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Author

Sarin A. Deshpande

Other affiliations: Cornell University
Bio: Sarin A. Deshpande is an academic researcher from Indian Institute of Technology Bombay. The author has contributed to research in topics: Etching (microfabrication) & Tunnel magnetoresistance. The author has an hindex of 10, co-authored 34 publications receiving 565 citations. Previous affiliations of Sarin A. Deshpande include Cornell University.

Papers
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Patent
14 Aug 2013
TL;DR: In this article, a method of manufacturing a magnetoresistive-based device having magnetic material layers formed between a first electrically conductive layer and a second electricallyconductive layer, including a tunnel barrier layer, was proposed.
Abstract: A method of manufacturing a magnetoresistive-based device having magnetic material layers formed between a first electrically conductive layer and a second electrically conductive layer, the magnetic materials layers including a tunnel barrier layer formed between a first magnetic materials layer and a second magnetic materials layer, including removing the first electrically conductive layer and the first magnetic materials layer unprotected by a first hard mask, to form a first electrode and a first magnetic materials, respectively; and removing the tunnel barrier layer, second magnetic materials layer, and second electrically conductive layer unprotected by the second hard mask to form a tunnel barrier, second magnetic materials, and a second electrode.

192 citations

Journal ArticleDOI
TL;DR: In this article, the authors developed a fully functional 64 Mb DDR3 ST-MRAM built on 90 nm CMOS technology, which is organized in an 8-bank configuration that can sustain 1.6 GigaTransfers/s.
Abstract: A spin torque magnetoresistive random access memory (ST-MRAM) holds great promise to be a fast, high density, nonvolatile memory that can enhance the performance of a variety of applications, particularly when used as a non-volatile buffer in data storage devices and systems. Towards that end, we have developed a fully functional 64 Mb DDR3 ST-MRAM built on 90 nm CMOS technology. The memory is organized in an 8-bank configuration that can sustain 1.6 GigaTransfers/s (DDR3-1600). We have run standard memory tests, such as a March6N pattern, on the full 64 Mb at 800 MHz with 0 fails for greater than 10 5 cycles. Full functionality was also verified from 0°C to 70°C with no significant change in performance. The bits are magnetic tunnel junctions (MTJs) having an MgO tunnel barrier and a magnetic free layer made of a CoFeB-based alloy with an in-plane magnetization, but with an out-of-plane anisotropy reduced by more than 50% due to an enhanced perpendicular surface anisotropy. To enable the 64 Mb performance, we developed an MTJ stack that has low switching voltage (Vsw), high breakdown voltage (Vbd), and excellent switching reliability with tight distributions. The ST switching distribution has σ ≈ 10%, and we found excellent agreement with a single Gaussian distribution down to an error rate . For our optimized material, the Vsw/Vbd ≈ 0.3, and the separation between Vsw and Vbd is ≈ 25σ. The energy barrier to magnetization reversal (Eb) was characterized using both time-dependent coercivity and higher temperature to accelerate reversal. We found the average Eb ≈ 70kbT.

118 citations

Proceedings ArticleDOI
01 Jun 2017
TL;DR: An unprecedented demonstration of a robust STT-MRAM technology designed in a 2x nm CMOS-embedded 40 Mb array with full array functionality, process uniformity and reliability, and 10 years data retention at 125C with extended endurance to ∼ 107 cycles is presented.
Abstract: Perpendicular Spin-Transfer Torque (STT) MRAM is a promising technology in terms of read/write speed, low power consumption and non-volatility, but there has not been a demonstration of high density manufacturability at small geometries. In this paper we present an unprecedented demonstration of a robust STT-MRAM technology designed in a 2x nm CMOS-embedded 40 Mb array. Key features are full array functionality with low BER (bit error rate), process uniformity and reliability, 10 years data retention at 125C with extended endurance to ∼ 107 cycles. All achieved with standard BEOL process temperatures. Data retention post 260°C solder reflow temperature cycle is demonstrated.

