Hiroshi Toshiyoshi

Electrostatic micro torsion mirrors for an optical switch matrix

We have developed a new type of compact optical switch using silicon micromachining technique. Torsion mirrors (300 /spl mu/m/spl times/600 /spl mu/m) supported by thin polysilicon beams (16 /spl mu/m wide, 320 /spl mu/m long, and 0.4 /spl mu/m thick) are arranged in a 2/spl times/2 matrix (total size 3 mm/spl times/5 mm, t 0.3 mm). The mirrors are independently attracted by electrostatic force of applied bias voltage to redirect the incident light in a free space. Using collimated beam fibers for optical coupling, we obtained small insertion loss (/spl les/-7.66 dB), considering the length of a light path (/spl ges/10 mm), a large switching contrast (/spl ges/60 dB), and small crosstalk (/spl les/-60 dB). The fabrication yield was higher than 80% thanks to the newly developed releasing technique that used a silicon oxide diaphragm as an etch-stop layer and as a mechanical support in the process. Holding voltage (/spl les/50 V) was lower than the voltage to attract the mirror (100/spl sim/150 V) because of the hysteresis of angle-voltage characteristic of electrostatic operation.

Light actuation of liquid by optoelectrowetting

Optical actuation of liquid droplets has been experimentally demonstrated for the first time using a novel optoelectrowetting (OEW) principle. The optoelectrowetting surface is realized by integrating a photoconductive material underneath a two-dimensional array of electrowetting electrodes. Contact angle change as large as 308 has been achieved when illuminated by a light beam with an intensity of 65 mW/cm 2 . A micro-liter droplet of deionized water has been successfully transported by a 4 mW laser beam across a 1 cm � 1 cm OEW surface. The droplet speed is measured to be 7 mm/s. Light actuation enables complex microfluidic functions to be performed on a single chip without encountering the wiring bottleneck of two-dimensional array of electrowetting electrodes. Published by Elsevier Science B.V.

A 5-V operated MEMS variable optical attenuator by SOI bulk micromachining

We report the design, fabrication, and successful demonstration of microelectromechanical variable optical attenuator (VOA) using an electrostatic microtorsion mirror (0.6 mm in diameter) combined with a fiber-optic collimator. The VOA operates at low voltages (dc 5 V or less) for large optical attenuation (40 dB, corresponding to mirror angle of 0.3/spl deg/) and a fast response time (5 ms or faster). The mirror made of a bulk-micromachined silicon-on-insulator wafer has been designed to be shock resistant up to 500 G without any mechanical failure. We also have suppressed temperature dependence of optical performance to be less than /spl plusmn/0.5 dB at 10-dB attenuation in the range of -5/spl deg/C-70/spl deg/C by mechanically decoupling the parasitic bimorph effect from the electrostatic operation.

Integrated Broadband Microwave and Microfluidic Sensor Dedicated to Bioengineering

This paper presents an innovative high-frequency- based biosensor, which combines both microwave detection and microfluidic network for time-efficient and accurate biological analysis. It is composed of a coplanar waveguide with a microfluidic channel placed on top. With the help of an appropriate de-embedding technique and modeling of the measurements, the relative effective permittivity of human umbilical vein endothelial cells has been evaluated successfully. Furthermore, experiments have been performed with the sensor on various cell concentrations in suspension, which validates its use in bioengineering applications such as cell quantification and counting in solution. This sensor requires no direct contact or use of labels on the cells, contrary to other usual types of biosensors (optical, mechanical or dc/low-frequency-detection-based ones).

Linearization of electrostatically actuated surface micromachined 2-D optical scanner

This paper presents an effective method of linearizing the electrostatic transfer characteristics of micromachined two-dimensional (2-D) scanners. The orthogonal scan angles of surface micromachined polysilicon scanner are controlled by using quadrant electrodes for electrostatic actuation. By using a pair of differential voltages over a bias voltage, we could improve the distortion of projected images from 72% to only 13%. A theoretical model has been developed to predict the angle-voltage transfer characteristics of the 2-D scanner. The simulation results agree very well with experimental data. Differential voltage operation has been found to suppress the crosstalk of two orthogonal scan axes by both experiment and theoretically. We have found that a circular mirror is expected to have the lowest angular distortion compared with square mirrors. Perfect grid scanning pattern of small distortion (0.33%) has been successfully obtained by predistorting the driving voltages after calibration.

