Patent Description:
Conventional magnetoresistive random access memory (MRAM) devices typically utilize a magnetoresistive (a/k/a magnetic) tunnel-junction (MTJ) as a nonvolatile memory element, which may be defined, in simplified form, as a vertical stack of three layers. These three layers include: (i) a magnetic reference layer, which is often referred to as a "pinned" or "fixed" magnetic layer, (ii) a tunneling barrier layer, which is often referred to as a tunneling dielectric layer, and (iii) a magnetic free layer. As will be understood by those skilled in the art, an MTJ may be programmed to define a "<NUM>" or "<NUM>" logic state by setting the "field" of the magnetic free layer to be parallel to, or anti-parallel to, the field of the magnetic reference layer during a memory write operation. Thus, as shown by <FIG>, an MTJ <NUM> can be set to have a "first" logic state by setting the magnetization of the magnetic free layer <NUM> to be parallel to the magnetization of the magnetic reference layer <NUM>, so that a relatively low resistance state is present when a read current is established across the layers of the MTJ <NUM>, including a tunneling barrier layer <NUM>, which separates the magnetic free layer <NUM> from the magnetic reference layer <NUM>. Alternatively, the MTJ <NUM> can be set to have a "second" logic state by setting the magnetization of the magnetic free layer <NUM> to be anti-parallel to the magnetization of the magnetic reference layer <NUM>, so that a relatively high resistance state is present when a read current is established across the layers of the MTJ <NUM>. Although not shown, a conventional MTJ may also be configured to support "vertical" or "perpendicular" spin directions rather than the "horizontal" ones illustrated by <FIG>.

In addition, as shown on the left side of <FIG>, a spin-transfer torque (STT) MRAM 20a (having a single "read/write" select transistor T1) may be programmed during a write operation by passing a "write" current in a first direction through the layers of the MTJ <NUM> in order to program a logic "<NUM>", and in a second direction, opposite the first direction, in order to program a logic "<NUM>". Moreover, shorter access times resulting from faster programming can be achieved by using higher write currents, but such higher currents can cause incremental damage to the layers of the MTJ <NUM> in response to repeated programming, and thereby lower the long term endurance and reliability of the STT-MRAM 20a.

Fortunately, as shown on the right side of <FIG>, a spin-orbit torque (SOT) MRAM 20b (having separate read and write select transistors T1, T2) may be programmed by passing a "write" current across a separate "strap" layer <NUM>, which shares an interface with the magnetic free layer <NUM>. As shown by the separate read current and write current paths, the use of the strap layer <NUM> to support the write current operates to decouple the write current path from the read current path, and thereby avoids the potential endurance and reliability limitations associated with the STT-MRAM 20a, but at the expense of a somewhat larger per-bit layout footprint caused by the additional write select transistor T2 within each memory cell.

Referring now to <FIG>, a more representative MTJ <NUM>' according to the prior art is shown as including a seed layer <NUM>, upon which a stack of a bottom magnetic reference layer 24a, a Ruderman-Kittel-Kasuya-Yosida (RKKY) spacer/coupling layer 24b, and a top magnetic reference layer 24c may be sequentially formed as a composite magnetic reference layer <NUM>. Conventional devices related to the MTJ <NUM>' are disclosed in an article by <NPL>. Moreover, the patent applications <CIT>, <CIT>, <CIT>, <CIT>,<CIT>, <CIT> and <CIT> disclose arrangements of MRAM devices according to prior art.

The MTJ <NUM>' also includes a tunneling barrier layer <NUM>, which may be configured as a magnesium oxide (Mg-O) layer, and a magnetic free layer <NUM> directly on the tunneling barrier layer <NUM>. An oxide cap <NUM>, which may be configured as a magnesium oxide (Mg-O) layer, is also provided on the magnetic free layer <NUM>, as shown. Although not wishing to be bound by any theory, an oxide cap for high efficiency and/or optimum tunnel magnetoresistance (TMR) may have inadequate post-annealing stability when compared to other lower performance oxide caps. Thus, there exists a need to develop MTJ-based nonvolatile memory elements having high performance oxide caps and superior post-anneal stability.

