Patent ID: 12190928

DETAILED DESCRIPTION

FIG.1is a block diagram of an MRAM device in accordance with example embodiments.

Referring toFIG.1, the MRAM device may include a cell array1, a row decoder2, a column decoder3, and a read/write circuit4and a control logic5.

The cell array1may include a plurality of word lines, a plurality of bit lines and memory cells. The memory cells may be connected at cross points the word lines and the bit lines, respectively. The cell array1will described below with reference toFIG.2.

The row decoder2may be connected to the cell array1by the word lines. The row decoder2may decode addresses input from an outside, and thus one of the plurality of word lines may be selected.

The column decoder3may be connected to the cell array1by the bit lines. The column decoder3may decode addresses input from the outside, and thus one of the bit lines may be selected. The bit line selected by the column decoder3may be connected to a read/write circuit4.

The read/write circuit4may supply a bit line bias for accessing a selected memory cell by controlling of the control logic5. In an implementation, the read/write circuit4may supply the bit line bias to a selected bit line for writing or reading data at the selected memory cell.

The control logic5may output control signals for controlling the MRAM device according to a command signal supplied from the outside. The control signals output from the control logic5may control the read/write circuit4.

FIG.2is a circuit diagram of a cell array of an MRAM device in accordance with example embodiments.FIG.3is a conceptual diagram of a unit memory cell of the MRAM device in accordance with example embodiments.

Referring toFIGS.2and3, the cell array1may include a plurality of bit lines BL, a plurality of word lines WL and a plurality of unit memory cells MC.

The word lines WL may extend (e.g., lengthwise) in a first direction, and the bit lines BL may extend (e.g., lengthwise) in a second direction crossing the first direction. The unit memory cells MC may be arranged in two-dimension or in three-dimension. The unit memory cells MC may be connected at cross points of word lines WL and bit lines BL, respectively. In an implementation, each of the unit memory cells MC connected to the word lines WL may be connected to the read/write circuit (4referred toFIG.1) by the bit lines BL.

In the MRAM device, the unit memory cell MC may include a magnetic tunnel junction (MTJ) structure100and a selection device200.

The MTJ structure100may be connected between the bit line BL and the selection device200, and the selection device200may be connected between the MTJ structure100and the word line WL. The MTJ structure100may include a pinned layer110, a tunnel barrier layer130, a free layer structure120, and an upper oxide layer140. The MTJ structure100will be described in greater detail below.

In an implementation, a lower electrode90may be under (e.g., at one side of) the MTJ structure100, and an upper electrode190may be on (e.g., another side of) the MTJ structure100. In an implementation, the pinned layer110may be between the lower electrode90and the tunnel barrier layer130, and the free layer structure120may be between the tunnel barrier layer130and the upper electrode190.

The selection device200may selectively control a flow of charges passing through the MTJ structure100. In an implementation, the selection device200may include a diode, a PNP bipolar transistor, an NPN bipolar transistor, an NMOS FET (field effect transistor), or a PMOS FET. When the selection device200includes a three-terminal device such as a bipolar transistor or a MOS FET, an additional wiring may be connected to the selection device200. As used herein, the term “or” is not an exclusive term, e.g., “A or B” would include A, B, or A and B.

The MTJ structure100may serve as a variable resistance element that may have one of two resistance states according to an electrical signal applied thereto. In an implementation, when a magnetization direction of the pinned layer110and a magnetization direction of the free layer structure120are parallel, the MTJ structure100may have a low resistance, and the state may be referred to as data ‘0’. When the magnetization direction of the pinned layer110and the magnetization direction of the free layer structure120are anti-parallel, the MTJ structure100may have a high resistance, and the state may be referred to as data ‘1’.

FIG.4is a cross-sectional view of a MTJ structure in an MRAM device in accordance with example embodiments.FIGS.5A,5B, and5Care cross-sectional views, respectively, of a distribution of a doped magnetic material in a metal insertion layer of a free layer structure in accordance with example embodiments.

Referring toFIG.4, the MTJ100may include the pinned layer110, the tunnel barrier layer130, the free layer structure120, and the upper oxide layer140sequentially stacked.

The pinned layer110may have a fixed magnetization direction. In an implementation, the magnetization direction of the pinned layer110may be fixed, regardless of program currents passing through the pinned layer110. The pinned layer110may have perpendicular magnetic anisotropy (PMA). In an implementation, the pinned layer110may have a magnetization easy axis in a direction perpendicular to an upper surface of the pinned layer110.

