Dielectric charging and contact degradations are the two major challenges to improve the lifetime of series ohmic electrostatic MEMS switches. This paper details our approach and our main results to overcome the failures due to dielectric charging. We introduce a time predictive model for charge accumulation that we use as a design tool for reliability. The key parameters are listed and a new switch design is proposed to reduce the charging: the dielectric materials between the actuation electrodes are removed as much as possible. This dielectric-free design gives remarkable results in terms of dielectric charging sensitivity: the pull-in voltage decreases a little bit at initial times, and remains steady for longer time. The second major challenge, that remains to be considered, deals with the contact reliability. For that purpose, gold and ruthenium contacts have been investigated under several operating conditions. Gold contacts give good results in cold switching conditions whereas ruthenium suffers from surface contamination which increases quickly the contact resistance. In hot switching conditions, both materials are sensitive to material transfer mechanism, the failure rate being proportional to the open circuit voltage. Nevertheless, ruthenium seems more resistant to a material transfer than gold, and offers performances acceptable for some specific applications. A hermetic packaging at wafer level should allow to improve the contact reliability thanks to an efficient management of the surface contamination issue.

Dielectric charging is a key failure mechanism in radio frequency (RF) microelectromechanical systems (MEMS). To date we lack suitable physical models for the prediction of long-term behavior of RF MEMS switches, susceptible to dielectric charging. In this paper, we present an original approach of studying dielectric charging including modeling of long-term behavior of RF MEMS switches based only on physical dielectric properties that are experimentally characterized. For the first time, we introduce explicitly the trapping kinetics in the model of charging in RF MEMS. In this study, the conduction mechanism and trapping properties of the plasma enhanced chemical vapor deposition (PECVD) SiNx and SiO2 dielectric layers used for the fabrication of RF MEMS switches are characterized. The conduction is determined from I-V sweeps in metal-insulator-metal (MIM) capacitors, whereas the trapping properties are determined from constant current injections in MIM capacitors. The SiNx material shows Poole-Frenkel conduction while Schottky conduction is found to be the best fitting model for the SiO2 dielectric material. The trapping properties of the SiNx layer is best fitted with a logarithmic model of repulsive trapping, while SiO2 fits better with an exponential model of first-order trapping. These extracted physical properties serve as input parameters to our model of pull-in voltage drift in RF MEMS switches. The results of modeling are verified against the pull-in voltage drifts measured on real fabricated capacitive-type RF MEMS switches. It is concluded that the simulated switch lifetime results are very consistent with experimental data obtained for electrostatic MEMS switches either made with PECVD SiNx or SiO2 dielectric materials.

This paper presents an original time predictive model to simulate the drift of the pull-in voltage due to dielectric charging for electrostatic MEMS switches. This model of charge accumulation is based on the characterization of the bulk dielectric properties by I-V sweeps and constant current injections performed on Metal-Insulator-Metal capacitors. The model can be successfully used to compare various dielectric materials, and lead to parametric studies without the need of any fitting parameters. Moreover, the simulated switch lifetime results are very promising as they are consistent with experimental data obtained for electrostatic MEMS switches either made with SiNx or SiO2 dielectric materials.

In this work, spots of charges have been injected on typical silicon nitride used for RF-MEMS switches. Several relative humidity (RH) conditions have been used for the charge injections. The evolution of these spots with time has been assessed thanks to electrostatic force microscopy (EFM) measurements. Experimental results confirm the hypothesis of surface conduction enhancement but also show a 30% increase of the density of injected charge by humidity. It has been also shown that a level of 40% RH decreases the charge relaxation time by a factor 10 to more than 100 compared to a charge relaxation process occurring under dry atmosphere. This phenomenon may be due to the ability of protons contained in the water to diffuse trough silicon nitride.

This paper presents a thorough methodology to evaluate the mechanical properties of RF MEMS switches. It includes an analytical electro-mechanical model and nanoindentation characterizations which allow explaining the electrostatic behavior of the MEMS switches.Experimental and theoretical aspects are compared through two runs of ohmic electrostatic switches which are different from geometric and process flow standpoint.The switch is modeled as a clamped-clamped beam with mobile vertical loads, two stretching axial forces and two reaction moments in the anchors.The mechanical properties are characterized by nanoindentation technique; specific test protocol for measuring very low stiffness has been specially implemented with an adapted continuous stiffness measurement method. The measured values of the stiffness at the membrane center are respectively 79 and 137 N/m for the two runs, and they remain in good agreement with the theoretical model. The difference between these two runs is explained by the difference of the tensile residual stress.Moreover, the nanoindentation data turn out to be useful to evaluate the contact quality: dimple deformation due to twisting of the beam (contact in multiple steps), or inhomogeneous surface (stiffness is increasing while in contact).The fitted model is also used to approximate the restoring and contact forces and to point out the influence of the mechanical properties on the electrostatic behavior. A simple model with two parallel-plate capacitors in parallel, used for calculation of the up- and down-state capacitances, shows no discrepancy with experimental values.Finally, it may be concluded that the electrostatic behavior of the switches (pull-in voltage, up- and down-state capacitances, and probability of stiction) can be better understood thanks to the mechanical characterizations made by nanoindentation. (c) 2010 Elsevier B.V. All rights reserved.

