Capacitance type pickup stylus and method of producing same

Claim 1

A method of producing a pickup stylus of the capacitance type having a shaped tip for tracking and a flat side face with an electrode film coated thereon for the pickup of information signals, inscribed in a recording medium as geometric variations of a track, as variations in the capacitance between the recording medium and the stylus upon relative movement on the track, the method comprising the steps of: growing by a modified edge defined film fed growth technique a single crystal of a hard mineral of a hexagonal system containing as an essential component aluminum oxide in the form of an elongated body having a substantially constant cross section; said modified edge defined film fed growth technique including the steps of (a) spreading a melt of said hard mineral as a film over a flat and circular surface through a capillary, the circular surface having a cross-sectional diameter no greater than about 0.3 mm and determining, but differing from the cross-sectional shape of the grown crystal, and (b) continuously growing said elongated body from said melt by vertically pulling up said film through the surface with a seed crystal of said hard mineral, said seed crystal being oriented such that an a-axis of said seed crystal coincides with the direction of the pullup of said seed crystal, whereby the longitudinal axis of said elongated body coincides with said a-axis of said single crystal and said elongated body has a pair of inherently flat and smooth side faces both parallel to said longitudinal axis and normal to the c-axis of said single crystal, so that said cross section is defined by a pair of parallel straight lines with a spacing less than the diameter of said circular surface and a pair of outwardly convex arcs generally conforming to the edge of said circular surface; on at least one of said flat and smooth side faces, forming a thin electrode film in intimate contact with the side face; and shaping an end portion of said elongate body with said electrode film thereon such that the shaped end portion serves as the tip of the stylus.

Claim 2

A method of producing a pickup stylus of the capacitance type having a shaped tip for tracking and a flat side face with an electrode film coated thereon for the pickup of information signals, inscribed in a recording medium as geometric variations of a track, as variations in the capacitance between the recording medium and the stylus upon relative movement on the track, the method comprising the steps of: growing by a modified edge defined film fed growth technique a single crystal of a hard mineral of a hexagonal system containing as an essential component aluminum oxide in the form of an elongated body having a substantially constant cross section; said modified edge defined film fed growth technique including the steps of (a) spreading a melt of said hard mineral as a film over a flat and circular surface through a capillary, the circular surface having a cross-sectional diameter no greater than about 0.3 mm and determining, but differing from the cross-sectional shape of the grown crystal, and (b) continuously growing said elongated body from said melt by vertically pulling up said film through the surface with a seed crystal of said hard mineral, said seed crystal being oriented such that an a-axis of said seed crystal coincides with the direction of the pullup of said seed crystal, whereby the longitudinal axis of said elongated body coincides with said a-axis of said single crystal and said elongated body has a pair of inherently flat and smooth side faces both parallel to said longitudinal axis and normal to the c-axis of said single crystal, so that said cross section is defined by a pair of parallel straight lines with a spacing less than the diameter of said circular surface and a pair of outwardly convex arcs generally conforming to the edge of said circular surface; on at least one of said flat and smooth side faces, forming a thin electrode film in intimate contact with the side face; and shaping an end portion of said elongate body with said electrode film thereon such that the shaped end portion serves as the tip of the stylus.