Takehito Jimbo

PREPARATION OF SRBI2TA2O9 THIN FILMS BY LIQUID-DELIVERY METALORGANIC CHEMICAL VAPOR DEPOSITION USING A DOUBLE ALCOHOLATE SOURCE

A liquid-delivery metalorganic chemical vapor deposition (MOCVD) apparatus for preparing SrBi2Ta2O9 (SBT) thin films was designed and set up. For the preparation of SBT thin films, a double alcoholate source, Sr[Ta(OC2H5)6]2, was used for supplying Sr and Ta atoms with a stoichiometric composition, while Bi(C6H5)3 was used for supplying Bi atoms. In the experiment, variation of the film composition with the deposition temperature and source-supply mol ratio was primarily investigated. It was found that the Bi/Ta mol ratio in the films varied with the deposition temperature and became smaller at lower deposition temperatures. It was also found that the Sr/Ta mol ratio was considerably smaller than stoichiometry above 500°C, probably because of the dissociation of Sr[Ta(OC2H5)6]2. It was ascertained that a 200-nm-thick SBT thin film with the Sr/Ta mol ratio of about 0.4, which was deposited at 350°C and subsequently annealed in O2 atmosphere at 750°C for 30 min, exhibited ferroelectricity. The dielectric constant of the film was about 120. Remanent polarization and coercive field at 10 V were 3.8 µC/cm2 and 73 kV/cm, respectively. However, the leakage current density was found to be as high as the order of 10-4 A/cm2 at 3 V. It is speculated from atomic force microscope (AFM) observation of the surface roughness of the film that the origin of the high leakage current density is the existence of local high electric field spots in the film.

Characterization of Thin-Film Decoupling and High-Frequency (Ba,Sr)TiO3 Capacitors on Al2O3 Ceramic Substrates

In this paper we present the results of the characterization of parallel-plate thin-film (Ba1-x,Srx)TiO3 (BST) capacitors, to demonstrate their suitability for use as decoupling capacitors (a capacitance as high as 0.34 µF and a capacitance density of up to 70 fF/µm2) and as tunable RF components (a small capacitance from 0.5 pF to 16 pF, a high tunability of 4.22:1 at 10 V and a capacitance density of up to 34 fF/µm2). BST films of different compositions, (Ba0.7Sr0.3)TiO3 and (Ba0.5Sr0.5)TiO3, were grown by metal-organic decomposition (MOD) and RF magnetron reactive sputtering on Pt/TiOx/SiO2/Al2O3 ceramic substrates. For large capacitors (2.25 mm2), capacitance and tan δ were measured at low frequencies (1 kHz) using an LCR meter. Smaller capacitors (16 µm2 to 961 µm2) were characterized in the frequency range of 0.01–20 GHz. Capacitance, tan δ and equivalent series resistance (ESR) were extracted from two port scattering parameters obtained using a vector network analyzer (VNA). The relationships between dielectric loss, tunability and commutation quality factor (CQF) vs BST composition and deposition conditions were outlined.

X-Ray and Photoluminescence Characterization of a Strain-Free GaAs-on-Si Structure Formed by Annealing under Ultrahigh Pressure

Characteristics of strain-free GaAs-on-Si structures formed by annealing under ultrahigh pressure were investigated by X-ray diffraction (XRD) analysis and photoluminescence (PL) measurement. It was found that a strain-free GaAs film was formed on a Si substrate without serious degradation of the optical and crystallographical properties of the film. It was also found that no additional strain or defects were generated during PL measurement at 77 K. Next, the strain-free GaAs-on-Si structure was reannealed at atmospheric pressure, and variation of the strain was investigated. It was found in this experiment that the strain in the GaAs film increased rapidly in the first 5 min of reannealing but within 20 to 30 min it reached to a constant value which was determined by the reannealing temperature. Finally, both XRD and PL data were compared and an intensity result on the depth distribution of strain in a GaAs film was derived.

Preparation of Ge 2 Sb 2 Te 5 Thin Film for Phase Change Random Access Memory by Magnetron Sputtering on Small Hole Patterns

Phase Change Random Access Memory [PRAM] is one of the candidates for next generation memory due to its non-volatility, high speed, high density and compatibility with Si-based semiconductor process. Ge 2 Sb 2 Te 5 [GST] thin film, an active layer in this device, is utilized because it has the well-known property of rapid crystallization without phase separation in erasable compact discs industry. In order to integrate PRAM to beyond 512Mbit, a high writing current and degradation of cell transition at small cell size become a problem. To resolve these problem, Confined Cell structure PRAM was suggested. However, it was difficult to fill GST layer in a small hole with a conventional sputtering tool because a big overhang occurred. In this work, we prepared GST films on the small hole patterned wafer by a new concept sputtering tool which designed developed a new concept sputtering tool. The structure of GST film was observed with cross section SEM and the film composition was measured with XRF. It was observed an overhang was suppressed and a GST film was filled in a small hole with a new concept tool. In addition, the uniformity of the GST film composition was good at less than 1% in 200mm φ substrate.

Effects of growth conditions and RF plasma on crystalline and electrical properties of SrBi2Ta2O9 thin films grown by liquid delivery MOCVD using a double alcoholate

Abstract SrBi2Ta2O9 (SBT) thin films were prepared by liquid delivery MOCVD using a double alcoholate, Sr[Ta(OC2H5)6]2. In order to crystallize the deposited films, annealing in low pressure plasma produced by RF power was conducted as well as furnace annealing in O2 atmosphere. It was found that the Sr/Ta and Bi/Ta ratios in the deposited-films approached to the stoichiometric ratio as both deposition temperature and reactor pressure were lowered. An SBT thin film which was deposited at 400°C under 1 Torr and subsequently annealed in O2 atmosphere at 750°C for 30 min showed relatively good ferroelectricity. Remanent polarization (Pr) and coercive field (Ec) of the film were 2.0 μC/cm2 and 45 kV/cm, respectively. It was also ascertained that SBT thin films were crystallized at 650°C by annealing in oxygen plasma and showed ferroelectricity. Pr and EC of the SBT film which was annealed at 650°C in oxygen plasma with RF power of 150 W and pressure of 5 Torr were 1.5 μC/cm2 and 45 kV/cm, respectively.

RF Magnetron Sputtering Process for (Ba,Sr)TiO 3 Thin Films with Higher Dielectric Constant

(Ba,Sr)TiO 3 (BST) films were deposited by RF magnetron sputtering using BST sintered ceramic targets and an approach to deposit BST films with higher permittivity by sputtering deposition was explored aiming to the application of thin film capacitor, RF tunable components and so on. Basic sputtering conditions such as RF power, deposition temperature and so on were varied in this study. BST films and Pt/BST/Pt capacitors were investigated by electrical properties, XRD analysis and SEM observation. It became clear that deposition temperature, deposition rate, and BST film thickness were important parameters for optimization of the dielectric constant. From the non-linearly relationship between dielectric constant and BST film thickness, we could also find that the interfacial layer between BST and Pt bottom electrode was important for controlling the BST film properties. Furthermore, an approach to enhance the crystalline quality has to be explored for further improvement of BST film properties. Dielectric constant could be raised up to 10% by just changing the gas flow sequence of BST sputtering process.