Effects of Transcutaneous Electrical Nerve Stimulation depending on Frequency and Intensity for Postural Sway during Sit to Stand with Stroke Patients

변동욱,신원섭 대한물리치료학회 2013 대한물리치료학회지 Vol.25 No.3

Purpose: The application of transcutaneous electrical nerve stimulation (TENS) is beneficial for joint movements, inhibition of spasticity, and the improvement of walking ability in patients with chronic hemiplegia. This study aimed to identify the effect of the application of TENS to the knee extensor on the affected side with respect to postural-sway distance and velocity during the sit-to stand movement. Methods: We included 19 patients with post-stroke hemiplegia in this study. They underwent measurements during the sit-to stand movement on a force plate with 5 different stimulation dosages applied over 7 s:No TENS, high-frequency and high intensity TENS, high-frequency and low intensity TENS, low-frequency and high intensity TENS, and low-frequency and low intensity TENS The 5 different condition were administered in random order. Results: The group that received TENS application exhibited a significant decrease in path length and average velocity of center of pressure (COP) displacement compared with the group that did not receive TENS application. TENS dosage at low frequency (3Hz) and high intensity yielded a significant decrease in path length, average velocity, mediolateral distance and anteroposterior distance of COP displacement (p<0.05). Conclusion: Our results demonstrated the effectiveness of the application of low-frequency TENS on STS performance. These findings provide useful information on the application of TENS for the reduction of postural sway during the sit-to-stand movement after stroke.

4H-SiC SBD와 JBS 소자의 Deep Level Defect 비교 분석

변동욱,신명철,문정현,방욱,신원호,오종민,박철환,구상모 한국전기전자재료학회 2021 전기전자재료학회논문지 Vol.34 No.3

We investigated deep levels in n-type 4H-SiC epitaxy layer of the Schottky barrier diodes (SBD) and Junction Barrier Schottky (JBS) diodes by using deep level transient spectroscopy (DLTS). The I-V characteristics of the JBS devices show ~100 times lower leakage current level than SBDs owing to the grid structures in JBS. The reliable responses of the diodes for deep level transient analysis showed from C-V characteristics. Several deep electron traps were revealed by DLTS measurements in epitaxial layers in 4H-SiC. In both types of diodes, the peaks corresponding to shallow energy levels were observed with slightly different values of 0.132 eV for JBS and 0.186 eV for SBDs. The two remarkable deep level peaks (J2 and J3) have been obtained with 0.257 eV and 0.273 eV in JBS, and they were analyzed to have a similar trap concentration of ~1014 cm-3. The comparison results showed that the defects could be related with device fabrication procedures such as ion-implantation and growth.

전위 장벽에 따른 4H-SiC MPS 소자의 전기적 특성과깊은준위 결함

변동욱,이형진,이희재,이건희,신명철,구상모 한국전기전자학회 2022 전기전자학회논문지 Vol.26 No.2

We investigated electrical properties and deep level traps in 4H-SiC merged PiN Schottky (MPS) diodes with different barrier heights by different PN ratios and metallization annealing temperatures. The barrier heights of MPS diodes were obtained in IV and CV characteristics. The leakage current increased with the lowering barrier height, resulting in 10 times larger current. Additionally, the deep level traps (Z1;2 and RD1;2) were revealed by deep level transient spectroscopy (DLTS) measurement in four MPS diodes. Based on DLTS results, the trap energy levels were found to be shallow level by 22~28% with lower barrier height It could confirm the dependence of the defect level and concentration determined by DLTS on the Schottky barrier height and may lead to incorrect results regarding deep level trap parameters with small barrier heights. 서로 다른 PN 비율과 금속화 어닐링 온도에 의해 장벽 높이가 다른 4H-SiC 병합 PiN Schottky(MPS) 다이오드의 전기적 특성 과 심층 트랩을 조사했다. MPS 다이오드의 장벽 높이는 IV 및 CV 특성에서 얻었다. 전위장벽 높이가 낮아짐에 따라 누설 전류가 증가하여 10배의 전류가 발생하였다. 또한, 심층 트랩(Z1;2 및 RD1;2)은 4개의 MPS 다이오드에서 DLTS 측정을 통해 밝혀졌다. DLTS 결과를 기반으로, 트랩 에너지 준위는 낮은 장벽 높이와 함께 22~28%의 얕은 수준으로 확인되었댜 이는 쇼트키 장벽 높이 에 대해 DLTS에 의해 결정된 결함 수준 및 농도의 의존성을 확인할 수 있댜

