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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 3 — Jan. 31, 2011
  • pp: 2573–2579
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Microelectrode fabrication by laser direct curing of tiny nanoparticle self-generated from organometallic ink

Bongchul Kang, Seunghwan Ko, Jongsu Kim, and Minyang Yang  »View Author Affiliations


Optics Express, Vol. 19, Issue 3, pp. 2573-2579 (2011)
http://dx.doi.org/10.1364/OE.19.002573


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Abstract

In this paper, we present a new laser direct patterning method that selectively cures nanoparticles self-generated from organometallic ink by proper thermal decomposition. This approach has several advantages in the curing rate, resolution and pattern quality compared with the conventional nanoparticle ink based direct laser curing method. It was found that a laser wavelength which is more weakly absorbed by the nanoparticles could produce a more stable and homogeneous curing condition. Finally, arbitrary shaped silver electrodes with narrow width and uniform profile could be achieved on a polymer substrate at a high curing rate of 25 mm/s. This process can be applied for flexible electronics fabrications on heat sensitive polymer substrates.

© 2011 OSA

1. Introduction

2. Self-generation of tiny nanoparticles

An organometallic silver (Ag) ink (Inktec Co., TEC-CO-010, 10% weight) was utilized as a precursor to generate tiny NPs during the processing. Silver/organic complexes, organometallic compounds, are produced by chemical reaction of silver oxide (Ag2O) and ammonium carbamates (H2NCO2NH4). The ammonium carbamates, chemical derivatives, are prepared by reacting dry carbon dioxide with aliphatic amines. The silver/organic complexes dissolve in isopropyl alcohol (C3H8O) used as solvent in the weight ratio of 4:6. The silver/organic complexes ink undergoes evaporation of the solvents by heating. And the Ag ions thermally decomposed from the residue silver/organic complexes are reduced to form Ag NPs. Finally, the Ag NPs are thermally grown and aggregated by continuous heating [11

11. Korea Patent 10–0727434–00–00.

]. These conversion processes occur almost concurrently. The organometallic ink is basically transparent and cannot be directly applied to LDC process development due to the absence of solid particles to directly absorb laser energy. However, a short thermal pre-baking below the sintering temperature, Ag NPs start to nucleate uniformly without agglomeration. Once the NPs are formed, a focused laser was irradiated to melt and transform the NPs into the continuous metal. Only the NPs where the laser was scanned will be molten and form continuous metal and other NPs will be simply washed away by organic solvent to leave metal patterns, as shown in Fig. 1(a), (b)
Fig. 1 (a) Schematics of the process steps: (i) spincoating of the organometallic ink at 1000 rpm on a soda-lime glass, (ii) pre-baking on a hotplate at 100 °C for 90 sec to create NPs, (iii) laser irradiation to induce local agglomeration and fusion of NPs into continuous metal microstructure, (iv) washing out the unexposed leftover ink. (b) Experiment setup (c) Variations of the thickness and absorbance (at 532 nm) of coated organometallic ink with the pre-baking time. (d) Statistical analysis of self-generated Ag NP size distribution and the corresponding TEM image after pre-baking for 90 sec.
.

The thickness and the optical absorption of the organometallic ink are important parameters for the process optimization. The transient change of those values of the organometallic ink was measured at various pre-baking time after spin-coating at 1000 rpm on a soda-lime glass (Fig. 1(c)). A baking temperature of 100 °C was carefully determined to acquire a uniform thickness and to avoid the agglomeration of NPs in preliminary experiments since the excessive increase of the baking temperature causes the spatial gradient of the pre-baked ink thickness. As shown in Fig. 1(c), the thickness converged to approximately 0.33 μm after 60 sec pre-baking while the optical absorption increased linearly with the pre-baking time. The optical absorption increase signifies the generation of nanoparticles from the organometallic ink. The statistical analysis on the NP size distribution after pre-baking for 90 sec was conducted by a transmission electron microscope (TEM) images as shown in Fig. 1(d). 88% of Ag NPs have a diameter below 3 nm and the average particle size is 2.54 nm with the standard deviation of 0.67 nm. It is clear that the uniform Ag NPs of 2~3 nm were self-generated inside the residual silver/organic complexes. As expected, it can be estimated that such tiny NPs were generated by the mild decomposition of the complexes and mild growth of the Ag NPs.

