Single-step Lithography Process Research Articles

Electrically tunable lens with a non-monotonic wavefront control capability.

We describe an electrically tunable liquid crystal lens that can produce a rich variety of wavefronts, including sombrero-type (non-monotonic) phase modulation, enabling the focusing of light into a ring-shaped intensity distribution. The lens can also generate axicons or standard spherical lenses with a bipolar response (providing both positive and negative optical powers). The design of the lens requires only a single-step lithography process, dramatically simplifying its manufacturing. We describe various driving modes of this lens and present the first experimental results and discuss its possible applications in miniature cameras and microscopes. We think that this device can revolutionize the optical design in many areas of photonics.

Single-Step-Lithography Micro-Stepper Based on Frictional Contact and Chiral Metamaterial.

Stepper motors and actuators are among the main constituents of control motion devices. They are complex multibody systems with rather large overall volume due to their multifunctional parts and elaborate technological assembly processes. Miniaturization of individual parts is still posing assembly problems. In this paper, a single-step lithography process to fabricate a micro-stepper engine with an accurate micrometric rotation axis and an overall sub-millimeter size is demonstrated. The device is based on the frictional contacts and chiral metamaterials to get rid of the dependence on the accuracy of parts. The functional aspects of fabricated samples are discussed for many rotation cycles and for different frictional surfaces.

Anisotropic wet etching of a novel micro-texture structure for an Al/n-Si/Al metal–semiconductor–metal photodetector fabrication

Micro-electro-mechanical system fabrication involves molding on a single substrate. Chemical wet etching is common in these systems because it can provide a very high etch rate and selectivity. This optical device has been successfully completed fabrication by using the single-step lithography process. The surface was coated with PR and patterned using a single mask to create U-shaped structures by a wide electrode gap on a silicon substrate. Then it was etched using anisotropic wet etching process in potassium hydroxide, tetramethylammonium hydroxide (TMAH), silicic acid and dissolved silicon powder. The etchant created a 58% increase in the light sensitive area of the U-shaped trench in the structure higher compared to the planar structure. Random micro-pyramids, formed on the silicon surface in the U-shaped structure by the silicic acid-added TMAH solution, led to a ∼254 times higher ratio between photon generated current and dark current at reverse bias. This processing technique is a promising technology for improving performance for next-generation optical sensors or silicon photodetector.

Highly efficient broadband silicon nitride polarization beam splitter incorporating serially cascaded asymmetric directional couplers.

The implementation of a polarization beam splitter (PBS) on a silicon nitride platform remains challenging owing to its relatively low index. We therefore propose a silicon nitride PBS that exploits serially cascaded asymmetric directional couplers (ADCs), leading to a high polarization extinction ratio (PER) over a broad bandwidth. The ADC spatially routes incident light through polarization-selective mode coupling under a small footprint of 112 µm. The proposed PBS does not require an active phase control. It is thus effectively realized via a single-step lithography process. The measured transverse-electric and transverse-magnetic PERs were determined to be above 23 dB and 10 dB over an 80-nm bandwidth, respectively, spanning λ=1520-1600nm. The proposed device is thus anticipated to play a key role in providing polarization diversity in photonic-integrated circuits.

Topotactic transformation in SrFeO3− δ triggered by low-dose Ga+ focused ion irradiation

We introduce a single-step lithography process based on Ga+-focused ion beam (FIB) irradiation to trigger a topotactic transformation on SrFeO3−δ thin films, from the perovskite to the brownmillerite (BM) crystal structure. The crystallographic transformation is triggered by preferential oxygen sputtering by Ga+-FIB irradiation, which favors the formation of the SrFeO2.5 BM phase. The transformation has been verified through micro-Raman spectroscopy on thin films subjected to Ga+-FIB irradiation under 5 kV and 30 kV. Inducing crystallographic transformations by FIB in a single-step process (without the need of resists), at a very high speed (low Ga+ doses are required, in the range of 1015 ions/cm2), with very high spatial resolution (limited by the ion beam spot, of a few square nanometers) and with potential for upscaling using broad Ga+ beams, this approach represents a significant forward step over previous methods using multistep lithographic or electrochemical procedures. All these virtues make this process appealing to develop applications based not only on SrFeO3−δ thin films but also on other oxide films harnessing topotactic transformations.

