 the cavity satisfies the following expression where the micro-gap is g, a width of the movable interdigitated electrode is W0, a width of the fixed interdigitated electrode is W0, and a height of the movable interdigitated electrode and fixed interdigitated electrode is h, namely:   D  ≤            h      g        ⁢                  (                  g          +          W0          +          W0                )            .       