The development of selective strain coupling structures for a novel MEMS resonant pressure sensor
This thesis proposes a novel form of MEMS (micro electro mechanical system) resonant
pressure sensor. The sensor incorporates a MEMS silicon resonator that is coupled to a macro
scale metallic diaphragm. The combination of a large metallic diaphragm with a micro
engineered MEMS resonator required an innovative selective strain coupling structure to be
designed. Without the proposed coupling structure, unwanted packaging or thermally induced
strain would severely degrade sensor performance, resulting in resonator misalignment, or
unwanted strain loading.
The feasibility of the proposed device is investigated though analysis and characterisation
work performed on a prototype resonator, and a prototype selective coupling structure. These
devices allowed fabrication processes to be developed, and their predicted performance to be
verified. The prototype resonator demonstrated high quality factors of 28,000 - 30,000 in a
vacuum, and resonant frequencies within 10% of modelled predictions. The selective
coupling structure was shown to provide a reduction of resonator misalignment of 100: 1,
while providing selective strain coupling of 900:1. Following this a fabrication route for
producing the fully integrated resonator and selectively coupling structure was developed.
This device was electrically tested to determine its resonant characteristics, and quality
factors greater that 40,000 were demonstrated.