3. Interaction of laser and self generated nanoparticles

Applied laser wavelength for the pre-baked organometallic Ag ink is one of the most important parameter for successful LDC process development. The organometallic Ag ink pre-baked for 90 sec shows an absorption peak around the 480 nm wavelength due to the surface plasmon oscillation modes of self-generated 2-3 nm sized Ag NPs [14

14. B. Choi, H. Lee, S. Jin, S. Chun, and S. Kim, “Characterization of the optical properties of silver nanoparticle films,” Nanotechnology 18(7), 075706–075710 (2007). [CrossRef] [PubMed]

], as shown in Fig. 2(a)
Fig. 2 (a) Absorption spectrum of the organometallic ink before and after pre-baking (90 sec). (b) Optical microscope and scanning electron microscope image of the cured pattern by a 532 nm wavelength laser at 35 mW (upper line)/40 mW (lower line) at 10 mm/s scan rate. (c) Optical microscope image of the peeled off patterns at a laser power at 30 mW (λ = 532 nm) and at 10 mm/s scan rate. (d) Schematics of laser curing condition at two different laser wavelengths (e) Scanning electron microscope image of the cured pattern by a 1070 nm wavelength laser at 40 mW (λ = 1070 nm) and at 10 mm/s scan rate.
(red line). To study the laser wavelength dependency, two different wavelength lasers (highly absorbing wavelength: 532 nm, mildly absorbing wavelength: 1070 nm) were used for comparison. A continuous wave laser with 532 nm wavelength (Spectra-physics Millennia) with 10 µm (1/e2) beam diameter was employed to enhance the optical absorption of the NPs.

The experiments were carried out as follows. The organometallic ink spincoated at 1000 rpm for 15 sec on a soda-lime glass substrate, was pre-baked on a hot plate 100 °C for 90 sec. After selective laser curing, the unexposed leftover ink was removed by n-hexane, isopropyl alcohol and acetone sequentially. The cured patterns were then dried on the hot plate at 150 °C for 2 min to remove the residual solvents. As a result, many voids was observed on the surface of the patterns cured at laser power of 35 mW and 40 mW and a scan rate of 10 mm/s, as shown in Fig. 2(b). They might have caused by the explosive evaporation of the trapped gas and the un-decomposed silver/organic complexes by the intensive light absorption of the pre-generated Ag NPs on the surface. Although such voids on the surface could be reduced by applying lower laser power, the cured patterns were easily stripped from the substrate during the washing of the unexposed leftover ink, as shown in Fig. 2(c). This signifies that the NPs at the bottom surface were not sufficiently cured by laser because the 532 nm wavelength laser light is absorbed mainly on the surface but cannot penetrated down to the bottom of the NP film, as shown in Fig. 2(d). For such reasons, the thickness that the ink could be cured without the voids formation and the pattern stripping, was limited to approximately 100 nm.

To relieve the explosive evaporation and the pattern delamination problem, more mildly absorbed wavelength (1070 nm) continuous wave ytterbium fiber laser (IPG Photonics YLM-10W) than 532 nm wavelength was applied. With 1070 nm wavelength laser, a uniform line pattern with approximately 10 µm width and above 100 nm thickness could be successfully fabricated on glass substrates under the same curing condition without the voids formation and pattern delamination problem, as shown in Fig. 2(e). From these observations, it was concluded that the 1070 nm wavelength laser makes more favorable curing condition of the ink compared with the use of 532 nm. In other words, the laser wavelength with relatively low absorbance is preferable to the LDC of the pre-baked organometallic ink.

4. Results and discussions

Figure 4(a)
Fig. 4 (a) Optical microscope image of cured patterns on glass at a laser power of 200 mW (λ = 1070 nm) and a scan rate of 25 mm/s (b) Photograph of cured patterns on polyimide (PI) film at a laser power of 200 mW (λ = 1070 nm) and a scan rate of 25 mm/s on glass (c) Adhesion property test.
shows the demonstration of the arbitrary letter patterning on a glass substrate at a laser power of 200 mW and a curing rate of 25 mm/s. Due to the low temperature process nature such as the melting temperature drop for small NPs and the low thermal diffusion, our proposed process can produce a electrode on a heat sensitive polymer substrate, as shown in Fig. 4(b) [17

17. M. Aminuzzama, A. Watanabe, and T. Miyashita, “Direct writing of conductive silver micropatterns on flexible polyimide film by laser-induced pyrolysis of silver nanoparticle-dispersed film,” J. Nanopart. Res. 12(3), 931–938 (2010). [CrossRef]

]. The reliability of the electrodes is an important evaluation index for the current technique to be applied in the real electronics fabrication industry. To investigate the adhesion property of the laser processed pattern, a peeling test which is so called “scotch tape” method was conducted by using a conventional adhesive tape (3M). The strong adhesion of the laser processed pattern on the polymer substrate was proved after for 100 times scotch tape test, as shown in Fig. 4(c).

