Sung-Hwan Choi

Effect of channel widths on negative shift of threshold voltage, including stress-induced hump phenomenon in InGaZnO thin-film transistors under high-gate and drain bias stress

We investigated the degradation of indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) for various channel widths under high-gate and drain bias stress. The threshold voltage of IGZO TFT with wide-channel width (W > 100 μm) was significantly shifted. This included stress-induced hump-effect in a negative direction after the stress, whereas IGZO TFT with narrow-channel width (W < 100 μm) shifted in a positive direction. This phenomenon may be attributed to the hole trapping into the back-interface region. In order to enhance the reliability of IGZO TFTs, we developed and verified that the multiple-channel device showed better bias-temperature stability (ΔVTH: −0.1 V), whereas the single-channel device exhibited a −0.4 VΔVTH shift.

Low-Temperature Organic (CYTOP) Passivation for Improvement of Electric Characteristics and Reliability in IGZO TFTs

We proposed and fabricated amorphous indium- gallium-zinc-oxide thin-film transistors (TFTs) employing a novel organic-passivation layer (CYTOP) that results in low damage and good dielectric quality. The TFT with the CYTOP- passivation layer successfully exhibited a relatively good electrical characteristic (μ_sat = 12.3 cm²/V · s) compared with that (μ_sat = 5.8 cm2/V · s) of the TFT with a SiOx-passivation layer. The CYTOP-passivated device exhibited relatively good stability (ΔV_TH : 2.8 V) under positive bias-temperature stress while the TFTs with the SiOx-passivation layer showed a 3.3-V ΔV_TH shift, respectively. The CYTOP passivation was performed at low annealing temperature (180^οC), and therefore, it is a good candidate for advanced flexible displays.

Effect of Deposition Temperature of SiOx Passivation Layer on the Electrical Performance of a-IGZO TFTs

We investigated the effect of the deposition temperature on the electrical performance of SiOx passivation layers for amorphous indium-gallium-zinc-oxide thin-film transistors (a-IGZO TFTs). Compared to the time-of-flight secondary ion mass spectroscopy depth profile of the IGZO film with a SiOx passivation layer deposited at low temperature (150oC ), that with the SiOx film formed at 300oC exhibited the significant migration of metal ions from the IGZO film into the SiOx passivation layer. These results were attributed to the high-energy ion bombardment on the IGZO channel layer. In order to suppress the interdiffusion of In, Ga, and Zn atoms between the IGZO and passivation layers, we proposed double SiOx passivation using different substrate temperatures. It combines the merits of low-temperature (150oC) and high-temperature (300oC) passivations and compensates for their individual weaknesses. We confirmed the enhanced electrical characteristics and improved reliability of the IGZO TFTs compared to those of the conventional device.

Effect of Excimer Laser Annealing on the Performance of Amorphous Indium Gallium Zinc Oxide Thin-Film Transistors

This article reports a method for reducing the contact resistance between amorphous-InGaZnO (a-IGZO) channel and source/drain layer via XeCl excimer laser annealing (ELA) and the device performance of a-IGZO thin-film transistors (TFTs) in terms of laser energy density. The source/drain region in the a-IGZO layer was selectively ELA-treated using a mask, and the resistivity dramatically reduced compared to that of the untreated film (from 10 4 to 10 ―3 Ω cm). Our TFTs had a field-effect mobility of 21.7 cm 2 /V s, an on/off ratio of 1.2 × 10 8 , a threshold voltage of ―0.15 V, and a subthreshold swing of 0.26 V/decade.

Nonsurgical miniscrew-assisted rapid maxillary expansion results in acceptable stability in young adults

OBJECTIVE To evaluate the stability of nonsurgical miniscrew-assisted rapid maxillary expansion (MARME) in young adults with a transverse maxillary deficiency. MATERIALS AND METHODS From a total of 69 adult patients who underwent MARME followed by orthodontic treatment with a straight-wire appliance, 20 patients (mean age, 20.9 ± 2.9 years) with follow-up records (mean, 30.2 ± 13.2 months) after debonding were selected. Posteroanterior cephalometric records and dental casts were obtained at the initial examination (T0), immediately after MARME removal (T1), immediately after debonding (T2), and at posttreatment follow-up (T3). RESULTS Suture separation was observed in 86.96% of subjects (60/69). An increase in the maxillary width (J-J; 1.92 mm) accounted for 43.34% of the total expansion with regard to the intermolar width (IMW) increase (4.43 mm; P < .001) at T2. The amounts of J-J and IMW posttreatment changes were -0.07 mm (P > .05) and -0.42 mm (P  =  .01), respectively, during retention. The postexpansion change in middle alveolus width increased with age (P < .05). The postexpansion change of interpremolar width (IPMW) was positively correlated with the amount of IPMW expansion (P < .05) but not with IMW. The changes of the clinical crown heights in the maxillary canines, first premolars, and first molars were not significant at each time point. CONCLUSIONS Nonsurgical MARME can be a clinically acceptable and stable treatment modality for young adults with a transverse maxillary deficiency.

