The mtj is composed of a fixed magnetic layer, a thin dielectric tunnel barrier, and a free magnetic layer. Material dependence of thermally assisted magnetization. Magnetic random access memories mrams are a new nonvolatile memory technology trying establish itself as a mainstream technology. Our studies based on the proposed scaling methodology show that inplane stt mram. Mram cell operation using a thermally assisted writing scheme tamram is. Design of nonvolatile memory based on improved writing. Among the various pma materials available, copd multilayers exhibit a wide variety of magnetic properties, including variation in the strength of pma and its temperature dependence, which can be controlled by varying the individual layer thickness, layer repetition number, and deposition conditions.
May, 2016 thermally assisted magnetic random access memory tas mram nanodevices are promising candidates for future memory applications, because they provide nonvolatile data storage at fast operation and low energy consumption. Abert2 1doppler laboratory, institute of solid state physics, vienna university of technology, 1040 vienna. Structure for thermally assisted mram free patents online. Watanabe, study of stacked nor type mram for universal. Scaling and power properties of thermally written mram 5th. The mram cell composed of a single free layer with inplane magnetization needs to be designed accordingly with an aspect ratio equal to or larger than 2. A few different designs have been proposed, but all rely on the idea of reducing the required switching fields by heating. Furthermore, 4 k u h k m s 2 where h k is the anisotropy field and m s is the saturation magnetization of the free layer. Electricfieldinduced thermally assisted switching of. The thermal stability factor of the free ferromagnetic layer of the. Significant reduction of critical currents in mram designs using dual free layer with perpendicular and in. A novel selfreference sensing scheme for mlc mram zheng li, m. According to motorola, samples of the new magnetoresistive random access memory, or mram, chips will be distributed to developers by the end of 2003, and cell phones and pdas incorporating mram should be on sale by mid2004.
The first generation is fielddriven mram, including thermally assisted mram relying on joule heating and exchange coupling which is still being pursued nowadays 26. In recent years, many researches have been performed to. The curie temperature of the tbcocofe layer free layer and the cofetbfeco layer pinned layer were and 230 c, respectively. Field assisted excitation of the magnetic free layer, however, can complement the stt effect. In this paper, we present a compact model for mtj switched by this approach, which integrates a number of physical models such as temperature evaluation and stt dynamic switching.
Spinorbittorquebased devices, circuits and architectures arxiv. Magnetic orientation of the free layer in the mtj is changed according to the induced magnetic field. The thermal stability issue can be solved differently in sot mram. The information storage device may be a magnetic random access memory mram device including a resistive cross point array of spin dependent tunneling sdt junctions or magnetic memory elements, with word lines extending along rows of the sdt junctions and bit lines extending along the columns of the sdt junctions. Orthogonal spintransfer magnetic random access memory ost mram has been proposed to increase the speed of magnetization reversal. Analysis of selfheating of thermally assisted spintransfer. Dram capacitor holds data, but needs to be refreshed as capacitance degrades approx. Toggle mram conventional mram issues for scaling high writing current, low density large switching field distribution sensitive to process half selection issueshalf selection issues retention alternatives 510 spin torque transfer stt mram thermally assisted switching tas mram. Mram timeline 2000 mram joint development started by ibm and infineon, and spintec created a patent with spin torque transfer 2003 128 kbit mram chip was manufactured using 180 nm technology 2005 record mram cell clocked at 2 ghz, renesas tech. Magnetoresistive randomaccess memory mram is a type of nonvolatile randomaccess memory which stores data in magnetic domains.
Mar 02, 2017 a mechanism is provided for fabricating a thermally assisted magnetoresistive random access memory device. The potential arrangements include thermal assisted switching tas mram, which briefly heats up reminiscent of phasechange memory the magnetic tunnel. Nov 22, 20 the field writing mram fwmram magnetic induction for storage of data bits. Magnetoresistive random access memory mram is different from conventional types of memory like sram, dram, and flash, where electric charge is used to store information. Each memory element uses a magnetic tunnel junction mtj device for data storage. Challenges and prospects at a finite temperature, thermal agitation plays an important role in reducing the switching current at long current pulses 10 ns.
