An oxygen vacancy mediated Ag reduction and nucleation mechanism in SiO2 RRAM devices

Abstract

Density Functional Theory (DFT) calculations were used to model the incorporation and diffusion of Ag inAg/a-SiO2 resistive randomaccess memory (RRAM) devices. The Ag clustering mechanism is vital for understanding device operation, but is poorly understood. In this paper, an O vacancy (VO) mediated model of the initial stages of Ag clustering is presented, where the VO is identified as the principle site for Ag + reduction. The Ag + interstitial is energetically favoured at the Fermi energies of Ag, W and Pt, indicating that Ag + ions are not reduced at any electrode via electron tunnelling. The adiabatic diffusion barriers of Ag + are lower than Ag 0 with a strong dependence on the local morphology, supporting Ag + being the mobile species during device operation. Ag + ions bind to VO forming the [Ag/VO] + complex, which reduce Ag + via charge transfer from the Si atoms in the vacancy. The [Ag/VO] + complex is then able to trap an electron forming [Ag/VO] 0 . The probability for a vacancy to act as a reduction site is 33, 33 and 11 % at the Ag, W and Pt electrodes respectively. This complex then acts as a nucleation site for Ag clustering with the formation of [Ag2/VO] + which is reduced by the above mechanism.

Advances of RRAM Devices: Resistive Switching Mechanisms, Materials and Bionic Synaptic Application

“…Compared with reactive metal, where Platinum (Pt) [12] always acts as BE in order to provide activity variation of RRAM devices. In addition, semiconductor materials like heavily doped silicon and indium tin oxide (ITO) are always chosen as electrodes due to their high electrical conductivity [13,14]. Currently, 2D thin film materials such as graphene and graphene oxide (GO) are also attracting increasing attention as candidates of electrode because of the excellent mobility of carriers and high thermal/electrical conductivity [15][16][17].…”

“…Materials of RS medium play a decisive role in the switching process, which has a direct and significant influence on the performance of RRAM devices such as ON/OFF ratio and device stability. On the other hand, electrode materials of RRAM devices more affect switching modes of RRAM devices, which should also be under further investigation [13,14,18,48,63,64].…”

Electro-thermal transport in disordered nanostructures: a modeling perspective

“…These two sets of equations must be solved iteratively until convergence is reached. The fulllment of this property can be veried by looking at the electrical current, eqn (18), and the sum of the electronic and thermal energy currents, eqn (19) and (25). Both quantities have to be conserved along the transport axis of the investigated device, when the GFs do not vary anymore.…”

“…Aer converging the electron and phonon densities, physical quantities can be extracted. In addition to the currents that are given by eqn (18) and (25), the lattice temperature is of particular interest to quantify the effect of self-heating. Different possibilities exist to assign a local temperature to individual atoms.…”

Modeling of Diffusion and Incorporation of Interstitial Oxygen Ions at the TiN/SiO2 Interface

“…The processing and handling benefits are derived from the abundance of SiO 2 expertise in the CMOS technology, particularly in the growth and electrical characterization of SiO 2 films. The SiO 2 based devices are divided into two main types: those based upon the inter-diffusion of metal ions, such as via electrochemical metalisation, [19][20][21][22][23][24][25][26] and valence change memory (VCM) where a CF is formed as a result of reduction under bias application. 1,2,[5][6][7][8]17 In VCM the CF is made up of oxygen vacancies, dependent upon material and mode of operation either V O or O i are suggested to be the mobile species during forming.…”