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The capacitance of 24°͓001͔ tilt calcium doped Y 1−x Ca x Ba 2 Cu 3 O 7−␦ grain boundaries has been measured for thin films with x in the range 0.0-0.3. The capacitance was determined from the hysteresis in the I-V characteristic. By measuring the capacitance as a function of the voltage across the junctions it was possible to observe the contribution of both parasitic substrate capacitance and heating to the hysteresis. These effects enable the determination of the intrinsic capacitance of the grain boundaries. The effect of thermal noise on the measurement is also assessed, and found to be much less than the observed changes in the capacitance. The capacitance is found to increase as the calcium doping increases: from 0.2 Fm −2 for x = 0.0 to a maximum of 1.2 Fm −2 for x = 0.3. The changes in the capacitance per unit area are observed to be inversely proportional to the corresponding changes in the resistance area product.

The uncompensated donor or acceptor atoms present within the depletion layer of a diode can be employed in an electrostatic actuator, which utilizes the force between opposing charges on either side of the semiconductor junction. We describe the theory of this actuator and demonstrate its application for the case of a diode on the top surface of a silicon cantilever. The Schottky diodes fabricated on the top surface of cantilevers were used to drive them into resonance. As the actuator driving voltages are varied, the amplitude of vibration of the cantilevers changes, which is in agreement with the theoretical predictions.

Using an optimized bridge geometry we have been able to make accurate measurements of the properties of YBa 2 Cu 3 O 7-d grain boundaries above T c .The results show a strong dependence of the change of resistance with temperature on grain boundary angle. Analysis of our results in the context of band-bending at the boundary allows us to estimate the height of the potential barrier present at the grain boundary interface.

Abstruct-We report a series of studies of grain boundary (GB) capacitance for YBazCu30,-s (YBCO) films grown on SrTi03 (STO) bicrystal substrates. By varying the film thickness and the width of the track containing the GB, we find that the substrate makes no contribution to the capacitance measured using Fiske resonances or hysteresis in most cases. This is due to the frequency dependence of the dielectric properties of SrTi03. We have also found that GB capacitance per unit area cGB correlates with the resistance-area product R,A. For our own GBs and GBs reported in the literature the data is is consistent with c G p ( R J ) -' . We attribute this to variations in GB barrier properties, which reduce the active area, whilst maintaining locally the transport mechanism as tunneling.