Reji Thomas

Optical and electrical properties of BaTiO3 thin films prepared by chemical solution deposition

Barium titanate sol was prepared using barium ethyl hexanoate and titanium isopropoxide. The sol was then spin coated on p-type single crystal silicon (100) wafers, stainless steel and fused silica substrates and annealed to give polycrystalline, transparent, and crack-free films. The surface morphology and structural properties of the films were studied using scanning electron microscopy and X-ray diffraction respectively. Crystalline phase could form only at an annealing temperature of 650°C and above. The effect of post deposition annealing on the optical and structural properties as well as on the band gap were analysed. Transmission spectra were recorded and from this, refractive index, extinction coefficient and thickness were calculated for films on fused silica annealed at different temperatures. The dispersion curve for the refractive index n of 650°C annealed film is fairly flat beyond 450 nm and rises sharply towards the shorter wavelength region, showing the typical shape of a dispersion curve near an interband transition. The present study indicates the validity of the DiDomenico model for the interband transition with a single electronic oscillator. The refractive indices lie in the range 1.75–2.5 for films annealed in the range 300–750°C. The electrical measurements were conducted on metal-ferroelectric-semiconductor (MFS) and metal-ferroelectric-metal (MFM) capacitors. The typical measured small signal dielectric constant was 66 and 140 at 1 MHz for the MFS and MFM capacitors respectively. Debye type dispersion was observed for films on stainless steel substrates with an activation energy of about 0.34 eV. The low field ac conduction was found primarily due to hopping of electrons through the trap centres. The I-V characteristics of the MFS capacitor were found to be ohmic at low fields and space charge limited at high fields. I-V characteristics of the MFM capacitor showed a strange behaviour, linear dependence of current on voltage up to 106 V/m and V5/2 dependence beyond 106 V/m.

Structural, electrical, and low-temperature dielectric properties of sol–gel derived SrTiO3 thin films

Strontium titanate sol was prepared using strontium ethyl haxanoate and titanium isopropoxide. The sol was then spin coated on fused silica, p-type single-crystal silicon wafers (100) and stainless-steel substrates and annealed to give polycrystalline, transparent, and crack-free films. The surface morphology and structural properties of the films were studied using scanning electron microscopy and x-ray diffraction, respectively, and differential thermal analysis was used to observe structural transition. The dielectric measurements were conducted on films with metal–insulator–metal and metal–insulator–semiconductor configurations. Capacitance–voltage (C–V) measurements were carried out and the effect of the annealing temperature was studied. The dielectric constant and loss tangent at 1 MHz at room temperature were found to be 105 and 0.02, respectively, for 1.1 μm thick films. These measurements were also carried out at low temperatures down to 20 K. There are indications for a phase transition from a ...

SrTa2O6 thin films for high-K dielectric applications grown by chemical vapor deposition on different substrates

SrTa2O6 thin films with thickness between 6 and 150 nm were deposited by metal-organic chemical vapor deposition in a multiwafer planetary reactor. The monomolecular precursor, strontium-tantalum-(methoxyethoxy)-ethoxide, was dissolved in toluene and injected by a liquid delivery system. A rather narrow process window for the deposition of stoichiometric SrTa2O6 was found for this precursor at low pressures and a susceptor temperature around 500 °C. Films were grown on Pt∕TiO2∕SiO2∕Si, TiNx∕Si, and SiO2∕Si substrates. The as-deposited films were x-ray amorphous and could be crystallized by postannealing at a temperature ⩾700°C. The distorted tetragonal tungsten bronze phase of SrTa2O6 was dominating within a broad range of compositions (Sr∕Ta: 0.4–0.7) and a perovskite-type phase was additionally observed for Sr∕Ta>0.7 and predominated for Sr∕Ta>1. The electrical properties have been investigated with metal-insulator-metal and metal-insulator-semiconductor capacitors after sputter deposition of Pt top ele...

Liquid Injection MOCVD of Dysprosium Scandate Films Deposition Characteristics and High- k Applications

Crystalline Dy 2 O 3 , Sc 2 O 3 , and amorphous high-k DyScO 3 thin films have been deposited on Si(100) substrates by metallorganic chemical vapor deposition (MOCVD) using two metal precursors M(EDMDD) 3 [M=Dy, Sc; EDMDD=6-Ethyl-2,2-Di Methyl -3,5-Decane Dionato]. The precursors were evaluated in terms of efficiency and growth rate under various conditions, viz. vaporizer and susceptor temperatures, reactor pressure, injection rate, and injection delay between the two precursors. Amorphous DyScO 3 films with nearly correct stoichiometry were deposited within the temperature range of 560-700°C. These amorphous films were smoother than the crystalline binary oxides and reached a density of around 85% of the bulk crystalline density. Amorphous structure and surface smoothness retained up to an annealing temperature as high as 950°C. The thickness of the SiO x interlayer did not vary with deposition temperature, but annealing at temperatures above 900°C increased the interlayer thickness. Electrical properties are promising; the dielectric constant of DyScO 3 (k ≈ 22) is much higher than that of the binary oxides Dy 2 O 3 and Sc 2 O 3 (k ≈ 10), and the leakage currents are very low compared to SiO 2 .

