Daesig Kim

Decomposition behaviors of bis(N-alkoxy-p-ketoiminate) titanium complexes in the depositions of titanium oxide and barium strontium titanate films

Abstract Five bis( N -alkoxy-β-ketoiminate) titanium complexes [Ti(ONO-1) 2 : titanium bis(2- N -(2-hydroxyethylimino)-4-pentanoate), Ti(ONO-2) 2 : titanium bis(2- N -(2-hydroxy-2-methylethylimino)-4-pentanoate), Ti(ONO-3) 2 : titanium bis(2- N -(2-hydroxy-1-methylethylimino)-4-pentanoate), Ti(ONO-4) 2 : titanium bis(2- N -(1,1-dimethyl-2-hydroxyethylimino)-4-pentanoate), Ti(ONO-5) 2 : titanium bis(2,6-dimethyl-3- N -(2-hydroxy-2-methylethylimino)-5-heptanoate)] have been synthesized and tested as liquid delivery metal–organic chemical vapor deposition (MOCVD) precursors for titanium oxide (TiO 2 ) and barium strontium titanate (Ba x Sr 1− x TiO 3 , BST) thin films. It is indicated from thermogravimetric (TG) analyses that Ti(ONO-2) 2 and Ti(ONO-3) 2 leave negligible amount of residue after thermal decomposition. 1 H nuclear magnetic resonance (NMR) spectra and mass spectroscopic data imply that Ti(ONO-2) 2 is chemically stable during the flash evaporation at 280 °C. The deposition rate of TiO 2 film with Ti(ONO-2) 2 and Ti(ONO-3) 2 was comparable to that with Ti(mpd)(tmhd) 2 , and approximately three times that with Ti(tmhd) 2 (O- i Pr) 2 [mpd: 2-methyl-2,4-pentanedioxy, tmhd: 2,2,6,6,-tetramethyl-3,5-heptanedionate, O- i Pr: isopropoxy]. Ti(ONO-2) 2 was utilized for the deposition of a BST film with conventional Ba and Sr precursors, Ba(methd) 2 and Sr(methd) 2 (methd: methoxy–ethoxy–tetramethyl-heptanedionate), and the as-deposited BST films showed very low carbon content, and smooth surface morphology without any impurity phase.

Effects of Oxide Electrode on PbZrxTi1-xO3 Thin Films Prepared by Metalorganic Chemical Vapor Deposition.

The effect of the RuOx /Pt multilayer electrode on the microstructure and ferroelectric properties of PbZrx Ti1-x O3 (x=0.52) prepared by metalorganic chemical vapor deposition (MOCVD) were studied. The variation of RuOx thickness resulted in changes in the RuOx surface morphology. These modifications of RuOx surfaces caused changes in the texture, surface morphology and ferroelectric properties of lead zirconate titanate (PZT) thin films deposited on the multilayer electrodes. The improvements in the ferroelectric properties were attributed to the altered microstructure. Remanent polarization (P r) and coercive voltage (V c) of the multilayer PZT capacitors were estimated to be 22 µ C/cm2 and 0.7 V at 5 V, respectively. The multilayer PZT capacitors did not degrade up to 1012 cycles at 2 V. In this study, the factors of the deposition of PZT on RuOx /Pt multilayer electrode by MOCVD were investigated and the integration process of the Pt/RuOx /PZT/RuOx /Pt capacitor was also discussed.

A new and efficient route for 1,3,3′-triketones

Abstract Cyclic and acyclic 1,3,3′-triketones were prepared by the reactions adopting β-diketones and anhydrides in the presence of barium or strontium hydrides in high yields. Crystal structure of 4-acetyl-2,2,6,6-tetramethyl-3,5-heptanedione ( 3a ) represented the dorminant keto form and provided evidence for intermolecular C H⋯O hydrogen bonds (average C⋯O distance; 3.437 A, average C H⋯O angle; 169.25°).

Effects of substrate modification on the growth and characteristics of mocvd PZT

Abstract Pb(ZrxTi1-x)O3 thin films(PZT) were deposited on Pt/Ti/SiO2/Si(100) and RuO2/Pt/Ti/SiO2/Si(100) substrates by metal-organic chemical vapor deposition(MOCVD). The surface morphology of the Pt substrate was altered with the deposition temperature and thickness. The variations in the microstructure of PZT films were investigated as a function of substrate morphology. In addition, the effects of RuO2/Pt multilayer electrode on the microstructure and electrical properties of PZT capacitor were also studied. Finally, the PZT capacitors integrated on 4” wafer with multilayer electrode were evaluated.

