The dielectric and electrical characteristics of Ce-doped (Ba0.6Sr0.4)TiO3 (BST) thin films were investigated as a function of Ce content. Both atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis showed that increasing the Ce doping ratio causes the decrease in grain size while the surface remains smooth and crack-free. The dielectric properties of the Ce-doped BST films were found to be strongly dependent on the Ce content. The dielectric constant and dielectric loss of the BST films decreased with increasing Ce content. However, it was also found that, compared with undoped films, the increase of Ce content improves the leakage current characteristics. The improvement of the electrical properties of Ce-doped BST films may be related to the decrease in the concentration of oxygen vacancies. The figure of merit (FOM) reached the maximum value of 48.9 at the 1 mol% of Ce doping. The dielectric constant, loss factor, and tunability of the 1 mol% Ce-doped Ba0.6Sr0.4TiO3 thin films were 320, 0.011, and 46.3%, respectively.

In this work, we investigated etching characteristics of BST thin films and higher selectivity of BST over Si using inductive coupled O"2/Cl"2/Ar plasma (ICP) system. The maximum etch rate of BST thin films and selectivity of BST over Si were 61.5nm/min at a O"2 addition of 1sccm, 9.52 at a O"2 addition of 4sccm into the Cl"2(30%)/Ar(70%) plasma, respectively. Plasma diagnostics was performed by Langmuir probe (LP), optical emission spectroscopy (OES) and quadrupole mass spectrometry (QMS). These results confirm that the increased etch rates at O"2 addition of 1sccm is the result of the enhanced chemical reaction between BST and Cl radicals and an ion bombardment effect.

The effect of lanthanides (A=La, Eu, Ce, Dy, Yb)-substitution on the ferroelectric properties of bismuth titanate (Bi3.25A0.75Ti3O12, BAT) thin films has been investigated. The structure and morphology of the films were analyzed using X-ray diffraction and scanning electron microscopy, respectively. After annealing at 700°C, the BAT films exhibited a polycrystalline structure. As a increasing the ionic radius of the lanthanides element (Eu, Ce) with a smaller ionic radius than La in the pseudoperovskite layer, the BAT thin films showed well saturated P–E curves and the remanent polarization (2Pr) values increased from 8.08 and 44μC/cm2 at an applied voltage of 10V. The BAT thin films exhibited no significant degradation of switching charge at least up to 5×109 switching cycles at a frequency of 100kHz. Moreover, the BAT film capacitors have appeared good retention properties after 3×104s at room temperature.

BST thin films were etched with inductively coupled plasmas. A chemically assisted physical etch of BST was experimentally confirmed by ICP under various gas mixtures. After a 20% addition of BCl3 to the Cl2/Ar mixture, resulting in an increased the chemical effect. As increases of RF power and substrate power, and decrease of working pressure, the ion energy flux and chlorine atoms density increased. The maximum etch rate of the BST thin films was 90.1 nm/min, and at the RF power, substrate power, and working pressure were 700 W, 300 W, and 1.6 Pa, respectively. It was proposed that sputter etching is dominant etching mechanism while the contribution of chemical reaction is relatively low due to low volatility of etching products.

Ferroelectric Bi3.25La0.75Ti3O12 (BLT) thin films were prepared using the spin-coating method onto Pt/Ti/SiO2/Si substrate by the metal organic decomposition. Crystallographic properties of BLT films were characterized as a function of annealing temperature. The effect of excess Bi content on the microstructure and ferroelectric properties was also investigated. X-ray diffraction (XRD) results show that predominant Bi4Ti3O12 phase can be obtained at 550 °C, while the films keep randomly oriented structure up to 750 °C. An increase in grain size of BLT films with increasing annealing temperature was observed by the field emission scanning electron microscopy (FE-SEM). The hysteresis loops of BLT films were found to be well defined for temperatures above 600 °C. The remanent polarization decreased when more than 10% of excess Bi has been used in the precursor solution. The films with both Bi deficiency and Bi excess over 10% in the BLT precursor solution annealed at 650 °C showed poor fatigue properties. This was attributed to the structure defects and to the presence of a secondary phase. The films prepared with the Bi content in excess of 10% and annealed at 650 °C exhibited an outstanding hysteresis behaviors with the remanent polarization (2Pr) of 25.66 as well as fatigue-free behavior up to 3.5×109 bipolar cycles.

