Dynamic method for characterizing potential wells of bubbles under charged walls

Abstract

The depth of the potential well H w of a bubble under a charged wall in an ion-implanted propagation pattern has been characterized by a quasistatic measurement of bubble radius r versus bias field on and off the pattern. The well depth at collapse is found to be considerably larger than at lower bias fields. The extent X w of the well, or alternatively its maximum gradient (∼H w /X w ), is determined by a dynamic method as a function of in-plane field H p and bias field. A pair of conductor lines is positioned above the ion-implanted structure and a pulsed field gradient is applied to drive the bubble out of the potential well. At long pulse lengths the critical gradient H'_{\max} needed to drive the bubble from the well is the maximum gradient of the well. Using a simple parabolic model for the well, the well's extent is given by X_{w}=2H_{w}/H'_{\max} . Experimental results for X w are considerably less than the observed minimum displacements at which a bubble will no longer spontaneously fall back into the well. These results indicate that the shape of the well is fairly flat with the principal rise in potential occurring at a large distance from the edge of the pattern.