Nonvolatile memories according to embodiments of the invention may utilize magnetoresistive tunnel-junction (MTJ) memory elements with improved thermal stability during fabrication, and improved post-fabrication yield and endurance. According to these embodiments, an MTJ memory element is provided, which includes a magnetic reference layer (RL), a magnetic free layer (FL), and a tunneling barrier layer, which extends between the magnetic RL and the magnetic FL. In addition, to enhance thermal stability, a diffusion-blocking layer (DBL) is provided on the magnetic FL, which extends between the DBL and the tunneling barrier layer. This DBL is configured to have: (i) relatively high thermal stability (e.g., annealing stability), (ii) relatively high diffusion barrier energy (Eb) or relatively high segregation tendencies towards its layer interface(s), and (iii) reduced lattice mismatch vis-à-vis adjacent layers, includes at least one material selected from a group consisting of bismuth (Bi), antimony (Sb), osmium (Os), rhenium (Re), tin (Sn), rhodium (Rh), indium (In), and cadmium (Cd). In these embodiments, an oxide layer, such as an oxide capping layer is provided on the DBL. The DBL may also have a thickness in a range from <NUM> to <NUM>, whereas the oxide layer may have a thickness in a range from <NUM> to <NUM>. Moreover, the DBL extends between the oxide layer and the magnetic FL to form interfaces with the oxide layer and the magnetic FL.

According to further embodiments of the invention, the DBL includes a stacked composite of a first DBL of a first material, and a second DBL of a second material, which extends between the first DBL and the oxide layer. This first material may be a material selected from a group consisting of magnesium (Mg), aluminum (Al), scandium (Sc), titanium (Ti), vanadium (V) and chromium (Cr). According to the present invention, the oxide layer is configured as a composite of: (i) a first oxide layer, which includes at least one oxide selected from a group consisting of scandium oxide (Sc-O), strontium oxide (Sr-O) and calcium oxide (Ca-O), and (ii) a second oxide layer, which includes at least one oxide selected from a group consisting of tantalum oxide (Ta-O) and hafnium oxide (Hf-O). This first oxide layer extends between the DBL and the second oxide layer, which may be thicker than the first oxide layer.

According to additional embodiments of the invention, a spin-transfer torque magnetoresistive random access memory (STT-MRAM) element is provided, which includes a magnetic reference layer (RL), a magnetic free layer (FL), a tunneling barrier layer extending between the magnetic RL and the magnetic FL, and a seed layer under the magnetic RL. In some of these embodiments, the magnetic RL may include a stacked composite of first and second magnetic reference layers having a Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling layer extending therebetween, which is designed to facilitate antiferromagnetic coupling between the bottom RL and the top RL.

In addition, a diffusion-blocking layer (DBL) is provided on the magnetic FL, and an oxide "capping" layer is provided on the DBL. Advantageously, the DBL operates to improve, among other things, the annealing stability of the memory element during fabrication, by suppressing out-diffusion from the magnetic FL (i.e., interdiffusion between the FL and oxide capping layer), and suppressing out-diffusion from the capping layer. In some of these embodiments, the DBL may have a thickness in a range from <NUM> to <NUM>, and may include at least one material selected from a group consisting of bismuth (Bi), antimony (Sb), osmium (Os), rhenium (Re), tin (Sn), rhodium (Rh), indium (In), and cadmium (Cd). The DBL may even be configured as a stacked composite of a first DBL, and a second DBL (of a different material) extending between the first DBL and the oxide capping layer. This first DBL may include a first material selected from a group consisting of magnesium (Mg), aluminum (Al), scandium (Sc), titanium (Ti), vanadium (V) and chromium (Cr), which contacts the magnetic FL. In embodiments of the invention, the oxide capping layer includes a stacked composite of: (i) a scandium oxide (Sc-O) layer, a strontium oxide (Sr-O) layer and/or a calcium oxide (Ca-O) layer, which contacts the DBL, and (ii) a tantalum oxide (Ta-O) layer and/or a hafnium oxide (Hf-O) layer thereon.