Thin Films of HfO2 for High-k Gate Oxide Applications from Engineered Alkoxide- and Amide-Based MOCVD Precursors

HfO 2 thin films with thickness between 2 and 20 nm were grown by liquid injection metallorganic chemical vapor deposition, LI-MOCVD, on SiO x /Si(100) substrates. Different mononuclear precursors ([Hf(OPr i ) 2 (tbaoac) 2 ], [Hf(NEt 2 ) 2 (guanid) 2 ], and [Hf(OBu t ) 2 (dmae) 2 ] were tested in combination with different solvents. Growth rate, surface morphology, crystal structure, and crystal density of the as-deposited films were analyzed as a function of deposition temperature. The influence of postdeposition annealing on the densification and crystallization was studied. Correlation of the structural properties with the electrical properties of metal insulator semiconductor capacitors with Pt top electrodes is discussed. Fully silicided metal gate stacks are additionally discussed for selected samples.

Electrical properties of (Ba,Sr)TiO3 thin films revisited : The case of chemical vapor deposited films on Pt electrodes

Due to the dependence on both bulk and interface properties neither the effective dielectric constant e nor the leakage current J can be scaled in a straightforward manner with film thickness for high-e thin film capacitors. Based on detailed investigations of different thickness series of (Ba,Sr)TiO3 films on platinized substrates the bulk and interfacial properties are separated. An approach to estimate the apparent interfacial layer thickness is discussed. The behavior of the leakage current is divided in two regions: for low voltages, ⩽1V, the currents are very low, ⩽10−10A∕cm2, and dominated by the relaxation currents (Curie–von Schweidler behavior). At higher voltages the change to a very strong power law dependence is observed, J∼E16. The thickness dependence is removed by scaling with the internal field or dielectric displacement of the film, D=e0eE. Hence, a direct connection between the increase in e and the increase in leakage with film thickness is revealed. This behavior is accompanied by a l...

Electrical Properties of Sol-Gel Processed Amorphous BaTiO3 Thin Films

BaTiO3 thin films were prepared on single crystal silicon (1 0 0) and platinum substrates by sol-gel technique. Amorphous films with thickness uniformity were obtained by spinning the solution at 3000 rpm for 30 s and by post-deposition annealing at 400°C. The films exhibited good dielectric and insulating properties. The dielectric constant and dissipation factor at a frequency of 100 kHz were 17 and 0.20, respectively, for 1400 Å thick film on platinum substrate (MIM). The corresponding values were 16 and 0.015 for films on Si (MIS). Dielectric properties were also studied as functions of frequency and voltage. The C-V curve for MIS structure exhibited a hysteresis. The density of interface states recharged during the bias cycle in hysteresis measurement was estimated to be of the order of 2.10 × 1011 cm−2 and total oxide charge density was about 4.28 × 1011 cm−2. I-V measurements were performed on films of different thicknesses. The leakage current densities at 5 V for the films having thicknesses 1400 and 2800 Å were 0.86 and 0.11 μA/cm2 respectively. The conduction mechanism is found to be Poole-Frenkel and Schottky mechanisms at low and high fields, respectively.

Electrical properties of SrTiO3 based MIS structures for dram applications

Abstract Polycrystalline SrTiO3 thin films were prepared on p-type silicon substrate by sol-gel technique. The films were deposited at room temperature and annealed at various temperatures. The integrability of the films with silicon substrate was investigated through the C-V characteristics of the MIS device. The C-V characteristics show a negative flat band shift due to the presence of positive charges existing in the film. The effective dielectric constant was determined from the capacitance value at accumulation region and it was found to depend on the annealing temperature. The maximum values of dielectric constant were obtained for films annealed in the range 600 to 700°C. The density of the interface states in the film is evaluated and found to be about 1011/cm2. The I-V characteristics exhibit behaviour similar to conventional MIS structures. The leakage currents are of the order of nanoamperes. The conduction mechanism has been analyzed.