Far-infrared spectrally selective LiTaO 3 and AlN pyroelectric detectors using resonant subwavelength metal surface stru
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.291
Far-infrared spectrally selective LiTaO3 and AlN pyroelectric detectors using resonant subwavelength metal surface structures Christopher Arose1, Anthony C. Terracciano2,3, Robert E. Peale1, Francisco Javier Gonzalez1, Zachary Loparo2,3, John Cetnar4, Subith S. Vasu2,3 1
Department of Physics, University of Central Florida, Orlando, Florida 32816, USA
2
Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, Florida 32816, USA
3
Center for Advanced Turbomachinery and Energy Research, University of Central Florida, Orlando, Florida 32816, USA
4
Air Force Research Lab, Sensors Directorate, Wright Patterson AFB OH
Plasmonic near-perfect absorbers, comprising metal films with a periodic array of subwavelength openings, were deposited on the surface of pyroelectric materials to create wavelength-selective far-infrared detectors. The detectors fabricated and investigated were based on one of two pyroelectric materials: (i) z-cut monocrystalline lithium tantalate (LiTaO3) wafers or, (ii) reactively sputtered aluminum nitride (AlN), with absorbers fabricated by contact photolithography. Spectrally selective absorption resonances were demonstrated by Fourier-transform spectroscopy. Spectrally-selective photoresponse was demonstrated with a tunable THz backward wave oscillator. Responsivity was estimated using a black body source to be ~ 1 mV/W for AlN samples and ~ 100 mV/W for LiTaO3 samples. Most similar work has focused on detectors for mid-wave and long-wave infrared spectral regions. Our focus on THz wavelengths beyond 20 µm is motivated by specific security and contraband sensing applications.
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INTRODUCTION: Pyroelectric detectors have relatively-high room-temperature sensitivity at farinfrared wavelengths beyond 20 µm [1] making them preferable to helium-cooled bolometers for certain field applications. Pyroelectrics are thermal detectors that produce a transient voltage. They are widely used for optical power sensing due to their broadband wavelength response [2], but there has been recent interest in integrating them with resonant absorbers to create spectral sensors [3-6]. For this, a thin-film metamaterial absorber is applied to the pyroelectric surface to engineer a surface impedance that matches that of free space, Z0≈377 Ω, at specific wavelengths. We have explored two pyroelectric materials as the basis of a spectrally selective far-IR detector, namely Aluminum Nitride (AlN) and Lithium Tantalate (LiTaO3). Complex permittivity at 1 THz [7,8], mass density , thermal conductivity k, specific heat c, and pyroelectric coefficient pi are collected in Table I. Table I: AlN and LiTaO3 permittiviy , mass density , thermal conductivity k, specific heat c, and pyroel
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