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Proceedings Paper

Low cost rapid fabrication of vertical LVOF microspectrometer on-chip for MIR sensing
Author(s): Simon Chun Kiat Goh; Li Lynn Shiau; Nan Chen; Shurui Wang; Kailiang Chuan; Henrik Ernst; Chengkuo Lee; Beng Kang Tay; Chuan Seng Tan
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Paper Abstract

This paper discusses the two-step fabrication of a novel in-plane Si-air linear variable optical filter (LVOF). LVOF has alternating quarter-wave stack layers of high refractive and low refractive index materials sandwiching a tapered cavity. Different passbands can be observed at various positions along the length of the filter. Challenges of LVOF fabrication include depositing consistent thickness of quarter-wave stacks and precise control of the taper angle to be in the range of milli-degrees. In many instances, due to the limitations of thin film deposition systems, surface roughness and deposition thickness vary across entire wafer surface. Such deviations could result in different LVOFs possessing varying response to input signal.

Electron-beam lithography (EBL) was utilized for accurate patterning of Si pillars and taper angle which are difficult to achieve using traditional fabrication methods. In the absence of hardmask, SU-8 was used for pattern transfer with Si:SU-8 etch selectivity as high as 60:1. By optimizing SF6 and C4F8 gas flow and time parameters, aspect ratio of 10:1 and almost- 90° pillars were deep etched into Si with scallop depth <30 nm. High Bragg contrast mirrors were obtained with [HLH]-wedge-[HLH] configuration.

This LVOF operates in free space with continuous tuning from 3.1-3.8 μm. FWHM of 95 nm is observed at 3.3 μm. Simulation and other characterization results are discussed. Finally, the proposed LVOF can be wafer-level packaged with normal incidence detector array, suitable light source and other essential optical elements.

Paper Details

Date Published: 14 May 2018
PDF: 8 pages
Proc. SPIE 10657, Next-Generation Spectroscopic Technologies XI, 106570E (14 May 2018); doi: 10.1117/12.2304774
Show Author Affiliations
Simon Chun Kiat Goh, Nanyang Technological Univ. (Singapore)
Excelitas Technologies Corp. (Singapore)
Li Lynn Shiau, Nanyang Technological Univ. (Singapore)
Excelitas Technologies Corp. (Singapore)
Nan Chen, National Univ. of Singapore (Singapore)
Shurui Wang, Park Systems (Singapore)
Kailiang Chuan, Excelitas Technologies Corp. (Singapore)
Henrik Ernst, Excelitas Technologies Corp. (Singapore)
Chengkuo Lee, National Univ. of Singapore (Singapore)
Beng Kang Tay, Nanyang Technological Univ. (Singapore)
Chuan Seng Tan, Nanyang Technological Univ. (Singapore)

Published in SPIE Proceedings Vol. 10657:
Next-Generation Spectroscopic Technologies XI
Mark A. Druy; Richard A. Crocombe; Steven M. Barnett; Luisa T.M. Profeta; Abul K. Azad, Editor(s)

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