PHOTORESIST-DERIVED POROUS CARBON FOR INTEGRATED ON-CHIP ENERGY STORAGE

We have developed a facile, and scalable fabrication process for high surface area porous carbon for microsupercapacitor applications. A porous carbon film is synthesized by pyrolysis of commercial SPR-220 photoresist in an H2/Ar mixture and tested for specific capacitance. A capacitance of about 2 mF/cm was achieved, matching or exceeding numerous other proposed microsupercapacitor technologies. The material was also demonstrated to be robust under cycling in aqueous electrolyte, retaining > 92% of its original capacitance after 10 cycles. INTRODUCTION The increasing technological demand for autonomous sensing platforms necessitates the development of integrated energy storage for powering sensors, actuators, and communications microsystems. Supercapacitors, one potential candidate for on-chip energy storage, store charge electrostatically at the electrode/electrolyte interface, in contrast batteries, which rely on electrochemical energy storage in the bulk electrode. Because of this interfacial charge storage mechanism, supercapacitors charge and discharge much more quickly (in seconds vs. in minutes or hours for batteries) and have much longer cycle lifetime (10 vs. 10 cycles for batteries), but they require high surface area electrodes to achieve good energy density [1]. Because of this high surface area requirement, activated carbon is a popular material choice for supercapacitor electrodes [2]. However, for integrated, planar, on-chip supercapacitors, activated carbon presents many fabrication challenges including patterning and placement of electrodes [3]. For on-chip supercapacitor applications, an effective approach is utilization of photoresist-derived carbon since photoresist processing is well-established in microfabrication methodologies. However, prior reports on photoresist-derived carbon from AZ4300 and microstructured SU-8 resists show relatively low capacitance values unless the electrode material is chemically activated or decorated with electroactive materials [4] [5] [6] [7]. In this manuscript, we demonstrate that the pyrolysis of another readily available photoresist, SPR-220, yields a highly capacitive film without any additional treatment. The resultant capacitance from our procedure is also competitive with other proposed carbon-based microsupercapacitor electrode materials including inkjet-printed carbon [3], carbide-derived carbon [8], and carbon