호흡 양상 장애에 대한 사각근의 역할과 치료법에 대한 소고

변동욱(Dong-Wook Byun),유홍창(Hong-Chang You),하원배(Won-Bae Ha),이정한(Jung-Han Lee) 턱관절균형의학회 2020 턱관절균형의학회지 Vol.10 No.1

There are studies on breathing pattern disorder (BPD), but the causes of BPD are still complex, and various studies are ongoing. This study reviewed several studies to investigate the possibility that pathological changes in the scalene muscles may be one of the causes of dyspnea, and that treatment of them may improve respiratory disorders. Anatomically, the scalene muscles are located between the cervical vertebrae and the transverse process of the ribs and act as a respiratory muscle. If there is a problem or excessive in its role, it can cause chest breathing or oral breathing. These problems may further affect respiratory diseases such as hyperventilation syndrome, obstructive disease, restrictive disease, and respiratory disorders. According to the results of previous studies, it seems that manual therapy or exercise therapy for the scalene muscles can contribute to the treatment of BPD.

실리콘에 Local Anodic Oxidation으로 만든 산화물의 영향

정승우,변동욱,신명철,Michael A. Schweitz1,구상모 한국전기전자재료학회 2021 전기전자재료학회논문지 Vol.34 No.4

In this work, we fabricated oxide on an n-type silicon substrate through local anodic oxidation (LAO) using atomic force microscopy (AFM). The resulting oxide thickness was measured and its correlation with load force, scan speed and applied voltage was analyzed. The surface oxide layer was stripped using a buffered oxide etch. Ohmic contacts were created by applying silver paste on the silicon substrate back face. LAO was performed at approximately 70% humidity. The oxide thickness increased with increasing the load force, the voltage, and reducing the scan speed. We confirmed that LAO/AFM can be used to create both lateral and, to some extent, vertical shapes and patterns, as previously shown in the literature.

깊은 준위 결함에 의한 SiC SBD 전기적 특성에 대한 영향 분석

이건희,변동욱,신명철,구상모 한국전기전자학회 2022 전기전자학회논문지 Vol.26 No.1

SiC is a power semiconductor with a wide bandgap, high insulation failure strength, and thermal conductivity,but many deep-level defects. Defects that appear in SiC can be divided into two categories, defects that appear inphysical properties and interface traps that appear at interfaces. In this paper, Z1/2 trap concentration 0 ∼ 9×1014cm-3 reported at room temperature (300 K) is applied to SiC substrates and epi layer to investigate turn-oncharacteristics. As the trap concentration increased, the current density, Shockley-read-Hall (SRH), and Augerrecombination decreased, and Ron increased by about 550% from 0.004 to 0.022 mohm. SiC는 차세대 전력반도체의 핵심 재료로 넓은 밴드갭과 높은 절연파괴강도, 열전도율을 가지고 있지만 deep level defect와 같은 다양한 문제를 야기하는 결함이 존재한다. SiC에서 나타나는 defect는 물성에서 나타나는 defect와 계면에서 나타나는interface trap 2가지로 나뉜다. 본 논문은 상온 (300 K)에서 보고되는 Z1/2 trap concentration 0 ∼ 9×1014 cm-3을 SiC substrate와 epi layer에 적용하여 turn-on 특성을 알아보고자 한다. 전류밀도와 SRH(Shockley-Read-Hall), Auger recombination을 통해 구조 내 재 결합률을 확인하였다. trap concentration이 증가할수록 turn-on시 전류밀도와 재 결합률은 감소하며 Ron은0.004에서 0.022 mΩ으로 약 550% 증가하였다.

