Impact of Metal Nanocrystal Size and Distribution on Resistive Switching Parameters of Oxide-Based Resistive Random Access Memories

The introduction of metal nanocrystals (NCs) has been confirmed to improve electrical uniformity of oxide-based resistive random access memory (RRAM) devices significantly; however, the current reports do not systematically elucidate the relationship between the size/distribution of NCs and the electrical uniformity of RRAM devices. In this paper, we focused on the impact of metal NCs size and areal density on the resistive switching (RS) performances of oxide RRAM by atomic layer deposition (ALD) based on the experimental results and theoretical calculation. The dependence of ALD cycles of 50-130 during Pt or CoPtx NCs growth on the RS parameters of Al ₂ O ₃ or HfO ₂ memory units has been evaluated systematically. The RRAM embedded Pt or CoPtx NCs shows the trends: with increasing ALD cycles, the forming voltage, set/reset voltage, the resistance in off and on state, and R _OFF /R _ON ratio entirely first decrease, then flatten, and increase later with a minimum value at about 100 cycles. Although all metal NCs with various sizes enhance the electric field strength compared to at the planar region, only metal NCs with proper NCs size and areal density (9 nm/6-10 × 10 ¹¹ /cm ² in this paper) can effectively produce stronger localized electric field at the tip of metal NCs, leading to optimal RS behavior.