M. Radhakrishnan

Dielectric behaviour of lanthanum oxide thin film capacitors

Abstract Thin film capacitors of lanthanum oxide were fabricated by electron beam gun evaporation. The dielectric properties of these films were studied over the frequency range 0.5–30 kHz at various temperatures (300–530 K). Measurements indicate two types of relaxation mechanisms in these films under investigation. Dielectric measurements have yielded a temperature coefficient of capacitance of about 170 ppm °C−1. The dielectric breakdown field strength was estimated as 2 × 106 V cm−1. The activation energy was also calculated and the results are discussed.

Thickness dependence of defect density in silver films

Abstract Silver films of thickness 270–1670 A were deposited onto galss substrates by vacuum evaporation. The films were subjected to heat treatment at a constant rate and the variation of the electrical resistance with temperature was measured. From a knowledge of the time and the change in electrical resistance with temperature the defect density and activation energy were calculated for various thicknesses. The defect density F 0 ( E ) max varies considerably from 21.4 to 5.25 μΩ cm eV -1 in the thickness range 270–1670 A, whereas no appraciable variation in the activation energy is observed. The dependence of the resistivity and temperature coefficient of resistivity (TCR) on thickness were studied in the above thickness range and the bulk resistivity and TCR were found to be 1.675 μΩ cm and 4.075 × 10 -3 K -1 respectively. As the structure of the annealed film was found to be polycrystalline, the mean free path of the conduction electrons was estimated assuming the scattering coefficient to be zero.

Dielectric properties of terbium fluoride thin film capacitors

Abstract The dielectric properties of thermally evaporated TbF 3 thin film capacitors (Al/TbF 3 /Al) of various thicknesses were studied in the frequency range 0.5–30 kHz at various temperatures (300–443 K). The dielectric constant was found to increase with increasing film thickness. The large increase in capacitance towards the low frequency region indicates the possibility of an interfacial polarization mechanism prevailing in that region. The frequency-temperature dependence of tan δ reveals a loss peak which shifts to higher frequencies with increasing temperature. The dielectric relaxation phenomenon in these films was explained on the basis of dipolar reorientation. The activation energy was calculated for the relaxation process. Cole-Cole diagrams were drawn and used to determine the spreading factor β and the mean relaxation time τ a .

Dielectric properties of ion plated titanium oxide thin films

Abstract Titanium oxide thin films have been deposited by an ion plating technique under rf glow. The structure of the deposited film has been found to be amorphous and the composition has been analysed by IR spectrum. Aging and annealing studies of the titanium oxide capacitors have been made. The dielectric constant of the film at 1 kHz has been estimated to be 12.4. The dependence of the capacitance and dielectric loss on frequency and temperature have been studied, and the results are discussed. The temperature coefficient of the capacitance has also been calculated.

Electrical properties of electron-beam-evaporated indium oxide thin films

Crystalline (b.c.c.) indium oxide (In2O3) powder was evaporated using an electron beam and the structure of the deposited films was found to be amorphous. Studies of the a.c. conductance of films of various thicknesses were carried out in the audio frequency range (200 Hz to 30 kHz) at various temperatures. The current-voltage characteristics of the films were also studied. The dielectric breakdown field strength was determined for several film thicknesses and at various temperatures. The activation energies for the a.c. and d.c. conduction processes were estimated and the results are discussed.

Electrical properties of samarium fluoride thin films

Abstract Thin film capacitors of SmF 3 were fabricated by thermal evaporation. The a.c. electrical properties of these films were studied in the frequency range 0.5–30 kHz at various temperatures (300–376 K). The measurements indicated an interfacial polarization in the low frequency region. The tan δ versus frequency plot exhibited a pronounced maximum which shifts to a higher frequency region with increasing temperature. The dielectric relaxation was explained on the basis of dipolar orientation in the film structure. An activation energy of 1.44 eV for the conduction process was estimated. The temperature coefficient of capacitance and breakdown field strength were estimated and the results are discussed.

Electrical conduction of LaF3 thin films

Abstract Thin film capacitors of lanthanum fluoride were fabricated by electron beam gun deposition. The current-voltage characteristics of these films were studied at different temperatures (300–470 K). It was observed that at high electric fields (>10 4 V cm −1 the current increases linearly with the square root of the field. The conduction mechanism appears to be predominantly by Poole-Frenkel emission in these films. The low field activation energy was estimated to be 0.40 eV and the results are discussed.

Electrical conduction and breakdown properties of silicon nitride films

The electrical conduction properties of ion-plated silicon nitride films in the form of aluminium-silicon nitride-aluminium structures have been studied in the temperature range 300 K to 470 K. The results obtained in the d.c. Conduction studies have been explained on the basis of the Poole-Frenkel conduction mechanism. The a.c. conduction studies in the frequency range 500 Hz to 30 kHz indicates that the conduction may be due to the electronic hopping mechanism. The breakdown strength of the silicon nitride capacitors for various dielectric thicknesses have also been studied and the results discussed.

Electrical conduction in evaporated terbium fluoride thin films

The current-voltage characteristics of thin-film capacitors with evaporated terbium fluoride dielectric have been studied as a function of temperature (in the range 300 to 418 K). For sufficiently high electric fields (> 104 V cm−1, the leakage current is found to increase exponentially with the square root of the applied electric field. Analysis of the data suggests an electrode-limited mechanism such as that suggested by Schottky. It is seen that the conduction mechanism is an activated process with the activation energy decreasing with increasing field. Dielectric break-down and its dependence on film thickness have also been investigated. Break-down field strength follows the Forlani-Minnaja relation.

Effect of vacuum on evaporated stearic acid films

Stearic acid, which belongs to the series of long-chain fatty acids, was deposited as a thin film by thermal evaporation in a vacuum (1.33 × 10−3 Pa). The effect of vacuum on such films was investigated by using a quartz crystal monitor. The change in crystal frequency corresponding to the mass variation of the deposited stearic acid film and hence the change in packing density of the film during prolonged as well as alternate cycles of evacuation and air admittance was studied. Simultaneously, changes in the capacitance and the dielectric loss of a thin film capacitor formed with stearic acid as the dielectric between aluminium electrodes were also measured. The changes observed in crystal frequency, capacitance and dielectric loss were attributed to water sorption by the dielectric film.