–f measurement. By fitting experimental C–f data with the model, we obtain a peak mobility of 2044 cm2/ $\text {V}\cdot \text {s}$ corresponding to a 2-DEG density of $8.2 \times 10^{12}$ cm−2 and a sheet resistance of $373~\Omega / \square$ on an Al0.25Ga0.75N/GaN heterostructure on silicon substrate. The advantage of two Schottky contacts is that they could be implemented by mercury probes with the same geometry, then achieving nondestructive and instant feedback on carrier transport properties and uniformity of as-grown III–V compound semiconductor wafers [ABSTRACT FROM AUTHOR]

This paper presents a novel design of mechanical latching shock stops (latching stops) for in-plane shock protection of microelectromechanical systems (MEMS). With three shock protection modes, latching stops are capable of limiting the displacement of silicon suspensions in a compliant manner with efficient energy dissipation. The energy dissipation and the impact force between suspensions and shock stops were analyzed by numerical simulation. The analysis results indicate that latching stops, under a half-sine shock impulse [3000 g (1 g ≈ 9.8 m/s2), 0.15 ms], reduce more than two-third of the impact force compared with hard stops, and additionally, dissipate 33.23% of the total mechanical energy during the latching process. Test specimens of both latching stops and conventional hard stops were developed for comparison. The experimental results demonstrate that test specimens of latching stops achieve more than double the robustness compared with those of hard stops. This new shock protection approach decouples the reliability design from the device design. Moreover, latching stops are compatible with wafer-level MEMS batch fabrication without the requirement of additional processes or materials. [ABSTRACT FROM AUTHOR]

We report the effect of the gate recess process and the surface of as-etched GaN on the gate oxide quality and first reveal the correlation between border traps and exposed surface properties in normally-off Al2O3/GaN MOSFET. The inductively coupled plasma (ICP) dry etching gate recess with large damage presents a rough and active surface that is prone to form detrimental GaxO validated by atomic force microscopy and X-ray photoelectron spectroscopy. Lower drain current noise spectral density of the 1/f form and less dispersive ac transconductance are observed in GaN MOSFETs fabricated with oxygen assisted wet etching compared with devices based on ICP dry etching. One decade lower density of border traps is extracted in devices with wet etching according to the carrier number fluctuation model, which is consistent with the result from the ac transconductance method. Both methods show that the density of border traps is skewed towards the interface, indicating that GaxO is of higher trap density than the bulk gate oxide. GaxO located close to the interface is the major location of border traps. The damage-free oxidation assisted wet etching gate recess technique presents a relatively smooth and stable surface, resulting in lower border trap density, which would lead to better MOS channel quality and improved device reliability. [ABSTRACT FROM AUTHOR]

In this letter, we demonstrate a recessed-anode Schottky barrier diode (SBD) on a double AlGaN/GaN heterojunction structure. A self-terminated, oxidation/wet etching with low-pressure chemical vapor deposition (LPCVD) Si3N4 mask is applied in the anode recess process. Unlike common plasma-based, dry etching techniques, the etched surface is not subjected to ion bombardment, and the etch depth is precisely controlled. As a result, a high effective channel mobility of 1079 cm2/ \text V~\cdot ~\text s is maintained in the channel beneath the recess surface. The fabricated devices with a 15- \mu \textm anode-to-cathode distance ( L \mathrm {AC} ) are found to exhibit a uniform, low turn-ON voltage ( V_\mathrm ON ) of 0.69 ± 0.03 V, and a low specific on-resistance ( R \mathrm{ON,SP} ) of 2.83 \textm\Omega \cdot \text cm^2 . The SBDs also show excellent off-state blocking characteristics due to the smooth recess interface together with the assistance of LPCVD grown Si3N4. A breakdown voltage of 1190 V is achieved for the SBDs with 15- \mu \textm~L \mathrm {AC} at a leakage current criteria of 1~\mu \textA /mm, and the Baliga’s figure-of-merit is 500 MW/cm2. [ABSTRACT FROM PUBLISHER]

A gate-recessed normally OFF GaN metal–oxide–semiconductor high-electron-mobility transistor on silicon substrate has been fabricated using a self-terminated, plasma-free oxidation and wet etching process with pre-recess low-pressure chemical vapor deposition (LPCVD) Si3N4 passivation layer. The LPCVD Si3N4 serves the dual role of gate-recess mask and passivation layer. Unlike conventional oxidation etching process using Si3N4 as post gate-recess passivation, the gate channel region was prevented from additional plasma bombardment during the gate window re-opening. As a result, a high-effective channel mobility of 843 $\text {cm}^{\text {2}} / \text {V}\cdot \text {s}$ , and low-channel resistance of $0.89~\Omega \cdot \text {mm}$ are achieved for a normally OFF channel with ${L}_{G} = \text {1.5}\,\,\mu \text{m}$. For $\text {3}~\mu \text{m}~{L}_{\text {GD}}$ , the fabricated devices exhibit a threshold voltage ( ${V}_{\text {th}}$ ) of 1.35 V, a maximum drain current of ~500 mA/mm, a high ON/ OFF current ratio of ~1010, and 560-V OFF-state breakdown voltage together with a low-forward gate leakage current of ~10−7 mA/mm up to 10 V. A high Baliga’s figure of merit of 1.26 GW/cm2 is achieved in devices with 10- $\mu \text{m}$ gate–drain distance. [ABSTRACT FROM AUTHOR]