43 citations

Proceedings ArticleDOI
01 Dec 2012
TL;DR: Key properties for commercial ST-MRAM circuits are reviewed, the challenges to achieving the many performance and scaling goals that are being addressed in current development around the world are discussed, recent results in the field are presented, and first results from a new, fully-functional 64Mb, DDR3, ST- MRAM circuit are presented.
Abstract: We review key properties for commercial ST-MRAM circuits, discuss the challenges to achieving the many performance and scaling goals that are being addressed in current development around the world, recent results in the field, and present first results from a new, fully-functional 64Mb, DDR3, ST-MRAM circuit.

37 citations

Journal ArticleDOI
TL;DR: In this article, the authors give a concise derivation of the Herman-Kluk propagator that fully exploits the symplectic structure of the problem and also show directly that the version of the thawed Gaussian semiclassical propagator obtained by Baranger and co-workers is equivalent to the linearized HK propagator.
Abstract: Following an earlier derivation by Miller, we give a concise derivation of the Herman–Kluk propagator that fully exploits the symplectic structure of the problem. We also show directly that the version of the thawed Gaussian semiclassical propagator obtained by Baranger and co-workers is equivalent to the linearized Herman–Kluk propagator.

33 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, a review of magnetic magnetic anisotropy at magnetic metal/oxide interfaces is presented, along with some applications of this interfacial PMA in STT-MRAM.
Abstract: Spin electronics is a rapidly expanding field stimulated by a strong synergy between breakthrough basic research discoveries and industrial applications in the fields of magnetic recording, magnetic field sensors, nonvolatile memories [magnetic random access memories (MRAM) and especially spin-transfer-torque MRAM (STT-MRAM)]. In addition to the discovery of several physical phenomena (giant magnetoresistance, tunnel magnetoresistance, spin-transfer torque, spin-orbit torque, spin Hall effect, spin Seebeck effect, etc.), outstanding progress has been made on the growth and nanopatterning of magnetic multilayered films and nanostructures in which these phenomena are observed. Magnetic anisotropy is usually observed in materials that have large spin-orbit interactions. However, in 2002 perpendicular magnetic anisotropy (PMA) was discovered to exist at magnetic metal/oxide interfaces [for instance Co(Fe)/alumina]. Surprisingly, this PMA is observed in systems where spin-orbit interactions are quite weak, but its amplitude is remarkably large—comparable to that measured at Co/Pt interfaces, a reference for large interfacial anisotropy (anisotropy ∼1.4 erg/cm2 = 1.4 mJ/m2). Actually, this PMA was found to be very common at magnetic metal/oxide interfaces since it has been observed with a large variety of amorphous or crystalline oxides, including AlOx, MgO, TaOx, HfOx, etc. This PMA is thought to be the result of electronic hybridization between the oxygen and the magnetic transition metal orbit across the interface, a hypothesis supported by ab initio calculations. Interest in this phenomenon was sparked in 2010 when it was demonstrated that the PMA at magnetic transition metal/oxide interfaces could be used to build out-of-plane magnetized magnetic tunnel junctions for STT-MRAM cells. In these systems, the PMA at the CoFeB/MgO interface can be used to simultaneously obtain good memory retention, thanks to the large PMA amplitude, and a low write current, thanks to a relatively weak Gilbert damping. These two requirements for memories tend to be difficult to reconcile since they rely on the same spin-orbit coupling. PMA-based approaches have now become ubiquitous in the designs for perpendicular STT-MRAM, and major microelectronics companies are actively working on their development with the first goal of addressing embedded FLASH and static random access memory-type of applications. Scalability of STT-MRAM devices based on this interfacial PMA is expected to soon exceed the 20-nm nodes. Several very active new fields of research also rely on interfacial PMA at magnetic metal/oxide interfaces, including spin-orbit torques associated with Rashba or spin Hall effects, record high speed domain wall propagation in buffer/magnetic metal/oxide-based magnetic wires, and voltage-based control of anisotropy. This review deals with PMA at magnetic metal/oxide interfaces from its discovery, by examining the diversity of systems in which it has been observed and the physicochemical methods through which the key roles played by the electronic hybridization at the metal/oxide interface were elucidated. The physical origins of the phenomenon are also covered and how these are supported by ab initio calculations is dealt with. Finally, some examples of applications of this interfacial PMA in STT-MRAM are listed along with the various emerging research topics taking advantage of this PMA.

