Soon-Yong Kweon

Noble FeRAM technologies with MTP cell structure and BLT ferroelectric capacitors

A 16 Mb 1TIC FeRAM with a novel cell structure has been successfully developed with 0.25 /spl mu/m process technology using (Bi,La)/sub 4/Ti/sub 3/O/sub 12/ (BLT) capacitors for the first time. The developed FeRAM is highly scalable and reliable as a result of applying an MTP (merged top electrode and plate line) structure and BLT stacked capacitor, respectively.

(Bi, La)4Ti3O12 (BLT) thin films grown from nanocrystalline perovskite nuclei for ferroelectric memory devices

Using nanocrystalline perovskite nuclei, (117) oriented-(Bi,La)4Ti3O12(BLT) thin films were grown using a noble bake process for nonvolatile ferroelectric memory devices. The c-axis oriented BLT thin films have a remanent polarization (2Pr) of 8.0μC∕cm2 at a 3V driving voltage, and the (117) oriented films have a 2Pr value of about 25μC∕cm2. The BLT capacitors, grown on a platinum electrode via nanocrystalline perovskite nuclei, had fatigue and imprint free characteristics after applying 1×1011 switching cycles and for ten years at a 125°C stress. The average sensing margin of the (117) oriented BLT thin films was approximately 700mV for a 0.65μm2 cell size and a sufficient signal margin for ten years was indicated, based on the extrapolation of the measured data for high density ferreoelectric random access memory applications.

Integration of Novel Capacitor Structure for High Density FeRAM With Barrier Metal TiAlN and (Bi,La)4Ti3O12

16M 1T1C ferroelectric random access memory was successfully integrated by newly proposed scheme named Recessed Open Barrier (ROB) structure with planar Pt/BLT/Pt/IrOx/Ir stacked capacitor. In conventional barrier metal scheme which bottom electrode was stacked, oxygen diffused through the bottom electrode interface formed during MTP structure integration, and oxidized the edge of barrier metal resulting compressive stress. The failure was accelerated by free oxygen diffusion as the stress built up to make the bottom electrode pop-up. In this paper, the barrier metal TiAlN was recessed and refilled by ALD Al2O3 after bottom electrode patterning. By this novel structure, oxidation resistance was greatly improved, because oxygen diffusion path to BM was much longer than conventional scheme. The contact resistance of storage node was below 10 kΩ/plug after all the thermal budget relevant to BLT capacitor.

Crystallographic Orientation Dependent Ferroelectric Characteristics of (Bi3.3,La0.8)Ti3O12 (BLT) Capacitors

ABSTRACT The 70 nm thick (Bi3.3,La0.8)Ti3O12 (BLT) thin films were fabricated by deposition multiple spin coating layers and then crystallized by RTA and FA on Pt/TiOx/SiO2/Si substrate. Films were synthesized by MOD (metal organic decomposition) derived precursor to easy mass production. The randomly oriented BLT thin films have resulted from newly developed noble bake process, while a highly c-axis preferred orientation occurs for conventional baked thin film. The texture coefficient of I(004), I(117), I(111) and I(200) of noble baked BLT capacitors has 0, 0.24, 1.35 and 1.92, respectively. The films were very dense with no apparent pore site. The switching polarization (P*-P∧) and coercive voltage (2 Vc) of randomly oriented BLT thin films were nearly saturated at 3 V to have 20.03 μ C/cm2 and 1.38 V, respectively. However, strongly c-axis oriented thin films have 10.1 μ C/cm2 and 1.42 V for drive 3 V. The random orientation BLT shows good insulating behavior (9.4E-7 A/cm2 at 3 V). Both randomly oriented capacitor and highly c-axis preferred orientation thin films show no degradation of polarization due to fatigue after 1E11 cycles using 3 V (428.5 kV/cm) bipolar square pulse at 1 MHz.

Ferroelectric Properties and Current Conducition mechanisms of Pt/(Bi,La) 4 Ti 3 O 12 /Pt Capacitors

We studied the ferroelectric properties and current conduction characteristics of (Bi,La) 4 Ti 3 O 12 (BLT) thin films. Random oriented BLT thin films were prepared on Pt/IrO x /Ir structure by MOD (metal-organic decomposition), and crystallized by RTA (rapid thermal annealing) and the subsequent furnace annealing process. The swichable polarization polarization (P*-P) and coercive voltage (2Vc) of BLT thin films were 20.1 w C/cm 2 and 1.8V at 3V driving voltage. The leakage current density (J L ) with bias polarity was 4.0E-7 A/cm 2 under positive and 9.7E-7 A/cm 2 under negative, respectively. The leakage current characteristics of BLT films on Pt/IrO x /Ir electrode were controlled by the modified Schottky emission, because the field emission of BLT capacitors are quite dependent upon temperature and the measured data are well straightly fitted in log(J/E) vs E 1/2 plots. This result is shown to combine interface and bulk controlled conduction properties. The barrier height ( | B ) of the Pt/BLT/Pt was calculated as 0.53 eV by temperature-dependent current-voltage measurements.

