Chang Woo Oh

Aplasia of the internal carotid artery.

Summary. Background: The majority of previous reports on this rare agenesis of the internal carotid artery (ICA) have been limited to reporting upon its association with other congenital anomalies case by case. In order to collectively summarize this congenital anomaly of ICA, we have reviewed nine cases of ICA aplasia and their associated abnormalities. Method: Nine cases of ICA aplasia were reviewed. The diagnosis of aplasia or agenesis of the ICA was based on angiographic findings and the presence of an absent or hypoplastic bony carotid canal by temporal bone computed tomography (TBCT). Their presumable embryological aetiologies, initial presenting symptoms, unusual collateral circulations, as demonstrated by angiographies, and various associated anomalies are reviewed. Findings: The initial presentations were; subarachnoid haemorrhage in three patients, headache in one patient and ischemic symptoms and signs in three patients. The remaining two cases were found incidentally during angiography for other diseases. Collateral circulations to the middle cerebral artery ipsilateral to the ICA aplasia were via posterior communicating artery (P-com) or anterior communicating artery (A-com). On TBCT, all cases but one demonstrated agenesis of the bony carotid canal and the remaining case showed a hypoplastic canal. Cerebral aneurysms were found in six patients, four with A-com aneurysm, one with a basilar bifurcation aneurysm, and one with both a right P-com and a left cavernous ICA aneurysm; two incidentally found cases had no aneurysm. Other associated abnormalities were found in four cases; one case of hypoplasia of the common carotid artery (CCA) with an arachnoid cyst at the temporal pole, one case of abnormal origin of the right CCA from the aorta and the right subclavian artery from the descending aorta, one case of congenital temporomandibular joint (TMJ) ankylosis, and one case of nasopharyngeal angiofibroma with atresia of the upper basilar artery. Except for the atresia of the upper basilar artery, all such abnormalities were found on the same side as the ICA aplasia. Interpretation: Agenesis or aplasia of ICA may be entirely harmless. However, associated conditions such as cerebral aneurysm or abnormal collateral channels should alert clinicians to the possibility of deterioration to life-threatening conditions, such as subarachnoid haemorrhage or irreversible ischemia. Other associated anomalies are commonly depicted on the same side as the ICA aplasia and may also give rise to issues of clinical importance.

Cathodoluminescent Characteristics of a Spherical Y 2 O 3:Eu Phosphor Screen for Field Emission Display Application

The cathodoluminescent characteristics (CL) of a spherical Y 2 O 3 :Eu phosphor screen were investigated for field emission display application. The phosphor screen as an anode plate was vacuum sealed (∼3 × 10 -6 Torr) with 0.7 in, diagonal Si-based Mo tip field emitter array with 25 × 25 pixels. It was prepared by electrophoretically depositing spherical Y 2 O 3 :Eu phosphors, which were synthesized by the aerosol pyrolysis method. The character image was displayed on this anode plate by an external driver circuit with PWM driving scheme. The CL brightness of 41 cd/m 2 with CIE chromaticity of x = 0.649, y = 0.346 could be obtained at 400 V anode voltage and 55 V gate voltage inducing a 48 μA/cm 2 current density in the de mode, corresponding to 0.63 lm/W. However, screen efficiency could be increased to 1.24 lm/W by reducing the charge dose on the screen, of which the operating conditions were of 400 V anode voltage and 60 V p-p gate voltage inducing an average 30 μA/cm 2 emission current density in 15% pulse mode. It was found that the electrical resistivity of the phosphor screen was the origin of a pool image of displayed character and even caused a sudden decrease of emission light. The charging effects of spherical Y 2 O 3 :Eu phosphors screen on the luminance under low voltage operation are examined in this work and the methodology for enhancing picture quality is discussed based on experimental observation.

Embolization of wide-necked aneurysms with using three or more microcatheters

SummaryBackground. A new and relatively simple endovascular technique, in which more than three microcatheters are used for endovascular treatment of cerebral aneurysms for the first time, is described. Method. Eight patients with wide necked aneurysms were successfully treated with detachable coils using the multiple microcatheter technique. Three patients presented with subarachnoid haemorrhage and five were unruptured. The aneurysm locations were superior hypophyseal artery (2), posterior communicating artery (2), middle cerebral artery bifurcation (1), distal anterior cerebral artery (1), basilar artery (1) and vertebral artery (1). The average neck size was 7.4 ± 2.8 mm (3.5–12 mm), average width of the aneurysms was 10.6 ± 5.7 mm (6.2–23 mm) and depth was 8.9 ± 5.8 mm (3–22 mm). Three microcatheters (7 patients) and four microcatheters (1 patient) were introduced and used for coil delivery. Three or four coils were deployed and intermingled to stabilize the whole coil mass as well as to occupy the aneurysmal sac. When a relatively stable coil frame was formed, one coil was detached and subsequent coils were inserted. After the coil mass became more stable, other coils were also detached and all microcatheters were used for subsequent coil deployment. Findings. All aneurysms were successfully treated without complications. Postemboilzation angiograms showed no contrast filling in 5 cases (100% occlusion) and a very small residual neck in 3 cases. There was no procedure related complication. Conclusion. The multiple microcatheter technique can be one technical option for the endovascular treatment of wide necked aneurysms.

Analysis of Sensing margin in Silicon-On-ONO (SOONO) Device for the Capacitor-less RAM Applications

In this study, we compared sensing margin according to the back gate bias and body doping concentration. We achieved large sensing margin of 62 uA/um at LG = 87 run and demonstrated sensing margin of 45 uA/um with LG = 47 nm that is the smallest device ever reported for the floating body RAM. For the scaling down to the sub 50 nm gate length, we should reduce the body thickness for the SCE with optimum body doping condition . Possibility of scaling down with the capacitor-less RAM is shown to the sub 50 nm from this result.