To check the electrical property characterization, resistivity of the patterns was measured to be 5.7 μΩ·cm. Although this value is about 3.5 times higher than that of bulk Ag (1.6 μΩ·cm), it was regarded as an enough good quality conductor to be used for high performance electronics. The resistance could be further improved by increasing Ag content in the organometallic ink.

5. Conclusion

We demonstrated that laser direct curing using the self-generation of tiny nanopartices (2~3 nm) from organometallic silver ink can improve the curing rate, resolution, cross-sectional profile, and surface roughness of the pattern compared with conventional methods using metal NPs dispersed inks. A longer wavelength with relatively low absorption was suitable to cure the pre-baked ink compared with a shorter wavelength near the surface plasmon mode peak. The determination of the optimized wavelength will be discussed in follow up research. The diverse substrate material choice including flexible polymer and the high quality metal patterning with low resistivity and strong adhesion on the substrate make our approach as a strong potential approach for flexible electronics fabrication on a heat sensitive polymer substrate. Therefore, this method is expected to contribute to continuing advance of fabrication of the flexible electronic devices, such as flexible display [18

18. A. C. Siegel, S. T. Phillips, M. D. Dickey, N. Lu, Z. Suo, and G. M. Whitesides, “Foldable Printed Circuit Boards on Paper Substrates,” Adv. Funct. Mater. 20(1), 28–35 (2010). [CrossRef]

], flexible solar cell [19

19. M. Pagliaro, R. Ciriminna, and G. Palmisano, “Flexible solar cells,” ChemSusChem 1(11), 880–891 (2008). [CrossRef] [PubMed]

], and wearable PC [20

20. J. A. Rogers, T. Someya, and Y. Huang, “Materials and mechanics for stretchable electronics,” Science 327(5973), 1603–1607 (2010). [CrossRef] [PubMed]

].

References and links

1.

M. Aminuzzaman, A. Watanabe, and T. Miyashita, “Fabrication of conductive silver micropatterns on an organic–inorganic hybrid film by laser direct writing,” Thin Solid Films 517(20), 5935–5939 (2009). [CrossRef]

2.

N. R. Bieri, J. Chung, S. E. Haferl, D. Poulikakos, and C. P. Grigoropoulos, “Microstructuring by printing and laser curing of nanoparticle solutions,” Appl. Phys. Lett. 82(20), 3529–3531 (2003). [CrossRef]

3.

A. Watanabe, Y. Kobayashi, M. Konno, S. Yamada, and T. Miwa, “Direct Drawing of Ag Microwiring by laser-induced pyrolysis of film prepared from liquid-dispersed metal nanoparticles,” Jpn. J. Appl. Phys. 44(23), 740–742 (2005). [CrossRef]

4.

N. R. Bieri, J. Chung, D. Poulikakos, and C. P. Grigoropoulos, “Manufacturing of nanoscale thickness gold lines by laser curing of a discretely deposited nanoparticle suspension,” Superlattices Microstruct. 35(3-6), 437–444 (2004). [CrossRef]

5.

J. Chung, S. Ko, N. R. Bieri, C. P. Grigoropoulos, and D. Poulikakos, “Conductor microstructures by laser curing of printed gold nanoparticle ink,” Appl. Phys. Lett. 84(5), 52–54 (2004). [CrossRef]

6.

N. R. Bieri, J. Chung, D. Poulikakos, and C. P. Grigoropoulos, “An experimental investigation of microresistor laser printing with gold nanoparticle-laden inks,” Appl. Phys., A Mater. Sci. Process. 80(7), 1485–1495 (2005). [CrossRef]

7.

S. Ko, H. Pan, C. P. Grigoropoulos, C. K. Luscombe, J. M. J. Fréchet, and D. Poulikakos, “Air stable high resolution organic transistors by selective laser sintering of ink-jet printed metal nanoparticles,” Appl. Phys. Lett. 90(14), 141103 (2007). [CrossRef]

8.

T. Baldacchini, A. C. Pons, J. Pons, C. N. Lafratta, J. T. Fourkas, Y. Sun, and M. J. Naughton, “Multiphoton laser direct writing of two-dimensional silver structures,” Opt. Express 13(4), 1275–1280 (2005). [CrossRef] [PubMed]

9.

