TMR device with low magnetostriction free layer

Abstract

A high performance TMR sensor is fabricated by employing a free layer comprised of CoB_X with a λ between −5×10⁻⁶ and 0 on a MgO_X tunnel barrier. Optionally, a FeCo/CoB_X free layer configuration may be used where x is about 1 to 30 atomic %. Trilayer configurations represented by FeCo/CoFeB/CoB_X, FeCo/CoB_X/CoFeB, FeCo_Y/CoFe_W/CoB_X, or FeCo_Y/FeB/CoB_X may also be employed. Alternatively, CoNiFeB or CoNiFeBM formed by co-sputtering CoB with CoNiFe or CoNiFeM, respectively, where M is V, Ti, Zr, Nb, Hf, Ta, or Mo may be substituted for CoBx in the aforementioned embodiments. A 15 to 30% in improvement in TMR ratio over a conventional CoFe/NiFe free layer is achieved while maintaining a low Hc and RA<3 ohm-um². In bilayer or trilayer embodiments, λ between −5×10⁻⁶ and 5×10⁻⁶ is achieved by combining CoBx (−λ) and one or more layers having a positive λ.

Description

RELATED PATENT APPLICATION[0001]This application is related to the following: Docket # HT05-015, Ser. No. 11 / 180,808, filing date Jul. 13, 2005; assigned to a common assignee, and which is herein incorporated by reference in its entirety.FIELD OF THE INVENTION[0002]The invention relates to a high performance tunneling magnetoresistive (TMR) sensor in a read head and a method for making the same, and in particular, to a composite free layer comprised of CoB that reduces magnetostriction while achieving acceptable RA (resistance×area) and dR / R values.BACKGROUND OF THE INVENTION[0003]A TMR sensor otherwise known as a magnetic tunneling junction (MTJ) is a key component (memory element) in magnetic devices such as Magnetic Random Access Memory (MRAM) and a magnetic read head. A TMR sensor typically has a stack of layers with a configuration in which two ferromagnetic layers are separated by a thin non-magnetic insulator layer. The sensor stack in a so-called bottom spin valve configurat...

AI Technical Summary

Benefits of technology

[0012]One objective of the present invention is to provide a TMR sensor with a free layer composition

Problems solved by technology

Unfortunately, the magnetostriction (λ) of a CoFeB free layer is considerably greater than the maximum acceptable value of about 5×10−6 for high density memory applications.

However,

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