Kwon Hong

Novel 3-dimensional Dual Control-gate with Surrounding Floating-gate (DC-SF) NAND flash cell for 1Tb file storage application

A novel 3-dimensional Dual Control-gate with Surrounding Floating-gate (DC-SF) NAND flash cell has been successfully developed, for the first time. The DC-SF cell consists of a surrounding floating gate with stacked dual control gate. With this structure, high coupling ratio, low voltage cell operation (program: 15V and erase: −11V), and wide P/E window (9.2V) can be obtained. Moreover, negligible FG-FG interference (12mV/V) is achieved due to the control gate shield effect. Then we propose 3D DC-SF NAND flash cell as the most promising candidate for 1Tb and beyond with stacked multi bit FG cell (2 ∼ 4bit/cell).

Integration of 4F2 selector-less crossbar array 2Mb ReRAM based on transition metal oxides for high density memory applications

4F2 selector-less crossbar array 2Mb ReRAM test chip with 54nm technology has been successfully integrated for high cell efficiency and high density memory applications by implementing parts of decoders to row/column lines directly under the cell area. Read/write specifications for memory operation in a chip are presented by minimizing sneak current through unselected cells. The characteristics of memory cell (nonlinearity, Kw >;8, Iop <;10uA, Vop<;60;3V), TiOx/Ta2O5, are modified for its working in a chip by adopting appropriate materials for a resistor stack and spacer. Write condition in a chip makes a critical impact on read margin and read/write operation in a chip has been verified.

Improvement of memory performance by high temperature annealing of the Al2O3 blocking layer in a charge-trap type flash memory device

The effect of postdeposition annealing (PDA) of the Al2O3 blocking layer in a charge-trap type memory device is investigated. Significant improvements are achieved by high temperature PDA at 1100 °C, achieving faster operation speed, good charge retention, and a wide program/erase window. Experimental evidence shows that the underlying mechanism is not the changes in the band gap of the crystallized Al2O3 but is due to the higher trap density in the Si3N4 trapping layer at a deeper energy level by the intermixing between Al2O3 and Si3N4. The reduced trapping efficiency of the annealed Al2O3 also helps improve the retention property.

Development of New TiN/ZrO2/Al2O3/ZrO2/TiN Capacitors Extendable to 45nm Generation DRAMs Replacing HfO2 Based Dielectrics

New ZrO₂/Al₂O₃/ZrO₂ (ZAZ) dielectric film was theoretically designed and successfully demonstrated to be applicable to 45nm DRAM devices. ZAZ dielectric film is a combined structure from tetragonal ZrO₂ and amorphous Al ₂O₃. Thus prepared ZAZ TFT capacitors showed very small Tox.eq value of 6.3Aring and low leakage current less than 1fA/cell. It was also confirmed that ZAZ TFT capacitor was thermally robust during backend full thermal process by applying it to the final DRAM product in mass production

Resistance Random Access Memory Based on a Thin Film of CdS Nanocrystals Prepared via Colloidal Synthesis

We demonstrate that resistance random access memory (RRAM) can be fabricated based on CdS-nanocrystal thin films. A simple drop-drying of the CdS-nanocrystal solution leads to the formation of uniform thin films with controlled thickness. RRAMs with a Ag/Al(2) O(3) /CdS/Pt structure show bipolar switching behavior, with average values of the set voltage (V(Set) ) and reset voltage (V(Reset) ) of 0.15 V and -0.19 V, respectively. The RRAM characteristics are critically influenced by the thickness of the Al(2) O(3) barrier layer, which prevents significant migration of Ag into the CdS layer as revealed by Auger electron spectroscopy (AES). Interestingly, RRAM without an Al(2) O(3) layer (i.e., Ag/CdS/Pt structure) also shows bipolar switching behavior, but the polarity is opposite to that of RRAM with the Al(2) O(3) layer (i.e., Ag/Al(2) O(3) /CdS/Pt structure). The operation of both kinds of devices can be explained by the conventional conductive bridging mechanism. Additionally, we fabricated RRAM devices on Kapton film for potential applications in flexible electronics, and the performance of this RRAM device was comparable to that of RRAMs fabricated on hard silicon substrates. Our results show a new possibility of using chalcogenide nanocrystals for RRAM applications.

