Low-loss Devices Research Articles

Active and Tunable Nanophotonics With Dielectric Nanoantennas

In recent years, high-index dielectric nanoantennas supporting Mie resonances have emerged as a promising platform to create low-loss nanophotonic devices. The multipolar resonances naturally supported by this kind of nanoantennas allow designing systems in which the out-coupling radiation, and in particular the directivity, can be tailored at will. Moreover, unlike plasmonic counterparts, local electromagnetic fields in resonant dielectric nanoparticles concentrate inside the structures rather than outside. This allows enhancing light–matter interactions in their volume and boosting their linear and nonlinear optical properties by choosing suitable semiconductors as the material platform to build them. In this article, we will discuss recent results on active and tunable nanophotonics based on resonant dielectric and semiconductor nanostructures. Specifically, we will focus on two main topics: active tuning of dielectric nanoantennas and enhancement and spectral shaping of light emission using dielectric nanoantennas, including lasing. Finally, future research directions and proposed practical applications will also be discussed.

Electromechanical losses in carbon- and oxygen-containing bulk AlN single crystals

Bulk single-crystalline aluminum nitride (AlN) is potentially a key component for low-loss high-temperature piezoelectric devices. However, the incorporation of electrically active impurities and defects during growth of AlN may adversely affect the performance of piezoelectric resonators especially at high temperatures. The electrical conductivity and electromechanical losses in bulk AlN single crystals are analyzed in the temperature range of 300–1200 K with respect to various contents of growth-related impurities in them. For AlN with [O]/[C] ≤ 1, an increase of electrical conductivity due to thermal activation of charge carriers in the temperature range of 850–1200 K has been observed and was determined to be a major contribution to electromechanical losses Q−1 rising up to maximum values of about 10−3 at 1200 K. As the oxygen content in AlN increased, the magnitude and the activation energy of high-temperature electrical conductivity increased. In oxygen-dominated AlN, two major thermally activated contributions to electromechanical losses were observed, namely, the anelastic relaxations of point defects at temperatures of 400–800 K and electrical conductivity at T > 800 K.

Efficiency and Conducted EMI Evaluation of a Single-Phase Power Factor Correction Boost Converter Using State-of-the-Art SiC Mosfet and SiC Diode

SiC-based diodes and mosfet s switch extremely quickly with low conduction losses. Thus, from the perspective of efficiency, such devices are ideal for a continuous conduction mode (CCM) boost power factor correction (PFC) converter. However, the circuit parasitic becomes alive while switching with high $dv/dt$ and $di/dt$ values, which necessitates the need for electromagnetic compatibility (EMC) compliance measurements. Employing the best available low-loss SiC mosfet and SiC diode, in this paper, a 1-kW PFC boost converter prototype was designed, developed, and evaluated with the objective of quantifying the efficiency and EMC signature. The efficiency is evaluated through two approaches, namely, a circuit simulation and a laboratory measurement. With the first approach, the switching losses are obtained using a widely accepted double-pulse test methodology, and the conduction losses are taken from the data sheet, whereas with the second approach, the current and voltage are recorded at the input and output of the PFC converter using power analyzer. The electromagnetic interference (EMI) is monitored using line impedance stabilizing network and EMC analyzer. To maximize the efficiency, a fast, clean switching of the silicon carbide (SiC) is necessary. Utilizing a low-parasitic printed circuit board design approach and switching the selected low-loss SiC devices with a 0 $\Omega$ external gate drive resistance, this PFC boost yields a peak efficiency of 97.2% at full-rated power when switched at 250 kHz. Furthermore, the EMI noise was measured at 66 and 250 kHz. It was found that the same EMI filter size satisfies the CISPR 11 Class B conducted EMI limit at both switching frequencies with a noise of approximately 10 dB higher at 250 kHz. As the main contribution of this paper, the best case efficiency and worst case EMI are evaluated in this paper.

Reversible Realization of 4-Bit Vedic Multiplier Circuit with Optimized Performance Parameters

Low power high speed calculating devices are foremost requirement of this era. Moreover, multiplication is considered as the most vital part of any calculating system. Multiplication process is generally considered as the speed limiting process as it requires more time as compared to other basic arithmetic calculations. So, here we focus on multiplication calculation using vedic method. Moreover, Reversible realization of any digital circuit improves the performance of the system by reducing the power loss from it. Here, the concept of vedic multiplication and Reversible approach are combined to propose a 4-bit multiplier circuit with optimized performance parameters. Proposed design is also analyzed and compared with existing designs. This approach may be employed to propose other low loss devices.

