Effect of seed layer stress on the fabrication of monolithic MEMS microstructure

This paper reported the effect of seed layer stress on the fabrication of monolithic polymer-metal MEMS microstructure and what is a better material for the seed layer. The monolithic microstructure is gaining more and more attentions in MEMS application, especially in three-dimensional microstructure and inkjet printhead. The polymer–metal MEMS microstructure can be fabricated by combining the lithography and electroforming technologies. It is an integrated technology by batch process at low cost. The metal seed layer with large stress will lead to cracks and failure during the process integration. Several metal materials and thicknesses were studied to find a better candidate as the seed layer for the monolithic MEMS microstructure. The relationship between the monolithic MEMS structure and seed layer selection is also discussed. The lower residual stress of seed layer will result in a better surface condition for the followed integration process. The pure Ti metal and two-layer Ti/Au composite are the better seed layer materials in this study for the followed electroforming process of the monolithic polymer-metal MEMS microstructure.