For devices with a 15 micron anode-to-cathode distance, nearly 1.5 times increase in the blocking (breakdown) voltage (from 692 to 1030 V) has been achieved by replacing the alloyed Ohmic contact at the anode electrode of the conventional MOS gated hybrid-anode lateral field-effect rectifier (CMLFER) with a low barrier Schottky contact. The new Schottky-MOS hybrid-anode lateral field-effect rectifier is found to offer comparable low onset voltage ( V{\textbf {ON}} of 0.68±0.13 versus 0.65±0.11 V for CMLFER) independent of the anode-to- cathode distance. The immunity of the punch through caused by drain induced barrier lowering effect is obtained through the low barrier Schottky contact in anode, which is believed to be responsible for the reduction in the leakage current, and the improvement of rectifier breakdown voltage. [ABSTRACT FROM AUTHOR]

In this letter, a gate recessed normally-off GaN metal–oxide–semiconductor high-electron-mobility transistor on silicon substrate is fabricated using AlN/Si3N4 as the passivation layer. The thin AlN layer serves the dual role of protecting the gate channel region from direct plasma bombardment during the RIE Si3N4 removal and passivating the surface states in the access region. As a result, the effective carrier mobility in the normally-off channel is found to improve from the 568 cm2/ \text V\cdot \text s in conventional Si3N4 passivation process to a high value of 1154 cm2/ \text V\cdot \text s . A saturated output current density of 603 mA/mm and an ON-resistance of 5.3~\Omega \cdot \text mm was obtained for devices with \textL\text {G}/\textL\text {GS}/\textL\text {GD}/\text{W}\text {G} = 1.5 /1.5/3/ 20~\mu \textm . Meanwhile, the degradation of dynamic ON-resistance is significantly suppressed due to the effective passivation of surface states by the AlN layer grown by plasma-enhanced atomic layer deposition. [ABSTRACT FROM AUTHOR]

Time-dependent OFF-state leakage behavior of AlGaN/GaN MISHEMTs on silicon substrate is investigated and a novel degradation mechanism is proposed in this paper. Under constant high voltage OFF-state stress, drain leakage current gradually increases with stress time and the behavior is gate bias and temperature-dependent. Consecutive OFF-state breakdown measurement with drain injection technique indicates that the negative shift of threshold voltage ( V\mathrm {th} ) is responsible for the increase of drain leakage current during stress measurement. It is proposed that the negative shift of V\mathrm {th} is mainly induced by the ionization of uncompensated donor like deep levels near the channel, which are most likely to be located in the 300-nm-thick unintentionally doped GaN layer above the carbon doped buffer layer. [ABSTRACT FROM PUBLISHER]

In this letter, a plasma-free etch stop structure is developed for GaN HEMT toward enhancement-mode operation. The self-terminated precision gate recess is realized by inserting a thin AlN/GaN bilayer in the AlGaN barrier layer. The gate recess is stopped automatically at the GaN insertion layer after high-temperature oxidation and wet etch, leaving a thin AlGaN barrier to maintain a quantum well channel that is normally pinched off. With addition of an Al2O3 gate dielectric, quasi normally OFF GaN MOSHEMTs have been fabricated with high threshold uniformity and low ON-resistance comparable with the normally ON devices on the same wafer. A high channel mobility of 1400 cm ^2/\textrm V\cdot \textrm s was obtained due to the preservation of the high electron mobility in the quantum-well channel under the gate. [ABSTRACT FROM AUTHOR]

The temperature dependence of current collapse (CC) in AlGaN/GaN high-electron mobility transistors on silicon substrate is studied in this paper. Devices without and with Si3N4 passivation are used to investigate the behavior of surface- and buffer-induced CC, respectively. It is found that the degree of surface-induced CC in unpassivated devices has a weak temperature dependence, which is induced by the cancelling out between enhanced carrier injection based on surface hopping and enhanced emission when the temperature is increased. On the other hand, the degree of buffer-induced CC in the Si3N4 passivated devices is reduced at higher temperature since the energy of hot electrons is reduced due to the phonon scattering and the trapping of hot electrons in the buffer is mitigated. Temperature-dependent transient measurement is also carried out to investigate the recovery process for these two type of CC. Two types of trap levels are identified in the unpassivated and Si3N4 passivated devices, respectively. The trap level $E1$ with an activation energy of 0.08 eV is supposed to be related to the surface trapping, while $E2$ with an activation energy of 0.22 eV is located in the buffer layer. [ABSTRACT FROM AUTHOR]