Microfabrication of sealable microcell array with ultrathin metal-graphene membrane

Abstract

A significant challenge in quasi-two dimensional (2D) materials applications is the fabrication of large, suspended layers. This issue is particularly critical when the fabrication of closed cells is required, for example in in-operando x-ray photoemission spectroscopy (XPS) or transmission electron microscopy (TEM), or the design of Golay cell-like detectors. In the quasi-totality of working protocols, the 2D layer transfer is performed in a liquid environment, and the large surface tension forces that are developed during the drying steps often result in the layer damage. This effect becomes dramatic when the fabrication of sealed cells is required. Here we propose an alternative route that involves the sealing in a two-step process, with, first, the fabrication of a large and suspended membrane and then a sealing step performed with the help of a microfabricated self-aligned sealing cork. As a 2D suspended membrane, we choose an ultrathin membrane of single-layer Graphene coupled with a 7.5 nm thick film of evaporated titanium which was transferred over a large array of micrometric holes fabricated on a 30 μm thick silicon membrane. As a cork, we used a silicone structure obtained by pouring liquid silicone in a microfabricated silicon well. The throughput of the whole fabrication process was assessed either by electronic or optical microscopy, to obtain the total yield of integer cells, and by generating a pressure difference within each cell to test the sealing efficiency. A fabrication and sealing yield larger than 95% on arrays as large as 10 mm2 were demonstrated.

Keywords

• Microfabrication
• Ultrathin films
• Graphene
• MEMS
• Mechanical sensor
• MGNC