The pinned layer110may include a ferromagnetic material. In an implementation, the pinned layer110may include, e.g., an amorphous rare earth element alloy, a multilayer in which a ferromagnetic metal (FM) and a non-magnetic metal (NM) are alternately stacked, a cobalt alloy, or combinations thereof. The amorphous rare earth element alloy may include, e.g., TbFe, TbCo, TbFeCo, DyTbFeCo, or GdTbCo. Layers included in the multilayer may include, e.g., Co/Pt, Co/Pd, CoCr/Pt, Co/Ru, Co/Os, Co/Au, Ni/Cu, or the like. The cobalt alloy may include, e.g., CoCr, CoPt, CoCrPt, CoCrTa, CoCrPtTa, CoCrNb, or CoFeB. In an implementation, the pinned layer110may include a CoFeB single layer.

The tunnel barrier layer130may be between the pinned layer110and the free layer structure120. The tunnel barrier layer130may serve as an insulated tunnel barrier for generating quantum mechanical tunneling between the pinned layer110and the free layer structure120.

The tunnel barrier layer130may include, e.g., magnesium oxide (MgO), aluminum oxide (Al2O3), silicon oxide (SiO2), tantalum oxide (Ta2O5), silicon nitride (SiN), aluminum nitride (AlN), or the like. In an implementation, the tunnel barrier layer130may include magnesium oxide.

The free layer structure120may include a plurality of magnetic layers122a,122b, and122c, and metal insertion layers124aand124bbetween the magnetic layers122a,122band122c. In an implementation, the magnetic layers and the metal insertion layers may be alternately disposed in the free layer structure120. The metal insertion layers124aand124bmay include a non-magnetic metal material doped with a magnetic material.

One or a plurality of metal insertion layers124aand124bmay be in the free layer structure120. In an implementation, a plurality of the metal insertion layers124aand124bmay be in the free layer structure120. Hereinafter, the free layer structure120including two metal insertion layers124aand124bwill be described.

In an implementation, as illustrated inFIG.4, the free layer structure120may include a first magnetic layer122a, a first metal insertion layer124a, a second magnetic layer122b, a second metal insertion layer124band a third magnetic layers122csequentially stacked.

The first and second magnetic layers122aand122bmay be separated from each other by the first metal insertion layer124a. In an implementation, the first metal insertion layer124amay be continuously on the first magnetic layer122a. The first metal insertion layer124amay cover (e.g., completely cover) the first magnetic layer122a.

The second and third magnetic layers122band122cmay be separated from each other by the second metal insertion layer124b. In an implementation, the second metal insertion layer124bmay be continuously on the second magnetic layer122b. The second metal insertion layer124bmay cover the second magnetic layer122b. In an implementation, the free layer structure120may include a plurality of metal insertion layers124aand124bspaced apart from each other.

The first to third magnetic layers122a,122band122cincluded in the free layer structure120may have perpendicular magnetic anisotropy (PMA). The first to third magnetic layers122a,122band122cmay include a ferromagnetic material. The first to third magnetic layers122a,122band122cmay include, e.g., iron (Fe), cobalt (Co), nickel (Ni), chromium (Cr), platinum (Pt), or the like. The first to third magnetic layers122a,122band122cmay include the ferromagnetic material, and may further include, e.g., boron (B), silicon (Si), or zirconium (Zr). The materials may be used alone or in combination of two or more. In an implementation, the first to third magnetic layers122a,122band122cmay include a composite material, e.g., CoFe, NiFe, FeCr, CoFeNi, PtCr, CoCrPt, CoFeB, NiFeSiB, or CoFeSiB. In an implementation, the first to third magnetic layers122a,122band122cmay include, e.g., CoFeB.

The non-magnetic metal material included in the first and second metal insertion layers124aand124bmay include, e.g., molybdenum, tungsten, tantalum, ruthenium, zirconium, niobium, yttrium, scandium, vanadium, chromium, tellurium, hafnium, or the like. In an implementation, the magnetic material doped into the non-magnetic metal material may include, e.g., iron (Fe), cobalt (Co), gadolinium (Gd) or nickel (Ni),. In an implementation, the first and second metal insertion layers124aand124bmay include, e.g., MoCoFe, WCoFe, TaCoFe, or the like. In an implementation, the first and second metal insertion layers124aand124bmay include, e.g., MoCoFe.

