Single Etch Step Research Articles

A high efficiency silicon nitride waveguide grating coupler with a multilayer bottom reflector

We propose a high efficiency apodized grating coupler with a bottom reflector for silicon nitride photonic integrated circuits. The reflector consists of a stack of alternate silicon nitride and silicon dioxide quarter-wave films. The design, fabrication and optical characterization of the couplers has been presented. The measured fiber to detector insertion loss was −3.5 dB which corresponds to a peak coupling efficiency of −1.75 dB. A 3 dB wavelength bandwidth of 76.34 nm was demonstrated for the grating coupler with a 20-layer reflector. The fabrication process is CMOS-compatible and requires only a single etching step.

Highly efficient passive InP polarization rotator-splitter.

Monolithically integrated polarization beam splitters (PBSs) are needed to reduce the form-factor and assembly cost of optical coherent receivers. A highly efficient passive polarization rotator and splitter based on mode-evolution is demonstrated. The device is fabricated on InP substrate with a single etch-step and uses an adiabatic mode-converter and an asymmetric Y-coupler. Despite its simple fabrication process, the device shows a polarization extinction ratio (PER) better than 19 dB over 1520 nm to 1620 nm, thus covering both C- and L-band. The peak value of 24 dB is obtained for TE and TM polarizations. Its fabrication tolerance is large, so that even under a width variation of +/- 200 nm the PER remains above 17 dB over the entire C- and L-band.

Single-Cell Point Constrictions for Reagent-Free High-Throughput Mechanical Lysis and Intact Nuclei Isolation.

Highly localized (point) constrictions featuring a round geometry with ultra-sharp edges in silicon have been demonstrated for the reagent-free continuous-flow rapid mechanical lysis of mammalian cells on a single-cell basis. Silicon point constrictions, robust structures formed by a single-step dry etching process, are arranged in a cascade along microfluidic channels and can effectively rupture cells delivered in a pressure-driven flow. The influence of the constriction size and count on the lysis performance is presented for fibroblasts in reference to total protein, DNA, and intact nuclei levels in the lysates evaluated by biochemical and fluoremetric assays and flow-cytometric analyses. Protein and DNA levels obtained from an eight-constriction treatment match or surpass those from a chemical method. More importantly, many intact nuclei are found in the lysates with a relatively high nuclei-isolation efficiency from a four-constriction treatment. Point constrictions and their role in rapid reagent-free disruption of the plasma membrane could have implications for integrated sample preparation in future lab-on-a-chip systems.

Subwavelength-grating-based compact and broadband TE-pass polarizer for slot waveguides on a SOI platform

We have numerically proposed a compact, broadband, and high-extinction-ratio (ER) TE-pass polarizer for vertical slot waveguides using a subwavelength grating slot (SWGS) waveguide on a silicon-on-insulator (SOI) platform. By carefully tailoring the equivalent material index, the TE fundamental mode (i.e., TE0) is supported in the SWGS waveguide, while the TM fundamental mode (i.e., TM0) is suppressed under the cutoff condition. Consequently, the input TE0 mode can pass through with negligible loss, whereas the injected TM0 mode will leak from the SWGS waveguide completely, realizing an efficient TE-pass polarizer. The proposed device only needs a single etching step, substantially reducing the fabrication difficulty compared with the previous counterparts. Moreover, thanks to the used SWGS configuration, such a device also exhibits a remarkable broadband property. From the results, the proposed polarizer with a total length of ∼56 μm has a high ER of 40.5 dB and an insertion loss (IL) of 0.42 dB at 1.55 μm, and its bandwidth is as large as ∼210 nm with ER>36 dB and IL<1 dB. In addition, fabrication tolerances to the key structural parameters are analyzed, and field evolution through the suggested polarizer is also presented.

A nanoporous GaN photoelectrode on patterned sapphire substrates for high-efficiency photoelectrochemical water splitting

The photoelectrode of highly ordered nanoporous GaN on patterned sapphire substrate (PSS) is exploited to address issues of optical absorption and photocarrier separation efficiency in solar water splitting. The introduced PSS reduces the threading dislocation (TD) density and defects of the GaN epilayer, resulting in the improved crystalline quality, which suppresses recombination of electron-hole pairs. A single-step top-down etching approach is developed to fabricate the nanoporous GaN using an anodic aluminum oxide (AAO) mask conveniently and economically. The highly ordered nanoporous morphologies of AAO membrane are well transferred into the GaN surface grown on PSS via inductively coupled plasma (ICP) dry etching. Surface nanostructuring significantly increases surface-volume ratio of GaN, more incident light is trapped and absorbed by nanoporous structure, and the unabsorbed light scattered by PSS upwards is re-absorbed in nanoporous GaN. The ultraviolet light absorptance and reflectance of nanoporous GaN grown on PSS were improved significantly, close to 89% and 9% respectively. The resulting improved absorption in the nanoporous GaN further enhances the generation of photocarriers. The increasing surface-volume ratio also contributes to increasing of photoelectrochemical (PEC) reaction area and photocarrier separation efficiency, decrease of photocarrier migration distance towards the GaN-electrolyte interface, more holes participate in the PEC reaction, leading to an improved PEC efficiency and photocurrent density by 470% times with respect to planar counterpart. This work will pave the way towards low-cost and mass production of nanoporous GaN photoelectrode for efficient solar water splitting.

