Kyungsu Lee

Nonvolatile Memory Characteristics of Double-Stacked Si Nanocluster Floating Gate Transistor

We have studied nonvolatile memory properties of MOSFETs with double-stacked Si nanoclusters in the oxide-gate stacks. We formed Si nanoclusters of a uniform size distribution on a 5 nm-thick tunneling oxide layer, followed by a 10 nm-thick intermediate oxide and a second layer of Si nanoclusters by using LPCVD system. We then investigated the memory characteristics of the MOSFET and observed that the charge retention time of a double-stacked Si nanocluster MOSFET was longer than that of a single-layer device. We also found that the double-stacked Si nanocluster MOSFET is suitable for use as a dual-bit memory.

Characteristics of Si Floating Gate Nonvolatile Memory Based on Schottky Barrier Tunneling Transistor

We fabricated a Si nano floating gate memory with Schottky barrier tunneling transistor structure. The device was consisted of Schottky barriers of Er-silicide at source/drain and Si nanoclusters in the gate stack formed by LPCVD-digital gas feeding method. Transistor operations due to the Schottky barrier tunneling were observed under small gate bias under write/erase voltages. However, the memory window decreased to 0.4V after 104seconds, which was attributed to the Er-related defects in the tunneling oxide layer. Good write/erase endurance was maintained until write/erase times. However, the threshold voltages moved upward, and the memory window became small after more write/erase operations. Defects in the LPCVD control oxide were discussed for the endurance results. The experimental results point to the possibility of a Si nano floating gate memory with Schottky barrier tunneling transistor structure for Si nanoscale nonvolatile memory device.

Recent results of multi-cathode electron beam plasma source

Abstract The basic experiments of the multi-cathode electron beam plasma source (MCEBPS) were carried out recently. The MCEBPS has characteristics of uniform plasma in large area. It can be extended to produce uniform plasmas in a very large diameter of several meter with addition of the other cathodes. The plasmas are made through direct interaction of electrons and neutral gases in the wide area with a diameter of 300 mm or above. The non-uniformity of the radial plasma density must be small to be suitable for the process of next generation semiconductor devices. The MCEBPS now has seven cathodes (multi-cathode) whose array is concentric to produce uniform plasmas in a large area at the target position. The energy of extracted electron beam from cathodes is about 50 eV. This can be controlled by changing the voltages of extraction electrodes. The electron beam current can be also controlled to the desired value by adjusting the cathode temperatures. The energy and the current of the electron beam can be controlled independently. In the working chamber, plasmas for the process of target material are produced through the direct interaction of the extracted electron beam and the neutral gases which are fed from outside. The plasma density above 1×1010 cm−3 and uniformity below ±3.0% in diameter of 320 mm were achieved recently. The adoption of multi-pole or additional permanent magnets is under consideration to enhance the plasma confinement and uniformity.

Optical Properties of SiNx Thin Films Grown by PECVD at 200

We deposited thin films by using PECVD technique at with various flow ratios of the gases. The photoluminescence measurements revealed that the maximum emission wavelength shifted to long wavelength as the ratio increased, however, positions of the several peak wavelengths, such as 1.9, 2.2, 2.4, and 3.1 eV, were independent on the ratio. Changes of the photoluminescence spectra were measured in the , , and -annealed films. The luminescence intensities increased after the annealing process. In particular, the maximum emission wavelength shifted to short wavelength after or -annealing. But there were still several peaks on the spectra of all annealed films, several peak positions remained to be unchanged after the annealing. As for the light emission mechanism, we have considered the defect states of the Si- and N- dangling bonds in the energy gap, so that the energy transitions from/to the conduction/valence bands and the defect states in the gap were attributed to the light emission in the films. The experimental results point to the possibility of a Si-based light emission materials for flexible Si-based electro-optic devices.