Study of Linear Coupling in NEMS

Cantilever beams are used as mass sensing device of chemical analyte by measuring the shift in frequency. However there resolution is linked to their size. As it become increasingly hard to produce smaller device an alternative is to use mode localisation caused by an absorption of a small mass on two identical beam shape coupled nano-resonator. Indeed the resolution of this system inversely proportional to coupling between the beam which make possible further improvement of the resolution by reducing the coupling strength. One of the principal limitation of this method is that it requires identical resonator which is very hard to achieve with conventional top down process. A solution would be to tune the eigenfrequency of one resonators by compressing one resonator using the piezoelectric effect. This project aim was set on the fabrication of coupled multilayered piezoelectric resonators. The fabrication process was optimized by investigating the best exposure energy to maximize the lithography resolution which was found to be 275 [mJ/cm2]. An analysis of the serifs design with four shapes (square, diamond, 4 point star and circle) for different serifs size showed non conclusive. We would advise to further analyse the shape of serif between 0.5 − 1 [μm]. In parallel to the design optimization process of the resonator, an exposure test was also conducted on nanopillars (radius from 200 [nm] to 500 [nm]), which found an optimal dose of 9 [mJ/cm2] and 15 [mJ/cm2] with a BARC layer. An etch test was also conducted in order to have the best aspect ratio while minimising the slope caused by the etching process. The 3 recipes used had a slope between 8 − 10◦. However the recipe that created the less scalloping also created silicon grass.