Design and development of innovative vanadium oxide, CNT, and graphene based high-performance microbolometer

Abstract

Present microbolometer technology for infrared (IR) sensing and imaging has featured microbridges comprising Si3N4 as well as VOx materials and shown decent performance for IR band detection applications. Nevertheless, further integration of carbon nanotubes (CNTs) and graphene can improve the temperature coefficient of resistance (TCR) to provide even higher dynamic range. For the development of high performance and low noise IR microbolometer detectors with improved TCR, vanadium oxide (VOx) layers were grown on 4-inch SiO2/Si wafers as well as on Si substrates using a DC sputtering process with flow of oxygen and argon gases. From energy-dispersive X-ray spectroscopy (EDS) measurements of the sputter-assisted VOx layer growth it was determined that reduced Ar:O flow resulted in lower measured O/V ratios, and therefore more optimal stochiometric properties in the VOx layers. Likewise, analysis of scanning electron microscopy (SEM) images demonstrated that DC sputtering power had a substantial impact on the deposition rates and corresponding VOx layer thickness. Using a gas flow ratio of 18.7:1.3, with DC sputtering powers of approximately 300 W, V/O ratios in the 1.8-1.9 target range and 200 nm target thicknesses, respectively, were achievable in VOx layer growth on SiO2/Si substrates. The electrical and performance properties of these optimized VOx layer test structures were then measured and characterized in view of integration with graphene and single wall and multiwall carbon nanotubes (CNTs) for advanced long-wave infrared (LWIR) detection. These demonstrated significant noise reductions and as well as enhancements in the TCR, indicating the potential for improved noise equivalent temperature difference (NETD) for high imaging cameras and microbolometer focal plane array (FPA) performance for defense and commercial LWIR sensing applications.