Reconfigurable metasurfaces and x-band RF devices employing the acoustoelectric effect
A reconfigurable metasurface device that leverages the interaction of phonon modes and a charge carrier distribution in a thin film semiconductor/piezoelectric film stack via the acoustoelectric interaction is disclosed. A surface acoustic wave (SAW) is launched into the piezoelectric layer. The SAW propagates through the piezoelectric layer, where the resulting strain wave induces a corresponding propagating electric field. This electric field capacitively couples to the thin film semiconductor, where it electrostatically induces periodic modulations of the charge carriers. The charge carrier distribution in the thin film semiconductor will form ribbons of charge carriers following the constant phase fronts of a sufficiently large amplitude SAW. By controlling the charge carrier patterning one can modulate the coupling to the plasmonic modes in the thin film semiconductor. By controlling the charge carrier patterning via the power and wavelength of the SAW, a reconfigurable metasurface results.
1 . A reconfigurable metasurface device comprising:
a piezoelectric substrate;
at least one interdigitated transducer (IDT), the at least one IDT located on the piezoelectric substrate, the at least one IDT adapted to receive a radio frequency (RF) input signal and to generate a surface acoustic wave (SAW) in the piezoelectric substrate in response to the RF input signal received; and
a thin film semiconductor layer, the thin film semiconductor layer located on the piezoelectric substrate adjacent the at least one IDT, the thin film semiconductor layer adapted to form a charge carrier pattern in response to the SAW in the piezoelectric substrate, the thin film semiconductor layer adapted to create plasmons in response to the charge carrier pattern.
2 . The reconfigurable metasurface device of claim 1 , wherein the piezoelectric substrate includes a piezoelectric layer, the piezoelectric layer including one of lithium niobate (LiNbO 3 ), aluminum nitride (AlN), or scandium aluminum nitride (ScAlN).
3 . The reconfigurable metasurface device of claim 2 , wherein the piezoelectric substrate further includes a cavity formed below at least a portion of the piezoelectric layer.
4 . The reconfigurable metasurface device of claim 1 , wherein the at least one IDT includes two IDTs, a first of the two IDTs adjacent a first edge of the thin film semiconductor layer, a second of the two IDTs adjacent a second edge of the thin film semiconductor layer opposite the first edge, each of the two IDTs adapted to receive a corresponding RF signal, the two IDTs adapted to generate a standing SAW in the piezoelectric substrate in response to the corresponding RF signal received.
5 . The reconfigurable metasurface device of claim 1 , wherein the at least one IDT includes two IDTs, a first of the two IDTs adjacent a first edge of the thin film semiconductor layer, a second of the two IDTs adjacent a second edge of the thin film semiconductor layer opposite the first edge, a first of the two IDTs adapted to receive a corresponding RF signal, the first of the two IDTs adapted to generate a standing SAW in the piezoelectric substrate in response to the corresponding RF signal received, a second of the two IDTs adapted to act as a reflector for the standing SAW.
6 . The reconfigurable metasurface device of claim 1 , wherein the at least one IDT includes two IDTs, a first of the two IDTs adjacent a first edge of the thin film semiconductor layer, a second of the two IDTs adjacent a second edge of the thin film semiconductor layer orthogonal to the first edge, each of the two IDTs adapted to receive a corresponding RF signal, each of the two IDTs adapted to generate a corresponding SAW in the piezoelectric substrate in response to the corresponding RF signal received.
7 . The reconfigurable metasurface device of claim 1 ,
wherein the at least one IDT includes four IDTs;
wherein a first of the four IDTs is adjacent a first edge of the thin film semiconductor layer, a second of the four IDTs is adjacent a second edge of the thin film semiconductor layer opposite the first edge, each of the first and second of the four IDTs adapted to receive a corresponding RF signal, the first and second of the four IDTs adapted to generate a first standing SAW in the piezoelectric substrate in a first direction in response to the corresponding RF signal received; and
wherein a third of the four IDTs is adjacent a third edge of the thin film semiconductor layer orthogonal to the first edge, a fourth of the four IDTs is adjacent a fourth edge of the thin film semiconductor layer opposite the third edge, each of the third and fourth of the four IDTs adapted to receive a corresponding RF signal, the third and fourth IDTs adapted to generate a second standing SAW in the piezoelectric substrate in a second direction orthogonal to the first direction in response the corresponding RF signal received.