515 citations

Journal ArticleDOI
TL;DR: A new structure with the third geometry, that is, with the easy axis collinear with the current (along the x axis), is presented and the switching operation driven by the spin-orbit torque due to Ta with a negative spin Hall angle is demonstrated.
Abstract: Spin-orbit torque, a torque brought about by in-plane current via the spin-orbit interactions in heavy-metal/ferromagnet nanostructures, provides a new pathway to switch the magnetization direction. Although there are many recent studies, they all build on one of two structures that have the easy axis of a nanomagnet lying orthogonal to the current, that is, along the z or y axes. Here, we present a new structure with the third geometry, that is, with the easy axis collinear with the current (along the x axis). We fabricate a three-terminal device with a Ta/CoFeB/MgO-based stack and demonstrate the switching operation driven by the spin-orbit torque due to Ta with a negative spin Hall angle. Comparisons with different geometries highlight the previously unknown mechanisms of spin-orbit torque switching. Our work offers a new avenue for exploring the physics of spin-orbit torque switching and its application to spintronics devices.

509 citations

Journal ArticleDOI
29 Aug 2016
TL;DR: A review of the developments in MRAM technology over the past 20 years is presented with a particular focus on spin-transfer torque MRAM (STT-MRAM) which is currently receiving the greatest attention.
Abstract: In this paper, a review of the developments in MRAM technology over the past 20 years is presented. The various MRAM generations are described with a particular focus on spin-transfer torque MRAM (STT-MRAM) which is currently receiving the greatest attention. The working principles of these various MRAM generations, the status of their developments, and demonstrations of working circuits, including already commercialized MRAM products, are discussed.

380 citations

Journal ArticleDOI
TL;DR: It is shown that when used in a non-conventional regime, STT-MTJs can additionally act as a stochastic memristive device, appropriate to implement a “synaptic” function in robust, low power, cognitive-type systems.
Abstract: Spin-transfer torque magnetic memory (STT-MRAM) is currently under intense academic and industrial development, since it features non-volatility, high write and read speed and high endurance. In this work, we show that when used in a non-conventional regime, it can additionally act as a stochastic memristive device, appropriate to implement a “synaptic” function. We introduce basic concepts relating to spin-transfer torque magnetic tunnel junction (STT-MTJ, the STT-MRAM cell) behavior and its possible use to implement learning-capable synapses. Three programming regimes (low, intermediate and high current) are identified and compared. System-level simulations on a task of vehicle counting highlight the potential of the technology for learning systems. Monte Carlo simulations show its robustness to device variations. The simulations also allow comparing system operation when the different programming regimes of STT-MTJs are used. In comparison to the high and low current regimes, the intermediate current regime allows minimization of energy consumption, while retaining a high robustness to device variations. These results open the way for unexplored applications of STT-MTJs in robust, low power, cognitive-type systems.

323 citations

Journal ArticleDOI
07 Jul 2016
TL;DR: The potential for these oscillators in a wide range of applications, from microwave signal sources and detectors to neuromorphic computation elements, is discussed together with the specific electronic circuitry that has so far been designed to harness this potential.
Abstract: This paper reviews the state of the art in spin-torque and spin-Hall-effect-driven nano-oscillators. After a brief introduction to the underlying physics, the authors discuss different implementations of these oscillators, their functional properties in terms of frequency range, output power, phase noise, and modulation rates, and their inherent propensity for mutual synchronization. Finally, the potential for these oscillators in a wide range of applications, from microwave signal sources and detectors to neuromorphic computation elements, is discussed together with the specific electronic circuitry that has so far been designed to harness this potential.

306 citations