Design, Fabrication and Measurement of Pyramid-Type Antireflective Structures on Columnar Crystal Silicon Lens for Millimeter-Wave Astronomy

• Published in: Journal of low temperature physics Vol. 193; no. 5-6; pp. 976 - 983
• Main Authors: Nitta, T., Sekimoto, Y., Hasebe, T., Noda, K., Sekiguchi, S., Nagai, M., Hattori, S., Murayama, Y., Matsuo, H., Dominjon, A., Shan, W., Naruse, M., Kuno, N., Nakai, N.
• Format: Journal Article
• Language: English
• Published: New York Springer US 2018; Springer Nature B.V
• Subjects: Astronomy; Broadband; Characterization and Evaluation of Materials; Condensed Matter Physics; Crystal structure; Dielectric loss; Electromagnetic fields; Electronics; Flat surfaces; Fourier transform spectrometers; Fourier transforms; Lenses; Low temperature physics; Magnetic Materials; Magnetism; Millimeter waves; Network analysers; Organic chemistry; Physics; Physics and Astronomy; Radius of curvature; Reflectance; Refractivity; Silicon; Simulation; Three axis; Antireflection coating; Subwavelength structure; Silicon lens
• ISSN: 0022-2291; 1573-7357
• DOI: 10.1007/s10909-018-2047-4

Pyramid-type antireflective subwavelength structures for large-diameter (
>
30
cm
) silicon lenses are promising for broadband astronomical observations. The refractive index and dielectric loss tangent of the lens material, columnar crystal silicon which is manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd., were measured at around 30 K using a Martin–Puplett-type Fourier transform spectrometer. The measured refractive index and dielectric loss tangent between 200 GHz and 1.6 THz were
∼
 3.42 and 1–
5
×
10
-
4
, respectively. Three different pyramid-type structures with a period of
265
μ
m
and depth of
600
μ
m
were simulated to obtain their reflectance using an electromagnetic field simulator, HFSS. The structures were fabricated on both sides of a 100-mm-diameter plane-convex lens made of columnar crystal silicon with a 150-mm radius of curvature using a metal-bonded V-shaped blade and a dedicated three-axis machine. The fabrication errors in the period and depth were less than
10
μ
m
. The reflectance of the lens flat surface was measured using a vector network analyzer to be between
-
8
and
-
17
 dB in the range of 110–170 GHz, which was consistent with the result from the simulation.