Analysis of device design and material structure on MEMS variable capacitor

Abstract

Micro-electromechanical system (MEMS) has been one of the most promising technologies for the 21st century. With this technology, MEMS components are not only depending on the electrical properties but also other physics properties. MEMS components can generate the effect as good as the conventional components despite the size of micrometres. In this research, the tuneable capacitor has been designed based on this technology. Nowadays, to improve capacitance range of tuneable capacitor, most of the researches focus on enhancing the gap tuning structure. However, with the moving parts in the structure, pull-in effect has become a major concern. To solve this problem, solution of applying temperature dependent dielectric materials into capacitors is suggested. Different dielectric materials are applied into the first phase simulation carried out by the COMSOL Multiphysics software to find out the best dielectric material based on their capacitance range. Then, the capacitor is put into second phase simulation to investigate the effect of different dimension variables. From the simulation results, Strontium Titanate has the largest tuning range 67.48% among the dielectric material candidates. For the dimension variables, the capacitance is inversely proportional to the thickness of dielectric layer decreasing from 49.479 pF to 10.023 pF in the range of 0.1 nm to 0.5 nm but directly proportional to the length of trench opening increasing from 11.236 pF to 21.969 pF in the range of 1 nm to 5 nm as well as depth of the trench increasing from 6.8256 pF to 16.605 pF in the range of 0 nm to 10 nm. In the end, a proposed tuneable capacitor with Strontium Titanate as dielectric layer, 0.3 μm of dielectric layer thickness, 3 μm of trench opening and 10 μm of trench depth is designed and put to the comparison with previous reported capacitors. The maximum capacitance of proposed capacitor is the second highest 16.605 pF but its tuning range 67.48% is the lowest in the comparison. Although the tuning range of proposed capacitor is not the highest among these capacitors, it does show a new idea to this topic.