Spin-orbit coupling controlled near-field propagation and focusing of Bloch surface wave.

Bloch surface wave (BSW) can be considered as the dielectric analogue of surface plasmon polariton (SPP) with less loss since it is sustained at the surface of a truncated dielectric multilayer. As dielectric materials show nearly no ohmic loss, BSW can propagates much farther compared to SPP, and thus is beneficial for planar optical devices. In this paper, we study the spin-orbital interaction between incident beam and BSW. We demonstrate that due to the spin-orbital coupling, the near-field properties of generated BSW can be controlled with a meta-antenna structure. The meta-antenna is composed of two gold nano-antennas oriented at 45° and 135° as a near-field coupler. By careful design of the meta-antenna, the generated BSW can be guided and focused depending on the chirality of the incident beam. Three examples of meta-antennas are demonstrated for chiral sensitive focusing, directional switching and asymmetric focusing. The proposed method can be applied as a design method for low-loss on-chip photonic devices.

(Invited) Development of SiC Schottky-PN Diode with Low on Resistance and High Blocking Voltage

4H-SiC is a promising material for low-loss, high frequency, and high temperature electronic devices. And nowadays, 4H-SiC Schottky diodes, MOSFETs, and its inverters were used in many applications. As well known, a conduction loss and a switching loss shows tread off relationship on these devices. Schottky diode shows high speed switching action and small recovery current based on its unipolar operation, but high series resistance of drift layer. On the other hand, PiN diode shows low series resistance of drift layer due to its conductivity modulation phenomenon based on the bipolar action. However, it causes an adverse reverse recovery current and limited switching speed. To break this tread off relationship, Schottky-PN diode structure so-called SPND or SNPD was proposed with a diamond semiconductor [1]. This diode has a structure with a low doped n- or p- drift layer where is sandwiched and completely depleted with Schottky junction and one side PN junction. Under forward bias condition, barrier height of PN junction is reduced and majority carrier was injected into the drift layer completely depleted with Schottky junction. Injected majority carrier drift to Schottky junction without recombining with minority carrier. It means minority carrier dose not contribute to current flow under forward bias. Then, this SPND structure is expected to show both very low on-resistance and high speed switching action. Under reverse bias condition, blocking voltage is shared throughout the drift layer. However, the diamond semiconductor material is under development and difficult to use production phase. In this study, we demonstrated the possibility of SPND by using 4H-SiC substrate under mass production. In this study, we grew low doped p-layer on n+ 4H-SiC C-face substrate by using hot-wall chemical vapor deposition (CVD) system with H2-SiH4-C3H8 gas system. Trimethylaluminum (TMA) was used as p-type dopant source. The thickness and doing concentration of grown p- layer is 1.1 μm and 5 x 1014 cm-3. Pt was evaporated in vacuum as Schottky electrode on as grown surface. The diameter of Schottky contact is 1mm. Al was used as ohmic back contact. The schematic cross-sectional structure of fabricated 4H-SiC SPND is shown inset of Figure 1. Figure 1 shows typical J-V characteristic of fabricated 4H-SiC SPND at room temperature. Good rectifying characteristic was observed. The blocking voltage of 300 V was obtained (Fig. 1(a)). From this result, we estimated dielectric breakdown field value of 2.5 MV/cm which is almost equal to ideal value of 4H-SiC one. On forward bias characteristic, the current raises at 2.2 V and the current density is reached at 1200 A/cm2 at 2.4 V (Fig. 1(b)). From this value, the differential on-resistance was estimated at 0.18 mΩcm2. In this study, we used 4H-SiC substrate with thickness of 200 μm and resistivity of 20 mΩcm. The calculated series on-resistance of 4H-SiC substrate part was estimated as 0.4 mΩcm2. This result means estimated differential on-resistance of 0.18 mΩcm2 is almost the resistance of substrate and the resistance of drift layer dose not contribute to the series resistance. These results mean 4H-SiC SPND structure was realized and its good performance of low on-resistance with high blocking voltage was confirmed. Details will be shown in this presentation.

