Patent Application
20240094314
A magnetic tunnel junction (MTJ) includes two ferromagnetic layers that are separated by a comparatively thin insulator layer, referred to as a tunnel barrier. The tunnel barrier layer is sufficiently thin to permit electrons to tunnel from one ferromagnetic layer to the other ferromagnetic layer when a bias voltage is applied between a pair of contact electrodes. In an MTJ, a tunneling current depends on the relative orientation of magnetizations of the two ferromagnetic layers, which can be changed by an applied magnetic field. This phenomenon is referred to as the tunneling magnetoresistance (TMR) effect. A sensing element including an MTJ (referred to as a TMR sensing element) may therefore enable a strength of an applied magnetic field to be measured.
In some implementations, a tunnel magnetoresistive (TMR) sensing element includes a free layer including: a first cobalt iron boron (CoFeB) layer; an interlayer over the first CoFeB layer; a second CoFeB layer over the interlayer; and a nickel iron (NiFe) layer over the second CoFeB layer.
In some implementations, a sensor includes a magnetoresistive (MR) sensing element including: a seed layer; a reference layer over the seed layer; a tunnel barrier layer over the reference layer; a free layer over the tunnel barrier layer, wherein the free layer includes: a first CoFeB layer, a second CoFeB layer, and an interlayer between the first CoFeB layer and the second CoFeB layer, and a NiFe layer over the second CoFeB layer; and a cap layer on the free layer.
In some implementations, a method includes forming a first CoFeB layer on a tunnel barrier layer; forming an interlayer on or over the first CoFeB layer; forming a second CoFeB layer on or over the interlayer; and forming a NiFe layer on or over the second CoFeB layer.
The following detailed description of example implementations refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements.
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Some implementations described herein provide an improved TMR sensing element having a free layer that includes multiple CoFeB layers. For example, a TMR sensing element may in some implementations have a free layer that includes a first CoFeB layer, an interlayer (e.g., a tantalum (Ta) interlayer) over the first CoFeB layer, a second CoFeB layer over the interlayer, and a NiFe layer over the second CoFeB layer. In some implementations, the inclusion of the second CoFeB layer in the free layer increases the TMR effect at an MgO tunnel barrier layer of the TMR sensing element, while also reducing magnetostriction of the TMR sensing element (e.g., as compared to the conventional TMR sensing element 100 described above). Additional details are provided below.
The seed layer 202 is a layer on which other layers of the TMR sensing element 200 may be formed. In some implementations, the seed layer 202 provides electrical contact with a bottom electrode (not shown) of the TMR sensing element 200. The seed layer 202 may comprise, for example, copper (Cu), Ta, or ruthenium (Ru). In some implementations, the seed layer 202 may have a thickness in a range from approximately 15 nanometers (nm) to approximately 50 nm.
The reference system 204 is a structure designed to have a fixed direction of magnetization. As shown, the reference system 204 may be a multilayer structure that includes the antiferromagnetic layer 206, the pinned layer 208, the interlayer 210, and the reference layer 212. The antiferromagnetic layer 206 may be, for example, an iridium manganese (IrMn) layer or a platinum manganese (PtMn) layer having a thickness in a range from approximately 5 nm to approximately 30 nm. The pinned layer 208 may be, for example, a CoFe layer having a thickness in a range from approximately 1 nm to approximately 4 nm. The interlayer 210 may be, for example, a Ru layer having a thickness in a range from approximately 0.7 nm to approximately 0.8 nm. The reference layer 212 may be, for example, a CoFeB layer having a thickness in a range from approximately 1 nm to approximately 3 nm. A magnetic moment orientation of the pinned layer 208 is constrained by an effective surface magnetic field, known as an exchange bias field, which arises from the interface with the antiferromagnetic layer 206. To increase stability of the reference system 204, the pinned layer 208 is antiferromagnetically coupled to the reference layer 212 via the interlayer 210, as indicated in
The tunnel barrier layer 214 is a layer designed to permit electrons to tunnel between the reference system 204 and the free layer 216 when a bias voltage is applied to electrodes of the TMR sensing element 200 (not shown) in order to provide the TMR effect. The tunnel barrier layer 214 may be, for example, an MgO layer having a thickness in a range from approximately 0.7 nm to approximately 1.5 nm.
The free layer 216 is a structure for which a direction of magnetization changes (e.g., rotates) in response to an external magnetic field applied at the TMR sensing element 200. As shown in
In some implementations, CoFeB is used in the free layer 216 to increase the TMR effect at the tunnel barrier layer 214. In some implementations, the first CoFeB 218 has a thickness in a range from approximately 1.0 nm to approximately 4.0 nm, such as in a range from approximately 1.5 nm to approximately 2.5 nm. In some implementations, the second CoFeB layer 222 has a thickness in a range from approximately 0.5 nm to approximately 4.0 nm, such as in a range from approximately 1 nm to approximately 2.5 nm.