The metal insertion layers124aand124bmay be included in the free layer structure120, and deterioration of properties of the free layer structure120at a high temperature, e.g., of about 400° C. or more, may be decreased. If a high-temperature process at 400° C. or more is performed, oxygen or a crystalline material could be diffused from the upper oxide layer140to the magnetic layers122a,122band122cincluded in the free layer structure120. In an implementation, the diffusion of the oxygen or the crystalline material into the magnetic layers122aand122bmay be prevented by the metal insertion layers124aand124b, so that a resistance distribution and a current distribution caused by the oxygen or the crystalline material may be decreased. In an implementation, two or more metal insertion layers124aand124bspaced apart from each other may be included in the free layer structure120, and the free layer structure120may have an excellent heat endurance characteristic. In an implementation, the two or more metal insertion layers124aand124bmay be included in the free layer structure120, and the diffusion of the oxygen or the crystalline material into the magnetic layers122aand122bmay be more effectively prevented. In an implementation, the resistance distribution and the current distribution may be improved (i.e., decreased).

In an implementation, electron spins in the free layer structure120may be maintained and transferred by the magnetic material doped into the metal insertion layers124aand124b, so that currents flowing through the free layer structure120may be increased during an operation of the MRAM device. In an implementation, switching currents of the MRAM device may be decreased, and a spin transfer torque (STT) efficiency may be improved.

In an implementation, each of the metal insertion layers124aand124bincluded in the free layer structure120may have a thickness of about 2 Å to about 10 Å. In an implementation, each of the first and second metal insertion layers124aand124bmay have a thickness of about 2 Å to about 10 Å. If each of the metal insertion layers124aand124bwere to have a thickness smaller than 2 Å, it could be difficult to continuously form the metal insertion layers124aand124bon the magnetic layer, and it could be difficult to prevent the diffusion of the oxygen or the crystalline material by the metal insertion layers124aand124b. If each of the metal insertion layers124aand124bwere to have a thickness greater than 10 Å, a magnetic exchange coupling between one of the magnetic layers122a,122band122band one of the metal insertion layers124aand124badjacent thereto could be difficult.

In an implementation, the magnetic material doped into the metal insertion layers124aand124bmay have a concentration (e.g., content) of about 5% (i.e., atomic %) to about 40% (i.e., atomic %). In an implementation, the magnetic material included in each of the first and second metal insertion layers124aand124bmay have a concentration of about 5% to about 40%. If the magnetic material included in each of the metal insertion layers124aand124bwere to have a concentration lower than 5%, an improvement effect of the STT efficiency could be decreased. If the magnetic material included in each of the metal insertion layers124aand124bwere to have a concentration higher than 40%, improvement effects of the resistance distribution and the current distribution could be decreased. In an implementation, the magnetic material included in the metal insertion layers124aand124bmay have a concentration of about 20% (i.e., atomic %) to about 40% (i.e., atomic %).

The magnetic material doped into the metal insertion layers124aand124bmay be arranged in various forms.

In an implementation, as shown inFIG.5A, the magnetic materials125doped into the metal insertion layers124aand124bmay have a structure partially connected in a vertical direction. In an implementation, a portion of the doped magnetic materials125may be connected to adjacent magnetic layers122a,122band122c. Due to the doped magnetic material, the magnetic exchange coupling characteristics between one of the magnetic layers122a,122band122band one of the metal insertion layers124aand124badjacent thereto may be improved.

In an implementation, as shown inFIG.5B, the magnetic materials125doped into the metal insertion layers124aand124bmay have a structure connected to adjacent magnetic layers122a,122band122c. In an implementation, the metal insertion layers124aand124bmay include magnetic bridge patterns penetrating the non-magnetic metal layers. The magnetic material125doped into the metal insertion layers124aand124bmay be connected to the adjacent magnetic layers. Due to the doped magnetic material125, the magnetic exchange coupling characteristics between one the magnetic layers122a,122band122band one of the metal insertion layers124aand124badjacent thereto may be improved.

In an implementation, as shown inFIG.5C, the magnetic material125doped into the metal insertion layers124aand124bmay be randomly distributed.

In an implementation, a sum of thicknesses of the magnetic layers122a,122band122cincluded in the free layer structure120may be greater than a sum of thicknesses of the metal insertion layers124aand124bincluded in the free layer structure120.

The upper oxide layer140may include a material that induces interfacial magnetic anisotropy (interfacial PMA) at an interface of the third magnetic layer122c. The upper oxide layer140may include a metal oxide. When the upper oxide layer140includes a metal oxide, oxygen atoms included in the upper oxide layer140may combine with a metal atom included in the third magnetic layer122c. In an implementation, a perpendicular magnetic anisotropy may be generated at the interface of the third magnetic layer122c.

