Protons: Critical Species for Resistive Switching in Interface‐Type Memristors

Abstract

Fe 2 O 3 , VO 2 ) and perovskite oxides (e.g., SrTiO 3 , BaTiO 3 , SrZrO 3 ) have been widely explored for RS and related applications. [5][6][7][8] Significant improvements have been made in memristor technology by realizing large on/off ratio, fast switching, excellent retention, low read/ write voltage, and integration with complementary metal-oxide semiconductor technology. [5,[9][10][11] In general, there are two types of memristive switching devices: filamenttype (FT) and interface-type (IT). Most of nanoionic memristors can be categorized as FT memristors and they use the migration of defects such as oxygen vacancy) and active metal electrode ions, such as Ag + . The operation of FT memristors relies on the formation of random filaments, which induces large cycle-tocycle, cell-to-cell, and device-to-device variations. [12][13][14] The underlying switching mechanisms in FT memristors have been well studied. In addition to the roles of ionic migration on the switching, [15,16] environmental effects such as role of ambient gases have also been extensively studied. [17] It was reported that ambient oxygen or water vapor partial pressure has a profound influence on the RS behavior in different FT memristors using SiO 2 , [18] Ta 2 O 5 , [19] TiO 2 , [20] HfO 2 , [19] and SrTiO 3 [21] as a switching Interface-type (IT) resistive switching (RS) memories are promising for next generation memory and computing technologies owing to the filament-free switching, high on/off ratio, low power consumption, and low spatial variability. Although the switching mechanisms of memristors have been widely studied in filament-type devices, they are largely unknown in IT memristors. In this work, using the simple Au/Nb:SrTiO 3 (Nb:STO) as a model Schottky system, it is identified that protons from moisture are key element in determining the RS characteristics in IT memristors. The Au/Nb:STO devices show typical Schottky interface controlled current-voltage (I-V) curves with a large on/off ratio under ambient conditions. Surprisingly, in a controlled environment without protons/moisture, the large I-V hysteresis collapses with the disappearance of a high resistance state (HRS) and the Schottky barrier. Once the devices are re-exposed to a humid environment, the typical large I-V hysteresis can be recovered within hours as the HRS and Schottky interface are restored. The RS mechanism in Au/Nb:STO is attributed to the Schottky barrier modulation by a proton assisted electron trapping and detrapping process. This work highlights the important role of protons/moisture in the RS properties of IT memristors and provides fundamental insight for switching mechanisms in metal oxides-based memory devices.

An Interface‐Type Memristive Device for Artificial Synapse and Neuromorphic Computing

“…[ 36,37 ] A detailed study on the RS mechanisms in the Au/Nb:STO interface‐type device is presented in our previous work, which explored the critical roles of protons (from moisture) in charge trapping/detrapping and Schottky barrier modulation. [ 34 ]…”

“…t \left.\right) \textrm{ } \alpha \textrm{ } t^{- 0.06}$ at 0.4 V. [ 36 ] This minor current decay may be due to the progressive trapping of charges which were detrapped during the set process. [ 34 ] As the negative read voltage promotes charge trapping process, LRS current decay was much faster with −0.4 V readout than with +0.4 V readout. The device maintained a high on/off ratio of ≈10 4 at −0.4 V and 10 5 at 0.4 V. The performance of the Au/Nb:STO IT devices was comparable or even better than that of some other metal oxide‐based FT memristors.…”

“…The switching mechanism of such systems has been explored carefully. [34][35][36] Our previous work has shown that protons-assisted electron trapping and detrapping are likely responsible for the switching at metal/Nb:STO interfaces. [34] By altering voltage polarity, amplitude, and duration, a multilevel nonvolatile analog resistance window is demonstrated.…”

“…[34][35][36] Our previous work has shown that protons-assisted electron trapping and detrapping are likely responsible for the switching at metal/Nb:STO interfaces. [34] By altering voltage polarity, amplitude, and duration, a multilevel nonvolatile analog resistance window is demonstrated. The proposed artificial synapse accurately emulates various critical functions of biological synapse, including paired-pulse facilitation (PPF), short-term potentiation/depression (STP/STD), long-term potentiation/ depression (LTP/LTD), and spike timing dependent plasticity (STDP).…”

Engineering of Grain Boundaries in CeO2 Enabling Tailorable Resistive Switching Properties

“…It was also reported that charge trapping and de-trapping mechanism is related to protons/moisture. [65] Therefore, it is possible that multiple sources contribute to the overall switching process.…”