Multilevel resistive switching in TiO2/Al2O3 bilayers at low temperature

Abstract

We report an approach to design a metal-insulator-metal (MIM) structure exhibiting multilevel resistive switching. Toward this end, two oxide layers (TiO2 and Al2O3) were combined to form a bilayer structure. MIM structures demonstrate stable bipolar switching relative to the resistive state determined by the bias voltage. The resistive state of such bilayer structures can be electrically tuned over seven orders of magnitude. The resistance is determined by the concentration of oxygen vacancies in the active layer of Al2O3. To elucidate a possible mechanism for resistive switching, structural studies and measurements have been made in the temperature range 50–295 K. Resistive switching occurs over the entire temperature range, which assumes the electronic character of the process in the Al2O3 layer. The experimental results indicate that hopping transport with variable-length jumps is the most probable transport mechanism in these MIM structures.

Contact Engineering Approach to Improve the Linearity of Multilevel Memristive Devices

“…Adding the Al 2 O 3 layer to the TiO 2 layer allows extending the range of the nonvolatile tuning of the structural resistance to seven orders of magnitude. Thus, in Pt-BE/TiO 2 /Al 2 O 3 (10 nm)/Pt-TE bilayer structures, aluminum oxide plays the role of an active (switching) layer [15]. This statement is supported by experimental observation of the resistive switching in single-layer Pt/Al 2 O 3 /Pt structures with an R OFF /R ON ratio of about seven orders of magnitude (Figure 4).…”

“…Compared to Pt-BE/TiO 2 /Al 2 O 3 /Pt-TE bilayer structures, for which the degree of power dependence of the corresponding part of I-V curves for HRS differs from those for LRS, Pt-BE/TiO 2 /Al 2 O 3 /Al-TE bilayer structures exhibit the same degree of power dependence for both HRS and LRS (Figure 5c). Previous experimental evidence [15,19] suggests the dominant role of electronic processes in the bipolar resistive switching in bilayer structures with platinum electrodes. The transition from the HRS to the LRS is associated with reaching the trap-filling limit (TFL) in the local conductive filamentary area at a high injection level.…”

“…Traps or localized states within the Al 2 O 3 bandgap are formed by the oxygen vacancies. The SCLC transport mechanism is manifested in power dependence of current on voltage with a changeable degree of power [15]. Both bipolar and multilevel resistive switching are clockwise for these structures.…”

“…Recently, we developed an approach to design thin-film TiO 2 /Al 2 O 3 bilayer structures [14,15], exhibiting electric-field analog tuning of the nonvolatile resistance state in the range of seven orders of magnitude. Despite a wide memory window and the existence of multiple nonvolatile resistance states, TiO 2 /Al 2 O 3 bilayer structures demonstrate nonlinear behavior originating from the initial difference in the resistive properties of TiO 2 and Al 2 O 3 layers.…”

Compact Model for Bipolar and Multilevel Resistive Switching in Metal-Oxide Memristors

“…In these structures, a 5 nm thick Al 2 O 3 layer oxide plays a role of an active (or switching) layer, while 30-60 nm 02.thick titanium oxide layer acts as a reservoir of oxygen vacancies. Moreover, the similar devices demonstrate high switching speed, low power consumption, wide dynamic range, high resistance to cyclic degradation, high scalability, and compatibility with CMOS technologies [25][26][27][28].…”