Patent Publication Number: US-2023145573-A1

Title: Magnetoresistive sensor element with synthetic antiferromagnet biasing

Description:
BACKGROUND 
     Magnetoresistive sensors can measure metrics of a magnetic field based on either giant magnetoresistive (GMR) or tunneling magnetoresistive (TMR) principles of operation. Electrical resistance of such magnetoresistive sensors varies in response to the relative orientation between the magnetic moments of two magnetic layers in close proximity with one another. Typically, one of the two magnetic layers (referred to as the reference ferromagnetic) has a magnetic moment that is pinned in a particular orientation, while the other magnetic layer (referred to as the sensing ferromagnet) is free to align with an externally applied magnetic field. The reference layer&#39;s magnetization direction is typically fixed or set (i.e., locked or frozen) during manufacture and does not significantly change in response to an externally applied magnetic field that is within the sensor&#39;s operating specifications. The magnetization directions and magnitudes of layers with fixed or set magnetic moments are established by forming such layers within an external magnetic field at temperatures above the blocking temperatures of such layers. The magnetization directions and magnitudes of such layers are then frozen by lowering the temperature below the blocking temperature. The sensing layer has a magnetic condition that readily changes in response to the externally applied magnetic field. 
     Because such magnetoresistive sensors include various layers that have magnetic moments, there is typically significant magnetic interaction between layers. Some of these interactions are by design, such as, for example proximate layers that are coupled to one another via exchange interaction. Others of these interactions can be undesirable, such as, for example, edge fields emanating from edges of layers with magnetic moments. Corralling such magnetic fields so as to ensure that these fields do not have undesirable interaction with other magnetic layers would be welcome. Furthermore, providing a predetermined or tunable magnetic bias to the sensing magnetic layers would also be welcome so as to provide better repeatability and controlled performance. 
     SUMMARY 
     Apparatus and associated methods relate to a magnetoresistive sensor element with synthetic antiferromagnet biasing. The magnetoresistive sensor element includes a GMR/TMR sensor, a synthetic antiferromagnetic biasing structure, and an exchange-tuning spacer. The GMR/TMR sensor includes a sensing ferromagnetic layer formed on an opposite side of a spacer layer from a reference structure. The synthetic antiferromagnetic biasing structure includes a sense pinned ferromagnetic layer formed on an opposite side of a sense non-magnetic spacer from a sense biasing ferromagnetic layer. The exchange-tuning spacer is sandwiched between the sensing ferromagnetic layer and the sense biasing ferromagnetic layer. 
     Some embodiments relate to a method of manufacturing a synthetic antiferromagnet biased magnetoresistive sensor. The method includes: depositing a reference ferromagnetic structure; depositing a spacer upon the reference structure; depositing a sensing ferromagnetic layer on the spacer; depositing an exchange-tuning spacer on the sensing ferromagnetic layer; depositing a synthetic antiferromagnetic biasing structure on the exchange-tuning spacer; and depositing a capping layer on the synthetic antiferromagnetic biasing structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective cross-sectional view of the core layers of a TMR/GMR sensor with synthetic antiferromagnetic biasing. 
         FIG.  2    is a perspective view of a TMR/GMR sensor with synthetic antiferromagnetic biasing depicting a coordinate system used for disclosing magnetic operation of the TMR/GMR sensor. 
         FIGS.  3 A- 3 B  are graphs of magnetoresistance of a TMR/GMR sensor with synthetic antiferromagnetic biasing configured to provide a first biasing configuration. 
         FIGS.  4 A- 4 B  are graphs of magnetoresistance of a TMR/GMR sensor with synthetic antiferromagnetic biasing configured to provide a second biasing condition. 
     
    
    
     DETAILED DESCRIPTION 
     Apparatus and associated methods relate to a TMR/GMR magnetoresistive sensor element with a synthetic antiferromagnetic biasing structure separated from a sensing ferromagnetic layer by a non-magnetic exchange-tuning spacer. The synthetic antiferromagnetic biasing structure includes two ferromagnetic layers separated from one another by a non-magnetic spacer. The synthetic antiferromagnetic biasing structure is biased during manufacture and pinned via exchange coupling with an adjacent antiferromagnetic layer. The synthetic antiferromagnetic biasing structure biases the sensing ferromagnetic layer through an exchange interaction that can be tuned via the thickness of the non-magnetic exchange-tuning spacer. 