4H-SiC PiN과 SBD 다이오드 Deep level trap 비교 분석

구상모,신명철,변동욱,이건희,신훈규,이남석,김성준 한국반도체디스플레이기술학회 2022 반도체디스플레이기술학회지 Vol.21 No.2

We investigated deep levels in n-type 4H-SiC epitaxy layer of the Positive-Intrinsic-Negative diode and Schottky barrier diodes by using deep level transient spectroscopy. Despite the excellent performance of 4H-SiC, research on various deep level defects still requires a lot of research to improve device performance. In Positive-Intrinsic-Negative diode, two defects of 196K and 628K are observed more than Schottky barrier diode. This is related to the action of impurity atoms infiltrating or occupying the 4H-SiC lattice in the ion implantation process. The I-V characteristics of the Positive-Intrinsic-Negative diode shows about ~100 times lower the leakage current level than Schottky barrier diode due to the grid structures in Positive-Intrinsic-Negative. As a result of comparing the capacitance of devices diode and Schottky barrier diode devices, it can be seen that the capacitance value lowered if it exists the P implantation regions from C-V characteristics.

어닐링이 RF 스퍼터링으로 제작된 Ga2O3/Al¬2O3/SiC 소자에 미치는 영향 연구

구상모,이희재,김민영,문수영,변동욱,정승우 한국반도체디스플레이기술학회 2022 반도체디스플레이기술학회지 Vol.21 No.2

We reported on annealing effect on Ga2O3/Al2O3/SiC devices grown by radio frequency sputtering method. Post-deposition annealing at 900 °C was performed, which results in crystallization in the Ga2O3 films. The major peaks (-401) and (403) of Ga2O3 which was thermally treated at 900 °C appears in the x-ray diffraction (XRD) results. Auger electron spectroscopy (AES) shows that Ga and Al atoms seems to be diffused into the opposite direction Al2O3 and Ga2O3 after annealing. Transfer and output characteristics of back-gate transistor were analyzed where SiC substrate is used as gate material. On-state current and on/off ratio increased almost 109 and 106 times higher in the 900 °C annealed sample.

β-Ga2O3/4H-SiC MESFETs에서의 Self-Heating

김민영,서현수,정승우,이희재,변동욱,신명철,Michael A. Schweitz,구상모 한국전기전자재료학회 2022 전기전자재료학회논문지 Vol.35 No.1

Despite otherwise advantageous properties, the performance and reliability of devices manufactured in ß-Ga2O3 on semi-insulating Ga2O3 substrates may degrade because of poorly mitigated self-heating, which results from the low thermal conductivity of Ga2O3 substrates. In this work, we investigate and compare self-heating and device performance of β-Ga2O3 MESFETs on substrates of semi-insulating Ga2O3 and 4H-SiC. Electron mobility in β-Ga2O3 is negatively affected by increasing lattice temperature, which consequently also negatively influences device conductance. The superior thermal conductivity of 4H-SiC substrates resulted in reduced ß-Ga2O3 lattice temperatures and, thus, mitigates MESFET drain current degradation. This, in turn, allows practically reduced device dimensions without deteriorating the performance and improved device reliability.

산소 후열처리가 Ga2O3/4H-SiC 이종접합 다이오드의 온도에 따른 전기적 특성에 미치는 영향 분석

구상모,정승환,이형진,이희재,변동욱 한국반도체디스플레이기술학회 2022 반도체디스플레이기술학회지 Vol.21 No.4

We analyzed the influence of post-annealing on Ga2O3/n-type 4H-SiC heterojunction diode. Gallium oxide (Ga2O3) thin films were deposited by radio frequency (RF) sputtering. Post-deposition annealing at 950℃ in an Oxygen atmosphere was performed. The material properties of Ga2O3 and the electrical properties of the diodes were investigated. Atomic Force Microscopy (AFM), X-Ray Diffraction and Scanning Electron Microscope (SEM) images show a significant increase in the roughness and crystallinity of the O2-annealed films. After Oxygen annealing X-ray Photoelectron Spectroscopy (XPS) shows that the atomic ratio of oxygen increases which is related to a decrease in oxygen vacancy within the Ga2O3 film. The O2-annealed diodes exhibited higher on-current and lower leakage current. Moreover, the ideality factor, barrier height, and thermal activation energy were derived from the current-voltage curve by increasing the temperature from 298 – 434K.