Stability of Pre-Orthodontic Orthognathic Surgery Using Intraoral Vertical Ramus Osteotomy Versus Conventional Treatment

PURPOSE Postoperative skeletal and dental changes were evaluated in patients with mandibular prognathism who underwent mandibular setback surgery using an intraoral vertical ramus osteotomy (IVRO) with and without presurgical orthodontic treatment. MATERIAL AND METHODS This retrospective cohort study included consecutive patients with skeletal Class III malocclusions who underwent IVRO. Patients treated with pre-orthodontic orthognathic surgery (POGS) were compared with patients treated with conventional surgery (CS) with presurgical orthodontics (control) using lateral cephalograms (taken preoperatively, 7 days postoperatively, and 12 months postoperatively). Predictor (group and timing), outcome (cephalometric measurements over time), and other (ie, baseline characteristics) variables were evaluated to determine the differences in postoperative horizontal and vertical positional changes of the mandible, such as point B. Baseline demographics were similar between the groups (N = 37; CS group, n = 17; POGS group, n = 20). The data were analyzed with an independent t test, the Mann-Whitney U test, the Fisher exact t test, Pearson correlation analysis, and simple linear regression analysis. RESULTS The mean setback of the mandible at point B was similar, but the mandible of the POGS group, particularly the distal segment, moved superiorly during the postoperative period in conjunction with the removal of premature occlusal contacts (P < .001). In the CS group, the mandible had significantly more backward movement 12 months after surgery compared with the POGS group (P < .01). In the POGS group, horizontal and vertical postsurgical changes were linearly correlated with the amount of setback and vertical movement of the mandible. CONCLUSIONS Mandibular setback surgery using IVRO without presurgical orthodontics leads to considerably different postoperative skeletal and dental changes compared with conventional treatment, with more superior movement being observed at point B during the 1-year postoperative period.

Surface changes of anodic oxidized orthodontic titanium miniscrew.

OBJECTIVE To evaluate the structural stability of anodic oxidation treatment of miniscrews during a self-drilling procedure and an initial loading period. MATERIALS AND METHODS Eight orthodontic miniscrews with a machined surface and an anodic oxidized surface were placed in the mandible of two beagle dogs. With all miniscrews, an orthodontic force was applied immediately after placement and was continued for 12 weeks. After beagle dogs were sacrificed, the miniscrews were carefully removed from decalcified bone fragments. Miniscrews were evaluated by comparing and quantitatively analyzing changes in surface roughness of unused and used miniscrews (machined surface vs anodic oxidized surface) utilizing both scanning electron microscopy (SEM) and atomic force microscopy (AFM). RESULTS SEM revealed that only a thread edge close to the tip of the used anodic oxidized miniscrew became smooth by smearing, compared with the unused anodic oxidized miniscrew. No definite changes were observed in the thread valleys of the two groups after placement. AFM measurements demonstrated that all surface roughness parameters of thread edges of the used anodic oxidized miniscrews were significantly reduced compared with the unused anodic oxidized miniscrew (P < .05). A middle thread edge of the used anodic miniscrew surface was rougher than the unused and used machined surface miniscrews (P < .05). CONCLUSION Anodic oxidized miniscrews had improved surface characteristics compared with machined surface miniscrews, even if the surface texture was changed by the self-drilling procedure and during the initial loading period.

Time-dependent effects of ultraviolet and nonthermal atmospheric pressure plasma on the biological activity of titanium

Here, we evaluated time-dependent changes in the effects of ultraviolet (UV) and nonthermal atmospheric pressure plasma (NTAPPJ) on the biological activity of titanium compared with that of untreated titanium. Grade IV machined surface titanium discs (12-mm diameter) were used immediately and stored up to 28 days after 15-min UV or 10-min NTAPPJ treatment. Changes of surface characteristics over time were evaluated using scanning electron microscopy, surface profiling, contact angle analysis, X-ray photoelectron spectroscopy, and surface zeta-potential. Changes in biological activity over time were as determined by analysing bovine serum albumin adsorption, MC3T3-E1 early adhesion and morphometry, and alkaline phosphatase (ALP) activity between groups. We found no differences in the effects of treatment on titanium between UV or NTAPPJ over time; both treatments resulted in changes from negatively charged hydrophobic (bioinert) to positively charged hydrophilic (bioactive) surfaces, allowing enhancement of albumin adsorption, osteoblastic cell attachment, and cytoskeleton development. Although this effect may not be prolonged for promotion of cell adhesion until 4 weeks, the effects were sufficient to maintain ALP activity after 7 days of incubation. This positive effect of UV and NTAPPJ treatment can enhance the biological activity of titanium over time.

Severe skeletal Class III malocclusion treated with 2-stage orthognathic surgery with a mandibular step osteotomy.

To reduce a large amount of mandibular setback and to prevent pharyngeal airway space narrowing when correcting a severe anteroposterior skeletal discrepancy, a mandibular step osteotomy is often combined with 2-stage orthognathic surgery. This case report describes a successful 2-stage orthognathic treatment combined with a mandibular step osteotomy. A 20-year-old man had severe mandibular protrusion, facial asymmetry, and macroglossia. Phase 1 surgery included the mandibular step osteotomy and a partial glossectomy; then we performed phase 2 surgery with a 2-piece LeFort I segmental osteotomy and a bilateral intraoral vertical ramus osteotomy to correct the patients mandibular protrusion and facial asymmetry. The total treatment period was 30 months, and the final result was improvement of the patients facial appearance.

Adult patient with hemifacial microsomia treated with combined orthodontics and distraction osteogenesis.

Distraction osteogenesis is an alternative treatment option for patients with facial asymmetry and mandibular hypoplasia. New bone is formed between bone segment surfaces that are gradually separated by incremental traction. The purpose of this article is to report the treatment of a 22-year-old man with hemifacial microsomia, facial asymmetry, and a skeletal Class II profile. The patients left mandibular ramus was lengthened with distraction osteogenesis, and miniscrew-assisted rapid palatal expansion was used to correct the maxillary transverse deficiency. Postoperative orthodontic treatment achieved tooth alignment and closure of the posterior open bite. The total treatment period was 27 months. These therapeutic treatments improved the patients facial appearance.