Dominique Collard

Scratch drive actuator with mechanical links for self-assembly of three-dimensional MEMS

The self-assembling of three-dimensional (3-D) MEMS from polysilicon surface micromachined part is very attractive. To avoid risky external manipulation, the practical use of integrated actuator to perform the assembling task is required. To that goal, this paper presents detailed characteristics of the electrostatic surface micromachined scratch drive actuator (SDA). First, from numerous SDA tests, it is shown that this actuator is able to produce a threshold force of 30 /spl mu/N, with a yield above 60%. With polysilicon devices consisting of SDA mechanically linked to buckling beam, a horizontal force of 63 mN has been demonstrated with /spl plusmn/112 V pulse, and up to 100 /spl mu/N can be obtained with higher voltage. With buckling beams, displacements up to 150 /spl mu/m have been obtained in the vertical direction. The generation of vertical force of 10 /spl mu/N was confirmed with a 100 /spl mu/m displacement producing 1 nJ work in the vertical direction. Finally, SDA overcomes the usual sticking of surface machined polysilicon by producing enough vertical force to completely release wide polysilicon plate (500 /spl mu/m/spl times/50 /spl mu/m) without external manipulation. The above characteristic, both in terms of structure releasing and vertical/horizontal forces and displacements provides the SDA with the capability of self-assembling complex 3-D polysilicon part, opening new integration capabilities and new application field of MEMS.

Fabrication and characterization of an SU-8 gripper actuated by a shape memory alloy thin film

In this paper, we present the fabrication process of a shape memory alloy (SMA) thin film in both monolithic and hybrid configurations. This provides an effective actuation part for a gripper made of SU-8 thick photoresist. We also extensively describe and discuss the assembly of the SMA thin film with the SU-8 mechanism. Measurements show that the SU-8 gripper is able to achieve an opening action of 500 μm in amplitude at a frequency of 1 Hz. Finite element model simulations indicate that a force of 50 mN, corresponding to 400 μm of opening amplitude, should be produced by the SMA actuator. Although the assembly of the TiNi SMA thin film with the SU-8 mechanism is demonstrated, the bond reliability needs further development in order to improve the thermal behavior of the interface. In this paper, we show that SU-8 is well suited as a structural material for microelectromechanical systems (MEMS) applications. An attractive feature in the MEMS design is that the SMA generated force is well matched with the elastic properties of SU-8. From the application point of view, a SMA-actuated SU-8 high-aspect-ratio microgripper can serve as a secure means to transport microelectronics device, because it provides good grasping and safe insulation. This is also a preliminary result for the future development of biogrippers.

Silicon Nanotweezers With Subnanometer Resolution for the Micromanipulation of Biomolecules

We describe electrostatically actuated silicon nanotweezers which are intended for the manipulation and characterization of filamentary molecules. The microelectromechanical system consists of a pair of opposing tips whose distance can be accurately adjusted by means of an integrated differential capacitive sensor. The fabrication process is based on silicon-on-insulator technology and combines KOH wet anisotropic etching and deep reactive ion etching of silicon to form sharp nanotips and high aspect ratio microstructures, respectively. In the designed prototype, the initial gap between the tips was around 20 mum. The device showed a maximum displacement of about 2.5 mum, and we could achieve a resolution better than 0.2 nm (in static mode). We measured a resonant frequency of 2.5 kHz and a quality factor (Q factor) of 50 in air. The instrument was used to perform static and dynamic mechanical manipulations on DNA molecules, and we could distinctly observe the viscoelastic behavior of DNA bundles from these experiments.

Analysis and application of a viscoelastic model for silicon oxidation

The numerical modeling of the oxidation of silicon is analyzed from a nonlinear viscoelastic approach. Its mechanical and stress dependent parameters are determined for silicon dioxide and nitride. The study focuses on the rheological behavior of the materials. The two dimensional simulations of silicon cylinders oxidation and local oxidation of silicon processing reveal that at 1000 °C, a nonlinear viscous modeling is equivalent to the nonlinear viscoelastic one. But, for lower temperatures, the discrepancies between these two models, observed in the stress calculation and final oxide shape, demonstrate the necessity for a complete nonlinear viscoelastic formulation. Finally, the calibrated model is used to study the growth of a recessed isolation structure. The investigations quantify the influence of geometrical parameters of the silicon groove on the shape of the final isolation oxide (e.g., parameters such as the silicon overetch under the pad oxide, the depth of silicon etching, the slope of the sil...

