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![(a) Schematic of a PMA-MTJ STT-MRAM cell, indicating the logic states of the device with the corresponding resistance levels. (b) Memory cells are written by switching the magnetization of the free layer (top) using STT from spin polarized current. [0] or [1] logic states can be written by simply reversing the current polarity. (c) Perpendicular magnetic anisotropy creates the energy barrier between the two orientations of the free layer's magnetization.](profile/Kenlin-Huang/publication/264595334/figure/fig3/AS:324775110037516@1454443828548/a-Schematic-of-a-PMA-MTJ-STT-MRAM-cell-indicating-the-logic-states-of-the-device-with.png)
(a) Schematic of a PMA-MTJ STT-MRAM cell, indicating the logic states of the device with the corresponding resistance levels. (b) Memory cells are written by switching the magnetization of the free layer (top) using STT from spin polarized current. [0] or [1] logic states can be written by simply reversing the current polarity. (c) Perpendicular magnetic anisotropy creates the energy barrier between the two orientations of the free layer's magnetization.
Source publication
Magnetic random access memories based on the spin transfer torque phenomenon (STT-MRAMs) have become one of the leading candidates for next generation memory applications. Among the many attractive features of this technology are its potential for high speed and endurance, read signal margin, low power consumption, scalability, and non-volatility....
Contexts in source publication
Context 1
... on magnetic tunnel junctions (MTJs) comprising two ferromagnetic electrodes separated by a thin tunnel barrier. Owing to the tunnel magnetoresistance (TMR) phenomenon, 3 parallel and antiparallel alignment of the ferromagnetic electrodes of the MTJs give rise to low or high resistance states corresponding to 0 or 1 logic states, respectively ( Fig. 1(a)). The read signal, hence the speed at which the bits can be read, depends on the TMR ratio. While the TMR ratio was limited to about 70% at room temperature in earlier MTJs based on amorphous Aluminum oxide barriers, tremendous improvement has followed the 2004 discovery of TMR through crystalline MgO tunnel barrier. 4,5 Values ...Context 2
... that MRAM cells could be written by spin transfer torque (STT) from spin-polarized electrical current 10,11 instead of a magnetic field rekindled the interest in MRAM technology. [12][13][14][15] Indeed, contrary to Field MRAMs, the same bit lines can be used to read and write STT-MRAM cells by simply driving current directly through the cell ( Fig. 1(b)). This allows for much simpler design, Author to whom correspondence should be addressed. Electronic mail: luc.thomas@headway.com. denser layout, improved scalability, and power consumption. The latest development of in-plane STT-MRAMs was reported recently by Everspin Technologies, which has demonstrated a fully functional 64 Mb ...Context 3
... nonvolatility using conventional magnetic materials magnetized in the plane of the MTJ. Non-volatility requires the orientation of the magnetic electrodes to be stable against thermal fluctuations. Thermal stability is determined by the energy barrier E B separating the two stable orientations of the magnetization of the free layer of the MTJ (Fig. 1(c)). Although the requirement depends significantly on chip design and applications, values larger than 55 k B T (k B ¼ 1.38 e À16 erg/K is the Boltzmann constant and T ¼ 300 K at room temperature) are needed to guarantee data retention for 10 yr. 17,18 E B is the product of the magnetic anisotropy of the free layer and an activation ...Context 4
... now turn to the writing performance our PMA-MTJ devices. Fig. 10 shows the results of a write error test performed on a 45-nm diameter device as a function of the write pulse current for pulse lengths between 2 and 8 ns. No external field is applied in this experiment. The device can be switched reliably with 2 ns pulses. Write error rate smaller than 10 À6 is achieved for pulses as short as 4 ns, ...Similar publications
In this work we perform investigations of the competition between domain-wall pinning and attraction by anti-notches and finite device borders. The conditions for optimal geometries, which can attain a stable domain-wall pinning, are presented. This allow us the proposition of a three-terminals device based on domain-wall pinning. We obtain, with v...
Spin-transfer torque magnetic random access memory (STT-MRAM) is currently explored to challenge the dynamic random access memory and embedded memory applications. Perpendicular magnetic tunnel junction (p-MTJ) stacks used in the STT-MRAM must be compatible with CMOS back-end-of-line processing, such as high perpendicular magnetic anisotropy, high...
