# Effect of Substrates on the Dynamic Properties of Inkjet-Printed Ag Thin Films
## 3 Measuring the Dynamic Properties of Ag Ink on Flexural Substrates  
### Specimen Fabrication and Experimental Setup  
The substrates used for the experiments were two polyimide (PI) films (SKC, Seoul, Korea) with thicknesses of 25 \(\upmu\)m and 225 \(\upmu\)m, slide glass with a thickness of 145 \(\upmu\)m, and a silicon wafer (LG Siltron Inc., Gumi, Korea) with a thickness of 200 \(\upmu\)m. To remove surface contamination, the substrates were first ultrasonicated in isopropyl alcohol (Daejung chemicals & metals, Siheung, Korea) for 20 min and rinsed with a deionized water for 10 min. For proper wettability of the substrates, C\({}_{4}\)F\({}_{8}\) gas (99.99%) (Daeung industrial gases Co., Seoul, Korea) was used. The substrates were treated in O\({}_{2}\) and Ar plasmas to remove any remaining contamination from organic matter. A MicroFab piezoelectric print head (MicroFab Co., Plano, TX, USA) with a 30 \(\upmu\)m nozzle diameter was used to perform inkjet printing on the plasma-treated surface.  
The Ag ink used in this study was a silver nanoparticle colloid in tetradecane (Harima Chemical Co., Tokyo, Japan). The ink contained 57.3 wt % silver nanoparticles with diameters below 10 nm. The viscosity of the Ag ink was 8.4 mPa-s at 20 \({}^{\circ}\)C. The applied voltage was controlled to ensure accuracy of the droplet generator (MicroFab Co., Plano, TX, USA). The printing resolution was adjusted to 800 dpi, and the drop diameter was set to 30 \(\upmu\)m. Due to the controlled conditions, the average diameter of a single droplet on the substrate was maintained at 55 \(\upmu\)m.  
The Ag thin films on the substrates were printed as shown in Figure 1. To satisfy the performance of conductivity and mechanical properties, the inkjet-printed thin films were sintered at 210 \({}^{\circ}\)C for one hour. The width and thickness of the film were designed to be 100 \(\upmu\)m and 1.5 \(\upmu\)m, respectively, when the number of overprints was one. The actual printed width and thickness had variations affected by the properties of the substrates. To conduct the vibration test, the beam shape specimens were obtained by Nd:YVO4 laser pulse cutting (with a 10 ps pulse width, a 343 nm wavelength, and a 400 kHz frequency). The printed specimens had different widths depending on the substrate: the PI and glass had widths of 500 \(\upmu\)m, and the silicon wafer had a width of 300 \(\upmu\)m.  
Figure 2 shows the experimental set-up with the printed bilayer beams. Transverse vibrations were excited on the beams by the vibration shaker. The vibration responses were measured with a laser Doppler vibrometer (LDV) (OFV-503, Polytec, Horsching, Austria) and an accelerometer (2250A -10, Endevco, Irvine, CA, USA). The two sensors were calibrated by measurement of the vibration response on the same point, with the clamped end of the beam excited with random noise. The location of the LDV was adjusted at \(x_{1}\) to obtain the vibration response of the beam. The transfer functions of the bare substrate and Ag-printed beam were measured to estimate the properties of the Ag films.  
Figure 1: Schematic of the printing procedure to fabricate the test specimen using a MicroFab piezoelectric print head and Nd:YVO4 laser pulse cutting.