Dynamic investigations of paddle MEMS cantilevers used in mass sensing applications

The dynamic behaviour of paddle MEMS cantilever oscillators under electrostatic actuation is investigated and presented in this paper. The scope is to estimate the influence of the geometrical dimensions and operating conditions on the frequency response of mechanical paddle cantilevers fabricated from polysilicon. Theoretical approach and finite element analysis are developed considering the multiphysics coupling between the electrical field and the mechanical structure of oscillators. The;experimental tests are performed under ambient condition and in vacuum in order to characterize the effect of operating condition on the frequency response of paddle cantilevers

Nanocharacterization of the Mechanical and Tribological Behavior of MEMS Micromembranes

This chapter presents the experimental investigation and numerical simulation of micromembranes supported by serial‐parallel connected hinges. The micromembranes can be used in optical applications or as the flexible mechanical element in radio frequency microelectromechanical system switches. A method to determine the micromembrane stiffness is presented. Experimentally, the out‐of‐plane micromembranes deflection is performed using an atomic force microscope. The dependence between deflection and the applied force gives the sample stiffness. The flexible plate of micromembranes is directly deflected to substrate, and the adhesion force is measured. The micromembranes are electroplated with gold, and two series of the serial connected hinges are investigated. Each of them has different parallel connected hinges. The experimental results of stiffness and adhesion force are compared with analytical and numerical results. The presented method is also applied to determine the stiffness of micromembranes supported by other types of hinges

NANOMATERIAL BEHAVIOUR OF A GOLD MICROCANTILEVER SUBJECTED TO PLASTIC DEFORMATIONS

The nanomechanical material behaviour of a gold microcantilever subjected to plastic deformations is presented in this paper. Using an atomic force microscope, experimental investigations are performed in order to determine the dependence between bending deflections of sample versus applied forces and to estimate the maximum stress in the beam structure. During testing, the force has successive positions on microcantilever, starting from the beam free-end and moving toward to the anchor. The plastic deformation of microcantilever occurs when the force is applied close to the beam anchor and performed large deflections. Finite element analysis is used to visualize the deflection of microcantilever and to estimate the maximum stress.FIRST Post-Doc n° 616365 (MOMIVAL

Nanomechanical and nanotribological characterization of microelectromechanical system

peer reviewedInvestigations of the mechanical and tribological properties of microelectromechanical system (MEMS) components on nanoscale can provide insights into failure mechanism of material. The main goal of this paper is focused on the mechanical and tribological characterizations of MEMS mechanical components in order to improve their reliability design. The mechanical properties of interests are stiffness, modulus of elasticity, stress, strain. Dynamical investigations are performed to analyze the resonant frequency response, velocity and amplitude of oscillations of electrostatically actuated microcomponents and to estimate the quality factor. Finite element analysis is used to validate the experimental results of mechanical properties and to simulate the dynamical behaviour of investigated microcomponents. Tribological investigations are developed to estimate the stiction and friction. Testing and the individual characterization of MEMS materials and structures, performed using advanced equipments such as atomic force microscope and optical vibrometer analyzer are presented.FIRST Post-Doc n°616365 (MOMIVAL

Impact of environmental conditions on the reliability of MEMS components from optical applications

The reliability design and the lifetime of MEMS from optical applications is strongly dependent on the operating conditions. In optical devices an additional stress is introduced by the temperature gradient appearing during operation. The thermal stress introduced in the structure modifies the component response and its lifetime. The investigated sample is a micromirror fabricated from gold using the MEMS technologies and tested by an atomic force microscope. The scope is to analyse the temperature and relative humidity influence on the mechanical and tribological behaviours. Using a mechanical force given by the bending deflection and stiffness of the AFM probe, the dependence between the applied force and the micromirror deformation is monitored as a function of temperature. By increasing the temperature of structures the stiffness decreases based on the thermal relaxation of the material. If the relative humidity increases the adhesion between the micromirror and substrate is improved based on the capillarity effect. The results obtained are useful to MEMS designers who can predict the micromirror response as a function of the operating conditions with influence on the actuation energy, the accuracy in response and the system lifetime

NANOTRIBOLOGICAL AND NANOMECHANICAL CHARACTERIZATIONS OF MEMS MATERIALS

FIRST Post-Doc n° 616365 (MOMIVAL

Impact of environmental conditions on the reliability of MEMS components from optical applications

The reliability design and the lifetime of MEMS from optical applications is strongly dependent on the operating conditions. In optical devices an additional stress is introduced by the temperature gradient appearing during operation. The thermal stress introduced in the structure modifies the component response and its lifetime. The investigated sample is a micromirror fabricated from gold using the MEMS technologies and tested by an atomic force microscope. The scope is to analyse the temperature and relative humidity influence on the mechanical and tribological behaviours. Using a mechanical force given by the bending deflection and stiffness of the AFM probe, the dependence between the applied force and the micromirror deformation is monitored as a function of temperature. By increasing the temperature of structures the stiffness decreases based on the thermal relaxation of the material. If the relative humidity increases the adhesion between the micromirror and substrate is improved based on the capillarity effect. The results obtained are useful to MEMS designers who can predict the micromirror response as a function of the operating conditions with influence on the actuation energy, the accuracy in response and the system lifetime

Geometrical Effects on the Dynamical Behavior of MEMS structures

peer reviewedThe influence of geometrical dimensions on the dynamical behavior of polysilicon MEMS structures configurations is studied and presented in this paper. Electrostatically actuated MEMS components as microbridges and microcantilevers are used to investigate the coupled electro-mechanic effect, frequency responses and the dynamic bending stress. The electrostatic principle is common in sensing and acting devices and there are many MEMS structures subjected to electrostatic forces.Project MOMIVA

AFM Characterization of Temperature Effect on the SU-8 Mechanical and Tribological Properties

This study presents the effect of temperature on the mechanical and tribological properties of SU-8 polymer. The temperature of investigated samples increasing during testing and the variation of mechanical and tribological properties were monitored. The samples for tests were SU-8 hard baked at different temperatures. The hard bake temperature changes the mechanical and tribological properties of polymers. The aim of this research work is the reliability design improvement of SU-8 microstructures from electro-thermally actuated devices where a thermal gradient produces the softening and modification of SU-8 behavior. As a function of the hard baked temperature, different mechanical and tribological properties were experimentally determined using the atomic force microscopy (AFM) technique. The mechanical properties of interest are the modulus of elasticity and hardness. The investigated tribological properties involve the adhesion and friction forces. The modulus of elasticity and hardness decrease if the operating temperature increases based on the thermal relaxation of material and their viscoelastic behavior. The adhesion force between AFM tip and investigated samples increases if the operating temperature increases, respectively. The same evolution was experimentally observed in the case of friction force. Moreover, for the same testing temperature, the modulus of elasticity and hardness increase, and the adhesion and friction forces decrease if the SU-8 is hard baked at high temperature