Lior Gal

Measurements and Simulations of Low Dark Count Rate Single Photon Avalanche Diode Device in a Low Voltage 180-nm CMOS Image Sensor Technology

This paper presents the key features of single photon avalanche diode (SPAD) devices fabricated in a low voltage commercial 180-nm CMOS image sensor technology exhibiting very low dark count rate (DCR). The measured DCR is <; 100 Hz at room temperature even for excess voltages above 2 V. The active junction of the SPAD measures 10 μm in diameter within a 24-μm test structure. The active region where Geiger avalanche occurs is determined by an implanted charge sheet. Edge avalanche is averted by utilizing a virtual guard ring, formed by the retrograde well profile. The design, measurements, and simulations of doping and electric field profiles that lead to such low DCR are reported and analyzed. The current-voltage characteristics and the temperature dependence of the breakdown voltage provide further, indirect evidence for the low DCR measured in the device. Thus, the key features of measured good SPADs are presented and are correlated with simulations that give physical insight on how to design high-performance SPADs.

Revealing the subfemtosecond dynamics of orbital angular momentum in nanoplasmonic vortices

Putting plasmons in a spin The ability of light to carry angular momentum provides an additional degree of freedom for applications such as optical tweezing and optical communication. Spektor et al. show that the optical angular momentum modes of light can be shrunk down to the nanometer scale through plasmonic transfer. They patterned spiral-like structures into an atomically smooth layer of gold, which allowed them to launch plasmons with controlled amounts of angular momentum. Science, this issue p. 1187 Rotating plasmonic excitations can be launched with controlled amounts of optical angular momentum. The ability of light to carry and deliver orbital angular momentum (OAM) in the form of optical vortices has attracted much interest. The physical properties of light with a helical wavefront can be confined onto two-dimensional surfaces with subwavelength dimensions in the form of plasmonic vortices, opening avenues for thus far unknown light-matter interactions. Because of their extreme rotational velocity, the ultrafast dynamics of such vortices remained unexplored. Here we show the detailed spatiotemporal evolution of nanovortices using time-resolved two-photon photoemission electron microscopy. We observe both long- and short-range plasmonic vortices confined to deep subwavelength dimensions on the scale of 100 nanometers with nanometer spatial resolution and subfemtosecond time-step resolution. Finally, by measuring the angular velocity of the vortex, we directly extract the OAM magnitude of light.

Hybrid approach for RF MEMS devices

This work presents the RF design considerations of electro-mechanical MEMS structures realized by the hybrid approach. Modeling of the MEMS devices capacitance in up state is different than for surface micromachined devices, due to significant fringing fields. RF MEMS demonstrators as switch and inductor have been modeled, simulated and RF characterized. The fabrication of the hybrid devices has been performed using bulk micromachining of an SOI wafer, followed by a vertical integration with a GaAs and InP circuit substrates.

First demonstration of plasmonic GaN quantum cascade detectors with enhanced efficiency at normal incidence

We have designed, fabricated and measured the first plasmon-assisted normal incidence GaN/AlN quantum cascade detector (QCD) making use of the surface plasmon resonance of a two-dimensional nanohole Au array integrated on top of the detector absorption region. The spectral response of the detector at room temperature is peaked at the plasmon resonance of 1.82 μm. We show that the presence of the nanohole array induces an absolute enhancement of the responsivity by a factor of ~30 over that of the bare device at normal incidence and by a factor of 3 with respect to illumination by the 45° polished side facet. We show that this significant improvement arises from two phenomena, namely, the polarization rotation of the impinging light from tangential to normal induced by the plasmonic structure and from the enhancement of the absorption cross-section per quantum well due to the near-field optical intensity of the plasmonic wave.

