In situ tunneling measurements in a transmission electron microscope on nanomagnetic tunnel junctions

Abstract

We showed that a chain of nanomagnetic tunnel junctions (MTJs) devices can be electrically addressed individually, in situ, in a transmission electron microscope, such that transport properties can be in principle, quantitatively correlated with each device’s defects and microstructure. A unique energy barrier was obtained for each device measured. Additionally, in situ tunneling magnetoresistance (TMR) measurements were obtained for a subset of devices. We found that TMR values for our nano-MTJs were generally smaller than TMR in the unpatterned film.

Structural controlled magnetic anisotropy in Heusler L1−MnGa epitaxial thin films

“…Recently, premature switching in MTJs have been attributed to defects in the junctions, whose microstructure has been studied by transmission electron microscopy showing local misorientations. 16 Our result here, namely, that film orientations could directly modify the magnetic anisotropy, can be one explanation for these nonuniform behaviors.…”

Magnetic nanostructures for advanced technologies: fabrication, metrology and challenges

“…This phenomenon is a conundrum of magnetic nanostructures and it has been problematic for the development of technologies like BPM where tight switching tolerances are required. The quest to directly correlate physical defects with magnetic properties distribution is at present an active area of research [52][53][54][55][56].…”

“…Of course, during manufacturing, various processes can produce defects such as pinholes and hot spots that fundamentally change the tunnelling barrier characteristics and therefore, the TMR distribution. In situ dc transport measurements were recently performed in a TEM to measure the TMR distribution in a row of fully operational, well-isolated nano-MTJs [55] (figure 9). Because the nano-MTJs had electron-transparent dimensions, such an experiment made it feasible to quantitatively compare transport characteristics, in addition to MR curves (not shown), with the corresponding device morphology and defect profile in adjacent devices.…”

Effect of annealing and applied bias on barrier shape in CoFe/MgO/CoFe tunnel junctions

“…Recently, in-situ, site-specific electrical biasing TEM experiments were introduced 36 allowing direct correlation between the microstructure and transport behavior. 37,38 The chemical composition of the tunnel barrier and its interfaces with the electrodes are controlling factors in the spindependent tunneling effect needed for high TMR. However, the exact evolution of the barrier shape as a fuction of changes to the barrier composition and structure during annealing is still not well understood, and the way in which barrier potential symmetry and effective width vary as a function of an applied electrical bias is also not fully understood.…”