11 results on '"Chen, Kevin J."'
Search Results
2. Assessment of osteoarthritis functional outcomes and intra‐articular injection volume in the rat anterior cruciate ligament transection model.
- Author
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Wang, Yuyan, Wagner, Emma S., Yu, Danqiao, Chen, Kevin J., Keel, Taidhgin J., Pownder, Sarah L., Koff, Matthew F., Cheetham, Jonathan, Samaroo, Kirk J., and Reesink, Heidi L.
- Subjects
INTRA-articular injections ,ANTERIOR cruciate ligament ,MAGNETIC resonance imaging ,FUNCTIONAL status ,RATS ,SPRAGUE Dawley rats - Abstract
The rat surgical anterior cruciate ligament transection (ACLT) model is commonly used to investigate intra‐articular osteoarthritis (OA) therapies, and histological assessment is often the primary outcome measure. However, histological changes do not always correlate well with clinical outcomes. Therefore, this study evaluated functional outcomes in the rat surgical ACLT model and compared intra‐articular injection volumes ranging from 20 to 50 μl. Unilateral ACLT was surgically induced and static weight‐bearing, mechanical allodynia, motor function, and gait were assessed in four groups of male, Sprague‐Dawley rats (n = 6 per group). Intra‐articular injections of 20 µl Dulbecco's phosphate‐buffered saline (DPBS), 50 µl DPBS, or 50 µl of synthetic biomimetic boundary lubricant were administered once weekly for 3 weeks postoperatively. Structural changes were evaluated histologically at 20 weeks. Rat cadaver knees were injected with 20, 30, 40, or 50 µl of gadolinium solutions and were imaged using magnetic resonance imaging (MRI). Static weight‐bearing, mechanical allodynia, and gait parameters in ACLT groups revealed differences from baseline and naïve controls for 4 weeks post‐ACLT; however, these differences did not persist beyond 6 weeks. Different intra‐articular DPBS injection volumes did not result in functional or histological changes; however, peri‐articular leakage was documented via MRI following 50, 40, and 30 µl but not 20 µl gadolinium injections. Statement of clinical significance: Differences in functional parameters were predominantly restricted to early, postoperative changes in the rat surgical ACLT model despite evidence of moderate histologic OA at 20 weeks. Injection volumes of 20–30 µl are more appropriate for investigating intra‐articular therapies in the rat knee. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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3. Strain Release in GaN Epitaxy on 4° Off‐Axis 4H‐SiC.
- Author
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Feng, Sirui, Zheng, Zheyang, Cheng, Yan, Ng, Yat Hon, Song, Wenjie, Chen, Tao, Zhang, Li, Liu, Kai, Cheng, Kai, and Chen, Kevin J.
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- 2022
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4. Suppression of Green Luminescence of Mg‐Ion‐Implanted GaN by Subsequent Implantation of Fluorine Ions at High Temperature.
- Author
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Takahashi, Masahiro, Tanaka, Atsushi, Ando, Yuto, Watanabe, Hirotaka, Deki, Manato, Kushimoto, Maki, Nitta, Shugo, Honda, Yoshio, Shima, Kohei, Kojima, Kazunobu, Chichibu, Shigefusa F., Chen, Kevin J., and Amano, Hiroshi
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ION implantation ,ION temperature ,HIGH temperatures ,GALLIUM nitride ,FERMI level ,LUMINESCENCE ,ENDOMETRIUM ,MAGNESIUM ions - Abstract
Herein, gallium nitride (GaN) samples implanted with magnesium (Mg) and fluorine (F) ions are investigated by photoluminescence (PL) measurements. In low‐temperature PL measurements, the characteristic green luminescence (GL) band attributable to nitrogen vacancies (VN) is observed in Mg‐ion‐implanted GaN. As VN are likely to act as donors, suppressing their formation is essential to realizing p‐type conductivity. The energy required for a F impurity to replace VN in GaN and eventually form F on a N site decreases when the Fermi level approaches the valence band maximum, and therefore F is employed as a subsequent implantation element to compensate for VN. The GL band peak disappears upon implanting Mg and F ions at a high temperature and adjusting the F concentration to an appropriate value. This result suggests that VN generated by Mg ion implantation can be suppressed using an element with a lower formation energy than that of VN. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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5. Bias Temperature Instability of Normally‐Off GaN MIS‐FET with Low‐Pressure Chemical Vapor Deposition SiNx Gate Dielectric.
- Author
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Hua, Mengyuan, Qian, Qingkai, Wei, Jin, Zhang, Zhaofu, Tang, Gaofei, and Chen, Kevin J.