In this work, we perform investigations of the competition between domain-wall pinning and attraction by antinotches and finite device borders. The conditions for optimal geometries, which can attain a stable domain-wall pinning, are presented. This allows the proposition of a three-terminal device based on domain-wall pinning. We obtain, with very...
Research explorations in new devices, new architectures
and algorithms are being performed to reduce leakage
power dissipation. As a solution to reduce the leakage power in
CMOS based designs, Magnetic Tunnel Junction (MTJ) devices
are being investigated to design MTJ/CMOS Logic-In-Memory
(LIM) circuits. The MTJ/CMOS circuits have advantages such
a...
Citations
... Slonczewski and Berger [1][2][3][4] proposed a mechanism of excitation and switching in magnetic nanostructures based on spin-transfer-torques (STT), which was demonstrated experimentally [5,6] and found wide use in magnetic random access memory (MRAM). STT-based MRAM has become a successful technology, offering fast, non-volatile, radiation and thermally hard (can operate at up to 400 • C) data storage in various industrial applications such as mobile, automotive, military, space [7][8][9]. ...
We investigate the switching of a magnetic nanoparticle comprising the middle free layer of a memory cell based on a double magnetic tunnel junction under the combined effect of spin-polarized current and weak on-chip magnetic field. We obtain the timing and amplitude parameters for the current and field pulses needed to achieve 100 ps range
inertia-free
switching under
least-power
dissipation. The considered method does not rely on the stochastics of thermal agitation of the magnetic nanoparticle typically accompanying spin-torque switching. The regime of ultimate switching speed-efficiency found in this work is promising for applications in high-performance nonvolatile memory.
... Furthermore, the PMA related SOT driven devices also need to satisfy the following requirements to fulfill the spin logic device applications: [20][21][22][23] (i) the critical switching current density Jc should be low to ensure low power consumption; (ii) the thermal stability should be high to guarantee data retention; and (iii) the stack should sustain significant processing thermal budgets ARTICLE pubs.aip.org/aip/apm (∼400 ○ C) to be compatible with the back-end-of-line processing in a complementary metal-oxide-semiconductor (CMOS) integration technique. ...
... (∼400 ○ C) to be compatible with the back-end-of-line processing in a complementary metal-oxide-semiconductor (CMOS) integration technique. 21,22 Generally, the thermal stability of a magnetic device is determined by the energy barrier (E b ) separating the two stable orientations of its magnetization. The thermal stability factor Δ (=E b /k B T, where k B is the Boltzmann constant and T = 300 K) larger than 55 is needed to guarantee data retention for 10 years. ...
... The thermal stability factor Δ (=E b /k B T, where k B is the Boltzmann constant and T = 300 K) larger than 55 is needed to guarantee data retention for 10 years. 22 Recently, we have reported that the PMA in the W/CoFeB/Zr/MgO multilayer by inserting a very thin Zr layer (about 0.43 nm) is robust upon annealing at 600 ○ C, 23 which can well meet the requirement for integrating SOT devices with CMOS. ...
We demonstrate the spin–orbit torque (SOT) induced perpendicular magnetization switching in an annealed W/CoFeB/Zr/MgO multilayer with high thermal stability. It is found that the thermal stability factor can reach 79 after annealing at 540 °C. With an increase in the annealing temperature, the absolute damping-like efficiency almost keeps a high constant value (about 0.3). The tungsten in the W/CoFeB/Zr/MgO multilayer could convert from the high resistive β-W to a mediate resistive amorphous-like structure. Therefore, the absolute spin Hall conductance increases from 765 of β-W to 1420 (ℏ/e)(Ω cm)−1 of the amorphous-like tungsten. These results pave a realistic way for the practical application of tungsten in the SOT-based spintronics devices with high thermal stability and SOT efficiency.
... However, the annealing temperature (T ann ) must not be excessive such that it causes atomic intermixing between the layers, which diminishes the TMR. Furthermore, for MTJs to be used in practical MRAM applications, they must maintain their characteristics at T ann values above 400 • C, the range in which complementary metal-oxide-semiconductor (CMOS) backend integration takes place [21][22][23]. ...