Low-loss and high-induction Fe-based soft magnetic composites coated with magnetic insulating layers

Abstract We have provided a new and simple coating strategy to fabricate high-performance metal-based magnetic composites exhibiting both high magnetic inductions and decreased core loss. High-purity submicron FeCo particles have been dispersed into silicone resin to form a magnetic insulating film, which is then coated uniformly on the particle surface of high-purity Fe powders with a particle size of 170 μm to form new-type Fe-based soft magnetic composites (SMCs). These insulated magnetic layers containing submicron FeCo particles in these Fe-based SMCs can maintain very high saturated magnetization (209 A·m2·kg−1) for the composites, and also result in their low core loss. For traditional metal-based SMCs, the low core loss is often obtained accompanying with seriously decreased magnetic inductions. In present work, both high magnetic inductions and decreased core loss in company with high compacted density are achieved in these Fe-based SMCs coated with magnetic insulating coating layers. Specifically, the extremely low eddy current loss occurring in these new Fe-based SMCs enables their latent applications in low-loss and high-power magnetic devices.

Atomistic tight binding study of quantum confined Stark effect in GaBixAs1−x/GaAs quantum wells

Recently, there has been tremendous research interest in novel bismide semiconductor materials (such as GaBixAs1−x) for wavelength-engineered, low-loss optoelectronic devices. We report a study of the quantum confined Stark effect (QCSE) computed for GaBixAs1−x/GaAs quantum well (QW) structures based on large-scale atomistic tight-binding calculations. A comprehensive investigation of the QCSE as a function of the applied electric field orientations and the QW Bi fractions reveals unconventional character of the Stark shift at low Bi compositions (). This atypical QCSE is attributed to a strong confinement of the ground-state hole wave functions due to the presence of Bi clusters. At technologically-relevant large Bi fractions (10%), the impact of Bi clustering on the electronic structure is found to be weak, leading to a quadratic Stark shift of the ground-state transition wavelength, similar to previously observed in other conventional III–V materials. Our results provide useful insights for the understanding of the electric field dependence of the electronic and optical properties of GaBixAs1−x/GaAs QWs, and will be important for the design of devices in the optoelectronics and spintronics areas of research.

Demonstration of a robust insertion loss measuring approach for low-loss silicon photonic devices.

A robust optical insertion loss measuring approach based on a symmetrically coupled add-drop microring resonator is demonstrated on silicon-on-insulator platform. Utilizing resonant wavelengths and relative values of measured optical power, this approach frees the insertion loss measurement from the uncertainties caused by experimental set-up, including system alignment and wavelength dependence of the couplers. Strip-slot mode converters were fabricated and measured to present the exemplary insertion loss measurement process. A series of experimental results confirm that the insertion loss of the low-loss silicon photonic devices can be accurately and reliably obtained even the adopted couplers are wavelength-dependent, and the fibers are deviated 15 μm from the horizontal direction and 110 μm from the vertical direction, exhibiting excellent robustness to the experimental set-up.

Obtaining Atomically Smooth 4H–SiC (0001) Surface by Controlling Balance Between Anodizing and Polishing in Electrochemical Mechanical Polishing

Single-crystal 4H–SiC is a promising next-generation semiconductor material for high-power and low-loss power devices. Electrochemical mechanical polishing (ECMP) is a very promising polishing technique for the manufacture of SiC wafers owing to its high efficiency and low cost. In this study, the effects of the balance between the anodic oxidation rate and the polishing rate of the oxide layer on the polishing performance of slurryless ECMP were studied in an attempt to obtain an atomically smooth surface efficiently. The polishing performance of ECMP was evaluated from the viewpoints of surface roughness, residual oxide, and material removal rate. It was found that the balance between the anodic oxidation rate and the polishing rate of the oxide layer strongly affects the surface roughness; the polishing rate of the oxide layer should be greater than the anodic oxidation rate to obtain an atomically smooth surface. By controlling this balance at a current density of 10 mA/cm2, we were able to decrease the surface roughness of a diamond-lapped 4H–SiC (0001) surface from Sq 4.290 to 0.577 nm and obtained a high material removal rate of about 10 μm/h. This study provides a promising way of obtaining atomically flat surfaces by slurryless ECMP.

Guiding and controlling light at nanoscale in field effect transistor

Metal–oxide–semiconductor field-effect transistor (MOSFET) and tunnel field-effect transistor (TFET) are proposed to guide and control the light at nanoscale utilizing the hybridization of plasmonic and optical modes. The hybrid plasmonic (HP) mode is confined in the dielectric sandwiched between the metal gate and semiconductor channel, which results from the coupling of surface plasmonic polariton mode at the metal–dielectric interface with the optical mode in the dielectric. Conventional conductivity modulations in the channel through gate and drain–source voltages are utilized to control the guided light. A long propagation length of 74 μm and a very small mode area of $$\lambda ^2/96$$ are reported for field-effect transistor at an operating wavelength of 1550 nm which are useful to realize low loss and compact optoelectronic devices. The charge-carrier dynamics along with the plasma dispersion effect in the silicon channel, through voltages applied on the gate and source–drain, result in the optical phase modulation in MOSFET and TFET. Phase shift of $$\pi$$ radian at a length of 1.2 mm and 0.21 mm is obtained in MOSFET and TFET, respectively. The proposed concept has the potential to enable multifunctionality of the mature field effect transistors.

