P.-A. Clerc

Applications of SOI-based optical MEMS

After microelectromechanical systems (MEMS) devices have been well established, components of higher complexity are now developed. Particularly, the combination with optical components has been very successful and have led to optical MEMS. The technology of choice for us is the silicon-on-insulator (SOI) technology, which has also been successfully used by other groups. The applications presented here give an overview over what is possible with this technology. In particular, we demonstrate four completely different devices: (a) a 2 /spl times/ 2 optical cross connector (OXC)with an insertion loss of about 0.4 dB at a switching time of 500 /spl mu/s and its extension to a 4 /spl times/ 4 OXC, (b) a variable optical attenuators (VOA), which has an attenuation range of more than 50 dB (c) a Fourier transform spectrometer (FTS) with a spectral resolution of 6 nm in the visible, and (d) an accelerometer with optical readout that achieves a linear dynamic range of 40 dB over /spl plusmn/6 g. Except for the FTS, all the applications utilized optical fibers, which are held and self-aligned within the MEMS component by U-grooves and small leaf springs. All devices show high reliability and a very low power consumption.

Integrated array sensor for detecting organic solvents

Abstract A new sensor array device has been designed to detect organic solvents; it comprises an array of six interdigital sensors lying upon a micromachined 0.5 μm thick silicon nitride membrane. There are three separate micromachined cells with two sensors per cell. In each cell, a thin film platinum resistance thermometer/heater is sandwiched in the middle of the silicon nitride layer in order to either monitor or control the temperature of the active layer. The array device has a low power consumption of ≈ mW/sensor at 400 °C and is capable of operating at temperatures in excess of 600 °C, making it suitable for inorganic (e.g., SnO2) as well as organic gas-sensitive materials. The sensor array device has been coated with both polymers and semiconducting oxides and its response to toluene, n-propanol and n-octane has been studied. The low power consumption and good thermal stability of this array device make it useful for application in portable gas monitoring equipment.

Advanced deep reactive ion etching: a versatile tool for microelectromechanical systems

Advanced deep reactive ion etching (ADRIE) is a new tool for the fabrication of bulk micromachined devices. Different sensors and actuators which use ADRIE alone or combined with other technologies such as surface micromachining of silicon are presented here. These examples demonstrate the potential and the design freedom of this tool, allowing a large number of different shapes to be patterned and new smart devices to be realized.

A clean wafer-scale chip-release process without dicing based on vapor phase etching

A new method to release MEMS chips from a wafer without dicing is presented. It can be applied whenever SOI wafers are used that are structured from both the device and the handle side using DRIE. This method enables the release of extremely fragile structures without any mechanical impact on the chips. No more dicing residues or debris are created and deposited onto the wafer. The basic idea consists of etching deep surrounding trenches on the device and the handle layer that are displaced by about 20 /spl mu/m and thus create overlapping areas. For release, the buried silicon dioxide between the overlapping areas is etched away using hydrofluoric acid vapor phase etching.

Arrays of High Tilt-Angle Micromirrors for Multiobject Spectroscopy

Micromirror arrays are promising components for generating reflective slit masks in future multiobject spectrographs. The micromirrors, 100 mum times200 mum in size, are etched in bulk single crystal silicon, whereas a hidden suspension is realized by surface micromachining. The micromirrors are actuated electrostatically by electrodes located on a second chip. The use of silicon on insulator (SOI) wafers for both mirror and electrode chip ensures thermal compatibility for cryogenic operation. A system of multiple landing beams has been developed, which latches the mirror at a well-defined tilt angle when actuated. Arrays of 5times5 micromirrors have been realized. The tilt angle obtained is 20deg at a pull-in voltage of 90 V. Measurements with an optical profiler showed that the tilt angle of the actuated and locked mirror is stable with a precision of 1 arcmin over a range of 15 V. This locking system makes the tilt angle independent from process variations across the wafer and, thus, provides uniform tilt angle over the whole array. The surface quality of the mirrors in actuated state is better than 10-nm peak to valley and the local roughness is about 1-nm root mean square

Novel process-insensitive latchable 2 /spl times/ 2 optical cross connector for single- and multimode optical MEMS fiber switches

A novel design of a process-insensitive latchable 2 /spl times/ 2 optical cross connector for single- and multimode optical MEMS fiber switches is proposed. This design utilizes suspension beams with integrated springs to provide stable positioning and process independence. The ANSYS simulation of the required force versus the displacement shows that the latching force is only 27 /spl mu/N, and the return force is only 6 /spl mu/N.

Tilting out-of-plane platform for optical applications

In this paper we present a novel concept for a tiltable optical platform. The platform is electrostatically actuated using two vertical comb drives that run through the whole thickness of the wafer causing out-of-plane deflection. The platform measures 2/spl times/2 mm/sup 2/ with a through-hole of 1.6/spl times/1.8 mm/sup 2/. For a first demonstrator an optical filter showing an angular dependency of the reflected wavelength will be glued onto the platform in order to act as a channel add/drop device for telecom applications.

Fiber-optic - MEMS accelerometer with high mass displacement resolution

A single mask, intensity modulated fiber-optic accelerometer with integrated squeezed film damping structures has been designed, fabricated and characterized. This device requires only an LED as light source and simple detection electronics in order to obtain a mass displacement resolution in the order of an Angstrom over a detection bandwidth of 300 Hz.

Optical Beam Steering Using a 2D MEMS Scanner

This paper presents the design, fabrication and operation principle of an optical beam steerer for laser fiber coupling based on a MEMS device. The MEMS chip consists on a bi-dimensional movable platform based on uni-dimensional comb drive actuation. An optical lens is assembled onto the mobile platform to focus and steer the light comping from a laser diode and couple it into an optical fiber. Assembly of a complete system and measurements were performed and compared to simulation results. Both the trajectory of the MEMS and resonance frewquency measurements agree with the simulated ones.

Silicon as material for mechanical wristwatches

Silicon has been widely used as the material of choice for the fabrication of MEMS I MST devices. The compatibility of MEMS manufacturing equipment with standard IC equipment presents one ofthe main reasons for this choice. However, over the past years, we have seen new equipment dedicated to MEMS fabrication enter the market place. One such example is the Deep Reactive Ion Etcher, which is capable of vertically etching silicon at a rate of several microns per minute. This type of equipment, now available from several vendors, has revolutionized the MEMS fabrication capabilities and has opened the door to a whole new family of MEMS devices [1].