Search

GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) on AlGaN/GaN heterostructure with a recess gate were fabricated and characterized. The device showed good pinch-off characteristics and a maximum field-effect mobility of 145.2 cm2·V−1·s−1. The effects of etching gas of Cl2 and SiCl4 were investigated in the gate recess process. SiCl4-etched devices showed higher channel mobility and lower threshold voltage. Atomic force microscope measurement was done to investigate the etching profile with different etching protection mask. Compared with photoresist, SiO2-masked sample showed lower surface roughness and better profile with stepper sidewall and weaker trenching effect resulting in higher channel mobility in the MOSFET.

A highly efficient and convenient method for the construction of C-hydroxydiketopiperazines has been developed using Lanthanum(III) triflate as a recyclable reagent. Microwave heating dramatically enhances the reaction rate without the epimerization of the existing chiral center in the substrate.

Background The purpose of this study was to investigate the therapeutic effects and mechanisms of hyperbaric oxygen (HBO) treatment on rats following spinal cord injury (SCI). Methods A total of 45 Sprague-Dawley (SD) rats were randomly divided into three groups. Sham-SCI group was surgically exposed but not subjected to the SCI procedure. SCI-control group was administered SCI and treated with regular air. SCI-HBO group was administered SCI and HBO treatment. Neuromotor functions were examined using the Basso, Beattie, and Bresnahan (BBB) locomotor rating scale and the inclined plane assessment at before SCI (baseline) and after SCI. Superoxide dismutase (SOD) activities and malondialdehyde (MDA) levels were measured. Results Starting from Day 1 after SCI but except Day 2, the SCI-HBO group has significantly higher BBB scores than the SCI-control group. After SCI, the maximum inclination angles at which rats could maintain were significantly lower in both SCI groups. But the maximum angles were significantly bigger for the rats in the SCI-HBO group than those on the SCI-control group at 5, 10 and 20 days after SCI. SOD activities in SCI-HBO rats were significantly higher and MDA levels were significantly lower than in SCI-control rats, at two and five days after SCI. There was also less cystic degeneration of spinal cord in SCI-HBO rats, compared to SCI-control rats. Conclusions These results suggest that HBO treatment has a therapeutic value in treating SCI. Increased oxygen free radical scavenging and reduced lipid oxidation may be one of the mechanisms.

FinFETs become dominant transistor architecture to replace planar metal-oxide-semiconductor field-effect transistors (MOSFETs) for larger effective channel width and better short channel controllability. Fin critical dimension (CD) of cross-fin direction is one of the most important parameters which impact MOSFET subthreshold swing and threshold voltage. However, CD loading between isolated and dense fins are naturally unavoidable in fin etch and STI filling process for different environments in these two areas. This paper mainly focuses on the fin formation process to give a demonstration of device performance and fin CD uniformity between different fin formation approaches.

GaN metal–oxide–semiconductor field-effect transistors (MOSFETs) with recessed gate on AlGaN/GaN heterostructure are reported in which the drain and source ohmic contacts were fabricated on the AlGaN/GaN heterostructure and the electron channel was formed on the GaN buffer layer by removing the AlGaN barrier layer. Negative threshold voltages were commonly observed in all devices. To investigate the reasons of the negative threshold voltages, different oxide thickness, etching gas and bias power of inductively-coupled plasma (ICP) system were utilized in the fabrication process of the GaN MOSFETs. It is found that positive charges of around 1 × 10 12 q/cm 2 exist near the interface at the just threshold condition in both silane- and tetraethylorthosilicate (TEOS)-based devices. It is also found that the threshold voltages do not obviously change with the different etching gas (SiCl 4 , BCl 3 and two-step etching of SiCl 4 /Cl 2 ) at the same ICP bias power level (20–25 W) and will become deeper when higher bias power is used in the dry recess process which may be related to the much serious ion bombardment damage. Furthermore, X-ray photoelectron spectroscopy (XPS) experiments were done to investigate the surface conditions. It is found that N 1s peaks become lower with higher bias power of the dry etching process. Also, silicon contamination was found and could be removed by HNO 3 /HF solution. It indicates that the nitrogen vacancies are mainly responsible for the negative threshold voltages rather than the silicon contamination. It demonstrates that optimization of the ICP recess conditions and improvement of the surface condition are still necessary to realize enhancement-mode GaN MOSFETs on AlGaN/GaN heterostructure.