Low-loss hybrid plasmonic coupler.

We demonstrate a low-loss coupling scheme between a silicon photonic waveguide and a hybrid-plasmonic waveguide. Measured coupling efficiencies reach up to 94% or -0.27 dB. The metal-insulator-semiconductor structure is fabrication-tolerant and adaptable to a wide range of materials including those used in CMOS processes. The coupler is a promising building block for low-loss active plasmonic devices.

Towards a photonic mid-infrared nulling interferometer in chalcogenide glass.

Nulling interferometry enables astronomers to advance beyond the resolving power of ground-based telescopes with the goal of directly detecting exo-planets. By diminishing the overwhelming emission of the host star through destructive interference, radiation from young companions can be observed. The atmospheric transmission window centered around 4 μm wavelength is of particular interest because it has a favorable contrast between star and planet as well as a reduced atmospheric disturbance. For robustness and high stability, it is desirable to employ integrated devices based on optical waveguide technology. Their development is hindered at this wavelength range due to the lack of suitable host materials and compatible fabrication techniques to create low-loss photonic devices. This paper details our work on femtosecond laser direct-written optical waveguides and key components for an on-chip nulling interferometer inside gallium lanthanum sulphur glass. By combining cumulative heating fabrication with the multiscan technique, single-mode optical waveguides with propagation losses as low as 0.22 ± 0.02 dB/cm at 4 μm and polarization-dependent losses of < 0.1 dB/cm were realized. Furthermore, S-bends with negligible bending loss and broadband Y-splitters with 50/50 power division across a 600 nm wavelength window (3.6 - 4.2 μm) and low losses of < 0.5 dB are demonstrated. Directional couplers with an equal splitting ratio complement these main building blocks to create a future compact nulling interferometer with a total projected intrinsic loss of < 1 dB, a value that is sufficient to perform future on-sky experiments in relatively short observation runs on ground-based telescopes.

Heterogeneous Integration of GaN and BCD Technologies and Its Applications to High Conversion-Ratio DC–DC Boost Converter IC

This letter presents a novel technology for the integration of gallium nitride (GaN) power devices with silicon control circuits. It comprises stacked GaN power transistors and bipolar-CMOS-double-diffused metal-oxide-semiconductor (DMOS) (BCD) circuits. It leverages on both advantages of the high-voltage low-loss GaN devices and the high-integration BCD circuits. Using conventional manufacturing, packaging, and assembly techniques and equipment, the proposed technology is technology transferrable and applicable for commercial power electronic applications. To validate the concept, a 3.3–70 V dc–dc boost converter is designed, implemented, and verified experimentally. It features a conversion efficiency of 70.3%, output power of 1.68 W, and compact size of ${\text{0.32}}\times {\text{0.18}}\,{\text{cm}}^{2}$ .

Perovskites cut energy losses

The realization of perovskite nanostructures featuring high emission efficiency and a wide Stokes shift is proving difficult, limiting their impact on luminescent solar concentration technology. Now, engineered exciton routing within multilayered perovskite nanoplatelets may open a path towards high-performing, low-loss devices.

RGB Magnetophotonic Crystals for High-contrast Magnetooptical Spatial Light Modulators

Magnetooptical spatial light modulators (MOSLMs) are photonic devices that encode information in photonic waveforms by changing their amplitude and phase using magnetooptical Faraday or Kerr rotation. Despite the progress on both MO materials and switching methods, significant improvements on materials engineering and SLM design are needed for demonstrating low-power, multicolor, analog and high-contrast MOSLM devices. In this study, we present design rules and example designs for a high-contrast and large figure-of-merit MOSLM using three-color magnetophotonic crystals (MPC). We demonstrate for the first time, a three-defect MPC capable of simultaneously enhancing Faraday rotation, and high-contrast modulation at three fundamental wavelengths of red, green and blue (RGB) within the same pixel. We show using 2D finite-difference time-domain simulations that bismuth-substituted yttrium iron garnet films are promising for low-loss and high Faraday rotation MOSLM device in the visible band. Faraday rotation and loss spectra as well as figure-of-merit values are calculated for different magnetophotonic crystals of the form (H/L)p/(D/L)q/(H/L)p. After an optimization of layer thicknesses and MPC configuration, Faraday rotation values were found to be between 20–55° for losses below 20 dB in an overall thickness less than 1.5 µm including three submicron garnet defect layers. The experimental demonstration of our proposed 3-color MOSLM devices can enable bistable photonic projectors, holographic displays, indoor visible light communication devices, photonic beamforming for 5 G telecommunications and beyond.