- Subjects
GALLIUM nitride ,METAL oxide semiconductor field-effect transistors ,LOW pressure (Science) ,CHEMICAL vapor deposition ,SILICON nitride - Abstract
In this work, characterizations are conducted to investigate the threshold voltage (V
TH ) stability of the normally‐off GaN metal–insulator–semiconductor (MIS‐) field‐effect transistor (FET) with fully recessed gate structure and highly reliable low‐pressure chemical vapor deposition SiNx gate dielectric. We conducted bias‐temperature instability (BTI) tests under both positive and negative gate bias. We demonstrated the highly stable VTH of the high‐performance MIS‐FETs with small BTI, which benefits from the effective interfacial protection layer. More specifically, combining the BTI tests and drain current 1/f noise analysis, we present extensive investigation of the physical origins of BTI. According to the experimental evidence and analysis, we ascribe the VTH instability to the trapping/detrapping of the pre‐existing trap states located at the SiNx /GaN interface and/or in the gate dielectric. [ABSTRACT FROM AUTHOR]- Published
- 2018
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6. SiC trench MOSFET with self-biased p-shield for low RON-SP and low OFF-state oxide field.
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Meng Zhang, Jin Wei, Huaping Jiang, Chen, Kevin J., and Ching-Hsiang Cheng
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METAL oxide semiconductor field-effect transistors ,FIELD-effect transistors ,MOLECULAR dynamics ,SEMICONDUCTOR materials ,ELECTRIC resistance - Abstract
A SiC trench metal-oxide-semiconductor field-effect transistor (MOSFET) with a self-biased p-shield (SBS-MOS) is proposed and comprehensively studied. The p-shield region is used to reduce the high oxide field at the OFF-state, which would otherwise be detrimental to the device long-term reliability. A self-biasing network is designed to raise the potential of the pshield in the SBS-MOS, so that the parasitic junction field effect transistor (JFET) is driven synchronously with the MOS-gate. Mixed-mode numerical simulations are carried out to study the performance of the proposed device. The SBS-MOS boasts a reduced specific ON-resistance (RON-SP) compared with the trench MOSFET with a grounded p-shield (GS-MOS), by the reduction of the JFET resistance and/or further down-scaling of the cell size. To synchronously drive the JFET region, only a slightly larger gate charge is required for the SBS-MOS. Therefore, a low OFF-state oxide field, a low RON-SP and a low QGD are simultaneously achieved in the proposed SBS-MOS. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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7. Trapping mechanisms in insulated-gate GaN power devices: Understanding and characterization techniques.
- Author
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Yang, Shu, Liu, Shenghou, Lu, Yunyou, and Chen, Kevin J.
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POWER transistors ,POWER field effect transistors ,TRANSISTORS ,FIELD-effect transistors ,SINGLE electron transistors - Abstract
In addition to surface- and buffer-trapping, interface/border trapping and the consequent V
TH shift in insulated-gate GaN power transistors could also cause RON increase, due to the reduced gate overdrive. This work reports on a systematic study of the trapping mechanisms in normally-on/off insulated-gate GaN transistors subjected to dynamic (AC) and static (DC) gate stress. The fast dynamic characterizations featuring an ultrashort measurement delay of 10−7 s minimize the recovery during measurement and enable a quantitative evaluation of VTH shift-induced RON increase. By analyzing the time-resolved instability in normally-on MIS-HEMT and normally-off MIS-FET with fully recessed barrier, we elucidate several key mechanisms including: (i) recessing the polarized III-nitride barrier layer can suppress VTH shift during ON/OFF switching; (ii) AC stress, which has more practical implication for lifetime projection for power switching applications, produces smaller VTH shift and RON increase comparing to DC stress; (iii) Sufficient gate overdrive at ON state and lower channel resistance in normally-on MIS-HEMT allow a better tolerance to VTH shift. Primary trapping effects in an insulated-gate GaN power transistor. [ABSTRACT FROM AUTHOR]- Published
- 2017
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8. Optoelectronic devices on AlGaN/GaN HEMT platform.
- Author
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Li, Baikui, Tang, Xi, Wang, Jiannong, and Chen, Kevin J.