Low-loss chirped grating for vertical light coupling in lithium niobate on insulator

We report a vertical chirped grating coupler with high coupling efficiency (CE) fabricated on lithium niobate on insulator (LNOI). According to finite difference time domain simulations, loss in a uniform grating in LNOI comes from downward diffracted light, internal reflections, and mode mismatch between the single-mode fiber and the out-coupled light from the grating. A chirped grating coupler, whose parameters were optimized to reduce the mode mismatch loss and internal reflections, was fabricated with integrated waveguides through a single etch-step and exhibited insertion losses as low as 3.6 dB, 1.9 dB lower than a uniform grating fabricated in the same process. The demonstrated grating features high CE, ease of manufacturing, and the ability to vertically couple light—a fundamental characteristic required to facilitate the integration of on-chip laser sources and detectors.

Mid-Infrared, Ultra-Broadband, Low-Loss, Compact Arbitrary Power Splitter Based on Adiabatic Mode Evolution

We designed and demonstrated TE-mode arbitrary power splitters based on adiabatic mode evolution. The power splitters are designed with a footprint of smaller than 12 × 2.9 μm 2 , fabricated on a 400-nm silicon-on-insulator platform, requiring only a single etch step. The optimization process and the conditions for arbitrary-power splitting are performed using three-dimensional-FDTD simulations. We prove this concept through the fabrication of asymmetrical adiabatic evolution-based power splitters with splitting ratios of 50:50, 60:40, and 70:30. The fabricated devices are shown to agree closely with simulation results. Broadband operation with low insertion loss of 0.11-0.6 dB is demonstrated across the 3.66-3.89 μm wavelength range (230 nm). This component has applications in a multitude of areas such as spectroscopic optical sensing and optical phased arrays photonic integrated circuits etc.

High positional freedom SOI subwavelength grating coupler (SWG) for 300 mm foundry fabrication.

We present an apodized, single etch-step, subwavelength grating (SWG) high positional freedom (HPF) grating coupler based on the 220 nm silicon-on-insulator (SOI) with 2μm BOX substrate. The grating coupler was designed for 1550 nm light with transverse electric (TE) polarization. It has a measured maximum coupling efficiency of -7.49 dB (17.8%) and a -1 dB/-3 dB bandwidth of ~14 nm/29.5 nm respectively. It was fabricated in a 300mm state of the art CMOS foundry. This work presents an SOI-based grating coupler with the highest-to the best of our knowledge- -1 dB single mode fiber lateral alignment of 21.4 μm × 10.1 μm.

Single-layer active-passive Al2O3 photonic integration platform

Amorphous Al2O3 is an attractive platform for integrated photonics, providing active and passive functionalities. We have developed an integration procedure to create active and passive regions at the same level on one wafer. This fabrication process reduces the number of fabrication steps compared to vertical integration of two materials. The main advantage is that all structures are defined within a single photolithography and etching step and are therefore automatically aligned. As a proof of principle, we demonstrated the luminescence of an active ring resonator with passive bus waveguide.

Refined isolation techniques for GaN-based high electron mobility transistors

This work investigates the Ar+/N+ based ion implantation and Ar based reactive ion etching (RIE) techniques for device isolation. A comparison of ion implantation technique with three ion energies (20/35/65 keV) and 4 energies (20/35/65/160 keV) of Ar+ and N+ with different ion doses for isolation was reported. Use of 4 energy ion implantation provided better isolation. Ar based single and dual step reactive ion etching process was also explored for the mesa isolation of GaN HEMTs. The etch rate increases (44.7%) significantly after mixing of Ar gas directly with BCl3: Cl2 combination. Hence, the Ar addition in the single step etching proved to be more beneficial as compared to the double step etching technique.

