Mass reduction patterning of silicon-on-oxide–based micromirrors

Thin Solid Films, 2005

Optical waveguides are being explored for on-chip purposes to overcome the speed limitations of electrical interconnects. Passive optical components like waveguides and vertical outcouplers are important components in such schemes. In this study, we fabricated planar waveguides with integrated vertical micromirrors using silicon back-end-of-the-line processes. Approximately 1.6 Am of a hybrid alkoxysiloxane polymer with a refractive index of 1.50 at the intended wavelength of 830 nm was used as the core and plasma-deposited silicon oxide with a refractive index of 1.46 was used as the cladding. The angular face in the polymer waveguide that would function as the mirror surface was fabricated by a templated pattern transfer method, which involved transferring the angle in a template to the waveguide using anisotropic etching. The sidewall angle generated in ShipleyR S1813, a positive photoresist, on patterning was used as the angle template. The photoresist sidewall angle was controlled using a two-step exposure method. A CF 4 /O 2 plasma chemistry was used for the anisotropic reactive ion etch. A gas composition of 50/50 CF 4 /O 2 was chosen to minimize the etch-related roughness of the alkoxy-siloxane polymer and the photoresist. The metallization of the mirror faces was done using two of the three proposed self-aligned techniques. A calibration-based technique was developed to measure the reflection efficiency of the micromirrors. In this technique, scattered light was used to estimate the incident power on the micromirror and a reflection efficiency of 83% was obtained at a wavelength of 650 nm.

Japanese Journal of Applied Physics, 2000

We have designed and fabricated an electromagnetic micromirror with a flat mirror plate capable of large angular deflection. Single-crystal silicon is used as a mirror plate to obtain an optically flat reflective surface. By a combination of surface and bulk micromachining processes, the single-crystal silicon mirror plate is connected to the substrate via an aluminum spring, which occupies a relatively small area without compromising the compliance. The proposed fabrication process can be applied to the fabrication of devices in which a flat moving part is supported by a compliant spring structure. Nickel electroplated onto the mirror plate enables a mirror rotation angle of up to 84.8° by applying an external magnetic field vertical to the substrate. This designed structure can be used individually or as an array in microphotonic applications.

IEEE Journal of Selected Topics in Quantum Electronics, 2015

This paper reports a novel class of deeply etched curved micromirrors enabling linear conversion between the reflection angle of incident light beam and displacement of the beam axis with respect to the curved mirror principal axis. Moreover, the mirror provides phase-transformation of the light beam independent of the inclination angle of the incident light on the mirror surface. The micromirrors are fabricated on SOI substrate by deep reactive ion etching technology. The profile of the curved surface is optimized and controlled precisely, thanks to the photolithographic process. High optical throughput micromirrors exhibiting submillimeter focal lengths are fabricated with 200-μm etching depth and with a sidewall angle deviation from perfect verticality, which is smaller than 0.1°. Optical measurements at wavelengths of 675 and 1550 nm show transformation of the optical beam with high optical spot size stability during a beam steering process with less than ±5% dependence on the inclination/reflection angle over a scanning angle range of 120°. The presented micromirror has applications in MEMS scanners, displacement/rotation sensing, and optical imaging. Index Terms-Curved micro-optics, displacement sensor, DRIE, MEMS optical bench technology, optical scanner.

Miniaturized optical benches process free-space light propagating in-plane with respect to the substrate and have a large variety of applications, including the coupling of light through an optical fiber. High coupling efficiency is usually obtained using assembled micro-optical parts, which considerably increase the system cost and integration effort. In this work, we report a high coupling efficiency, monolithically integrated silicon micromirror with controlled three-dimensional (3D) curvature that is capable of manipulating optical beams propagating in the plane of the silicon substrate. Based on our theoretical modeling, a spherical micromirror with a microscale radius of curvature as small as twice the Gaussian beam Rayleigh range provides a 100% coupling efficiency over a relatively long optical path range. Introducing dimensionless parameters facilitates the elucidation of the role of key design parameters, including the mirror's radii of curvature, independent of the wavelength. A micromachining method is presented for fabricating the 3D micromirror using fluorinated gas plasmas. The measured coupling efficiency was greater than 50% over a 200-μm optical path, compared to less than 10% afforded by a conventional flat micromirror, which was in good agreement with the model. Using the 3D micromirror, an optical cavity was formed with a round-trip diffraction loss of less than 0.4%, resulting in one order of magnitude enhancement in the measured quality factor. A nearly 100% coupling was also estimated when matching the sagittal and tangential radii of curvature of the presented micromirror’s surface. The reported class of 3D micromirrors may be an advantageous replacement for the optical lenses usually assembled in silicon photonics and optical benches by transforming them into real 3D monolithic systems while achieving wideband high coupling efficiency over submillimeter distances.