The upper oxide layer140may include, e.g., magnesium oxide (MgO), magnesium aluminum oxide (MgAlO), hafnium oxide (HfO), zirconium oxide (ZrO), aluminum oxide (AlO), tantalum oxide (TaO), iridium oxide (IrO), or combinations thereof.

In an implementation, the upper oxide layer140may have a thickness of about 2 Å to about 15 Å.

In an implementation, the free layer structure120may be formed using a PVD apparatus having a multi-chamber.

In order to form the free layer structure120, a process of forming a magnetic layer and a process of forming a metal insertion layer may be alternately performed. The process of forming the magnetic layer and the process of forming the metal insertion layer may be performed in different chambers of the PVD apparatus, and may be performed in situ without a vacuum break. In an implementation, defects between the magnetic layer and the metal insertion layer may be decreased.

The process of forming the magnetic layers122a,122band122cmay include a sputtering process using a target including a material of the magnetic layers.

The process of forming the metal insertion layers124aand124bmay include a sputtering process using a target including a material of the metal insertion layers. In an implementation, the target for forming the metal insertion layers124aand124bmay be an alloy target including a non-magnetic metal material doped with a magnetic material. In an implementation, a plurality of targets for forming the metal insertion layers124aand124bmay be used, and a target of a non-magnetic metal material and a target of a magnetic material may be used together.

In an implementation, the process of forming the free layer structure120may be performed at a temperature of about 5° C. to about 250° C.

FIGS.6A and6Bare diagrams for explaining an operation of an MRAM device in accordance with example embodiments.

Write currents may be applied to the MTJ structure100so that magnetization directions of the free layer structure120and the pinned layer110may be a parallel state.

In an implementation, as shown inFIG.6A, in a state in which the magnetization directions of the free layer structure120and the pinned layer110are antiparallel, electrons (e−) may flow in a direction toward the free layer structure120from the pinned layer110. In an implementation, as shown inFIG.6B, the magnetization direction of the free layer structure120may be reversed by the spin transfer torque STT induced from the pinned layer110.

In an implementation, the magnetization directions of the first to third magnetic layers122a,122band122cmay be reversed by the spin transfer torque induced from the pinned layer110. The spin transfer torque may be maintained by the first and second metal insertion layers124aand124bbetween the first to third magnetic layers122a,122band122c, and thus the magnetization directions of the first to third magnetic layers122a,122band122cmay be easily reversed. In an implementation, operating currents applied to the MTJ structure100may be decreased, and the MRAM device may be operated by low operating currents.

In an implementation, the metal insertion layers124aand124bmay be included in the free layer structure120, and a thermal stability of the free layer structure120may be improved. In an implementation, the resistance distribution of the free layer structure120and a distribution of currents flowing through the free layer structure120may be decreased during an operation of the MRAM device.

In an implementation, the upper oxide layer140may be on the third magnetic layer122cin the free layer structure120, and the free layer structure120may have sufficient perpendicular magnetic anisotropy.

Hereinafter, a MTJ structure having various stacked structures may be described. For convenience of description, parts described with reference toFIGS.3to6Bmay be briefly described or omitted.

FIG.7is a cross-sectional view of an MTJ structure in an MRAM device in accordance with example embodiments.

Referring toFIG.7, the pinned layer110in the MTJ structure may include a lower magnetic layer112, a non-magnetic layer114, and an upper magnetic layer116, for forming a synthetic anti-ferromagnetic (SAF) substance.

The synthetic antiferromagnetic (SAF) substance or material may have anti-ferromagnetic coupling (AFC) characteristics due to, e.g., a RKKY (Ruderman-Kittel-Kasuya-Yosida) interaction. In an implementation, the magnetization directions of the lower magnetic layer112and the upper magnetic layer116may be anti-parallel, so that a total magnetization amount of the pinned layer110may be minimized. Each of the lower magnetic layer112and the upper magnetic layer116may have a fixed magnetization direction.

The lower magnetic layer112and the upper magnetic layer116may include a ferromagnetic material. In an implementation, each of the lower magnetic layer112and the upper magnetic layer116may include amorphous rare earth element alloy, a multilayer in which a ferromagnetic metal (FM) and a non-magnetic metal (NM) are alternately stacked, a cobalt alloy, or a combination thereof. The non-magnetic layer114may be between the lower magnetic layer112and the upper magnetic layer116. The non-magnetic layer114may include, e.g., ruthenium (Ru), chromium (Cr), platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), osmium (Os), rhenium (Re), gold (Au), copper (Cu), or a combination thereof.

