**4.3 Multi-nozzle electrohydrodynamic printing**

The main draw-back of single nozzle electrohydrodynamic printing is the limitation of low throughput. In order to address this drawback and attain high production efficiency electrohydrodynamic inkjet printing process for industrial production of printed displays, PCBs, printed TFTs and printed solar cells, many researcher are working on a multi-nozzle electrohydrodynamic inkjet printing process(Lee et al., 2008). However, due to the interaction (cross-talk) between the electrically charged neighboring jets, it is difficult to precisely control and reproducible multi-nozzle EHD inkjet printing process. To overcome the limitation of low throughput of EHD inkjet printing process, a multi-nozzle EHD inkjet printing head consisted of three nozzles is fabricated and successfully tested by printing simultaneously conductive lines of silver nanoparticles ink onto glass substrate (Arshad et al 2011). Multi-nozzle electrohydrodynamic inkjet printing is consisted of three parts i.e. PDMS (Polydimethylsiloxane) holder, glass capillaries and copper electrodes. PDMS holder is manufactured through molding technique with the channels for capillaries, ink-supply and electrodes. The schematic of the mold and multi-nozzle head is shown in figure 19(a) and (b). The tapered glass capillaries of 100µm internal diameter and 120µm are then inserted in the outlet channels of the PDMS part. Finally, three copper electrodes having outer diameter of 500μm are inserted from the top of the PDMS holder. The nozzle to nozzle distance is kept at 3mm. The complete schematic of the multi-nozzle EHD inkjet printing head is shown in Figure 19(c).

Fig. 19. Schematic illustration of the multi-nozzle EHD inkjet printing head fabrication process: (a) Simplified fabrication steps of mold preparation (b) Resulted PDMS holder having L-shaped channels for ink supply and clasping of glass capillaries (c) Complete multi-nozzle EHD inkjet printing head (Khan et al 2011)

Figure 20 shows images of stable meniscus formed at the tip of individual nozzles. Cone-jets are formed at the tip of each nozzle i.e. nozzle 1, nozzle 2 and nozzle 3 at an applied DC voltage and flow rate of 3.5kV and 20μl/h respectively.

The main draw-back of single nozzle electrohydrodynamic printing is the limitation of low throughput. In order to address this drawback and attain high production efficiency electrohydrodynamic inkjet printing process for industrial production of printed displays, PCBs, printed TFTs and printed solar cells, many researcher are working on a multi-nozzle electrohydrodynamic inkjet printing process(Lee et al., 2008). However, due to the interaction (cross-talk) between the electrically charged neighboring jets, it is difficult to precisely control and reproducible multi-nozzle EHD inkjet printing process. To overcome the limitation of low throughput of EHD inkjet printing process, a multi-nozzle EHD inkjet printing head consisted of three nozzles is fabricated and successfully tested by printing simultaneously conductive lines of silver nanoparticles ink onto glass substrate (Arshad et al 2011). Multi-nozzle electrohydrodynamic inkjet printing is consisted of three parts i.e. PDMS (Polydimethylsiloxane) holder, glass capillaries and copper electrodes. PDMS holder is manufactured through molding technique with the channels for capillaries, ink-supply and electrodes. The schematic of the mold and multi-nozzle head is shown in figure 19(a) and (b). The tapered glass capillaries of 100µm internal diameter and 120µm are then inserted in the outlet channels of the PDMS part. Finally, three copper electrodes having outer diameter of 500μm are inserted from the top of the PDMS holder. The nozzle to nozzle distance is kept at 3mm. The complete schematic of the multi-nozzle EHD inkjet printing

Fig. 19. Schematic illustration of the multi-nozzle EHD inkjet printing head fabrication process: (a) Simplified fabrication steps of mold preparation (b) Resulted PDMS holder having L-shaped channels for ink supply and clasping of glass capillaries (c) Complete

Figure 20 shows images of stable meniscus formed at the tip of individual nozzles. Cone-jets are formed at the tip of each nozzle i.e. nozzle 1, nozzle 2 and nozzle 3 at an applied DC

multi-nozzle EHD inkjet printing head (Khan et al 2011)

voltage and flow rate of 3.5kV and 20μl/h respectively.

**4.3 Multi-nozzle electrohydrodynamic printing** 

head is shown in Figure 19(c).

Fig. 20. Photographs of axisymmetric cone-jet established at the nozzles tips of multi-nozzle electrohydrodynamic inkjet printing head (Khan et al 2011)

Printing is performed by applying a DC voltage of 3.5kV and flow rate of 20μl/h to each nozzle. The nozzles to substrate distance is set as 300μm while substrate speed is kept constant at 10mm/sec. Figure 21 shows the high zoom static camera and optical microscope image of continuous silver tracks simultaneously printed by three nozzles on glass substrate without any defects such as bulges or coffee-ring effects. The average line width of the printed lines is 140μm.

Fig. 21. Camera and optical microscope image of continuous silver patterns printed on glass substrate by multi-nozzle printing at an applied voltage of 3.5 kV and flow rate of 20μlh (Khan et al 2011)

Electrohydrodynamic Inkjet – Micro Pattern Fabrication for Printed Electronics Applications 565

0.5mm/s. As clear from the figures, the best layer quality is achieved at a nozzle to substrate distances of 6 mm and 8 mm the dense layers is produced and particles are completely intact and no pores or islands are visible as in the case of nozzle to substrate distances of 13mm the layer is porous and contain voids. These pores will case defect in the functionality

Fig. 23. Operating envelope for the CIS ink, showing different modes (Muhammad et al.,

Fig. 24. FE-SEM micrographs of the deposited layer at stand-off distance of a. 6 mm, b. 8 mm, c. 10 mm, d. 13 mm, at substrate speed of 0.5 mm/s and flow rate of 150 ml/h

Electrohydrodynamic inkjet printing is relatively new but very power tool and process for the direct patterning of the functional materials on substrate. Electrohydrodynamic inkjet

of the deposited layer.

2010)

(Muhammad et al., 2010)

**5. Conclusions** 

Moreover, the SEM images of a typical printed line as shown in figure 22 also illustrates that nanoparticles are three-dimensionally interconnected with each other, which favorably affect the electrical conductivity.

Fig. 22. SEM image of continuous silver pattern deposited by multi-nozzle electrohydrodynamic inkjet printing (Khan et al 2011)