산소플라즈마 전처리된 Polyethylene Naphthalate 기판 위에 증착된 ZnO:Ga 투명전도막의 특성

Transparent conducting oxide (TCO) films are widely used for optoelectronic applications. Among TCO materials,zinc oxide (ZnO) has been studied extensively for its high optical transmission and electrical conduction. In this study, the effectsof O2 plasma pretreatment on the properties of Ga-doped ZnO films (GZO) on polyethylene naphthalate (PEN) substrate werestudied. The O2 plasma pretreatment process was used instead of conventional oxide buffer layers. The O2 plasma treatmentprocess has several merits compared with the oxide buffer layer treatment, especially on a mass production scale. In this process,an additional sputtering system for oxide composition is not needed and the plasma treatment process is easily adopted as anin-line process. GZO films were fabricated by RF magnetron sputtering process. To improve surface energy and adhesionbetween the PEN substrate and the GZO film, the O2 plasma pre-treatment process was used prior to GZO sputtering. As theRF power and the treatment time increased, the contact angle decreased and the RMS surface roughness increased significantly.It is believed that the surface energy and adhesive force of the polymer surfaces increased with the O2 plasma treatment andthat the crystallinity and grain size of the GZO films increased. When the RF power was 100W and the treatment time was120 sec in the O2 plasma pretreatment process, the resistivity of the GZO films on the PEN substrate was 1.05×10-3Ω-cm,which is an appropriate range for most optoelectronic applications.

Low Temperature Sintering of PNN-PZT Ceramics and Its Electrical Properties

To fabricate a multi-layered piezoelectrics/electrodes structure, the piezoelectrics should be sintered at the temperature lower than to use the silver electrode, which is cheaper than the electrodes containing noble metals such as Pd and Pt. Therefore, in this study, we modified the composition of -based material as to lower the sintering temperature and to improve the piezoelectric properties. Small amount of , , and were also added to lower the sintering temperature of the ceramic. The prepared raw powders were mixed by using a ball mill for 24 hours. And then the mixed powders were calcinated for 2 hours at . The calcinated powders were again crushed with the ball mill for 72 hours. The final powders were pressed for making the shape of disk. The disk-type samples were sintered at temperature range of . The crystal phases of the sintered specimens were perovskite structure without secondary phases. All of the measured electrical properties such as electromechanical coupling coefficients (), mechanical quality factors (), and piezoelectric charge constants () were decreased with decreasing the sintering temperatures. The electrical properties measured at the sample sintered at were 54% of , 503 of , and 390 pC/N of , respectively. These properties were considered to be fairly good for the application of multi-layered piezoelectric generators or actuators.

Random-Oriented (Bi,La) 4 Ti 3 O 12 Thin Film Deposited by Pulsed-DC Sputtering Method on Ferroelectric Random Access Memory Device

A ferroelectric (BLT) thin film fabricated by the pulsed-DC sputtering method was evaluated on a cell structure to check its compatibility to high density ferroelectric random access memory (FeRAM) devices. The BLT composition in the sputtering target was . Firstly, a BLT film was deposited on a buried Pt//Ir bottom electrode stack with W-plug connected to the transistor in a lower place. Then, the film was finally crystallized at for 30 seconds in oxygen ambient. The annealed BLT layer was found to have randomly oriented and small ellipsoidal-shaped grains (long direction: ~100 nm, short direction: ~20 nm). The small and uniform-sized grains with random orientations were considered to be suitable for high density FeRAM devices.

Microstructures and Electrical Properties of (Na,K)NbO 3 Piezoceramics with Various Solvents at Milling Process

Na,K)NbO3-based piezoelectric ceramics were synthesized by a solid phase sintering method with various milling solvents. The solvents were varied with acetone, ethanol, and pure water to investigate the effect on the microstructure and electrical properties. NKN ceramics showed the maximum values of the relative density (94%), the mechanical quality factor (Qm: 78) and the electro-mechanical coupling factor (kp: 0.25) at the ethanol solvent. It might mean that a solid phase sintering of the NKN piezoelectrics with a suitable solvent could improve the relative density and the piezoelectric properties.

Manufacturing and Thermal Process Optimization of Ag-paste for Fabricating High Efficiency Mono-Si Solar Cell

A New Ag-pastes were developed for integrating the high efficiency mono-Si solar cell. The pastes were the mixture of 84 wt% Ag, 2 wt% glass frit, 11 wt% solvent of buthyl cabitol acetate, and 3 wt% additives. After fabricating the Ag-pastes by using a 3-roll mill, they were coated on a SiNx/n+/p- stacks of a commercial mono-Si solar cell. And the post-thermal process was also optimized by varying the process conditions of peak temperature. The optimized solar cell efficiency on a 6-inch mono-Si wafer was 18.28%, which was the one of the world best performances. It meaned that the newly developed Ag-paste could be adopted to fabricate a commercial bulk Si solar cell.