BCB Based Packaging for Low Actuation Voltage RF MEMS Devices

This paper outlines the issues related to RF MEMS packaging and low actuation voltage. An original approach is presented concerning the modeling of capacitive contacts using multiphysics simulation and advanced characterization. A similar approach is used concerning packaging development where multi-physics simulations are used to optimize the process. A devoted package architecture is proposed featuring very low loss at microwave range

Modélisation et conception des micro commutateurs RF MEMS a actionnement électrostatique et/ou piezoélectrique

The majority of RF MEMS switches are actuated using the electrostatic forces to vary the distance between the two electrodes to cut or transmit the signal. This type of actuation, despite its advantage, has a major drawback which is the dielectric charging which lead to the failure of the switch. To solve this problem, we worked in parallel in two directions. The first direction consists of using of piezo-electric actuation to suppress the dielectric charging. The second one is based on the improving of mechanical behavior of the structure by increasing the restoring force without increasing the actuation voltage. The proposed design has been validated using a multiphysic simulation platform.La majorité des MEMS RF (Micro Electro Mechanical Systems Radio Fréquence) sont actionnés en utilisant une force électrostatique. La distance entre les deux électrodes est ainsi modifiée pour transmettre ou couper le signal RF. Ce type d'actionnement, malgré ses avantages, a un défaut majeur qui concerne le chargement des diélectriques. Ce dernier mène à terme à la défaillance du dispositif. Pour résoudre ou minimiser ce problème, nous avons travaillé dans deux directions. La première consiste à utiliser l'actionnement piézo-électrique à la place de l'actionnement électrostatique. La seconde direction concerne l'amélioration du comportement mécanique de la structure en augmentant la force de rappel sans modifier la tension d'actionnement. Les designs proposés ont été validés en utilisant une plateforme de simulation multi-physique

A macro model based on finite element method to investigate temperature and residual stress effects on RF MEMS switch actuation

International audienceTill nowadays, MEMS design suffers from the lake of efficient and easy-to-use simulation tools covering the complete MEMS design procedure, from individual MEMS component design to complete system simulation. Finite element analysis (FEA) methods offer high efficiency and are widely used to model and simulate the behaviour of MEMS components. However, as MEMS are subject to multiple coupled physical phenomena at process level and play, such as initial stress, mechanical contact, temperature, thermoelastic, electromagnetic effects, thus finite element models may involve large numbers of degrees of freedom so that full simulation can be prohibitively time consuming. As a consequence, designers must simplify models or specify interesting results in order to obtain accurate but fast solution. Some multiphysics' softwares, such as COMSOL [3], allow Reduced Order Modeling (ROM) or macro models which considers the global behaviour of the device. Thus designers can create automatically, for example, their own Simulink (Matlab ©) library from a multiphysics finite element modelization, in order to develop a behavioural model of the whole component. This work deals with a Simulink macro model, generated by a three-dimensional multiphysics finite element analysis (FEA) using COMSOL, aiming to investigate the pull-in and pull-out voltage of microswitches

Effect of Contact Force Between Rough Surfaces on Real Contact Area and Electrical Contact Resistance

International audienceUntil nowadays, surface roughness effects were ignored in the analysis, due to the difficulty to generate a rough surface model and also to simplify the model in order to reduce calculation time. However, many engineering fields, such as MEMS, seek to improve the behaviour of the system at the surface level or the interface between surfaces. Thus, with the advance of numerical capabilities, the topography of the surface can be included in finite element simulations. This paper presents two methods for generating rough surfaces, one using the real shape with an original reverse engineering method and the other one by using a parametric design language to generate a normally distributed rough surface. As an application to demonstrate the power of these methods, we choose to predict by simulation the electrical contact resistance and the real contact area between rough surfaces as a function of the contact force. This application is a major concern in RF MEMS ohmic Switches and shows an original approach to extract a guideline in choosing a design, materials and process flow to minimize the contact resistance. The agreement between the numerical model and an analytical model is very good and validates this novel numeric approach

A macro model based on finite element method to investigate temperature and residual stress effects on RF MEMS switch actuation

