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The use of carbon-based (C-based) liners is investigated for RESET current reduction in self-heating, pillar-shaped phase-change memory (PCM) cells for storage class memory (SCM) technologies. The liner is inserted between the top electrode and the phase-change layer. A finite element analysis (FEA) is done to simulate the effect of this liner on the RESET current, using the melting current as a proxy. From this FEA, we see that the high resistance of the C-based liner increases the heat generation at the interface with the phase-change layer, changing the cell from being solely self-heated by the phase-change layer to a combination of the phase-change layer’s self-heating and heating from the C-based liner. The simulation results are validated against experimental results from fabricated pillar cells. We show the liner reduces the melting current of the pillar cell by 60%. The effect of the thickness of the C-based liner and the phase-change layer on the melting current is quantified, showing a strong dependence on the liner thickness and a weak dependence on the phase-change layer thickness. These findings can guide the design of PCM cells with high-resistance liners between the electrode and phase-change layer for RESET current reduction.

The coming of age of AR, VR and MR applications and usage scenarios relies on the development of ever-improved advanced light management systems, both for sensing (camera) and actuation (display), e.g., solid-state dToF or FMCW scanning or flash LiDAR, polarimetric imaging or resettable structured light illumination for 3D mapping, directional imager for light field registration, plasmonic or dielectric color filters and directors for efficient spectroscopic information acquisition. Indeed, optics remains the dominant user interface modality while large portions of required information can be retrieved in optical domain. These systems rely on the emergence of mature mass-manufacturing integrated photonics platforms in near infrared and visible wavelength ranges. This presentation introduces developments at imec of diffractive components for reflective, transmissive and guided applications on opaque (Si/CMOS) and transparent (quartz) substrates, relying on sub-wavelength nano-patterning techniques (from DUV dry and wet (immersion) lithography through 200mm wafer-scale e-beam, nano-imprint lithography, block-co-polymer to EUV), novel CMOS-compatible material toolbox beyond Si and SiN (passive, active, resettable and tunable) and high-aspect ratio re-filling to enable stacking of optical features to define complex functional system. In particular, we will report on pixel-integrated Fresnel phase plates for local eQE optimization, on process complexity trade-off enabled by optical meta-materials, aspherical and non-cylindrical optical components for directed light, tunable structured light scanners, plasmonic and dielectric-based color filters and directors, optical beamformer in near infrared, sub-wavelength spatial light modulator in the visible and finally novel developments for 2D optical waveguides.

We investigate hybrid dielectric-metallic transmission color filters for cost-effective, narrow linewidth filters that are fully CMOS compatible. Through the interference of the resonance phenomena in a metallic hole array with a magnetic dipole resonance in a dielectric nanopillar, a narrow linewidth transmission window is opened. An additional metal cover on top of the pillar further suppresses transmission at longer wavelengths due to a localized surface plasmon polariton. FDTD simulations predict a transmission of over 50% and a linewidth of down to 25 nm for the green filter. The out-of-band suppression is lower compared to previously reported metal-insulator-metal filters.

A grating coupler having asymmetric grating trenches for low back reflections is experimentally demonstrated. Conventional and asymmetric-trench grating couplers have been fabricated on a silicon nitride waveguide platform. Both grating couplers have fully etched trenches, which normally result in higher back reflections than shallow-etched trenches. For evaluating the back reflection characteristics, test structures based on a 3-dB multimode interference power splitter have been measured and the backreflection has been extracted from each grating coupler using an equivalent optical circuit. The designed grating coupler has no critical penalty (

While it is well established that elevated temperatures can induce surface roughening of metal surfaces, the effect of a high electric field on the atomic structure at ambient temperature has not been investigated in detail. Here we show with atomic resolution using in situ transmission electron microscopy how intense electric fields induce reversible switching between perfect crystalline and disordered phases of gold surfaces at room temperature. Ab initio molecular dynamics simulations reveal that the mechanism behind the structural change can be attributed to a vanishing energy cost in forming surface defects in high electric fields. Our results demonstrate how surface processes can be directly controlled at the atomic scale by an externally applied electric field, which promotes an effective decoupling of the topmost surface layers from the underlying bulk. This opens up opportunities for development of active nanodevices in e.g. nanophotonics and field-effect transistor technology as well as fundamental research in materials characterization and of yet unexplored dynamically-controlled low-dimensional phases of matter., Comment: The manuscript is 10 pages long and the supplemental material is 15 pages. There are six supplemental movies that can be provided upon request to LDK

We investigate niobium oxide (NbO) as an alternative waveguide material for applications in the visible spectral range. NbO has a refractive index ranging between 2.3 and 2.35, which is about 25% higher than SiN, the most widely used material for waveguides in the visible spectral range. This increased index contrast between NbO and the cladding material allows to fabricate optical components with much smaller footprint, and consequently to increase the density of photonic integrated circuits substantially. We benchmark this waveguide platform to imec’s CMOS compatible PECVD SiN platform and observe fairly similar loss numbers for both materials.