GaN MOSFETs were developed on an AlGaN/GaN heterostructure in which the drain and source ohmic contacts were fabricated on the AlGaN/GaN heterostructure, and the electron channel was formed on the GaN buffer layer by removing the AlGaN barrier layer. For devices with different types and sizes, discrepant field-effect mobilities were observed and the origins of the discrepancy were analyzed. One reason causing the discrepancy is the discrepancy of gate dimension between the design and fabrication. In devices with only mesa as the device isolation, the real channel width would be larger than the mesa width because a parallel channel might have formed in the isolation region just outside the device mesa. Boron ion implantation was found to be effective to cutoff the current path in the isolation region. Another reason causing the discrepancy is that the real channel length would be larger than the designed one owing to the lithography and gate dry recess process. To extract the correct mobility and effective channel length of the GaN MOSFET fabricated on AlGaN/GaN heterostructure with variation in the channel dimensions, several methods were proposed and compared basing on ring-type MOSFETs.

Conjugates (A1–A5) of the Pt(IV) derivative (A6) with amino groups from peracetyl glucose, rhamnose and mannose with a propyl amino or ethyl amino linker at the reducing end were synthesized and exhibited significant therapeutic efficacy in tumour cells, especially for prostate cancer (PCa). The antitumor activities are greatly affected by glycosyl groups. Cytotoxic experiments in vitro indicated that the antitumor activities were increased by 5-fold when its Pt(IV) derivative was conjugated to S18 (IC50 = 4.82 ± 0.45 μM) and by 12-fold when conjugated to S21 (IC50 = 1.9 ± 0.67 μM). The mannose substituted Pt(IV) complexes A4 and A5 were also over an order of magnitude more potent towards HeLa, A549, MCF-7 and PC3 than cisplatin and oxaliplatin. Importantly, the glycosylated Pt(IV) derivatives A4 and A5 displayed potential safety for clinical therapeutic exposure with IC50 of 84 μM and 169 μM compared with cisplatin (IC50 = 8 μM) to 3T3. Cellular uptake and DNA platination are higher than cisplatin and oxaliplatin. ESI-MS analysis of A5 binding to 5′-dGMP revealed that bifunctional DNA lesions were formed. The antitumor activities in vivo showed that the MTD and LD50 for A4 and A5 are nearly 4-fold higher than that of oxaliplatin indicating the potential safety for the glycosylated Pt(IV) complexes.

A new series of glycosylated Pt(iv) complexes were designed, synthesized and evaluated for antitumor activities in vitro and in vivo. The incorporation of glycosyl groups to the Pt(iv) system has much influence on the antitumor abilities. Four lead compounds with activities comparable or even superior to cisplatin and oxaliplatin are screened out. These Pt(iv) complexes could be reduced to release Pt(ii) complexes and cause the death of tumour cells. The apoptosis-inducing properties of these compounds are similar to cisplatin. The accumulation of the glycosylated Pt(iv) complexes in cells and DNA is higher than cisplatin and oxaliplatin. The in vivo assay demonstrates that the tested compounds inhibit the growth of HepG2 tumors with low toxicity.

