Pb,Sr)TiO3 Research Articles

Preparation of Ferroelectric (Pb,Sr)TiO3/Polyethylene Nanocomposites and Their Dielectric Properties

Ziegler–Natta catalysts were supported on nanosized ferroelectric (Pb,Sr)TiO3 (PST) powders and then (Pb,Sr)TiO3/polyethylene (PST/PE) nanocomposites were prepared by in situ polymerization. PST/PE nanocomposites with different volume fractions of PST were obtained by changing the polymerization time. The dispersion and element distribution of PST powders in the PST/PE nanocomposite were investigated. The results indicated that PST homogeneously dispersed in the PE matrix and PST/PE nanocomposite was formed. Moreover, the dielectric constant of PST/PE appeared to have a strong concentration dependence.

Dry etching of (Pb,Sr)TiO3 thin films using inductively coupled plasma

In this study (Pb,Sr)TiO3 (PST) thin films were etched with inductively coupled Cl2∕(Cl2+Ar) plasmas. The etch characteristics of PST thin films as a function of Cl2∕(Cl2+Ar) gas mixtures were analyzed by using a quadrupole mass spectrometer. Systematic studies were carried out as a function of the etching parameters, including the radio frequency power and the working pressure. The maximum PST film etch rate is 56.2nm∕min, because a small addition of Cl2 to the Cl2∕Ar mixture increased the chemical effect. It was proposed that sputter etching is the dominant etching mechanism while the contribution of a chemical reaction is relatively low due to low volatility of the etching products.

Preparation of (Pb,Sr)TiO3 Films by Sol-Gel Technique

Ferroelectric (Pb,Sr)TiO3 (PST) thin films with a perovskite structure were prepared by the sol-gel technique. PST precursor solutions were prepared from lead (II) acetate, titanium tetraisopropoxide, and strontium acetate hemihydrate with solvents of acetic acid and 2-methoxyethanol. The PST film fabricated on an Ir/SiO2/Si substrate with a perovskite structure exhibited a ferroelectric hysteresis curve. The Pb/Sr ratio of the PST films could be controlled, however the Ti composition was larger than the stoichiometric value. It is important to obtain stoichiometric PST films for device applications, such as ferroelectric random access memories and piezoelectric filters.

High-dielectric-tunability of ferroelectric (Pb,Sr)TiO3 thin films on (001) LaAlO3

Ferroelectric (Pb,Sr)TiO3 (PSTO) thin films were epitaxially grown on (001) LaAlO3 (LAO) by using pulsed laser deposition. Microstructural characterizations with x-ray diffraction and transmission electron microscopy indicate that the as-grown films have excellent single crystalline quality and a (001)PSTO∕∕(001)LAO and [100] PSTO∕∕ [100] LAO interface relationship. Dielectric property measurements reveal that the as-grow films have a very high dielectric constant value of 3100 and very large dielectric tunability of 48% at 40V∕cm at room temperature. These excellent results suggest that the highly epitaxial ferroelectric (Pb,Sr)TiO3 thin films can be developed for room-temperature tunable microwave elements in wireless communication applications.

Anisotropic in-plane strains and dielectric properties in (Pb,Sr)TiO3 thin films on NdGaO3 substrates

Anisotropic in-plane strain can be induced in (Pb,Sr)TiO3 (PST) thin film by using orthorhombic NdGaO3 (110) as a substrate. High-resolution x-ray diffraction was used to measure the strain of the PST thin film. A rocking curve with full width at half maximum of ∼0.04° illustrated that the film had nearly perfect single-crystalline quality. Reciprocal space maps around the (001), (103), and (013) reflections of the PST film revealed anisotropic in-plane strain of 485 ppm along [100] and 26 ppm along [010], respectively. Coplanar capacitance measurements also showed systematic changes in the dielectric constant and tunability due to strain; about a 15% difference in tunability at surface field of 50 kV/cm and a 20% difference in the zero-field dielectric constant were observed along [100] and [010], respectively.

(Pb,Sr)TiO3 thin films etching characteristics using inductively coupled plasma

Etching characteristics of (Pb,Sr)TiO3 (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 Cl2/(Cl2+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.

Etch characteristics of (Pb,Sr)TiO3 thin films using CF4/Ar inductively coupled plasma

The investigations of the (Pb,Sr)TiO3 (PST) etching characteristics in CF4/Ar plasma were carried out using the inductively coupled plasma system. Experiments showed that an increase of the Ar mixing ratio under constant pressure and input power conditions leads to increasing etch rate of PST, which reaches a maximum of 740 Å/min when the Ar is 80% of the gas mixture. To understand the etching mechanism, the surface state of the etched PST samples was investigated using x-ray photoelectron spectroscopy. It was found that Pb and Ti atoms were removed mainly by the ion-assisted etching mechanism. At the same time, Sr forms extremely low volatile fluorides and therefore can be removed only by physical (sputter) etching.

Electrical Properties of Epitaxial (Pb,Sr)TiO3 Thin Films Prepared by RF Magnetron Sputtering

(Pb,Sr)TiO3 (PST) thin films were prepared by rf magnetron sputtering using a multi-element target on (111)Ir/SiO2/Si, (100)SrTiO3:La and (100)Ir/(100)SrTiO3 substrates. Polycrystalline films were obtained on the (111)Ir/SiO2/Si substrate and epitaxial thin films were obtained on (100)SrTiO3:La and (100)Ir/(100)SrTiO3 substrates. Their dielectric properties were measured with and without DC bias field. The electric field dependence of the dielectric constant with a value of 70% was measured under a bias of 200 kV/cm at room temperature from the epitaxial thin films.

(Pb,Sr)TiO3 Thin Films for a ULSI DRAM Capacitor Prepared by Liquid Source Misted Chemical Deposition

(Pb,Sr)TiO3 (PST) thin films have been successfully grown on Pt-coated Si(100) wafers by the liquid source misted chemical deposition method. The PST thin film has high crystallinity, a smooth surface, and uniform elemental composition. Electrical measurements revealed the PST thin film has a high dielectric constant, low dielectric loss, and good insulating properties. These results indicate that the PST thin film is a promising material for a ULSI DRAM capacitor and other microelectronic device applications.