MEMS graphene strain sensor

Abstract

<p>Graphene is a two dimensional honeycomb structure of sp^2 hybridized carbon atoms that has possibilities in many applications due to its excellent mechanical and electrical properties. One application for Graphene is in the field of sensors. Graphene’s electronic properties do not degrade when it undergoes mechanical strain which is advantageous for strain sensors. In this thesis, certain properties, such as the piezo-resistivity and flexibility, of graphene will be explored to show how they can be utilized to make a strain sensing device. Our original fabrication process of patterning graphene and the transfer process of graphene onto a flexible substrate will be discussed. The development of a stretchable and flexible graphene based rosette strain sensor will also be detailed.</p> <p>Developing a novel, reliable patterning process for the graphene is the first step to manufacture a stretchable graphene based sensor. The graphene was patterned using a photolithography and etching process that was developed by our research team, then it was transferred to a flexible polymer substrate with the use of a combination of soft lithography and wet etching of the Ni foil with ferric chloride solution. Graphene patterning is an essential step in fabricating reliable and sensitive sensors. With this process, graphene can be consistently patterned into different shapes and sizes. To utilize the graphene as the sensing material it also needs to be transferred onto a flexible substrate. The innovative transfer process developed by our research team consistently adheres graphene to a flexible PDMS substrate while removing the original nickel substrate. In the end, the graphene was transferred from the metal substrate to the desired flexible substrate. This process was repeated multiple times to create a stack and multilayer device.</p> <p>While many graphene-based strain sensors have been developed, they are uni-directional and can only measure the strain applied on the sensor in a principle direction. This issue was solved in this thesis by arranging the graphene sensors in a rosette pattern which enabled for multi-directional strain detection. The strain sensor was further improved by stacking the graphene sensors in a rosette pattern; which was possible by leveraging the advantages of soft lithography and bonding processes and the flexibility of graphene. Our final device was a stacked rosette graphene strain sensor that was able to successfully measure strain in multiple directions and magnitudes simultaneously.</p>