Boron Nitride Nanotube Coatings for Thermal Management of Printed Silver Inks on Temperature Sensitive Substrates

Abstract

sive, high throughput technology to integrate functional inks on low-temperature flexible substrates and to mass-fabricate electronics. A wide range of ink formulations have already been successfully incorporated into electronics using screenprinting, including flake-based ink, [7] nanowire inks, [8] nanoparticle (NP) inks, [9][10][11] and molecular inks. [12,13] Molecular inks derived from metal carboxylate salts have become a viable option to address costly or performative limitations exhibited by flake-based and NP inks. [13] They achieve high electrical performance due to their near bulk conductivity, and mechanically robust traces can be printed with low surface roughness and superior adhesion onto flexible substrates. Through the decomposition of the metal complex by means of photonic or thermal sintering, several ink formulations containing salts such as silver i) and copper ii) ethylene glycol carboxylates, and silver neodecanoate have all demonstrated a capacity to print highly conductive traces. [14][15][16] Silver neodecanoate (AgND) in particular can produce metallic traces that exhibit high current carrying capacity (CCC), low sheet resistivity, and low surface roughness upon printing. [13] Although AgND inks provide a performance-competitive alternative to particle-based inks, the high irradiative and thermal budget required to decompose and convert the ink to its metallic state necessitates a highly calibrated sintering sequence to avoid damaging the substrate.Printed electronics provide inexpensive and light weight electrical components to fuel emerging applications. One major challenge is the high temperature required to sinter conductive metal inks, which leads to thermal degradation of the substrate and subsequently poor performance. A boron nitride nanotube (BNNT) interfacial film is reported for thermal management in rapid processing of a printable silver molecular ink platform using intense pulsed light (IPL) sintering techniques. The inclusion of BNNT thin films of varying surface concentrations deposited between the substrate and the printed features reduces thermal damage to the substrate during sintering while simultaneously improving electrical performance, achieving a sheet resistance value as low as 140 mΩ sq −1 . A wide range of sintering energies ranging from 2.0 and 3.2 J cm −2 are investigated along with printed trace widths ranging from 5 mil (0.127 mm) to 20 mil (0.508 mm). Increases in the rate of cooling and in the current carrying capacity are confirmed with the inclusion of the BNNTs. Overall the thin coating of BNNTs presents no drawbacks while significantly improving the electrical properties of IPL sintered conductive traces and thus represents a simple approach that will advance the adoption of IPL for fabricating printed electronic components.

Engineering Silver Microgrids with a Boron Nitride Nanotube Interlayer for Highly Conductive and Flexible Transparent Heaters

“…This softening can lead to warpage and subsequent hardening of the printed design, as previously demonstrated. [ 39 ] Surface profiles presented in Figure A,B show that after exposure to the 1.0–2.5 V testing range, the microgrid printed on bare PET has become significantly more deformed, with three clear areas in the post‐tested trace (Figure 8B) below the substrate surface due to the substrate softening and hardening into the irregular morphology. The heat being absorbed by the substrate therefore contributes little to electrical sintering, as evident by the fact that there is little change in the measured resistance before and after testing.…”

“…[48][49][50] The use of a thin BNNT interlayer at the substrate-trace interface has been initially demonstrated for use in rapid AgND ink processing to minimize the extent of deformation of low temperature substrates that sintering induces. [39] The thermal conductivity of the BNNT interlayer assisted in reducing warpage of the substrate and subsequently improved the morphology of printed silver lines, as well as reducing hot spot formation in the features when current was applied. However, no insight into the mechanical properties of the BNNT film were investigated in the previous work, and with the TCE microgrids having significantly thinner and more complex designs, the BNNT thin film may be sufficient in providing a degree of mechanical stability that will reduce the microgrids' susceptibility to damage during mechanical deformation.…”

“…Applying voltage to the microgrid directly printed on bare PET activates the electrical sintering process but causes the substrate to absorb heat from the microgrid at the substrate-feature interface, such that the semicrystalline nature of the substrate undergoes a phase change as it nears the glass transition temperature (T g ) of the substrate and results in the substrate This softening can lead to warpage and subsequent hardening of the printed design, as previously demonstrated. [39] Surface profiles presented in Figure 8A,B show that after exposure to the 1.0-2.5 V testing range, the microgrid printed on bare PET has become significantly more deformed, with three clear areas in the post-tested trace (Figure 8B) below the substrate surface due to the substrate softening and hardening into the irregular morphology. The heat being absorbed by the substrate therefore contributes little to electrical sintering, as evident by the fact that there is little change in the measured resistance before and after testing.…”

“…[38] To improve processability and accommodate rapid electronics printing, it is possible to use coating techniques to deposit BNNTs as a discrete film by utilizing solutionprocessable dispersions of BNNTs. [39,40] In addition to utilizing BNNT thin films as a buffer toward mechanical deformation, the inherent thermal conductivity and stability of the BNNT thin film interlayer can also provide beneficial thermal diffusion to areas within the microgrid shapes that are void of the Ag trace. It is clear that the optimized electro-optical properties of the high performance microgrid paired with the BNNT interlayer demonstrates specific interest in utilizing the microgrid in transparent heater applications.…”

Formation Mechanisms of Hexagonal Boron Nitride Nanosheets in Solvothermal Exfoliation

“…The invention of graphene has stimulated great research passion for various two-dimensional nanomaterials, , and boron nitride nanosheet (BNNS) is one of them, showing high chemical stability, oxidation temperature, thermal conductivity, and band gap energy . These properties enable BNNSs to be ideal candidate materials in many application scenarios, such as high-temperature and corrosion protection, , thermal conduction, , electrical insulation, lubrication, adsorptions, separations, energy storage, etc. Nevertheless, these applications are often affected by the purity, crystallinity, thickness, and lateral size of BNNSs.…”