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This paper investigates the effect of electrical contact on the thermal contact stress of a microrelay switch. A three-dimensional elastic-plastic finite element model with contact elements is used to simulate the contact behavior between the microcantilever beam and the electrode. A model with thermal-electrical coupling and thermal-stress coupling is used in the finite element analysis. The effects of contact gap, plating film thickness and number of switching cycles on the contact residual stress, contact force, plastic deformation, and temperature rise of the microrelay switch are explored. The numerical results indicate that the residual stress increases with increasing contact gap or decreasing plating film thickness. The results also show that the residual stress increases as the number of switching cycles increases. A large residual stress inside the microcantilever beam can decrease the lifecycle of the microrelay.

Microrelays are widely used in the field of electromechanical control, telecommunications, test equipment, and other MEMS devices. The general requirements for microrelays are low power consumption, good insulation, low contact resistance, and good reliability during its lifecycle. Among all types of actuation of the microrelay, the electrostatical actuation consumes less power. However, its high driving voltage requires additional circuits in practical applications. The magnetically actuated microrelay has the advantages of large actuating force, large displacement, low driving voltage as well as its insensitivity to the operating environment, which make it popular in many applications. Besides these noticeable features, to be of commercial interest, a magnetically actuated microrelay has to be as reliable as a conventional relay. Although a magnetically actuated microrelay has structural similarities with a conventional relay and can be regarded as a miniature of it, the design of a microrelay should not be as simple as reducing all the dimensions with the same proportions compared with a conventional relay. To function well and to have a good reliability, the knowledge of design parameters, such as the contact gap, plating film thickness of the electrode, contact force, and contact resistance is required.

To improve the reliability of the magnetically actuated microrelay, not many researches have been focused on the study of its design parameters as well as performing characteristics. Hosaka et al. [

In this work, the effect of electrical contact on the thermal contact stress of a magnetically actuated microrelay switch is investigated. A three-dimensional elastic-plastic finite element model with contact elements is used to simulate the contact behavior between the microcantilever beam and the electrode. The effects of contact gap, plating film thickness and number of switching cycles on the contact residual stress, contact force, plastic deformation, and temperature rise of the microrelay switch are studied. The simulation data show that the residual stress increases with increasing contact gap or decreasing plating film thickness. The results also show that the residual stress increases with increasing switching cycles. A large residual stress inside the microcantilever beam can decrease the lifecycle of the microrelay.

Typically, a microrelay consists of a microcantilever beam, a substrate (electrode) and a fixed support end.

_{c}_{1}_{2}_{x}_{1} and _{x}_{2} are the bending stresses and can be expressed as:
_{2} / _{1}. _{eq}_{n}_{1} and _{2} are the distances from the top surface of the microcantilever beam to the centroid of the beam and the film, respectively. From _{1} and _{2} can be obtained as _{1}/2 and, _{1}+ _{2}/2, respectively. The moment resultant of the bending stresses is equal to the bending moment _{eq}_{eq}_{1}_{2}_{eq}_{1}. The deflection _{max}_{c}_{c}_{c}_{x,max(tensile)}

The effects of film thickness, contact gap and contact force on the contact deformation and residual stress distribution of the microrelay are studied. Three different film thicknesses, i.e. 1, 4 and 6

In this study, a three-dimensional elastic-plastic finite element model is used to simulate the electrical contact between the microcantilever beam and the electrode. The numerical simulations are performed using the ABAQUS commercial finite element package. A model with thermal-electrical coupling and thermal-stress coupling is used in finite element analysis to simulate interactions between the electricity, temperature and deformation arisen during the contact process. Due to the symmetry of the geometry, the finite element analysis considers only one half of the model. Various finite element mesh sizes are performed for the convergence test of the bending stress and contact resistance of the microcantilever beam. The total number of elements used in each simulation varies with the variation of film thickness. In this research, numerical simulations involve approximately 6760 eight-node brick elements and 8968 nodes, and a total of 480 contact elements are used to model the contact between the microcantilever beam and the electrode. The finite element model is shown in

At first, the elastic finite element approach is adopted to check the feasibility of using the contact model to simulate the microcantilever-electrode interaction. _{x,max(tensile)}^{2} is applied. The solid line and the symbol in

The bending stress distribution on the top surface of the microcantilever beam, i.e. the x-z plane at y=20 _{x}_{x}

The effect of contact gap on the residual stress _{x,r}

The effect of plating film thickness on the residual stress _{x,r}^{2}, respectively. It is obvious that the residual stress _{x,r}^{2}

In addition, the variations in contact location and contact force induced by the variation of contact gap change the size of the contact area. As presented above, in this case, the maximum contact area occurs when the contact gap

_{x,r}_{c}^{2}, respectively. It can be obtained that the compressive residual stress increases with increasing switching cycles. This can be attributed to the plasticity occurs on the top surface near the fixed support end of the cantilever beam. As the number of switching cycles increases, the amount of plasticity accumulates and the residual stress increases. A larger residual stress remains in the microcantilever beam can decrease the lifecycle of the beam. The accumulation of plasticity also makes the variation in vertical displacement at the free end increase, as shown in ^{2} and 10

This study has investigated the electrical contact and the residual stress of a microrelay using a three-dimensional elastic-plastic finite element model. A model with thermal-electrical coupling and thermal-stress coupling is used in finite element analysis. The effects of contact gap, plating film thickness and number of switching cycles on the contact residual stress, contact force, plastic deformation, and contact temperature of the microrelay switch are explored. Based upon the current simulation results, the following conclusions can be drawn:

The residual stress is affected significantly by the contact gap and the film thickness. The residual stress increases with the increase of the contact gap and decreases as the film thickness increases.

A smaller contact gap results in a larger microcantilever-electrode contact force. The contact location of the microcantilever beam and the electrode is varied with the size of the contact gap. The contact location is moved toward the free end of microcantilever beam as the contact gap increases.

The residual stress increases as the number of switching cycles increases. A larger residual stress remains in the microcantilever beam can decrease the lifecycle of microrelay.

The plastic deformation at the microcantilever tip increases as the number of switching cycles increases. This plastic deformation at the microcantilever tip decreases the gap distance between the microcantilever beam and the electrode, and changes the microcantilever-electrode contact location as well.

Geometrical configuration of the microrelay switch.

Schematic illustration of the contact load and the cross section of the microrelay.

Typical finite element model.

Variation of maximum tensile bending stress _{x,max(tensile)}

Bending stress _{x}

Residual stress _{x,r}

Residual stress _{x,r}

The electric current density distribution on the contact area for various contact gaps.

Contact reactive force as a function of the contact gap.

Variation in maximum contact resistance at the microcantilever-electrode contact area for various contact gaps.

Variation in switching time used in the thermal-electrical coupling finite element simulation.

Distribution of residual stress _{x,r}

Variation in vertical displacement for various switching cycles at the free end.

Effect of switching numbers on the maximum contact temperature rise.

Mechanical, electrical and physical properties used in finite element simulations.

| |||
---|---|---|---|

255 | 120 | 73 | |

0.3 | 0.35 | 0.26 | |

280 [ |
127 | – | |

568 [ |
435 | 180 | |

^{−1} |
13.347 E-6 | 16.483 E-6 | 3.0 E-6 |

49.99 | 386.52 | 71 | |

6.249 E+6 | 58.06 E+6 | 60 E+6 | |

^{3} |
9200 | 8935 | 3100 |

419.99 | 383.62 | 710 |