Enhancement of the Electrical Characteristics for 3D NAND Flash Memory Devices Due to a Modified Cell Structure in the Gate Region.

The effect of a modified cell structure in the gate region on the electrical characteristics of three-dimensional (3D) NAND flash memory devices was investigated by using a technology computeraided design simulation. The interference in the memory devices induced by the pass voltage (Vpass) interference of 3D NAND flash was significantly affected depending on the cell size. The Vpass memory device with a modified cell structure was reduced due to an increase in the electron density of the inversion layer in comparison with conventional 3D flash memory devices, and their program operation was enhanced by the increased electric field. Furthermore, the program/erase margin of the proposed 3D NAND flash memory device was 15% larger than that of the conventional 3D NAND flash memory device.

Highly-stable write-once-read-many-times switching behaviors of 1D-1R memristive devices based on graphene quantum dot nanocomposites.

One diode and one resistor (1D-1R) memristive devices based on inorganic Schottky diodes and poly(methylsilsesquioxane) (PMSSQ):graphene quantum dot (GQD) hybrid nanocomposites were fabricated to achieve stable memory characteristics. Current-voltage (I-V) curves for the Al/PMSSQ:GQDs/Al/p-Si/Al devices at room temperature exhibited write-once, read-many-times memory (WORM) characteristics with an ON/OFF ratio of as large as 104 resulting from the formation of a 1D-1R structure. I-V characteristics of the WORM 1D-1R device demonstrated that the memory and the diode behaviors of the 1D-1R device functioned simultaneously. The retention time of the WORM 1D-1R devices could be maintained at a value larger than 104 s under ambient conditions. The operating mechanisms of the devices were analyzed on the basis of the I-V results and with the aid of the energy band diagram.

Improvement of Resistive Random Access Memory Device Performance via Embedding of Low-K Dielectric Layer.

The switching mechanisms of resistive random access memories (ReRAMs) were strongly related to the formation and rupture of conduction filaments (CFs) in the transition metal oxide (TMO) layer. The novel method approached to enhance the electrical characteristics of ReRAMs by introducing of the local insertion of the low-k dielectric layer inside the TMO layer. Simulation results showed that the insertion of the low-k dielectric layer in the TMO layer reduced the switching volume and the generation of CFs. The large variation of resistive switching properties was caused by the stochastic characteristics of the CFs, which was involved in switching by generation and rupture. The electrical characteristics of the novel ReRAMs exhibited a low reset current of below 20 microA, the high uniformity of the resistive switching, and the narrow variation of the resistance for the high resistance state.

Reliability Degeneration Mechanisms of the 20-nm Flash Memories Due to the Word Line Stress.

The electrical characteristics of NAND flash memories with a high-k dielectric layer were simulated by using a full three-dimensional technology computer-aided design simulator. The occurrence rate of the errors in the flash memories increases with increasing program/erase cycles. To verify the word line stress effect, electron density in the floating gate of target cell and non-target cell, the drain current in the channel of non-target cell and depletion region of the non-target cell were simulated as a function of program/erase cycle, for various floating gate thicknesses. The electron density in the floating gate became decreased with increasing program/erase cycles. The reliability degradation occured by the increased depletion region at the bottom of the polysilicon floating gate in the continued program/erase cycle situation due to the word line stress. The degradation mechanisms for the program characteristics of 20-nm NAND flash memories were clarified by examining electron density, darin current and depletion region.

Influence of ankle fracture surgery on glycemic control in patients with diabetes.

BACKGROUND: Although ankle fracture surgery can affect glycemic control by either trauma-induced stress or a postoperative decrease in physical activity, there is little evidence on this issue. This study aimed to evaluate the influence of ankle fracture surgery on glycemic control and to assess the risk factors for poor glycemic control after surgery in patients with diabetes. METHODS: We reviewed the medical records of consecutive patients with diabetes who underwent open reduction and internal fixation for the treatment of ankle fracture at our hospital. Patients who underwent blood testing, including fasting blood glucose (FBG), glycated hemoglobin (HbA1c), and cholesterol levels, as part of a routine check-up before surgery and again more than 2 times after surgery were included. Changes in blood test results were adjusted by multiple factors using a linear mixed model with sex, age at time of surgery, body mass index (BMI), and type of ankle fracture as the fixed effects and each subject and timing of blood test as the random effects. RESULTS: Sixty patients were ultimately included in this study. At 1 month postoperatively, mean FBG and cholesterol levels had increased significantly compared with preoperative levels (p = 0.011 and 0.024, respectively). After surgery, FBG levels showed an estimated monthly decrease of 2.2 mg/dL (p = 0.017). Sex, age at time of surgery, and type of ankle fracture did not significantly affect the monthly change in FBG level. FBG returned to the preoperative level at an estimated period of 8.1 months. BMI significantly affected preoperative FBG level (p = 0.015) but not the postoperative change in FBG level (p = 0.500). CONCLUSION: Ankle fracture surgery increased the FBG level at 1 month postoperatively. FBG levels decreased gradually after surgery at an estimated monthly rate of 2.2 mg/dL. Physicians should be aware of the difficulty in postoperative blood glucose control in patients with diabetes, even several months after surgery.

