Method and apparatus for controlling the throat height of batch fabricated thin film magnetic transducers

In a process for lapping batch produced transducer elements to a final throat height, a method for accurately determining the position of a lapping plane with respect to a desired throat height comprising:

• depositing on each side of a substrate an electrical lapping guide means, each of said guide means having an electrical resistance proportional to a change in lapping plane position;
• forming adjacent each of said electrical lapping guide means a series circuit made from a plurality of switching means, each switching means of a plurality having a distinct switching plane which changes state when said lapping plane is coincident therewith, producing a stepwise change in resistance thereof, each series circuit producing during lapping of said transducer elements discrete resistance changes corresponding to a change in state of one of said switching element means;
• measuring the resistance of each lapping guide means and each corresponding series circuit during lapping of said transducer elements;
• and,
• determining from a plurality of stepwise changes in resistance of each series circuit and measured guide means resistance levels the position of the lapping plane with respect to each side of said substrate.

In a process for batch fabricating thin film transducer elements, wherein said transducer element pole tips are lapped to a final throat height, a method for measuring a final throat height during lapping of said transducer elements, comprising:

• forming a plurality of switching junctions on a substrate bearing said transducer elements, each of said switching junctions having a switching plane a known distance away from a desired throat height of said pole tips;
• forming shunt resistance elements across each of said switching junctions;
• forming a series circuit including said switching junctions;
• forming an electrical lapping resistance on said substrate which provides a resistance proportional to the position of said lapped pole tips;
• measuring during lapping the resistance of said series circuit and said lapping resistance;
• deriving a resistance versus lapping plane position characteristic from said measured lapping resistance and each detected step change in said series circuit resistance measurements;
• and
• measuring subsequent lapping plane positions by measuring said resistance.

In a process for batch fabricating thin film magnetic transducers, said transducers formed in a row on a substrate and each having pole tip regions, a method for lapping said pole tip regions to a final throat height comprising:

• depositing first and second electrical lapping guide structures on each end of the substrate, said lapping guides including a serial connection of switching junctions, each switching junction having a switching plane a known distance away from a final pole tip plane and terminated with a parallel resistance;
• lapping said substrate along an edge parallel to said pole tip regions;
• applying first and second forces to each of said ends of said substrate in a direction perpendicular to said substrate edge, said forces controlling the lapping rate at each end of said substrate;
• monitoring the state of each switching junction by measuring the resistance of series connections of switching junctions;
• and,
• establishing a force differential between said first and second forces when a switching junction of one of said electrical lapping guide switching junctions changes state, said force differential being in a direction to maintain said substrate edge level.

In apparatus for batch fabricating thin film transducers, said apparatus comprising an electrical lapping guide for measuring the position of a lapped edge of a substrate supporting said thin film transducers, said apparatus comprising:

• a plurality of switching junctions formed on said substrate, in known spaced relation to said thin film transducers, each of said switching junctions having a distinct switching plane parallel to and a known distance away from a desired position for said lapped edge;
• a shunt resistance formed in parallel with each of said switching junctions and spaced apart from the lapped edge to avoid severing by lapping;
• an electrical circuit comprising each of said switching junctions connected in a series circuit, said electrical circuit having a first and a second terminal;
• and
• a resistor element having two terminals formed on said substrate adjacent to said plurality of switching junctions, said resistor element having a resistance which changes with lapping of said substrate,
• whereby, upon connection of means for measuring resistance across said first and second terminals, stepwise changes in said series circuit resistance can be detected during lapping of said substrate, each of said changes indicating a change of state of one of said switching junctions thereby identifying the position of said lapped edge to be coincident with said switching plane of said switching junction which changes state, and whereby, upon connection of means for measuring resistance across said two terminals, a lapping edge position versus resistance characteristic can be determined for said resistor element each time a switching junction changes state, whereby said resistor element is recalibrated each time a switching junction changes state.