Single‐Shot Laser Additive Manufacturing of High Fill‐Factor Microlens Arrays

Abstract

Various methods have been adopted for the high-FF fabrication of MLA. Hexagonal arrays with 100% FF have been demonstrated by self-assembly methods based on dewetting, [7] localized water condensation, [8] or surface wrinkling, [9] but these approaches typically lack control in the design and positioning of the microlenses. In contrast, photolithography techniques have become the gold standard for the production of customized high-FF MLA. [10][11][12][13] Even if unrivaled industrial upscaling is possible, photolithography is optimized for planar substrates and requires multistep processing in expensive clean room facilities. More importantly, the need of masks imposes an additional limit in the degree of tunability of the MLA designs in timely fashion.Alternatively, direct-write technologies (DWTs) such as inkjet printing, [14] microdispensing, [15] two-photon polymerization, [16] laser-induced forward transfer (LIFT), [17,18] or multibeam interferencebased holography [19] enable the direct and maskless fabrication of polymeric microlenses and MLA with perfectly optical quality on a variety of substrates. In this case, though, the use of liquid prepolymers can result in merging of adjacent microlenses that seriously constraints the attainable FF of the arrays. [20] Recent works to improve the FF using DWTs include the fabrication of concave MLA using laser ablation followed by a replica molding step. [21,22] Despite excellent results in terms of uniformity and FF, this approach impedes the direct fabrication of MLA on substrates of interest. Furthermore, most DWTs require complex systems or ultrafast lasers for parallelization, which limit the overall throughput of these systems. Simply put, a low-cost and maskless technique capable of directly generating high-FF arrays at high-throughputs, with controlled geometry and at targeted positions on nonplanar substrates does not exist.In this work, we present a novel laser-based method for the realization of high-FF polymeric microlens arrays that addresses the limitations of traditional direct-write and photolithographic approaches. Our method, termed laser catapulting or LCP, exploits short (in the nanosecond scale) high-energy laser pulses to transfer polymeric solid microdiscs from a uniform film into targeted positions on a receiver substrate. After thermal reflow, namely the heating of the microdiscs above their glass transition temperature (T g ), planoconvex microlenses are obtained. Notably, the direct printing of discs in the solid-state enables the generation of highly close-packed High fill-factor microlens arrays (MLA) are key for improving photon collection efficiency in light-sensitive devices. Although several techniques are now capable of producing high-quality MLA, they can be limited in fill-factor, precision, the range of suitable substrates, or the possibility to generate arbitrary arrays. Here, a novel additive direct-write method for rapid and customized fabrication of high fill-factor MLA over a variety of substrates is demonstrated. This appro...

Laser‐Induced Forward Transfer: Fundamentals and Applications

“…Thus, it has been proved that the technique is feasible for printing biomolecules like DNA and some proteins, and therefore for biosensor fabrication (Sections and ), and more recently it has been shown that FF‐LIFT is especially suited for printing living cells for tissue engineering applications (Section ). Another set of materials very attractive to be printed with the film‐free approach are optical grade adhesives, normally used in the fabrication of micro‐optical components …”

Additive Manufacturing: Applications and Directions in Photonics and Optoelectronics

“…Typical requirements for the donor film are therefore a high absorption coefficient at the incident laser wavelength and high mechanical resistance upon bending to avoid internal rupture of the irradiated area during the deflection caused by expansion of the gas. [194,196,197] Microdisks of a positive photoresist (S1813) have been transferred onto flat and curved surfaces to form arrays of microlenses. [196] To this aim, the microdisks have been heated up to their glass transition temperature, which allow the formation of plano-convex microlenses through thermal reflow (Figure 12f-i).…”

“…[194,196,197] Microdisks of a positive photoresist (S1813) have been transferred onto flat and curved surfaces to form arrays of microlenses. [196] To this aim, the microdisks have been heated up to their glass transition temperature, which allow the formation of plano-convex microlenses through thermal reflow (Figure 12f-i). LIFT is highly versatile, allowing materials with diverse physicochemical properties to be assembled, and the geometries of the unitary building block to be varied during device building at variance with most AM methods, where the unitary building block is fixed by the laser spot size, the nozzle, or the printhead shape.…”

“…(f)-(i) Reproduced with permission. [196] Copyright 2018, Wiley-VCH. j,k) Images of a LED embedded in a polyimide substrate before (j) and after (k) printing of the interconnects.…”

Laser‐Induced Forward Transfer: A Digital Approach for Printing Devices on Regular Paper

“…In LIFT, the receiver substrate does not need to be rigid so that flexible substrates such as polymers or paper can be employed as well. [ 25–32 ] In contrast to IJP, the absence of nozzle sets almost no restriction on the rheological properties of the ink. Several studies have proved the feasibility of LIFT for printing liquids with a wide range of viscosities (from 1 to 10 6 mPa s), [ 33–35 ] and suspensions containing large loading particles (up to 30 µm).…”