Full Length ArticleFacile fabrication of microlenses with controlled geometrical characteristics by inkjet printing on nanostructured surfaces prepared by combustion chemical vapour deposition
Graphical abstract
Introduction
Microlenses and microlens arrays are used to redirect light and improve collection efficiency in sensing devices, light-coupling in optical fiber communication systems, light extraction from light emitting diodes (LEDs) or optical performance in displays [1], [2], [3], [4], [5], [6], [7], [8], [9]. In many of these applications, the precise positioning of microlenses with short focal lengths and high numerical aperture (NA) is highly demanded. For example, microball lenses beyond the hemispherical geometry, adequately integrated and precisely positioned, are useful elements to efficiently focus light from a laser diode into single-mode fibers for communication systems. The development of photolithographic techniques, that enabled the extraordinary progress of the semiconductor industry, also facilitated the first practical miniaturization of lenses into microlenses [10]. These were prepared starting with circular microposts created by using a photoresist. The posts were later thermally treated to melt the resist leading, through a thermal reflow process, to a lens with a spherical profile dictated by surface tension. Curing of the photoresist ultimately stabilizes the final microlens shape [11], [12]. Other photolithographic approaches such as gray-scale microlens projection as well as other chemical or mechanical methods, for example hot embossing, have also been used in the production of microlens arrays with well-defined profiles redirecting light in a controlled fashion [13], [14], [15], [16]. The preparation of microlenses has also been undertaken using inkjet printing technology. Compared to photolithographic or embossing based methods, inkjet printing digitally positions droplets of ink leading to microlenses at well-defined locations on virtually any type of substrate, with no contact and minimal post-processing [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30].
Typically a polymerizable material solution is used as a base material for the microlens fabrication. The final refractive index of the microlens, key in its optical performance, can be tailored to a large extent through the ink formulation. A solvent, not present in the final solid lens, is usually employed to adjust the ink properties so jetting is possible without clogging of the printhead nozzle [19], [23], [24], [27]. The prepolymer solution is then jetted and deposited on top of a substrate. After all the solvents are evaporated, the so generated microlens, can be fixed by polymerization [18], [19]. Disadvantageously, this solvent evaporation post-printing step complicates the manufacturing process and it can additionally result in undesired changes in the geometry and the optical properties of the final solid microlenses.
Besides the intrinsic properties of the ink, the interaction of this ink with the target substrate is also of key importance for the resultant microlens geometry and therefore for its optical characteristics. For the typical volumes of single droplets deposited by inkjet printing, their final shape on the substrate is not influenced by gravity, generally reaching a spherical cap geometry [31]. For a flat surface, the solid angle of the spherical cap is dictated by the contact angle and their volume determined by the amount of deposited ink [32]. For example, in order to generate microlenses with high NA, modified substrates leading to sessile ink droplets with large contact angles have been typically targeted. Simple chemical modification of conventional glass with fluorosilanes has been used for this purpose however the achieved ink contact angles are limited and therefore the lens NA is limited too (NA values around 0.4 are typically achieved) [18]. Besides, photolithographically structured substrates with pillars have been generated to create, on top of them, high NA microlenses by inkjet printing, however the preparation process is complex and involves sophisticated and expensive equipment [20], [21], [22], [33], [34]. Interestingly, Luo et al [27] prepared nanostructured layers consisting on fluorinated nanopillars to create high NA microlenses on top of these layers. The method to prepare them comprises the generation of a thin ZnO seed layer (30 nm thick) onto a glass substrate using a radio frequency (RF) magnetron sputter-deposition technique. Afterwards, ZnO nanopillars are synthesized onto the substrate in an aqueous solution of zinc nitrate hexahydrate and methenamine in deionized water. Finally a C4F8 coating is done by inductively coupled plasma chemical vapour deposition process, using C4F8 and CHF3 gases. The so prepared surfaces can be used to generate microlenses beyond the hemisphere (contact angle of 115°). Overall, despite all these advances and the intense efforts, the developed techniques involve complicated steps, difficult to implement in an industrial environment and in a cost-effective way.
Here we report a facile, robust, cost-effective and high-throughput method for the preparation of microlenses with well-defined optical characteristics on flat substrates by inkjet printing technology. A solvent-free photoacid catalyzed hybrid organic–inorganic polymerizable formulation has been used as an ink for microlens preparation. The deposited ink is directly cured just after deposition without need of any evaporation post-printing step. As a result, the lens geometry is immediately fixed after deposition, with no post-processing, facilitating the control of the lens optical properties. In order to tune the contact angle of the prepolymer droplets, a simple two-step method to modify the receiving substrate has been developed. Firstly, the combustion chemical vapour deposition (CCVD) of a silane leads to a nanostructured layer on top of the substrate. Secondly, this layer is chemically coated with a fluorosilane by conventional chemical vapour deposition (CVD) [35]. The introduction of the nanoroughness on the surface by CCVD and its subsequent fluorination by CVD leads to larger contact angles of the photopolymerizable ink droplets and microball lenses beyond the hemisphere can be attained. The drops can be immediately fixed by ultraviolet (UV) photopolymerization. The preparation of microlenses with controlled geometrical characteristics using this simple method, compatible with a continuous industrial production process, together with the lens morphological and optical characterization are described in this paper.
