Infrared pixel based on Seebeck nanoantennas
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.471
Infrared pixel based on Seebeck nanoantennas Francisco Javier González,1,2,3 Nagendra Dhakal,1 Tommy Boykin II,1 Javier Méndez-Lozoya,3 Robert E. Peale1,2 1
Physics, University of Central Florida, Orlando FL 32789 USA
2
Truventic LLC, 1209 W. Gore St. Orlando FL 32805 USA
3
LANCYTT/UASLP, Sierra Leona 550, Lomas 2a Sección, SLP, 78210, Mexico
Abstract
Bolometric arrays dominate in commercial terahertz and millimeter wave imagers. Bolometers tend to be slow and require an operating bias that increases the power budget. This paper presents first results on antenna-coupled thermo-electric junction detectors, a potentially attractive alternative to microbolometers. The nanoscale junctions have small thermal mass and can be much faster than bolometers. These junctions are heated by currents excited in spectrally-selective antennas and generate a voltage based on the Seebeck effect without any externally applied power. A pixel comprising a series array of antenna coupled junctions with peak response at 7.5 THz (40 m wavelength) is designed and experimentally demonstrated. Responsivity of 5 MV/W, 500 Hz chopping frequency, and D* of 3.5 x 1010 Jones are demonstrated.
INTRODUCTION Antennas used to receive electromagnetic waves [1] generate detectable currents [2]. Antennas offer polarization sensitivity, directivity, small footprint, tunability and the possibility of integration into electronic and photonic circuits [3]. Antenna tunability allows spectrally-selective detection from visible to terahertz wavelengths [4].
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By changing their shape and size antennas can be tuned to detect infrared frequencies, induced AC currents at infrared frequencies are traditionally rectified to produce a DC signal that can be measured by conventional electronics [5]. This approach relies on the high switching speeds achieved by tunneling taking place in metal-insulating-metal diodes. Such “rectennas” have low efficiency due to impedance mismatch between antenna and the rectifier [6,7]. We propose antennas comprising two dissimilar materials with different thermoelectric coefficients and whose junction is Joule heated by the induced AC currents, generating a Seebeck voltage. Figure 1 presents a schematic with color-coded temperature distribution. The dissimilar materials are labelled “n” and “p”, as a nonlimiting example, since the materials might be semiconductors with opposite conductivity sign, however these materials might be conductors, semiconductors or a combination of semiconductor and metal. By eliminating a rectifying element, the impedance mismatch is reduced, and the detection efficiency is increased. The antennas are sub-wavelength scale, and the junctions can be nano-scale, such that these devices are called “Seebeck nano
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