Microstructure Control in Mocvd PZT Thin Films

It was shown that Pb(Zr x Ti 1−x )O 3 thin films (PZT) can be successfully deposited by metalorganic chemical vapor deposition (MOCVD) in a wide deposition temperature range starting from 400°C to 600°C. Variations in texture, morphology and grain size of the films as a function of process parameters were systematically investigated by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The deposition temperature and gas composition in the reactor are the two key parameters that control the film microstructure. The accompanying changes in the ferroelectric properties with respect to the variations of the process parameters will also investigated. In addition, we found an interrelationship between the grain orientation and surface roughness of the films. Films with (111) preferred orientation are significantly smoother than the films with other preferred orientations. We also demonstrate, for the first time, fine grained PZT films with very low surface roughness, which show excellent electrical properties can be obtained by lowering the deposition temperature (e.g. 430°C)

Metalorganic chemical vapor deposition of ferroelectric Pb(ZrxTi1- xO3thin films

Ferroelectric Pb(ZrxTi1-x)O3 (PZT) thin films were successfully deposited on Pt/Ti/SiO2Si substrates by metalorganic chemical vapor deposition (MOCVD). Pb(C2H5)4, Zr(O-t-C4H9)4, and Ti(O-i-C3H7)4 were used as metalorganic precursors. Variations in crystalline structure, surface morphology, and grain size of deposited films were systematically investigated as a function of process parameters by using X-ray diffraction and scanning electron microscopy. The deposition temperature and gas composition in the reactor are the main parameters that control the microstructure and composition of films. An interrelationship between the grain orientation and surface roughness of the films was found. Films with (111) preferred orientation are significantly smoother than films with other preferred orientations. The ferroelectric properties of the films were also measured by RT66A ferroelectric tester for hysteresis loop and fatigue property. Electrical measurements revealed that the films had good ferroelectric characteristics with the high remanant polarization (32 μC/cm2) and low coercive voltage (1.1 V).

C-Axis Oriented MOCVD YMnO3 Thin Film and Its Electrical Characteristics in MFIS FeTRAM

Yttrium manganate (YMO) thin films were prepared on SiO2 buffered silicon as a candidate for ferroelectric transistor random access memory (FeTRAM). The films were deposited by flash evaporated MOCVD at low temperature and post annealed to crystallize the c-axis oriented hexagonal YMO phase. It is found that oxygen content and substrate temperature are major parameters determining c-axis orientation. For the electrical characteristics, Pr (remnant polarization) ∼2 μ C/cm2 and ϵ (dielectric constant) ∼ 20 are obtained in Pt/YMO/Pt structures. It is also found that a top buffer layer of 30 nm ZrO2 helps to reduce the leakage current of Pt/top buffer/YMO/SiO2/Si stack to 10− 7 A/cm2 and improves the C-V memory window from 0.2 V to 2 V.

Investigation on Resistive Memory Switching Mechanism of NiO

ABSTRACT Experimental investigations on the resistive memory switching in sub-micron sized NiO memory cell are presented to elucidate the resistive memory switching mechanism. The voltage or current-biased I-V measurements show that the resistive switching transitions can be regarded as the combination of a voltage-controlled negative differential resistance phenomenon and a current-controlled negative differential resistance phenomenon. Along with experimental observations of multiple resistance states, these indicate that the memory switching in NiO would come from the percolative formation and rupture of filamentary conducting paths. Pulse experiments further suggest that the memory switching would come from local domains inside filaments.

Characterization of MFMIS and MFIS Structures for Non-volatile Memory Applications

To eliminate the interface reaction problems between ferroelectric and semiconductor in MFS (metal-ferroelectric-semiconductor) as well as ferroelectric and insulator in MFIS (metal-ferroelectric-insulator-semiconductor) structures, a gate layer sandwich of the MFMIS (metal-ferroelectric-metal-insulator-semiconductor) is proposed. This structure consists of Pt-SBT-Pt-ZrO2-SiO2-Si stacks. In the MFMIS structure the MIS capacitor is separated from the ferroelectric MFM capacitor through a metal as a floating gate. Therefore, the MIS capacitor with SiO2 and ZrO2 as an insulator with excellent interface properties can be used and MFM acts as an ideal ferroelectric capacitor. As MFMIS is a series combination of MFM and MIS capacitors, it behaves as a voltage divider. The gate voltage is divided according to the capacitance ratio of the MIS and MFM structures. Since the fabricated devices have access to the floating gate, characteristics of the MFM and MIS capacitors can be determined independently to compare the characteristics of the MFMIS structure as a single capacitor. The ferroelectric can be programmed in one direction and the field effect due to that can be analyzed. The MFMIS structures showed significant memory window due to the polarization of ferroelectric thin films but the retention time was short. The short retention time was due to the depolarization field being larger than coercive field of the ferroelectric thin film.