8 . The reconfigurable metasurface device of claim 1 ,
wherein the at least one IDT includes four IDTs;
wherein a first of the four IDTs is adjacent a first edge of the thin film semiconductor layer, a second of the four IDTs is adjacent a second edge of the thin film semiconductor layer opposite the first edge, the first IDT adapted to receive a first RF signal, the first IDT adapted to generate a first standing SAW in the piezoelectric substrate in a first direction in response to the first RF signal received, the second IDT adapted to act as a reflector for the first standing SAW; and
wherein a third of the four IDTs is adjacent a third edge of the thin film semiconductor layer orthogonal to the first edge, a fourth of the four IDTs is adjacent a fourth edge of the thin film semiconductor layer opposite the third edge, the third IDT adapted to receive a second RF signal, the third IDT adapted to generate a second standing SAW in the piezoelectric substrate in a second direction orthogonal to the first direction in response to the second RF signal received, the fourth IDT adapted to act as a reflector for the second standing SAW.
9 . The reconfigurable metasurface device of claim 1 , wherein the at least one IDT includes N pairs of IDTs; and wherein a first of each corresponding pair of the N pairs of IDTs is adjacent an edge of the thin film semiconductor layer, and a second of each corresponding pair of the N pairs of IDTs is adjacent an edge of the thin film semiconductor layer opposite the first of each corresponding pair of the N pairs of IDTs.
10 . The reconfigurable metasurface device of claim 1 , wherein each of the at least one IDTs is a chirped IDT.
11 . The reconfigurable metasurface device of claim 1 , wherein the thin film semiconductor layer includes one of graphene, twisted bilayer graphene, gallium arsenide (GaAs), or indium gallium arsenide (InGaAs).
12 . The reconfigurable metasurface device of claim 1 , wherein the thin film semiconductor layer includes a waveguide, the waveguide adapted to carry an optical signal.
13 . The reconfigurable metasurface device of claim 12 , wherein each of the at least one IDT is a focusing IDT adapted to generate a SAW in the piezoelectric substrate below the waveguide.
14 . The reconfigurable metasurface device of claim 1 further comprising two bias electrodes, the two bias electrodes located on the thin film semiconductor layer, a first of the two bias electrodes adjacent a first edge of the thin film semiconductor layer, a second of the two bias electrodes adjacent a second edge of the thin film semiconductor layer opposite the first edge, the two bias electrodes adapted to be in ohmic electrical contact with the thin film semiconductor layer, the two bias electrodes adapted to receive a bias voltage and to cause a current to flow in the thin film semiconductor layer.
15 . The reconfigurable metasurface device of claim 14 , wherein each of the two bias electrodes includes at least one of titanium (Ti), gold (Au), or silver (Ag).
16 . The reconfigurable metasurface device of claim 1 , wherein the thin film semiconductor layer is adapted to receive an optical signal and to reflect a first portion of the optical signal, to transmit a second portion of the optical signal, and to absorb a third portion of the optical signal.
17 . The reconfigurable metasurface device of claim 16 further comprising a reflector, the reflector formed on a side of the piezoelectric substrate opposite the thin film semiconductor layer, the reflector adapted to reflect the optical signal.
18 . The reconfigurable metasurface device of claim 1 further comprising a buffer layer, the buffer layer located between the piezoelectric substrate and the thin film semiconductor layer.
19 . The reconfigurable metasurface device of claim 18 , wherein the buffer layer includes one or more of aluminum arsenide (AIAs), aluminum nitride AlN, barium fluoride (BaF2), beryllium oxide (BeO), calcium oxide (CaO), hafnium oxide (HfO2), gallium arsenide (GaAs), gallium nitride (GaN), gallium phosphide (GaP), indium arsenide (InAs), indium phosphide (InP), indium antimonide (InSb), magnesium oxide (MgO), manganese oxide (MnO), nickel oxide (NiO), lead zirconium titanate (PZT), silicon carbide (SiC), silicon nitride (Si3N4), or silicon oxide (SiO2).
20 . The reconfigurable metasurface device of claim 1 , wherein the reconfigurable metasurface device is adapted to function as one of an RF amplifier, a one-dimensional reconfigurable metasurface device, a two-dimensional metasurface device, or an optical modulator.