Spin transfer torque stt mram devices contain a free layer fl and a reference, or pinned, layer rl. A heatassisted multiferroic solidstate memory design is proposed and analysed, based on a pbnbzrsntio 3 antiferroelectric substrate and ni 81 fe 19 magnetic free layer. Mram present stateoftheart and future challenges dr g. The magnetic tunnel junction includes a top ferromagnetic layer formed on a tunnel barrier. Introduction spintransfer torque magnetic random access memory stt mram is the solid state magnetic memory. The two standard measurements of thermal stability of a single mram cell rely on accelerating the switching rate by either application of the magnetic field fielddriven switching or current currentdriven switching of various amplitude and study of. The fixed layer is a permanent magnet and the free layer is magnetic effect at the current given time. Debuted as a humble 4 mb product by freescale in 2006, the mram has grown to a 256 mb product of everspin in 2016. Magnetoresistive random access memory mram through the merging of magnetics spin and electronics, the burgeoning field of spintronics has created mram memory with characte ristics of nonvolatility, high density, high endurance, radiation hardness, high speed operation, and. Repeatedly heating an mtj free layer could degrade the device reliability andor its lifetime due to the repeated thermal. The magnetisation of the free layer can be changed by passing a. Combination of currents through the bit line ib and the digit line id.
Us7372116b2 heat assisted switching in an mram cell. Trends in magnetic information data storage and magnetic. In addition, the magnetization in this thermally assisted mtj is inplane. It is important to ensure good selectivity of a single magnetic tunnel junction storage cell within a memory array without affecting nearby storage cells. In this slow thermal activated switching regime, the switching current is dependent on the current pulse width. The increased write temperature is typically achieved. Theory of spin torque assisted thermal switching of single. Thermally assisted mram including magnetic tunnel junction. The spin torque efficiency could be improved by thermally assisted switching designs 3. Finally, a conclusion of this work is provided in section 5. Spintransfer torque magnetic random access memory sttmram. Femn exchange biased storage layer for thermally assisted mram.
Basic principles of sttmram cell operation in memory arrays. Index terms mram, negative differential resistance, tunneling diode, tunneling fet, write termination, read margin, read. Structure for thermally assisted mram free patents. Analysis of selfheating of thermally assisted spintransfer torque magnetic random access memory thermal assistance has been shown to significantly reduce the required operation power for spin torque transfer magnetic random access memory stt mram. University of pittsburgh, 2017 magnetic random access memory mram is a promising nonvolatile memory technology targeted on onchip or embedded applications. Ultrafast mram with thermally assisted switching as a comparison to the 2terminal sot device, we will also discuss another path to ultrafast operation of mram, which can be realized by the thermally assisted switching mechanism. Thermal assistance has been shown to significantly reduce the required operation power for spin torque transfer magnetic random access memory stt mram. Thermally assisted ta mram crocus demonstrated 1mbit mram with thermally assisted stt operation. Presented at the 5th annual nonvolatile memory technology symposium november 16, 2004, orlando, fla. Though ibmhad previously announced plans to release its mram chips in.
Sutaria, chengen yang, chaitali chakrabarti, yu cao school of electrical, computer and energy engineering, arizona state university tempe, arizona 85287, usa email. Analysis of selfheating of thermally assisted spin. Stt mram, thermal assisted sttswitching, exchangedcoupled gdfecotbfe bilayer, perpendicular magnetic anisotropy some figures may appear in colour only in the online journal 1. High performance soc design using magnetic logic and memory weisheng zhao1, lionel torres3. The nonvolatility is achieved through the use of magnetic tunnelling junctions mtjs in an mram cell. A bottom thermal barrier is formed on a bottom contact. A free powerpoint ppt presentation displayed as a flash slide show on id. Information is stored as magnetisation direction in the free layer of a magnetic tunnel junction element. Introduction spintransfer torque magnetic random access memory sttmram is the solid state magnetic memory. Thermally assisted writing for perpendicular mram sciencedirect. This approach is compared to conventional mram, highlighting the improvements in write selectivity, power consumption and thermal stability. In this structure have three layer free layer, fixed layer and tunnel barrier. High performance soc design using magnetic logic and. Thermally assisted magnetic random access memory tas mram nanodevices are promising candidates for future memory applications, because they provide nonvolatile data storage at fast operation and low energy consumption.
