Deep Proton Writing Research Articles

Deep proton writing of high aspect ratio SU-8 micro-pillars on glass

Deep proton writing (DPW) is a fabrication technology developed for the rapid prototyping of polymer micro-structures. We use SU-8, a negative resist, spincoated in a layer up to 720μm-thick in a single step on borosilicate glass, for irradiation with a collimated 12MeV energy proton beam. Micro-pillars with a slightly conical profile are irradiated in the SU-8 layer. We determine the optimal proton fluence to be 1.02×104μm−2, with which we are able to repeatably achieve micro-pillars with a top-diameter of 138±1μm and a bottom-diameter of 151±3μm. The smallest fabricated pillars have a top-diameter of 57±5μm. We achieved a root-mean-square sidewall surface roughness between 19nm and 35nm for the fabricated micro-pillars, measured over an area of 5×63.7μm. We briefly discuss initial testing of two potential applications of the fabricated micro-pillars. Using ∼100μm-diameter pillars as waveguides for gigascale integration optical interconnect applications, has shown a 4.7dB improvement in optical multimode fiber-to-fiber coupling as compared to the case where an air–gap is present between the fibers at the telecom wavelength of 1550nm. The ∼140μm-diameter pillars were used for mold fabrication with silicone casting. The resulting mold can be used for hydrogel casting, to obtain hydrogel replicas mimicking human tissue for in vitro bio-chemical applications.

Deep proton writing with 12 MeV protons for rapid prototyping of microstructures in polymethylmethacrylate

Deep proton writing (DPW) is a fabrication technology developed for the rapid prototyping of polymer microstructures. We use polymethylmethacrylate (PMMA) substrates, which act as a positive resist, for irradiation with a collimated 12-MeV energy proton beam. Using 12 MeV enables the irradiation of increasingly thick PMMA substrates with less conicity of the sidewalls compared to the lower energies used in previous work. A microhole of 47.7 μm diameter over a depth of 1 mm is achieved, leading to a maximum aspect ratio of 21∶1. The sidewalls of the irradiated structures show a slightly conical shape and their root-mean-square surface roughness is lower than 50 nm averaged over 72 measured areas of 56 μm×44 μm. This means that DPW components have optical surface quality sidewalls for wavelengths larger than 400 nm. Based on the trade-off among the sidewall roughness, conicity, and the development time, we determine that the optimal proton fluence for 12-MeV DPW in PMMA is 7.75×106 μm−2. Finally, we discuss some high aspect ratio microstructures with optical surface quality that were created with DPW to be used for a myriad of applications, such as micromirrors, microlenses, optofluidic devices, and high-precision alignment structures for single-mode optical fiber connectors.

Hot-embossing replication of self-centering optical fiber alignment structures prototyped by deep proton writing

This paper presents the hot-embossing replication of self-centering fiber alignment structures for high-precision, single-mode optical fiber connectors. To this end, a metal mold insert was fabricated by electroforming a polymer prototype patterned by means of deep proton writing (DPW). To achieve through-hole structures, we developed a postembossing process step to remove the residual layer inherently present in hot-embossed structures. The geometrical characteristics of the hot-embossed replicas are compared, before and after removal of the residual layer, with the DPW prototypes. Initial measurements on the optical performance of the replicas are performed. The successful replication of these components paves the way toward low-cost mass replication of DPW-fabricated prototypes in a variety of high-tech plastics.

Plastic light coupler for absorbance detection in silicon microfluidic channels

We present a micro-optical system for ultraviolet/visible absorbance detection in silicon microfluidic channels, which consists of a micro-optical light coupler placed on top of the silicon fluidic channel to probe the molecules under test with laser light. We use nonsequential optical ray-tracing simulations to model the system and to optimize its performance with respect to optical efficiency and system complexity. Deep Proton Writing is used to prototype the plastic light coupler and its spacer baseplate which contains marks to align the micro-optics with respect to the microfluidic channel and which allows for an accurate control of the position of the micro-optics with respect to the excitation source. We demonstrate the proof of concept of this microfluidic light probe by measuring standard samples of coumarin 102 dye with concentrations between 0.6 µM and 6 mM. Calibrating the system yields a detection limit of 4.3 µM. To conclude, we show that the concept of this microfluidic detection system is generic in that it can be applied at different positions on different microfluidic channel configurations.

Deep Proton Writing for the rapid prototyping of polymer micro-components for optical interconnects and optofluidics

The use of photonics in data communication and numerous other industrial applications brought plenty of prospects for innovation and opened up different unexplored market opportunities. This is a major driving force for the fabrication of micro-optical and micro-mechanical structures and their accurate alignment and integration into opto-mechanical modules and systems. To this end, we present Deep Proton Writing (DPW) as a powerful rapid prototyping technology for such micro-components. The DPW process consists of bombarding polymer samples (PMMA or SU-8) with swift protons, which results after chemical processing steps in high-quality micro-optical components. One of the strengths of the DPW micro-fabrication technology is the ability to fabricate monolithic building blocks that include micro-optical and mechanical functionalities which can be precisely integrated into more complex photonic systems. In this paper we comment on how we shifted from using 8.3 to 16.5MeV protons for DPW and give some examples of micro-optical and micro-mechanical components recently fabricated through DPW, targeting applications in optical interconnections and in optofluidics.

Hot Embossing of Microoptical Components Prototyped by Deep Proton Writing

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this letter, we present the replication of out-of-plane coupling microcomponents using hot embossing, through the fabrication of a metal mould by electroforming a polymer template patterned by means of deep proton writing (DPW). We compare the surface roughness and the optical performance of the hot embossed replicas with the DPW prototypes and can conclude that the replicated components exhibit only a small increase in surface roughness and a very small decrease in coupling performance. This paves the way towards low-cost mass replication of DPW-fabricated prototypes in a variety of high-tech plastics. </para>

Characterization of Refractive Index Distribution in Spherical Microlenses Fabricated by Deep Proton Writing

In this letter, we present the results of the refractive index measurements on deep proton writing microlenses. The measurement method used is interferometric tomography. It is a nondestructive method for the determination of the 3-D internal refractive index distributions. The influence of the different fabrication steps on the refractive index distribution is discussed.

Deep proton writing: a rapid prototyping polymer micro-fabrication tool for micro-optical modules

One of the important challenges to deploying the emerging breed of nanotechnology components is interfacing them with the external world, preferably accomplished with low-cost micro-optical devices. In our labs at the Vrije Universiteit Brussel (VUB), we are therefore focusing on the continuous development of a rapid prototyping technology for the fabrication of micro-optical modules. In this technology, which we call deep proton writing (DPW), we bombard polymer samples with swift protons, which will result after chemical processing steps in high quality micro-optical components. The strength of the DPW micro-machining technology is the ability to fabricate monolithic building blocks that include micro-optical and mechanical functionalities which can be precisely integrated into more complex photonic systems. The DPW technology is furthermore compatible with low-cost mass-replication techniques such as micro-injection moulding and hot embossing. In this paper we give an overview of the process steps of the technology and the characteristic qualities we can expect from the components made by DPW. The general overview of the technology is followed by three case studies of different micro-optical components that were fabricated at our labs: (i) two-dimensional fibre connectors, (ii) out-of-plane couplers for optical waveguides embedded in printed circuit boards (PCBs), (iii) intra multi-chip-module (MCM) level optical interconnection via free space optical modules.