Fu-Li Hsiao

Computational Study of Photonic Crystals Nano-Ring Resonator for Biochemical Sensing

We investigated the characteristics of photonic crystals (PCs) nano-ring resonators as biochemical sensors theoretically. The new nano-ring resonators were formed by removing holes of a hexagon from a two-dimensional (2-D) silicon PC slab in hexagonal lattice. Resonant peak with quality factor of about 3000 is reported. Biomolecules, e.g., DNAs, trapped in a hole functionalized with molecule probes made the wavelength shift of resonant peak derived in the output terminal. The sensitivity of various sensing holes along the nano-ring was characterized. This new PC nano-ring resonator demonstrated promising features as a biochemical sensor.

A 1-V Operated MEMS Variable Optical Attenuator Using Piezoelectric PZT Thin-Film Actuators

A rotational Si mirror driven by PZT actuators has been investigated for variable optical attenuator (VOA) applications. The PZT actuators deploy 3.1-mum PZT layer. The developed PZT-driven microelectromechanical systems VOA comprising a large Si reflection mirror integrated with a dual core fiber collimator in 3-D light attenuation arrangement. The curve of the attenuation versus driving voltage shows rather uniform changing rate taking the advantage of the linear relation between the optical angle and the driving voltage. Dynamic range of 40-50 dB is achieved at 1 and 1.2 dc driving voltages, respectively.

Nanophotonic biosensors using hexagonal nanoring resonators: computational study

The characteristics of biochemical sensors based on photonic crystal (PC) resonators are investigated in this work. The PC structure consists of holes arranged in a hexagonal lattice on a silicon slab. The nanoring resonator is formed by removing certain holes along a hexagonal trace. The hexagonal nanoring resonator is sandwiched by two PC waveguides that are formed by removing two lines of holes. The trapping of biomolecules, e.g., DNAs or proteins, in a functionalized sensing hole introduces a shift in resonant wavelength peak in the output terminal. We demonstrate two resonator designs: single and dual nanorings. The quality factor of the single nanoring resonator is 2400. The dual nanoring resonator reveals two different resonant modes. The propagated directions of dropped light for these two modes are antiparallel. The quality factors for these two resonant modes are 2100 and 1855, respectively. This dual nanoring resonator has a novel sensing mechanism, making it capable of simultaneously sensing two different biomolecules.

Computational Characterization of a Photonic Crystal Cantilever Sensor Using a Hexagonal Dual-Nanoring-Based Channel Drop Filter

We investigated photonic crystal-based dual-nanoring (DNR) channel drop filters for nanomechanical sensor applications. The backward drop mechanism is explained by a proposed model. A resonant peak at 1553.6 nm with a quality factor better than 3800 is observed at the backward drop port. When this DNR is integrated at the junction between the silicon cantilever and the substrate, the deformation of the silicon cantilever can be detected in terms of the resonant wavelength and resonant wavelength shift. The derived minimum detectable force is 37 nN.

Experimental Investigation of a Cavity-Mode Resonator Using a Micromachined Two-Dimensional Silicon Phononic Crystal in a Square Lattice

A 2-D silicon phononic crystal (PnC) slab of a square array of cylindrical air holes in a 10-μm-thick freestanding silicon plate with line defects is characterized as a cavity-mode PnC resonator. A piezoelectric aluminum nitride (AlN) film is employed as the interdigital transducers to transmit and detect acoustic waves, thus making the whole microfabrication process CMOS compatible. Both the band structure of the PnC and the transmission spectrum of the proposed PnC resonator are analyzed and optimized using finite-element method. The measured quality factor (Q factor) of the microfabricated PnC resonator is over 1000 at its resonant frequency of 152.46 MHz. The proposed PnC resonator shows promising acoustic resonance characteristics for radio-frequency communications and sensing applications.

Silicon two-dimensional phononic crystal resonators using alternate defects

We present the numerical and experimental investigations of micromechanical resonators made by creating alternate defects with different central-hole radii (r′) in a two-dimensional (2-D) phononic crystal (PnC) slab. The PnC structures were fabricated by etching a square array of cylindrical air holes in a 10 μm thick free-standing silicon plate using a CMOS-compatible process. Preliminary experimental results show that the performance of the PnC resonators in terms of resonant frequency, Q factor, and insertion loss (IL) is highly dependent on r′. A Q factor of more than 3000 is achieved for the case of r′ = 6 μm while all the designed resonators with alternate defects have higher Q factor and lower IL than the resonators based on the normal Fabry-Perot structure due to the reduction in the mode mismatch.

