Single-step Electron Beam Lithography Research Articles

Diatom Cribellum-Inspired Hierarchical Metamaterials: Unifying Perfect Absorption Toward Subwavelength Color Printing.

Diatom exoskeletons, known as frustules, exhibit a unique multilayer structure that has attracted considerable attention across interdisciplinary research fields as a source of biomorphic inspiration. These frustules possess a hierarchical porous structure, ranging from millimeter-scale foramen pores to nanometer-scale cribellum pores. In this study, this natural template for nanopattern design is leveraged to showcase metamaterials that integrates perfect absorption and subwavelength color printing. The cribellum-inspired hierarchical nanopatterns, organized in a hexagonal unit cell with a periodicity of 300nm, are realized through a single-step electron beam lithography process. By employing numerical models, it is uncovered that an additional induced collective dipole mode is the key mechanism responsible for achieving outstanding performance in absorption, reaching up to 99%. Analysis of the hierarchical organization reveals that variations in nanoparticle diameter and inter-unit-cell distance lead to shifts and broadening of the resonance peaks. It is also demonstrated that the hierarchical nanopatterns are capable of color reproduction with high uniformity and fidelity, serving as hexagonal pixels for high-resolution color printing. These cribellum-inspired metamaterials offer a novel approach to multifunctional metamaterial design, presenting aesthetic potential applications in the development of robotics and wearable electronic devices, such as smart skin or surface coatings integrated with energy harvesting functionalities.

Lithium Niobate Thin Film Polarization Beam Splitter Based on Asymmetric Directional Coupling

Polarization devices on lithium niobate thin film (LNTF) are vital components for photonic integrated circuits (PICs) on the novel platform. Because both linear and nonlinear devices on the anisotropic platform are intrinsically polarization-dependent. Here, we demonstrate compact polarization beam splitters (PBS) on LNTF based on two asymmetric directional couplers with an effective length of only 180 μm. The PBS is fabricated via a single-step electron beam lithography (EBL) and inductively coupled plasma (ICP) etching process. Our device shows efficient PBS operation at the telecom bands with an extinction ratio over 26 dB and 13 dB for fundamental TE and TM modes, respectively. The device holds promise for efficient on-chip polarization division multiplexing and polarization manipulation, which would become an indispensable component in future LNTF PICs.

Plasmonic Surface Lattice Resonances in Suspended Symmetric Double-Layer Gratings

Surface lattice resonances (SLRs) with high-quality factors supported by metal nanoparticle arrays are useful for plasmonic nanolasers, biochemical sensors, and surface-enhanced Raman spectroscopy. Most nanoparticle arrays are fabricated on a substrate, and the refractive index mismatch between the substrate and superstrate suppresses the performance of SLRs. In this work, we propose unique SLRs excited in suspended, self-aligned symmetric double-layer gratings with index-matched environment. The self-aligned double-layer gratings are fabricated using a single-step electron beam lithography and exhibit a Fano-like spectra resulting from interference between out-of-plane plasmonic resonances and diffraction modes. By changing the incident angle and refractive index of the surrounding medium, the SLRs can be tuned from visible to near-infrared regions with a high-quality factor of 120.

Ultrathin Suspended Chiral Metasurfaces for Enantiodiscrimination (Adv. Mater. 37/2022)

Metasurfaces A self-aligned suspended chiral bilayer metasurface via single-step electron-beam lithography is reported by Tun Cao, Yan Jun Liu, and co-workers in article number 2203956. A huge optical chirality of 221° μm−1 is achieved by the free-standing metasurfaces with overall thickness of 100 nm. The bilayer metasurface demonstrates label-free discrimination of chiral molecules at zeptomole level, with sensitivity orders of magnitude larger than conventional circular dichroism spectroscopy.