       FIG.  1    is a perspective cross-sectional view of the core layers of a TMR/GMR sensor with synthetic antiferromagnetic biasing. In  FIG.  1   , synthetic antiferromagnet biased magnetoresistive sensor  10  includes magnetoresistive sensing structure  12  separated from synthetic antiferromagnetic biasing structure  14  by exchange-tuning spacer  24 . Magnetoresistive sensing structure  12  is configured to sense a magnetic field. Synthetic antiferromagnetic biasing structure  14  is configured to generate a magnetic field so as to provide a bias to magnetoresistive sensing structure  12  via exchange-tuning spacer  24 . 
     Magnetoresistive sensing structure  12  includes reference structure  16 , sensing ferromagnetic layer  18 , and spacer layer  20 . Reference structure  16  includes reference antiferromagnetic layer  19 , reference pinned ferromagnetic layer  23 , reference non-magnetic spacer  22 , and reference ferromagnetic layer  21 . In the depicted embodiment, reference antiferromagnetic layer  19  is immediately adjacent (i.e., in direct contact with) reference pinned ferromagnetic layer  23 . In some embodiments, reference structure  16  can omit reference non-magnetic spacer  22  and reference pinned ferromagnetic layer  23 . In such embodiments, for example, it might not be critical to minimize stray fields generated by reference ferromagnetic layer  21 . In some embodiments, reference antiferromagnetic layer  19  can also be omitted. In such embodiments, the preferential orientation of reference ferromagnetic layer  21  could be set by thickness, shape, or other forms of strong magnetic anisotropies, such as, for example, those in alternating ferromagnetic/non-magnetic multilayer stacks with perpendicular magnetic anisotropy. In some embodiments, a difference between the blocking temperatures of reference structure  16  and synthetic antiferromagnetic biasing structure  14  is greater than 30° C. Such a difference permits fixing of the magnetic moment of the second deposited of the structures  14  and  16  without disturbing the magnetic moment of the first deposited of the structures  14  and  16 . 
     Spacer layer  20  is sandwiched between (i.e., in direct contact with each of) reference structure  16  and sensing ferromagnetic layer  18 . In some embodiments, spacer layer  20  is conductive. Such conductive spacer material selection results in magnetoresistive sensing structure  12  capable of Giant Magnetoresistive (GMR) sensing operation. In other embodiments, spacer layer  20  is insulative. Such insulative spacer material selection results in magnetoresistive sensing structure  12  capable of Tunnel Magnetoresistive (TMR) sensing operation. In either case, magnetoresistive sensing structure  12  has a resistance that changes in response to changes in an external magnetic field. 
     Typically, electrical resistance Rz of magnetoresistive sensing structure  12  is detected along a vertical dimension Z. Such electrical resistance Rz of magnetoresistive sensing structure  12  is indicative of the relative alignment of magnetic moments of reference ferromagnetic layer  21  and sensing ferromagnetic layer  18 . Electrical resistance Rz of magnetoresistive sensing structure  12  is relatively low when the magnetic moments of both reference ferromagnetic layer  21  and sensing ferromagnetic layer  18  are oriented parallel to one another. Electrical resistance Rz of magnetoresistive sensing structure  12  is relatively high when the magnetic moments of reference ferromagnetic layer  21  and sensing ferromagnetic layer  18  are oriented anti-parallel to one another. The descriptors “relatively-high resistance” and “relatively-low resistance” are used in comparison with each other. Electrical resistance Rz of magnetoresistive sensing structure  12  is relatively high for parallelly-aligned magnetic moments of reference ferromagnetic layer  21  and sensing ferromagnetic layer  18  in comparison with electrical resistance Rz of magnetoresistive sensing structure  12  for anti-parallelly-aligned magnetic moments of reference ferromagnetic layer  21  and sensing ferromagnetic layer  18 . 