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PHOTONS ,ALUMINUM gallium nitride ,GALLIUM nitride ,MODULATION-doped field-effect transistors ,SCHOTTKY barrier diodes - Abstract
Integration of a photon source into the AlGaN/GaN high election mobility transistor (HEMT) platform will realize the functionality of on-chip optical pumping of deep electron traps which suppress the dynamic performances of power HEMTs. Here, we report a Schottky-on-heterojunction light-emitting diode (SoH-LED) realized on the p-doping-free lateral AlGaN/GaN heterostructure. A physical mode based on hot electron induced surface states impact ionization was proposed to explain the hole generation and injection processes in this p-doping-free SoH-LED. Since the SoH-LED shares identical epitaxial structures with HEMT, integration of SoH-LED and HEMT requires no additional epi-layers during the wafer growth and minimum process modification during device fabrication. The SoH-LED structure was seamlessly integrated into the HEMT platform as an on-chip photon source. Experiment results showed that the SoH-LED photons can effectively assist the electron de-trapping processes from both of the surface and bulk deep traps, demonstrating the feasibility of using on-chip generated photons to improve the dynamic performances of AlGaN/GaN power HEMTs. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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9. On-chip addressable Schottky-on-heterojunction light-emitting diode arrays on AlGaN/GaN-on-Si platform.
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Xi Tang, Baikui Li, Yunyou Lu, and Chen, Kevin J.
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SCHOTTKY barrier diodes ,ALUMINUM gallium nitride ,LIGHT emitting diodes ,GALLIUM nitride synthesis ,MICROPROCESSORS - Abstract
In this work, the Schottky-on-heterojunction light-emitting diodes (SoH-LED) are monolithically integrated with the AlGaN/GaN high-electron-mobility transistors (HEMT) on an AlGaN/GaN-on-Si platform commonly used for GaN lateral electronic devices. The on-chip electro-optic modulation is realized in a single device fabricated using HEMT-compatible process. Also, SoH-LED arrays are fabricated to demonstrate the on-chip addressable functionality with each SoH-LED pixel in the array individually controlled by the integrated HEMT. High-resolution micro-scale SoH-LED seven-segment displays are demonstrated to show the potential of using SoH-LEDs as a robust alternative for micro flat-panel displays. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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- View/download PDF
10. Toward reliable MIS- and MOS-gate structures for GaN lateral power devices.
- Author
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Chen, Kevin J., Yang, Shu, Liu, Shenghou, Liu, Cheng, and Hua, Mengyuan
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TRANSISTORS , *ELECTRIC potential , *THRESHOLD voltage , *TECHNOLOGICAL innovations , *TECHNOLOGICAL literacy , *SEMICONDUCTORS - Abstract
GaN power switching transistors featuring MIS- and MOS-gate structures are highly preferred over the Schottky-gate counterpart, because of suppressed gate leakage, enlarged gate swing, and more scalable threshold voltage. Nevertheless, MIS-/MOS-gate GaN devices are confronted with stability and reliability challenges, which arise from interface traps at the critical dielectric/III-nitride interface, as well as bulk traps inside the gate dielectric including border traps near the critical interface. In this work, we present several key techniques toward reliable MIS-/MOS-gate GaN power devices, including advanced interface engineering technology, gate structure optimizations for high-performance/stability normally-off GaN power transistors, and long-lifetime gate dielectric technology. Schematic cross sections of GaN-based MIS-HEMT and MOS-channel-HEMT. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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11. Surface nitridation for improved dielectric/III-nitride interfaces in GaN MIS-HEMTs.
- Author
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Chen, Kevin J., Yang, Shu, Tang, Zhikai, Huang, Sen, Lu, Yunyou, Jiang, Qimeng, Liu, Shenghou, Liu, Cheng, and Li, Baikui
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NITRIDATION , *CHEMICAL reactions , *GALLIUM nitride , *HETEROSTRUCTURES , *HETEROJUNCTIONS - Abstract
Effective interface engineering techniques in III-nitride heterojunction power devices, aiming at yielding high VTH stability in insulated-gate devices and suppressed current collapse in high-voltage switching operation, are of critical significance to enhance device performance and reliability. In this work, we present an interface enhancement technology featuring in situ low-damage NH3/Ar/N2 pre-gate plasma treatment prior to the ALD-Al2O3 deposition for high-performance III-nitride MIS-HEMTs. It is manifest that this technology can effectively remove the native oxide while forming a monocrystal-like nitridation interfacial-layer (NIL) on the III-nitride surface. The Al2O3(NIL)/GaN/AlGaN/GaN MIS-heterostructures with high-quality interface exhibit well-behaved electrical characteristics, including a small subthreshold swing of ∼64 mV/dec, a small hysteresis of ∼0.09 V, tiny f/T dispersions in the C- V characteristics, and low interface trap density of ∼1 × 1012-6 × 1012 cm−2eV−1. Cross-sectional TEM micrograph of the Al2O3/III-nitride gate stack with a monocrystal-like nitridation interfacial-layer (NIL). [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
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