Dr. Tien-Jen Chang Profile

Dr. Tien-Jen Chang

at Technical Univ of Denmark

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Publications (2)

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Proceedings Article | 5 March 2021 Poster + Presentation + Paper

Submicron scale stereolithography using HD-DVD optical pickup unit

Tien-Jen Chang, Lukas Vaut, Martin Voss, Oleksii Ilchenko, Line Hagner Nielsen, Anja Boisen, En-Te Hwu

Proceedings Volume 11677, 1167718 (2021) https://doi.org/10.1117/12.2575936

KEYWORDS: 3D printing

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It is challenging for stereolithography systems to print submicron features without two-photon lasers. For the first time, we implement an HD-DVD optical pickup unit (OPU) for building a customized stereolithography 3D printer. The OPU equips a 405 nm single-photon laser and an objective lens with a numerical aperture of 0.65. This has a focal laser spot diameter of 430 nm (1/e²) and can thereby, achieve submicron scale features photopolymerization. Moreover, the OPU embeds astigmatic optical path and voice coil motor which can be used for closed-loop printing alignment and this increases printing stability significantly. The OPU 3D printing system integrates an XYZ linear stage, providing nanoscale positioning resolution and macroscale printing area (c.a. 50 X 50 X 25 mm). A commercial photo-resin is utilized for the assessment of the system performance. The OPU printer crosslinks structures ranging from tens of microns down to submicron scale by tuning the printing parameters (laser intensity, printing speed, and photo-resin thickness). After optimization of the system, the OPU printer achieved the highest printing resolution of 210 nm which is beyond conventional stereolithography systems. Furthermore, several microstructures have been printed for verifying multiple layer printing performance. In conclusion, the mass-produced, low-cost and compact size OPU can not only dramatically simplify the stereolithography 3D printer design, but also achieve submicron printing performance.

Proceedings Article | 5 March 2021 Presentation + Paper

Hacking blu-ray drives for high-throughput 3D printing

Edwin En-Te Hwu, Martin Voss, Tien-Jen Chang, Hsien-Shun Liao, Anja Boisen

Proceedings Volume 11677, 116770A (2021) https://doi.org/10.1117/12.2576491

KEYWORDS: 3D printing, Printing, Photopolymers, Spindles, Solids, Signal detection, Scanning electron microscopy, Raster graphics, Multilayers

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Conventional microscale 3D printing techniques mostly rely on the raster scanning method, which needs constant changing of printer head/light beam/substrate directions to print a solid structure. Therefore, throughput is a longstanding bottleneck and it is more challenging to print microfeatures in large areas. This study demonstrates the possibility of 3D printing microfeatures on a fast-spinning disc. A Blu-ray drives based high-throughput 3D printer (BRIGHT^3D) is developed to demonstrate the spin printing on disc concept and evaluate the highest linear printing speed. The BRIGHT^3D integrates two Blu-ray drives that are synchronized by a customized controller. The printing substrate is a standard Blu-ray RW disc spun by a spindle motor. Both drives utilize the same optical pick-up unit (OPU), which equips a voice coil motor (VCM) for the disc wobbling compensation. The bottom OPU detects the disc wobbling and feeds the VCM control signal back to top OPU for maintaining laser (405 nm, 658 microwatts) focused on the spinning substrate disc. The BRIGHT^3D can directly spin-coat (up to 6,440 rpm) commercial photopolymers with a controllable thickness on top of the substrate disc. The top OPU laser was switched with a frequency of 1~500 kHz (duty cycle: 80 %) for the preliminary spinning 3D printing evaluation. Microfeatures can be cured by the BRIGHT^3D while the disc is spinning at a speed of 265 rpm, which has a linear speed from inner diameter, 20 mm, to the outer diameter, 58.5 mm, of 0.55~1.63 meters per second. After removing the photopolymer residues by 75% ethanol, various microscale features on the disc can be seen and measured by scanning electron microscopy. Microscale lines (height/width: 1.43/8.25 microns) and dots (length: 5.97 microns) were successfully printed on the disc. The BRIGHT^3D is aiming for multiple layer printing on the disc to realize sophisticated features of high-throughput 3D printing in the near future.

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