Patent ID: 7764000

Claim:
A motor comprising: a rotor hub including a shaft rotatable about a central axis, a substantially circular plate portion extending from an upper portion of the shaft outward in a radial direction perpendicular to or substantially perpendicular to the central axis, and a cylindrical portion which is hollow and substantially cylindrical and projects from the substantially circular plate portion downward in an axial direction parallel to or substantially parallel to the central axis; a sleeve portion arranged to receive the shaft; and a thrust dynamic pressure bearing portion; wherein a lower surface of the substantially circular plate portion includes an outer portion continuous with an inner peripheral surface of the cylindrical portion, an inner portion continuous with an outer peripheral surface of the shaft, and a stepped portion connecting the outer portion and the inner portion to each other, the inner portion and the outer portion being substantially annular, the outer portion of the substantially circular plate faces the sleeve portion in the axial direction, the thrust dynamic pressure bearing portion includes a hub thrust portion, a sleeve thrust portion which is a portion of the sleeve portion and axially opposes the hub thrust portion, and a working fluid arranged between the hub thrust portion and the sleeve thrust portion, and the stepped portion is arranged to step up such that an inner gap provided between the inner portion and the sleeve portion is smaller than an outer gap provided between the outer portion and the sleeve portion.