Evolution of Filament Formation in Ni/HfO₂/SiO_x/Si‐Based RRAM Devices

Abstract

(high resistance) processes of unipolar switching devices depend on the amplitude of the applied voltage rather than its polarity. This occurs because the formation and rupture of the metal nanofi lament (MNF) in unipolar switching is triggered by Joule heating (which is polarity-insensitive). For bipolar switching devices on the other hand, the polarity of the applied voltage must be opposite for SET and RESET, as this mode operates via the reversible voltage-dependent drift of oxygen vacancies and ions. [9][10][11][12][13] Hence, understanding the fundamental microstructural and compositional evolution of the fi lament and conduction path (mainly oxygen vacancies) in the dielectric layers is the key to controlling and optimizing RRAM devices both in terms of performance and reliability.Previous studies using physical microscopy techniques have shown that the shape of MNFs can be conical or hyperboloidal and the number of MNFs formed in the dielectric stack can vary from one device to another. [14][15][16][17] The structural and compositional evolution of the conduction paths and fi laments has been studied in various materials systems, including TiO 2 /Pt, ZnO/Pt, SiO 2 /Ag, a-TaO 2-x /Pt, and SrTiO 3 /Ag. [18][19][20][21][22] Our study on Ni/HfO 2 /SiO x /n + Si-based (i.e., MIS) RRAM is crucial because this material system is the most obvious potential candidate for commercial RRAM devices, as it is based on the established silicon device CMOS platform. In this study, we designed an asymmetric test structure for in situ transmission electron microscope (TEM) characterization, electrical testing, and chemical analysis with nanometer spatial precision. The test structure comprises a Ni top electrode and HfO 2 /SiO x dielectric layers on an n + doped Si substrate (doping concentration N D ≈10 19 cm −3 ). For our sample, the conventional (100) Si wafers were used as the starting substrate. The HfO 2 / SiO x dielectric layers were fabricated through a precisely controlled rapid thermal annealing process under 700 °C and N 2 ambient. Based on this test structure, we carried out a structural and compositional nanoscale characterization of the stressed devices in both the SET and RESET states. Our study provides suffi cient evidence to quantify the role of the top Ni electrode and its partial migration toward the dielectric and Si substrate for SET and RESET sweep conditions. The evolution of the MNF shape and its chemical composition in the dielectric layers is studied here, as these fi laments are the critical features that determine RRAM device reliability and scalability.The layout of the fabricated test structure is shown in Figure 1 a,b. The Ni (100 nm)/HfO 2 (3 nm)/SiO x (3 nm)/n + Si stack blanket wafer was prepared into a comb-shaped structure by focused ion beam (FIB) milling with in situ liftoff and low-energy ion cleaning. The resultant test structures have multiple "isolated" test units which were mounted to a grounded Although the resistive switching phenomenon in dielectric layers was fi rst documented...

Recommended Methods to Study Resistive Switching Devices

“…Another possibility is to fabricate an ultrathin electron-transparent MIM structure and place a mechanical probe on the top electrode (Figure 10b). [11,19] Computational studies may also help to shed light into this issue. For this reason, when doing this experiment, it is recommendable first to characterize such parameters doing additional experiments using reference samples.…”

Enhanced stability of filament-type resistive switching by interface engineering

“…It is well acknowledged that there are only two stable stoichiometric solid phases in TaO x : (a) high oxygen defective phase (or conductive path) and (b) low oxygen defective phase (or insulating matrix)910. Such property guarantees relatively stable filaments formation in the TaO x based RRAM devices1112.…”

Oxygen migration during resistance switching and failure of hafnium oxide memristors

“…[1][2][3][4][5] There has been particular interest in understanding the role of migration of oxygen atoms in determining the operation of memristors. [6][7][8][9][10][11] Similar recent advances in understanding the localized nanoscale physico-chemical changes underlying resistance switching 4,[12][13][14][15] have opened up fresh interests into studying the effect of atomic movements on extended device operation and the nanoscale material behavior during eventual failure and possible techniques to mitigate such failure. [16][17][18] To enable scanning transmission x-ray microscopy (STXM) measurements, each device was built on a 200 nm low-stress Si 3 N 4 film suspended over 50 µm x 50 µm holes etched through a silicon substrate.…”