According to further embodiments of the invention, a spin-orbit torque magnetoresistive random access memory (SOT-MRAM) element is provided, which includes a magnetic reference layer (RL), a magnetic free layer (FL), and a tunneling barrier layer, which extends between the magnetic RL and the magnetic FL. In addition, to enhance thermal stability during fabrication, a diffusion-blocking layer (DBL) is provided on the magnetic FL. This DBL includes at least one material selected from a group consisting of bismuth (Bi), antimony (Sb), osmium (Os), rhenium (Re), tin (Sn), rhodium (Rh), indium (In), and cadmium (Cd).

The present invention now will be described more fully with reference to the accompanying drawings, in which examples for understanding and preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments and examples are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

In the drawing, the thickness of layers and regions are exaggerated for clarity. It will also be understood that when a layer is referred to as being "on" another layer or substrate, it can be directly on the other layer or substrate, or an intervening layer(s) may also be present. In addition, each reference to a metal (M) oxide (O) herein, which is identified as M-O, represents a metal oxide compound MxOy, where M designates a metal, O designates oxygen, with varying stoichiometric subscripts: x ≥ <NUM>, y ≥ <NUM>.

It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.

It will be further understood that the terms "comprising", "including", "having" and variants thereof, when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. In contrast, the term "consisting of" when used in this specification, specifies the stated features, steps, operations, elements, and/or components, and precludes additional features, steps, operations, elements and/or components.

Referring now to <FIG>, a nonvolatile magnetoresistive tunnel-junction (MTJ) memory element 100a is illustrated as including a vertical stack of: (i) a seed layer <NUM>, (ii) a magnetic reference layer (RL) <NUM> on the seed layer <NUM>, (iii) a tunneling barrier layer <NUM> on the magnetic RL <NUM>, and (iv) a magnetic free layer (FL) <NUM> on the tunneling barrier layer <NUM>. As shown, the magnetic RL <NUM> is configured as a stacked composite of a bottom magnetic RL 124a, a Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling/spacer layer 124b, and a top magnetic RL 124c on the spacer layer 124b.

The seed layer <NUM> may include a material selected from a group consisting of Ir, Ru, Ta, for example, and may have a thickness in a range from about <NUM> to about <NUM>. In addition, the bottom magnetic RL 124a may include a material selected from a group consisting of Co/Pt multilayers or Co-Pt alloys or another material including multilayers of magnetic materials such as Co or Fe with non-magnetic materials such as Pt or Pd, and may have a thickness in a range from about <NUM> to about <NUM>; the Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling layer 124b may include a material selected from a group consisting of Ru, Rh, Ir and alloys thereof, and may have a thickness in a range from about <NUM> to about <NUM>; and the top magnetic RL 124c may include a material selected from a group consisting of Co/Pt multilayers or alloys with an optional non-magnetic or weakly-magnetic insertion layer and CoFeB next to the tunneling barrier layer <NUM>, and may have a thickness in a range from about <NUM> to about <NUM>. The tunneling barrier layer <NUM> may be configured as a magnesium oxide (Mg-O) layer and/or a Mg-Al-O layer, for example, and have a thickness in a range from about <NUM> to about <NUM>. The magnetic FL <NUM> may include a material selected from a group consisting of Co, Fe, B, Nb, Ta, Mo, Si, Zr, Ge, W, and may have a thickness in a range from about <NUM> to about <NUM>.