Aluminum air bridges for superconducting quantum devices realized using a single-step electron-beam lithography process

In superconducting quantum devices, air bridges enable increased circuit complexity and density, and mitigate the risk of microwave loss arising from mode mixing. We implement aluminum air bridges using a simple process based on single-step electron-beam gradient exposure. The resulting bridges have sizes ranging from 20 µm to 100 µm, with a yield exceeding 99% for lengths up to 36 µm. When used to connect ground planes in coplanar waveguide resonators, the induced loss contributed to the system is negligible, corresponding to a loss per bridge less than 1.0×10−8. The bridge process is compatible with Josephson junctions and allows for the simultaneous creation of low loss bandages between superconducting layers.

Unidirectional coupling and efficient detection of near-infrared surface plasmon polaritons for on-chip optoelectronic interconnection.

Plasmonic interconnection is one kind of the possible methods to construct next-generation optoelectronic integrated circuits. In this paper, the plasmonic interconnection device based on Ge in infrared band is constructed, through efficient electron-hole pair generation, the device can achieve high photocurrent response (0.25A/W). Because of the low plasmon coupling efficiency of the conventional basic periodic gratings, this paper optimized the design of the coupling structure and improved the coupling efficiency by 4 times through constructing a binary Bragg/periodic grating coupler which can realize unidirectional plasmon coupling with a simulated extinction ratio of 12.5 dB. The devices can be easily fabricated by single-step electron beam lithography and lift-off process. The experimental results verified a 3.5 times improvement in the SPPs current of the designed plasmonic interconnection device, which provides a technical path to realize efficient plasmon transmission and detection for on-chip optoelectronic interconnection.

Single step electron-beam lithography archiving lift-off for T-gate in high electron mobility transistor fabrication

In this paper, a new method of electron-beam lithography was proposed to directly obtain a floating T-shaped gate. In the method, only one step of exposure and one step of development were operated on a three-layer photoresist of PMMA/P(MMA-MAA)/ P(MMA-MAA) to form an obvious undercut structure which is very benefit for subsequent lift-off process of gate metal. A high electron mobility transistor (HEMT) with an 80 nm floating T-shaped gate was fabricated on a SiC substrate which has a 10 nm InAlN barrier. Finally, the obtained device by above process has a fT/fmax of 90/200 GHz.

Weak link nanobridges as single flux quantum elements

This paper investigates the feasibility of using weak link nanobridges as Josephson junction elements for the purpose of creating Josephson circuits. We demonstrate the development of a single-step electron beam lithography procedure to fabricate niobium nanobridges with dimensions down to . The single-step process facilitates fabrication that is scalable to complex circuits that require many junctions. We measure the IV-characteristics (IVC) of the nanobridges between temperatures of and and find agreement with numerical simulations and the analytical resistively shunted junction (RSJ) model. Furthermore, we investigate the behaviour of the nanobridges under rf irradiation and observe the characteristic microwave-induced Shapiro steps. Our simulated IVC under rf irradiation using both the RSJ model and circuit simulator JSIM are in agreement with the experimental data. As a potential use of nanobridges in circuits requiring many junctions, we investigate the theoretical performance of a nanobridge-based Josephson comparator circuit using JSIM.

T‐Gate Fabrication of InP‐Based HEMTs Using PMGI/ZEP520A/PMGI/ZEP520A Stacked Resist

PMGI/ZEP520A/PMGI/ZEP520A fourlayer resist stack is firstly proposed for T-gates fabrication of InP-based High electron mobility transistors (HEMTs). Gate-head and gate-foot are exposed in single-step Electron beam lithography (EBL), which avoids alignment deviation by automatic self-alignment. The newly introduced PMGI at the bottom greatly improves the adhesiveness of ZEP520A resist with the substrate. The optimal gate-foot length reaches 101nm for a design of 50nm gate footprint pattern, and which can be improved to be 66.8nm for 30nm gate footprint pattern. Finally, Tgates in nanometer regime have been successfully incorporated into InP-based HEMTs fabrication. Benefiting from both the narrow gate-foot and the reduced parasitic gatecapacitance by single-step EBL technique with the fourlayer resist stack, the fabricated devices with gate-foot length of 101nm demonstrate excellent DC and RF performances: the maximum extrinsic transconductance, the current-gain cutoff frequency and maximum oscillation frequency are 1051mS/mm, 249GHz and 415GHz, respectively.