International audienceTill nowadays, MEMS design suffers from the lake of efficient and easy-to-use simulation tools covering the complete MEMS design procedure, from individual MEMS component design to complete system simulation. Finite element analysis (FEA) methods offer high efficiency and are widely used to model and simulate the behaviour of MEMS components. However, as MEMS are subject to multiple coupled physical phenomena at process level and play, such as initial stress, mechanical contact, temperature, thermoelastic, electromagnetic effects, thus finite element models may involve large numbers of degrees of freedom so that full simulation can be prohibitively time consuming. As a consequence, designers must simplify models or specify interesting results in order to obtain accurate but fast solution. Some multiphysics' softwares, such as COMSOL [3], allow Reduced Order Modeling (ROM) or macro models which considers the global behaviour of the device. Thus designers can create automatically, for example, their own Simulink (Matlab ©) library from a multiphysics finite element modelization, in order to develop a behavioural model of the whole component. This work deals with a Simulink macro model, generated by a three-dimensional multiphysics finite element analysis (FEA) using COMSOL, aiming to investigate the pull-in and pull-out voltage of microswitches

VERIFICATION OF CONTACT MODELING WITH COMSOL MULTIPHYSICS SOFTWARE

Contact analysis is of major concern in a lot of applications and addresses often multi-field effects (thermal, electromagnetic effects...). Due to the nonlinearity and difficulty in predicting the behaviour of bodies coming into and go out of contact, the need of software able to simulate a structural contact problem and couple it with other physics is a major stake. The last version 3.3 of COMSOL Multiphysics allows the analysis of multiphysics contact problem and appears attractive. Being new and under development, COMSOL 3.3 needs therefore to be validated in terms of contact modelling. Only the cases of frictionless problem are taken into account. A static contact Hertz model and a model containing a rigid-flexible contact and a flexible-flexible contact are studied and describe the capabilities, advantages, originalities and drawbacks of COMSOL 3.3. A good user interface and the capabilities to couple all physics with facilities make attractive the software. However, contact algorithm implemented in COMSOL doesn't allow the resolution of all contact problems. The more evident problem, like for example the case of a solid compressed on a rigid surface (contact of Hertz) can be solved efficiently with a reduced computational time. A problem that contains an initial gap between two deformable surfaces requires more computational costs and solver fails to find a solution easily. The user has to spend enough time to set up the contact parameters. But it isn't always evident to check these parameters to optimise the accuracy of the solution and the time of resolution. More investments have to be provided to improve the contact algorithms in Comsol and to facilitate the user to choose the contact parameters

Validation of simulation platform for modeling of RF MEMS contacts

International audienceFor the DC contact RF MEMS, it has been identified that most of the limitations are related to the quality and the repeatability of the contact that drive the RF performances and the reliability. In order to propose new generation of RF MEMS devices, it is important to get a deeper insight on the physic of contact in order to choose appropriate materials. As part of our study on the electrical contacts of RF MEMS micro switches, the need of multiphysics software offering a well developed solver to simulate many mechanical contact problems coupled with other physics, with a reduced time of calculation and good accuracy on the results is under investigation. As a first step, we need to validate the results of the numerical platforms existing in our laboratory. To do so, a static Hertz contact problem is simulated using ANSYS 10 and COMSOL 3.3 and we compared the results of the simulation with the analytical model. The second step consists of comparing the capabilities of each software to model interaction between objects and solve a variety of contact problems. Then we compare the facilities for the user to fit the contact parameters in the model in order to obtain an accurate solution of our problem. This study permits us to choose the software the most efficient for our application. The accuracy of ANSYS, the various methods available to solve the wide variety of contact problems and with a minimum effort from the user, makes of ANSYS's solver an excellent candidate to be used in our project. Especially, the real topography of the contact surfaces can be included in finite element simulations

Contact Modeling of DC Contact RF MEMS for Investigation of the Microcontact Degradation Mechanism

RF MEMS devices have already demonstrated very attractive performances to introduce some intelligence in the front end architectures. The insertion of RF MEMS into real architecture will necessitate reduced actuation voltage, dimensions and a better control of the electrical and electromechanical behavior that will give more importance to surface effects and their understanding and modeling. So far, surface effects were ignored in the analysis, because of the difficulty to generate a rough surface model and also to simplify the model in order to reduced computation times. With the increase of computation capabilities, the topography of the surface can be included in finite element simulations if appropriate simulation methodology is implemented. In order to give an explanation to the microcontact degradation phenomenon, gold DC contact switches are tested on an experimental set up in NOVAMEMS that allows the switch ageing under controlled atmosphere and makes possible the analysis of contact behavior with cycling. A correlation is established between the electromechanical characterizations and finite element simulations. From the surface characterization, we generate the real shape of both rough surfaces that come into contact and to predict the real contact area and size of each contact spots. The obtained results show actually an increase in contact resistance with cycling. However, the variation isn't as large as the experimental measurements. Other failure phenomena have to be taken into account such as organic deposits, contamination or hardening to complete the analysis