Study On An Electrothermal And Mechanical Latching Microswitch

MEMS microswitch is a kind of important component fabricated by MEMS technology. Compared with the traditional electronic relays, it has a series of advantages which include microscale dimensions, low power consumptions, low contact resistance and fast response. In addition, microswitches can be integrated with IC. In this paper, a kind of electrothermal and mechanical latching microswitch is designed and fabricated. The design, materials selection, micro fabrication process and the performance of the microswitch were investigated. The microswitch is composed of two electrothermal bimorph actuator beams, which can maintain the bistable state by mechanical latching, so the power consumption can be reduced. The main contributions of this paper include the following aspects:Firstly, the prototype of the microswitch is designed based on the bimetal effect. The bimorph actuator beam comprises two layers of materials with different thermal expansion coefficients. When the beam is heated, the mismatch of the thermal expansion coefficients causes it to bend. We use the metal(Ni) and electrophoretic polymer as the two layers of the bimorph actuator beams, the choice is directed by the performance of materials and the technological factors. The displacement and temperature distribution of the electrothermal actuator with different layout of Ni resistor have been simulated by ANSYS, which verifies the feasibility of the design.Secondly, the microswitch is fabricated using a non-silicon surface micromachining technology which is compatible with many kinds of materials. Before this step, the electrophoretic polymer is patterned by two methods. The results show that the electrophoretic polymer can be patterned by plasma etching which is compatible with the surface micromachining technology, but it’s time-consuming; it also can be patterned by photolithography electrodeposition which is simple and efficient, but this process is not well compatible with photoresist. With regards to this, we attempt to apply a novel electrophoretic polymer solidified at 120℃. And then, some detail processes have been emphasized, such as processes about etching of Cu sacrificial layer、 etching of Cr/Au seed layers and the application of the novel electrophoretic polymer in microswitch.Finally, static and dynamical performances of the fabricated microswitch devices have been characterized. When an 80 m A pulse current with 10% duty cycle is applied to the electrothermal actuator, the bending displacement of the actuator can reach to 58.1μm, which is enough for the designed requirement(56μm). In order to observe the implementation of bistable micromechanisms, a timing sequence is proposed to actuate the microswitch. The design principle and operation of the PCB, which output the timing sequence, have been introduced mainly. When the timing sequence pulse current is applied, the electrothermal mechanical latching microswitch can control the on/off state of the external circuit. The result demonstrates the bistable of the microswitch is implemented successfully.