Flexible printed sensor tape for novel applications

Abstract

We are developing a blast sensor tape to detect the occurrence of events that cause traumatic brain injury (TBI) in military environments. TBI is a medical condition that is cumulative and triggered by events such as blast pressure waves, noise, acceleration and possibly also extremely bright light. In order to meet the low cost target of the tapes, fabrication techniques such as inkjet printing, laser machining and lamination are employed with all deposition and patterning steps been compatible with future roll-to-roll manufacturing. The sensor tape has integrated sensors, signal conditioning electronics, non-volatile memory and a thin film battery. The electronic circuits are based on jet-printed organic electronics with the emphasis on low-voltage electronics due to the limitations of the battery size. In one approach we have explored atomic layer deposition (ALD) for forming thin gate dielectric layers for thin- film-transistors with a printed polythiophene (PQT-12) semiconductor and jet-printed nano-silver contacts. A 100 nm aluminum oxide dielectric layer results in a specific capacitance of 70 nF/cm2, which is at least a factor of 4 higher than what has been achieved with typical solution processed polymer dielectric layers. New deposition methods have enabled ALD to be compatible with roll-to-roll processing. We integrate pressure, acoustic, acceleration and temperature sensors based on piezoelectric polymers such as PVDF or PVDF-TrFE copolymer. These materials were chosen because of low-power requirements, low drift and relatively simple fabrication. Moreover, blast events require only the measurement of dynamic signals for which piezoelectric sensors are intended. Printing methods allow rapid design or sensor layout variations for specific applications and also large-area sensor arrangements. In one example, our sensor tape is designed so that multiple sensors are positioned at different locations around a helmet. The design allows stretching or shaping of the tape according to the size of the helmet. In this paper we will describe aspects of the system and fabrication of the flexible sensor tape.