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Method of Optimizing the Anneal time for PtMn Type Antiferromagnets

IP.com Disclosure Number: IPCOM000015559D
Original Publication Date: 2002-May-02
Included in the Prior Art Database: 2003-Jun-20
Document File: 2 page(s) / 80K

Publishing Venue

IBM

Abstract

Disclosed is a method of optimizing the anneal time for setting PtMn type antiferromagnets (AF’s). This can be applied to giant magnetoresitive (GMR) and tunneling magnetoresitive (TMR) sensors. When deposited at room temperature, PtMn and NiMn are chemically disordered. In this state, they are paramagnetic, and offer no exchange bias. Upon anneal at temperatures >240ºC for times ranging from 1-20 hours, chemical and magnetic order set in and exchange anisotropy is observed. The anneal time required to induce the phase transition (from disordered to the L10 phase) is possibly the longest step in processing a wafer. This ties up costly equipment and slows throughput. In addition, the DR/R value for spin valves can suffer for prolonged anneals at temperatures >250ºC. Thus, minimizing this anneal step would be very advantageous to the production of spin valve and tunnel valve sensors. It has been found that the resistivity of the AF layer increases significantly as magnetic order sets in. The method disclosed here takes advantage of this to detect the endpoint of the anneal. The Figure below shows how resistance (R, normalized to the start of the anneal) and the exchange field (Hex) vary with time (t) for a series of spin valves annealed at 265ºC. R(t) tacks Hex(t) closely. The resistance changes are significant (8%), and can be easily detected. Thus one could monitor R(t) and detect the endpoint of the anneal. When deposited at room temperature, PtMn and NiMn are chemically disordered. In this state, they are paramagnetic, and offer no exchange bias. Upon anneal at temperatures >240ºC for times ranging from 1-20 hours, chemical and magnetic order set in and exchange anisotropy is observed. The anneal time required to induce the phase transition (from disordered to the L10 phase) is possibly the longest step in processing a wafer. This ties up costly equipment and slows throughput. In addition, the DR/R value for spin valves can suffer for prolonged anneals at temperatures >250ºC. Thus, minimizing this anneal step would be very advantageous to the production of spin valve and tunnel valve sensors. It has been found that the resistivity of the AF layer increases significantly as magnetic order sets in. The method disclosed here takes advantage of this to detect the endpoint of the anneal. The Figure below shows how resistance (R, normalized to the start of the anneal) and the exchange field (Hex) vary with time (t) for a series of spin valves annealed at 265ºC. R(t) tacks Hex(t) closely. The resistance changes are significant (8%), and can be easily detected. Thus one could monitor R(t) and detect the endpoint of the anneal.

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Method of Optimizing the Anneal time for PtMn Type Antiferromagnets

Disclosed is a method of optimizing the anneal time for setting PtMn type antiferromagnets (AF's). This can be applied to giant magnetoresitive (GMR) and tunneling magnetoresitive (TMR) sensors.

When deposited at room temperature, PtMn and NiMn are chemically disordered. In this state, they are paramagnetic, and offer no exchange bias. Upon anneal at temperatures >240ºC for times ranging from 1-20 hours, chemical and magnetic order set in and exchange anisotropy is observed. The anneal time required to induce the phase transition (from disordered to the L10 phase) is possibly the longest step in processing a wafer. This ties up costly equipment and slows throughput. In addition, the DR/R value for spin valves can suffer for prolonged anneals at temperatures >250ºC. Thus, minimizing this anneal step would be very advantageous to the production of spin valve and tunnel valve sensors.

It has been found that the resistivity of the AF layer increases significantly as magnetic order sets in. The method disclosed here takes advantage of this to detect the endpoint of the anneal. The Figure below shows how resistance (R, normalized to the start of the anneal) and the exchange field (Hex) vary with time (t) for a series of spin valves annealed at 265ºC. R(t) tacks Hex(t) closely. The resistance changes are significant (8%), and can be easily detected. Thus one could monitor R(t) and detect the endpoint of the anneal. When deposited at room temperature, PtMn and NiMn are chemically disordered. In this state, they are paramagnetic, and offer no exchange bias....