A scanning micromirror with angular comb drive actuation

Describes a single crystal silicon, 1/spl times/1 mm/sup 2/, scanning micromirror, which incorporates a novel angular vertical comb drive actuator. Results from our model for the angular vertical comb show that a 50% higher scan angle can be achieved when compared to a staggered vertical comb of equivalent dimensions. The simplified, cost effective, silicon on insulator micro-electromechanical systems, (SOI MEMS), process features self-alignment of the fixed and moving teeth and is fabricated on a single SOI wafer. Static deflection for our fabricated device fits well with the model and a resonant mode optical scan angle of /spl plusmn/18/spl deg/ at 1.4 kHz has been measured.

Theory and experiments of angular vertical comb-drive actuators for scanning micromirrors

We report on the theory and experiments of scanning micromirrors with angular vertical comb-drive (AVC) actuators. Parametric analyses of rotational vertical comb-drive actuators using a hybrid model that combines two-dimensional finite-element solutions with analytic formulations are described. The model is applied to both AVC and staggered vertical comb-drive (SVC) actuators. Detailed design tradeoffs and conditions for pull-in-free operations are discussed. Our simulation results show that the fringe fields play an important role in the estimation of maximum continuous rotation angles, particularly for combs with thin fingers, and that the maximum scan angle of the AVC is up to 60% larger than that of the SVC. Experimentally, a large dc continuous scan angle of 28.8/spl deg/ (optical) has been achieved with a moderate voltage (65 V) for a 1-mm-diameter scanning micromirror with AVC actuators. Excellent agreement between the experimental data and the theoretical simulations has been obtained.

Bistable nanowire for micromechanical memory

We present a micromechanical device designed to be used as a non-volatile mechanical memory. The structure is composed of a suspended slender nanowire (width: 100 nm, thickness: 430 nm, length: 8 to 30 ?m) clamped at both ends. Electrodes are placed on each side of the nanowire to (1) actuate the structure during the data writing and erasing mode and (2) determine its position by measuring the capacitive bridge in the reading mode. The structure is patterned by electron beam lithography on a pre-stressed thermally grown silicon dioxide layer. When later released by plasma etching, the stressed material relaxes and the beam buckles by itself to a position of lower energy. These symmetric bistable Euler beams exhibit two stable deformed. This paper presents the microfabrication process and analysis of the static buckling of nanowires. Snapping of these nanowires from one stable position to another by mechanical or electrical means will also be discussed.

Surface- and bulk- micromachined two-dimensional scanner driven by angular vertical comb actuators

In this paper, we present the design, fabrication, and measurements of a two-dimensional (2-D) optical scanner with electrostatic angular vertical comb (AVC) actuators. The scanner is realized by combining a foundry-based surface-micromachining process (Multi-User MEMS Processes-MUMPs) with a three-mask deep-reactive ion-etching (DRIE) postfabrication process. The surface-micromachining provides versatile mechanical design and electrical interconnect while the bulk micromachining offers high-aspect ratio structures leading to flat mirrors and high-force, large-displacement actuators. The scanner achieves dc mechanical scanning ranges of /spl plusmn/6.2/spl deg/ (at 55 Vdc) and /spl plusmn/4.1/spl deg/ (at 50 Vdc) for the inner and outer gimbals, respectively. The resonant frequencies are 315 and 144 Hz for the inner and the outer axes, respectively. The 1-mm-diameter mirror has a radius of curvature of over 50 cm. [1454].

Surface-micromachined 2-D optical scanners with high-performance single-crystalline silicon micromirrors

We have developed a novel batch-fabrication single-crystalline silicon micromirror bonding process to fabricate optically flat micromirrors on polysilicon surface-micromachined two-dimensional (2-D) scanners. The electrostatically actuated 2-D scanner has a mirror area of 460 /spl mu/m/spl times/460 /spl mu/m and an optical scan angle of /spl plusmn/7.5/spl deg/. Compared with micromirror made by standard polysilicon surface-micromachining process, the radius of curvature of the micromirror has been improved by 150 times from 1.8 to 265 cm, with surface roughness <10 nm.