Electrical resistivities and thermal stabilities of carbon-doped Cu films on silicon have been investigated. The films were prepared by magnetron sputtering using a Cu–C alloy target. After annealing at 400 °C for 1 h, the resistivity maintains a low level at 2.7 μΩ-cm and no Cu–Si reaction is detected in the film by X-ray diffraction (XRD) and transmission electron microscopy (TEM) observations. According to the secondary ion mass spectroscopy (SIMS) results, carbon is enriched near the interfacial region of Cu(C)/Si, and is considered responsible for the growth of an amorphous Cu(C)/Si interlayer that inhibits the Cu–Si inter-diffusion. Fine Cu grains, less than 100 nm, were present in the Cu(C) films after long-term and high-temperature annealings. The effect of C shows a combination of forming a self-passivated interface barrier layer and maintaining a fine-grained structure of Cu. A low current leakage measured on this Cu(C) film also provides further evidence for the carbon-induced diffusion barrier interlayer performance.

A highly efficient and convenient method for the construction of C-hydroxydiketopiperazines is developed using Lanthanum(III) triflate as a recyclable reagent.

In this study, titanium nitride (TiN) is synthesized using reactive sputtering for a self-aligned gate process. The Schottky barrier height of the TiN on n-GaN is around 0.5 to 0.6 eV and remains virtually constant with varying nitrogen ratios. As compared with the conventional Ni electrode, the TiN electrode presents a lower turn-on voltage, while its reverse leakage current is comparable with that of Ni. The results of annealing evaluation at different temperatures and duration times show that the TiN/W/Au gate stack can withstand the ohmic annealing process at 800°C for 1 or 3 min. Finally, the self-aligned TiN-gated AlGaN/GaN heterostructure field-effect transistors are obtained with good pinch-off characteristics.

Self-aligned-gate heterostructure field-effect transistor (HFET) is fabricated using a wet-etching method. Titanium nitride (TiN) is one kind of thermal stable material which can be used as the gate electrode. A Ti/Au cap layer is fixed on the gate and acts as an etching mask. Then the T-shaped gate is automatically formed through over-etching the TiN layer in 30% H2O2 solution at 95 °C. After treating the ohmic region with an inductively coupled plasma (ICP) method, an Al layer is sputtered as an ohmic electrode. The ohmic contact resistance is approximately 0.3 Ωmm after annealing at a low-temperature of 575 °C in N2 ambient for 1 min. The TiN gate leakage current is only 10−8 A after the low-temperature ohmic process. The access region length of the self-aligned-gate (SAG) HFET was reduced from 2 μm to 0.3 μm compared with that of the gate-first HFET. The output current density and transconductance of the device which has the same gate length and width are also increased.

An Al-based ohmic process assisted by an inductively coupled plasma (ICP) recess treatment is proposed for AlGaN/GaN heterostructure field-effect transistors (HFETs) to realize ohmic contact, which is only needed to anneal at 500 °C. The recess treatment was done with SiCl4 plasma with 100 W ICP power for 20 s and annealing at 575 °C for 1 min. Under these conditions, contact resistance of 0.52 Ωmm was confirmed. To suppress the ball-up phenomenon and improve the surface morphology, an Al/TiN structure was also fabricated with the same conditions. The contact resistance was further improved to 0.30 Ωmm. By using this plasma-assisted ohmic process, a gate-first HFET was fabricated. The device showed high drain current density and high transconductance. The leakage current of the TiN-gate device decreased to 10−9 A, which was 5 orders of magnitude lower than that of the device annealed at 800 °C. The results showed that the low-temperature ohmic contact process assisted by ICP treatment is promising for the fabrication of gate-first and self-aligned gate HFETs.

Gallium nitride (GaN) metal-oxide-semiconductor field-effect transistors (MOSFETs) with boron field implantation isolation and mesa isolation were fabricated and characterized. The process of boron field implantation was altered and subsequently conducted after performing high-temperature ohmic annealing and gate oxide thermal treatment. Implanted regions with high resistivity were achieved. The circular MOSFET fabricated in the implanted region showed an extremely low current of 6.5 × 10−12 A under a gate voltage value up to 10 V, thus demonstrating that the parasitic MOSFET in the isolation region was eliminated by boron field implantation. The off-state drain current of the rectangular MOSFET with boron field implantation was 5.5 × 10−11 A, which was only one order of magnitude higher than the 6.6 × 10−12 A of the circular device. By contrast, the rectangular MOSFET with mesa isolation presented an off-state drain current of 3.2 × 10−9 A. The field isolation for GaN MOSFETs was achieved by using boron field implantation. The implantation did not reduce the field-effect mobility. The isolation structure of both mesa and implantation did not influence the subthreshold swing, whereas the isolation structure of only the implantation increased the subthreshold swing. The breakdown voltage of the implanted region with 5 μm spacing was up to 901.5 V.

