US-12620426-B2 - Deterministic voltage-controlled magnetic anisotropy (VCMA) MRAM with spin-transfer torque (STT) MRAM assistance

Abstract

An approach for providing a semiconductor structure for a stacked magnetoresistive random-access memory (MRAM) device that includes a first magnetic tunnel junction on a bottom electrode and at least one second magnetic tunnel junction above the first magnetic tunnel junction. The semiconductor structure includes the first magnetic tunnel junction is a voltage-controlled magnetic anisotropy (VCMA) magnetic tunnel junction of a voltage-controlled magnetic anisotropy (VCMA) MRAM device. The VCMA-MRAM device is composed of a first reference layer, a first tunnel barrier layer, and a first free layer. The semiconductor structure includes the second magnetic tunnel junction that is a spin-transfer torque (STT) magnetic tunnel junction of a STT-MRAM device. The STT-MRAM device is composed of a second reference layer, a second tunnel barrier layer, and a second free layer where the STT magnetic tunnel junction has a smaller cross-sectional area than the VCMA magnetic tunnel junction (MTJ).

Inventors

• Heng Wu
• Julien Frougier
• Ruilong Xie
• Kangguo Cheng
• Dimitri Houssameddine

Assignees

• INTERNATIONAL BUSINESS MACHINES CORPORATION

Dates

Publication Date

20260505

Application Date

20220321

Claims (18)

1. 1 . A semiconductor structure comprising: a first magnetic tunnel junction on a bottom electrode; and a second magnetic tunnel junction above the first magnetic tunnel junction, wherein: a reference layer of the second magnetic tunnel junction contacts a free layer of the first magnetic tunnel junction; and the first magnetic tunnel junction has a larger cross-sectional area than the second magnetic tunnel junction.
2. 2 . The semiconductor structure of claim 1 , wherein the first magnetic tunnel junction is a voltage-controlled magnetic anisotropy (VCMA) magnetic tunnel junction of a VCMA-MRAM device that is composed of a first reference layer, a first tunnel barrier layer, and a first free layer.
3. 3 . The semiconductor structure of claim 2 , wherein the second magnetic tunnel junction is a spin-transfer torque (STT) magnetic tunnel junction of an STT-MRAM device that is composed of a second reference layer, a second tunnel barrier layer, and a second free layer.
4. 4 . The semiconductor structure of claim 3 , wherein a stray field generated by magnetization of the second free layer of the second magnetic tunnel junction aligns a magnetization of the first free layer of the VCMA-MRAM device with the second free layer of the STT-MRAM.
5. 5 . The semiconductor structure of claim 3 , wherein an etch stop layer is over the first free layer of the VCMA-MRAM device.
6. 6 . The semiconductor structure of claim 3 , wherein the second magnetic tunnel junction of the STT-MRAM is surrounded by a sidewall spacer.
7. 7 . The semiconductor structure of claim 6 , wherein a dielectric material encapsulates vertical sides of the sidewall spacer around the second magnetic tunnel junction of the STT-MRAM and the first magnetic tunnel junction of the VCMA-MRAM.
8. 8 . The semiconductor structure of claim 1 , wherein the first magnetic tunnel junction is a spin-transfer torque (STT) magnetic tunnel junction of an STT-MRAM and the second magnetic tunnel junction is a voltage-controlled magnetic (VCMA) tunnel junction of a VCMA-MRAM.
9. 9 . The semiconductor structure of claim 8 , wherein the STT magnetic tunnel junction of the STT-MRAM has a smaller cross-sectional area than the second magnetic tunnel junction of the VCMA tunnel junction of the VCMA-MRAM.
10. 10 . The semiconductor structure of claim 3 , wherein a second STT magnetic tunnel junction of the STT-MRAM device is tuned to ensure that a Resistance-Area product of the second tunnel barrier layer of the STT magnetic tunnel junction is less than a Resistance-Area product of a first VCMA magnetic tunnel junction of the VCMA-MRAM.
11. 11 . The semiconductor structure of claim 1 , further comprising: a hardmask over the second magnetic tunnel junction; and a top electrode over the hardmask.
12. 12 . The semiconductor structure of claim 1 , wherein a width of a hardmask on the second magnetic tunnel junction corresponds to a width of the second magnetic tunnel junction.
13. 13 . A method comprising: performing a write operation by applying a single voltage pulse to a stacked magnetoresistive random-access memory (MRAM) device, wherein the stacked MRAM device is composed of: a bottom voltage-controlled magnetic anisotropy (VCMA) MRAM device; and a top spin-transfer torque (STT) MRAM device with a smaller width than the VCMA-MRAM device.
14. 14 . The method of claim 13 , wherein the single voltage pulse switches the top STT-MRAM and a stray field of the top STT-MRAM switches the bottom VCMA-MRAM to match a magnetization of the top STT-MRAM.
15. 15 . A method comprising: performing a write operation by applying current to switch a top spin-transfer torque (STT) magnetoresistive random-access memory (MRAM) device that is over a bottom voltage-controlled magnetic anisotropy (VCMA) MRAM device to switch the top STT-MRAM device; and applying a voltage across a top electrode and a bottom electrode.
16. 16 . The method of claim 15 , wherein the voltage lowers an energy barrier of the VCMA-MRAM device.
17. 17 . The method of claim 16 , wherein a stray field of the top STT-MRAM device switches the VCMA-MRAM device.
18. 18 . The method of claim 17 , wherein a first free layer of the VCMA-MRAM device has a same direction as a second free layer of the STT VCMA device.

