1. Ink Jetted Metallization Mikko Ruskola Marianne Joutti Anas Al-Azawi Jukka Heikkurinen Sasha Hoshian

2. 2 Contents Inkjetting Ink formulation and nanoparticle properties Sintering Electrical characterization Smallest line width

3. 3 Ink Jetting (1/5) Etch-mask patterning Deposition and patterning simultaneously Low temperature process Large area devices All additive process Wide variety of ink materials Source: IDTechEx

4. 4 Ink Jetting (2/5) Continuous InkJet Droplet charging Deflection Ink recirculation Can degrade inks Unusually used for functional materials Annu. Rev. Mater. Res. 2010. 40:395–414

5. 5 Ink Jetting (3/5) Drop-on-Demand Piezoelectric actuator or Resistive heater Vapour bubble near the nozzle Annu. Rev. Mater. Res. 2010. 40:395–414

6. 6 Ink Jetting (4/5) Piezoelectric DoD No thermal degradation of ink Usually for functional materials Nozzle size -> 20-30um Droplet volume -> 10-20pl Droplet generation -> 1-20kHz Droplet diameter on paper -> 20-50um Narrowest linewidth -> between 14 and 25um (without surface treatment)

7. 7 Ink Jetting (5/5) Ink Jetting can be divided to –Droplet formation –Aligning droplets and their interaction with the substrate –Sintering or drying on the substrate Performance –Carrier mobility –Reduction of traps –Materials compatibility Possible applications –Sensors, actuators, displays, rapid prototyping

8. 8 Ink formulation Properties of the ink The most critical parameters for selecting an ink are its fluid properties such as viscosity, density and surface tension. They determine the “jettability” of the material, influence the size and shape of the deposited droplets and indicate the wetting of the substrate and the presence of satellite drops The viscosity of the ink must be low enough to enable the refill of the ink reservoir in about 100 ms and the expulsion of a drop out of the nozzle by the transient pressure pulse. The surface tension must be high enough to prevent unwanted dripping from the nozzle but low enough such that the ejected droplet can break away from the nozzle The best values of these properties depend on used printer but on average for inkjet printing the viscosity should be within the range of 1- 25mPa · s and the surface tension would be between 25 and 50mNm21. Source: Inkjet printing of conductive materials:a review. Gerard Cummins and Marc P.Y. Desmulliez. Circuit World. Volume 38 · Number 4 · 2012 · 193–213

9. 9 Ink formulation The fluid properties part I

10. 10 Source: Inkjet printing of conductive materials:a review. Gerard Cummins and Marc P.Y. Desmulliez. Circuit World. Volume 38 · Number 4 · 2012 · 193–213 Ink formulation The fluid properties part II

11. Ink formulation Different ink types 11 Different types of used conductive inks include colloidal suspensions of nanoparticles, organometallic compounds in solution and conductive polymers. Indepent on the conductive component or solvent used these inks will often contain other constituents such as dispersants, adhesion promoters, surfactants, thickeners, stabilizing agents and other additives Depending on the conductive agent these inks can be distributed on following categories Organometallic inks which are not easily clogged and have high conductivities Conductive polymers (PEDOT, polyaniline and Carbon nanotubes etc.) Nanoparticle inks (=> continues in the next slide) Source: Inkjet printing of conductive materials:a review. Gerard Cummins and Marc P.Y. Desmulliez. Circuit World. Volume 38 · Number 4 · 2012 · 193–213

12. Different ink types Nanoparticle inks 12 Nanoparticle inks are a suspension of nanoparticles either in water or an organic solvent such as toluene, ethylene glycol or cyclohexanone. The solvent chosen must be easily evaporable once deposited but not so quickly that it forms a viscous film to the top of nozzle which prevents drop ejection. Nanoparticles are commonly used in inks because they are easy to make,can be dispersed in high concentrations and have good electrical conductivities. According to G. Cummins and M. Desmulliez, the particle size should be less than 1/100 of the diameter of the nozzle. In addition, “particles should also have a narrow distribution of sizes and be homogeneously distributed throughout the solution to ensure good jetting.” The advantage of these inks is that high surface area to volume ratio of these particles enables sintering at temperatures lower than that of the bulk material. For example, gold nanoparticles with diameters less than 5nm are predicted to melt at 300-500 °C, compared to the melting point of bulk gold (1 064 °C) Source: Inkjet printing of conductive materials:a review. Gerard Cummins and Marc P.Y. Desmulliez. Circuit World. Volume 38 · Number 4 · 2012 · 193–213

