Wafer level test structure for detecting multiple domains and magnetic instability in a permanent magnet stabilized MR head

In a wafer having a magnetoresistive material from which plural permanent magnet stabilized magnetoresistive transducers are to be constructed, the improvement comprising:

• a plurality of wafer level test structures for indicating an unstable single magnetic domain state or multiple magnetic domain state in the magnetoresistive material, each test structure comprising:
• a first magnetoresistive sensor formed in the magnetoresistive material on the wafer and arranged to be held in a single magnetic domain state by shape anisotropy;
• and
• a second magnetoresistive sensor formed in the magnetoresistive material on the wafer and arranged to be held in a single magnetic domain state by permanent magnet;
• means for applying a variable magnetic field to the first and second magnetoresistive sensors of at least a selected test structure;
• and
• a circuit disposed and arranged to be connected to the first and second magnetoresistive sensors of at least one selected test structure to detect a difference between a resistance of the first magnetoresistive sensor and a resistance of the second magnetoresistive sensor of the selected test structure and to detect a change in the difference between the resistances of the first and second magnetoresistive sensors of the selected test structure upon a change in the applied magnetic field.

A process for testing magnetic domains in a magnetoresistive material on a wafer, the process comprising:

• providing a test structure on the wafer having a first magnetoresistive sensor designed to be held in a single magnetic domain state by shape anisotropy, a second magnetoresistive sensor and a permanent magnet designed to stabilize the second magnetoresistive sensor in a single magnetic domain state, the first and second magnetoresistive sensors being formed in the magnetoresistive material;
• applying a magnetic field to the first and second magnetoresistive sensors;
• changing the applied magnetic field;
• and
• detecting a change in a difference between a resistance of the first magnetoresistive sensor and a resistance of the second magnetoresistive sensor upon a change in the applied magnetic field.

A process for indicating unstable single magnetic domain states or multiple magnetic domain states in a magnetoresistive material on a wafer, comprising:

• forming a test structure on the wafer, the test structure comprising a first magnetoresistive sensor arranged to a single magnetic domain state by shape anisotropy and a second magnetoresistive sensor arranged to a single magnetic domain state by permanent magnet, the first and second magnetoresistive sensors being formed in the magnetoresistive material;
• applying a magnetic field to the first and second magnetoresistive sensors so that the sensors each assume single magnetic domain states;
• changing the applied magnetic field;
• and
• detecting change in a difference between resistances of the first and second magnetoresistive sensors upon the change in the applied magnetic field.