We report on the fabrication, integration, and simulation, both optical and optoelectrical, of two-dimensional photonic nanostructures for advanced light trapping in thin crystalline silicon (c-Si) solar cells. The photonic nanostructures are fabricated by the combination of various lithography (nanoimprint, laser interference, and hole mask colloidal) and etching (dry plasma and wet chemical) techniques. The nanopatterning possibilities thus range from periodic to random corrugations and from inverted nanopyramids to high aspect ratio profiles. Optically, the nanopatterning results in better performance than the standard pyramid texturing, showing a more robust behavior with respect to light incidence angle. Electrically, wet etching results in higher minority carrier lifetimes compared to dry etching. From the integration of the photonic nanostructures into a micron-thin c-Si solar cell certain factors limiting the efficiencies are identified. More precisely: (a) the parasitic absorption is limiting the short circuit current, (b) the conformality of thin-film coatings on the nanopatterned surface is limiting the fill factor, and (c) the material damage from dry etching is limiting the open circuit voltage. From optical simulations, the optimal pattern parameters are identified. From optoelectrical simulations, cell design considerations are discussed, suggesting to position the junction on the opposite side of the nanopattern.

While the number of techniques for patterning materials at the nanoscale exponentially increases, only a handful of methods approach the conformal patterning of strongly non-planar surfaces. Here, using the direct surface self-assembly of colloids by electrostatics, we produce highly conformal bottom-up nanopatterns with a short-range order. We illustrate the potential of this approach by devising functional nanopatterns on highly non-planar substrates such as pyramid-textured silicon substrates and inherently rough polycrystalline films. We further produce functionalized polycrystalline thin-film silicon solar cells with enhanced optical performance. The perspective presented here to pattern essentially any surface at the nanoscale, in particular surfaces with high inherent roughness or with microscale features, opens new possibilities in a wide range of advanced technologies from affordable photovoltaics and optoelectronics to cellular engineering.

Gold (Au) nanoshells are known to exhibit many attractive optical properties caused by the excitation of localized surface plasmon resonances (LSPRs). Reducing the symmetry of these nanoshells has a number of interesting consequences, such as exciting different plasmon modes, making the optical response angle-dependent, and enhancing the local electric field intensity. In this paper, a versatile procedure involving ion milling has been developed to fabricate reduced-symmetrical Au semishells. This allows us to precisely control the reduced-symmetrical geometry and, particularly, the upward orientation of the created nanoaperture. These features, along with a combination of finite different time domain (FDTD) calculations, suggest Au semishell monolayer structures for a potential application in surface-enhanced Raman spectroscopy (SERS)-based biomolecule detection. Au semishells, additionally, exhibit advantageous features over Au nanoshells, for example, a more pronounced red shift of LSPR bands by tuning...

Plasmon rulers are an emerging concept in which the strong near-field coupling of plasmon nanoantenna elements is employed to obtain structural information at the nanoscale. Here, we combine nanoplasmonics and nanomagnetism to conceptualize a magnetoplasmonic dimer nanoantenna that would be able to report nanoscale distances while optimizing its own spatial orientation. The latter constitutes an active operation in which a dynamically optimized optical response per measured unit length allows for the measurement of small and large nanoscale distances with about 2 orders of magnitude higher precision than current state-of-the-art plasmon rulers. We further propose a concept to optically measure the nanoscale response to the controlled application of force with a magnetic field.

Quasicrystals are structures that possess long-range order without being periodic. We investigate the unique characteristics of a photonic quasicrystal that consists of plasmonic Ag nanodisks arranged in a Penrose pattern. The quasicrystal scatters light in a complex but spectacular diffraction pattern that can be directly imaged in the back focal plane of an optical microscope, allowing us to assess the excitation efficiency of the various diffraction modes. Furthermore, surface plasmon polaritons can be launched almost isotropically through near-field grating coupling when the quasicrystal is positioned close to a homogeneous silver surface. We characterize the dispersion relation of the different excited plasmon modes by reflection measurements and simulations. It is demonstrated that the quasicrystal in-coupling efficiency is strongly enhanced compared to a nanoparticle array with the same particle density but only short-range lateral order. We envision that the system can be useful for a number of advanced light harvesting and optoelectronic applications.