Mobility degradation mechanisms of MOSFETs with a high-k dielectric layer.

The electrical characteristics of MOSFETs with a high-k dielectric layer were simulated by using a full three-dimensional technology computer-aided design simulator. The MOSFETs leakage current increased when their size decreased. The mobility variation mechanisms due to the polarization variation with the positive fixed charges in the high-k dielectric layer and with the negative trap charges in the SiO2 layer were clarified by using a modified mobility model of the universal model taking into account remote phonon scattering effects. The induced polarization in the high-k dielectric layer was dominantly attributed to the magnitude and the polarity of the charges in an interfacial layer. The mobility degradation was dominantly attributed to the polarization effects. The mobility values of the channel region in the MOSFETs, calculated by using the modified mobility model, were in reasonable agreement with their real mobility magnitudes. This result improves the enhancement of the electrical characteristic of the MOSFETs with a high-k layer.

Changes in vitamin D status after surgery in female patients with lumbar spinal stenosis and its clinical significance.

STUDY DESIGN: A prospective cohort study. OBJECTIVE: To demonstrate the changes in vitamin D status after surgery in female patients with lumbar spinal stenosis (LSS), and its correlation with surgical outcomes. SUMMARY OF BACKGROUND DATA: In patients with LSS, general health including walking ability and nutritional status can be markedly improved by decompressive surgery. It can be hypothesized that such improvement may have a positive effect on their vitamin D status. METHODS: In total, 31 female patients who underwent decompression and instrumented posterolateral fusion for LSS were enrolled. Serum 25-hydroxyvitamin D (25-OHD) level was measured before the surgery and at 1 year postoperative visit. According to serum 25-OHD level, patients were classified into 3 groups: (1) deficient group, when 25-OHD level was less than 20 ng/mL (< 50 nmol/L); (2) insufficient group, when 25-OHD level was between 20 to 30 ng/mL (50 nmol/L ≤ 25-OHD < 75 nmol/L); (3) and normal group, when 25-OHD level was 30 ng/mL or more (≥ 75 nmol/L). The Oswestry Disability Index (ODI) score and health-related quality of life (EQ-5D) were compared according to the level of 25-OHD at 1 year postoperatively. RESULTS: Preoperatively, there were 20 patients in the deficient group, 11 patients in the insufficient group and no patient in the normal group. There were no differences in age, body mass index, preoperative ODI scores, preoperative EQ-5D index scores, and EQ-5D visual analogue scale scores between the 2 groups. Mean preoperative 25-OHD level was 15.8 ng/mL (range, 5.2-29.4 ng/mL) and increased to 19.5 ng/mL (range, 6.3-47.7 ng/mL) 1 year after surgery (P = 0.075). Significant increase of 25-OHD was noted only in the deficient group (P = 0.017). Postoperatively, there were 18 patients in the deficient group, 8 patients in the insufficient group, and 5 patients in the normal group. In the postoperative deficient group, postoperative ODI scores and EQ-5D index scores showed significantly worse outcomes than those in the other groups. The changes in serum 25-OHD level were significantly correlated with the changes in ODI scores (r = -0.580; P = 0.001) and with the changes in EQ-5D index scores (r = 0.379; P = 0.035). In all the groups, postoperative ODI scores (r = -0.665; P < 0.001) and EQ-5D index scores (r = 0.601; P < 0.001) were significantly correlated with postoperative 25-OHD level. CONCLUSION: Vitamin D deficiency was common in patients with LSS. However, vitamin D status was improved after decompressive surgery, and postoperative 25-OHD level was significantly correlated with surgical outcomes.