Nonpolar resistive memory switching with all four possible resistive switching modes in amorphous LaHoO₃ thin films

We studied the resistive memory switching in pulsed laser deposited amorphous LaHoO₃ (a-LHO) thin films for non-volatile resistive random access memory applications. Nonpolar resistive switching (RS) was achieved in Pt/a-LHO/Pt memory cells with all four possible RS modes (i.e., positive unipolar, positive bipolar, negative unipolar, and negative bipolar) having high R_ON/R_OFF ratios (in the range of ∼10⁴–10⁵) and non-overlapping switching voltages (set voltage, V_ON ∼ ±3.6–4.2 V and reset voltage, V_OFF ∼ ±1.3–1.6 V) with a small variation of about ±5–8%. Temperature dependent current-voltage (I–V) characteristics indicated the metallic conduction in low resistance states (LRS). We believe that the formation (set) and rupture (reset) of mixed conducting filaments formed out of oxygen vacancies and metallic Ho atoms could be responsible for the change in the resistance states of the memory cell. Detailed analysis of I–V characteristics further corroborated the formation of conductive nanofilaments based on metal-like (Ohmic) conduction in LRS. Simmons-Schottky emission was found to be the dominant charge transport mechanism in the high resistance state