High‐Performance Programmable Memory Devices Based on Co‐Doped BaTiO₃

Abstract

Recently, resistive random access memory (RRAM) devices have attracted great attentions for a variety of advantages such as high-density, high-speed, low-power, and thus promising applications in next-generation nonvolatile memory technology. [1][2][3][4] The memory effect is realized through switching between high resistance state (HRS) and low resistance state (LRS), controlled by electric fi eld with either opposite polarity (bipolar) or different magnitude (unipolar). In understanding this resistive switching (RS) effect, quite a number of microscopic mechanisms have been proposed, while the formation/rupture of conductive fi laments in insulating matrix as one of the major switching mechanisms has been intensively studied. [3][4][5] It is demonstrated that the composition of the conductive fi laments and their formation/rupture are remarkably materials-dependent, thus the RRAM device performance is materials dependent too. For the favored device performance, complex transition metal oxides may be the most promising candidates. [ 3 ] The strong correlation of electrons in these oxides brings out rich competing phenomena between various electronic phases in a delicate balance, allowing a phase change and thus dramatic change of the electrical property, e.g. resistance, in response to a minute external perturbation, e.g., an applied electric fi eld. [ 6 ] Furthermore, the atomic and/or electronic reconstruction at grain boundaries or doping centers in these oxides enriches the electronic phases, providing an opportunity for advanced electronics. [ 7 , 8 ] By an extensive testing of various oxide materials in terms of the RRAM performance, we eventually choose ferroelectric BaTiO 3 for the present study. A low-doping at the Ti-site can introduce itinerant electrons, leading to the presence of inhomogeneous state, i.e., the coexistence of metallic and ferroelectric phases. [ 9 ] As an electric fi eld is applied on this inhomogeneous state, the local Joule heating induced by inhomogeneous current distribution may lead to the reconstruction of local atomic and/or electronic phases, causing the large change in conductance. [ 8 , 10 ] Besides, earlier works suggested that the ferroelectric displacements will also change the electronic structure. [ 11 ] Hence, BaTiO 3 -based materials offer a good opportunity to develop the RRAM devices with more promising functionalities. In this work, we fabricate 5at% Co-doped BaTiO 3 (BTCO) fi lms. The unipolar RS characteristics with the endurance of more than 10 5 and switching time of less than 10 ns in addition to other preferred properties are demonstrated.We fabricated the BTCO-based memory cell, with the entire materials stack (thicknesses) of Au(400 nm)/BTCO(400 nm)/ Pt(300 nm)/Ti(50 nm)/SiO 2 (500 nm)/Si. The X-ray diffraction (XRD) data indicate that the BTCO fi lms are polycrystalline, as shown in Figure 1 a. Figure 1 b and c depict a schematic drawing of the measurement confi guration and the scanning electron Figure 1 . (a) XRD data of the as-prepared BaTi 0.95 Co ...

Resistive switching in hafnium dioxide layers: Local phenomenon at grain boundaries

“…Until now RS was observed only in lithographically fabricated devices (MIM capacitors or transistors), the gate areas of which are covered by a metal film, which prevents a direct observation of the post-forming features of the dielectric material. 8,9 Therefore, a device-level study cannot unambiguously address the questions of (a) whether the switching is filament-driven and (b) which morphological properties of the dielectric can be responsible for the RS. In this study, the RS phenomenon in HfO 2 dielectric, in both the amorphous and polycrystalline phases, was studied at the nanoscale using conductive atomic force microscopy (CAFM).…”

Enhanced bipolar resistive switching behavior in polar Cr-doped barium titanate thin films without electro-forming process

“…[26][27][28][29][30] Li et al 31 and Chang et al 28 reported the BRS behavior in the multilayer BTO thin film with a very high compliance current ∼ 100 mA. Similarly, Yan et al 32 reported URS behavior in the Co doped BTO thin films with a compliance current ∼ 100 mA. In addition, Chang et al reported an ON/OFF ratio study with varying top electrodes such as Al, ITO, Au and Pt; where it shows that Au and Pt as top metal electrodes offer the R off /R on ratio ∼10.…”

Enhanced resistive switching effect in Ag nanoparticle embedded BaTiO3 thin films

“…More interestingly, the resistive switching occurs at bias as low as 1 V, without a forming process by large voltage, which is usually required by most resistive switching system. [12][13][14] This is very promising for RRAM memories with ultralow operation bias.…”