Showing papers by "Navab Singh published in 2016"

Active Control of Electromagnetically Induced Transparency Analog in Terahertz MEMS Metamaterial

Abstract: 1 wileyonlinelibrary.com C o m m u n iC a io n and their possible applications. The ultimate form of active manipulation of EIT phenomenon will be when all three primary parameters are controlled independently. The independent control of individual resonators demands for the controllability at unit cell level, and conventional approaches such as optical pumping of photoconductive elements or thermally controlled superconductor are restricted to provide only global control. Recently, microelectromechanical systems (MEMS) based tunable metamaterials have been reported to achieve controllability at unit cell level, along with the added advantage of being electrically controlled, miniaturized size and enhanced electrooptic performance. The versatility of MEMS design has enabled active manipulation of numerous THz properties such as magnetic resonance,[19–22] electrical resonance,[23–25] anisotropy,[26] broadband response,[27] isotropic resonance switching[28] multiresonance switching,[29–31] and coupling strength between resonators.[32] The enhanced controllability and direct integration of MEMS actuators into metamaterial unit cell geometry is an ideal fit for the realization of selective control of coupled mode resonators. In this Communication, reconfigurable metamaterial with independently controlled bright and dark mode resonators is proposed for advanced manipulation of the classical analog of EIT and slow light effects in THz spectral region. The active control of bright mode resonator enables modulation of EIT intensity, while the tuning of dark mode resonance causes the EIT peak to tune in frequency. Furthermore, simultaneous switching of bright and dark mode resonators results in dynamic switching of the system between coupled and uncoupled states. The proposed approach of selective reconfiguration can be scaled for multiresonator systems, which can be coupled either through inductive, capacitive, or conductive means. The metamaterial consists of 80 × 80 periodic array of cut wire resonator (CWR) with closely placed split ring resonators (SRRs), as shown in Figure 1 and Figure 2. The periodicity of unit cell is 100 μm along both axial directions. The CWR has length, lC = 60 μm and width, wC = 5 μm, respectively. The SRRs have a base length, bS = 30 μm, side length, lS = 20 μm, and split gap, gS = 4 μm. The SRRs are placed at a distance of S = 2 μm from the CWR. When the polarization of the excitation field is along the CWR arm, the dipole mode resonance of the CWR will be the bright mode and the inductive-capacitive (LC) mode of SRR resonance acts as the dark mode. Thus for the incident THz polarization, the direct excitation of the bright mode induces image charges on the nearby SRRs through nearfield inductive coupling, thereby exciting the LC resonance of the SRRs. These bright-dark resonances have contrasting line widths with identical resonance frequencies and under a strong coupling regime they experience an EIT-type of interference that gives rise to a sharp transmission peak. Thus, through Active Control of Electromagnetically Induced Transparency Analog in Terahertz MEMS Metamaterial

Large Area Artificial Spin Ice and Anti‐Spin Ice Ni80Fe20 Structures: Static and Dynamic Behavior

Abstract: Artificial spin ice has been the subject of extensive investigation in the last few years due to advances in nanotechnology and characterization techniques. So far, most of the studies have been limited to local probe of small area magnetic elements due to limitations with lithographic techniques used. In this study, large area spin ice and anti-spin ice Ni80Fe20 structures with three lattice configurations have been fabricated using deep ultraviolet lithography at 193 nm exposure wavelength. The static and dynamic properties are systematically characterized using vibrating sample magnetometer, magnetic force microscopy, and broadband ferromagnetic resonance spectroscopy. Intriguing static and dynamic behaviors are observed due to the geometrical arrangement of the nanomagnets in the lattice. When the nanomagnets are saturated at high field, multiple resonance peaks whose frequencies are strongly dependent on the orientation of the applied magnetic field are observed. The experimental results are in qualitative agreement with the micromagnetic simulations. These findings may find application in the design of magnetically controlled tunable microwave filters.

A High Coupling Coefficient 2.3-GHz AlN Resonator for High Band LTE Filtering Application

Abstract: This letter reports an aluminium nitride (AlN)-based micromechanical resonator with high-effective coupling coefficient ( $k_{\textrm {eff}}^{2})$ and low insertion loss (IL), which are comparable with those of Film Bulk Acoustic Resonators (FBARs). The in-house-fabricated resonator comprises of lithographically patterned top and bottom molybdenum interdigitated electrode fingers and a layer of 1- $\mu \text{m}$ -thick AlN sandwiched in between. Synergetic inter-mode coupling between the constituent thickness mode and the lateral mode can be realized within a wide frequency range, which can be treated as a subcategory of degenerated cross-sectional Lame mode, enabling the capability of lithographic tuning of resonant frequency yet not compromising $k_{\textrm {eff}}^{2}$ . Measurement results show that the designed 2.3-GHz resonator achieves a $k_{\textrm {eff}}^{2}$ of 6.34% and an IL of 0.26 dB upon direct connection to a network with 50- $\Omega $ termination, making it a promising candidate for Wireless Local Area Network (WLAN) and high band Long Term Evolution (LTE) band selection filtering applications.

Analysis of spurious modes, Q, and electromechanical coupling for 1.22 GHz AlN MEMS contour-mode resonators fabricated in an 8″ silicon fab

Abstract: A systematical study is performed to analyze the spurious modes, Q and electromechanical coupling of 1.22 GHz AlN MEMS contour-mode resonators. A total of 135 different geometrical configurations were studied. An unloaded Q of up to 3157, an electromechanical coupling of up to 2.3%, and a figure of merit of up to 61.6 were achieved. In particular, we found that Q is primarily affected by finger length and anchor type. Also, overhang extension and finger numbers are the only parameters that change the relative location of main mode and spurs. Ultimately, by optimizing these two parameters it is possible to attain a high figure of merit while pushing the spurious modes away from the main mode of resonance.

Hermetic Wafer Level Thin Film Packaging for MEMS

Abstract: We report a hermetic thin film packaging on aluminum nitride AlN RF MEMS platforms that is entirely CMOS compatible and wafer level executed. The process flow, including release of multiple free-moving body and encapsulation of the functional structures are demonstrated using 8" wafer level thin film micromachining technology. The encapsulated devices are reported to survive post CMOS assembly processes such as wafer level dicing and flip-chip bonding. Both fabrication outcome and measurement results indicate high possibility in cost effective and footprint reduction in MEMS integration technology.

Active control of electromagnetically induced transparency analogue and slow light phenomena via MEMS based terahertz metamaterials

Abstract: Classical analogue of electromagnetically induced transparency mediated by near field coupling in meta-atom resonators form the basis for design of slow light metamaterial devices. Here, we experimentally demonstrate the active control of individual resonators in the near-field coupled system. This allows for active modulation and spectral tuning of the transparency peak and hence the slow light behavior in terahertz spectral range.