Spin-momentum transfer between a spin-polarized current and a ferromagnetic layer can induce steady-state magnetization precession, and has recently been proposed as a working principle for ubiquitous radio-frequency devices for radar and telecommunication applications. However, so far, the development of industrially attractive prototypes has been hampered by the inability to identify systems that can provide enough power. Here, we demonstrate that microwave signals with device-compatible output power levels can be generated from a single magnetic tunnel junction with a lateral size of 100 nm, seven orders of magnitude smaller than conventional radio-frequency oscillators. We find that in MgO magnetic tunnel junctions the perpendicular torque induced by the spin-polarized current on the local magnetization can reach 25% of the in-plane spin-torque term, although showing a different bias dependence. Both findings contrast with the results obtained on all-metallic structures, previously investigated, reflecting the fundamentally different transport mechanisms in the two types of structure. Improvements in the microwave output efficiency of MgO-based magnetic tunnel junctions brings them a step closer to practical applications and enables greater insight into the physics of spin transfer in such devices.

Bias-driven high-power microwave emission from MgO-based tunnel magnetoresistance devices

A large tunnel magnetoresistance (TMR) ratio of 753% has been observed at 2 K in a magnetic tunnel junction (MTJ) using a Co2MnSi Heusler alloy electrode and a crystalline MgO tunnel barrier. This TMR ratio is the largest reported to date in MTJs using a Heusler alloy electrode. Moreover, we have observed a large TMR ratio of 217% at room temperature (RT). This TMR at RT is much larger than that of MTJs using an amorphous Al-oxide tunnel barrier. However, the temperature dependence of the TMR ratio is still large because of inelastic tunneling in the antiparallel magnetic configuration.

Large tunnel magnetoresistance in magnetic tunnel junctions using a Co2MnSi Heusler alloy electrode and a MgO barrier

A magnetic cell core includes a seed region with a plurality of magnetic regions and a plurality of nonmagnetic regions thereover. The seed region provides a template that enables formation of an overlying nonmagnetic region with a microstructure that enables formation of an overlying free region with a desired crystal structure. The free region is disposed between two nonmagnetic regions, which may both be configured to induce surface/interface magnetic anisotropy. The structure is therefore configured to have a high magnetic anisotropy strength, a high energy barrier ratio, high tunnel magnetoresistance, a low programming current, low cell-to-cell electrical resistance variation, and low cell-to-cell variation in magnetic properties. Methods of fabrication, memory arrays, memory systems, and electronic systems are also disclosed.

Memory cells, methods of fabrication, semiconductor devices, memory systems, and electronic systems

A magnetic cell includes an attracter material proximate to a magnetic region (e.g., a free region). The attracter material is formulated to have a higher chemical affinity for a diffusible species of a magnetic material, from which the magnetic region is formed, compared to a chemical affinity between the diffusible species and at least another species of the magnetic material. Thus, the diffusible species is removed from the magnetic material to the attracter material. The removal accommodates crystallization of the depleted magnetic material. The crystallized, depleted magnetic material enables a high tunnel magnetoresistance, high energy barrier, and high energy barrier ratio. The magnetic region may be formed as a continuous magnetic material, thus enabling a high exchange stiffness, and positioning the magnetic region between two magnetic anisotropy inducing oxide regions enables a high magnetic anisotropy strength. Methods of fabrication and semiconductor devices are also disclosed.

Memory cells, methods of fabrication, and semiconductor devices

A magnetic cell includes a magnetic region formed from a precursor magnetic material comprising a diffusive species and at least one other species. An amorphous region is proximate to the magnetic region and is formed from a precursor trap material comprising at least one attracter species having at least one trap site and a chemical affinity for the diffusive species. The diffusive species is transferred from the precursor magnetic material to the precursor trap material where it bonds to the at least one attracter species at the trap sites. The species of the enriched trap material may intermix such that the enriched trap material becomes or stays amorphous. The depleted magnetic material may then be crystallized through propagation from a neighboring crystalline material without interference from the amorphous, enriched trap material. This enables high tunnel magnetoresistance and high magnetic anisotropy strength. Methods of fabrication and semiconductor devices are also disclosed.

Memory cells, semiconductor structures, semiconductor devices, and methods of fabrication

Dependence on annealing temperatures of tunneling spectra in high-resistance CoFeB/MgO/CoFeB magnetic tunnel junctions

We present a reliable magnetic tunnel junction (MTJ) TDDB model using 40Mb 22FDX® STT-MRAM at sub-PPM failure rate. This model is based on the precise estimation of voltage across MTJ at bit-cell level derived from compact model and design simulations to cover the product level endurance performance from MTJ diameter, resistance-area product, and temperature effects. We discuss the implications of pre/post MTJ switching, circuit variations and write pulse on MRAM endurance. By using design-process-test co-optimization, we show robust MRAM product reliability to meet >1M cycles with solder reflows and path towards achieving >E12 cycles for cache applications.

Extended MTJ TDDB Model, and Improved STT-MRAM Reliability With Reduced Circuit and Process Variabilities

Embedded STT-MRAM has emerged to high-volume ramp stage. To sustain yield and to guarantee reliable operation of the memory arrays, a solid line of defense strategy is required. The unprecedented complexity of the MTJ, acting as the memory element in this new technology, can be compensated by an equally unprecedented reservoir of versatile characterization methodologies allowing for the prediction of yield and reliability critical properties of the final memory cell. To enhance the turnaround time of tool monitoring and to enable fast film level and patterned MTJ metrology, the transition of classical lab-based methodologies, such as perpendicular magneto-optical Kerr effect, current-in-plane tunneling and ferromagnetic resonance, to full on-chip capability is essential. The complementary use of these magneto-electrical and magneto-optical techniques for drift partitioning as well as their correlation to the final wafer electrical test and reliability are key for establishing a strong line of defense.

Yuichi Otani

Papers

Dependence on annealing temperatures of tunneling spectra in high-resistance CoFeB/MgO/CoFeB magnetic tunnel junctions

Extended MTJ TDDB Model, and Improved STT-MRAM Reliability With Reduced Circuit and Process Variabilities

From Emergence to Prevalence: 22FDX® Embedded STT-MRAM