Orla Slattery

Modelling electrostatic behaviour of microcantilevers incorporating residual stress gradient and non-ideal anchors

The electrostatic behaviour of micromachined cantilevers incorporating residual stress gradient and non-ideal anchors is studied in this work. Using finite-element simulation data, behavioural models that predict the electrostatic deflection and pull-in voltage of such structures have been established. The models account for the effects of residual stress gradient and real supports on the mechanical behaviour of the microcantilevers, and have been validated via comparison with experimental data. For the deflection models, the level of correlation achieved was within 7%, and in the case of pull-in voltage analysis, the calculated and measured values agree to within 4%. The completed models offer an efficient means of design, analysis and optimization of cantilever-based electrostatically actuated MEMS devices. They can also be utilized for material property measurement and analysis.

Evaluation of Packaging Effect on MEMS Performance: Simulation and Experimental Study

The thermal cure required for die attach during microelectro-mechanical systems (MEMS) packaging causes thermal mismatch that induces undesirable stresses and strains in surface micromachined structures, which may adversely affect the performance and reliability of the packaged component. Understanding the influence of the packaging process is, therefore, critical for successful device design. This paper analyzes the influence of the die attach process on the electromechanical behavior of doubly-anchored surface micromachined beams. A number of different adhesive materials were considered, and the results of parametric studies on the effects of die attach on the pull-in behavior of beams of various lengths, widths, and anchor types are presented. An upward shift in pull-in voltage of the studied devices was observed in both simulation and experiment; modelled and measured data were found to correlate closely.

Comprehensive spring constant modelling of tethered micromechanical plates

A study of the spring constant of elastically suspended plates, commonly used in MEMS tunable capacitors and RF switches, is carried out in this paper. Formulae for calculating the spring constant of a plate suspended by four straight tethers incorporating residual stress and non-ideal anchor compliance are presented. The model was extracted from FEM simulation data and is validated experimentally. A measurement/modelling correlation of 13% was achieved. It is also shown that significant errors (over 100%) may result in predicting the spring constant when the combined effects of residual stress, non-ideal anchors and non-rigidity of the plate are neglected or underestimated. The model presented in this paper can be used for the design, analysis and optimization of MEMS structures based on elastically suspended plates.

Finite difference scheme for the accurate modelling of boundary layers in microchannels

Singularly perturbed heat equations are studied in the case when the heat/diffusion flux is given on the domain boundary. This paper shows that (depending on the value of perturbation parameter) the errors in the approximate solution, computed by a classical hnite difference scheme, can exceed the exact solution many times. The computed normalised heat flux fails to converge when the perturbation parameter is small. For the boundary value problem considered here, a special finite difference scheme has been constructed that allows the solution and the normalised heat flux to be found. The errors in the computed solution and normalised flux for this scheme are independent of the perturbation parameter and depend only on the number of the nodes in the grid used.

Adaptation of Photorefractive Holographic Camera for Observation of Micro-Mechanical Structures

The photorefractive holographic camera initially working on large scattering objects has been adapted to observe centimetric to micrometric objects. Application on micro-mechanical systems is presented.

Modelling effects of packaging on pull-in behaviour of doubly-anchored beams

Understanding the influence of the packaging process on MEMS device performance is critical for a successful design and analysis of both the device and the package. This paper is concerned with accurate prediction of the effects of packaging processes on the pull-in behaviour of doubly anchored microbeams. Results of parametric studies on the effect of gluing (die attach) on the pull-in behaviour of beams of various lengths, widths, anchor types, adhesives and adhesive thicknesses are presented. Where experimental data were available, a good correlation between measured and simulated results was achieved

Evaluation of spring constant in plates with straight suspensions

The mechanical spring constant is one of the most important characteristics of micromechanical structures, providing a key tool for accurate behavioural modelling of the devices. It is also one of the main controllable parameters allowing maximum flexibility for the designer. A study of the spring constant of elastically suspended plates, common to MEMS tunable capacitors and RF switches, is carried out in this paper. A model for the spring constant of the plate suspended by four cantilevers incorporating residual stress is presented. The model also accounts for nonideal anchors. The model was extracted from FEM simulation data and validated experimentally. Correlation to within 3% was achieved. The model can be used for design, analysis and optimisation of tunable capacitors and radio frequency switches or other structures based on elastically suspended plates. The presented model also predicts that significant errors may result in predicting the spring constant when combined effects of residual stress, nonideal anchors and nonrigidity of the plate are neglected or underestimated.

Simulating piezoelectric transformers for lighting applications

Advanced piezoelectric transformer technology is being investigated for lighting applications. This technology is substituting magnetic transformers used in driver circuits for more traditional electronic converters to supply and ignite lighting discharge lamps. The use of piezoelectric technology reduces the size, volume and weight of the transformer. This reduces the whole circuit and enables the development of smaller equipment that could be used in a range of applications. These piezoelectric transformers were designed to have higher efficiencies, higher output power and increased power density. This paper considers 2 piezoelectric transformers of differing geometries; a 110mm long transformer and a 50mm long transformer. This paper deals with the analysis of these piezoelectric transformers based on three-dimensional finite element modelling (3D FE). Simulation techniques are applied to design optimum packaging solutions for the transformers and to assess piezoelectric performance for a range of operating conditions.