Advantageously, to enhance thermal stability, a diffusion-blocking layer (DBL) <NUM> is provided, which extends between (and forms interfaces with) the magnetic FL <NUM> and an oxide capping layer <NUM>, as shown. In particular, to suppress interdiffusion between the FL <NUM> and the oxide capping layer <NUM>, the DBL <NUM> preferably has: (i) relatively high thermal stability (e.g., annealing stability), (ii) relatively high diffusion barrier energy (Eb) or relatively high segregation tendencies towards its layer interface(s), and (iii) reduced lattice mismatch vis-à-vis the adjacent magnetic FL <NUM> and the oxide capping layer <NUM>. In particular, as described in the <CIT>, the annealing stability of the oxide capping layer <NUM> can be improved by configuring the DBL <NUM> such that, among other things, an increase in diffusion barrier energy (Eb) or relatively high segregation tendency, and a reduced lattice mismatch is achieved relative to a conventional interface between a magnetic FL and an oxide (e.g., Mg-O) capping layer (while maintaining sufficient perpendicular magnetic anisotropy (PMA) relative to the conventional interface).

Moreover, the DBL <NUM> may have a thickness in a range from <NUM> to <NUM>, and includes at least one material selected from a group consisting of bismuth (Bi), antimony (Sb), osmium (Os), rhenium (Re), tin (Sn), rhodium (Rh), indium (In), and cadmium (Cd). Although not wishing to be bound by any theory, osmium (Os), rhenium (Re) and rhodium (Rh) are believed to have a lower segregation tendency towards the free layer and oxide layer interfaces, but a relatively high diffusion barrier, which suggests that these elements may remain as deposited during post-annealing. Alternatively, bismuth (Bi), indium (In) and cadmium (Cd) are believed to have a lower diffusion barrier, but a higher segregation tendency towards the interfaces so diffusion during post-annealing is not likely to move these elements out of the interfaces. Moreover, within the group of eight elements, a first sub-group of bismuth (Bi), antimony (Sb), osmium (Os), rhenium (Re), and tin (Sn) may be chosen relative to a second sub-group of rhodium (Rh), indium (In), and cadmium (Cd), in some embodiments, based on a likelihood of stability (and other properties) of a subsequently formed oxide cap, which is described hereinbelow. A uniformity in the thickness of the DBL <NUM> may also be enhanced by cooling an intermediate-stage substrate containing the magnetic FL <NUM> to a temperature of about -<NUM> to about -<NUM> prior to deposition of the DBL <NUM>.

The oxide capping layer <NUM> of <FIG>, which is provided on the DBL <NUM>, may have a thickness in a range from <NUM> to <NUM>. However, as shown by the magnetoresistive tunnel-junction (MTJ) memory element 100b of <FIG>, an alternative oxide capping layer <NUM>' may include at least one of strontium oxide (Sr-O), scandium oxide (Sc-O), beryllium oxide (Be-O), calcium oxide (Ca-O), tantalum oxide (Ta-O), yttrium oxide (Y-O), zirconium oxide (Zr-O), and hafnium oxide (Hf-O), which may provide lower formation energies and a high oxygen diffusion barrier.

In addition, as shown by the magnetoresistive tunnel-junction (MTJ) memory element 100c of <FIG>, the DBL <NUM> of <FIG> may be modified to include a stacked composite of a first DBL 140a of a first material, and a second DBL 140b of a second material, which extends between the first DBL 140a and the oxide capping layer <NUM>'. This first material may be a material selected from a group consisting of magnesium (Mg), aluminum (Al), scandium (Sc), titanium (Ti), vanadium (V) and chromium (Cr), whereas the second material may include at least one of bismuth (Bi), antimony (Sb), osmium (Os), rhenium (Re), tin (Sn), rhodium (Rh), indium (In), and cadmium (Cd). Although not wishing to be bound by any theory, the first DBL 140a may operate to suppress out-diffusion of atoms from the second DBL 140b into the magnetic FL <NUM> (e.g., during deposition and post-annealing of the second DBL 140b).

Referring now to the magnetoresistive tunnel-junction (MTJ) memory element 100d of <FIG>, according to the present invention, the oxide capping layers <NUM>, <NUM>' of <FIG> are modified to include a stacked composite of: (i) a first oxide layer 130a for superior annealing stability, which includes at least one oxide selected from a group consisting of scandium oxide (Sc-O), strontium oxide (Sr-O) and calcium oxide (Ca-O), and (ii) a second oxide layer 130b for good figure-of-merit (FOM), which includes at least one oxide selected from a group consisting of tantalum oxide (Ta-O) and hafnium oxide (Hf-O), and may be thicker than the first oxide layer 130a.

