Spindle motor and hard disk drive including the same

A spindle motor comprising:

• a lower thrust member fixed to a base member;
• a shaft fixed to the lower thrust member;
• a sleeve disposed above the lower thrust member and installed so as to be rotatable with respect to the shaft;
• and
• a rotor hub coupled to the sleeve to be rotated together therewith,
• wherein the lower thrust member includes a fitting protrusion protruding upwardly in the axial direction and fitted into a fixing groove formed in a lower end of the shaft so as to be depressed upwardly in the axial direction, a thrust bearing surface forming a thrust bearing between the thrust bearing surface and a lower surface of the sleeve, and an extension part protruding from an outer edge of the lower thrust member in a radial direction upwardly in the axial direction to form a liquid-vapor interface between the extension part and an outer surface of the sleeve while enclosing the sleeve, and
• the thrust bearing surface has inner and outer concave parts depressed in one of inner and outer diameter directions thereof, respectively.