Abstract
Inkjet printing offers an attractive method for the deposition of metal interconnects in electronic systems and enables a low-cost, environmentally friendly route to manufacture. However, virtually all current metal inkjet processes require post-deposition sintering treatments to achieve the optimum electrical conductivity, because the growth mechanism involves coalescence of discrete nanoparticles. A manufacturing process that reduces the number of steps by directly printing silver, removing the need to sinter the printed metal, would be highly advantageous. Here we describe a, sinter-free process that results in the direct printing of crystalline silver. This process exploits the chemistries developed for Atomic Layer Deposition (ALD), to form the basis of a new ink formulation, which we term; Reactive Organometallic inks (ROM). These ROM ink formulations are capable of depositing low temperature, high conductivity metal films, without the need for subsequent sintering treatments. To reduce the temperature for direct formation of metallic Ag, we have added an alcohol as a catalytic reducing agent to dissociate the organometallic component. Silver films printed from our novel ROM ink, on a glass substrate at 120 °C, are electrically conductive with a typical resistivity as low as 39.2% that of bulk silver, without the need for sintering.
Highlights
Printing passes are required to obtain an adequate sheet resistance
Post-treatment sintering processes are still required to fully consolidate the conductive films, if the initial growth process is from discrete NP intermediates which is common in Metalorganic Decomposition (MOD) ink processes
We have developed a new class of ink with which we exploit surface chemistries to achieve a sinter-free route to printing metal tracks
Summary
Printing passes are required to obtain an adequate sheet resistance. Post-treatment sintering processes are still required to fully consolidate the conductive films, if the initial growth process is from discrete NP intermediates which is common in MOD ink processes. We have developed a new class of ink with which we exploit surface chemistries to achieve a sinter-free route to printing metal tracks This involves the careful tailoring of the substrate temperature and the enthalpy of reaction of the organometallic (OM) component with a co-reducing agent, in this instance an alcohol, to ensure a surface-driven process rather than a liquid-phase homogeneous process. The role of the alcohol in catalysing the process is significant and it has been reported that the affinity of cationic silver to alcohols and aldehydes leads to its chemical reduction[18] This approach has been modified to prepare a reactive organometallic-based ink formulation suitable for inkjet processing to achieve sinter-free printing of silver films with high electrical conductivity, whilst being deposited at a low thermal budget
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