Localized and propagating surface plasmon resonances are known to show very pronounced interactions if they are simultaneously excited in the same nanostructure. Here, we study the Fano interference that occurs between localized surface plasmon resonance (LSPR) and propagating surface plasmon polariton (SPP) modes by means of phase-sensitive spectroscopic ellipsometry. The sample structures consist of periodic gratings of gold nanodisks on top of a continuous gold layer and a thin dielectric spacer, in which the structural dimensions were tuned in such a way that the dipolar LSPR mode and the propagating SPP modes are excited in the same spectral region. We observe pronounced anti-crossing and strongly asymmetric line shapes when both modes move to each other’s vicinity, accompanied of largely increased phase differences between the respective plasmon resonances. Moreover, we show that the anti-crossing can be exploited to increase the refractive index sensitivity of the localized modes dramatically, which result in largely increased values for the figure-of-merit which reaches values between 24 and 58 for the respective plasmon modes.

Localized surface plasmon resonances possess very interesting properties for a wide variety of sensing applications. In many of the existing applications, only the intensity of the reflected or transmitted signals is taken into account, while the phase information is ignored. At the center frequency of a (localized) surface plasmon resonance, the electron cloud makes the transition between in- and out-of-phase oscillation with respect to the incident wave. Here we show that this information can experimentally be extracted by performing phase-sensitive measurements, which result in linewidths that are almost 1 order of magnitude smaller than those for intensity based measurements. As this phase change is an intrinsic property of a plasmon resonance, this opens up many possibilities for boosting the figure-of-merit (FOM) of refractive index sensing by taking into account the phase of the plasmon resonance. We experimentally investigated this for two model systems: randomly distributed gold nanodisks and gold nanorings on top of a continuous gold layer and a dielectric spacer and observed FOM values up to 8.3 and 16.5 for the respective nanoparticles. ispartof: Nano Letters vol:12 issue:3 pages:1655-1659 ispartof: location:United States status: published

We show experimentally the successful use of colloidal lithography for the fabrication of negative index metamaterials in the near-infrared wavelength range. In particular, we investigated a specific implementation of the widely studied double fishnet metamaterials, consisting of a gold-silica-gold layer stack perforated by a hexagonal array of round holes. Tuning of the hole diameter allows us to tailor these self-assembled metamaterials both as single- ({\epsilon} < 0) and double ({\epsilon} < 0 and {\mu} < 0) negative metamaterials.

With a view to biomedical and environmental applications, we investigate the plasmonic properties of a rectangular gold nanodisk array in water to boost surface enhanced Raman scattering (SERS) effects. To control the resonance wavelengths of the surface plasmon polariton and the localized surface plasmon, their dependence on the array period and diameter in water is studied in detail using a finite difference time domain method. A good agreement is obtained between calculated resonant wavelengths and those of gold nanodisk arrays fabricated using electron beam lithography. For the optimized structure, a SERS enhancement factor of 7.8 × 107 is achieved in water experimentally.

We investigate the plasmonic properties of gold nanorings in close proximity to a gold film. The rings have been fabricated using nanosphere lithography and are optimized to boost their near-infrared surface enhanced Raman scattering (SERS) effects. A SERS enhancement factor as large as 1.4×107 has been achieved by tuning the separation between the gold nanorings and the gold film. In addition, we have numerically and experimentally demonstrated an enhanced tunability of the plasmon resonance wavelength and a narrowing of the plasmon linewidth for increasing ring-film interaction.

We study the spectral properties of a triangular plasmonic nanoslit-cavity with periodic triangular grooves to optimize the field enhancement inside the nanoslit. This work is mainly based on numerical calculations and also partly supported by experimental evidence. In the nanoslit-cavity, we can distinguish following three main contributions to the field enhancement: electrostatic interaction in the nanoslit, surface plasmon polariton standing waves in the cavity and excitation, and reflection of surface plasmon polaritons by the grating. The importance of phase matching between surface plasmons generated at the nanoslit and the gratings is also investigated in order to optimize the local field intensity in the nanoslit.