Wafer counter-bonding for integrating cte-mismatched substrates and its application to MEMS tuneable metamaterials

This paper presents symmetrical counter-bonding as a method for integrating multiple substrates of noncompatible thermo-mechanical properties. This technique is successfully applied to fabricate MEMS tuneable high-impedance surfaces combining four substrates of two otherwise fabrication-incompatible materials (silicon and AF45 glass) on a wafer-level. A large-scale high-impedance surface with 200 x 52 array elements with a pitch of 350 mum and a total size of 70 x 18 mm² has been fabricated and the microwave properties of the devices have successfully been characterized at 70-114 GHz. Furthermore, micron-sized surface waviness in the glass substrates, induced by the thermal cycling under mechanical stress in the bonding process, has been investigated during temperature cycling.