13. 04-05-2015 13 Metallic nano-particle inks are widely applied in realizing conductive structures in printed electronics Typically Au or Ag nano-particles (d = 2-50 nm) encapsulated with protective shell and dispersed in a liquid Sintering temperature is 100 – 300 deg. C Thermal oven sintering has several drawbacks: 1)Time consuming ( up to 60 min ) 2)Low cost sintering substrates are prone to shrinkage 3)Undesired gas emission from the heated substrate 4)The entire substrate has to be sintered ( no option for selectivity )

14. 04-05-2015 14 Au nano-particles 2 – 3 nanometer in diameter are protected by SAM and dispersed in the solvent Local laser heating is advantageous because 1)Reduced heat affected zone and more efficient energy is induced 2)Laser sintered gold lines showed much greater uniformity and higher resolution ( few microns ) than those sintered by heater ( ~ 100 µm )

15. 04-05-2015 15 OFET is fabricated by inkjet printing by inkjet printing and selective laser sintering

16. 04-05-2015 16 Ink used is dispersion of silver nano- particles in Tetradecane The substrate is polymer PI ( T g = 385 o C) Unsintered non-conductive silver lines are treated in microwave reactor operating in constant power mode ( 300 W) SEM inspection of silver tracks after sintering. The sintered lines consist of clusters with diameter ~ 500 nm

17. 04-05-2015 17 A method for sintering nano particles by applying voltage over printed structure. Advantages of electrical sintering: 1)Reduced substrate heating 2)In-situ monitoring of the sintering quality 3)Short sintering time 4)The conductivity can be determined and can reach high values

18. Electrical characterization Metallization  Fabrication of different electrical components (Interconnectors, Transistors, Capacitors, …)  Electrical parameters (Resistance, Impedance, Current, Voltage, mobility, …)

19. Electrical characterization Metallization 19

20. Electrical characterization Metallization 20 Interconnectors time-domain frequency-domain TDR/TDT(Time Domain Reflectrometer s-parameter /Time Domain Transmission) characteristic impedance, propagation delay, dielectric constant, Impedance profile, series resistance of the samples

21. Electrical characterization Metallization 21 TDR TDT Equivalent Circuit at DC

22. Electrical characterization Metallization 22  OTFTs current-voltage characteristics 1. the I ds vs V ds curve, named output characteristic, where the gate voltage is kept constant. 2. the I ds vs V gs curve, named transfer characteristic, where the drain voltage is kept constant. Two Keithley 2600 source meters

23. Electrical characterization Metallization 23 Output characteristics of an inkjet printed OTFT with L=50 µm and W=2 mm

24. Electrical characterization Metallization 24 transfer plot of OTFTs with gravure-printed semiconductor and dielectric layers

25. 25 Direct wire printing with width of few microns is possible with NanoPaste(tm) NanoPaste consists of 5 nm silver particles Ink drop size is only 2 pl which is 16 μm in diameter No surface pretreatment or hydrophobic/hydrofilic patterning is needed Source: Inkjet printing of conductive materials:a review. Gerard Cummins and Marc P.Y. Desmulliez. Circuit World. Volume 38 · Number 4 · 2012 · 193–213 Ultra fine lines using Ink jet printing

26. 26 Ultra fine lines using Ink jet printing Source: ”Super-fine ink-jet printing: toward the minimal manufacturing system” Kazuhiro Murata et al. 2005 DOI 10.1007/s00542-005-0023-9

27. 27 Ultra fine lines using Ink jet printing *Source: Nature Materials ”Dewetting of conducting polymer inkjet droplets on patterned surfaces” J. Z. Wang et al. 2004. If hydrofilic/-phobic pretreatment is possible a line width of 500 nm can be achieved This has been demonstrated* using poly(3,4-ethylenedioxythiophene) ink SiO 2 substrate that is modified with fluorinated SAM

28. 28 Conclusions Piezoelectric D-o-D for functional inks Ink properties can be estimated by dimensioless fluid numbers Three sintering techniques are introduced enabling formation of uniform high resolution metallic lines in a fast way Most important way of resistance measurement is four-point probe for electrical characterization Line width of inkjetted wires can be less than 1 micron with masking

29. 29 Thanks!