Ag-GST/HfO_x-based unidirectional threshold switching selector with low leakage current and threshold voltage distribution for high-density cross-point arrays

초록

The use of electrochemical-metallization-based volatile threshold switching selectors in cross-point arrays has been widely explored owing to their high on-off ratios and simple structure. However, these devices are unsuitable for cross-point architectures because of the difficulty in controlling the random filament formation that results in large fluctuations in the threshold voltage during operation. In this study, we investigated the unidirectional threshold transition characteristics associated with an Ag/GST/HfOx/Pt-based bilayer selector and demonstrated the occurrence of a low leakage current (< 1 x 10(-11) A) and low distribution of the threshold voltage (triangle 0.11 V). The bilayer structure could control the filament formation in the intermediate state through the insertion of an HfOx tunneling barrier. By stacking a bilayer selector with NiOx-based resistive random-access memory, the leakage and programming currents of the device could be significantly decreased. For the crossbar array configuration, we performed equivalent circuit analysis of a one-selector one-resistor (1S1R) devices and estimated the optimal array size to demonstrate the applicability of the proposed structure. The maximum acceptable crossbar array size of the 1S1R device with the Ag/GST/HfOx/Pt/Ti/NiOx/Pt structure was 5.29 x 10(14) (N-2, N = 2.3 x 10(7)).

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