S. H. Ko, H. Pan, C. P. Grigoropoulos, C. K. Luscombe, J. M. J. Fréchet, and D. Poulikakos, “All inkjet printed flexible electronics fabrication on a polymer substrate by low temperature high resolution selective laser sintering of metal nanoparticle,” Nanotechnology 18(34), 345202 (2007). [CrossRef]

10.

S. H. Ko, H. Pan, C. P. Grigoropoulos, C. K. Luscombe, J. M. J. Fréchet, and D. Poulikakos, “Lithography-free high-resolution organic transistors on polymer substrate by low temperature selective laser ablation of inkjet printed nanoparticle film,” Appl. Phys. A: Mater. Sci. Process. 92(3), 579–587 (2008). [CrossRef]

11.

Korea Patent 10–0727434–00–00.

12.

P. A. Buffat and J. P. Borel, “Size effect on the melting temperature of gold particles,” Phys. Rev. A 13(6), 2287–2298 (1976). [CrossRef]

13.

X. Li, H. Li, J. Liu, X. Qi, and X. Zeng, “Conductive line preparation on resin surfaces by laser micro-cladding conductive pastes,” Appl. Surf. Sci. 233(1-4), 51–57 (2004). [CrossRef]

14.

B. Choi, H. Lee, S. Jin, S. Chun, and S. Kim, “Characterization of the optical properties of silver nanoparticle films,” Nanotechnology 18(7), 075706–075710 (2007). [CrossRef] [PubMed]

15.

S. Sun, L. Zhang, and S. Jahanshahi, “From viscosity and surface tension to marangoni flow in melts,” Metall. Mater. Trans., B, Process Metall. Mater. Proc. Sci. 34(5), 517–523 (2003). [CrossRef]

16.

P. Beckmann, and A. Spizichino, The Scattering of Electromagnetic Waves from Rough Surfaces (Pergamon Press. Oxford. 1963).

17.

M. Aminuzzama, A. Watanabe, and T. Miyashita, “Direct writing of conductive silver micropatterns on flexible polyimide film by laser-induced pyrolysis of silver nanoparticle-dispersed film,” J. Nanopart. Res. 12(3), 931–938 (2010). [CrossRef]

18.

A. C. Siegel, S. T. Phillips, M. D. Dickey, N. Lu, Z. Suo, and G. M. Whitesides, “Foldable Printed Circuit Boards on Paper Substrates,” Adv. Funct. Mater. 20(1), 28–35 (2010). [CrossRef]

19.

M. Pagliaro, R. Ciriminna, and G. Palmisano, “Flexible solar cells,” ChemSusChem 1(11), 880–891 (2008). [CrossRef] [PubMed]

20.

J. A. Rogers, T. Someya, and Y. Huang, “Materials and mechanics for stretchable electronics,” Science 327(5973), 1603–1607 (2010). [CrossRef] [PubMed]

OCIS Codes
(140.3390) Lasers and laser optics : Laser materials processing
(160.4890) Materials : Organic materials
(310.1860) Thin films : Deposition and fabrication
(310.3840) Thin films : Materials and process characterization
(160.4236) Materials : Nanomaterials

ToC Category:
Laser Microfabrication

History
Original Manuscript: December 16, 2010
Revised Manuscript: January 20, 2011
Manuscript Accepted: January 20, 2011
Published: January 26, 2011

Citation
Bongchul Kang, Seunghwan Ko, Jongsu Kim, and Minyang Yang, "Microelectrode fabrication by laser direct curing of tiny nanoparticle self-generated from organometallic ink," Opt. Express 19, 2573-2579 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-3-2573


