Effects of surface roughness on electromagnetic characteristics of capacitive switches

Abstract

This paper studies the effect of surface roughness on up-state and down-state capacitances of microelectromechanical systems (MEMS) capacitive switches. When the root-mean-square (RMS) roughness is 10 nm, the up-state capacitance is approximately 9% higher than the theoretical value. When the metal bridge is driven down, the normalized contact area between the metal bridge and the surface of the dielectric layer is less than 1% if the RMS roughness is larger than 2 nm. Therefore, the down-state capacitance is actually determined by the non-contact part of the metal bridge. The normalized isolation is only 62% for RMS roughness of 10 nm when the hold-down voltage is 30 V. The analysis also shows that the down-state capacitance and the isolation increase with the hold-down voltage. The normalized isolation increases from 58% to 65% when the hold-down voltage increases from 10 V to 60 V for RMS roughness of 10 nm.

Influence of adhesive rough surface contact on microswitches

“…22. The critical value of separation z 0 in Maugis theory equals 0.97r 0 , where r 0 is the equilibrium separation of atoms for the Lennard-Jones potential.…”

“…The material considered for the DC pads is aluminum, and a thin layer of SiN was deposited above the lower DC pad. 22 The expected pull-in voltages V pull in is successively set up to be 20, 40, 60, and 80 V.…”

“…Silicon nitride has a Young's modulus E ranging from 220 to 295 GPa and a Poisson's ratio around 0.26. 22,39,40 The mechanical properties for other materials can be found in Refs. 29 and 39.…”

“…In MEMS, the surface properties do not only depend on the material of the surface but they also depend on the microfabrication processes and treatment conditions. Using AFM, Yu and Liu measured the surfaces of microcapacitive switches, 22 for a 0.15 m SiN layer deposited on Ti, Cr, Al, and Cu thin films respectively, the rms roughness was found to range from 2.19 to 14.81 nm, asperities radius R from 31.11 to 63.22 nm, and the asperities' density D from 158 to 41 m −2 . rms roughnesses of 0.6 and 0.8 nm were reported for treated and untreated silicon nitride layers respectively in Ref.…”

Μελέτη Και Βελτιστοποίηση Των Ηλεκτρικών Ιδιοτήτων Λεπτών Μονωτικών Υμενίων Που Χρησιμοποιούνται Σε Μικρο-Ηλεκτρο-Μηχανικά Συστήματα (MEMS)

“…Η τραχύτητα αυτή σχετίζεται με τις μεθόδους εναπόθεσης της γέφυρας και γραμμής μεταφοράς (CPW) πάνω από την οποία εναποτίθεται το υμένιο και στην καλύτερη περίπτωση είναι μερικές δεκάδες νανόμετρα. Λόγω της σοβαρότητας του προβλήματος αυτού αρκετές θεωρητικές μελέτες προσομοίωσης της τραχύτητας των επιφανειών έχουν γίνει [12], [13] οι οποίες έχουν δείξει ότι η αύξηση της τραχύτητας συνεπάγεται μείωση της τιμής της χωρητικότητας Cdown. Η τιμή της χωρητικότητας Cup αυξάνεται αμελητέα λόγω της μεγάλης απόστασης των μεταλλικών οπλισμών στην κατάσταση OFF σε σχέση με την τραχύτητα που εμφανίζεται.…”