Role of Ti and Pt electrodes on resistance switching variability of HfO2-based Resistive Random Access Memory

Abstract

This paper deals with the role of platinum or titanium–titanium nitride electrodes on variability of resistive switching characteristics and electrical performances of HfO2-based memory elements. Capacitor-like Pt/HfO2 (10nm)/Pt and Ti/HfO2 (10nm)/TiN structures were fabricated on top of a tungsten pillar bottom electrode and integrated in-between two interconnect metal lines. First, quasi-static measurements were performed to apprehend the role of electrodes on electroforming, set and reset operations and their corresponding switching parameters. Memory elements with Pt as top and bottom electrodes exhibited a non-polar behavior with sharp decrease of current during reset operation while Ti/HfO2/TiN capacitors showed a bipolar switching behavior, with a gradual reset. In a second step, statistical distributions of switching parameters (voltage and resistance) were extracted from data obtained on few hundreds of capacitors. Even if the resistance in low resistive state and reset voltage was found to be comparable for both types of electrodes, the progressive reset operation observed on samples with Ti/TiN electrodes led to a lower variability of resistance in high resistive state and concomitantly of set voltage. In addition Ti–TiN electrodes enabled gaining: (i) lower forming and set voltages with significantly narrower capacitor-to-capacitor distributions; (ii) a better data retention capability (10years at 65°C instead of 10years at 50°C for Pt electrodes); (iii) satisfactory dynamic performances with lower set and reset voltages for ramp speed ranging from 10−2 to 107V/s. The significant improvement of switching behavior with Ti–TiN electrodes is mainly attributed to the formation of a native interface layer between HfO2 oxide and Ti top electrode.