FIG.8is a cross-sectional view of an MTJ structure in an MRAM device in accordance with example embodiments.

Referring toFIG.8, the MTJ structure may further include a seed layer150under the pinned layer110.

The perpendicular magnetic anisotropy of the pinned layer110may be enhanced by the seed layer150. In an implementation, the magnetization direction of the pinned layer110may be fixed. The seed layer150may include, e.g., tantalum (Ta), ruthenium (Ru), titanium (Ti), palladium (Pd), platinum (Pt), magnesium (Mg), aluminum (Al), or combinations thereof.

FIG.9is a cross-sectional view of an MTJ structure in an MRAM device in accordance with example embodiments.

Referring toFIG.9, a polarization enhancement layer160may be further included between the tunnel barrier layer130and the free layer structure120. The polarization enhancement layer160may increase a spin polarization of the free layer structure120. A magnetization direction of the polarization enhancement layer160may be parallel to the magnetization direction of the upper magnetic layer116in the pinned layer110. The polarization enhancement layer160may include a ferromagnetic material. The polarization enhancement layer160may include a material having a high spin polarization rate and a low damping constant. In an implementation, the polarization enhancement layer160may include, e.g., cobalt (Co), nickel (Ni), iron (Fe), or a combination thereof.

FIG.10is a cross-sectional view of an MTJ structure in an MRAM device in accordance with example embodiments.

Referring toFIG.10, the MRAM device may further include an amorphous layer170between the tunnel barrier layer130and the pinned layer110. The amorphous layer170may help prevent a diffusion of materials constituting the pinned layer110, so that the tunnel barrier layer130may be protected. In an implementation, the upper magnetic layer116included in the pinned layer110may include a crystalline material of, e.g., cobalt (Co) or a cobalt (Co) alloy, and the amorphous layer170may include a CoFeB amorphous material.

FIG.11is a cross-sectional view of an MRAM device in accordance with example embodiments.

Referring toFIG.11, the MRAM device may include a substrate10, a selection device, and an MTJ structure100.

An isolation pattern11may be in a trench of a substrate10, and the substrate10may be divided into an active region and a field region by the isolation pattern.

The selection device may be a MOSFET, a diode, or a bipolar transistor. In an implementation, as shown inFIG.11, the selection device may be the MOSFET. The selection device may include a source region13, a drain region12, a gate electrode2,2and a gate insulation layer21. The gate electrode22may extend in one direction, and may serve as a word line.

A first insulating interlayer20may be on the substrate10to cover the selection device. A first contact plug23may pass through the first insulating interlayer20, and may be electrically connected to the source region13. In addition, a second contact plug24may pass through the first insulating interlayer20, and may be electrically connected to the drain region12.

A source line26may be formed on the first insulating interlayer20and the first contact plug23.

A second insulating interlayer30may be formed on the first insulating interlayer20, the second contact plug24and the source line26. A lower electrode contact32may pass through the second insulating interlayer30, and may be electrically connected to the second contact plug24.

A lower electrode90, an MTJ structure100, and an upper electrode190may be on the lower electrode contact32. In an implementation, the MTJ structure100may be any one of the embodiments described with reference toFIGS.3to10.

A third insulating interlayer40may be on the second insulating interlayer30to cover the lower electrode90, the MTJ structure100and the upper electrode190. An upper electrode contact42may pass through the third insulating interlayer40, and may be electrically connected to the upper electrode190. A bit line50may be on the third insulating interlayer40and the upper electrode contact42. The bit line50may be electrically connected to the MTJ structure100via, e.g., the upper electrode contact42.

By way of summation and review, a memory device may be an STT-magnetic memory device that stores data using a spin transfer torque (STT) phenomenon. The STT-MRAM may have improved resistance distribution, improved current distribution and low operating power.

One or more embodiments may provide a spin-transfer torque-MRAM (STT-MRAM).

The MRAM device in accordance with example embodiments may be used as a memory device included in electronic products such as a mobile device, a memory card, or a computer.

One or more embodiments may provide an MRAM device having good characteristics.

In the MRAM device, a resistance distribution and a current distribution may be improved. Further, in the MRAM device, switching currents may be reduced, and a STT efficiency may be improved.

Example embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. In some instances, as would be apparent to one of ordinary skill in the art as of the filing of the present application, features, characteristics, and/or elements described in connection with a particular embodiment may be used singly or in combination with features, characteristics, and/or elements described in connection with other embodiments unless otherwise specifically indicated. Accordingly, it will be understood by those of skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.