Mram description mram is based on magnetic memory elements integrated with cmos. As long as the write current is set high enough to write the cell that has the highest write threshold, all cells in the memory can be. Advanced information storage 14 university of york. Thermally assisted magnetic random access memory tasmram nanodevices are promising candidates for future memory applications. Introduction spin transfer torque stt switching has been extensively. For this purpose, this memory array of storage cells preferably comprises a an array of electrically conducting bit lines and electrically conducting word lines which form intersections therebetween, b a storage cell disposed at each of. The thermal stability factorensuringa10year retentiontimewas obtainedbyadjusting the free layer thickness as well as assuming improvement in the crystalline anisotropy. Analysis of selfheating of thermally assisted spintransfer torque magnetic random access memory. Section 4 describes the design of core circuit such as row decoder and estimation of the pattern area. Us6385082b1 thermallyassisted magnetic random access. Storage density is one of the major design concerns of mram. Instead of exploiting the charge of an electron, mram uses its spin to store data. A lower curie temperature of the free layer than that of the pinned layer cotbfeco enables us to switch the magnetization of the free layer by thermally assisted writing while that of the. However, the heating temperature needs to surpass b 200 c of the free layer.
Analysis of selfheating of thermally assisted spintransfer torque. Design method of stacked type thermally assisted mram. The thermal stability has been determined by measuring the spin torque assisted thermal switching of the free layer and analyzing the time evolution of the switching probability by. The free layer of the mram elements was switched using a magnetic field at fixed heatingsmt current bias. Apr 26, 2016 a variation of mram technology includes a thermallyassisted magnetoresistive random access memory tasmram. We investigate the nmfmafm trilayer system the spin current is generated from nm layer.
A magnetic tunnel junction is formed on the bottom thermal barrier. Tunneling negative differential resistanceassisted stt. Simulation of switching maps for thermally assisted mram. A compact model for magnetic tunnel junction mtj switched. The current injected into the junction heats the mtj and the spin transfer torque defines the direction of the magnetization in the free layer. Giant thermal spintorque assisted magnetic tunnel junction switching aakash pushpa,1,2. A mechanism is provided for fabricating a thermally assisted magnetoresistive random access memory device. Thermally assisted mram i in thermally assisted mram ta mram a current passes through the device and heats one of the antiferromagnets above its. Thermalassisted switching, or tas, is one of the new secondgeneration approaches to magnetoresistive randomaccess memory mram currently being developed. It is shown that, for the successful performance of write and read. Spin injection in thermally assisted magnetic random.
It is shown that, for the successful performance of. Design method of stacked type thermally assisted mram with. A solution to overcome these problems is the thermally assisted writing technique. Section 3 presents the read and write operation of newly proposed thermally assisted mram. Electricfieldinduced thermally assisted switching of monodomain magnetic bits p. Mram designs and the outlook of emerging topological materials for enhanced sotbased switching. Spin injection in thermally assisted magnetic random access. Process step and analysis of bit cost for stacked type mram. A tas mram device requires heating of the magnetic tunnel junction stack to a write temperature t write higher than the operating temperature t op in order to write the device.
Significant reduction of critical currents in mram designs. The two standard measurements of thermal stability of a single mram cell rely on accelerating the switching rate by either application of the magnetic field fielddriven switching or current currentdriven switching of. Developed in the mid1980s, proponents have argued that magnetoresistive ram will eventually surpass competing technologies to become a dominant or even universal memory. Mram reliability issues and the potential for scaling mram for future device generations concludes the chapter. Spin torque transfer magnetic random access memory sttmram, a type of. Femn exchange biased storage layer for thermally assisted mram article pdf available in ieee transactions on magnetics 466. The thermal stability factor of the free ferromagnetic layer of the device. A tasmram device requires heating of the magnetic tunnel junction stack to a write temperature t write higher than the operating temperature t op in order to write the device. Thermally assisted mram 6 to write the bit state of tunnel junctions by circulating a current in the write lines 22, 23, 24 and heating the magnetic layers in the mram cell above their magnetic. Thermally assisted mram i in thermally assisted mram tamram a current passes through the device and heats one of the antiferromagnets above its blocking temperature.
Magnetic random access memory, in epitaxial ferromagnetic films and spintronic applications. Mtj to generate spintransfer torque stt for switching free layer but the write current. Behavior of seriesconnected mtj and ndr devices a b. Here, on top of the free layer an antiferromagnet is deposited which. Watanabe, design method of stacked type thermally assisted mram with nand structured cell, contemporary engineering sciences, vol. Thermally assisted mram i l prejbeanu, m kerekes, r c sousa et al. Compact modeling of sttmtj for spice simulation zihan xu, ketul b. Simulations of thermally assisted magnetization reversal of 0. Page 3 of 3 a halfselect condition, the switching uniformity requirement is eased considerably. Cristian papusoi, bernard dieny spintec, grenoble, france acknowledgments. The magnetic free layer is a square of side 320 nm and 5 nm thickness with the material set as magnetostrictive nirich permalloy ni 81 fe 19.