Papers by Keyword: Resistance Change

Abstract: In order to research the resistance characteristic of silicon-based composite tiles under high temperature thermal load on aircraft during its reentry into the earth's atmosphere, the ordinary resistance measurements were comparatively discussed according to the operational environment of composite, two parallel electrodes probe test method was proposed, and the resistance test platform under high temperature thermal load was developed, by which the resistance characteristic of silicon-based composite tiles was continuous monitored under different thermal load. The result shows that: If the temperature is not higher than 600°C, the resistance will increase with the decrease of temperature until it reached the resistance value at room temperature; If the temperature is higher than 700°C, the resistance characteristic will be changed everlastingly; If the temperature is higher than 800°C, the resistance will be less than 1kΩ and will not change any more.

Abstract: Each material contains defects and in-homogeneities in a structure volume. It has influence on the properties of material (conductivity, mass density, mechanical properties). Interaction of the ultrasonic waves with defects or in-homogeneities in the solid state is not clear. Electro-ultrasonic spectroscopy can help to clarify this phenomenon. The electro-ultrasonic spectroscopy describes defects and un-homogeneities inside the sample structure. This method is quite different from electro-acoustic effect. Ultrasonic signal is in range from 20 kHz to 150 kHz. Ultrasonic signal changes geometry of the sample in elastic range only. The sizes of cracks are changing also in the sample volume. Conductivity near the area of cracks is strongly changing due to ultrasonic vibrations. It has influence on resistance of the sample which is changing along with a frequency of ultrasonic vibrations. The amplitude of the resistance change depends on the material, number of cracks, size of cracks and Eigen frequencies of the sample excited by ultrasonic wave. We applied the electro-ultrasonic spectroscopy on two types of varistors. It can be useful for understanding the relation between microstructure and mechanical properties of these types of varistors.

Abstract: Hafnium oxide thin films were deposited on silicon substrates by RF reactive magnetron sputtering. The effects of oxygen partial pressure, tuned by the O2/Ar flow ratio, on the microstructure and electrical properties were characterized. All HfOx thin films exhibit monoclinic phases. As the increase of O2/Ar flow ratio from 0.08 to 0.33, the crystallinity is improved accompanied with the decreases of flat band voltage and leakage current density. However, when the O2/Ar flow ratio further increases to 0.5, the crystallinity becomes worse with the increase of flat band voltage and leakage current. The HfOx based resistive random-access memory (RRAM) has been fabricated and its storage properties were also investigated.

Abstract: New non-destructive testing (NDT) method is based on the effect of the ultrasonic vibrations on the electron transport in samples with macroscopic defects as cracks or defect centers affecting electrical conductivity. On the frequency given by the subtraction of exciting frequencies new intermodulation signal appears. Its value is given by electric resistance modulation by the defects and un-homogeneities in the sample structure. In our experiment we used the ultrasonic actuator with frequency fU when the period of wave is longer than the dielectric relaxation time in analyzed sample. In this case the effects of electron bunching by ultrasonic wave are negligible. The ultrasonic wave length is much larger than the electrons mean free path and the wave period is much longer than the mean free time among the electrons collision with scattering centers and defects. Then the electron transport is described by the quasi-steady state transport equation in one-electron approximation. Because of the requirement of charge neutrality, no net AC electric current with the ultrasonic wave frequency fU can be carried by the wave. Similar situation exists for samples excited by standing ultrasonic waves. The electrical conductivity varies with time due to that the cracks geometry is changed with frequency of the ultrasonic vibration. The sample conductivity is affected mainly by the presence of cracks and defects boundaries perpendicular to the electric current density vector. In our experiment the amplitude of ultrasonic vibration is so low that no new cracks are generated and then the proposed testing method belongs to NDT.

Abstract: Programmable metallization cell (PMC) memory is based on the electrochemical control of nanoscale quantities of metal in thin films of solid electrolyte. We investigate the nature of thin films formed by the photo-dissolution of Ag into Ge-Se-Te glasses for use in programmable metallization cell devices. Glassy alloys of a-Ge25Se75-xTex(x = 0, 25) are prepared by well known melt-quenching technique. Thin films of a-Ge25Se75-xTex(x = 0, 25) glassy alloys are evaporated by vacuum evaporation technique at ~10-6 torr on glass substrate at room temperature. Optical properties in this study concerns photo-diffusion of Ag on Ag-doped Ge-Se-Te electrolytes. With these promising properties, the composition a-Ge25Se75-xTex(x = 0, 25) is recommended as a potential candidate for PMC-RAM.

Abstract: Resistance-switching behaviors of the Pr0.7Ca0.3MnO3(PCMO) films based metalinsulator- metal (MIM) devices has been investigated. In this work, resistance change of PCMO films deposited with SRO buffer layers by using RF-magnetron sputtering system investigated at room temperature. The ratio of the resistance change of the PCMO films with SRO buffer layers in the high-resistance state to that in the low-resistance state turned out to be much lager than that of the PCMO films without SRO buffer layers. Moreover, The reproducible property of the fabricated samples were improved. Origin of resistance change is not clear, but PCMO films with SRO buffer layers have the possibility of application for nonvolatile memory device.