Laterally coupled distributed feedback type-I quantum well cascade diode lasers emitting near 322 μm

The laterally coupled distributed feedback (LC-DFB) GaSb-based type-I quantum well cascade diode lasers using the second- and the sixth-order gratings to stabilize the output spectrum near 3.22μm were designed and fabricated. The laser heterostructure contained three cascades. The devices were manufactured using a single dry etching step defining the ∼5-μm-wide ridge with ∼5-μm-wide gratings sections adjacent to the ridge sides. The grating coupling coefficients were estimated to be about 1 cm-1. The stability of the single-frequency operation was ensured by alignment of the DFB mode to the relatively wide gain peak. The 2-mm-long second-order LC-DFB lasers generated above 10mW of continuous-wave (CW) output power at 20°C in epi-side-up configuration and demonstrated power conversion efficiency above 2%. The sixth-order LC-DFB lasers showed lower efficiency but still generated several milliwatts of CW output power. The devices demonstrated a CW current tuning range of about 3.5nm at the temperature of 20°C.

Dispersion control of silicon nanophotonic waveguides using sub-wavelength grating metamaterials in near- and mid-IR wavelengths

Controlling the group velocity dispersion of silicon nanophotonic waveguides has been recognized as a key ingredient to enhance the development of various on-chip optical applications. However, the strong wavelength dependence of the dispersion in waveguides implemented on the high index contrast silicon-on-insulator (SOI) platform substantially hinders their wideband operation, which in turn, limits their deployment. In this work, we exploit the potential of non-resonant sub-wavelength grating (SWG) nanostructures to perform a flexible and wideband control of dispersion in SOI waveguides. In particular, we demonstrated that the overall dispersion of the SWG-engineered metamaterial waveguides can be tailored across the transparency window of the SOI platform, keeping easy-to-handle single-etch step manufacturing. The SWG silicon waveguides overcladded by silicon nitride exhibit significant reduction of wavelength dependence of dispersion, yet providing intriguing and customizable synthesis of various attractive dispersion profiles. These include large normal up to low anomalous operation regimes, both of which could make a great promise for plethora of emerging applications in silicon photonics.

Single-step inductively coupled plasma etching of sputtered Nb2O5/SiO2 multilayer stacks using chromium etch mask

This paper presents the dry etching characteristics of Nb2O5/SiO2 multilayer stacks deposited using ion beam sputtering. Dry etching is achieved by using a combination of CHF3 and Ar gases in an inductively coupled plasma (ICP)-reactive ion etching system. The effect of the etching parameters such as the gas ratio (CHF3/Ar), radio-frequency power, ICP power, chamber pressure, and temperature is investigated. An etching recipe is optimized to achieve a high etch rate, good selectivity, and optimum etch profile. The optimized etching recipe provides a single step etch solution for both dielectric materials. Furthermore, the deposition and structuring process of a chromium based etch mask is investigated.

Surface morphological influence on the in vitro bioactivity and response of mesenchymal stem cells

The surface properties of any biological implant are imperative in a cell-material interaction point of view. The current study compared three different surface morphologies of titanium (Ti) samples in terms of adhesion, proliferation and differentiation of cells. A net-porous nanostructure, randomly arranged nano-wires and micron/submicron-crater like morphologies were on the Ti samples by single step etching with H2O2, NaOH, and HCl solutions, respectively. Although cell proliferation was decreased by the surface modifications described above, osteogenic differentiation was induced in the cells grown on the etched-Ti samples compared to the polished-Ti samples. In particular, osteocalcin (OC) and osteopontin (OPN) osteogenic phenotype markers induced significantly in the HCl-etched-Ti samples, whereas only OC was induced on the H2O2-etched-Ti and OPN was expressed significantly in the NaOH-etched-Ti sample compared to polished-Ti. In addition, the NaOH-etched-Ti samples showed faster apatite deposition compared to the HCl- and H2O2-etched samples in the simulated body fluid.

Optical pump-rejection filter based on silicon sub-wavelength engineered photonic structures.

The high index contrast of the silicon-on-insulator (SOI) platform allows the realization of ultra-compact photonic circuits. However, this high contrast hinders the implementation of narrow-band Bragg filters. These typically require corrugation widths of a few nanometers or double-etch geometries, hampering device fabrication. Here we report, for the first time, to the best of our knowledge, on the realization of SOI Bragg filters based on sub-wavelength index engineering in a differential corrugation width configuration. The proposed double periodicity structure allows narrow-band rejection with a single etch step and relaxed width constraints. Based on this concept, we experimentally demonstrate a single-etch, 220 nm thick, Si Bragg filter featuring a corrugation width of 150 nm, a rejection bandwidth of 1.1 nm, and an extinction ratio exceeding 40 dB. This represents a 10-fold width increase, compared to conventional single-periodicity, single-etch counterparts with similar bandwidths.