Ba0.6Sr0.4TiO3 (BST) dielectric thin films doped by Cr were prepared using an alkoxide-based sol–gel method on the Pt/Ti/SiO2/Si substrate. Atomic force microscopy and X-ray diffraction analysis showed that increasing the Cr-doping ratio causes increased grain size while the surface remains smooth and crack-free. It was also found that compared with undoped films the increase of Cr content in BST improves the dielectric constant and the leakage-current characteristics. The figure of merit reached the maximum value of 72.3 at the 5 mol% of Cr doping. This composition showed the dielectric constant of 426, the loss factor of 0.0065, tenability of 47.7%, and leakage-current density (at the electric field of 100 kV/cm) of 5.31×10−8 A/cm2. The results show that the Cr-doped BST thin films are prospective candidates for applications in tunable devices.

The etching characteristics of LaNiO3 (LNO) thin films and SiO2 in Cl2/Ar plasma were investigated. LNO etch rates decreased with increasing Cl2 fraction in Ar plasma and the working pressure. Langmuir probe measurement showed a noticeable influence of Cl2/Ar mixing ratio on electron temperature, electron density, and ion current density. The modeling of volume kinetics for charged particles and OES measurements for neutral atoms indicated monotonous changes of both densities and fluxes of active species such as chlorine atoms and positive ions. The LNO etch rate behavior may be explained by physical mechanisms.

The investigation of Pb(Zr,Ti)O3 (PZT) etching mechanism in both Cl2/Ar and CF4/Ar plasmas was carried out. It was found that, in CF4/Ar plasma, etch rate has a maximum at 80% Ar, while for Cl2/Ar plasma, etch rate keeps a constant value up to 40% Ar. The volume densities and fluxes of active species in both gas mixtures derived from the zero-dimensional (0-D) plasma models change in same manner while a nonmonotonic behavior was not observed. However, the analysis of surface kinetics confirmed the possibilities of nonmonotonic etch rate behavior in both gas mixtures due to a concurrence of physical and chemical pathways in ion-assisted chemical reaction.

In this study, we used an inductively coupled plasma (ICP) source for etching Al2O3 thin films because of its high plasma density, low process pressure and easy control bias power. Al2O3 thin films were etched using Cl2/BCl3, N2/Cl2/BCl3, and Ar/Cl2/BCl3 plasma. The experiments were carried out measuring the etch rates and the selectivities of Al2O3 to SiO2 as a function of gas-mixing ratio, rf power, and chamber pressure. When Cl2 50% was added to Cl2/BCl3 plasma, the etch rate of the Al2O3 films was 118nm/min. We also investigated the effect of gas addition. In case of N2 addition, the etch rate of the Al2O3 films decreased while N2 was added into Cl2/BCl3 plasma. However, the etch rate increased slightly as Ar added into Cl2/BCl3 plasma, and then further increase of Ar decreased the etch rate. The maximum etch rate was 130nm/min at Ar 20% in Cl2/BCl3 plasma, and the highest etch selectivity was 0.81 in N2 20% in Cl2/BCl3 plasma. And, we obtained the results that the etch rate increases as rf power increases and chamber pressure decreases. The characteristics of the plasmas were estimated using optical emission spectroscopy (OES). The change of Cl radical density was measured by OES according as the plasma parameters change. As the rf power increases and chamber pressure decreases, we measured that the intensity of Cl radical increases.

Etching characteristics of (Pb,Sr)TiO 3 (PST) thin films were investigated using inductively coupled chlorine-based plasma system as functions of gas-mixing ratio, radio frequency power and direct current bias voltage. It was found that increasing of Ar content in gas mixture lead to sufficient increasing of etch rate and selectivity of PST to Pt. The maximum etch rate of PST film is 56.2 nm/min and the selectivity of PST film to Pt is 0.8 at Cl 2 /(Cl 2 +Ar) of 20%. It was proposed that sputter etching is the dominant etching mechanism while the contribution of chemical reaction is relatively low due to low volatility of etching products.

The etching behaviour of MgO thin films in BCl3/Ar plasma was investigated. It was found that the increasing Ar mixing ratio under the constant total pressure conditions causes the monotonic decrease of MgO etch rate, which falls from 93 to 17nm/min. Plasma diagnostics combined with a 0-dimensional plasma model showed the noticeable sensitivity of both electron temperature and electron density to the process parameters as well as monotonic changes of both densities and fluxes of active species. The analysis of etching kinetics and mechanisms was performed. The results showed in the BCl3-rich plasma the etching process is dominantly supplied by the chemical pathway through the ion-assisted chemical reaction.