Lateral dimension tuned ultra-low loss effective surface plasmonic waveguide

Recent theoretical and experimental works demonstrate that effective surface plasmon polaritons (ESPPs) induced by structural dispersion in bounded waveguide are perfect low-frequency counterparts of optical SPPs both for the double-layered and multi-layered systems. In all these efforts, the lateral dimension of each layer was assumed to be the same and the dispersion of the ESPPs was only tuned by the dielectric permittivity in each layer. Inevitably, the dielectric loss will deteriorate the transmission performance of ESPPs due to the huge field confinement and enhancement. In this work, we propose a simple but robust scheme to dramatically enhance the transmission efficiency of ESPPs by introducing a double-layered air-filled plasmonic waveguide with different lateral dimensions. Simulation and experimental results demonstrate that an ultra-low loss plasmonic waveguide with tunable bandwidth can be easily built by changing the lateral dimension of the upper air layer. This work provides valuable guidance for flexible design of low-loss plasmonic devices and systems at microwave and terahertz frequencies.

Towards low-loss telecom-wavelength photonic devices by designing GaBixAs1-x/GaAs core-shell nanowires.

Nanowires are versatile nanostructures, which allow an exquisite control over bandgap energies and charge carrier dynamics making them highly attractive as building blocks for a broad range of photonic devices. For optimal solutions concerning device performance and cost, a crucial element is the selection of a suitable material system which could enable a large wavelength tunability, strong light interaction and simple integration with the mainstream silicon technologies. The emerging GaBixAs1-x alloys offer such promising features and may lead to a new era of technologies. Here, we apply million-atom atomistic simulations to design GaBixAs1-x/GaAs core-shell nanowires suitable for low-loss telecom-wavelength photonic devices. The effects of internal strain, Bi Composition (x), random alloy configuration, and core-to-shell diameter ratio (ρD) are analysed and delineated by systematically varying these attributes and studying their impact on the absorption wavelength and charge carrier confinement. The complex interplay between x and ρD results in two distinct pathways to accomplish 1.55 μm optical transitions: either fabricate nanowires with ρD≥ 0.8 and x∼ 15%, or increase x to ∼30% with ρD≤ 0.4. Upon further analysis of the electron hole wave functions, inhomogeneous broadening and optical transition strengths, the nanowires with ρD≤ 0.4 are unveiled to render favourable properties for the design of photonic devices. Another important outcome of our study is to demonstrate the possibility of modulating the strain character from a compressive to a tensile regime by simply engineering the thickness of the core region. The availability of such a straightforward knob for strain manipulation without requiring any external stressor component or Bi composition engineering would be desirable for devices involving polarisation-sensitive light interactions. The presented results document novel characteristics of the GaBixAs1-x/GaAs nanowires with the possibility of myriad applications in nanoelectronic and nanophotonic technologies.

State-of-the-Art Technologies for Development of High Frequency Transformers with Advanced Magnetic Materials

With the development of advanced soft magnetic materials of high-saturation flux density and low specific core loss and semiconductor power devices, the high-frequency transformer (HFT) has received significant attention in recent years for its widespread emerging applications. The optimal design of high-power-density HFTs for high-performance energy conversion systems is, however, a multiphasic problem that needs special considerations on various aspects such as core material selection, minimization of parasitic components, and thermal management. This paper presents a comprehensive review on advancement of soft magnetic materials for high-power-density magnetic devices and advanced technologies for characterizations and optimal design of HFTs. The future research and development trends are also discussed.

Hypersonic Surface Phononic Bandgap Demonstration in a CMOS-Compatible Pillar-Based Piezoelectric Structure on Silicon

The promise of surface phononic crystals (PnCs) for $e.g.$ rf signal processing in wireless communication (like your mobile phone) has not been realized, due to the complexity of acoustic wave propagation in such structures, plus the lack of a low-loss, CMOS-compatible platform. The authors identify a wide, hypersonic surface phononic band gap in a pillar-based surface PnC. The significance of their platform lies in the reduced phononic material loss in dielectric pillars, and the use of CMOS-compatible AlN. This allows dense integration of low-loss hypersonic devices with electronics on the same die, enabling many exciting applications of surface PnCs.