Calcium Copper Titanate Thin Films Research Articles

Morphological and electrical properties of RF sputtered calcium copper titanate thin films with the incorporation of intermediate layer

In this research work, an attempt has been undertaken to improve the structural, morphological and electrical properties of RF sputtered CCTO thin films with the incorporation of HfO2 as a buffer layer and Zn as an intermediate layer. RF sputtering technique was used to deposit all the films with the optimized sputtering parameters. XRD pattern of HfO2 buffered CCTO thin films have shown an increase in (220) peak intensity with the enhancement in buffer layer thickness from 2.5 nm to 20 nm. Field emission scanning electron microscope images depicted the formation of smooth surface morphology. In addition, improved electrical and interface properties are observed with the increase in buffer layer thickness. CCTO films, deposited on 20 nm of HfO2 buffer layer, have shown lower leakage current of 3.15 × 10−7 Amp. In addition, reduced Dit value of 5.3 × 1010 eV−1cm−2 has been observed for film with 20 nm buffer layers. Improved morphological and electrical properties in CCTO films are attributed to suppression of defect states due to the presence of HfO2 buffer layer. Furthermore, the effect of different position of Zn intermediate layer, sandwiched between two CCTO layers, was also investigated. The appearance of splitted (220) peak has confirmed the incorporation of Zn in CCTO lattice. The surface morphology was found to be strongly dependent upon the multilayer geometry. Improved dielectric constant of 1078 at 100 kHz frequency is observed for the film configuration of 40-10-60, in which the Zn layer is situated towards the middle position.

Effect of RF sputtering power on morphological and electrical properties of calcium copper titanate thin films

Calcium copper titanate (CCTO) thin films were deposited on p-type silicon substrate by RF magnetron sputtering at various RF powers. Post deposition annealing was carried out for all the samples at 950 °C for 1 h in air atmosphere. Various types of surface morphology have been observed for CCTO thin films with the variation of RF power. The evolution of polycrystalline structure of the CCTO thin films was confirmed by XRD studies. The FTIR characteristic absorption band of CCTO was observed in the range of 400–700 cm−1. The capacitance–voltage (C–V) and current–voltage (I–V) characteristics of the films were investigated employing Al/CCTO/Si MOS capacitors. CCTO films with higher dielectric constant, lower oxide and interface charge density were obtained at higher RF power. Leakage current was also found to be minimum for RF power of 105 W.

Thickness Dependent Structural and Dielectric Properties of Calcium Copper Titanate Thin Films Produced by Spin-Coating Method for Microelectronic Devices

Calcium copper titanate (CaCu3Ti4O12, CCTO) thin films have been deposited on platinized silicon [(111)Pt/Ti/SiO2/Si] substrate through a sol–gel spin coating technique and annealed at 600–900°C with a variation of 100°C per sample for 3 h. The activation energy for crystalline growth, as well as optimal annealing temperature (900°C) of the CCTO crystallites was studied by x-ray diffraction analysis (XRD). Thickness dependent structural, morphological, and optical properties of CCTO thin films were observed. The field emission scanning electron microscopy (FE-SEM) verified that the CCTO thin films are uniform, fully covered, densely packed, and the particle size was found to be increased with film thickness. Meanwhile, quantitative analysis of dielectric properties (interfacial capacitance, dead layers, and bulk dielectric constant) of CCTO thin film with metal–insulator–metal (M–I–M) structures has been investigated systematically using a series capacitor model. Room temperature dielectric properties of all the samples exhibit dispersion at low frequencies, which can be explained based on Maxwell–Wagner two-layer models and Koop’s theory. It was found that the 483 nm thick CCTO film represents a high dielectric constant (er = 3334), low loss (tan δ = 3.54), capacitance (C = 4951 nF), which might satisfy the requirements of embedded capacitor.

Investigation of surface and interface properties of RF sputtered calcium copper titanate thin films on silicon substrate

Structural and electrical properties of RF sputtered Calcium copper titanate (CCTO) thin films have been investigated. CCTO thin films were sputtered on p-type silicon (100) substrate by varying deposition pressure from 2.5 × 10−3 to 1 × 10−2 mbar without using platinum buffer layer. Post deposition annealing of all the samples were carried out at 950 °C. A correlation between morphological and electrical properties of the CCTO films was established with the variation of deposition pressure. The evolution of polycrystalline structure of the CCTO thin films was confirmed by XRD studies. The characteristic FTIR absorption peaks in the range of 400–700 cm−1 depicted the formation of CCTO for all the samples. The films grown at higher pressure have irregular grains with the evolution of (310) peak. Electrical properties of the dielectric films were investigated by fabricating Al/CCTO/Si metal oxide semiconductor structure. The electrical properties of the CCTO films were found to be deteriorated at higher sputtering pressure. Thin films, deposited at 5 × 10−3 mbar, possess higher dielectric constant, lower charge density and also lower leakage current.

Full range dielectric characteristics of calcium copper titanate thin films prepared by continuous composition-spread sputtering.

Perovskite CaCu3Ti4O12 has drawn a great deal of attention for various electronic applications due to its giant dielectric property as well as a strong stability in a wide range of temperature. In this paper, we use an off-axis continuous composition-spread (CCS) sputtering method to investigate the full range dielectric characteristics of calcium copper titanate thin films. The film compositions are continuously distributed by deposition from two targets of CaTiO3 and CuTiO3. A slightly Ca-deficient, Cu- and Ti-rich film, which has a 0.9:3.2:4.3 ratio for Ca:Cu:Ti, demonstrated the best performance by showing a dielectric constant of 781 at 100 kHz. On the other hand, all other films far away from the CaCu3Ti4O12 composition showed suppressed dielectric properties. Analyses by X-ray photon spectroscopy, micro-Raman microscopy, transmission electron microscopy, and Rutherford backscattering spectroscopy reveal that there are three possible origins for such superior performance at off stoichiometric thin films: (1) bulk doping by excessive Cu and Ti ions, (2) chemically modified grain boundary, and (3) the lowered electrode-sample interface resistance. Our result will provide a new insight into engineering the dielectric properties using off-stoichiometric synthesis.

Barrier layer mechanism engineering in calcium copper titanate thin film capacitors through microstructure control

A peak permittivity greater than 10 000 has been achieved for calcium copper titanate (CCT) thin films by engineering a thin film microstructure that maximizes space charge contributions to polarizability. This permittivity is an order of magnitude greater than previous polycrystalline thin film efforts. This unique microstructure control is accomplished using a chemical solution deposition process flow that produces highly dense parallel layers ∼100 nm in thickness. We observe a thickness dependent permittivity where the entire film thickness constitutes the conducting region of a barrier layer capacitor despite the presence of multiple grain boundaries within that thickness. The model predictions are in good agreement with experimental data and are consistent with existing literature reports. These trends in permittivity with dielectric thickness raise new questions regarding the nature of barrier layers in CCT—and specifically, these results suggest that grain boundaries may not always participate as high resistance interlayers.

A Novel Approach to Synthesizing Calcium Copper Titanate Thin Films with Giant Dielectric Constants

Good quality CaCu3Ti4O12 giant dielectric constant films have been prepared by metal–organic chemical vapor deposition on LaAlO3 (001) substrates, using a multimetal molten precursor source. The growth of the oxide layer by a two‐step in‐situ process, namely deposition of an amorphous matrix and the consequent in‐situ annealing, has resulted in epitaxial (00l) CaCu3Ti4O12 thin films.