G. Bourbon

Analysis of the dynamic behavior of a doped silicon U-shaped electrothermal actuator

The dynamic behavior of a U-shaped electrothermal actuator is investigated in this paper based on experimental findings and FEM simulations. Few previous works are found in the literature that have addressed the dynamic response of U-shaped actuators. A lack of data on the transient displacement of the actuator in the heating and cooling cycles is noted. Experiments are made in order to characterize the dynamic response of the actuator. The actuators are micro-fabricated on doped SOI wafers and the displacement is recorded with a high speed camera. FEM simulations are in good agreement with the experimental findings. Simulations and experiments show that the shape of displacement follows evolution of the temperature distribution inside the actuator. The influence of the dynamic behavior on the control of the actuator is finally discussed.

Dynamic characterization of an electrothermal actuator devoted to discrete MEMS positioning

This paper focuses on the dynamic characterization of an electrothermal actuator devoted to discrete MEMS positioning. Based on U-shape structure, such actuator has been employed in several MEMS applications where fine and repeatable positioning is required. The studied electrothermal actuator here is microfabricated on a doped SOI substrate and its dynamic response, during heating and cooling cycles, is recorded using precise and high-speed camera. To explain its dynamic behavior, FEM simulations, using Comsol multiphysics software facility, are carried out. The result of this numerical analysis shows a strong relationship between the temperature distribution and the displacement provided by the actuator. Finally, the influence of the dynamic behavior on the control of the actuator is discussed using experimental characterizations of its displacements under several voltage pulses with different frequencies.

X-Y nanopositioners using high-density arrays of mechanical oscillators

Rapid positioning devices having nanometer accuracy are being used in the production of semiconductors. Micro- mechanical-oscillators made by silicon surface micromachining are expected to suit with such devices, according to their direct-drive capabilities. This communication investigates a first generation of microconveyers using high density arrays of micro- mechanical-oscillators. Densities as high as 1000 actuators/mm2 have been already achieved, therefore allowing shape recognition using tactile information on the near future. Thus, depending on the overall size of the conveyance system, millimeter size moving parts having different shapes are expected to be selected, and then independently distributed onto intelligent surfaces. The proposed conveyance system have been fabricated using a multi layer silicon surface micromachining process. Basically, electrodes are deposited onto a silicon substrate, in order to selectively address each elementary actuation cell. Each elementary cell is mechanically connected to a 1.2 micrometers thick polysilicon sheet frame which is deposited above distributed electrodes. The oscillators are activated by electrostatic force. The operating mechanism that is investigated in the communication is as follow: out-of-plane displacements of the frame are synchronized with the motion of mechanical oscillators, in order to allow the declutching mechanism which is needed to convey the moving part. The very first presented here allow us to expect a nanometer positioning resolution in open loop-control.

Toward high-torque electrostatic tubular motors

A new generation of electrostatic micro-motors is investigated using cooperation of arrayed direct-drive actuators. Electrostatic scratch-drive actuators (SDA), which combine active frictional contact mechanisms with electrostatic actuation, are particularly analyzed. Active polysilicon sheets of 2*3 mm2 that integrate up to several thousands of electrostatic scratch drive actuators are fabricated by silicon surface micro-machining process. Each elementary actuator provides its contribution according to the driving force superposition principle, with internal forces as high as 105uN are available from this sheet. According to their natural flexibility, active polysilicon sheets can be coated onto large surfaces. A new generation of self-assembled tubular electrostatic micromotors is developed using this concept. A prototype of a cylindrical micromotor, whose external diameter and length are 1 mm and 2 mm, respectively, has been realized through the insertion of a flexible active polysilicon sheet at the rotor/motor- frame interface. After final assembling, the sheet has to be jammed onto the chassis, in order to allow the rotor to be moved with respect to the motor frame. Thus, the sheet must be in close contact with both the rotor and the motor frame, whatever the gap, which separates the two macroscopic parts. The problem related to the micro/macro world interfacing is solved during the design of sheet in allowing an out-of- plane motion of SDA in order to provide a self gap compensation, whatever both the thermal expansion effects and the macroscopic machining tolerances. The expected driving characteristics show the interest of both cooperative arrayed microactuators and direct drive frictional mechanisms.