A miniaturized SQUID fabricated on a silicon chip

A new article introduces a planar SQUID with a broad temperature and magnetic-field operational range made with a single-step lithography process on a silicon chip, which may expand the use and applications for quantum technologies.

Gaussian beam-to-slab waveguide coupler by graded index photonic crystal lens

In this numerical study, a Gaussian beam-to-slab waveguide coupler for both modes of TM and TE has been studied. For this purpose, a concrete structure is suggested, in which the graded index photonic crystal lens and the slab waveguide are in the same structure composed of Si material, and can be fabricated with a single-step lithography process. For maximum power coupling, half-holes have been used as an input matching layer. Power coupling of 80% over a 450 nm bandwidth for the TM mode, and 60% over a 180 nm bandwidth for the TE mode is achieved.

Fiber-to-chip coupler designed using an optical transformation

An integrated silicon photonics coupler for fiber to waveguide conversion was designed employing a transformation optics approach. Quasi-conformal mapping was used to obtain achievable material properties, which were realized by a distorted hexagonal lattice of air holes in silicon. The coupler, measuring only 10 μm in length and fabricated with a single-step lithography process, exhibits a peak simulated transmission efficiency of nearly 100% for in-plane mode conversion and a factor of 5 improvement over butt coupling for fiber to waveguide mode conversion in experimental testing.

Lateral air cavities for microfluidic pumping with the use of acoustic energy

An acoustically activated micropump is fabricated and demonstrated using a single step lithography process and an off-chip acoustic energy source. Using angled lateral cavities with trapped air bubbles, acoustic energy is used to oscillate the liquid–air interface to create a fluidic driving force. The angled lateral cavity design allows for fluid rectification from the first-order pulsatile flow of the oscillating bubbles. The fluid rectification is achieved through the asymmetrical flow produced by the oscillating interface generating fluid flow away from the lateral cavity interface. Simulation and experimental results are used to develop a pumping mechanism that is capable of driving fluid at pressures of 350 Pa. This pumping system is then integrated into a stand-alone battery operated system to drive fluid from one chip to another.

A Novel SR Latch Device Realized by Integration of Three-Terminal Ballistic Junctions in InGaAs/InP

In this letter, a novel sequential logic device based on three-terminal ballistic junctions (TBJs) is proposed and demonstrated. Two TBJs and two in-plane gates are laterally integrated in a high-electron-mobility InGaAs/InP quantum-well material by a single-step lithography process. Electrical measurements reveal that the integrated device functions as a set-reset (SR) latch with voltage gains at room temperature. The demonstrated device provides a new and simple circuit design for SR latches in digital electronics.

A very short planar silica spot-size converter using a nonperiodic segmented waveguide

To reduce the coupling loss of a fiber-to-ridge waveguide connection, a planar silica spot-size converter for a wavelength of 1.55 /spl mu/m is implemented in the form of a nonperiodic segmented waveguide structure with irregular tapering. A simple single-step lithography process is sufficient for the fabrication of the planar structures. An evolutionary algorithm has been successfully applied for the optimization. The simulated results obtained with a three-dimensional (3-D) finite difference beam propagation method (FD-BPM) program are compared with measurements of implemented couplers, showing very good agreement. A waveguide-to-fiber coupling efficiency improvement exceeding 2 dB per converter is shown. Structures obtained with this approach are very short (/spl sim/140 /spl mu/m) and simple to integrate on the same wafer with other planar structures such as phased arrays or ring resonator structures.