Two-dimensional simulation of local oxidation of silicon: calibrated viscoelastic flow analysis

Local Oxidation of Silicon (LOCOS) remains the common isolation technology for mass-production of integrated circuits. The work reported in this paper contributes to the improvement of the numerical modeling of the LOCOS process. A physical two-dimensional (2-D) modeling of the thermal oxidation of silicon has been developed based on the explicit treatment of the reaction expansion. The originality of this modeling is to propose a general solution taking into account of the silicon deformation, incorporating the viscoelastic behaviour of oxide and nitride and, particularly, giving a complete calibration of the stress-dependent parameters. The prediction capabilities are demonstrated by the calculations of oxide shapes and oxidation-induced stresses in a silicon substrate for very advanced isolation techniques.

The stability and pull-in voltage of electrostatic parallel-plate actuators in liquid solutions

This paper deals with parallel-plate electrostatic actuators in liquids. We study the stability conditions of such actuators and show that the pull-in effect can be shifted beyond one-third of the gap, and can even be suppressed. We demonstrate that the insulating layers of the actuator plates, which are originally designed to avoid any current leakages or short-circuits, play a major role in this phenomenon. Experiments are performed on fabricated devices; silicon nitride layers are used to completely encapsulate the actuator plates. The voltages required to close the actuator gap are measured in various liquids and compared to the values obtained by analytical calculations. This study gives guidelines for the design of parallel-plate actuators featuring in liquids either a binary-state operation when the pull-in effect occurs, or a continuous displacement within the full gap.

Microactuated self-assembling of 3D polysilicon structures with reshaping technology

This abstract proposes and experimentally confirms the automatic self-assembling of 3D polysilicon structures, compatible with both mass production and IC based surface machining. This technique combines an integrated actuation based on the scratch drive actuator (SDA), for the structure raising up, and the reshaping technology to obtain the permanent 3D shapes. Complex 3D structures have been successfully realised and their electrostatic actuation have been obtained. This self-building capability of 3D devices from silicon surface micromachining opens new integration capabilities and new application field for MEMS.

A large stepwise motion electrostatic actuator for a wireless microrobot

An original large stepwise motion electrostatic microactuator for a wireless microrobot using a distributed Ciliary Motion System (CMS) [1] is presented. Coventorware/sup TM/ cosolver simulations have shown x-displacement of 240 nm for one actuation step. Design of the antennas for inductive powering has been optimized in order to maximize the energy transfer. 24 /spl mu/m gold electroplated hollow micro-coils have been fabricated on an epoxy substrate as receiver antennas. Q-factor of 29 at 13.56 MHz and induced voltage up to 100 V on a 1 k/spl Omega/ load has been obtained. Remote actuation of an array of actuators supporting a 0.25 mm/sup 2//380 /spl mu/m-thick piece of silicon has been successfully demonstrated with a pull-in voltage of 80 V.

Electrostatic impact-drive microactuator

A fully packagable micromachined actuator was developed for generating precise but unlimited displacement. A suspended silicon mass is encapsulated between glass plates and driven by electrostatic force. By hitting a stopper, it generates impact force to drive the whole actuator in a small step (/spl sim/10 nm). It is a micromachined and electrostatic version of the impact-drive actuator.

Piezoresistive simulation in MOSFETs

Abstract The piezoresistivity effects in MOSFET devices have been experimentally determined. The Pgr;11, Pgr;12 and Pgr;44 2D piezoresistive coefficients in both n- and p-type inversion layers have been analytically developed including the quantum effects, the intravalley-intervalley scattering effects, the different saturation velocity effects and the hot-electron effects. In addition, the hole stress-induced effective-mass modification has been applied to determine the piezoresistive coefficients in p-type inversion layers. The carrier population variation due to the change of the band gap has also been taken into account in the weak inversion regime. A mixed 2D/3D model for the piezoresistivity effects has been introduced in the process/ device simulator IMPACT and a good agreement between simulation and experiment has been achieved.