     The magnetic moments of the layer(s) composing reference structure  16  have a fixed or pinned orientation. Such pinning is typically performed by forming a ferromagnetic layer proximate a pinning layer, such as, for example, locating reference pinned ferromagnetic layer  23  adjacent to reference antiferromagnetic layer  19 . Reference antiferromagnetic layer  19  pins an orientation of the magnetic moment of reference pinned ferromagnetic layer  23 , thereby functioning as a pinning layer. With appropriate choice of material and thickness for reference non-magnetic spacer layer  22 , reference pinned ferromagnetic layer  23  will then act to strongly bias the orientation of the magnetic moment of reference ferromagnetic layer  21  in an antiparallel manner, thus forming a synthetic antiferromagnetic structure for reference structure  16 . Coupling between reference pinned ferromagnetic layer  23  and reference ferromagnetic layer  21  is called Ruderman-Kittel-Kasuya-Yoshida (RKKY) exchange coupling. Such RKKY exchange coupling occurs between ferromagnetic layers separated by ultra-thin non-magnetic spacers, such as reference non-magnetic spacer layer  22 . 
     The orientation of the magnetic moments of the constituent layers of reference structure  16  do not significantly change in response to an external magnetic field (for typical operational magnitudes of such external magnetic fields). Such strong pinning can be provided by the exchange interaction between reference antiferromagnetic layer  19  and reference pinned ferromagnetic layer  23  adjacent thereto. In contrast to the strongly pinned condition of reference ferromagnetic layer  21 , the orientation of the magnetic moment of sensing ferromagnetic layer  18  can change in response to even small changes in an external magnetic field. When the external magnetic field aligns the magnetic orientation of sensing ferromagnetic layer  18  parallel to the magnetic orientation of reference ferromagnetic layer  21 , electrical resistance Rz of magnetoresistive sensing structure  12  reaches a minimum value. When the external magnetic field aligns the magnetic orientation of sensing ferromagnetic layer  18  antiparallel to the magnetic orientation of reference ferromagnetic layer  21 , resistance Rz of magnetoresistive sensing structure  12  reaches a maximum value. 
     Synthetic antiferromagnetic biasing structure  14  includes exchange-tuning spacer  24 , sense biasing ferromagnetic layer  26 , sense non-magnetic spacer  30 , and biasing pinned magnetic structure  28 . The magnetic moment of biasing pinned magnetic structure  28  has a fixed or pinned orientation. Such pinning can again be performed by locating a ferromagnetic layer proximate a pinning layer, such as, for example, locating sense pinned ferromagnetic layer  31  adjacent (i.e., in direct contact with) sense antiferromagnetic layer  32 . The orientation of the magnetic moment of biasing pinned magnetic structure  28  does not significantly change in response to an external magnetic field (for typical magnitudes of such external magnetic fields). The orientation of biasing pinned magnetic structure  28  causes the magnetic moment of sense biasing ferromagnetic layer  26  to be oriented in a predetermined manner. 
     Orientation of sense biasing ferromagnetic layer  26  is established by exchange coupling with biasing pinned magnetic structure  28 . In some embodiments, reference ferromagnetic layer  21  and sense biasing ferromagnetic layer  26  are pinned in in-plane directions that are parallel to one another. Sense non-magnetic spacer  30  is sandwiched between biasing pinned magnetic structure  28  and sense biasing ferromagnetic layer  26 . Coupling between biasing pinned magnetic structure  28  and sense biasing ferromagnetic layer  26  is mediated by RKKY exchange coupling, similar to the exchange interaction described for reference structure  16 . 
     Such a layer structure as shown in  FIG.  1    is not to scale, but for the purpose of disclosing an example of layer ordering only. By varying the thickness of sense non-magnetic spacer  30  by mere angstroms the exchange coupling of biasing pinned magnetic structure  28  and sense biasing ferromagnetic layer  26  can oscillate between antiparallel and parallel. Thickness of sense non-magnetic spacer  30  may be set such that biasing pinned magnetic structure  28  and sense biasing ferromagnetic layer  26  are magnetized antiparallel to one another. For example, thickness of synthetic antiferromagnet non-magnetic spacer can be tuned to 0.7, 0.8, 0.9, 1.0, or 1.1 nm, to provide effective pinning. The optimal thickness of non-magnetic spacer layer  30  can vary depending on the film roughness, defect density, thermal treatment, etc. Thus, the term “synthetic antiferromagnet” is used as there is not a coherent antiferromagnetic atomic layered ordering of moments throughout the entire structure, but a longer range RKKY interaction aligning nanoscale thickness ferromagnetic layers (e.g., in an antiparallel fashion). 