This study investigates the effects of annealing on the tunnel magnetoresistance (TMR) ratio in CoFeB/MgO/CoFeB-based magnetic tunnel junctions (MTJs) with different capping layers and correlates them with microstructural changes. It is found that the capping layer plays an important role in determining the maximum TMR ratio and the corresponding annealing temperature (Tann). For a Pt capping layer, the TMR reaches ~95% at a Tann of 350 °C, then decreases upon a further increase in Tann. A microstructural analysis reveals that the low TMR is due to severe intermixing in the Pt/CoFeB layers. On the other hand, when introducing a Ta capping layer with suppressed diffusion into the CoFeB layer, the TMR continues to increase with Tann up to 400 °C, reaching ~250%. Our findings indicate that the proper selection of a capping layer can increase the annealing temperature of MTJs so that it becomes compatible with the complementary metal-oxide-semiconductor backend process.
... A TMR of around 100% is measured associated with a sharp reversal of the magnetisation when sweeping the magnetic field ( Figure 1b, 150 nm diameter MTJ). The voltage dependence of the anisotropy field can be extracted from the switching probability vs magnetic field at different bias voltages 45,46 (see Figure 1c, Figure 1d). The linear dependence of the coercive and anisotropy fields on bias voltage (Figure 1d Operando STXM magnetic microscopy of MTJ To unambiguously demonstrate the skyrmion electrical detection and nucleation in the MTJ, it is essential to be able to simultaneously observe the free layer magnetisation and measure the MTJ resistance. ...
... The voltage control of magnetic anisotropy (VCMA) effect in the MTJ was characterized using two different experiments. Firstly, from the voltage dependence of the out-of-plane magnetic field (Hz) switching probability (see Figure 1c of the main text) 45,46 . To this end, the probability curves were measured for different voltages, and were fitted with the following distribution 45,46 : ...
... Firstly, from the voltage dependence of the out-of-plane magnetic field (Hz) switching probability (see Figure 1c of the main text) 45,46 . To this end, the probability curves were measured for different voltages, and were fitted with the following distribution 45,46 : ...
Magnetic skyrmions are topological spin textures which are envisioned as nanometre scale information carriers in magnetic memory and logic devices. The recent demonstration of room temperature stabilization of skyrmions and their current induced manipulation in industry compatible ultrathin films were first steps towards the realisation of such devices. However, important challenges remain regarding the electrical detection and the low-power nucleation of skyrmions, which are required for the read and write operations. Here, we demonstrate, using operando magnetic microscopy experiments, the electrical detection of a single magnetic skyrmion in a magnetic tunnel junction (MTJ) and its nucleation and annihilation by gate voltage via voltage control of magnetic anisotropy. The nucleated skyrmion can be further manipulated by both gate voltage and external magnetic field, leading to tunable intermediate resistance states. Our results unambiguously demonstrate the readout and voltage controlled write operations in a single MTJ device, which is a major milestone for low power skyrmion based technologies.
... It is necessary to compare the for the sake of understanding the electrical switching properties more comprehensively, since the energy barrier and switching current density are relative to it. As shown in Fig. 3(a), the of the SOMP-MTJ is estimated to be 128 by fitting the switching probability (P SW ) vs. magnetic field (H ) curve [25]. In addition, the statistical of the SOMP-MTJs has more concentrated distribution with higher average value than that of the NSOMP-MTJs, as is shown in Fig. 3 (b). ...
We investigate the magnetic and electric transport performance of the spin-orbit torque magnetic tunnel junction (SOT-MTJ) with perpendicular magnetic anisotropy (PMA) by stop-on-MgO etching process. This process etches away the hard mask (HM), synthetic antiferromagnetic layer (SAF) and reference layer (RL) while keeping the MgO barrier layer and free layer (FL) retained. Compared with the SOT-MTJ without stop-on-MgO etching process, the SOT-MTJ with stop-on-MgO etching process exhibits nearly zero offset field (
H<sub>off</sub>
) and lower critical switching current density (
J<sub>c</sub>
) with higher thermal stability factor (Δ). Although the magnetic property of the FL underneath the MgO is retained, the switching speed can still reach as fast as 1 ns. Furthermore, the SOT-MTJ with stop-on-MgO etching process presents much more concentrated distribution of the statistical coercivity (
H<sub>c</sub>
), tunneling magnetoresistance (TMR),
H<sub>off</sub>
, Δ, and
J<sub>c</sub>
. The resistance-based MTJ yield can raise up to 100%, which is advantageous in the high-speed and large-scale memory application.
