Patchwork metasurface quantum well photodetectors with broadened photoresponse.

Complex lightwave manipulation such as broadband absorption has been realized with metasurfaces based on laterally arranged metal-dielectric-metal cavities with different geometries. However, application of these metasurfaces for optoelectronic devices by incorporating functional dielectrics remains challenging. Here, we integrate a quantum well infrared photodetector (QWIP) with a metasurface made of a patchwork of square cavities with different dimensions arranged in a subwavelength unit cell. Our detector realizes wideband photoresponse approaching the entire responsivity spectrum of the QWIP-single-sized square cavities can utilize only 60% of the possible bandwidth-and external quantum efficiencies of up to 78% at 6.8 µm. Our highly flexible design scheme enables integration of photodetectors and metasurfaces with arbitrary arrangements of cavities selectively responding to incidence with a specific wavefront.

Fast Atom Beam- and Vacuum-Ultraviolet-Activated Sites for Low-Temperature Hybrid Integration.

The evolution of surface chemical structures of polyimide induced by Ar fast atom beam (Ar-FAB) bombardment and vacuum ultraviolet (VUV) irradiation was investigated using X-ray photoelectron spectroscopy (XPS) to clarify the activated sites for low-temperature hybrid bonding. These sites in molecular chains are considered corresponding to the bonding sites. They affect interfacial properties. Therefore, such analyses are necessary to optimize the processing parameters in different surface-modification methods. The XPS results demonstrated that Ar-FAB physical bombardment transformed the polyimide surface into benzene-dominant structures, whereas the effect of VUV irradiation was located at side chain groups such as ether and carbonyl, resulting in much longer molecular fragments (i.e., less matrix damage). Moreover, the calculated thickness of the VUV-induced modification layer grew to around 0.6 nm at its maximum.

Synchronously wired infrared antennas for resonant single-quantum-well photodetection up to room temperature.

Optical patch antennas sandwiching dielectrics between metal layers have been used as deep subwavelength building blocks of metasurfaces for perfect absorbers and thermal emitters. However, for applications of these metasurfaces for optoelectronic devices, wiring to each electrically isolated antenna is indispensable for biasing and current flow. Here we show that geometrically engineered metallic wires interconnecting the antennas can function to synchronize the optical phases for promoting coherent resonance, not only as electrical conductors. Antennas connected with optimally folded wires are applied to intersubband infrared photodetectors with a single 4-nm-thick quantum well, and a polarization-independent external quantum efficiency as high as 61% (responsivity 3.3 A W-1, peak wavelength 6.7 µm) at 78 K, even extending to room temperature, is demonstrated. Applications of synchronously wired antennas are not limited to photodetectors, but are expected to serve as a fundamental architecture of arrayed subwavelength resonators for optoelectronic devices such as emitters and modulators.

Organic-Inorganic Solid-State Hybridization with High-Strength and Anti-Hydrolysis Interface.

Organic-inorganic material hybridization at the solid-state level is indispensable for the integration of IoT applications, but still remains a challenging issue. Existing bonding strategies in the field of electronic packaging tend to employ vacuum or ultrahigh temperature; however, these can cause process complications and material deterioration. Here we report an easy-to-tune method to achieve hybrid bonding at the solid-state level and under the ambient atmosphere. Vacuum-ultraviolet (VUV)-induced reorganization with ethanol was used to develop hydroxyl-carrying alkyl chains through coordinatively-bonded carboxylate onto aluminum, whereas numerous hydroxyl-carrying alkyls were created on polyimide. The triggering of dehydration through these hydroxyls by merely heating at 150 °C for a few minutes produced robust organic-inorganic reticulated complexes within the aluminum/polyimide interface. The as-bonded aluminum/polyimide interface possessed an superior fracture energy of (2.40 ± 0.36) × 103 (J/m2) compared with aluminum and polyimide matrices themselves, which was mainly attributed to crack deflection due to the nano-grains of inorganic-organic reticulated complexes. The interfacial adhesion was successfully kept after humidity test, which was contributed by those anti-hydrolytic carboxylates. To the best of our knowledge, for the first time organic-inorganic bonding at the solid-state level was achieved using the ethanol-assisted VUV (E-VUV) process, a strategy which should be applicable to a diversity of plastics and metals with native oxides.

Low-temperature direct heterogeneous bonding of polyether ether ketone and platinum.

Direct heterogeneous bonding between polyether ether ketone (PEEK) and Pt was realized at the temperatures lower than 150°C. In order to create sufficient bondability to diverse materials, the surface was modified by vacuum ultraviolet (VUV) irradiation, which formed hydrate bridges. For comparison, direct bonding between surfaces atomically cleaned via Ar fast atom bombardment (FAB) was conducted in a vacuum. The VUV irradiation was found to be effective for creating an ultrathin hydrate bridge layer from the residual water molecules in the chamber. Tight bonds were formed through dehydration of the hydrate bridges by heating at 150°C, which also contributed to enhancing interdiffusion across the interface. The VUV-modified surfaces showed bondability as good as that of the FAB-treated surfaces, and the VUV-modified samples had shear strengths at the same level as those of FAB-treated surfaces. This technology will be of practical use in the packaging of lightweight, flexible biomedical devices.