     Sense biasing ferromagnetic layer  26 , which has a magnetic moment that is oriented as described above, biases sensing ferromagnetic layer  18  of magnetoresistive sensing structure  12 , via magnetic exchange coupling. The strength of biasing acting upon sensing ferromagnetic layer  18  can be tuned by varying the thickness of exchange-tuning spacer  24 , which is sandwiched between (i.e., in direct contact with each of) sensing ferromagnetic layer  18  and sense biasing ferromagnetic layer  26 . Orientation of the magnetic moment of sense biasing ferromagnetic layer  26  determines the orientation of sensing ferromagnetic layer  18  when in an absence of an external magnetic field. Thus, orientation of sense biasing ferromagnetic layer  26  must be established so as to bias sensing ferromagnetic layer  18  in a predetermined fashion. 
     Again, orientation of the magnetic moment of biasing pinned magnetic structure  28  is pinned via sense antiferromagnetic layer  32 . Orientation of the magnetic moment of biasing pinned magnetic structure  28  then determines the orientation of the magnetic moment of sense biasing ferromagnetic layer  26 . Orientation of the magnetic moment of sense biasing ferromagnetic layer  26  determines the orientation of the magnetic moment of sensor sensing ferromagnetic layer  18  in the absence of an external magnetic field. In this way, in the absence of an external magnetic field, the magnetic moment of sensing ferromagnetic layer  18  is ultimately oriented by the direction of the exchange interaction occurring between sense antiferromagnetic layer  32  and sense pinned ferromagnetic layer  31 . By biasing sensing ferromagnetic layer  18  in such a fashion, the stray magnetic field of sense biasing ferromagnetic layer  26  is largely contained by biasing pinned magnetic structure  28  via dipole coupling. Such dipole coupling between sense biasing ferromagnetic layer  26  and biasing pinned magnetic structure  28  reduces stray magnetic field interactions with sensing ferromagnetic layer  18 , especially at the edges of the patterned structures. 
     Additional layers depicted in  FIG.  1    includes substrate  34 , seed/adhesion layer  36 , and capping layer  38 . Synthetic antiferromagnet biased magnetoresistive sensor  10  is typically fabricated upon a suitable substrate material, such as, for example, substrate  34 . Seed layer  36  is then deposited upon substrate  34  so as to provide a layer to which reference antiferromagnetic layer  19  can adhere and can provide suitable crystalline texturing to promote desired properties in upper layers. Capping layer  38  is deposited upon the final layer structure of synthetic antiferromagnet biased magnetoresistive sensor  10  so as to passivate the fabricated device against oxidation or other unintended damage. Electrical contacts, which are not depicted in  FIG.  1   , to synthetic antiferromagnet biased magnetoresistive sensor  10  can be provided either peripherally or vertically. The layer thicknesses, as depicted in  FIG.  1   , are not to scale. For example, sense non-magnetic spacer  30  and exchange-tuning spacer  24  control exchange coupling therethrough, and thus have well-controlled thicknesses, which typically are measured as single-digit nanometers or less. 
       FIG.  2    is cross-sectional view of a portion of a TMR/GMR sensor with synthetic antiferromagnet biasing. In  FIG.  2   , magnetoresistive sensing structure  12  and synthetic antiferromagnetic biasing structure  14  of synthetic antiferromagnet biased magnetoresistive sensor  10  are shown annotated with exemplary layer thicknesses. Magnetoresistive sensing structure  12  includes reference structure  16 , sensing ferromagnetic layer  18 , and spacer layer  20 . In the embodiment depicted, reference structure  16  can have a thickness between 5 and 30 nm, spacer layer  20  can have a thickness between 0.4 and 3.0 nm, and sensing ferromagnetic layer  18  can have a thickness between 1 and 10 nm. Because TMR or GMR operation is determined by a thickness and material of spacer layer  20 , thickness of spacer layer  20  is less than a mean free path λ of electrons between spin-state disrupting scattering events in such a material as is selected. In some embodiments spacer layer  20  can include Cu, Ag, Au and/or binary/ternary alloys of those three materials. In addition to such alloys having low amounts of oxygen content, TMR spacer layers can include predominantly AlO x , MgO and other less used oxide layers, such as ScO. Spacer layers involving carbon or graphene could also be utilized. 
