Laser-induced forward transfer for manufacture of graphite-based heaterson flexible substrate

Flexible heaters have recently gained considerable interest owing to their ability to be integrated into a wide variety of miniaturized devices. They are used to perform thermal management, strain engineering, and even electrothermal actuation. These heaters are mainly fabricated using thin film techniques, which typically in- volves a multi-step lithography process that can be complex and expensive. Alternatively, wet coating methods are also employed; however, these possess several limitations when dealing with high viscosity inks. In this paper, we use a laser driven process called laser-induced forward transfer (LIFT) to fabricate graphite-based heaters on a flexible substrate. LIFT is a non-contact printing process that, unlike ink-jet printing, is nozzle- free, which makes it suitable to print any ink regardless of its viscosity. We report the first use of LIFT to print flexographic graphite ink to pattern heaters. The flexographic ink possesses high viscosity in the order of 1300–1700 mPa⋅s. The smallest deposit obtained using the graphite ink was 176 μm in diameter. Characteri- sation of the heaters shows that they can reach a wide range of temperatures at different voltage inputs. A maximum temperature of 123 ◦C was reached over an area of approximately 18 mm2 at 5.2 V.