Improving the Memory Window/Resistance Variability Trade-Off for 65nm CMOS Integrated HfO2 Based Nanoscale RRAM Devices

In this work, we have addressed cycle to cycle switching variability by modifying a key step in CMOS integrated RRAM devices fabrication, namely the atomic layer deposition (ALD) process used to deposit the HfO
₂
switching layer. Two different HfO
₂
ALD processes were utilized, one with an organic-based precursor, the other with a chlorine-based precursor. The trade-off between memory window (MW) and variability in the high resistance state (HRS) for RRAM cells was investigated with respect to compliance currents and reset voltages for multiple devices using both ALD precursors. The RRAM devices fabricated with the Cl-based precursor showed significant improvement in their MW/HRS resistance variability trade-off, compared to devices fabricated with the organic-based precursor over a range of compliance currents (150 μA to 450 μA) and reset voltages (-1.3V to -1.7V). Additionally, the MW shows stronger correlation with resistance variability as a function of reset voltage, mostly due to the significant change in average HRS values. To gain a statistically significant comparison, all 64 1 Transistor 1 RRAM (1T1R) cells in an 8×8 RRAM array were tested on a center die on wafers processed using both ALD precursors. Based on those 64 tested 1T1R cells, we demonstrated more than 80% switching yield for the Cl precursor HfO
₂
based RRAM devices, as compared to 38% for the organic precursor devices. Additionally, 1T1R RRAM arrays fabricated using the Cl-based precursor showed more than 2× improvement in MW versus those fabricated using the organic-based precursor.