Silicon microphone with impact proof structure
Improved impact proof capability of a silicon microphone sensing element is achieved with a stopper element that limits the maximum vibration of moveable parts. The stopper has a lower anchor portion and upper finger portion that is elevated a certain distance above the diaphragm and overhangs the outer edges of the perforated plates. The stopper is formed on a stack consisting of a lower substrate, a middle dielectric layer, and an upper membrane layer. There is a back hole in the substrate and an air gap in the dielectric layer to allow sound to impinge on the diaphragm. The number of fingers and composition of the stopper is variable. Optionally, the stopper has a center support design and is formed on a center anchor within an opening in the diaphragm. An upper finger region overhangs the diaphragm near the center opening and thereby prevents breakage due to large vibrations.
1. A microphone sensing element without a dedicated backplate component, comprising:
(a) a substrate having a front side and a back side with one or a plurality of back holes formed therein;
(b) a dielectric spacer layer formed on the front side of the substrate;
(c) a diaphragm that is aligned above said one or plurality of back holes and is made of a membrane layer formed on the dielectric spacer;
(d) a plurality of perforated plates with a plurality of holes therein which adjoin the diaphragm, said perforated plates are suspended over the substrate with an air gap therebetween and are made of said membrane layer;
(e) a plurality of mechanical springs made of said membrane layer and attached to said diaphragm wherein each mechanical spring has two ends in which one end is attached to the diaphragm and a second end is connected to a pad that is formed on the dielectric layer and anchored to the substrate; and
(f) a plurality of stopper structures comprised of a lower anchor portion and an upper finger portion having one or a plurality of fingers that overhang the perforated plates and restrict an upward motion of the diaphragm and perforated plates away from the substrate during a vibration.
2. The microphone sensing element of claim 1 wherein said membrane layer is comprised of silicon or doped polysilicon having a low resistivity.
3. The microphone sensing element of claim 1 wherein said lower anchor portion is formed on the membrane layer.
4. The microphone sensing element of claim 3 wherein the stopper structures are made of a plated metal or another material that has good impact resistance and has good adhesion to the membrane layer.
5. The microphone sensing element of claim 1 wherein said plurality of fingers are separated from the underlying perforated plates by a certain distance.
6. The microphone sensing element of claim 1 wherein said upper finger portion overlaps a perforated plate to an extent that restricts an upward motion of the diaphragm and perforated plate in a direction away from the substrate.