Finally, as shown by <FIG>, a spin-orbit torque magnetoresistive random access memory (SOT-MRAM) element 100e according to an example includes: (i) a magnetic reference layer <NUM> having a capping layer <NUM> thereon (e.g., nitride, such as Ta-N, Ti-N), (ii) a magnetic free layer <NUM>, (iii) a tunneling barrier layer <NUM> extending between the magnetic reference layer <NUM> and the magnetic free layer <NUM>, and (iv) a diffusion-blocking layer <NUM> on the magnetic free layer <NUM>. The magnetic reference layer <NUM> is shown as including a stacked composite of a top reference layer 224a, a Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling/spacer layer 224b, and a bottom reference layer 224c. In some examples of the memory element 100e, the layers (i) through (iv) may be configured as described hereinabove with respect to memory elements 100a-100d of <FIG>.

The SOT-MRAM element 100e of <FIG> further includes a thin shunt-current reducing oxide (SRO) layer <NUM>, which extends between the diffusion-blocking layer <NUM> and a SOT write/read line <NUM>, which may have a relatively high resistance and perform the same function as the strap layer <NUM> of the SOT-MRAM 20b of <FIG> during write and read operations. Advantageously, the SRO layer <NUM> is thin (to improve interfacial transparency) and provides a relatively high parallel resistance relative to the SOT write/read line <NUM>, so that a lateral shunt current Jc is blocked from passing laterally through the relatively low resistance free layer <NUM> during a write operation. The diffusion-blocking layer <NUM> also enhances the annealing stability of the thin SRO layer <NUM>.

The SRO layer may include at least one material selected from a group consisting of magnesium oxide (Mg-O), calcium oxide (Ca-O), scandium oxide (Sc-O), titanium oxide (Ti-O), vanadium oxide (V-O), iron oxide (Fe-O), nickel oxide (Ni-O), cobalt oxide (Co-O), zirconium oxide (Zr-O), niobium oxide (Nb-O), tantalum oxide (Ta-O), tungsten oxide (W-O), and osmium oxide (Os-O), and has a thickness in a range from about <NUM> to about <NUM>.

Claim 1:
A magnetoresistive tunnel-junction, MTJ, memory element (100a-e), comprising:
a magnetic reference layer, RL (<NUM>);
a magnetic free layer, FL (<NUM>);
a tunneling barrier layer (<NUM>) extending between the magnetic RL (<NUM>) and the magnetic FL (<NUM>);
a diffusion-blocking layer, (<NUM>; 140a, 140b) on the magnetic FL (<NUM>), said DBL (<NUM>; 140a, 140b) comprising at least one material selected from a group consisting of bismuth, Bi, antimony, Sb, osmium, Os, rhenium, Re, tin, Sn, rhodium, Rh, indium, In, and cadmium, Cd; and
an oxide layer (<NUM>; <NUM>'; <NUM>") on the DBL (<NUM>; 140a, 140b), wherein the DBL (<NUM>; 140a, 140b) extends between the oxide layer (<NUM>; <NUM>'; <NUM>") and the magnetic FL (<NUM>) to form interfaces with the oxide layer (<NUM>; <NUM>'; <NUM>") and the magnetic FL (<NUM>),
wherein the oxide layer (<NUM>") comprises a composite of:
a first oxide layer (130a) comprising at least one oxide selected from a group consisting of scandium oxide, Sc-O, strontium oxide, Sr-O, and calcium oxide, Ca-O; and
a second oxide layer (130b) comprising at least one oxide selected from a group consisting of tantalum oxide, Ta-O, and hafnium oxide, Hf-O, and
wherein the first oxide layer (130a) extends between the second oxide layer (130b) and the DBL (<NUM>).