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References

  1. M. Aminuzzaman, A. Watanabe, and T. Miyashita, “Fabrication of conductive silver micropatterns on an organic–inorganic hybrid film by laser direct writing,” Thin Solid Films 517(20), 5935–5939 (2009). [CrossRef]
  2. N. R. Bieri, J. Chung, S. E. Haferl, D. Poulikakos, and C. P. Grigoropoulos, “Microstructuring by printing and laser curing of nanoparticle solutions,” Appl. Phys. Lett. 82(20), 3529–3531 (2003). [CrossRef]
  3. A. Watanabe, Y. Kobayashi, M. Konno, S. Yamada, and T. Miwa, “Direct Drawing of Ag Microwiring by laser-induced pyrolysis of film prepared from liquid-dispersed metal nanoparticles,” Jpn. J. Appl. Phys. 44(23), 740–742 (2005). [CrossRef]
  4. N. R. Bieri, J. Chung, D. Poulikakos, and C. P. Grigoropoulos, “Manufacturing of nanoscale thickness gold lines by laser curing of a discretely deposited nanoparticle suspension,” Superlattices Microstruct. 35(3-6), 437–444 (2004). [CrossRef]
  5. J. Chung, S. Ko, N. R. Bieri, C. P. Grigoropoulos, and D. Poulikakos, “Conductor microstructures by laser curing of printed gold nanoparticle ink,” Appl. Phys. Lett. 84(5), 52–54 (2004). [CrossRef]
  6. N. R. Bieri, J. Chung, D. Poulikakos, and C. P. Grigoropoulos, “An experimental investigation of microresistor laser printing with gold nanoparticle-laden inks,” Appl. Phys., A Mater. Sci. Process. 80(7), 1485–1495 (2005). [CrossRef]
  7. S. Ko, H. Pan, C. P. Grigoropoulos, C. K. Luscombe, J. M. J. Fréchet, and D. Poulikakos, “Air stable high resolution organic transistors by selective laser sintering of ink-jet printed metal nanoparticles,” Appl. Phys. Lett. 90(14), 141103 (2007). [CrossRef]
  8. T. Baldacchini, A. C. Pons, J. Pons, C. N. Lafratta, J. T. Fourkas, Y. Sun, and M. J. Naughton, “Multiphoton laser direct writing of two-dimensional silver structures,” Opt. Express 13(4), 1275–1280 (2005). [CrossRef] [PubMed]
  9. S. H. Ko, H. Pan, C. P. Grigoropoulos, C. K. Luscombe, J. M. J. Fréchet, and D. Poulikakos, “All inkjet printed flexible electronics fabrication on a polymer substrate by low temperature high resolution selective laser sintering of metal nanoparticle,” Nanotechnology 18(34), 345202 (2007). [CrossRef]
  10. S. H. Ko, H. Pan, C. P. Grigoropoulos, C. K. Luscombe, J. M. J. Fréchet, and D. Poulikakos, “Lithography-free high-resolution organic transistors on polymer substrate by low temperature selective laser ablation of inkjet printed nanoparticle film,” Appl. Phys. A: Mater. Sci. Process. 92(3), 579–587 (2008). [CrossRef]
  11. Korea Patent 10–0727434–00–00.
  12. P. A. Buffat and J. P. Borel, “Size effect on the melting temperature of gold particles,” Phys. Rev. A 13(6), 2287–2298 (1976). [CrossRef]
  13. X. Li, H. Li, J. Liu, X. Qi, and X. Zeng, “Conductive line preparation on resin surfaces by laser micro-cladding conductive pastes,” Appl. Surf. Sci. 233(1-4), 51–57 (2004). [CrossRef]
  14. B. Choi, H. Lee, S. Jin, S. Chun, and S. Kim, “Characterization of the optical properties of silver nanoparticle films,” Nanotechnology 18(7), 075706–075710 (2007). [CrossRef] [PubMed]
  15. S. Sun, L. Zhang, and S. Jahanshahi, “From viscosity and surface tension to marangoni flow in melts,” Metall. Mater. Trans., B, Process Metall. Mater. Proc. Sci. 34(5), 517–523 (2003). [CrossRef]
  16. P. Beckmann, and A. Spizichino, The Scattering of Electromagnetic Waves from Rough Surfaces (Pergamon Press. Oxford. 1963).
  17. M. Aminuzzama, A. Watanabe, and T. Miyashita, “Direct writing of conductive silver micropatterns on flexible polyimide film by laser-induced pyrolysis of silver nanoparticle-dispersed film,” J. Nanopart. Res. 12(3), 931–938 (2010). [CrossRef]
  18. A. C. Siegel, S. T. Phillips, M. D. Dickey, N. Lu, Z. Suo, and G. M. Whitesides, “Foldable Printed Circuit Boards on Paper Substrates,” Adv. Funct. Mater. 20(1), 28–35 (2010). [CrossRef]
  19. M. Pagliaro, R. Ciriminna, and G. Palmisano, “Flexible solar cells,” ChemSusChem 1(11), 880–891 (2008). [CrossRef] [PubMed]
  20. J. A. Rogers, T. Someya, and Y. Huang, “Materials and mechanics for stretchable electronics,” Science 327(5973), 1603–1607 (2010). [CrossRef] [PubMed]

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