The most important failure mechanism for electrostatic MEMS switches is dielectric charging, which contributes to a significant reduction of the device lifetime. In this study the correlation between the dielectric properties and the switch lifetime is evaluated. The conduction mechanism and trapping kinetics for two types of PECVD SiNx are determined by I–V sweeps and constant-current injections from Metal–Insulator–Metal (MIM) capacitors. This type of procedure is used as a basis for modeling the charge build-up in a switch. Despite significant differences between the dielectrics, in terms of leakage current and trapping properties, the numerical model of charge build-up fits well with experimental data. We conclude that the switch lifetime can be correlated with the trapping properties of the dielectric itself.

This paper deals with dielectric charging phenomenon - a key failure mechanism for electrostatically actuated MEMS. Conduction mechanisms and trap properties of silicon nitride are investigated by current-voltage measurements on Metal-Insulator-Metal (MIM) capacitors and RF MEMS capacitive switches. Both structures show a similar behavior with two bulk-controlled conduction mechanisms: space-charge-limited current below 1.5MV/cm and Poole-Frenkel conduction above 1.5MV/cm. The number of trapped charges is extracted from the hysteresis of I-V sweeps and used to estimate the corresponding shift of the pull-in voltage on the switches. These results are in agreement with functional tests performed on the switches.

In this study, a nanoindentation technique is used to characterize the mechanical properties of RF MEMS series ohmic switches. We present the methodology, analytical models and test setup which allow to measure stiffness, gap heights and to evaluate contact forces. To validate this methodology, the nanoindentation of two types of RF MEMS switches, fabricated by CEA-LETI, is carried out. These data are fitted with an electro-mechanical model of the switch and are then compared with the results of electrical functional tests.

This paper presents a methodology developed to characterize the mechanical properties of MEMS switches. Mechanical experiments have been performed to explain the electrostatic behavior of an ohmic electrostatic series switch made by CEA-LETI. The mechanical properties of switches are characterized by nanoindentation experiments : membrane stiffness, gap heights and contact load. These results have been compared to the results obtained by simple analytical models : the mechanical model shows a good correlation with a membrane stiffness currently around 50-100 N/m, and the electrostatic model gives capacitance values in accordance with measurements. Based on these results, the electrostatic behavior of switches has been analysed : the influence of the mechanical properties on the ohmic and capacitive responses is pointed out.

The nanomechanical behaviour of micromembranes for high temperature applications of a microelectro mechanical system pressure sensor has been studied by use of atomic force microscopy. A method was elaborated and used for measure nanometre deformation of the membrane under application of high loads. This method was also useful for identifying failures of a membrane. e.g., undesired position against the substrate of the structure. The tests were performed for a series of membranes. The characteristics of the mechanical behaviour were plotted for different geometrical features of the membranes to identify the influence of geometry and dimension. The method was found to be very effective for the process characterisation of the fabricated MEMS micromembranes devoted, e. g., to high temperature pressure sensors.

Mold releasing is one of the important issues in nanoimprint lithography (NIL). In this paper, de-molding force and friction coefficients for deteriorated surface statuses are quantitatively investigated to evaluate the surface quality of the mold. The mold surface is successfully deteriorated by UV irradiation as a durability inspection. The de-molding force and the friction coefficient are strongly depend on the contact angle of the mold surface. These results quantitative evaluation of the de-molding process and propose durability inspection method for anti-stiction layer.

In this experiment one set of ultrathin polymeric resist samples were used to investigate their nanomechanical properties. The set consisted of two silicon wafers with thermoplastic polymer. The samples were denoted as sample 1 and sample 2. The glass transition temperature determined with DSC (differential scanning calorimetry) was 60°C. Prepared by micro resist technology, these films were spin-coated (3000 rpm for 30 sec) on silicon 4” wafers that were treated previously with an oxygen plasma for 10 minutes. After spin coating the films were soft-baked on a hot plate for 2 minutes in 140°C to evaporate solvent and form a solid layer. The thickness of this film was measured and it was 208 nm and 202 nm for sample 1 and 2, respectively. The testing equipment, used in this study was an AFM (Microtestmachines Co., Belarus) with optical cantilever’s deflection detection system (photodiode). For temperature experiments the microscope was equipped with heating unit that enabled con