A Fabry–Perot interferometer-based long-wavelength infrared spectrometer utilizing a novel PDMS patterning technique

Abstract

We report a Fabry–Perot interferometer (FPI)-based infrared (IR) spectrometer designed for long-wavelength infrared (LWIR) region. To fabricate the proposed FPI-based LWIR spectrometer, we developed a novel poly(dimethylsiloxane) (PDMS) patterning technique by combining photolithography and dry etching. The proposed PDMS patterning technique has advantages such as clear shape of PDMS pattern and no damage to the silicon (Si) substrate. Especially, the final height of PDMS pattern is easily adjusted by controlling the thickness of spin-coated photoresist. The proposed FPI-based IR spectrometer, which is composed of upper and lower substrate were fabricated separately utilizing newly proposed PDMS patterning technique. Experimental results show that maximum transmittance of filtered wavelength component by the proposed FPI-based IR spectrometer lies at the wavelength of 16 µm. The proposed IR spectrometer can detect a specific wavelength at LWIR region by controlling the air etalon gap that is adjusted by utilizing the proposed PDMS patterning technique.

Tunable Fabry-Perot Interferometer Designed for Far-Infrared Wavelength by Utilizing Electromagnetic Force

“…In this experiment, because the uniformity of the Al that was used as a mirror was an important factor, the SiO 2 that was grown on both sides of the Si substrate was removed using dilute hydro fluoric acid (DHF) solution. Because materials, such as Ag and Au, have close to 100% transmittance in the far-IR light region, Al having a transmittance of about 95% was chosen for the upper IR light reflector [ 20 , 28 ]. For FPI, the reflectivity of the reflector is one of the most important factors.…”

“…With respect to the aluminum (Al) used as the lower mirror of TFPI, 30 Å was deposited to obtain a 30% transmittance. More detailed fabrication processes have been described in [ 20 ].…”

“…Therefore, in this experiment, a PDMS pattern process is designed to fabricate clear PDMS patterns on a substrate without damaging it. This was carried out successfully through a photolithography process and dry etching [ 20 ]. To pattern PDMS on a 6″-Si substrate, 8.5-μm-high AZ9260 PR was patterned by performing a photolithography process.…”

“…To date, owing to the many difficulties that are associated with this field of research, there have been few studies on the fabrication of TFPI-type wavelength filters that can operate in the far-IR light region. Because the distance between the upper and lower mirrors must be at least 7 μm for it to operate in the far-IR light region, it is difficult to fabricate TFPI, which operates in the far-IR light region, while using electrostatic forces [ 20 , 21 , 22 , 23 ]. Other drawbacks include the difficulty that is involved in fabrication using semiconductor processes, and, when compared with the wavelength filters that operate at low wavelengths, a very high voltage is required when the distance between the upper and lower mirrors is increased [ 24 , 25 ].…”

“…The PDMS served as supporting layer to provide an air gap, and its thickness was controlled by the fabrication process parameters (etching time or etcher concentration). Once the fabrication of the FPI was completed, the thickness of PDMS was fixed, giving a specific wavelength characteristic [ 20 ].…”