Jean-Pierre Nozieres

Thermally assisted switching in exchange-biased storage layer magnetic tunnel junctions

A thermally assisted writing procedure is proposed in a tunnel junction based magnetic random access memory cell. The magnetic layers of the tunnel junction are both exchange-biased with antiferromagnetic layers, the reference layer having a much higher blocking temperature than the storage layer. In the operating mode, a current pulse sent through the junction generates enough heat to raise the temperature of the storage layer above its blocking temperature, without affecting the pinning of the reference layer. The concept is demonstrated here for an isolated junction using an homogeneous external magnetic field.

Beyond MRAM, CMOS/MTJ Integration for Logic Components

Spintronics is a new discipline in which the spin of the electron is used as an additional degree of freedom besides its electrical charge to build innovative electronic components. Magnetic materials can be used as spin polarizer/analyzer in association with semiconductors or insulators, resulting in hybrid CMOS/magnetic architectures. Magnetic Tunnel Junctions (MTJ) are the basic elements of a new kind of memory, called MRAM (Magnetic Random Access Memory). Besides MRAM, it has recently been shown that by combining MTJ and CMOS components, one can also develop new functionalities for logic devices. This paper aims at giving a general overview of these novel hybrid magnetic/CMOS architectures and the design tools required for their design.

Reversing exchange bias in thermally assisted magnetic random access memory cell by electric current heating pulses

The temperature required to set the exchange bias of a ferro∕antiferromagnetic (F∕AF) storage bilayer as a function of the heating pulse width was studied on magnetic tunnel junctions (MTJs) of thermally assisted magnetic random access memories. Heating is produced by a pulse of electric current flowing through the junction. For sufficiently long heating pulse (>20ns), a quasiequilibrium temperature profile is reached in the MTJ. In this stationary regime, a relationship between the temperature of the storage layer and the power of the pulse was established by using an Arrhenius–Neel model of thermal relaxation. The introduction of thermal barriers between the junction tunnel barrier and the electrodes allows a significant reduction of the power required to achieve a given temperature rise of the storage layer. When the heating pulse duration is reduced from 1sto2ns, the heating power required for setting the F∕AF storage bilayer increases by about 80%. This experimental observation is quantitatively inte...

Pulsewidth Dependence of Barrier Breakdown in MgO Magnetic Tunnel Junctions

Dependence of time-dependent dielectric breakdown with pulsewidth was investigated on MgO magnetic tunnel junctions. Barrier breakdown measurements were performed using different pulsewidths, from 10 ns up 1 s. The equivalence of the breakdown results between DC and pulsed voltage experiments was established using the total cumulated pulse time under electrical stress as the relevant parameter. Two different breakdown regimes were identified: the first one corresponding to pulses longer than 100 ns up to the DC limit and a second regime for pulses shorter than 100 ns. The barrier lifetime is increased for pulsewidths lower than 100 ns pulses. The breakdown process was shown to be thermally activated, but the longer lifetime at shorter pulses cannot be simply explained assuming a lower temperature during the pulse application.

IrMn and FeMn blocking temperature dependence on heating pulse width

We have determined the write power density dependence on heating pulse width and antiferromagnet (AF) thickness using magnetic tunnel junctions whose storage layer is exchange biased with IrMn or FeMn. An increase in write power density needed to write the storage layer has been observed for both AF as pulse width is decreased from 0.1 ms to 10 ns. Quasistatic blocking temperatures (Tb) were measured on both full sheet and patterned samples, showing a reduction in Tb for patterned samples which we link to process induced damages. Power-temperature relationship was established based on a correspondence between writing power for long pulse duration and quasistatic Tb measurement. Both write power density and associated temperature results show a dependence of the Tb on AF thickness at pulse width as short as 10 ns. Particularly for IrMn, the relationship between write power and pulse width becomes weakly dependent on the AF thickness above a certain AF thickness. The write power density is significantly low...

FeMn Exchange Biased Storage Layer for Thermally Assisted MRAM

Thermally assisted MRAM cells with FeMn exchange biased storage layers were successfully written using 50 ns current pulses with write power densities below 10 mW/¿m2 and current densities below 1.3 ×10 6 A/cm2. These low power density values were achieved without using thermal barriers to confine the heat in the cell. Introducing thermal barriers would even further lower the write power density by increasing the heating efficiency. The storage layer coercivity increased upon anneal at 340 C. This could be related to manganese diffusion or to a texture incompatibility between the CoFe and the FeMn antiferromagnetic layer, a problem which can be fixed by insertion of appropriate diffusion barrier or texture control layer. Successful writing was observed for repeated write attempts with heating pulse power densities in the 7-12.5 mW/¿m2 range.