Abstract
In this work, SiNx/a-Si/SiNx caps on conductive coplanar waveguides (CPWs) are proposed for thin film encapsulation of radio-frequency microelectromechanical systems (RF MEMS), in view of the application of these devices in fifth generation (5G) and modern telecommunication systems. Simplification and cost reduction of the fabrication process were obtained, using two etching processes in the same barrel chamber to create a matrix of holes through the capping layer and to remove the sacrificial layer under the cap. Encapsulating layers with etch holes of different size and density were fabricated to evaluate the removal of the sacrificial layer as a function of the percentage of the cap perforated area. Barrel etching process parameters also varied. Finally, a full three-dimensional finite element method-based simulation model was developed to predict the impact of fabricated thin film encapsulating caps on RF performance of CPWs.
Highlights
Radio-frequency microelectromechanical systems (RF MEMS) technology is emerging as a key enabling solution to address the demanding requirements that upcoming fifth generation (5G)
To enable widespread implementation of RF MEMS, the package ideally should be low cost, require little additional space on the wafer, and be easy to incorporate in microwave integrated circuits
Mixed frequency plasma-enhanced chemical vapor deposition (PECVD) provides low stress silicon nitride layers that are stable if processed at high temperature [13]
Summary
Aluminum nitride, amorphous silicon, and silicon nitride are the most used [7,9,10,11,12] for thin encapsulating layers They satisfy some essential requirements to make the packaging process suitable for industrial production, these include: a good structural integrity and selectivity with respect to the sacrificial material during the chemical etching; an excellent insulation during device operation; and an optimized deposition rate in relation to the thickness to achieve. Mixed frequency plasma-enhanced chemical vapor deposition (PECVD) provides low stress silicon nitride layers that are stable if processed at high temperature [13] Another crucial issue of thin film encapsulation is that the etch times required to remove the sacrificial material can be excessively long, especially as the size of encapsulation becomes larger, limiting the manufacturability of the package. A full three-dimensional (3D) finite element method-based (FEM) simulation model was used to predict the RF performance of uncapped and capped CPWs
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