Resistive switching properties of amorphous Pr0.7Ca0.3MnO3 films grown on indium tin oxide/glass substrate using pulsed laser deposition method

Amorphous Pr0.7Ca0.3MnO3 (APCMO) films, which were grown on indium tin oxide (ITO)/glass at room temperature (RT), were n-type materials. The APCMO/ITO/glass device exhibited an average transparency of 77% in the visible range with a maximum transparency of 84% at a wavelength of 530 nm. The Pt/APCMO/ITO device showed stable bipolar resistive switching behavior over 200 cycles that did not degrade after 105 s at RT. The resistance of the APCMO film decreased in both low- and high-resistance states with increasing device area. The resistive switching behavior of the Pt/APCMO/ITO device can be explained by the trap-charged space-charge-limited current mechanism.

Crystallized HfLaO embedded tetragonal ZrO2 for dynamic random access memory capacitor dielectrics

Cubic-structured HfLaO embedded tetragonal ZrO2 is investigated for application to a dynamic random access memory capacitor dielectric. It is found that hole injection is the determining factor of the leakage current in the ZrO2–HfLaO stack and thus HfLaO should be kept away from the electrode interface due to its smaller valance band offset than that of ZrO2. The insertion of cubic-structured HfLaO into tetragonal ZrO2 with an optimized thickness combination can effectively reduce the equivalent oxide thickness without increasing the leakage current.

Potassium Permanganate as Oxidizer in Alkaline Slurry for Chemical Mechanical Planarization of Nitrogen-doped Polycrystalline Ge2Sb2Te5 Film

For phase-change memory beyond the 30 nm design rule, chemical mechanical planarization (CMP) performing at a high polishing rate, reasonable selectivity, and no corrosion-induced pits is essential for planarizing nitrogen-doped polycrystalline Ge 2 Sb 2 Te 5 (GST) deposited on the confined memory cell structure. We develop a new alkaline slurry added with KMnO 4 used as an oxidizer. The alkaline slurry added with 0.3 wt % KMn0 4 has a polycrystalline GST film polishing rate of 5200 A/min, a polishing rate selectivity between polycrystalline GST and SiO 2 film of 100:1, and no corrosion-induced pit. In addition, polycrystalline GST film CMP using the alkaline slurry added with KMn0 4 is observed to follow a cyclic reaction polishing mechanism.

Fabrication of Highly Dense Ru Thin Films by High-Temperature Metal-Organic Chemical Vapor Deposition with NH3 Gas as Ru Oxidation Suppressing Agent

We attempted to fabricate highly dense Ru thin films by metal-organic chemical vapor deposition at an elevated temperature of 400°C, employing NH3 gas to suppress Ru oxidation. A solution of 0.2 mol/L tris(2,4-octanedionato)ruthenium [Ru(od)3, Ru(C8H13O2)3] dissolved in n-butylacetate was used as a Ru source and O2 as a reactant gas. It was revealed that NH3 gas effectively eliminated residual oxygen from the Ru films. However, at higher feeding rates of a metal-organic source, Ru films showed poor densities and high electrical resistivities mainly due to significant carbon incorporation. By optimizing Ru(od)3 flow rate to less than 0.3 g/min to reduce contaminating carbon supply, we successfully produced highly dense and conductive Ru films. The best Ru film had a density of 12.2 g/cm3 and a resistivity of 12.0 µΩcm, which were excellent values close to the bulk ones.

Effect of Drying Liquid on Stiction of High Aspect Ratio Structures

In this paper, we studied stiction behavior of HAR pattern (line and space pattern) dependence on adhesion force with surface tension of drying liquid and surface contact angle. Surface tension effect was evaluated with various drying liquids such as IPA, ethanol and HFE (hydrofluoroether) chemical. Patterns treated by dHF, APM and surface modifier were introduced to investigate dependence of pattern collapse on contact angle. The high temperature D.I. water rinse followed by high temperatures drying using liquid with low surface tension was a most effective. Furthermore, surface modification method using HMDS (hexamethyldisilazane) chemical was also effective.