D. C. Dube

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.

THE EFFECT OF BOTTOM ELECTRODE ON THE PERFORMANCE OF THIN FILM BASED CAPACITORS IN THE GIGAHERTZ REGION

Capacitors in metal–insulator–metal structure have been fabricated with different bottom electrodes. It has been found that the observed losses are enormous at gigahertz frequencies unless due care is taken not only for the conductivity of the bottom electrode but also its thickness. Very thin bottom electrodes (thickness ∼100 nm) modify the dielectric response substantially and major loss contributions arise from the substrate, the electrode resistance, and the contacts. A simple approach is suggested to model and experimentally evaluate the electrode resistance.

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 ...

Experimental evidence of redistribution of fields during processing in a high-power microwave cavity

A sensing probe has been introduced to profile the magnetic fields in a 2.45GHz, high-power single-mode microwave cavity. The treatment of a ferrite sample inside the cavity has established that, during the heating process, there is an unusual concentration of a magnetic field around the sample. During field heating, intense magnetic fields have been monitored, and are analogous to the redistribution of an electric field reported by Riedel and Svoboda [Proceedings of the Eighth Ampere Conference and Microwave Heating (2001)] in their simulation studies on microwave sintering.

High temperature dielectric study of Cr2O3 in microwave region

A unique cavity perturbation method has been used to study the dielectric behavior of chromium oxide (Cr2O3) in the microwave region at ∼3.5GHz and temperatures up to ∼1100°C. The specimen in the form of pellet was heated by microwave power at 2.45GHz in e-field of a single mode cavity. In the temperature range of measurement, the dielectric constant is found to increase within 10% and loss factor within one and a half times the room temperature values. Results are discussed in the light of agitated ionic motion in the material.

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.

Rapid alloying of silicon with germanium in microwave field using single mode cavity

Abstract Silicon and germanium alloys have been formed for the first time by heating powdered mixtures of 75%Si and 25%Ge in just 2 min in the H field in a single mode 2˙45 GHz microwave cavity. As is well known, alloy formation in conventionally heated silicon–germanium mixtures is difficult, even when processed for much longer time durations at the same temperature. Further, any oxide contaminants, if present in the starting material or formed during heating, somehow, appear on the surface of the specimen after microwave treatment.

DIELECTRIC FILMS IN THE MICROWAVE REGION

Abstract Dielectric thin films now have a wider range of applications in high frequency micro and digital circuits. Therefore, their dielectric investigation in gigahertz region are of much technical consequence. The paper reviews different experimental techniques available for thin film characterization at microwave frequencies. An extended cavity perturbation technique is also discussed.

In situ probing of magnetic parameter variations of nickel zinc ferrites during microwave H heating

Changes in magnetic parameters of nickel zinc ferrite (NZF) ceramics have been monitored in situ during microwave H heating using an indigenous technique developed in the laboratory. The technique utilizes the concept based on combining a small measurement signal with a high power-processing signal, which permits a study on materials heated either in an electric or in a magnetic field of a TM103 single mode cavity. Coupling and decoupling of these two signals are suggested by the use of a simple arrangement. Experimental results obtained on various compositions of NZF ceramics up to 1200°C are presented. The results indicate that the higher zinc end compositions of the ferrites demonstrate the phenomenon of decrystallization under the influence of microwave H.

Dielectric permittivity of Y1Ba2Cu3O7−δ in the microwave region

Abstract Complex electrical permittivity of Y 1 Ba 2 Cu 3 O 7−δ superconductor ( T c ≈90 K ) has been measured at 9.2 GHz using a perturbation resonance technique. The dielectric constant and microwave absorption exhibit a sharp fall in the vicinity of 90 K, both parameters rise again below the transition temperature.