Composite Dielectric Inks for Humidity Sensing

The NASA technology is based on a perovskite ceramic developed at MSFC, reduced lanthanum barium titanate (rLBT). rLBT is comprised of reduced barium titanate (BaTiO3) doped with lanthanum (La) and co-doped with potassium hydroxide (KOH). rLBT was developed while exploring the suitability of sintered perovskites to produce screen-printed ultracapacitors; the prototypes unexpectedly demonstrated an extreme sensitivity to moisture, prompting exploration of the material for use as a vapor-sensitive dielectric ink. To eliminate inconvenient high temperature firing necessary to produce capacitors, the inventors developed rLBT-loaded polymer composites capable of curing under low heat (110 degrees C) for epoxy or under ultraviolet (UV) light for UV-sensitive resin. At suitable ceramic particle loading concentrations, thin ink layers (30 micrometers) demonstrate RH sensitivity, instantaneously detecting breath vapor (RH change from 30% to 93%) with a recovery time of only 1s. Prototypes demonstrated near log-linear response curves over three orders of magnitude of capacitance with minimal drift (see Figures 1 and 2). NASA’s low temperature dielectric ink for humidity sensing is at technology readiness level (TRL) 4 (component performance has been validated in a lab setting) and the related patent is now available to license. Please note that NASA does not manufacture products itself for commercial sale. Inventors at NASA Marshall Space Flight Center (MSFC) have developed humidity sensing dielectric ink formulations for use in printed electronic and sensor manufacturing applications. Novel ceramic powders with favorable dielectric properties are mixed with liquid resins to form a polymer-ceramic composite that can be deposited and cured at room temperature, eliminating high temperature sintering steps previously required to produce ceramic elements. The inks' epoxy and UV curable resin binders form consistent dispersions with viscosities suitable for deposition via aerosol jet or screen printing processes. Prototype humidity sensors produced using the novel ink formulations demonstrate high sensitivity and rapid, log-linear response to changes in relative humidity (RH) and have been explored for in-helmet breath sensing applications for astronauts or pilots. Suitability of the ink for use in capacitive energy storage applications has also been explored.