Electrical Evaluation of Epitaxial Chromia Thin Films by Pulsed Laser Deposition for Spintronic Device Application
Chromia (Cr2O3) is an antiferromagnetic magnetoelectric (ME) material that demonstrates the phenomenon of boundary magnetization at room temperature. This novel form of magnetism is insensitive to surface roughness and can be reversed isothermally via ME switching. As a strongly insulating dielectric, manipulation of the boundary magnetization of chromia by purely electrical means is highly desirable, as it offers a route to low power consumption and ultrafast switching in post-CMOS spintronic technologies. While there has previously been much success in the electrical control of the interface magnetism in exchange bias heterostructures, realized in bulk chromia, it remains a significant challenge to demonstrate this phenomenon in thin films due to current leakage that develops at high electric fields (>100 kV/cm). In order to develop fully functional devices, in which the chromia exhibits high endurance in response to repeated switching, it is therefore necessary to eliminate leakage mechanisms at high fields.
In this study, we thus report on investigations of the leakage mechanisms in high-quality, crystalline chromia thin films, synthesized on different substrates. By studying the variation of the leakage over a wide range of temperature (77 – 400 K), distinct contributions to the leakage are identified. At low electric fields ohmic conduction dominates, whereas for higher fields a crossover to space-charged-limited conduction (the so-called Mott-Gurney mechanism) is observed. An analysis of these mechanisms reveals a low carrier mobility typical of impurity mediated transport, which increases exponentially with increasing temperature (10-8 < µ < 10-5 cm2/Vs, 80 < T < 400 K). Our studies moreover reveal a profound influence on the electrical properties, of the specific metallic substrate on which the chromia is grown. This effect is discussed in terms of the extent to which the different substrates lead to the formation of twinning defects in the resulting chromia films. Through proper choice of the substrate, we are able to suppress the twinning and so to achieve resistivity values in the films that approach those associated with bulk chromia. These results suggest a highly-promising direction for the realization of spintronic devices based on this material.