Discrete MRAM products have been on the market for 18 years and have been primarily used for industrial applications. Recently, spin-transfer torque (STT) MRAM in both stand-alone and embedded forms is expanding the scope of applications to the automotive market because automobiles are moving toward electrification and automation, and MRAM is suited for elevated temperature environments. Everspin's latest xSPI STT-MRAM product is shipping in volume with an operating temperature from -40 degrees C to +105 degrees C (Automotive Grade 2 temperature) into the industrial market. Everspin plans to introduce Automotive Grade 1 temperature (-40 degrees C to +125 degrees C) xSPI STT-MRAM to address a wider market.

We present Everspin’s new spin-transfer torque (STT) MRAM product, with magnetic tunnel junction arrays optimized for low-latency industrial applications, including higher speed, lower error rate, and longer cycling endurance. Performance metrics demonstrated include high-speed functionality with symmetric read and write throughput of an unprecedented 400MB/s over the full operating temperature range from -40°C to +85°C, with sufficient data retention and cycling endurance for industrial applications.

We present the new generation of Everspin's STT-MRAM device with extended Serial Peripheral Interface (xSPI). The device is capable of persistent memory operation with random reads and writes while supporting page-buffered program and optional erase for compatibility with Serial NOR Flash protocol. MRAM technology has been optimized for the needed improvements to enable low-latency industrial applications. Two bank architecture with a new write scheme is employed for fast write providing up to 4 orders of magnitude write energy improvement over traditional NOR. We demonstrate full 64Mb die high-speed functionality with symmetric read and write throughput of up to 400MB/s.

In this paper, we review key materials and process technology developments to successfully commercialize 1Gb standalone Spin-Transfer Torque (STT) MRAM. Magnetic tunnel junction (MTJ) stack and process integration were developed to reduce the operation voltage and to minimize the distribution of essential parameters across MTJ arrays. We demonstrate endurance cycles over 1x1010 and data retention of 20 years at 105°C. Reliable STT switching with a current pulse width less than 10 ns was achieved with no impact on endurance cycles.

There is a growing need for fast, endurant, non-volatile solutions for automotive that can meet the harsh requirements of automotive conditions. Automotive applications place severe demands memory devices. In the case of data retention, Automotive Grade 0 requires survival of T ambient 150 °C for 20 years with no loss in data integrity. In order to meet the higher temperature grades, an increase in data retention temperature capability is required. However, simply increasing the data retention can have a negative impact on write voltage, and, consequently, on endurance. Therefore, a similar methodology to improve write distribution as has been used on our 1 Gb memory array for datacenter applications is beneficial when applied to these products.

In this paper, we describe a fully-functional 1 Gb standalone spin-transfer torque magnetoresistive random access memory (STT-MRAM) integrated on 28 nm CMOS and based on perpendicular magnetic tunnel junctions (pMTJ’s). Electrical short flows were used to guide the pMTJ stack development. We demonstrate reliable operation of the 1 Gb devices, including well-behaved STT write distributions, an endurance cycling lifetime up to at least 2×1011 cycles, and data retention of 10 years at 85°C. Testing results at -35°C to 110°C for the 1 Gb devices indicate good capability for industrial temperature range applications.

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.

First-generation MRAM, based on a field switching innovation called “Savtchenko switching,” is mass produced by Everspin in densities up to 16Mb.

In this paper we present an overview of important features for reliable and manufacturable ST-MRAM as well as new results in two areas: pMTJ arrays with data retention sufficient for programming before 260°C wave solder, and performance of a 256Mb, DDR3 ST-MRAM product chip.

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 (V sw ), high breakdown voltage (V bd ), 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 V sw /V bd ≈ 0.3, and the separation between V sw and V bd is ≈ 25σ. The energy barrier to magnetization reversal (E b ) was characterized using both time-dependent coercivity and higher temperature to accelerate reversal. We found the average E b ≈ 70kbT.

