Soft and Morphable Displays and Profilometers: Self-Assembled Out-of-Plane by Capillary Pressure Acting on a Gel

High aspect ratio, conductive sharp tips have geometrical advantages in sensing and actuation. Developing these structures on soft, stretchable and bendable materials would provide distinct advantages, such as conformable sensors for biosignals, morphable displays, profilometers for curved surfaces, and so on. A major challenge in using soft materials as substrates is that the fabrication technique should be conducted in close to ambient conditions, particularly at low temperature. In this paper, the fabrication of high aspect ratio conductive sharp tips on elastomers is discussed. Without using fine feature molds, a capillary bridge is created by containing and separating a conductive viscous gel between two plates. The capillary pressure experienced by the capillary bridge shapes the gel to a sharp tip (similar to 100 nm) before it solidifies. The process flow is quantified by measuring the mechanical force needed for tip creation and extracting the coefficients of the standard linear solid model for the viscoelastic gel. Electron emission is demonstrated at 22 mu bar and 1 mbar, and appears to be determined by Fowler-Nordheim tunneling for most cases. Elastomeric field emission displays and profilometers are demonstrated.