Engineering High-K Switching Devices for in-Memory Computing
Authors: Zeinati Aseel , Misra Durga , Triyoso Dina , Tapily Kandabara , Clark Robert D , Consiglio Steven , Lombardo Sarah , Wajda Cory S , Leusink Gert 
Published: August 2024

Selecting and processing of appropriate stack materials for HfO2-based RRAM devices significantly influences the distribution of defects and oxygen vacancies (Vo) within the switching layer, thereby playing an important role in their switching behavior (1). Controlling this distribution to have more oxygen vacancies near the top electrode (TE) while reducing them near the bottom electrode (BE) results in reduced switching power and enhanced multilevel cell characteristics (MLC) of RRAM devices (2) and that makes them as promising options for in-memory computing. Since RRAM devices fabricated as metal-insulator-metal stack, exploring the impact of each layer remains an active area of research.
In this work, we compared different devices by varying the materials of each layer. The first comparison is by varying the oxide layer with same TE (Ru) and BE (TiN) by (i) using stoichiometric HfO2 and (ii) employing HfO2 treated with hydrogen plasma at the midpoint. The device treated with hydrogen plasma consumed nanowatts power compared to the stoichiometric device that consumed hundreds of microwatts to be switched. The introduction of hydrogen plasma treatment at the midpoint of the HfO2layer redirects more Vo towards the TE, explaining the reduction in the switching power (1). While applying pulse SET operation, the hydrogen plasma-treated device exhibited excellent conductance quantization, whereas the stoichiometric device quickly saturated and remaining stuck in a low-resistance state (LRS) due to a lack of Vo (3). Introducing a bilayer Al2O3/HfO2 dielectric significantly decreased switching power consumption to a few microwatts range compared to the stoichiometric device. This reduction is attributed to the rapid formation of Vo within the Al2O3 layer, subsequently stimulating Vo formation within the HfO2layer (4). However, the hydrogen plasma-treated device still maintains the lowest power consumption.
Further investigation involved in changing the TE material, Ru and TiN to understand the impact of the TE, given its working function and interface barriers significantly affect the distribution of Vonear the TE. The device using Ru as the TE switched with a 3nA compliance current (1). Introducing nitrogen plasma treatment to the bottom electrode of the TiN device improved its switching behavior due to the reduction Vo near the BE because of formation of the Hf-N bond and led to increase the Vo near the TE (5). This enhancement was marked by a reduction in switching power to picowatts and stabilization of the conductive filament within the oxide. This device demonstrated improved conductance quantization.
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