Electrons have a charge and a spin, but until recently these were considered separately. In classical electronics, charges are moved by electric fields to transmit information and are stored in a capacitor to save it. In magnetic recording, magnetic fields have been used to read or write the information stored on the magnetization, which 'measures' the local orientation of spins in ferromagnets. The picture started to change in 1988, when the discovery of giant magnetoresistance opened the way to efficient control of charge transport through magnetization. The recent expansion of hard-disk recording owes much to this development. We are starting to see a new paradigm where magnetization dynamics and charge currents act on each other in nanostructured artificial materials. Ultimately, 'spin currents' could even replace charge currents for the transfer and treatment of information, allowing faster, low-energy operations: spin electronics is on its way.

/pdf/the-emergence-of-spin-electronics-in-data-storage-1vrnm5549k.pdf

The emergence of spin electronics in data storage

http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

https://ralphgroup.lassp.cornell.edu/papers/JMMM-320-1190-2008.pdf

Spin transfer torques

We survey recent developments in the design of large-capacity content-addressable memory (CAM). A CAM is a memory that implements the lookup-table function in a single clock cycle using dedicated comparison circuitry. CAMs are especially popular in network routers for packet forwarding and packet classification, but they are also beneficial in a variety of other applications that require high-speed table lookup. The main CAM-design challenge is to reduce power consumption associated with the large amount of parallel active circuitry, without sacrificing speed or memory density. In this paper, we review CAM-design techniques at the circuit level and at the architectural level. At the circuit level, we review low-power matchline sensing techniques and searchline driving approaches. At the architectural level we review three methods for reducing power consumption.

https://www.pagiamtzis.com/pubs/pagiamtzis-jssc2006.pdf

Content-addressable memory (CAM) circuits and architectures: a tutorial and survey

Non-volatile 'flash' memories are key components of integrated circuits because they retain their data when power is interrupted. Despite their great commercial success, the semiconductor industry is searching for alternative non-volatile memories with improved performance and better opportunities for scaling down the size of memory cells. Here we demonstrate the feasibility of a new semiconductor memory concept. The individual memory cell is based on a narrow line of phase-change material. By sending low-power current pulses through the line, the phase-change material can be programmed reversibly between two distinguishable resistive states on a timescale of nanoseconds. Reducing the dimensions of the phase-change line to the nanometre scale improves the performance in terms of speed and power consumption. These advantages are achieved by the use of a doped-SbTe phase-change material. The simplicity of the concept promises that integration into a logic complementary metal oxide semiconductor (CMOS) process flow might be possible with only a few additional lithographic steps.

Low-cost and nanoscale non-volatile memory concept for future silicon chips.

Magnetoresistive random access memory (MRAM) technology combines a spintronic device with standard silicon-based microelectronics to obtain a combination of attributes not found in any other memory technology. Key attributes of MRAM technology are nonvolatility and unlimited read and write endurance. Magnetic tunnel junction (MTJ) devices have several advantages over other magnetoresistive devices for use in MRAM cells, such as a large signal for the read operation and a resistance that can be tailored to the circuit. Due to these attributes, MTJ MRAM can operate at high speed and is expected to have competitive densities when commercialized. In this paper, we review our recent progress in the development of MTJ-MRAM technology. We describe how the memory operates, including significant aspects of reading, writing, and integration of the magnetic material with CMOS, which enabled our recent demonstration of a 1-Mbit memory chip. Important memory attributes are compared between MRAM and other memory technologies.

Magnetoresistive random access memory using magnetic tunnel junctions

A low-power 1-Mb magnetoresistive random access memory (MRAM) based on a one-transistor and one-magnetic tunnel junction (1T1MTJ) bit cell is demonstrated. This is the largest MRAM memory demonstration to date. In this circuit, the magnetic tunnel junction (MTJ) elements are integrated with CMOS using copper interconnect technology. The copper interconnects are cladded with a high-permeability layer which is used to focus magnetic flux generated by current flowing through the lines toward the MTJ devices and reduce the power needed for programming. The 25-mm/sup 2/ 1-Mb MRAM circuit operates with address access times of less than 50 ns, consuming 24 mW at 3.0 V and 20 MHz. The 1-Mb MRAM circuit is fabricated in a 0.6-/spl mu/m CMOS process utilizing five layers of metal and two layers of poly.

A 1-Mbit MRAM based on 1T1MTJ bit cell integrated with copper interconnects

Rapid advances in portable communication and computing systems are creating an increasing demand for nonvolatile random access memory that is both high-density and highspeed. Existing solid-state technologies are unable to provide all of the needed attributes in a single memory solution. Therefore, a number of different memories are currently being used to achieve the multiple functionality requirements, often compromising performance and adding cost to the system. A new technology, magnetoresistive random access memory (MRAM) based on magnetoresistive tunneling, has the potential to replace these memories in various systems with a single, universal solution. The key attributes of MRAM are nonvolatility, high-speed operation. and unlimited read and write endurance. This technology is enabled by the ability to deposit high-quality, nanometer scale tunneling barriers that display enhanced magnetoresistive response. In this article we describe several fundamental technical and scientific aspects of MRAM with emphasis on recent accomplishments that enabled our successful demonstration of a 256-Kb memory chip.

The science and technology of magnetoresistive tunneling memory

We have measured thermally activated magnetization reversal of the free layers in submicron magnetic tunnel junctions to be used for magnetoresistive random access memory. We applied magnetic field pulses to the bits with a pulse duration tp ranging from nanoseconds to 0.1 ms. We have measured the switching probability as a function of tp with a fixed field amplitude H, and as a function of H for fixed tp. For both cases, we find good agreement with the switching probability predicted by the Arrhenius–Neel theory for thermal activation over a single energy barrier.

Thermally activated magnetization reversal in submicron magnetic tunnel junctions for magnetoresistive random access memory

A magnetic random access memory (“MRAM”) device can be selectively written using spin-transfer reflection mode techniques. Selectivity of a designated MRAM cell within an MRAM array is achieved by the dependence of the spin-transfer switching current on the relative angle between the magnetizations of the polarizer element and the free magnetic element in the MRAM cell. The polarizer element has a variable magnetization that can be altered in response to the application of a current, e.g., a digit line current. When the magnetization of the polarizer element is in the natural default orientation, the data in the MRAM cell is preserved. When the magnetization of the polarizer element is switched, the data in the MRAM cell can be written in response to the application of a relatively low write current.

Nicholas D. Rizzo

Papers

Magnetoresistive random access memory using magnetic tunnel junctions

A 1-Mbit MRAM based on 1T1MTJ bit cell integrated with copper interconnects

The science and technology of magnetoresistive tunneling memory

Thermally activated magnetization reversal in submicron magnetic tunnel junctions for magnetoresistive random access memory

Spin-transfer based mram using angular-dependent selectivity