     Synthetic antiferromagnetic biasing structure  14  includes exchange-tuning spacer  24 , sense biasing ferromagnetic layer  26 , sense pinned ferromagnetic layer  31 , sense non-magnetic spacer  30 , and sense antiferromagnetic layer  32 . In the embodiment depicted, exchange-tuning spacer  24  has a thickness between 0.0 and 0.8 nm, sense biasing ferromagnetic layer  26  has a thickness between 1 and 3 nm, sense non-magnetic spacer  30  has a thickness on the order of 1 nm, sense pinned ferromagnetic layer  31  has a thickness between 1 and 3 nm, and antiferromagnetic layer  32  has a thickness between 5 and 20 nm. Also annotated in  FIG.  2    are magnetic field lines of dipole coupled layers sense biasing ferromagnetic layer  26  and sense pinned ferromagnetic layer  31 . Note that these magnetic field lines are localized away from sensing ferromagnetic layer  18  of magnetoresistive sensing structure  12 . Exchange-tuning spacer  24  can include thin nonmagnetic materials (e.g., &lt;1 nm in thickness) of Ta, Ru and/or MgO. Sense biasing ferromagnetic layer  26  and/or sense pinned ferromagnetic layer  31  are magnetic layers that are typically less than 5 nm thick and can include alloys of Co, Fe, Ni and/or B. Sense pinned ferromagnetic layer  31  could be a bilayer structure with a NiFe alloy (typically a relative composition of 80/20 in atomic percent) adjacent to sense antiferromagnetic layer  32  and a Co, Fe, Ni, B alloy layer adjacent to sense non-magnetic spacer  30 . Sense non-magnetic spacer  30  is a non-magnetic metallic layer that can be Ru, Cu, Cr or other alloys that allow a strong/tunable RKKY magnetic exchange interaction between sense pinned ferromagnetic layer  31  and sense biasing ferromagnetic layer  26 . Sensing ferromagnetic layer  18  can consist of either a monolayer or bilayer ferromagnetic material composed of Co, Fe, Ni, and B alloys, as well as several types of Heusler alloys containing, for instance, Al, Si, Ga, or Ge and other transition metals. 
     The pinning orientation imparted onto sense pinned ferromagnetic layer  31  by sense antiferromagnetic layer  32 , may not be aligned parallel to the pinning orientation imparted onto reference pinned ferromagnetic layer  23  by reference antiferromagnet layer  19 . Relative alignment of the two synthetic antiferromagnetic biasing structures can be controlled through the fabrication process and/or tailored materials property selection. For instance, by means of carefully controlled composition, thickness, crystalline texture, and materials choice of the antiferromagnetic layers and other layers adjacent thereto. Thus, the pinning orientations imparted on sense pinned ferromagnetic layer  31  and reference pinned ferromagnetic layer  23 , and by extension the exchange bias imparted on sensing ferromagnetic layer  18  and reference ferromagnetic layer  21 , could be set into multiple possible configurations as demonstrated below. 
       FIGS.  3 A- 3 B  are graphs of magnetoresistance of a TMR/GMR sensor with synthetic antiferromagnetic biasing configured to provide a first biasing configuration. In FIGS.  3 A- 3 B, graphs  40  and  50  depict magnetoresistive (MR) responses to an applied field for synthetic antiferromagnet biased magnetoresistive sensor  10 , in which the magnetic moments of reference ferromagnetic layer  21  and sensing ferromagnetic layer  18  are parallel to one another (in the x-y plane). In graphs  40  and  50 , horizontal axes  42  and  52 , respectively, are indicative of the magnitude and direction (e.g., positive, or negative) of the external applied magnetic field. In graphs  40  and  50 , vertical axes,  44  and  54 , respectively, are indicative of the MR response to the external magnetic field. 