Section snippets
Ink material
3-glycidoxypropyltrimethoxysilane (GPTMS), a monomer with an epoxy and a trialkoxysilane group, was purchased from Alfa Aesar (Haverhill, MA, USA). The epoxy resin Epikote 157, a monomer with eight epoxide groups, was obtained from Momentive (Waterford, NY, USA). Dimethoxydiphenylsilane (dPDMS), a disilane monomer bearing two aromatic rings was acquired from Aldrich (Madrid, Spain). Triarylsulfonium hexafluorophosphate salts (50% in propylene carbonate) purchased from Aldrich (Madrid, Spain)
Microlens ink material
To generate the microlenses by inkjet printing we use as ink a solvent-free photoacid catalyzed organic–inorganic hybrid formulation previously developed in our laboratory, named HRI ink [37]. The ink consists mainly of three different monomers: an organic–inorganic hybrid molecule named GPTMS (50 wt%), bearing an epoxy and a triethoxysilane group, the multifunctional epoxide Epikote 157 (25 wt%) and dPDMS (25 wt%) as disilane. These two last monomers, are expected to polymerize with the epoxy
Conclusions
In this work we have presented a facile and robust methodology for the preparation of microlenses with controlled geometrical characteristics on flat substrates by using inkjet printing technology. A solvent-free photocurable organic–inorganic hybrid formulation has been used as an ink for microlens fabrication. This ink uses no solvent and therefore can be cured immediately after printing, without any evaporation or annealing post-printing step, notably simplifying the microlens preparation
CRediT authorship contribution statement
Jorge Alamán: Conceptualization, Methodology, Investigation, Writing - original draft. Ana María López-Villuendas: Investigation. María López-Valdeolivas: Investigation. María Pilar Arroyo: Methodology, Investigation. Nieves Andrés: Methodology, Investigation. Carlos Sánchez-Somolinos: Conceptualization, Methodology, Writing - original draft.
Declaration of Competing Interest
The authors declared that there is no conflict of interest.
Acknowledgements
Carlos Sánchez Somolinos acknowledges funding from the Spanish Ministry project BIO2017-84246-C2-1-R, Gobierno de Aragón project LMP150_18 and FEDER (EU). Authors would like to acknowledge the use of Servicio General de Apoyo a la Investigación-SAI, Universidad de Zaragoza.
References (63)
- et al.
Microlens arrays for light extraction enhancement in organic light-emitting diodes: a facile approach
Org. Electron.
(2013) - et al.
Microplastic embossing process: experimental and theoretical characterizations
Sens. Actuators, A
(2002) - et al.
Deposition of micropatterned coating using an ink-jet technique
Thin Solid Films
(1999) - et al.
Deposition of optical microlens arrays by ink-jet processes
Thin Solid Films
(2001) - et al.
Fabrication of multi-scale micro-lens arrays on hydrophobic surfaces using a drop-on-demand droplet generator
Opt. Laser Technol.
(2015) - et al.
Fabrication of high numerical aperture micro-lens array based on drop-on-demand generating of water-based molds
Opt. Laser Technol.
(2015) - et al.
Direct fabrication of microlens arrays with high numerical aperture by ink-jetting on nanotextured surface
Appl. Surf. Sci.
(2013) - et al.
Micro-ball lens structure fabrication based on drop on demand printing the liquid mold
Appl. Surf. Sci.
(2016) - et al.
Flexible biconvex microlens array fabrication using combined inkjetprinting and imprint-lithography method
Opt. Laser Technol.
(2019) - et al.
Fabrication of microlens array with controllable high NA and tailored optical characteristics using confined ink-jetting
Appl. Surf. Sci.
(2018)
A new adhesive technology for all-ceramics
Dent. Mater.
Superhydrophobic surfaces: from natural to biomimetic to functional
J. Colloid Interface Sci.
Superhydrophobic and superoleophobic properties in nature
Mater. Today
Chemical structure and morphology of ultrathin combustion CVD layers on zinc coated steel
Appl. Surf. Sci.
A new concept of metal — resin adhesion using an intermediate layer of SiOx-C
Thin Solid Films
Improvement of adhesion strength of self-adhesive silicone rubber on thermoplastic substrates – comparison of an atmospheric pressure plasma jet (APPJ) and a Pyrosil® flame
Int. J. Adhes. Adhes.
Fabrication, testing and integration technologies of polymer microlens for Pt/Si schottky-barrier infrared charge coupled device applications
Chinese Phys. Lett.
Semi-ellipsoid microlens simulation and fabrication for enhancing optical fiber coupling efficiency
Sensor Actuat. A-Phys.
Digital cameras with designs inspired by the arthropod eye
Nature
Microlens arrays by direct-writing inkjet print for LCD backlighting applications
J. Disp. Technol.
Measurement and modeling of microlenses fabricated on single-photon avalanche diode arrays for fill factor recovery
Opt. Express
Design, fabrication, and characterization of thermoplastic microlenses for fiber-optic probe imaging
Appl. Opt.
Microlens arrays for integral imaging system
Appl. Opt.
Efficiency improvement and image quality of organic light-emitting display by attaching cylindrical microlens arrays
Opt. Express
Light to shape the future: from photolithography to 4D printing
Adv. Optical Mater.
Technique for monolithic fabrication of microlens arrays
Appl. Optics
Micro-ball lens array fabrication in photoresist using PTFE hydrophobic effect
Microsyst. Technol.
Fabrication of arrays of microlenses with controlled profiles using gray-scale microlens projection photolithography
Langmuir
Fabrication, characterization, and applications of microlenses
Appl. Optics
Fabrication of polymer microlens array with controllable focal length by modifying surface wettability
Opt. Express
Fabrication of high quality and low cost microlenses on a glass substrate by direct printing technique
Appl. Optics
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