Two-dimensional material enhanced dielectric and conductive inks for printable electronics

Abstract

Printed and flexible electronics is emerging as the next ubiquitous platform for the electronic industry. The pairing of functional conductive, semiconducting, and dielectric inks with printing technologies enables the production of low-cost, large-scale electronic devices and systems. There are some drawbacks of current functional inks, such as high material cost, complex processing requirements, and low electrical conductivities/dielectric constants. For example, currently available conductive inks are based on metal salts or particles (i.e. silver) which are expensive and require complex curing conditions. While the carbon-based conductive inks do not demand such curing conditions, they offer insufficient electrical conductivities for a wide variety of applications. On the other hand, traditionally printable dielectric inks use polymers which have relatively low dielectric constant (εr~2-5), or use ceramics which are difficult to print and cure. Two-dimensional (2D) materials in this case offer a great potential for alternation due to their exceptional properties (i.e. electronic properties, high mechanical strength and flexibility) and the capability of solution phase processing for printable inks. However, there is still a lack of exploration and understanding in the impact of 2D materials on specific conductive or dielectric properties in their functional ink formulation and the feasibility of these inks to printing processes. In my PhD study, I focus on the conductive and dielectric functional inks and their related applications by functional printing. I develop a graphene-based ink which bridges the gap between metal and carbon-based inks. I achieve a sheet resistance of screen-printed film as low as ~64 Ω/sq on PET substrate. I investigate the three-dimensional (3D) conformal printing of graphene ink on arbitrarily shaped surfaces which could provide new functionalities beyond 2D flat surfaces. Dielectric inks, although are not widely explored compared to conductive inks, plays an important role in fully printable electronics such as in resonators, memory elements and capacitive touch sensors. I utilise hexagonal boron nitride (h-BN) as a nanofiller to enhance the dielectric constant of polyurethane (PU) polymer inks and achieve a two-fold increase in εr by adding only 6.4 mg/mL h-BN, while keeping the resulting composite flexible and optically transparent. In order to further study the printability of h-BN enhanced polymer inks, I also incorporate h-BN in poly(4-vinylphenol)(PVP) a commonly used polymer for inkjet printing. These demonstrations would potentially allow versatile printed electronics applications enhanced by 2D materials.