Design And Fabrication Of Integrated Parabolic Reflector Nano-Antenna Coupled Infrared Detector
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Date
2018-04-01
Authors
Mubarak Ramadan, Mohamed Habashy
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
This work focuses upon the design and fabrication process of a novel parabolic
reflector integrated nano-antenna coupled Infrared (IR) detector which is presented
here for the first time. As this device stems from antenna coupled IR detectors, it will
still also offer the advantages of the fast response, uncooled operation, frequency selectivity, polarization sensitivity and CMOS compatibility. However, the challenging fabrication techniques limited researchers’ work in many aspects. Most of the research in the literature was thus confined to 2D antenna design only, while developing the fabrication process through 3D micro-machining can add more varieties of 3D high gain
antenna structure such as the parabolic reflector antenna proposed through this work.
Such a structure is theoretically expected to add a space diversity gain and reduce the
substrate mode losses. Therefore, the new structure has a high promising potential
for efficiently increasing the specific detectivity of these devices paving the way towards commercialization. The fabrication process is presented and optimized through this work facilitated mainly by automated EBL and XeF2 etching. The structure is designed of seven layers encountering a 4.2 µm half wave dipole feeding antenna for
operation in the long wave infrared band (LWIR) at wavelength 10.6 µm coupled with
a 450 nm × 750 nm niobium batch as a sub-wavelength localized bolometric sensor.
The SU8-10 photoresist is used permanently for low cost insulating and flat cavity
filling purposes showing a height variation of less than 400 nm over the whole cavity
aperture through the morphology analysis. The integrated parabolic cavity has 75 µm
and 13 µm on average for its aperture diameter and cavity depth respectively. The
presented XeF2 etching analysis reveals that, according to the proposed structure design, the proper etching recipe is described by 5 cycles, with 30 s each, at an etching
gas pressure of 3 Torr. This recipe is sufficient to etch approximately a total volume of 0.3425 mm3, resulting in the required cavity profile, through a 2.2 µm SU8 mask that provides mainly circular windows pattern of 38 µm in diameter and few markers representing a total patterned area of 3.7122 mm2. The different geometrical analyses that are encountered for characterizing the fabrication process have been presented
and the SEM of final structure has showed a good agreement with the proposed design. The I-V measurements have showed, however, non-linear characteristics with an
extremely high impendence of 222 kΩ that hinder introducing the fabricated devices
for the optical measurements. This problem is referred to the non-clean liftoff as it
results in discontinuity of all the fabricated devices’ layers. A detailed discussion with
the aid of the statistical analysis had been finally presented. The fabrication process
of this device is thus presented successfully including micro-machining and patterning
techniques, but more efforts can be encountered in the future work to overcome the
highlighted issues and introduce the proposed device to the field.