Clinical analysis of vertebrobasilar dissection

SummaryBackground. The natural history of vertebrobasilar artery dissection (VAD) is not fully known. The purpose of this study was to review the clinical outcome of the patients with VAD, then to propose an appropriate management strategy for VAD.Method. From 1992 to 2004, 35 VAD patients admitted to our institutes were retrospectively reviewed. There were 28 men and 7 women, whose age ranged from 4 to 67 years with a mean age of 44 years. Angiography was assessed to document the shape, and location of the dissecting aneurysm with respect to the posterior inferior cerebellar artery (PICA). A modified Rankin score was assigned for functional outcome. The functional outcome scores were analyzed according to the patient’s age, gender, hypertension history, the pattern of initial manifestation, angiographic shape of VAD, angiographic location of VAD, treatment modality.Findings. There was no statistically significant difference between the functional outcome with age, gender, trauma history and past medical history of hypertension. Of 35 patients, 22 presented with SAH, 11 with ischemic symptoms and 2 were incidentally detected. The patients without SAH had a better functional outcome than those with SAH (p = 0.029). There was statistical significance between Hunt–Hess (H–H) grade and clinical outcome (p = 0.032). The shape and location of VAD was not significantly related to the functional outcome (p = 0.294, 0.840). But all the cases of rebleeding and mortality (except one case with initially poor H–H grade) developed exclusively in patients with aneurysms. There was no statistically significant correlation between the treatment modality and the outcome (p = 0.691).Conclusion. The VAD patients with SAH would be recommended to be managed by either surgical or endovascular treatment, but those without SAH, could be managed conservatively with antiplatelet therapy and/or anticoagulation.

Fabrication of metal field emitter arrays for low voltage and high current operation

This article describes a new fabrication process for a metal field emitter to achieve low voltage and high current operation. The key element of the fabrication process is that the isotropic silicon etching and oxidation process used in silicon tip fabrication are utilized for gate hole size reduction and gate oxide layer formation. A reliable structure with a small gate hole can be easily obtained. Metal field emitter arrays were fabricated in order to demonstrate the validity of the new process and submicron gate apertures were successfully obtained from 2.25-μm-diam disk patterns defined by a conventional contact mask aligner. The required gate voltage to obtain an anode current of a 0.1 μA/tip was 54 V, and emission currents above 20 μA/tip were stable at a gate bias of 96 V without any disruption.

Influence of getter activation and aging in a frit-sealed field emission display panel

A field emission display (FED) panel system was successfully built through integration of a 0.7 in diagonal Si-based Mo-tip field emitter array with 25×25 pixels, a Y2O3:Eu or ZnO:Zn phosphor screen, and vacuum sealing through an exhausting glass tube, including a getter. The panel system was driven by an external driver circuit that has a pulse width modulation driving scheme. We have tried to evaluate quantitatively the activation effect of a getter. The getter activated at a relatively low temperature was shown to act as a good in situ minipump during the life of the FED. Before character imaging, it was stabilized through tip aging by slowly increasing a pulse-mode emission current and phosphor aging by a Coulombic charging process. After aging, luminescent characteristics such as emission uniformity, charging and arcing phenomena were shown to be improved significantly.

Highly scalable and reliable 2-bit/cell SONOS memory transistor beyond 50nm NVM technology using outer sidewall spacer scheme with damascene gate process

We present a 2-bit/cell SONOS memory transistor and investigate its scalability and reliability beyond 50nm NVM technology. This new memory, which is implemented by the damascene gate and our newly developed outer sidewall spacer processes, shows not only stable 2-bit operation but also high reliabilities (>10/sup 5/ endurance and good retention at 150/spl deg/C) down to 80nm gate length that applies to next-generation NVM technology. In addition, dimensional effect (the lateral distance between two storage nodes) on the memory operation is reported to estimate the ultimate scaling limit of 2-bit/cell SONOS memory transistor.

Electrical aging of molybdenum field emitters

As an approach to improve the stability and reliability of molybdenum field emitters with rough surfaces and impurities at tip apex, electrical aging was studied on the basis of the important tip heating mechanism, Nottingham heating, in dc and pulse mode. The effects of electric field in dc mode were investigated using single tips to avoid the averaging effect commonly arising in arrays. The fluctuations of emission currents were remarkably reduced after the exposure to high electric field (∼100 MV/cm). It was responsible for surface migration and impurity desorption at tip apex achieved under high electric field. Since the continuous exposure to high electric field can bring undesirable effects such as tip failures, electrical aging in pulse mode was also investigated. As the peak voltage of pulse was increased, the fluctuation of emission current was rapidly reduced. From the electrical aging experiments for a 0.7 in. field emission display (FED), it was proven that the poor uniformity of FED could be ...

Metal–oxide–semiconductor field effect transistor-controlled field emission display

A metal–oxide–semiconductor field effect transistor-controlled field emission display (MCFED) was fabricated to evaluate the validity of MCFEAs (MOSFET-controlled field emitter arrays) for display application. The electrical properties of FEAs, HVMOSFETs (high voltage MOSFETs), and MCFEAs were measured. The gate hole diameter of a fabricated FEA is 1.25 μm and the extraction gate voltage to obtain the anode current of 10 nA/tip is 71 V. The threshold voltage and the breakdown voltage of a HVMOSFET are 1.4 and 81 V, respectively. The I–V characteristics of a MCFEA show that the emission currents of FEA are well controlled by the control gate voltage of the HVMOSFET. To exclude the harmful effects generated during the packaging process, the performance of the MCFED was evaluated in a high vacuum chamber. It was proven that the uniformity of a conventional FED could be improved by the integration with a MOSFET.