Enhancement of Roll-to-Roll Gravure-Printed Cantilever Touch Sensors via a Transferring and Bonding Method

Sensor miniaturization offers significant advantages, including enhanced SoC integration efficiency, reduced cost, and lightweight design. While the roll-to-roll printed electronics fabrication process is advantageous for the mass production of sensors compared to the traditional MEMS technology, producing sensors that require air gap-based 3D structures remains challenging. This study proposes an integration of roll-to-roll gravure printing with a transferring and bonding method for touch sensor fabrication. Unlike previously reported methods for sacrificial layer removal, this approach prevents stiction issues, thus enabling sensor miniaturization and providing the flexibility to select materials that minimize sensitivity degradation during scaling. For the lower part of the sensor, Ag and BaSO4 were roll-to-roll gravure-printed on a flexible PET substrate to form the bottom electrode and dielectric layer, followed by BaSO4 spin coating on the sensor's anchor area to form a spacer. For the upper part, a water-soluble PVP sacrificial layer was roll-to-roll gravure-printed on another flexible PET substrate, followed by spin coating Ag and SU-8 to form the top electrode and the structural layer, respectively. The sacrificial layer of the upper part was removed with water to delaminate the top electrode and structural layer from the substrate, then transferred and bonded onto the spacer of the lower part. Touch sensors of three different sizes were fabricated, and their performances were comparatively analyzed along with that of an epoxy resin-based sensor, demonstrating that our sensor attained miniaturization while achieving relatively high sensitivity.