Hybrid RF-MEMS Switches Realized in SOI Wafers by Bulk Micromachining

This paper presents an RF microelectromechanical systems (MEMS) switch based on hybrid technology. Electromechanical, microwave, and fabrication design considerations are presented. The methodology is illustrated using shunt contact MEMS switches. The fabrication of the MEMS devices was performed using bulk micromachining processing of a silicon-on-insulator wafer, followed by vertical (3-D) integration with a microwave coplanar transmission line on a GaAs and silicon substrates. The electromechanical and RF performance of the switch were characterized. An isolation of 34 dB at 35 GHz and an insertion loss of 0.1 dB at 35 GHz for a shunt switch were achieved. The concept of a packaged RF switch described in this paper enables a modular implementation of a flexible switch design, independent of the RF circuit substrate material or technology being used.

Linearly dichroic plasmonic lens and hetero-chiral structures.

We present an experimental study of Hetero-Chiral (HC) plasmonic lenses, comprised of constituents with opposite chirality, demonstrating linearly dichroic focusing. The lenses focus only light with a specific linear polarization and result in a dark focal spot for the orthogonal polarization state. We introduce the design concepts and quantitatively compare several members of the HC family, deriving necessary conditions for linear dichroism and several comparative engineering parameters. The HC lenses were experimentally investigated using aperture-less near field scanning microscope collecting the amplitude of the plasmonic near-field. Our results exhibit an excellent match to the simulation predictions. The demonstrated ability for linearly dichroic functional focusing could lead to novel sensing applications.

Single Photon Avalanche Diode Collection Efficiency Enhancement via Peripheral Well-Controlled Field

Single-photon avalanche diodes photon detection efficiency (PDE) and breakdown uniformity are studied. An approach to increase the PDE based on controlled breakdown of the peripheral region of the junction is described. Parameters influencing and controlling the peripheral region breakdown are discussed. A collection efficiency >60% is demonstrated, nearly twice that of a conventional, planar breakdown device.

Vertically Integrated MEMS SOI Composite Porous Silicon-Crystalline Silicon Cantilever-Array Sensors: Concept for Continuous Sensing of Explosives and Warfare Agents

This study focuses on arrays of cantilevers made of crystalline silicon (c-Si), using SOI wafers as the starting material and using bulk micromachining. The arrays are subsequently transformed into composite porous silicon-crystalline silicon cantilevers, using a unique vapor phase process tailored for providing a thin surface layer of porous silicon on one side only. This results in asymmetric cantilever arrays, with one side providing nano-structured porous large surface, which can be further coated with polymers, thus providing additional sensing capabilities and enhanced sensing. The c-Si cantilevers are vertically integrated with a bottom silicon die with electrodes allowing electrostatic actuation. Flip Chip bonding is used for the vertical integration. The readout is provided by a sensitive Capacitance to Digital Converter. The fabrication, processing and characterization results are reported. The reported study is aimed towards achieving miniature cantilever chips with integrated readout for sensing explosives and chemical warfare agents in the field.

High tuning range MEMS capacitor for microwave applications

This paper presents a novel MEMS comb-structured variable capacitor at 20GHz that features a wide capacitance tuning range of 200%, yet avoids unwanted coupling through the springs. This new varactor consists of three comb structures — two of which are anchored to the substrate, while the third, which capacitively couples the two anchored ones, is movable, suspended on mechanical springs. This new design decouples the mechanical mechanism from the RF capacitor and allows an independent optimal design of the two.

Doubly Resonant Nanoantennas on Diamond for Spatial Addressing of Spin States

The negatively charged nitrogen-vacancy (NV) color center in diamond is an important atom-like system for emergent quantum technologies and sensing at room temperature. The light emission rates and collection efficiency are key issues toward realizing NV-based quantum devices. In that aspect, we propose and experimentally demonstrate a selective and spatially localized method for enhancing the light-matter interaction of shallow NV centers in bulk diamonds. This was achieved by polarized doubly resonant plasmonic antennas, tuned to the NV phonon sideband transition peak in the red and the narrowband near infrared (NIR) singlet transition. We obtained a photoluminescence (PL) enhancement factor of about 10 from NV centers within the hot spot of the antenna area (excluding the extraction efficiency enhancement) and similar emission lifetime reduction. The functionality of the double resonance antenna is controlled by the impinging light polarization.