A Nonvolatile Phase‐Change Metamaterial Color Display

Abstract

difference in their electrical and optical properties between their amorphous and crystalline phases. Moreover, they can be switched (optically, electrically, or thermally) between phases reversibly (potentially >10 15 cycles) and quickly (nanoseconds or faster). [1][2][3] Both phases (and indeed intermediate phases between fully crystalline and fully amorphous) are also stable at room temperature for a time on the order of years. [4,5] All these properties have made phasechange materials extremely attractive for commercial data storage technologies, in the form of rewritable optical disks and nonvolatile electronic memories. [6][7][8] More recently, as a result of the rather unique properties that phase-change materials possesses, their use has been extended to a number of exciting emerging applications including neuromorphic computing, [9,10] integrated photonic memories [11,12] and, the focus of this work, reconfigurable optical metamaterials/metasurfaces, [13][14][15][16][17][18][19][20][21][22] which we here exploit for the realization of a new form of nonvolatile color display.Optical metasurfaces have great potential to generate color, and several different structures suited to this task have been suggested in the literature. [23][24][25][26][27][28][29][30][31] A common approach is to utilize metallic (or metal-dielectric) nanorods [26,27,30,31] or other lithographically patterned metal-dielectric nanostructures [24,28,29] that generate structural (i.e., noncolorant) color using plasmonic effects. Such approaches are in general though "fixed-by-design," meaning that colors and images are essentially written permanently into the metasurface by the specific nanostructures used. For display and electronic signage applications, however, the ability to change the displayed image or information in real time is required. Here we provide just such a capability by combining a metal-insulator-metal (MIM) resonant absorber type optical metasurface [32,33] with a thin layer of chalcogenide phase-change material (PCM), so providing the key attributes of nonvolatile color generation and dynamic reconfigurability, the latter achieved by turning the MIM resonance "on" and "off" by switching the PCM-layer between its crystalline and amorphous states. Nonvolatility is a particularly attractive feature offered by phase-change based displays, since no power is needed to retain an image once it is written into the phase-change layer/pixels. [34][35][36][37] Moreover, the displays can work using only ambient (natural or artificial) light, which can Chalcogenide phase-change materials, which exhibit a marked difference in their electrical and optical properties when in their amorphous and crystalline phases and can be switched between these phases quickly and repeatedly, are traditionally exploited to deliver nonvolatile data storage in the form of rewritable optical disks and electrical phase-change memories. However, exciting new potential applications are now emerging in areas such as integrated phase-change photonics, phase...

Simple technique for determining the refractive index of phase-change materials using near-infrared reflectometry

“…The proposed methodology is based on simple reflectance measurements of thin films forming Fabry-Perot absorbing nanocavities; this restricts multiple (n and k) solutions, since the FP cavities possess unique mapping features (reflectance at resonance, resonant wavelength λ res and Q factor). Although here we have concentrated on the determination of n and k values over the near infrared spectral region, the method is extendable to the visible, mid-and long-wave infrared red regions (where phase-change materials have many interesting applications, see e.g., [1][2][3]9,15,41]), the only proviso being that the nanocavities used (designed) should have a resonance in the relevant wavelength range.…”

“…Novel device technologies based on the use of chalcogenide phase-change materials (PCMs), whose refractive index can be controlled on-demand, are currently the subject of many fascinating research trends [1][2][3][4]. These include PCM-based reconfigurable reflective displays [1,3], tuneable filters [2], perfect absorbers/modulators [4], devices for active wavefront shaping [5], and integrated phase-change photonic memories and processors [6][7][8]. This is of course in addition to the use of PCMs in more conventional non-volatile optical (and electrical) memories (see e.g., [9,10]).…”

Design for quality: reconfigurable flat optics based on active metasurfaces

“…Compared to VO 2 , chalcogenide O-PCMs exemplified by GST offer even larger optical contrast in the near-IR and UV spectral regimes with an index change up to 2.8 [172][173][174][175][176]. In addition to tuning response of identical metaatom arrays [177][178][179][180][181][182][183][184][185][186][187][188][189], advanced active control of metasurface devices, including varifocal metalenses [190][191][192][193], metasurface color display [194], spatial light modulators [188], spectral filters [180,187,189], beam-steering metadevice [195], reconfigurable holograms [196], tunable thermal absorbers [197] and emitters [198][199][200][201], switches [202], free-form rewritable metasurfaces [203,204], and topologically optimized metadevices [205], have also been experimentally demonstrated leveraging phase-change behavior of GST alloys.…”

Phase Change Materials for Nonvolatile, Solid‐State Reflective Displays: From New Structural Design Rules to Enhanced Color‐Changing Performance

“…[ 17–23 ] Because of the variability of their optical properties (mainly optical constants, [ 9,24,25 ] reflectivity, [ 26,27 ] transmission, [ 25,28,29 ] absorption, [ 30,31 ] and emissivity [ 32 ] ), PCMs been widely applied in nonvolatile photonic applications, such as all‐photonic memories, [ 26,33,34 ] active absorbers, [ 35 ] filters, [ 25 ] lenses, [ 34,36 ] sensors, [ 36 ] displays, etc. [ 26,27,37–39 ] Among the above optical applications, the PCM‐based solid‐state reflective display [ 27 ] is a revolutionary display technology. It has many advantages, such as high resolution, rich colors, and fast color switching over traditional technologies, such as electrophoresis and electronic ink display.…”