Fabrication of suspended, three-dimensional chiral plasmonic nanostructures with single-step electron-beam lithography

Suspended 3D chiral plasmonic nanostructure fabricated with only one-step electron-beam lithography.

Aluminum plasmonics based highly transmissive polarization-independent subtractive color filters exploiting a nanopatch array.

Nanophotonic devices enabled by aluminum plasmonics are saliently advantageous in terms of their low cost, outstanding sustainability, and affordable volume production. We report, for the first time, aluminum plasmonics based highly transmissive polarization-independent subtractive color filters, which are fabricated just with single step electron-beam lithography. The filters feature selective suppression in the transmission spectra, which is realized by combining the propagating and nonpropagating surface plasmons mediated by an array of opaque and physically thin aluminum nanopatches. A broad palette of bright, high-contrast subtractive colors is successfully demonstrated by simply varying the pitches of the nanopatches. These subtractive color filters have twice the photon throughput of additive counterparts, ultimately providing elevated optical transmission and thus stronger color signals. Moreover, the filters are demonstrated to conspicuously feature a dual-mode operation, both transmissive and reflective, in conjunction with a capability to exhibit micron-scale colors in arbitrary shapes. They are anticipated to be diversely applied to digital display, digital imaging, color printing, and sensing.

Subwavelength Plasmonic Color Printing Protected for Ambient Use

We demonstrate plasmonic color printing with subwavelength resolution using circular gap-plasmon resonators (GPRs) arranged in 340 nm period arrays of square unit cells and fabricated with single-step electron-beam lithography. We develop a printing procedure resulting in correct single-pixel color reproduction, high color uniformity of colored areas, and high reproduction fidelity. Furthermore, we demonstrate that, due to inherent stability of GPRs with respect to surfactants, the fabricated color print can be protected with a transparent dielectric overlay for ambient use without destroying its coloring. Using finite-element simulations, we uncover the physical mechanisms responsible for color printing with GPR arrays and suggest the appropriate design procedure minimizing the influence of the protection layer.

Three-tiered Au nano-disk array for broadband interaction with light

We demonstrate a straightforward method to enlarge the spectral window for broadband interaction with light, by creating a plasmonic nanostructure composed of closely spaced multiple Au nano-disks. The vertically stacked, Au nano-disks of three different sizes make it possible to merge the individual spectral windows of the internal nano-disks into one broadband window, and can be simply generated by a single-step electron-beam lithography step with subsequent sputter deposition.

Fabrication of polynomial 3-D nanostructures in Si with a single-step process

This work demonstrated the ability to transfer a nanoscale 3-D polynomial structure of arbitrary shape into Si with a single step electron-beam lithography process. The technique involved employing a proximity correction algo- rithm, PYRAMID, to derive the dose distribution for a given 3-D structure by accounting for the electron scattering ef- fects of the surrounding pixels. The pattern was written into a polymethyl methacrylate (PMMA) resist and then succes- sively transferred into Si via reactive ion etching, where a 1:1 etching ratio between PMMA and Si was achieved. The pattern transferred into Si possessed nanoscale features and matched the desired pattern with high fidelity. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI: 10.1117/1.3563601) Subject terms: 3-D nanolithography; single-step lithography; proxim- ity correction.

A single-step electron beam lithography of buried nanostructures using cathodoluminescenceimaging and low temperature

We report a new electron beam lithography process using the cathodoluminescenceproperties of semiconductors to visualize nanostructures buried underneath the resist andto subsequently write the pattern associated with these nanostructures. This single-stepprocess could be used, for example, to make electrical contacts to nanowires (asillustrated in this work) or to design a photonic crystal resonator centered on asingle quantum dot. Fabrication speed and positioning accuracy are significantlyincreased as compared to the standard process since no alignment marks andthe mapping step of the nanostructures with respect to these marks are needed.We show also that low temperature (down to 5 K) could be used to improve theobservation of the nanostructures through the resist while keeping very good spatialresolution.

