Conformal laser printing and laser sintering of Ag nanoparticle inks: a digital approach for the additive manufacturing of micro-conductive patterns on patterned flexible substrates

Figures & data

Figure 1. Non planar substrates schematics (a) Top view of the substrate (b) Cross section schematics of the substrate indicating the gate electrode printing direction (c) Side view schematics illustrating the distinct layers including LIFT printed gate electrodes.

Figure 2. Schematic presentation of laser station (a) Gate electrode laser printing process on top of OTFT stack (b) Gate electrode laser sintering process on top of OTFT stack.

Figure 3. Three nanoparticle inks exhibiting differences regarding the nanoparticle size distribution and the viscosity value and the corresponding scanning electron microscope images (a) ink exhibiting standard nanoparticle size and distribution (Type 1) (b) ink with reduced nanoparticle size and distribution (Type 2) (c) ink with further reduced nanoparticle size and distribution (Type 3).

Table 1. Properties of the Ag inks utilised in the experiments.

Inks	Type 1	Type 2	Type 3
Viscocity Metal loading Nanoparticle size distribution	632 cP 70% d50 = 70 nm d90 = 120 nm	2300 cP 70% d50 = 56 nm d90 = 71 nm	12800 cP 70% d50 = 49 nm d90 = 67 nm

Figure 4. Resistivity investigation graphs and corresponding scanning electron microscope images of Ag inks films with 1.5 µm thickness (a) Oven temperature baking process and (b) laser sintering process.

Figure 5. High speed imaging for the evaluation of the rheological behaviour-jetting for (a) standard nanoparticle size ink (b) reduced nanoparticle size ink (c) further reduced nanoparticle size ink.

Figure 6. Microscope photos and profile measurements for (a) Type 1 d50 = 70 nm d90 = 120 nm ink (b) Type 2 ink d50 = 56 nm d90 = 71 nm.

Figure 7. LIFT printed patterns on flexible substrates (a) Demanding design printed on planar flexible dielectric (b) Profile measurements of printed lines.

Table 2. Morphological properties and adhesion behaviour of laser printed and laser sintered lines.

Morphology	Width	85 ± 5 µm
	Height	410 ± 35 nm
Adhesion	0.39 − 7.87N/cm	no delamination nor crack issues
	> 7.87N/cm	failure

Figure 8. LIFT printed patterns on flexible substrates (a) Conformal LIFT printed and sintered 3 cm on non planar flexible substrate (b) Prior to the printing process profile measurement of the non planar substrate (c) corresponding scanning electron microscope image (d) successful connection of the non planar active area with electrical components.

Table 3. Resistivity values comparison for Type 2 ink for laser sintering.

Laser sintering power	160 mW	300 mW
1.5 µm film on quartz slide 410 nm lines on fully patterned samples	non conductive 25 ± 4 μOhm * cm	200 ± 10 μOhm * cm destroyed gate dielectric

Figure 9. (a) Microscope image of an OTFT device using a laser printed gate (b) Transfer curves measurements for devices with LIFT printed and sintered gate (c) Transfer curves measurements for devices with sputtering deposited gate.