Electrical properties of metal-oxide-metal diode prepared by evaporation method are discussed with the theory by R. Stratton on tunneling currents through thin insulating films. Experimental results are successfully interpreted by the theory and the temperature dependency of tunneling current is found to agree in its general trend with the theory.
Characteristics of Ta-Ta2O5-Al diode are measured over a temperature range from 77°K to 373°K to study. the mechanism of current flow. The Ta2O5 film is made in various thicknesses by anodic oxidation of Ta vacuum deposited on a glass substrate by electron beam heating. When Al is made positive, the current is composed of the tunnel current and Schottky current with domination of the former at low temperatures and of the latter above the room temperature. When the polarity is reversed, the flow is solely of the tunnel current. The result of experiment gives 1.1 eV as the approximate barrier height of Ta-Ta2O5.
Cold cathode of evaporated Al-Al2O3-Au composite thin film structure is made. Its working is stable up to 15 volts of impressed voltage and emission current of 50 μA/cm2 is obtained. Current transfer ratio of the Au film is observed to be 10-3_??_10-4. The Al2O3 film is made by exposing Al film to air at room temperature in thickness of a few ten Å. A diode with this cathode shows in its current-voltage relation the negative characteristic reported by Hickmott.
Cerment resistive films are prepared by the flash evaporation of Cr-SiO mixtures. The fol-lowing properties of evaporated Cr-SiO films are investigated: dependence of resistivity upon film composition and film thickness, temperature coefficient of resistivity and aging effects. The results of these measurements indicate that the evaporated Cr-SiO film is more resistive than metal films and its temperature coefficient is small and very stable.
Preparation and characteristics of BeNi film are described. Beryllium, often used in some alloys as an anti-oxidation material, seems to be also suitable as a constituent of film resistors. BeNi intermetallic compound film is found useful as a resistor because of its small temperature. coefficient of resistance of ± (1_??_5)×10-5/deg and fair stability even at 300°C. The film is made by vacuum deposition on glass, quartz, alumina and porcelain substrates in various thicknesses giving the resistance from 100 Ω/sq to 8 kΩ/sq. At about 100 Ω/sq, the power dissipated steadily can be as high as 2 watt/cm2. As to the effect of substrate on the film characteristics, when the substrate is of smooth surface such as glass or quartz, films of over a few hundred Å in thickness begin to crack all over the surface at 250°C, but when the substrate is of coarse surface such as alumina or porcelain, they remain unaltered even at 300°C. To protect the film against atmospheric oxygen and water vapour, SiO, MgF2 and epoxy resin are tried as coating, among which epoxy resin is found most effective.
The fluorescent X-ray method is applied to measure the composition and thickness of nickel alloy films evaporated on glass substrates. The results obtained are often spoilt by the presence of iron in glass. The composition of nickel alloy films (Ni-Fe, Ni-Cu and Ni-Cr) is greatly influenced by the evaporation rates, and also by the reaction between alloy and evaporator. Fairly large differences in composition between films and master alloys are found by inspecting the composition ratio of films in the process of evaporation.
Dielectric constant and loss of vacuum-deposited SiO films are measured at frequencies from 10-2 c/s to 50 Mc/s. Two loss peaks are observed: one at about 10-1 c/s and the other above 50 Mc/s. The activation energy associated with the ultra-low frequency peak is determined as 8.2 kcal/mole. The relaxation strength of both peaks decreases with decreasing deposition rate and/or with increas-ing air pressure during deposition. Heat treatment of deposited films in air also brings about the decrease in relaxation strength. Impurity contents in original SiO samples result in no detectable effect on the dielectric behavior of deposited films. The ultra-low frequency loss is concluded to come from the migration of free Si ions. The high frequency loss is attributed to the local relaxational motion of SiO chains.
Thin germanium film is deposited on Pyrex glass, mica, single-crystal germanium and single-, crystal gallium arsenide substrates by vacuum evaporation. The film formed on single-crystal germanium substrate at temperatures above 500°C is of single, crystal, which is confirmed by electron diffraction examination and electrical measurements. The preparation of N-type film by vacuum evaporation has been considered difficult, but when germanium and phosphorus or arsenic are evaporated at the same time, the formed film is of N-type. In this paper, the characteristics of this N-type film together with the doping process with donor impurity are described and the effect of heat treatment on the electrical properties of the film is examined. As applications of the film to electronics, a P-N junction photocell and a tunnel diode are made by the contact of the film with single-crystal germanium substrate, and formation of hetero-junction is experimented with the film and single-crystal gallium arsenide substrate.
Transparent electroluminescent films of ZnS: Cu, Mn phosphor have been prepared by the vacuum evaporation method. Eletroluminescent spectrum, voltage and frequency dependence of brightness, electroluminescent wave form and some electrical properties of the film are studied. It is shown that the electroluminescence of the film is due to the direct exitation of Mn center by the accelerated electron, and that both the excitation of Mn center and the light emission occur in the same half-cycles of the applied sine wave voltage. The electroluminescent brightness follows the equation B=B0 exp (-C/√V), where V is the applied voltage and B0 and C are constants. In a high field region, however, the value of C becomes larger than that in a low field region. This can be explained by the injection of tunnelling electron from the metal electrode into the phosphor film at high field.