MOS Diodes Research Articles

Instabilities of MOS Structure

The surface charge density of MOS structure is strongly affected by the bias and temperature (BT) treatment. Ordinary and “clean” MOS diodes are prepared by using the (100) and (111) planes. The results on the “clean” diodes during the BT treatment at high electric field of both polarities show the presence of an electrochemical reaction. It has an activation energy of 11 kcal/mole concerning the generation and disappearance of oxygen vacancy at the silicon to silicon dioxide interface. On the positive BT treatment for the ordinary MOS diodes, an anomalous behavior during the high field treatment is found. This phenomenon is qualitatively explained by assuming another reaction in addition to the oxygen vacancy mechanism and the fixed charge, Sodium ions are speculated as the impurity ions in the silicon dioxide film of the ordinary diodes.

The Effects of Co60 Gamma Radiation on MOS Diodes

MOS diodes were fabricated on silicon substrates and exposed to Co60 gamma radiation. A change in both surface state density and oxide charge density was noted. Non-irradiation annealing studies were carried out to determine the nature of the oxide charge. It was deduced on the basis of annealing data that the oxide charge was due to mobile alkali ions. The radiation was seen to cause a decrease in the oxide charge density. A model attempting to explain this change was fabricated assuming Compton scattering in the oxide. The change in semiconductor surface charge density caused by the gamma irradiation was found producable or reversible by means of elevated temperature, applied bias annealing.

Surface inversion of MOS diodes

MOS diodes were fabricated on p-type silicon substrates. The oxide was grown at 1200°C in a steam ambient Capacitance-bias voltage curves were taken before and after elevated-temperature, applied-bias annealing periods. It was found that the device surface could be permanently converted to n-type and then recovered.

Interface Properties of MOS Structures Prepared by Reactive Sputtering

It is the purpose of this investigation to develop the techniques of depositing SiO2, Ta2O5 films on silicon by reactive sputtering. The infrared absorption, the refractive indexes, the dielectric constants, the dielectric breakdown strengths and ultraviolet absorptions of these films indicate that the oxides may be considered as stoichiometric SiO2, Ta2O5. The interface properties of these systems are evaluated mostly by the C-V curves of MOS diodes. The surface state charge density of 120 × 1011/cm2 is measured, they can be decreased by selecting the discharge conditions to minimize the bombardment effects of ions and electrons. C-V curves of MOS diodes with large surface states show frequency dependence. Frequency dependences of these elements are examined experimentally and theoretically. The qualitative agreement between the theoretical and experimental C-V curve is obtained. But these surface states produced by sputtering can be decreased by heat treatments above 700°C.

Theory of the Influence of Surface States on the Impedance of a Semiconductor‐Insulator Interface

AbstractMeasurements of the impedance of MOS diodes, carried out by several workers, show that the frequency response of these devices is affected by the presence of semiconductor surface states. Quantitative considerations are generally difficult due to the complexities of the explicit mathematical description of the underlying physical mechanism. In the present paper it is emphasized that a numerical solution of the set of differential equations, which describes the problem, can allow a rigorous interpretation of possible measurements of ac impedances performed at several frequencies with a bridge in a series arrangement. The determination of the ac series resistance in addition to the ac capacitance, for many types of band bending on the semiconductor surface gives a more complete picture of the situation: while the energy levels and the population of the surface states can be adequately determined by ac capacitance measurements only, the ac resistance evaluation gives more information for establishing the relaxation times, which directly affect the frequency cut‐off of the device. After an outline of the mathematical procedure, some particular cases are discussed and it is shown how the measured quantities can be related to the surface state parameters.

Deposition of Silica Films on Germanium by the Carbon Dioxide Process

An ambient composed of hydrogen (≥ 95%), carbon dioxide (0.5–5%), and silicon tetrabromide (0.1–1%) will deposit a film of silica on a substrate heated to 800°–850°C. The process has particular application for coating germanium for high‐speed planar device technology; it is useful for silicon also. The reaction may be carried out immediately after epitaxial germanium deposition in the same equipment.Silica growth rates are of the order of 100 Aå/min; rates for various temperatures and concentrations are presented. Apparent activation energy is 30 kcal/mole. The oxide films are clear, vitreous, and adherent, with no detectable structure. Electrical properties of MOS diodes made on silicon are comparable to, or superior to, conventional steam‐grown oxide. The film is a satisfactory mask against 1200° boron diffusion. The silica contains about 2% residual bromine, apparently in a form in which it is not free to migrate.

Effect of Orientation on Surface Charge Density at Silicon-Silicon Dioxide Interface

The effect of the orientation of the silicon substrate on the surface charge density, NFB, at the silicon-silicon dioxide interface is studied. Surface oxidation of silicon is carried out at 1140°C in dry oxygen. The surface charge density is determined from the capacitance-voltage characteristics of the MOS diode. Measurements are made at 1 Mc/sec small singnal superposed on a dc bias. The orientation of silicon has a remarkable influence on NFB, and its magnitude becomes smaller in the order of (111), (211), (110), and (100) planes. In the case of (100) silicon substrate, the depletion of electrons at the silicon-silicon dioxide interface is observed.

Evaluation of Surface States at Si–SiO2 Interface from the Characteristics of P-Type MOS Diodes

Evaluation of Surface States at Si–SiO2 Interface from the Characteristics of P-Type MOS Diodes

Determination of conductivity type from capacitance measurements on MOS diodes

Determination of conductivity type from capacitance measurements on MOS diodes

Theory of noise in metal oxide semiconductor devices

Noise in MOS diodes arises from different sources: fluctuations in occupation of surface states, shot noise, and leakage noise. Fluctuations in the occupation of surface states produce changes in the surface space-charge distribution which in turn produce currents. Shot noise is produced by fluctuations of the individual drift and diffusion flows toward the surface. Leakage noise is associated with the small flow of current through the oxide. In MOS triodes these three mechanisms give rise to gate noise and thus input noise in the amplifier, but the first one produces an important indirect effect. Fluctuations in the occupation of interface states result in modulation of the channel conductance. At low frequencies this modulation is the dominant effect, giving rise to a noise power spectrum which resembles <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/f</tex> noise. At high frequencies, where only thermal noise in the channel and input noise are of importance, MOS triodes are similar to junction field effect devices from the noise point of view.

Observations of negative–resistance phenomena and oscillations in the MOS diode

Observations of negative–resistance phenomena and oscillations in the MOS diode