Non-volatile resistive random-access memory (RRAM) devices are currently being investigated as a low power, high density and high-speed alternative DRAM (1). A transition metal oxide dielectric layer is typically used as an insulating layer in a metal-insulator-metal (MIM) structure. To reduce the large variability of switching parameters and high operation current in these RRAM devices, bilayer dielectric structures are being explored.

In this work we have used several different bilayer structures using different dielectrics. In each device the bottom electrode (BE) was 10nm Ti/50nmTiN followed by 1nm Al₂O₃. The second dielectric layer or the switching layer was a 7-nm HfO₂ (R3), HfZrO₂ (R4 with Hf:Zr%=50%) or HfAlO₂ (R1 with Hf:Al%= 3%) followed by the top electrode (TE) constituting of 8nm Ti/6nm ALD TiN+50nm PVD TiN. In some cases, the top electrode was varied to 2nm ALD TiN/8nm Ti/6nm ALD TiN+50nm PVD TiN (R5) by adding a 2nm ALD TiN layer prior to 8nm Ti. Some devices with HfZrO₂ (R2) were subjected to a post deposition anneal (PDA) at 700^oC for 60 s. In all cases, to enhance the switching characteristics on the top electrode 8 nm Ti was used as the cap layer material except in the case of R5 where 2nm of ALD TiN was deposited prior to 8 nm of Ti. The use of thin dielectric layer of 1nm Al₂O₃ was to suppress the sneak-path problem (3) in the low resistance state (R_ON).

Comparing the variation of switching layer, it was observed that the device with 1nm Al₂O₃/7nm HfAlO₂ (R1) provided the superior average R_off/R_on values and both set and reset power compared to HfO₂ (R3), and HfZrO₂ (R4) devices. When the HfZrO₂ (R4) devices were compared with the identical device with PDA (R2) Ron increased and Roff decreased for the PDA device, reducing the R_off/R_on value. Variation of cap layer to TiN instead of Ti also showed similar R_off/R_onbehavior.

1. D. Ielmini, Semicond. Sci. Technol. Vol. 31, 063002, 2016.
2. Xiaorong Chen and Jie Feng, Appl. Phys. A, vol. 120, 67 2015
3. U. Chand, K-C. Huang, C-Y. Huang, and T-Y. Tseng, IEEE Trans. on Electron Devices, vol. 62(11), 3665, 2015