We investigated etching mechanism of the SrBi2Ta2O9 (SBT) thin films using Cl-2/Ar and CF4/Ar plasmas. The investigations were carried out through the analysis of the influence of gas mixing ratio on etch rate, plasma parameters and volume and surface chemistries. In both gas mixtures, increasing the Ar mixing ratio leads to an increase of the SBT etch rate, which reaches a maximum value at 80% Ar. The maximum etch rates are 970 and I 100 Angstrom/min for Cl-2/Ar and CF4/Ar plasmas, respectively. CF4/Ar plasma exhibits higher electron temperature but lower electron density while for Cl-2/Ar plasma, these parameters are more sensitive to gas composition. The increase of Ar content in both gas mixtures causes monotonic changes of fluxes for all kinds of active species. Simplified description of ion-assisted etching mechanism indicates that a combination of physical sputtering and chemical etching activated by ion bombardment can account for the experimental data explaining the appearance of etch rate maximum as well as the differences in SBT etch rate in Cl-2/Ar and CF4/Ar plasmas. (C) 2004 Elsevier B.V. All rights reserved.

The metal-ferroelectric-semiconductor (MFS) structure is widely studied for nondestructive readout (NDRO) memory devices, but conventional MFS structure has two critical problems. First, the one that is difficult to obtain ferroelectric films like PZT on Si substrate without interdiffusion of impurities such as Pb, Ti and other elements. Diffusion of Pb or Ti induces increased trap density and Fermi-level pinning. The other one is that PZT/Si structure generates nonferroelectric and low-dielectric constant layer at the interface. In order to solve these problems, the metal-ferroelectric-insulator-semiconductor (MFIS) structure has been proposed with a buffer layer of high dielectric constant such as MgO, Y2O3, and CeO. Buffer layer candidate should meet the following requirements of low lattice mismatch, low leakage current, low interface-state density, high dielectric constant, chemical stability, and prevention of interdiffusion.In this study, the etching characteristics (etch rate, selectivity) of MgO thin films were etched using Cl-2/Ar plasma. The maximum etch rate of 85 nm/min for MgO thin films was obtained at Cl-2(30%)/Ar(70%) gas mixing ratio. Moreover, the etch rate was measured by varying the etching parameters such as ICP rf power, dc-bias voltage, and chamber pressure. Plasma diagnostics was performed by Langmuir probe (LP) and optical emission spectroscopy (OES). (C) 2004 Elsevier B.V. All rights reserved.

Pb-0.5,Sr0.5TiO3 (PST) thin films were deposited on the LaNiO3 (LNO(100))/Si and Pt/Ti/SiO2/Si substrates by the alkoxide-based sol-gel method. Structural and dielectric properties of PST thin films for the tunable microwave device applications were investigated. The PST films, which were directly grown on the Pt/Ti/SiO2/Si substrates, showed the random orientation. For the LNO/Si substrates, the PST thin films exhibited highly (100) orientation. Compared with randomly oriented films, the highly (100)-oriented PST thin films showed better dielectric constant, tunability and figure of merit (FOM). The dielectric constant, tunability and FOM of the highly (100)-oriented PST thin film increased with increasing annealing temperature due to the decrease in lattice distortion. The differences in dielectric properties may be attributed to the change in the film stress and the in-plane oriented polar axis depending on the substrate that was used. The dielectric constants, dielectric loss and tunability of the PST thin films deposited on the LNO/Si substrates measured at 1 MHz were 483, 0.002 and 60.1%, respectively. (C) 2003 Elsevier Science B.V. All rights reserved.

Pb0.5Sr0.5TiO3 (PST) thin films were fabricated by the alkoxide-based sol–gel process using spin-coating method on Pt/Ti/SiO2/Si substrate. The PST films annealed from 500 °C to 650 °C for 1 h show a perovskite phase and dense microstructure with a smooth surface. The grain size and dielectric constant of PST films increase with the increase in annealing temperature, which reduces the SiO2 equivalent thickness of the PST film. The crystallinity or internal strain in the PST thin films analyzed from the diffraction-peak widths correlates well with the decrease in the dielectric losses. The dielectric constants and dielectric loss (%) of the PST films annealed at 650 °C (teq=0.89 nm) were 549 and 0.21%, respectively.

