Title: LaCoO3-basedIMT Selector Update
Presenter(s): Darrell Schlom, Jake Sun (Cornell), Suman Datta, Abhishek Khanna (Notre Dame), Jeff Bokor (UC Berkeley)
Abstract: The electrical properties of insulator-to-metal (IMT)-based threshold switching events fulfill many of the requirements for use as cross-point selectors to suppress sneak-path leakage currents. Unfortunately,IMT- based threshold switching is traditionally incompatible with memory chip operating temperature requirements of Tchip >358 K, thus hindering the realization of an IMT-based cross-point selector. Here, we discuss our recent progress in the demonstration of the high-temperature spin-state IMT phase transition in the perovskite LaCoO3 (LCO) with vertical LCO devices made with conducting La0.5Sr0.5CoO3 (LSCO) bottom electrodes. This work is a collaboration within Theme #1 of ASCENT involving film synthesis (Schlom), device fabrication and testing (Datta), and spectroscopy (Bokor).
We begin by showing the device performance achieved on these vertical LCO/LSCO devices. The inherent switching event is characterized using D.C. measurements to evaluate potential device nonlinearity, temperature dependence, and threshold voltage. Further, projections towards an ultra-scaled20x20 nm2 device are simulated to predict the feasibility of anLCO-based 1-selector-1-ReRAM (1S1R) memory array.
We then describe the growth of the epitaxial LCO/LSCO bilayers from which the devices were fabricated, including the effect of non-stoichiometry in the LCO layer on the structural characteristics of the stack. For the planer LCO-based IMT-based cross-point selectors we have studied in the past, device performance was found to be best for off-composition LCO at about LaCo1.1O3+x. For the much thicker LCO layers involved in the vertical LCO/LSCO bilayers, deviating from the stoichiometric LaCoO3composition is seen to result in the formation of impurity phases, increased roughness, and the loss of coherent epitaxy. Long-range in-plane order is present in stoichiometric LaCoO3that quickly disappears in non-stoichiometric films.
We end with some preliminary results of optical characterization of LCO andLCO/LSCO layers, in preparation for high-speed optical measurements of ultrafast switching dynamics.
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