1. Ink-Jet Metalization
Dalla Costa Giovanni, Honkala Salomon, Kalliala Olli, Multaharju Miikka

2. Contents Ink jetting Nanoparticle properties Sintering Process
Electrical analysis

3. Jetting the ink Generally used print heads: Thermal bubble ink-jet
Piezoelectric ink-jet
Continuous stream ink-jet
Lin,L. Bai,X.

4. Generally used print heads:
Thermal bubble ink-jet
Piezoelectric ink-jet
High nozzle density→ compact devices, low printhead costs
Ink fluid limitations→ vaporizable ink
Coating formation on the heater→ degrades efficiency, reduces life time
Printheads expensive
Wide range of ink fluids
Controllable jetting mechanism
High reliability
Long life time
Professional and industrial applications
Ezzeldin. van den Bosch. Weiland.

5. Piezoelectric DOD print heads
Bend-mode
Squeeze-mode
Push-mode
Shear-mode
Cummins. Desmulliez.

6. Ink jetting mechanism with piezoelectric actuator
An electric voltage is applied to the actuator
The channel enlarges and a negative pressure is created
Negative pressure waves advance towards the reservoir and the nozzle
Pressure wave at the reservoir reflects as a positive wave (open end)
Pressure wave at the nozzle reflects and causes the meniscus to retract (closed end)
Reflected wave from the reservoir reaches to the middle just when the actuator decreases the volume of the channel thus creating an amplified wavefront
Amplified wave results the drop injection
Ezzeldin. van den Bosch. Weiland.

7. Actuation pulse control
To avoid crosstalk and residual vibrations that causes drop velocity and volume variation!
Crosstalk influences neighboring channels changing their pressure and volume.
Residual vibrations of individual channel affect in sequential ejections.
Model-based (differential wave equations) feedforward control
Model-free (optimized velocity) feedforward control
Ezzeldin. van den Bosch. Weiland.

8. Actuation pulse control
Normal actuation pulse leads to variation in drop volume and its velocity. Which consequently affects accuracy and printing quality.
Using feedforward control reduces such variations.
Ezzeldin. van den Bosch. Weiland.

9. One nozzle jetting test
Experiment shows a single nozzle ejecting 16 drops with 48 kHz.
Optimized pulse results in congruent lines excluding the first and the satellite.
Standard pulse produces drops traveling with different speeds and many of them are merged and misplaced.
Multichannel control with asynchronous actuation needed to minimize crosstalk.
Ezzeldin. van den Bosch. Weiland.

10. Minimum line width Some variables has to be set beforehand:
Cummins. Desmulliez.
Some variables has to be set beforehand:
1 < 1/Oh < 10
η ≈ 7…20*10-3 Pas
σ ≈ 25…35*10-3 N/m
v ≈ 4…8 m/s
ρ ≈ 1300 kg/m3
Pixel/D ≈ 1,5
We want D to be as small as possible.

11. Nanoparticle properties
The size and crystallographic structure of the nanoparticle has an essential role in determining the catalytic properties
Different crystal structures (and faces) such as nanoplates, nanocubic and near-spherical has different kind of properties
For silver example it has shown that the highest rate of reaction is achieved with nanocubic structure
Development towards increase of the more-reactive crystal planes and a decrease in less-reactive planes.
Other important properties than crystal structure are the ratio of surface area high vs (improves sintering in low temperatures), chemical stability, low chemical reactivity and high conductivity.

12. Nanoparticle properties: Shape factor example (silver)
The catalytic activity of the nanoparticles greatly depends on the crystal planes that the nanoparticles expose. For example in silver nanocubes shows higher activity than near-spherical or nanoplate particles because of their more reactive [100] planes.
On the other hand truncated triangle form nanoplate (A) has the most uniform structure which decreases the amount of grain boundaries  increase to conductivity
Fig.1. TEM images of A)truncated triangular nanoplates,
B)near-spherical nanoparticles, C)nanocube
[R. Xu, D.S. Wang, J.T. Zhang, Y.D. Li, Shape-dependent catalytic activity of
silver nanoparticles for the oxidation of styrene, Chem. Asian J. 1 (2006) 888–893.]