     In  FIG.  3 A , graph  40  depicts the MR response  46  to an external magnetic field applied orthogonal to the directions of the magnetic moments of reference ferromagnetic layer  21  and sensing ferromagnetic layer  18 . As depicted in  FIG.  3 A , the MR response  46  to external magnetic field directions orthogonal to a pinning direction of both reference ferromagnetic layer  21  and sense biasing ferromagnetic layer  26  is unipolar and symmetric (i.e., has even symmetry about the origin or zero-bias condition), increasing its resistance as the magnitude of the orthogonal external field increases. This MR response  46  indicates that as the magnitude of the external field increases, the percentage of electrons within sensing ferromagnetic layer  18  having electron spin aligned with the magnetic moment of reference ferromagnetic layer  21  decreases. Such a response can be useful for unipolar switching applications where only a metric of the magnitude of the external magnetic field is desired. 
     In  FIG.  3 B , graph  50  depicts the MR response  56  to an external magnetic field antiparallel to the directions of the magnetic moments of reference ferromagnetic layer  21  and sensing ferromagnetic layer  18 . As depicted in  FIG.  3 B , the MR response  56  is asymmetric, increasing its resistance as the external magnetic field increases in the antiparallel direction (e.g., the positive polarity), but saturating as the external magnetic field increases in the parallel direction (e.g., the negative polarity). This MR response  56  indicates that as the external field increases in the antiparallel direction, the percentage of electrons within sensing ferromagnetic layer  18  having electron spin oriented with the magnetic moment of reference ferromagnetic layer  21  decreases, but as the external field increases in the parallel direction, the percentage of electrons within sensing ferromagnetic layer  18  having electron spin oriented with the magnetic moment of reference ferromagnetic layer  21  increases. Such a response can be useful for bipolar switching applications where a metric of the direction of the external magnetic field is desired. 
       FIGS.  4 A- 4 B  are graphs of magnetoresistance of a TMR/GMR sensor with synthetic antiferromagnetic biasing configured to provide a second biasing condition. In  FIGS.  4 A- 4 B , graphs  60  and  70  depict MR responses of synthetic antiferromagnet biased magnetoresistive sensor  10 , in which the magnetic moments of reference ferromagnetic layer  21  and sensing ferromagnetic layer  18  are orthogonal to one another (in the x-y plane). In graphs  60  and  70 , horizontal axes  62  and  72 , respectively, are indicative of the magnitude and direction (e.g., positive, or negative) of the external magnetic field. In graphs  60  and  70 , vertical axes,  64  and  74 , respectively, are indicative of the MR response to the external magnetic field. 
     In  FIG.  4 A , graph  40  depicts the MR response  66  to an external magnetic field applied parallel to the direction of the magnetic moment of reference ferromagnetic layer  21  and orthogonal to the direction of the magnetic moment of sensing ferromagnetic layer  18 . As depicted in  FIG.  4 A , the MR response  66  exhibits low hysteresis over a large span of the external magnetic field (i.e., the difference between the response to an external field changing in opposite directions is less than 2%, 3%, 5% of the total response) decreasing its resistance as the magnitude of the orthogonal external field increases in the direction of the magnetic moment of reference ferromagnetic layer  21 . This MR response  66  indicates that as the magnitude of the external field increases, the percentage of electrons within sensing ferromagnetic layer  18  having electron spin oriented with the magnetic moment of reference ferromagnetic layer  21  increases. Such a response can be useful for switching applications where metrics of both the magnitude and the direction of the external magnetic field are desired. 
     In  FIG.  4 B , graph  70  depicts the MR response  76  to an external magnetic field applied parallel with an easy axis of sense layer  18 . As depicted in  FIG.  4 B , the MR response  76  exhibits hysteresis and is biased away from the origin, Furthermore, the MR response is relatively insensitive to changes in the magnetic field outside of the hysteresis. This configuration can permit a bipolar linear response of the material along the sense direction (depicted in  FIG.  4 A ). Usefully, the biasing structure restricts the sensor to have only one permitted configuration at zero applied field. Without the biasing structure, the loop delineated in  FIG.  4 B  would be centered at zero applied field H=0 Oe, thereby permitting either a high-resistance or low-resistance state to form. In such an unbiased configuration, the resulting resistance of the sensor at zero applied field would be determined by the specific history of the external field applied along the sensor&#39;s off-axis. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made, and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention is not limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.