A novel thermal reflow method for the fabrication of microlenses with an ultrahigh focal number

Wang, M.; Yu, Weixing; Wang, Tao; Han, Xiumei; Gu, Erdan; Li, X.

doi:10.1039/c5ra00957j

Cited by 37 publications

(22 citation statements)

References 22 publications

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“…Some other applications are also possible with the proposed dome-shaped structure. [26][27][28] The structures were made in the form of an array and could be used as a mold to make a microlens array.…”

Section: Applications Of the Proposed Processmentioning

confidence: 99%

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Unconventional Use of a Photoresist as a Nitrogen Gas Generator Forming Transparent Dome‐Shaped Microcavities

Han

Seo

et al. 2015

Adv Eng Mater

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The phenomenon that a common positive photoresist (PR) releases nitrogen (N2) gas when exposed to UV light has never been used or received any particular attention. Fabrication process to intentionally trap the generated N2 gas during UV exposure, thereby, to form the microcavity structure is proposed. Various dome-shaped structures are demonstrated with the proposed process. This process is best suited to make various cavity packages in microelectromechanical systems. Also, microlens arrays are fabricated using plastic replication of the dome-shaped microcavities. All these results lead to a different view of the conventional positive photoresist and inspire various new applications.

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Section: Applications Of the Proposed Processmentioning

confidence: 99%

“…Because the domeshaped structure could easily be formed in a size range from micrometers to millimeters, the proposed technique is a promising method for making lens arrays in sizes not usually achievable by micromachining or macromachining. [26][27][28]…”

Section: Applications Of the Proposed Processmentioning

confidence: 99%

Unconventional Use of a Photoresist as a Nitrogen Gas Generator Forming Transparent Dome‐Shaped Microcavities

Han

Seo

et al. 2015

Adv Eng Mater

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“…In addition, these lenses can provide a large DOF due to a small focal length and a small aperture diameter, which allows near-to-infinity imaging 17 . Recently, diverse microfabrication methods of microlens arrays, such as thermal reflow, inkjet printing or 3D direct laser writing, have been actively incorporated with biologically inspired cameras 15,18,19 . However, these methods are still under development to prevent optical crosstalk between microlenses for high-contrast imaging.…”

Section: Introductionmentioning

confidence: 99%

Biologically inspired ultrathin arrayed camera for high-contrast and high-resolution imaging

et al. 2020

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Compound eyes found in insects provide intriguing sources of biological inspiration for miniaturised imaging systems. Here, we report an ultrathin arrayed camera inspired by insect eye structures for high-contrast and super-resolution imaging. The ultrathin camera features micro-optical elements (MOEs), i.e., inverted microlenses, multilayered pinhole arrays, and gap spacers on an image sensor. The MOE was fabricated by using repeated photolithography and thermal reflow. The fully packaged camera shows a total track length of 740 μm and a field-of-view (FOV) of 73°. The experimental results demonstrate that the multilayered pinhole of the MOE allows high-contrast imaging by eliminating the optical crosstalk between microlenses. The integral image reconstructed from array images clearly increases the modulation transfer function (MTF) by~1.57 times compared to that of a single channel image in the ultrathin camera. This ultrathin arrayed camera provides a novel and practical direction for diverse mobile, surveillance or medical applications.

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“…Hexagonal arrays with 100% FF have been demonstrated by self‐assembly methods based on dewetting, localized water condensation, or surface wrinkling, 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 . Even if unrivaled industrial upscaling is possible, photolithography is optimized for planar substrates and requires multistep processing in expensive clean room facilities.…”

Section: Introductionmentioning

confidence: 99%

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

Surdo

Carzino

Diaspro

et al. 2018

Advanced Optical Materials

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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...

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A novel thermal reflow method for the fabrication of microlenses with an ultrahigh focal number

Cited by 37 publications

References 22 publications

Unconventional Use of a Photoresist as a Nitrogen Gas Generator Forming Transparent Dome‐Shaped Microcavities

Unconventional Use of a Photoresist as a Nitrogen Gas Generator Forming Transparent Dome‐Shaped Microcavities

Biologically inspired ultrathin arrayed camera for high-contrast and high-resolution imaging

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

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