Methods and devices for providing a minimally-invasive placement of a mechanical structure for reducing the volume of a hollow body organ. Cross-linked polyimide oligomers are used as the recording layers in atomic force data storage device, giving significantly improved performance when compared to previously reported cross-linked and linear polymers. An isolation trench is provided around the collection node to provide better control of the width of the collection node. The gain compensator generates the charge pump reference current by replicating a reference scale current using unit current sources.