Dielectric spacer for enhanced squeeze-film damping of movable members of MEMS devices
In one embodiment, a capacitive micro electro-mechanical systems (MEMS) device includes a dielectric spacer between a bottom electrode and a movable member. The movable member may serve as a top electrode. A gap separates the top electrode from the dielectric spacer. The movable member may be actuated to deflect towards the bottom electrode by electrostatic force. The dielectric spacer reduces the height of the gap that would otherwise be formed between a top surface of the bottom electrode and a bottom surface of the movable member, thereby improving squeeze-film damping. The movable member may be a ribbon of a ribbon-type diffractive spatial light modulator, for example.
1. A capacitive micro electro-mechanical systems (MEMS) device comprising:
a bottom electrode formed over a substrate;
a movable member serving as a top electrode, the movable member being configured to deflect towards the bottom electrode by electrostatic force to modulate incident light, the movable member comprising a reflective material formed over a resilient material; and
a dielectric spacer formed over the bottom electrode, the dielectric spacer having a thickness at least half a distance between a bottom surface of the movable member and a top surface of the bottom electrode, the dielectric spacer being separated from the bottom surface of the movable member by a gap;
wherein the dielectric spacer has a thickness of 2G/3 scaled according to a dielectric constant of the dielectric spacer, where G is the distance between the bottom surface of the movable member and the top surface of the bottom electrode.
2. The device of claim 1 wherein the device comprises a ribbon-type diffractive spatial light modulator.
3. The device of claim 1 wherein the dielectric spacer comprises silicon dioxide.
4. The device of claim 1 wherein the reflective material comprises aluminum and the resilient material comprises silicon nitride.
5. The device of claim 1 wherein the dielectric spacer comprises a stack of dielectric layers.
6. The device of claim 1 wherein the dielectric spacer is configured to serve as a reflective mirror.
7. The device of claim 1 further comprising:
a projection formed on the dielectric spacer and directly underneath the movable member.
8. The device of claim 1 further comprising:
a ridge formed on the dielectric spacer and running parallel with a long axis of the movable member and directly underneath the movable member.
9. The device of claim 1 further comprising:
a plurality of bumps formed on the dielectric spacer and directly underneath the movable member.