By means of two-dimensional device simulator, the effects of vanadium-compensated concentration on the electrical characteristics of 6H SiC photoconductive semiconductor switches (PCSS) are explored. In the simulator, the model of PCSS is an n-type device doped with 1×1014 cm−3, and is compensated by vanadium (V). Under a bias of 1500 V, the dark current in case of V-concentration of 1×1012 cm−3 is 1 A, and decreased to 5×10−7 A for V-concentration of 1×1015 cm−3. Illuminated by 0.4 um incident light with a power of 2500 W/cm−2, the peak current in case of V-concentration of 1×1012 cm−3 is 160 A, and decreased to 6 A for V-concentration of 1×1015 cm−3. The spectral responsivity of 6H SiC PCSS is maximized in 0.3875 um with a value of 4.8 mA/W under a bias of 1500 V. From the results, the V-concentration should be chosen to achieve the insulation characteristics and photocurrent according to the doped concentration.

There are two empirical studies in this paper. In the first study we investigated what were the important factors which would impact on the perceived factors of consumers’ shopping online in China through interviewing, email and internet investigation, and obtained three important factors which were products, websites and personal factors based on 1075 valid respondents. In the second study we designed a questionnaire with 29 items used to measure the three kinds of influence factors verified in the first study and 792 valid data were collected. The differences between consumers with different shopping experiences and genders were compared and tested according to statistical and ANOVA analysis. The results indicate that: shopping experiences are important influent factors which will cause the differences of consumers’ perceived factors in the process of shopping online; consumers’ attitudes for online shopping would gradually be changed as the times of their shopping experience add up; there are significant differences about products factors between consumers both with different shopping experiences and with different genders.

We report a new approach in fabricating a self-aligned gate GaN MOSFET. The fabrication technique is based on a double-layer photoresist (PR) and low-temperature-Ohmic formation process assisted by an inductively coupled plasma (ICP) dry etching process. In this process, the active region was automatically defined by the combination of a subsequently developed positive PR and the existing negative PR pattern. The Al Ohmic electrodes on the ICP-treated active region were formed by a lift-off process followed by 500 °C N2 1 min annealing. The specific contact resistance of 4.8 × 10−6 Ω cm2 was obtained in this process. Operation up to a gate bias of 30 V was confirmed. The maximum output current of 98 mA mm−1 and field-effect mobility of 110 cm2 V−1 s−1 were observed in the device with a gate length of 4 μm. Some non-ideal effects in this device, including the negative threshold voltage, larger off-state leakage and unsaturated on-state drain current, were also observed and analyzed. Some possible ways to improve the performance of the device were proposed.

GaN MOSFETs on a AlGaN/GaN heterostructure with a recess gate were fabricated. The charges near the SiO2/GaN interface of the GaN MOSFETs with different etching conditions were evaluated. It was found that stronger bombardment damage in the dry process will bring more charges near the interface and finally make the threshold voltage of the device negative. Nitrogen plasma treatment and ammonia water (NH4OH) treatment were investigated to recover or remove the damaged layer in order to achieve an enhancement-mode (E-mode) device with positive threshold voltage on the dry-recessed semi-insulating (SI) GaN surface. The influence of these treatments on the interface state density was also characterized using the Terman method by using the GaN MOS capacitor. An E-mode GaN MOSFET with a maximum field-effect mobility of 148.1 cm2 V−1 s−1 and a MOS capacitor with an interface state density of 3 × 1011 cm−2 eV−1 were realized by the NH4OH treatment.

