MEMS accelerometer with vertical stops

A microelectromechanical system (MEMS) device comprising:

• a substrate;
• a set of at least four spring assemblies;
• and
• a proof mass suspended above the substrate, coupled to the substrate by the set of spring assemblies, and configured to move along a vertical direction toward and away from the substrate when the proof mass experiences an acceleration force along the vertical direction;
• wherein each spring assembly belonging to the set of spring assemblies comprises:
• an anchor disposed on the substrate;
• a beam having a fixed end and free end, wherein the fixed end is coupled to the substrate and the free end is free to translate vertically with respect to the proof mass and free to translate vertically with respect to the substrate;
• a first linkage coupling the fixed end of the beam to the anchor;
• and
• a second linkage coupling the beam to the proof mass at a location between the fixed end and the free end of the beam;
• wherein the anchors of each spring assembly are disposed symmetrically along a circular path centered around a center of the proof mass;
• wherein, when the proof mass is at rest, the spring assemblies are disposed within openings in the proof mass;
• wherein the beam of each spring assembly extends from the anchor of that spring assembly toward a corresponding corner of the proof mass and a long axis of the beam of each spring assembly is oriented toward the center of the proof mass wherein each spring assembly is not in contact with the corresponding corner;
• and
• wherein the spring assemblies and the proof mass are jointly configured such that, when a vertical displacement of the proof mass toward the substrate reaches a predefined value, the free end of each spring assembly contacts the substrate and prevents the proof mass from contacting the substrate;
• and
• wherein each anchor of each spring assembly disposed along the circular path are further disposed on the circular path closest to a corner of the proof mass.

A method comprising:

• forming, on a substrate, a set of spring assemblies and proof mass;
• wherein the proof mass is suspended above the substrate, coupled to the substrate by the set of spring assemblies, and configured to move along a vertical direction toward and away from the substrate when the proof mass experiences an acceleration force along the vertical direction;
• wherein forming each spring assembly belonging to the set of spring assemblies comprises:
• forming an anchor disposed on the substrate;
• forming a beam having a fixed end and free end, wherein the fixed end is coupled to the substrate and the free end is free to translate vertically with respect to the proof mass and free to translate vertically with respect to the substrate;
• forming a first linkage coupling the fixed end of the beam to the anchor;
• and
• forming a second linkage coupling the beam to the proof mass at a location between the fixed end and the free end of the beam;
• wherein the anchors of each spring assembly are disposed symmetrically along a circular path centered around a center of the proof mass;
• wherein, when the proof mass is at rest, the spring assemblies are disposed within openings in the proof mass;
• wherein the beam of each spring assembly extends from the anchor of that spring assembly toward a corresponding corner of the proof mass and a long axis of the beam of each spring assembly is oriented toward the center of the proof mass;
• wherein each spring assembly is not in contact with the corresponding corner;
• wherein the spring assemblies and the proof mass are jointly configured such that, when a vertical displacement of the proof mass toward the substrate reaches a predefined value, the free end of each spring assembly contacts the substrate and prevents the proof mass from contacting the substrate;
• and
• wherein each anchors of each spring assembly disposed along the circular path are further disposed on the circular path closest to a corner of the proof mass.