13. Nanoparticle properties: Metals for nanoparticles
Ag and Au are widely used due to their high chemical stability, low chemical reactivity and high conductivity.
Copper and nickel inks have also been produced but their tendency to oxidise can affect the lifetime of the ink or require the use of additional specialized coatings in printing in inert atmospheres
Ag nanoparticles can be sintered with a relatively low temperature( ˚C) when printed on substrates.
High surface area vs. volume is needed. For example Au nanoparticles with diameters less than 5nm are predicted to melt at ˚C

14. Challenges in nanoparticle properties
Low sintering temperatures needed due to use of flexible substrates
Metals have the tendency for agglomeration which further leads to increase in viscosity.
Clogging can be prevented by using specialised polymer coatings on the nanoparticles. However, removing of the surface needs high sintering temperatures which makes it unsuitable for flexible substrates.
Organic coating can be removed by photonic or microwave flash sintering at low temp.
As the nanoparticle size decreases so does the conductance as well. This means that the conductivity of sintered nanoparticle rarely matches to bulk form.
Because of the flexible electronic device polymer substrate, the sintering temperature must be lowered to 100˚C. In this temperature it is not clear yet how low resistance can be obtained in the printed film.

15. Sintering
Consolidate the metallic particles in order to create a continuous conductive path
Removing of organic solvent or binder
Diffusion process
Parameters
Particle size and shape
Process environment
Time and Temperature

16. Mechanism

17. Thermal Tm Nanoparticles < Tm Bulk T needed << Tm
up to 500˚C less
T needed << Tm ˚C
Increase of sintering time is useless
Long time is needed

18. Q. Huang et al. / Applied Surface Science 258 (2012) 7384– 7388

19. Light curing Use of a light source: IR, Camera-flash, Laser
Laser is a slow process
Difference of light absorption is important
250 times difference in temperature increase
Substrate interaction with light is important

20. D. Tobjörk et al. / Thin Solid Films 520 (2012) 2949–2955

21. Q. Huang et al. / Applied Surface Science 258 (2012) 7384– 7388

22. K.C. Yung et al. / Journal of Materials Processing Technology 210 (2010) 2268–2272

23. Plasma Need of vacuum chamber Not for thick layer Long time process
J. Mater. Chem., 2009, 19, 3384–3388

24. Sheet resistance Resistance in 3D conductor:
𝑅=𝜌 𝐿 𝐴 =𝜌 𝐿 𝑊𝑡
Combining resistivity with thickness:
𝑅= 𝜌 𝑡 𝐿 𝐴 = 𝑅 𝑠 𝐿 𝑊 [ohms/square; Ω/□]

25. Greek-cross test structure
𝑅 (0°) = 𝑉 𝐷𝐶 − 𝑉 𝐶𝐷 𝐼 𝐴𝐵 − 𝐼 𝐵𝐴
𝑅 (90°) = 𝑉 𝐴𝐷 − 𝑉 𝐷𝐴 𝐼 𝐵𝐶 − 𝐼 𝐶𝐵
𝑅 𝑠 = 𝜋 ln⁡(2) 𝑅 (avg)
(Van Der Pauw, 1958)
Enderling et al. (2006), “Sheet resistance measurement of non-standard cleanroom materials using suspended Greek cross test structures”, IEEE Transactions on Semiconductor Manufacturing, Vol. 19 No. 1, pp. 2-9.

26. High-frequency characterization
Many HF-applications (RFID, antennas…)
Losses due to microstructure at high frequencies , depending on printing parameters, inks and substrates
Transmission-line test structures
Use vector network analyzer to determine scattering parameters
Pynttäri et al. (2010), ”Application of Wide-Band Material Characterization Methods to Printable Electronics”, IEEE Transactions on Electronics Packaging Manufacturing, Vol. 33 No. 3, pp

27. Thanks