Taro Hino

Measurement of dipolar relaxation times and dielectric constants using thermally stimulated current

A method for measuring the distribution of dipolar relaxation times and the dielectric constants by thermally stimulated current (TSC) is described. A technique of ’’thermal sampling’’ is used to isolate the TSC due to dipoles with a single relaxation time from the TSC due to dipoles with distributed relaxation times. A theory is developed to calculate distributions of the relaxation times from the TSC measured by the thermal sampling. Dielectric loss factors in polyethylene terephthalate are calculated from the TSC data and they are compared with the experimental values of the dielectric loss factors obtained from the absorption current measurement.

Thermally Stimulated Characteristics in Solid Dielectrics

Thermally stimulated current (TSC), thermally stimulated surface potential (TSSP or thermally stimulated charge decay, TSCD) and thermoluminescence (TL) in dielectrics are due to dipoles, electronic trapped charges and mobile ions. Dipolar TSC has been well analyzed mathematically [1], but there is no complete thermally stimulated analysis on trapped charges and mobile ions because of the complexity of the phenomena. However, the electronic trap levels can be calculated from the initial rise of TSC [2] and the space charge polarization due to mobile ions can be measured from the TSC charge [3].

Thermally Stimulated Current Properties of Mobile Ion in SiO2 Film of MOS Structure and Its Numerical Analysis

The behavior of sodium ions in the SiO2 layer of MOS structures was analyzed using a new numerical method. The method is based on ionic hopping, and drift in the space charge field and diffusion were also taken into account. The computed results were applied to interpret the properties of a thermally stimulated current obtained experimentally. This is a useful method for measuring transient ionic motion in insulating films. It was found that the observed characteristics could be understood by ionic hopping, without assuming a surface ionic trap which has been proposed as a model for the behavior of ions in the SiO2 film of MOS structures.

Neutralization of mobile ions in the SiO2 film of MOS structures

Space‐charge polarization of sodium ions in the SiO2 layer of MOS structures is observed by comparing thermally stimulated currents with capacitance‐voltage characteristics. The results cannot be interpreted by only a space‐charge polarization of a constant excess charge. Charge exchange at the interface is suggested and this idea is supported by the results of thermally stimulated surface potentials. Further, estimation of some parameters of ions are discussed for the case when neutralization of ions occurs at the interface.

A Measurement of Relaxation Time of Dipole and Dielectric Loss Factor in Very Low Frequency by Thermally Stimulated Current

A new method of measuremeing dielectric properties such as relaxation time of dipole, its activation energy and dielectric constant in very low frequency (less than 0.1 Hz) by thermally stimulated current (TSC) is described. Relations between the dielectric properties and TSC are theoretically analyzed, and experimental results on SiO2 films are illustrated. It is shown that this method is more useful than the other methods in the measurement of dielectric properties due to dipoles having the distributed relaxation time and the activation energy. The distribution of the activation energy on SiO2 films was obtained by computer calculation.

Rapid Measuremnent of the Deterioration of Oil-Immersed Paper

A rapid measurement of thermal deterioration of oil-immersed papers by mass spectrometer and gas chromatograph is described. A special assembly was developed using a mercury diffusion pump and automatic Topler pump to extract a very small quantity of generated gas from the oil and to collect it in a reservoir. The gas collected by the above assembly is analyzed by mass spectrometer and gas chromatograph. Logarithm of the generation rate of (CO + CO2) [log (CO + CO2)] is proportional to the reciprocal of absolute temperature (1/T). This linear relationship can be explained by chemical reaction-rate theory and it is shown that the thermal endurance and the thermal life of insulating papers in oil can be estimated by the generation rate of (CO + CO2) in a few weeks as was reported previously for air and vacuum. But the change of the slope of the line log (CO + CO2) versus 1/T at the temperature near 130°C was observed. This is a new mechanism of thermal deterioration of insulating paper in oil, which is apparently unexplained.

Analysis of Space Charge in Insulating Materials under Non-Uniform Electric Fields

A simple technique to calculate the charges induced on electrodes by space charges distributed in a dielectric is presented. The technique is based on Greens theorem and does not depend on the type of electrode system. A needle-plane electrode system is analyzed and the charges induced on each electrode are calculated. Experimental results of thermally stimulated current measurements usinig a needle-plane electrode system have been analyzed and the mean location of trapped charge has been determined.

Study on the Electrical Conduction Mechanism in Al2O3/Polyimide Langmuir-Blodgett Film Systems

We fabricated Al/Al2O3/polyimide Langmuir-Blodgett films (PI LB)/Al (MIM) and Al/Al2O3/PI LB/Al/Al2O3/PI LB/Al (MIMIM) junctions by means of the LB technique, and then examined the electrical transport properties of the junctions from the tan δ values of these junctions. For MIM junctions, the tunneling conduction mechanism dominated in PI LB films when the number of deposited PI LB films was less than 4. In contrast, the bulk conduction mechanism dominated when the number of deposited PI LB films was greater than 5. For MIMIM junctions, the tan δ value of the junctions was about 10% of that of MIM-external wire-MIM junctions. It was concluded that middle Al/Al2O3 layers sandwiched between top Al and base Al electrodes control the number of electrons passing through MIMIM junctions.

Determination of the Polarity of Carrier Traps in Gammairradiated Polyethylene by Thermally Stimulated Current Measurements Using a Temperature Gradient

The thermally stimulated current measurement using a temperature gradient has been applied to the determination of the polarity of carrier traps in ¿-irradiated low density polyethylene films. A method for determining the polarity of carrier traps has been analyzed theoretically and it was found experimentally that carrier traps in the films were electron traps. Further, we found that there was no space charge field in the films.

A method for studying interface states in MIS structures by thermally stimulated surface potential

A thermally stimulated surface potential (TSSP) method has been developed to estimate the parameters of the insulator‐semiconductor interface in MIS structures. As TSSP is measured in the open‐circuit condition, charge on the gate electrode and voltage applied across the insulating layer are both constant in the measurement. For the above reasons, the analysis of TSSP is simplified, and theoretical TSSP curves can be calculated under non‐steady‐state and steady‐state conditions. The samples used for our experiments are Al‐SiO2‐Si MIS structures. To estimate the energy distribution of interface states, the temperature‐vs‐potential characteristic is used, particularly the point where the interface changes from non‐steady‐state to steady state. The characteristic can be clearly and easily obtained by a convenient method devised in the present work. The total amount of interface states, their energy distribution, and their lifetime are estimated in a wide energy range from the characteristic by simple calculation. Further, the relaxation mechanisms of the interface are discussed for samples having substrates of both p‐ and n‐type Si.