C. Linder

Micromechanical comb actuators with low driving voltage

Comb actuators with submicrometer-wide suspensions have been fabricated and tested. Measurements proved that they are reliable devices for displacements in the range of several micrometers with a precision in the tens of nanometers. Due to the very flexible suspensions (10 mN m-1) only low voltages-around 20 V- were required for the actuation. As an application, the author have fabricated and characterized an xy microstage which allows precise two-dimensional positioning. The limits of the devices were also tested. A main source of problems is the sticking phenomenon. Depending on the design of the actuator, the movable comb will, at a critical voltage, either stick on the sides of the fixed fingers (side sticking) or on the front ends of the fixed finger (front sticking). Analytical calculations, simulation and measurements are compared.

Optical microshutters and torsional micromirrors for light modulator arrays

The fabrication and operation of surface micromachined light modulators are described. In particular, comb-driven polysilicon microshutters for interrupting a focused laser beam of 5 mu m in diameter are characterized. The shutters are suspended by novel compact meander springs, which favor their application in dense light modulator arrays. Torsional micromirrors working in a reflection mode, having two mirror states, were realized using the same technology. Electrical pulses of less than 2 mu s are sufficient to switch the mirror position.<<ETX>>

Electrostatic polysilicon microrelays integrated with MOSFETs

The fabrication and characterization of electrostatically-driven microrelays integrated together with IC components are presented. The mechanical part of the microrelays consists of a polysilicon-silicon nitride-polysilicon microbridge realized by sacrificial layer technology and allowing one to separate the actuation and the working circuit. The main operational parameters are actuation voltages in the 50 V to 75 V range depending on the beam lengths of the relays; switching frequencies up to 20 kHz with negligible electrical cross-talk between actuation and working port; a maximum measured frequency of 75 kHz without damaging the microrelay; a rise time of 4 /spl mu/s and a fall time of 1 /spl mu/s. First experiments in nitrogen atmosphere have shown that the relay is able to cycle over 10/sup 9/ times with no significant changes in its electromechanical properties.

Line-addressable torsional micromirrors for light modulator arrays

Note: 116 Reference SAMLAB-ARTICLE-1994-010 Record created on 2009-05-12, modified on 2016-08-08

Deep dry etching techniques as a new IC compatible tool for silicon micromachining

Deep dry etching of single-crystal silicon with IC-compatible masking materials for microstructure fabrication is reported. Reactive ion etching using chlorine/fluorine gases and positive photoresist mask produces up to 30 mu m deep silicon steps with vertical sidewalls. Plasma etching with fluorine/oxygen gas mixtures shows rather isotropic etch behavior; however, high selectivities of 20, 85, and greater than 300 for photoresist, silicon dioxide, and aluminum masks, respectively, permit etch depths of up to several hundreds of microns. Since these dry etching techniques are reproducible and controllable they indicate favorable features for application in silicon micromachining. Several examples are described: bipolar-compatible accelerometers where dry etching and KOH etching are combined, free-standing thin film microstructures (out of aluminum or silicon dioxide) realized by isotropic etching of the substrate, and thin silicon membranes fabricated by plasma etching.<<ETX>>

Investigations on free-standing polysilicon beams in view of their application as transducers

Abstract Free-standing polysilicon structures can be fabricated by lateral etching of a sacrificial silicon dioxide layer that has been sandwiched between the substrate and the polysilicon film. If the fabrication process of these three-dimensional structures is IC compatible, it is possible to realize integrated transducers such as resonant microbeam sensors, microswitch actuators, microvalves or electrostatic micromotors. Undoped and phosphorus-doped (P-doped) sacrificial silicon dioxide/polysilicon beam material combinations are investigated. The P-doped polysilicon beams show larger free-standing beam lengths than the undoped beams. Slight buckling is observed only for P-doped beams longer than 500 μm. The maximum length of all the other beams is limited by downward deflection to the substrate, which might be due to electrostatic forces induced by surface charges. A test chip containing IC-compatible capacitive microbeam transducers has been realized. Applications are switch actuators and resonant sensors. For a 300 μm long and 1 μm thick doubly supported polysilicon beam, the first resonance frequency is calculated to be about 100 kHz and an estimation of the capacitance change due to the beam deflection yields 8.6 fF. For the same structure, evaluation of the voltage necessary to switch the beam gives 13.5 V and measurement (in an SEM) about 15 V.

Mechanical and optical properties of surface micromachined torsional mirrors in silicon, polysilicon and aluminum

This paper presents a comparative study of surface micromachined structures fabricated in three different materials, using torsional micromirrors as test vehicle. The devices are realized in single-crystal silicon, polycrystalline silicon and aluminum. Mechanical properties such as internal strains, sticking phenomena, yield strains and endurance test resistance as well as optical properties such as surface reflectivities and scattering characteristics are investigated on the devices. the characterization points out that the silicon and polysilicon structures present higher yield strains and are less prone to surface sticking while the aluminum mirrors have higher surface refiectivities.

Novel polysilicon comb actuators for xy-stages

Different types of polysilicon comb actuators have been designed, fabricated, and operated. The design was based on a finite-element stiffness modeling of the suspensions. In particular, a new straight beam structure showed an improved mechanical stability compared with the classical folded beam actuators. IC-compatible sacrificial layer technology was used for the fabrication of the polysilicon structures. Electrostatic actuation of the straight beam elements resulted in displacements as a function of the applied voltage; a maximum of 2.7 mu m was achieved for 200 V. To lower this rather high driving voltage, the authors propose a comb actuator where several combs are placed in parallel to form a sarcomere actuator. By assembling four actuators, a comb-driven xy-microstage has been realized. Mechanical operation of this microrobot allowed the positioning of the center stage at any point in a 30 by 30 mu m area. Electrostatically the table was moved up to 1 mu m in each of the four directions.<<ETX>>

Design and fabrication of an overhanging xy-microactuator with integrated tip for scanning surface profiling

This paper presents a microsystem consisting of an overhanging xy-microstage with integrated tip and comb actuators for scanning surface profiling. The design is optimized with respect to precise xy positioning at low drive voltages and accurate detection of vertical deflection. The structure is micromachined in monocrystalline silicon, requiring only three masks and combining various techniques such as KOH and sacrificial layer etching, silicon fusion bonding and wet isotropic and dry anisotropic etching.

AFM imaging with an xy-micropositioner with integrated tip

We have fabricated an xy-microstage with integrated protruding tip and electrostatic comb actuators for scanning probe surface imaging. This device, which is micromachined in monocrystalline silicon, has been actuated and characterized and, for the first time with such a microtool, an atomic force microscope (AFM) profile has been achieved.