Polymer‐Based Photonic Crystals Fabricated with Single‐Step Electron‐Beam Lithography

A suspended PMMA quasi-3D PC slab with a hexagonal array of air holes fabricated by using a single-step electron-beam lithography process is shown in the figure (PMMA = polymethylmethacrylate). The extension of the single-step lithography technique to the fabrication of 3D multilayer nanostructures with photonic band gaps in the visible-light region is demonstrated.

Towards nano-fluidics by solvent deformation of electron beam resist

Improvements in the fabrication technology of planar micro- and nano-fluidic systems are continually being sought. In this work, we demonstrate and characterize a potential method for making planar nano-fluidic channels in cross-linked UV-3 resist using a single-step electron-beam lithography process. Earlier work indicated that the fluids used in the resist development process influenced the final form of the nano-fluidic structures. In this study the development, rinsing and drying conditions for the resist processing have been investigated in detail to find the best conditions for channel formation. The process was then exploited to construct more complex planar nano-fluidic features, including Y- and T-shaped junctions that are required for practical systems.

Single step electron-beam lithography for asymmetric recess and gamma gate in high electron mobility transistor fabrication

We have developed an asymmetric recess etch in conjunction with a gamma metal gate process for the fabrication of high electron mobility transistors (HEMTs). This process is based on direct electron-beam lithography with a single exposure of a three stack poly(dimethylglutarimide) and poly(methylmethacrylate) photoresists. It can modify the voltage drop over a wider region fabricated by the so called wide-recess technique as compared with the conventional approach, while maintaining a low source resistance, to reduce the electric field intensity at the gate edge, and therefore enhance the breakdown voltage. This gate engineering process for the 0.2 μm InAlAs/InGaAs metamorphic HEMTs achieved a 45% off-state breakdown voltage improvement as compared with the traditional bilayer T-gate device.

Diffraction limit of the focusing waveguide grating coupler for optical probeinformation storage

A focusing waveguide grating coupler (FWGC) has been applied to anoptical information storage element. To achieve minimum diffraction,focusing and high-coupling efficiency with high power, several fabrication anddesign difficulties have to be overcome. In this work, we report some newstrategies to improve the fabrication and design, and greatly improvethe pattern quality in defining curved gratings in the nanometre rangeusing single-step electron-beam lithography with a conventional exposuremode. We also present the optimum fabrication conditions for the FWGCand the minimum diffraction limit (1.1 µm)obtained for the structure, which is optically the smallest diffraction spot sizeobtainable from diffraction gratings focusing beams into a spot in air.

Fabrication Technology of the Focusing Grating Coupler using Single-step Electron Beam Lithography

A focusing grating coupler (FGC) was not fabricated by the 'Continuous Path Control'writing strategy but by an electron-beam lithography system of more general exposure mode, which matches not only the address grid with the grating period but also an integer multiple of the address grid resolution (5 nm). To more simplify the fabrication, we are able to reduce a process step without large decrease of pattern quality by excluding a conducting material or layer such as metal (Al, Cr, Au), which are deposited on top or bottom of an e-beam resist to prevent charge build-up during e-beam exposure. A grating pitch period and an aperture feature size of the FGC designed and fabricated by e-beam lithography and reactive ion etching were ranged over 384.3 nm to 448.2 nm, and 0.5 <TEX>$\times$</TEX> 0.5 mm<TEX>$^2$</TEX>area, respectively. This fabrication method presented will reduce processing time and improve the grating quality by means of a consideration of the address grid resolution, grating direction, pitch size and shapes when exposing. Here our investigations concentrate on the design and efficient fabrication results of the FGC for coupling from slab waveguide to a spot in free space.