A nano-ring resonator based on 2-D hexagonal-lattice photonic crystals

We proposed a novel channel drop filter based on two dimensional (2-D) silicon hexagonal-lattice photonic crystals (PCs). The PC filters consist of hexagonal silicon nano-ring resonator and two terminal waveguides by removing arrays of air cylinders of the same trace arranged in the hexagonal lattice of a silicon thin plate. The effects of the coupling distance between resonator and waveguides are studied. By integrating dual nano-ring resonators to form the filter, we demonstrated a two-port channel drop function.

Numerical and experimental study on silicon microresonators based on phononic crystal slabs with reduced central-hole radii

In this paper, we report the numerical and experimental study on micromechanical resonators which are made by introducing defects on an otherwise perfect two-dimensional (2D) silicon phononic crystal (PnC) slab. The 2D PnC slab is made by etching a square array of cylindrical air holes in a free-standing silicon plate with a thickness of 10??m, while the defects are created by reducing the radii of three rows of air holes at the centre of the 2D PnC slab. Three resonators with different values of reduced radii, i.e., 2??m, 4??m and 6??m, are included in this study. The finite-element-modelling method is used to calculate the band structure of the perfect 2D PnC slab and to analyse the different mode shapes of the structure. The design, numerical modelling, fabrication process, as well as characterization results and discussions of the three PnC resonators are also included. Due to its CMOS-compatibility, aluminium nitride is chosen to be the piezoelectric material of the inter-digital transducers, which are used to generate and detect acoustic waves. Testing is done to characterize the resonant frequency (f), quality factor (Q), as well as insertion loss of each of the three microfabricated PnC resonators and the results are discussed by analysing the simulated transmission spectra, the defected band structures, and the steady-state displacement profiles of the structures at their respective resonant frequencies. The experimental results show that the designed PnC resonators with reduced central-hole radii have higher resonant frequency and higher quality factors as compared to their normal Fabry?Perot counterpart, thanks to the higher-frequency modes supported within the cavity and slow sound effect in the lateral direction introduced by the central holes with reduced radii, respectively. As a result, the achieved (f-Q) product can be as high as 2.96???1011, which is among the highest for silicon resonators operating in air.

Micromechanical Resonators Based on Silicon Two-Dimensional Phononic Crystals of Square Lattice

Phononic crystal (PnC) resonators of Bloch-mode resonance made by replacing periodically arranged two or three rows of air holes with one row of air holes on a two-dimensional (2-D) silicon slab with air holes of square lattice have been investigated. Piezoelectric aluminum nitride (AlN) film is employed as the interdigital transducers to transmit and detect acoustic waves, thus making the whole microfabrication process CMOS compatible. We also fabricate a PnC structure which has a stopband of 140 MHz <; f <; 195 MHz which agrees well with the simulation results. From our experimental results, we found that the two kinds of microfabricated PnC resonators have different optimization conditions in terms of resonant frequency and Q factor, as well as insertion loss, despite their similar design approach. As compared to PnC resonators of hexagonal lattice, the proposed Bloch-mode PnC resonators of square lattice demonstrated higher resonant frequency, higher Q factor, and a smaller device area. The promising acoustic characteristics may be further optimized for applications such as microfluidics, biomedical devices, and radio-frequency communications in the gigahertz range.

Investigation on the optimized design of alternate-hole-defect for 2D phononic crystal based silicon microresonators

This paper shows the design, fabrication, and characterization of the Bloch-mode micromechanical resonators made by creating alternate defects to form a resonant cavity on a two-dimensional silicon phononic crystal slab of square lattice. The length of the resonant cavity (L) and the central-hole radius (r′) are varied to optimize the performance of the resonators. CMOS-compatible aluminium nitride is used as the piezoelectric material of the interdigital transducer to launch and detect acoustic waves. The extent of energy confinement within the cavity, as shown by the simulated displacement profiles of the resonators, agrees with the measured Q factors. We also quantitatively analysed the band structure of the proposed resonators and found that the Q factors are generally in an inverse relationship with the standard deviation of the band, due to the slow sound effect brought by flat bands which reduces the energy loss along the lateral direction (Y direction) and enhances the Q factor.