Bi3.25La0.75Ti3O12 (BLT) thin films were prepared by using metal organic decomposition method onto the LaNiO3 (LNO) bottom electrode. Both the structure and morphology of the films were analyzed by X-ray diffraction and atomic force microscope. Even at low temperatures ranging from 450°C to 650°C, the BLT thin films were successfully deposited on LNO bottom electrode and exhibited (1 1 7) orientation. The BLT thin films annealed as low as 600°C showed excellent ferroelectricity, higher remanent polarization and no significant degradation of switching charge at least up to 5×109 switching cycles at a frequency of 100 kHz and 5 V. For the annealing temperature of 600°C, the remanent polarization Pr and coercive field were 23.5 μC/cm2 and 120 kV/cm, respectively.

Bi4-xEuxTi3O12 (BET) thin films were etched by using a inductively coupled Cl-2/Ar plasma. We obtained a maximum etch rate of 69 nm/min at a gas mixing ratio Of Cl-2 (20%)/Ar (80%). This result suggests that an effective method for BET etching is chemically assisted physical etching. With increasing coil RF power, the plasma density increases so that the increased reactive free radicals and ions enhance the etch rates of BET, Pt, and SiO2. As the dc-bias voltage is increased, the increased ion energy leads to an increased etch rate of BET films. From X-ray photoelectron spectroscopy, the intensities of the Bi-O, the Eu-O, and the Ti-O peaks change with increasing Cl-2 concentration. For a pure Ar plasma, the peak associated with the oxygen-metal (O-M: TiO2, Bi2O3, Eu2O3) bond seems to disappear while the pure oxygen peak does not appear. After the BET thin films is etched by using a Cl-2/Ar plasma, the peak associated with the O-M bond increases slowly, but more quickly than the peak associated with pure oxygen atoms, due to a decrease in the Ar-ion bombardment. These results seem to indicate that Bi and Eu react little with Cl atoms and are removed predominantly by argon-ion bombardment. Also, Ti reacts little with Cl radicals and is mainly removed by chemically assisted physical etching.

We investigated the structural and electrical properties of Bi3.25La0.75Ti3O12 (BLT) films grown on Si covered with ZrO2 buffer layer. The BLT thin film and ZrO2 buffer layer were fabricated using a metalorganic decomposition method. The electrical properties of the metal–ferroelectric–insulator–semiconductor (MFIS) structure were investigated by varying thicknesses of the ZrO2 layer. The width of the memory window in the capacitance–voltage curves for the MFIS structure decreased with increasing thickness of the ZrO2 layer. It is considered that the memory window width of MFIS is not affected by remanent polarization. Leakage current density decreased by about 4 orders of magnitude after using ZrO2 buffer layer. Transmission electron microscopy shows no interdiffusion and reaction that was suppressed using the ZrO2 film as a buffer layer.

The etch characteristics of SBT films were investigated using Cl-2/Ar inductively coupled plasma with BCl3 added. A 10% addition of BCl3 into the Cl-2/Ar plasma caused an increase in the etch rate, but an addition of over 20% BCl3 caused a decrease in the etch rate. As the rf power and the dc bias were increased, the etch rate of SBT increased. At 800 W and -200 V, we obtained the maximum etch rate of 764 Angstrom/min. The etch rate change in SBT was studied by using a combination of optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS). In the OES analysis, the volume densities of Cl radicals and BCl molecules were monitored. In the XPS analysis, SrCl and B-O bonds were detected on the surface of SBT treated with a BCl3/Cl-2/Ar plasma. The SrCl layer on the surface prohibits any possible chemical reaction or reduction of physical sputtering by positive ions.

In this work, we carried out investigations aimed at understanding the effect of gas mixing ratio on plasma parameters, gas phase composition and etch rate in CF4/Ar inductively coupled plasma. For this purpose, a combination of experimental methods and modelling was used. Experiments showed that electron temperature and electron density are not very sensitive to variations of Ar content in CF4/Ar plasma. From a zero-dimensional plasma model, the densities of both neutral and charged particles change monotonically. The analysis of surface kinetics based on an ion-assisted etching mechanism showed the possibility of non-monotonic etch rate behaviour due to a concurrence of chemical and physical etching pathways.