With the recent sampling of Everspin Technologies spin torque magnetoresistive random access memory (ST-MRAM), the performance gap between the high speed volatile memories of SRAM and DRAM and the non-volatile memories of hard disk drives (HDD), Flash and PCRAM has been significantly reduced. We have demonstrated a fully functional 64Mb DDR3 ST-MRAM built on 90nm CMOS technology. This device combines the high speed operation of DDR3 with 1.6 GT/s (DDR3-1600) and the endurance of DRAM with the non-volatility of HDD, Flash or PCRAM. Full functionality has been verified from 0°C to 70°C at up to 800MHz using a March6N pattern with full memory cycling and 0 fails. The memory element used was a magnetic tunnel junction (MTJ) with CoFeB-based magnetic layers and an MgO tunnel barrier. This paper compares the performance of ST-MRAM in speed, non-volatility and endurance with the various memory solutions available on the market.

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.

Spin torque oscillators with nanoscale electrical contacts 1 , 2 , 3 , 4 are able to produce coherent spin waves in extended magnetic films, and offer an attractive combination of electrical and magnetic field control, broadband operation 5 , 6 , fast spin-wave frequency modulation 7 , 8 , 9 , and the possibility of synchronizing multiple spin-wave injection sites 10 , 11 . However, many potential applications rely on propagating (as opposed to localized) spin waves, and direct evidence for propagation has been lacking. Here, we directly observe a propagating spin wave launched from a spin torque oscillator with a nanoscale electrical contact into an extended Permalloy (nickel iron) film through the spin transfer torque effect. The data, obtained by wave-vector-resolved micro-focused Brillouin light scattering, show that spin waves with tunable frequencies can propagate for several micrometres. Micromagnetic simulations provide the theoretical support to quantitatively reproduce the results.

We study the interaction between a nano-contact spin torque oscillator (STO) and injected radio-frequency and microwave currents. Modulation of the STO signal is observed over a wide frequency range from 100 MHz to 3.2 GHz. The modulation side-bands agree well with macrospin simulations. When the injected microwave frequency approaches that of the STO, we observe injection locking, frequency pulling/pushing, and intermodulation peaks. While the intermodulation peaks are reasonably well reproduced by macrospin simulations, they do not follow the Adler's model. We argue that this discrepancy is due to intrinsic ringing effects stemming from the internal dynamics of the STO.

Magnetization dynamics in nano-contact spin torque oscillators (STOs) is investigated from an experimental and theoretical point of view. The fundamentals of magnetization dynamics due to spin transfer torque are given. A custom-made high frequency (up to 46 GHz) in large magnetic fields (up to 2.2 T) microwave characterization setup has been built for the purpose and described in this thesis. A unique feature of this setup is the capability of applying magnetic fields at any direction θe out of the sample plane, and with high precision. This is particularly important, because the (average) out-of-plane angle of the STO free magnetic layer has fundamental impact on spin wave generation and STO operation. By observing the spin wave spectral emission as a function of θe, we find that at angles θe below a certain critical angle θcr, two distinct spin wave modes can be excited: a propagating mode, and a localized mode of solitonic character (so called spin wave bullet). The experimental frequency, current threshold and frequency tuneability with current of the two modes can be described qualitatively by analytical models and quantitatively by numerical simulations. We are also able to understand the importance, so far underestimated, of the Oersted field in the dynamics of nano-contact STOs. In particular, we show that the Oersted field strongly affects the current tuneability of the propagating mode at subcritical angles, and it is also the fundamental cause of the mode hopping observed in the time-domain. This mode hopping has been observed both experimentally using a state-of-the-art real-time oscilloscope and corroborated by micromagnetic simulations. Micromagnetic simulations also reveal details of the spatial distribution of the spin wave excitations. By investigating the emitted power as a function of θe, we observed two characteristic behaviors for the two spin wave modes: a monotonic increase of the power for increasing out-of-plane angles in the case of the propagating mode; an increase towards a maximum power followed by a drop of it at the critical angle for the localized mode. Both behaviors are reproduced by micromagnetic simulations. The agreement with the simulations offers also a way to better understand the precession dynamics, since the emitted power is strongly connected to the angular variation of the giant magnetoresistance signal. We also find that the injection locking of spin wave modes with a microwave source has a strong dependence on θe, and reaches a maximum locking strength at perpendicular angles. We are able to describe these results in the theoretical framework of non-linear spin wave dynamics.