Effect of dispersion on metal-insulator-metal infrared absorption resonances
- PDF / 453,916 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 8 Downloads / 218 Views
Research Letter
Effect of dispersion on metal–insulator–metal infrared absorption resonances Seth R. Calhoun, Vanessa C. Lowry, Reid Stack, Rachel N. Evans, Jonathan R. Brescia, Chris J. Fredricksen, Janardan Nath, and Robert E. Peale, Physics Department, University of Central Florida, Orlando, FL 32816, USA Evan M. Smith, KBRWyle, Beavercreek, OH 45440, USA; Air Force Research Laboratory, Sensors Directorate, Wright-Patterson AFB, OH 45433, USA Justin W. Cleary, Air Force Research Laboratory, Sensors Directorate, Wright-Patterson AFB, OH 45433, USA Address all correspondence to Seth R. Calhoun at [email protected] (Received 23 January 2018; accepted 19 April 2018)
Abstract Metal–insulator–metal (MIM) resonant absorbers comprise a conducting ground plane, a thin dielectric, and thin separated metal top-surface structures. The dielectric SiO2 strongly absorbs near 9 µm wavelength and has correspondingly strong long-wave-infrared (LWIR) dispersion for the refractive index. This dispersion results in multiple absorption resonances spanning the LWIR, which can enhance broad-band sensitivity for LWIR bolometers. Similar considerations apply to silicon nitride Si3N4. TiO2 and AlN have comparatively low dispersion and give simple single LWIR resonances. These dispersion-dependent features for infrared MIM devices are demonstrated by experiment, electrodynamic simulation, and an analytic model based on standing waves.
Introduction Metal–insulator–metal (MIM) resonant absorbers have application to infrared (IR) sensing. The important long-wave-infrared (LWIR) spectral range is easily served by structures that can be fabricated by ordinary contact photolithography. Different types of absorbers would be of interest. Ones that span the 8–12 µm LWIR would be suitable for standard night vision applications. Ones that absorb narrowly within this band have application to spectral sensing. MIM LWIR absorbers have been applied to IR bolometers[1] and to pyroelectric detectors.[2] MIMs that absorb in the 3–5 µm mid-wave-infrared (MWIR) band would be useful for, e.g., tracking very hot objects. This region requires very small metal patterns that are at the limit of what can be achieved by contact photolithography. The fabrication challenge is relaxed by choosing a dielectric with a low index. Several of the coauthors recently published[3] a comprehensive study of MIM absorbers at 50 µm wavelength in the far-IR spectral region, where the dispersion of the insulator used (SiO2) was weak. The resulting resonant absorption spectrum was simple and accurately agreed with the analytic standingwave model introduced in that paper. This paper investigates MIM absorbers designed for MWIR, where dispersion is also weak for nearly all common dielectrics, and for LWIR, where dispersion can be strong. The main theme of this paper is the effect of that dispersion, which should inform the materials choice for MIMs intended for different applications. A secondary observation is that, though the analytic model follows the
general trend in
Data Loading...