... Spin current injected into a ferromagnetic material produces a spin-transfer torque (STT) [148], which is essential for low-power manipulation of magnetization in spintronic devices, such as magnetic random-access memory, racetrack memory, and logic circuit [149][150][151][152][153][154]. Recently, many studies have been reported on the STT of spin currents generated by the spin Hall effect [155][156][157][158][159] and the Rashba-Edelstein effect [160][161][162], where momentum locking due to spin-orbit coupling (SOC) plays a significant role in the spin-current generation [163]. ...
The discovery of atomic monolayer magnetic materials has stimulated intense research activities in the two-dimensional (2D) van der Waals (vdW) materials community. The field is growing rapidly and there has been a large class of 2D vdW magnetic compounds with unique properties, which provides an ideal platform to study magnetism in the atomically thin limit. In parallel, based on tunneling magnetoresistance and magneto-optical effect in 2D vdW magnets and their heterostructures, emerging concepts of spintronic and optoelectronic applications such as spin tunnel field-effect transistors and spin-filtering devices are explored. While the magnetic ground state has been extensively investigated, reliable characterization and control of spin dynamics play a crucial role in designing ultrafast spintronic devices. Ferromagnetic resonance (FMR) allows direct measurements of magnetic excitations, which provides insight into the key parameters of magnetic properties such as exchange interaction, magnetic anisotropy, gyromagnetic ratio, spin-orbit coupling, damping rate, and domain structure. In this review article, we present an overview of the essential progress in probing spin dynamics of 2D vdW magnets using FMR techniques. Given the dynamic nature of this field, we focus mainly on the broadband FMR, optical FMR, and spin-torque FMR, and their applications in studying prototypical 2D vdW magnets including CrX3 (X = Cl, Br, I), Fe5GeTe2, and Cr2Ge2Te6. We conclude with the recent advances in laboratory- and synchrotron-based FMR techniques and their opportunities to broaden the horizon of research pathways into atomically thin magnets.
... Terminals T2-T4 (T4 grounded, GND) are used to apply the bias voltage Vb for VCMA. Terminals T1-T2 are used for STT, and terminals T1-T3 for SOT [28][29][30][31][32][33][34]. ...
Probabilistic computing using random number generators (RNGs) can leverage the inherent stochasticity of nanodevices for system-level benefits. Device candidates for this application need to produce highly random “coinflips” while also having tunable biasing of the coin. The magnetic tunnel junction (MTJ) has been studied as an RNG due to its thermally-driven magnetization dynamics, often using spin transfer torque (STT) current amplitude to control the random switching of the MTJ free layer magnetization, here called the stochastic write method. There are additional knobs to control the MTJ-RNG, including voltage-controlled magnetic anisotropy (VCMA) and spin orbit torque (SOT), and there is need to more systematically study and compare these methods. We build an analytical model of the MTJ to characterize using VCMA and SOT to generate random bit streams. The results show that both methods produce high quality, uniformly distributed bitstreams. Biasing the bitstreams using either STT current or an applied magnetic field shows a sigmoidal distribution vs. bias amplitude for both VCMA and SOT, compared to less sigmoidal for stochastic write. The energy consumption per sample is calculated to be 0.1 pJ (SOT), 1 pJ (stochastic write), and 20 pJ (VCMA), revealing the potential energy benefit of using SOT and showing using VCMA may require higher damping materials. The generated bitstreams are then applied to two tasks: generating an arbitrary probability distribution and using the MTJ-RNGs as stochastic neurons to perform simulated annealing, where both VCMA and SOT methods show the ability to effectively minimize the system energy with small delay and low energy. These results show the flexibility of the MTJ as a true RNG and elucidate design parameters for optimizing the device operation for applications.
... Terminals T2-T4 (T4 grounded, GND) are used to apply the bias voltage Vb for VCMA. Terminals T1-T2 are used for STT, and terminals T1-T3 for SOT [25][26][27][28][29][30][31]. ...
