Unveiling Texture Transfer in Dielectric Thin Films via In Situ Electron Microscopy

Transition metal oxide (TMO) dielectric layers are pivotal for applications like field-effect transistors, supercapacitors, and emerging memories such as resistive random access memory (RRAM) [1]. Careful selection of the thin film layer materials and growth techniques in an RRAM device is essential to engineering the desired microstructure via texture transfer to improve performance and reliability [2], [3].<br/>Usually, texture transfer is achieved via epitaxial growth at elevated temperatures, which, in the case of RRAM, might be more challenging to integrate in current complementary metal oxide semiconductor (CMOS) back-end-of-line (BEOL) processes. Therefore, a question arises if texture transfer is also possible when annealing amorphous HfO₂ thin films grown via reactive molecular beam epitaxy (RMBE) on highly textured (111) thin films. Here, we have employed in situ electron microscopy to precisely determine the minimum required temperature and the origin of grain growth.<br/>Crystallization of amorphous HfO₂ starts at 180 °C, non-adjacent to an interface. The developing grains, as shown by automated crystal orientation mapping (ACOM) in ASTAR of the 4D-STEM data set, are nanocrystalline or amorphous until reaching an adjacent textured layer. The resulting (11-1+010) monoclinic phase of the annealed HfO₂ thin films indicates that texture transfer is possible, which is also represented in the improvement of the RRAM device's performance.<br/>To summarize, the presented findings in our study are not only relevant in the field of dielectric thin films by connecting microstructural changes to device fabrication and performance but are generally useful when tracking the origins of grain growth with nanometer precision by analyzing 4D STEM via automated crystal orientation mapping (ACOM).<br/><br/>References:<br/>[1] R. Dittmann, S. Menzel, and R. Waser, ‘Nanoionic memristive phenomena in metal oxides: the valence change mechanism’, <i>Advances in Physics</i>, vol. 70, no. 2, pp. 155–349, Apr. 2021, doi: 10.1080/00018732.2022.2084006.<br/>[2] R. Winkler <i>et al.</i>, ‘Controlling the Formation of Conductive Pathways in Memristive Devices’, <i>Advanced Science</i>, vol. 9, no. 33, p. 2201806, 2022, doi: 10.1002/advs.202201806.<br/>[3] S. U. Sharath <i>et al.</i>, ‘Control of Switching Modes and Conductance Quantization in Oxygen Engineered HfO_x based Memristive Devices’, <i>Adv. Funct. Mater.</i>, Jul. 2017, doi: 10.1002/adfm.201700432.