Uncorrelated multiple conductive filament nucleation and rupture in ultra-thin high-κ dielectric based resistive random access memory
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(Color online) SET and RESET in a bipolar resistive switching device. Top inset shows the cross-sectional TEM micrograph of the ultra-thin dielectric based NiSi/HfO2/SiO2/p+-Si MIS structure. The electrical data shows the bipolar I-V switching trends where the compliance current was capped to 1 mA. Two discrete increases in the current (SET) that accompany the formation of two individual conductive paths have been identified. The first SET occurred at voltage +4.2 V with S = 0.06, which indicates the first conductive path was near the source. The bottom inset shows the details of the first SET. The second SET occurred at voltage +4.8 V. Is ∼ Id , so the S value was 0.5, implying the effective conductive paths location is in the center of the channel. The second conductive path might be at the drain edge of the transistor since the contribution of Is and Id were roughly the same. Two discrete RESETs have been observed during the negative voltage sweep. The current first abruptly decreased from 80 μA to 1 μA at −1.3 V, followed by a second current decreased from about 2 μA to 80 nA at −1.7 V. Both the switching events are of about two orders in magnitude change in the gate current.
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(Color online) (a) STEM-HAADF micrographs of the MIS device in Fig. 1 after RESET showing two ruptured CFs: CF A and CF B. The bright contrast of the region in the Si-substrate beneath CF A is the lateral diffusion of Ni-based silicide compounds from the source, which is termed as DBIM (Refs. 22–24). DBIM can also be the vertical diffusion of NiSi from TE (anode) into the broken-down path in the dielectric. DBIM from both lateral and vertical directions could be the physical defects responsible for CF A and CF B, forming a sub-capacitor-like MIM structure. (b) and (c) High resolution TEM micrographs of CF A and CF B, respectively. Here, the term HK represents the high-κ dielectric of HfO2, while the term IL represents the interfacial layer of SiO2. The diameter of the ruptured conductive filament is around 5-10 nm.
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(Color online) (a) Ni (dashed line) and O (solid line) EELS signal profiles for the line scans across the NiSi TE, the dual-layer dielectric of HfO2 and SiO2, and the Si substrate at three different locations near the CF A region. The horizontal line is the position along the stack, while the vertical line is the intensity of each chemical element signal. The intensity values are normalized for comparison. The three line scan locations are shown in (b): a ruptured filament (black line), a region absent of the ruptured filament above DBIM (blue line), and a non-filament spot (red line). At the ruptured filament location, the O intensity is lower than the absence of filament region, while Ni diffuses into the dielectrics. (c) and (d) Ni (dashed line) and O (solid line) EELS line profiles of CF B acquired at two locations indicated in the inset STEM micrograph. Similar Ni and O distribution trends as in CF A have been observed.
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