Development of multi-layer anti-reflection structures for millimeter-wave silicon optics using deep reactive ion etching process

25 Jul 2019, 17:45
1h 15m
Piazza Città di Lombardia (Milano)

Piazza Città di Lombardia

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
Poster Low Temperature Detector fabrication techniques and materials Poster session

Speaker

Dr Takashi Hasebe ( Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency)

Description

Recent millimeter-wavelength telescopes require cryogenically cooled optics to achieve a high-sensitivity observation. A broadband anti-reflection (AR) technology that works at cryogenic temperature has been desired. Silicon is one of the suitable materials for millimeter-wave optics in cryogenic use. This is because it shows low-loss at a cryogenic temperature in the millimeter wavelength.
AR methods using sub-wavelength structures (SWS) have been reported. We designed the SWS on silicon that shows the averaged reflection of 2 % from 100 to 450 GHz. The structure that we designed consists of 4-layer discrete grid structures $^{[1]} $.

The most challenging part of the fabrication for the structures is to make the high-aspect-ratio trenches which have 13 $\mu $m width and 620 $\mu $m depth. To realize this, we employed a deep reactive ion etching (DRIE) process. This technique allows to make an anisotropic high-aspect-ratio structure. Using DRIE process, we succeeded to fabricate trenches which have required shape (Fig. 1).

We studied two methods to fabricate 4-layer structures. The first one is to adopt the DRIE process for fabrication of all the layers. The second one is to use a combination of the DRIE and the direct machining process with a dicing saw. We present the prototypes of the multi-layer SWS on silicon using these two different methods.
Cross section of the test sample fabricated by the DRIE
Reference
$^{[1]}$ T. Hasebe et al., “Concept study of optical configurations for high-frequency telescope for LiteBIRD,” J. Low Temp. Phys. 193, 5 (2018).

Less than 5 years of experience since completion of Ph.D Y
Student (Ph.D., M.Sc. or B.Sc.) N

Primary author

Dr Takashi Hasebe ( Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency)

Co-authors

Dr Tasuku Hayashi (Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency) Dr Yutaro Sekimoto (Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency) Dr Yuichiro Ezoe (Tokyo Metropolitan University) Dr Kumi Ishikawa (Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency) Dr Tom Nitta (University of Tsukuba) Dr Yoshinori Shohmitsu (Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency)

Presentation Materials