Electrical and Compositional Evaluation

This scanned mercury electrode technique is not a conventional measurement approach. We have compared Hg as a top electrode to other thin-film counterelectrodes, particularly platinum and aluminum, using known dielectric materials including a-SiOx, a-TaO and a-Al203 thin films. Current-voltage curves measured using mercury top electrodes are comparable to those measured using Pt or A1 top electrodes. 

Information on the dielectric properties of a material might also be obtained using noncontact scanning techniques. These can include rf or microwave measurements made with an electrode that is held in the vicinity of the surface. This approach has the advantage that samples remain undamaged by the measurement and thus can be reevaluated or subjected to other studies as needed. However, this approach cannot provide accurate values for the capacitance, in very thin films such that d/e 4 A. Moreover, the current-voltage measurements are still needed in order 

Knowledge of the composition of samples in an off-axis deposited phase spread is important. Calibration runs were used to determine the thickness vs position for single components deposited in our system at a given power setting. The drop-off in thickness as a function of distance from the gun is approximately exponential and can be modeled accurately to about 5 at%. We find that the deposition rates are additive for the three guns. RBS measurements have been made on a number of samples to validate our assumptions. In addition, we routinely use RBS measurements as a double check on the specific compositions that we identify as having superior properties. 

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