Journal of Microelectromechanical Systems, 2004

This paper presents the design, fabrication, and testing of a two-axis 320 pixel micromirror array. The mirror platform is constructed entirely of single-crystal silicon (SCS) minimizing residual and thermal stresses. The 14-m-thick rectangular (750 800 m 2 ) silicon platform is coated with a 0.1-m-thick metallic (Au) reflector. The mirrors are actuated electrostatically with shaped parallel plate electrodes with 86 m gaps. Large area 320-mirror arrays with fabrication yields of 90% per array have been fabricated using a combination of bulk micromachining of SOI wafers, anodic bonding, deep reactive ion etching, and surface micromachining. Several type of micromirror devices have been fabricated with rectangular and triangular electrodes. Triangular electrode devices displayed stable operation within a ( 5 , 5 ) (mechanical) angular range with voltage drives as low as 60 V.

Orthopaedics & Traumatology-surgery & Research, 2004

We report in this work the fabrication and optical characterization of micromirrors with inversed pyramidal shape (pits). The pyramids are etched on silicon using an anisotropic etchant and then gold coated to form a mirror.

Sensors and Actuators A: Physical, 2005

High-density micromirror arrays (1296 mirrors) have been fabricated with a process that combines the benefits of both bulk and surface micromachining. Arrays fabricated with this technique are characterized by optically flat mirrors characterized by radius of curvature (ROC) ∼1 m, spring constant uniformity (∼6%) across the array, and yields greater than 90%. Each array element consists of a mirror-in-gimbal structure that allows the mirror to rotate about two orthogonal axes when voltage is applied to electrodes beneath the mirror. A dry release process combined with through wafer etching and spin-cast polyimide is introduced as a simple, effective alternative to critical point drying for releasing the structures. Tilt angle measurements for these devices show stable angular range of ±5 • (mechanical) at 160-170 V.

2019

Micromirror devices which consisted of one SU-8 2050 layer, two different exposures, and a series of metal depositions were constructed and evaluated. By varying the exposure, a micromirror structure was fabricated with different thicknesses, a ratio of 1.083 μm/( mJ cm2 ) was found. The initial design consisted of four layers. The pillar was made of one SU-8 layer, and the top portion had three layers in the following order: gold, SU-8, and gold. This design could not be released and did not have characteristics of a flat and conformal reflective surface. Several variations of the initial design were explored and all of them lacked a flat and conformal top reflective surface. Both interferometric and statistical software showed that using a 60 mJ/cm mirror exposure dosage and a 370 mJ/cm square pillar exposure dosage yields a micromirror with a conformal top reflective surface. The length and width of the pillars are 200μm by 200μm, with a height of 75 μm. The mirror’s length and w...

Micromachines

A large-area and ultrathin MEMS (microelectromechanical system) mirror can provide efficient light-coupling, a large scanning area, and high energy efficiency for actuation. However, the ultrathin mirror is significantly vulnerable to diverse film deformation due to residual thin film stresses, so that high flatness of the mirror is hardly achieved. Here, we report a MEMS mirror of large-area and ultrathin membrane with high flatness by using the silicon rim microstructure (SRM). The ultrathin MEMS mirror with SRM (SRM-mirror) consists of aluminum (Al) deposited silicon nitride membrane, bimorph actuator, and the SRM. The SRM is simply fabricated underneath the silicon nitride membrane, and thus effectively inhibits the tensile stress relaxation of the membrane. As a result, the membrane has high flatness of 10.6 m−1 film curvature at minimum without any deformation. The electrothermal actuation of the SRM-mirror shows large tilting angles from 15° to −45° depending on the applied D...

2001

This paper will present a method for rapidly developing MEMS micro-mirrors by utilizing CAD tools currently available. Design begins with a mask layout which leads to analysis of one mirror. These results are then used to model a complete array.