We report on a gate-first GaN metal–oxide–semiconductor field-effect transistor (MOSFET) based on a non-annealing ohmic process. The device was formed on an n+-GaN (30 nm, 1 × 1019 cm−3)/semi-insulating GaN wafer. The source and drain (Ti/Al/Ti/Au) were deposited after the contact region was treated using an inductively coupled plasma (ICP) dry etching system. Ohmic contact with a contact resistance of 0.48 Ω mm was realized at room temperature. A device fabricated by a gate-first process shows good pinch-off characteristics and a maximum field-effect mobility of 163.8 cm2 V−1 s−1.

In this paper, the influence of deposition conditions and post annealing upon the device performance of sputtering-deposited TiN/AlO/AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors is reported. The metal-oxide-semiconductor structure on GaN with AlO deposited in a medium O2/Ar ratio possessed the smallest interfacial state density and reverse leakage current. Metal-oxide-semiconductor heterostructure field-effect transistors with a small hysteresis and a low leakage current were obtained by depositing AlO with a medium O2/Ar ratio and post-annealing at 600 °C for 1 min. After annealing, the maximum transconductance shows some decrease, resulting in a decrease of saturation drain current.

We report the investigation of boron ion implantation as a device field isolation process for GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) on AlGaN/GaN heterostructure. In the mesa isolation region of a bar-type MOSFET, a parasitic MOS-channel existed and widened the designed channel width, which would result in an overestimated mobility compared with a ring-type MOSFET. After boron ions implantation in the isolation region, the overestimation of field-effect mobility of bar-type MOSFETs was eliminated. The sub-threshold characteristics and on-state drain current of the bar-type MOSFETs coincide with the ring-type devices. Long-channel ring-type MOSFETs, with and without ion implantation, were fabricated on the recess region to evaluate the sub-threshold characteristics. The MOSFETs with boron ions implanted into the recess region showed a low drain current up to the gate bias of 10V. The result indicated that boron ion implantation prevented the formation of parasitic MOS-channel in the isolation region and achieved field isolation. The current–voltage characteristics of MOSFETs with the normal recess condition demonstrated no degradation of device performance after boron ions implanted into the isolation region. Boron ion implantation by further optimization can be a field isolation method for GaN MOSFETs.

This study evaluates the thermal stability of different refractory metal nitrides used as Schottky electrodes on GaN. The results demonstrate that TiN, MoSiN, and MoN possess good rectification and adhesion strength, with barrier heights of 0.56, 0.54, and 0.36 eV, respectively. After thermal treatment at 850 °C for 1 min, the TiN and MoN electrodes still exhibit rectifying characteristics, while the MoSiN degrades to an ohmic-like contact. For further study, several TiN films are deposited using different N2/Ar reactive/inert sputtering gas ratios, thereby varying the nitrogen content present in the sputtering gas. Ohmic-like contact is observed with the pure Ti contact film, and Schottky characteristics are observed with the samples possessing nitrogen in the film. The average Schottky barrier height is about 0.5 eV and remains virtually constant with varying nitrogen deposition content. After examining Raman spectra and x-ray photoelectron spectroscopy results, the increase in the film resistivity after thermal treatment is attributed to oxidation and/or nitridation. Films deposited with a medium (40% and 60%) nitrogen content show the best film quality and thermal stability.

The dry recessed-gate GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) on AlGaN/GaN heterostructure using boron trichloride (BCl3) as etching gas were fabricated and characterized. Etching with different etching power was conducted. Devices with silicon tetrachloride (SiCl4) etching gas were also prepared for comparison. Field-effect mobility and interface state density were extracted from current-voltage (I-V) characteristics. GaN MOSFETs on AlGaN/GaN heterostructure with BCl3 based dry recess achieved a high maximum electron mobility of 141.5 cm2V−1s−1 and a low interface state density.