Design And Fabrication Of Graphene Mems Switches

RF switches is one of commonly used devices in wireless telecommunication systems.With the fast development of micro electronic telecommunication technology,we've seen a surging demand for RF switches with higher RF performances that cannot be met by solid state switches but can be possibly met by fast-developing MEMS technology.However,despite its excellent RF performances compared with its solid state counterpart,MEMS switches is inferior in reliability.Worse is that most electrostatic MEMS switches require relatively higher voltage to be actuated,delaying the commercialization of MEMS switches.By inspection,this problem can be ascribed to properties of materials like Si and metals.These materials cannot be easily shaped to lower pull-in voltages and electrodes made from these materials are commonly suffered from cracking and adhesion due to co-function of force,electricity and heat.Brighter future may be brought from the discovery of two-dimensional material graphene,because thin graphene can keep pull-in voltage low and its high strength and hydrophobic surface can help to avoid cracking and adhesion.One research focus is designing fabrication technique for graphene MEMS switches and the key to fabricate is realizing suspended graphene structure.Fabrication techniques proposed recently feature commonly a complex and time-consuming route resulting poor precision.Here we propose a technique to fabricate graphene MEMS switches based on high precision graphene transfer coming from our previous research work.We study key fabrication process,fabricate samples and test them.In view of pull-in voltage,one of key parameters of MEMS switches,relations are analytically studied for switches featuring fixed-fixed beam and cantilever beam respectively.Impacts of different parameters on pull-in voltage are studied,including load distribution and location,equivalent spring constant,length,width,thickness and Young's modulus of movable electrode and gap between electrodes.Given impacts of these parameters,we provide guiding advice in designing switch structure and choosing materials to realize low pull-in voltage switches.Furthermore,we justify the reason why choose graphene as material for movable electrode.In order to find ways to fabricate suspended graphene,most techniques available so far are perused and analyzed.We compare these techniques and point out their defectsand then propose an improved graphene transfer technique and a graphene MEMS switch fabrication procedure.In order to find out feasibility of the improved fabrication procedure,corresponding experiments were designed and conducted.Impacts of baking on solubility of PVA and impacts of introducing PVA on EBL exposure of PMMA in PVA-PMMA double-layered membranes are studied respectively.It is shown that there is no disadvantaged impacts of setting baking temperature according to PMMA on solubility of PVA in PVA-PMMA double-layered membranes and that due to introducing of PVA EBL exposure dose needs to be increased accordingly.Switch samples are fabricated using the high precision transfer technique and characterized via SEM.It is observed that graphene is raised above horizontal plane naturally hence a suspended graphene structure is realized.Preliminary testing is conducted on fabricated switch samples.Testing shows that relatively low pull-in voltages can be realized by using graphene as movable electrode material,graphene electrode features a low failure tendency,and failures are usually observed in Au electrodes.