Dispersion flattened single etch-step waveguide based on subwavelength grating

A novel subwavelength-grating-assisted (SWG-assisted) waveguide is proposed for dispersion flattening. Tuning the refractive index, which is a powerful tool in dispersion engineering, can be carried out through adjusting the properties of the SWG regions. It is particularly beneficial for controlling the flattened dispersion bandwidth. This will also eliminate the need for integration of other less compatible materials with silicon. Moreover, the SWG-assisted waveguide can be easily fabricated through a single etch-step process. By engineering the structural parameters of the waveguide, an ultra-flat dispersion profile with a total dispersion variation of 10 (ps/nm/km) over a wide bandwidth of 1615nm is obtained. The possibility of bandwidth expansion, the fabrication friendly design, and the flattened dispersion profile of the proposed waveguide make it promising for wideband nonlinear applications.

Cylinder and metal grating polarization beam splitter

We propose a novel and compact metal grating polarization beam splitter (PBS) based on its different reflected and transmitted orders. The metal grating exhibits a broadband high reflectivity and polarization dependence. The rigorous coupled wave analysis is used to calculate the reflectivity and the transmitting spectra and optimize the structure parameters to realize the broadband PBS. The finite-element method is used to calculate the field distribution. The characteristics of the broadband high reflectivity, transmitting and the polarization dependence are investigated including wavelength, period, refractive index and the radius of circle grating. When grating period d = 400 nm, incident wavelength λ = 441 nm, incident angle θ = 60° and radius of circle d/5, then the zeroth reflection order R0 = 0.35 and the transmission zeroth order T0 = 0.08 for TE polarization, however, T0 = 0.34 and R0 = 0.01 for TM mode. The simple fabrication method involves only single etch step and good compatibility with complementary metal oxide semiconductor technology. PBS designed here is particularly suited for optical communication and optical information processing.

Demonstration of an As2S3-on-LiNbO3 Grating Coupler and its Application of Measuring a Grating-based Filter

We demonstrate the design, fabrication, and measurement results for an As2S3 grating coupler on a LiNbO3 substrate. The proposed coupler was fabricated by a single lithography step followed by a single reactive ion etching step, which substantially reduces the processing steps compared to previously reported coupling between vertically integrated As2S3 and LiNbO3 waveguides. The measured grating coupling loss is 3.75 dB at 1563 nm for TE polarization. In addition, a sidewall Bragg grating cavity was fabricated using the grating input and output couplers. The Bragg grating response had a full width at half maximum (FWHM) of 0.0375 nm around the resonance wavelength and a cavity free spectral range (FSR) of 0.36 nm. Applications of these vertically integrated As2S3 grating couplers include 2-D beam steering using the electro-optic tuning afforded by the LiNbO3 substrate and electro-optic sensing.

Demonstration of integrated polarization rotator based on an asymmetric silicon waveguide with a trench

An integrated polarization rotator is demonstrated experimentally by forming a strip waveguide with an asymmetric trench on a silicon-on-insulator wafer. The trench is located asymmetrically in the strip waveguide. It induces the evolution of an orthogonal polarization mode upon a linearly polarized beam input, and thus causes polarization rotation. The device is fabricated using a conventional complementary metal oxide semiconductor process with a single dry etching step. The fabricated device shows a maximum transverse electric (TE)-to-transverse magnetic (TM) polarization conversion efficiency of 21.3 dB and an insertion loss of −0.95 dB at a 1550 nm wavelength with a device length of 67 μm. The device exhibits a polarization conversion efficiency and insertion loss of 21.1 dB and −2.12 dB, respectively, for the TM-to-TE polarization conversion. The optimum parameters for the waveguide size and trench size are investigated by performing numerical simulations, and by demonstrating experimental fabrication and measurement.

OPTIMIZATION OF CHEMICAL PRETREATMENT FOR REMOVING COBALT ON TUNGSTEN CARBIDE SUBSTRATE USING RESPONSE SURFACE METHODOLOGY

Diamond coating are commonly used in industries especially for application such as cutting tools, biomedical components, optical lenses, microelectronics, engineering, and thermal management systems. The diamond coating quality is strongly depending on substrate preparation prior to diamond coating. Thus, the several process parameters must be studied to obtain optimal parameters which lead high quality diamond coating. In this present work, an attempt was made to optimize pretreatment parameters namely temperature and time on cobalt removal of tungsten carbide. Full factorial experimental designs followed by Response Surface Methodology (RSM) were employed in this study to plan and analyze the experiment. The cobalt removal was the independent response variables. Empirical model was successfully developed to predict amount of cobalt removal on the substrate after single step etching process. Experimental results have shown that the temperature, time and time2 are found to be the most significant factors for cobalt removal. Whereas for interaction of time and temperature were insignificant factors to influence cobalt removal. According to this study, the minimum cobalt content can be obtained at working temperature from 48 to 50C for 3 minute.