Description

BACKGROUND OF THE INVENTION The present invention relates generally to the field of semiconductor memory device technology and more particularly to stacked magnetoresistive random-access memory devices using spin-transfer torque and voltage-controlled magnetic anisotropy. A magnetic tunnel junction (MTJ) device, which is a primary storage element in a magnetic random-access memory (MRAM), is a magnetic storage and switching device in which two ferromagnetic layers are separated by a thin insulating barrier (e.g., magnesium oxide) to form a stacked structure. One of the ferromagnetic layers has a magnetization that is fixed, and it is therefore referred to as a pinned layer or reference layer. However, the other ferromagnetic layer has a magnetization that can change, and it is therefore referred to as a free layer. When a bias is applied to the MTJ device, electrons that are spin-polarized by the ferromagnetic layers traverse the insulating barrier through a process known as quantum tunneling to generate an electric current whose magnitude depends on an orientation of the magnetization of the ferromagnetic layers. The MTJ device will exhibit a low resistance when a magnetic moment of the free layer is parallel to the fixed layer magnetic moment, and it will exhibit a high resistance when the magnetic moment of the free layer is oriented antiparallel to the fixed layer magnetic moment. In via spin-transfer-torque (STT)-MRAM devices, a Magnetic-Tunnel-Junction (MTJ) is formed by having magnetic (e.g., ferromagnetic) layers separated by an intermediary non-magnetic tunnel barrier layer. During operation, the magnetization orientation in the free layer of the MTJ is flipped using a spin-polarized electronic current via Spin-Transfer-Torque (STT) mechanism. The spin-polarization of the electronic current is generated by flowing the electrons though the magnetic reference layer exhibiting a fixed magnetization orientation. This spin-polarized electronic current subsequently flows through a magnetic free layer which changes the free layer orientation of its magnetization through the transfer of the spin angular momentum via the spin-transfer-torque mechanism. A new approach to magnetic switching is evolving using voltage-controlled magnetic anisotropy. Voltage-controlled magnetic anisotropy (VCMA), which is generally observed at the interface between ultrathin 3d transition ferromagnetic metals (e.g., Fe, CoFeB) and nonmagnetic insulators (e.g., MgO, Al2O3), has emerged for use in MRAM devices. The discovery of the VCMA effect enables using a voltage or an electric field for switching an MTJ device. The utilization of a voltage instead of a charge current for writing data into an MTJ allows for much lower energy dissipation, as Ohmic loss or Joule heating can be greatly reduced. Furthermore, the VCMA effect enables fast, precessional switching of an MTJ by lowering the energy barrier between the two magnetization states of the MTJ. Based on this effect, a new generation of MRAM has emerged as VCMA-MRAM, which utilizes the VCMA effect to write or to assist STT to write data information into a magnetic tunnel junction (MTJ). SUMMARY Embodiments of the present invention provide a semiconductor structure for stacked magnetoresistive random-access memory (MRAM) device that includes a first magnetic tunnel junction on a bottom electrode and at least one second magnetic tunnel junction that is above the first magnetic tunnel junction. Embodiments of the present invention disclose that the first magnetic tunnel junction is a voltage-controlled magnetic anisotropy (VCMA) magnetic tunnel junction of a voltage-controlled magnetic anisotropy (VCMA) MRAM device. The VCMA-MRAM device is composed of a first reference layer, a first tunnel barrier layer, and a first free layer. Embodiments of the present invention include a semiconductor structure where the at least one second magnetic tunnel junction is a spin-transfer torque (STT) magnetic tunnel junction of a STT-MRAM device. The STT-MRAM device is composed of a second reference layer, a second tunnel barrier layer, and a second free layer where the STT magnetic tunnel junction has a smaller cross-sectional area than the VCMA magnetic tunnel junction (MTJ). Embodiments of the present invention provide a method of performing a write operation on a stacked magnetoresistive random-access memory (MRAM) device composed of a bottom voltage-controlled magnetic anisotropy (VCMA) MRAM device and STT MRAM device where the STT MRAM device has a smaller cross-sectional area than the VCMA-MRAM device. Embodiments of the present invention include the method where the voltage applied on the VCMA-MRAM modulates the magnetic anisotropy of the VCMA-MTJ free layer effectively leading to a reduction of the energy barrier of the VCMA-MRAM device. In embodiments of the present invention, the STT-MRAM device switches due a smaller critical switching voltage (Vc) of the STT-MRAM device compared to th