In this work, the devices were designed to have a coupling ratio of 0.85, which is extremely high for memory applications. Results and discussion The TEM image in Figure 1b shows the rounded corners of the twin TFT device structure. First, the NW tri-gated structure, formed by e-beam lithography, was dipped into DHF solution, forming rounded corners. Then, thermal oxidation was performed to form the selleck kinase inhibitor tunneling this website oxide; the junction of the channel and the tunneling oxide exhibits some
rounding, protecting the tunneling oxide against excessive damage when it is written and erased. The P/E speed and reliability are balanced by Ω-gate formation. By technology computer-aided design (TCAD) simulation, Figure 2 shows the electric field of NWs using tri-gate and Ω-gate structures. The result indicates that the Ω-gate structure has more programming sites around the NWs than the tri-gate structure which are only at the upper corners and that the Ω-gate structure also has smoother electric field. Figure 2 Electric field of NWs. By TCAD simulation,
cut from the AA’ line in the (a) schematic, the electric field around the NWs of (b) tri-gate and (c) Ω-gate structures is shown. Figure 3 compares the P/E speed of the BBHE operation with that of the FN operation. The device was programmed by FN injection at V gs = 17 V and by BBHE injection at V gs = 7 V with V ds = −10 V. The BBHE operation exhibits higher programming speed than the FN operation. Figure 3 Programming and erasing characteristics of the EEPROM cell with devices. The P/E speed of BBHE operation is compared with that ABT-263 mouse GBA3 of FN operation. Figure 4a shows the twin poly-Si TFT-based (W eff/W 2/L = 113 nm × 10/6 μm/10 μm) EEPROM P/E cycling endurance characteristics by FN and BBHE, respectively, using the same input voltage. As the number of P/E cycles increased, the magnitude of the memory window disappeared. The floating-gate memory device maintained a wide threshold voltage window of 3.5 V (72.2%) after 104 P/E cycles for FN operation.
For BBHE operation, the memory window was almost closed after 104 P/E cycles. Figure 4b shows high-temperature (85°C) retention characteristics of NW-based (W eff/W 2/L = 113 nm × 10/6 μm/10 μm) EEPROMs. This figure reveals that after 10 years, the memory window was still 2.2 V when using FN operation. For BBHE operation, the device exhibited almost no data retention capacity. The Ω-gate structure has a higher P/E efficiency than the tri-gate structure because the four corners of the channel are all surrounded by the gate structure [13, 14]. The Ω-gate structure contributes to the equal sharing of the electric field and reduces the probability of leakage in the floating-gate devices in the form of stress-induced leakage current, improving the reliability of the device. Also, the extra corners improve the P/E speed. Figure 4 Endurance and retention characteristics.