Probabilistic computing using random number generators (RNGs) can leverage the inherent stochasticity of nanodevices for system-level benefits. The magnetic tunnel junction (MTJ) has been studied as an RNG due to its thermally-driven magnetization dynamics, often using spin transfer torque (STT) current amplitude to control the random switching of the MTJ free layer magnetization, here called the stochastic write method. There are additional knobs to control the MTJ-RNG, including voltage-controlled magnetic anisotropy (VCMA) and spin orbit torque (SOT), and there is need to systematically study and compared these methods. We build an analytical model of the MTJ to characterize using VCMA and SOT to generate random bit streams. The results show that both methods produce high quality, uniformly distributed bitstreams. Biasing the bitstreams using either STT current or an applied magnetic field shows an approximately sigmoidal distribution vs. bias amplitude for both VCMA and SOT, compared to less sigmoidal for stochastic write for the same conditions. The energy consumption per sample is calculated to be 0.1 pJ (SOT), 1 pJ (stochastic write), and 20 pJ (VCMA), revealing the potential energy benefit of using SOT and showing using VCMA may require higher damping materials. The generated bitstreams are then applied to two example tasks: generating an arbitrary probability distribution using the Hidden Correlation Bernoulli Coins method and using the MTJ-RNGs as stochastic neurons to perform simulated annealing in a Boltzmann machine, where both VCMA and SOT methods show the ability to effectively minimize the system energy with small delay and low energy. These results show the flexibility of the MTJ as a true RNG and elucidate design parameters for optimizing the device operation for applications.
... The MTJ device we will mainly focus on hereafter (device A) has a diameter D of 34 nm (results for device B with t CoFeB = 1.82 nm, RA = 8.1 Ωμm 2 , and D = 28 nm will be also shown later). In this size range, the magnetisation can be represented by a single vector without significant effects of spatial inhomogeneity for the present stack structure 16,27,40 . Both CoFeB layers have a perpendicular easy axis. ...
... Matsumoto et al. pointed out that n I rapidly decreases from 2 to 1.4 with increasing K 2 /K 1 eff from 0 to~0.25 51 . Experimentally, some assumed 1 25,[27][28][29][30]36,39 whereas others assumed 2 26,[31][32][33] , and importantly no studies access the number. The present experimental results support the scenario of Matsumoto et al., but, similarly to n H , the reduction of n I is more moderate than the theoretical prediction. ...
Modulation of the energy landscape by external perturbations governs various thermally-activated phenomena, described by the Arrhenius law. Thermal fluctuation of nanoscale magnetic tunnel junctions with spin-transfer torque (STT) shows promise for unconventional computing, whereas its rigorous representation, based on the Néel-Arrhenius law, has been controversial. In particular, the exponents for thermally-activated switching rate therein, have been inaccessible with conventional thermally-stable nanomagnets with decade-long retention time. Here we approach the Néel-Arrhenius law with STT utilising superparamagnetic tunnel junctions that have high sensitivity to external perturbations and determine the exponents through several independent measurements including homodyne-detected ferromagnetic resonance, nanosecond STT switching, and random telegraph noise. Furthermore, we show that the results are comprehensively described by a concept of local bifurcation observed in various physical systems. The findings demonstrate the capability of superparamagnetic tunnel junction as a useful tester for statistical physics as well as sophisticated engineering of probabilistic computing hardware with a rigorous mathematical foundation.
... The intrinsic critical switching current I c0 is evaluated for a 50-nm-wide and 5-nm-thick SOT track an MTJ diameter of 50 nm using a parallel resistor model. Δ was extracted using the B c field distribution method [198]. Data: courtesy of IMEC. ...
Spin-orbit torques (SOT) provide a versatile tool to manipulate the magnetization of diverse classes of materials and devices using electric currents, leading to novel spintronic memory and computing approaches. In parallel to spin transfer torques (STT), which have proven their place among leading non-volatile memory technologies, SOT broaden the scope of current-induced magnetic switching to applications that run close to the clock speed of the central processing unit and unconventional computing architectures. In this paper, we review the fundamental characteristics of SOT and their use to switch magnetic tunnel junction (MTJ) devices, the elementary unit of the magnetoresistive random access memory (MRAM). In the first part, we illustrate the physical mechanisms that drive the SOT and magnetization reversal in nanoscale structures. In the second part, we focus on the SOT-MTJ cell. We discuss the anatomy of the MTJ in terms of materials and stack development, summarize the figures of merit for SOT switching, review the field-free operation of perpendicularly magnetized MTJs, and present options to combine SOT, STT and voltage-gate assisted switching. In the third part, we consider SOT-MRAMs in the perspective of circuit integration processes, introducing considerations on scaling and performance, as well as macro-design architectures. We thus bridge the fundamental description of SOT-driven magnetization dynamics with an application-oriented perspective, including device and system-level considerations, goals, and challenges.
