Sung-Bok Lee

Layer Selection by Multi-Level Permutation in 3-D Stacked NAND Flash Memory

In this letter, we propose a layer selection method by permutations (LSMPs) of string select line (SSL) bias and string select transistor with multi-level states. Due to the increased number of threshold voltage orderings by the permutation, the number of required SSLs for the layer selection and the space occupied by SSLs can be minimized. Also, the operation scheme for the layer selection is discussed. To verify the operation of proposed LSMP, a fabricated pseudo-LSM is measured. As a result, it is clearly revealed that the number of selectable layer can be increased drastically by the LSMP.

Structural and optical properties of undoped and doped ZnSe/GaAs strained heterostructures

Abstract Double-crystal X-ray rocking curve (DCRC), Auger electron spectroscopy (AES), transmission electron microscopy (TEM), photoluminescence (PL), and Raman scattering measurements on undoped and doped ZnSe epitaxial films grown on GaAs (100) substrates by molecular beam epitaxy were performed to investigate the structural and optical properties of the ZnSe films. From the DCRC analyses, the grown layer was found to be a ZnSe epitaxial film with high quality. The results of TEM measurements showed that the misfit dislocations of the nitrogen-doped ZnSe thin films was reduced in comparison with those of the undoped ZnSe films. The PL spectra of the nitrogen-doped ZnSe epilayer was dominated by donor–acceptor pair recombination and by a sequence of its longitudinal optical phonon replicas. Raman spectroscopy measurements showed that there was a lattice mismatch between the ZnSe epitaxial layer and the GaAs substrate and that a plasma–phonon coupling mode existed together with its characteristic longitudinal optical phonons. These results indicate that the ZnSe epitaxial films grown on GaAs hold promise for applications as buffer layers for the growth of Zn 1− x Mg x S y Se 1− y .

70nm NAND flash technology with 0.025 /spl mu/m/sup 2/ cell size for 4Gb flash memory

A 4 Gb NAND flash memory with a 70 nm design rule is developed for mass storage applications. The cell size is 0.025 /spl mu/m/sup 2/, which is the smallest value ever reported. For the integration, an ArF lithography process along with resolution enhancing techniques was utilized, and poly-Si/W gate technology with an optimized re-oxidation process was implemented.

Spot size converter integrated semiconductor optical amplifier

Spot size converter (SSC)-SOA consists of a slightly tensile bulk 0.2 /spl mu/m thick InGaAsP (/spl lambda/=1.55 /spl mu/m) active layer and 0.1 /spl mu/m thick InGaAsP (/spl lambda/=1.3 /spl mu/m) waveguides, which were grown by selective area growth (SAG) using MOCVD to implement SSC. The total device length is 1500 /spl mu/m. The thickness enhancement factor was greater than 3 by using SiO/sub 2/ mask. The SAG method with lateral tapering technique provided a typical beam divergences of 8/spl deg//spl times/15/spl deg/. To reduce facet reflectivity, window regions of 20 /spl mu/m length were introduced and the waveguides were tilted by 7/spl deg/. Both facets were antireflection coated to minimize the reflection from the cleaved facet. The gain measurement was done by coupling lensed fibers to both sides. To obtain the higher coupling efficiency in SOA module, taper lensed fiber with AR coating were used. Larger than 22 dB of the fiber to fiber gain was obtained for -20 dBm input power and 150 mA at 1540 nm.

Monolithic integration of laser and spot size converter using selective area MOCVD growth

Laser diodes with a narrow radiation beam is necessary to reduce the package cost in access networks. However, it is difficult to achieve both a narrow divergence angle of output beam and low threshold current and high quantum efficiency of the laser because the broadening of the mode profile, which is required to get a narrow beam, increase cavity loss and threshold current. To meet these requirements, spot size converted laser diodes (SSC-LD) integrated with a tapered passive waveguide, which is fabricated using a selective area MOCVD growth, have been proposed by many groups. This SSC-LD allows high direct coupling efficiency to the single mode optical fiber and extended alignment. Therefore, the number of packages can be reduced, and the passive alignment between the LD and fiber is realized.