Development of a Non-Destructive Interfacial Imaging Technique

An idea to utilise a scanning electron microscope to investigate buried interfaces within samples non-destructively has been developed. A repeatable methodology to apply this non-destructive interfacial imaging technique has been devised and tested. In addition a Monte Carlo simulation tool, CASINO, has been used to optimise the depth at which the imaging technique probes. This technique was further developed to study devices in situ. This was used to define and measure an effective area in lateral spin valves.

This technique has been applied to numerous systems, including thin films and devices. When used to investigate the effects of varying the Ta seed layer thickness in a series of Si/Ta/CoFeB/MgO/Ta thin films it identified differing densities of domain wall pinning sites, increasing as the seed layer became thicker. The effect on the magnetic moment was observed by sweeping a plus/minus 1 T field in a vibrating sample magnetometer. This identified a preferred seed layer thickness of 0.5 nm.

Magnetic tunnel junction devices were also investigated. These devices are designed for use in either data storage or magnetic sensor applications. The non-destructive imaging technique, as well as energy dispersive X-ray spectroscopy, was used to optimise the fabrication of these devices. This combined study increased the total yield by 15% by identifying the formation of an aluminium carbide along the edge of failed devices. Production quality devices were characterised using the non-destructive interfacial imaging technique. This demonstrated the varying dome on the pillar and also allowed the encapsulation layer to be measured.

The thin film for an organic magnetic tunnel junction was also investigated. The organic molecule, Cobalt(II) Phthalocyanine, was deposited in 0.32 and 3.2 nm thick layers. The non-destructive imaging technique identified the formation of channels in this organic layer. The channels were more dense in the 3.2 nm sample. Cross-sectional transmission electron microscopy was employed to investigate the structure. This identified the likely cause of these channels to be mis-orientation of the organic molecule during deposition. These results unambiguously prove the applicability of this imaging technique developed for interface assessment and improvement, for a wide variety of spintronic devices.