ASCENT Theme 1(A) LaCoO3-based IMT Selector Update

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 T_chip >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 La_0.5Sr_0.5CoO₃ (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 LaCo_1.1O_3+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.

This meeting is only available to the JUMP research community, such as Principal Investigators, Postdoc researchers, Students, and Industry/Government liaisons.