Composite Dielectric Inks for Humidity Sensing
Electrical and Electronics
Composite Dielectric Inks for Humidity Sensing (MFS-TOPS-132)
Perovskite dispersed in polymer resin for low-temperature deposition and cure
Overview
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.
The Technology
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.
Benefits
- Sensitivity: near-instantaneous vapor detection
- Fast recovery: under 1 second for 63% change in RH
- Low temperature: no sintering process required
- UV curability: for printed electronic components
- Durability: strong adhesion of epoxy to substrate
Applications
- Printed electronics: dielectric ink for producing functional circuit elements with impedance or capacitance
- Humidity sensing: functional element for RH sensing
- Medical instruments: detection of breathing patterns for patients or astronauts
Technology Details
Electrical and Electronics
MFS-TOPS-132
MFS-33813-1
MFS-33214-1
Hanekohm, K.R. and T.D. Rolin. Fabrication and Testing of a Novel Ceramic-Based Additively Manufactured Humidity Sensor. Marshall Space Flight Center. Huntsville, AL. December 2022.
Sherrard, C.G. and T.D. Rolin. Solid-State Ultracapacitor Polymer Composite. Marshall Space Flight Center. Huntsville, AL. December 2022.
Similar Results
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The NASA solid-state ultracapacitor technology is based on the novel materials design and processes used to make the IBLC-type ultracapacitor. The IBLC concept is known to provide outstanding capacitance behavior but has been difficult to reproduce. NASA has developed a careful process to produce dielectric ink materials to be used in printed electronic applications with reproducibility. An individual cell is created by building electrodes on each side of the dielectric layer, and complete modules can be constructed by stacking multiple cells.
Closely related NASA innovations on dielectric and conductive ink (electrode) formulations are key to the ultracapacitor construct, and are included in the technology package. Target performance criteria of this technology include the following:
- Use of standard materials and processing methods
- Robust solid-state device with no liquid electrolytes
- High-energy densitytarget energy densities of 60 J/cc at a minimum operating voltage of 50 V
- High dielectric breakdown strength (>250 V)
- Excellent pulse-power performance; rapid discharge and charge
- Reliable performance under repeated cycling (>500,000 cycles)
Additional development work is underway to build and test complete capacitor
modules and to further improve material properties and performance.
New, High-Performance Conductor Inks
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The conductor ink formulation exhibits conductivity equivalent to commercially available, conventional, silver thick-film inks. Adhesion to various substrate materials and solderability using lead-tin and silver-bearing electronic solders has been tested and verified.
New Dielectric Material for High-Performance, Solid-State Ultracapacitors
NASA's technology is a dielectric materials formulation comprising polymers, organic binders, solvents, and surfactants, formulated together with a ceramic perovskite nanopowder. The ceramic nanopowder can be optimized for the required dielectric properties of capacitance, voltage breakdown, and leakage. This involves the addition of dopants or the use of advanced coatings on the powder particulates, and subsequent thermal treatments.
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The ink composition is a careful blend of polyimide or polyvinylidene fluoride (PVDF) polymers, solvents, surfactants, and barium titanate nanopowders. Proper ratios are needed for viscosity and processability (e.g., nanopowder wetting and dispersion), along with the optimal ultracapacitor device performance.
Fabricating printable electronics and biosensor chips
The plasma system consists of a glass tube with a diameter of 0.5 mm or larger, if desired. The electrodes are separated by 10 mm. Helium, argon or cold dry air can be used as a plasma gas source. An applied high voltage between the electrodes causes the gas to breakdown within the central core of the glass capillary generating atmospheric plasma. Nanostructures colloids/organic/inorganic precursors are placed in a glass container with an inlet and outlet for carrier gas and are seated on an ultrasonic nebuliser. The aerosol is then carried into the plasma stream by the carrier gas and is deposited.
The atmospheric plasma deposition system can be modified for depositing multiple materials, either simultaneously or sequentially, and for high-throughput processing by having multiple jets. Each capillary can either be connected to the container containing a single precursor material or to different containers containing different precursor materials to facilitate multiple depositions. The multi-jet plasma system can be automated and controlled individually to precisely control surface characteristics. This technique is independent of the chosen substrate, and has proven to work for many substrates, including paper, plastic, semiconductors and metals.
Solid-State Ultracapacitor for Improved Energy Storage
NASAs solid-state ultracapacitor technology is based on the novel materials design and processes used to make the IBLC-type ultracapacitor. The IBLC concept is known to provide outstanding capacitance behavior but has been difficult to reproduce. NASA has developed a careful process to produce dielectric materials to be used in printed electronic applications with reproducibility. An individual cell is created by building electrodes on each side of the dielectric layer, and complete modules can be constructed by stacking multiple cells.
Closely related NASA innovations on dielectric and conductive ink (electrode) formulations are key to the ultracapacitor construct, and are included in the technology package.
Target performance criteria of this technology include the following:
• Use of standard materials and processing methods
• Robust, solid-state device with no liquid electrolytes
• High-energy densitytarget energy densities of 60 J/cc at a minimum operating voltage of 50 V
• High dielectric breakdown strength (> 25 MV/m)
• Excellent pulse-power performance; rapid discharge and charge
• Reliable performance under repeated cycling (> 500,000 cycles)
Additional development work is underway to build and test complete capacitor modules and further improve material properties and performance.