In some implementations, NiFe is used in the free layer 216 to facilitate rotation of the direction of magnetization of the free layer 216 by reducing coercivity of the free layer 216 (e.g., due to NiFe being a magnetically softer material as compared to, for example, CoFe). In some implementations, the NiFe layer 224 has a thickness in a range from approximately 5 nm to approximately 20 nm.
In some implementations, the interlayer 220 facilitates interlayer exchange coupling of the first CoFeB 218 and the second CoFeB layer 222. In one example, the interlayer 220 may be an MgO layer having a thickness in a range from approximately 0.1 nm to 0.5 nm, such as in a range from approximately 0.1 nm to approximately 0.3 nm. In another example, the interlayer 220 may be a tantalum (Ta) layer having a thickness in a range from approximately 0.1 nm to approximately 0.5 nm, such as in a range from approximately 0.2 nm to approximately 0.3 nm. In another example, the interlayer 220 includes an MgO layer and a tantalum (Ta) layer, each having a thickness in a range from approximately 0.1 nm to approximately 0.5 nm, such as in a range from approximately 0.1 nm to approximately 0.3 nm.
In some implementations, the first CoFeB layer 218 and the second CoFeB layer 222 in the free layer 216 serve to increase the TMR effect at the tunnel barrier layer 214. For example, a TMR effect in a TMR sensing element 200 with a free layer including a pair of CoFeB layers, each with a thickness of 1.5 nm, is 20% (or more) higher than a TMR effect in a compared to a conventional TMR sensing element 100 with a free layer including a single CoFeB layer with a thickness of 1.5 nm.
Further, the first CoFeB layer 218 and the second CoFeB layer 222 in the free layer 216 serve to decrease magnetostriction. For example, a conventional TMR sensing element 100 with a free layer including a single Co2FeB layer with a thickness of 1.5 nm has a magnetostriction coefficient (λ) of 2.20. Conversely, a TMR sensing element 200 with a free layer including a pair of CoFeB layers, each with a thickness of 1.5 nm, has a magnetostriction coefficient of 0.96.
The cap layer 226 is a layer to provide electrical contact with a top electrode of the TMR sensing element 200 (not shown). The cap layer 226 may comprise, for example, tantalum (Ta), tantalum nitride (TaN), Ru, titanium (Ti), titanium nitride (TiN), or the like. In some implementations, the cap layer 226 may have a thickness in a range from approximately 10 nm to approximately 30 nm.
In some implementations, the TMR sensing element 200 may include a second interlayer.
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Process 400 may include additional implementations, such as any single implementation or any combination of implementations described below and/or in connection with one or more other processes described elsewhere herein.
In a first implementation, the second CoFeB layer 222 has a thickness in a range from approximately 1 nm to approximately 2 nm.
In a second implementation, alone or in combination with the first implementation, the first CoFeB layer 218 has a thickness in a range from approximately 1 nm to approximately 2 nm.
In a third implementation, alone or in combination with one or more of the first and second implementations, the NiFe layer 224 has a thickness in a range from approximately 5 nm to approximately 15 nm.
In a fourth implementation, alone or in combination with one or more of the first through third implementations, the interlayer 220 is a first interlayer, and the method further comprises forming a second interlayer 228, the second interlayer 228 being between the second CoFeB layer 222 and the NiFe layer 224.
In a fifth implementation, in combination with the fourth implementation, the second interlayer has a thickness in a range from approximately 0.1 nm to approximately 0.3 nm.
In a sixth implementation, in combination with one or more of the fourth and fifth implementations, the second interlayer 228 comprises tantalum.
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The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the implementations to the precise forms disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the implementations.
As used herein, the term “component” is intended to be broadly construed as hardware, firmware, and/or a combination of hardware and software. It will be apparent that systems and/or methods described herein may be implemented in different forms of hardware, firmware, or a combination of hardware and software. The actual specialized control hardware or software code used to implement these systems and/or methods is not limiting of the implementations. Thus, the operation and behavior of the systems and/or methods are described herein without reference to specific software code—it being understood that software and hardware can be designed to implement the systems and/or methods based on the description herein.
As used herein, satisfying a threshold may, depending on the context, refer to a value being greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, or the like.
Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of various implementations. In fact, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various implementations includes each dependent claim in combination with every other claim in the claim set. As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiple of the same item.
No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. Also, as used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more.” Further, as used herein, the article “the” is intended to include one or more items referenced in connection with the article “the” and may be used interchangeably with “the one or more.” Furthermore, as used herein, the term “set” is intended to include one or more items (e.g., related items, unrelated items, or a combination of related and unrelated items,), and may be used interchangeably with “one or more.” Where only one item is intended, the phrase “only one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise. Also, as used herein, the term “or” is intended to be inclusive when used in a series and may be used interchangeably with “and/or,” unless explicitly stated otherwise (e.g., if used in combination with “either” or “only one of”). Further, spatially relative terms, such as “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the apparatus, device, and/or element in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.
