Leakage current through the poly-crystalline HfO2: Trap densities at grains and grain boundaries

Abstract

We investigate the role of grains and grain boundaries (GBs) in the electron transport through poly-crystalline HfO2 by means of conductive atomic force microscopy (CAFM) measurements and trap-assisted tunneling simulations. CAFM experiments demonstrate that the leakage current through a thin dielectric film preferentially flows via the GBs. The current I-V characteristics measured on both types of sites, grains, and GBs are successfully simulated by utilizing the multiphonon trap-assisted tunneling model, which accounts for the inelastic charge transport via the electron traps. The extracted density of electrically active traps, whose energy parameters match those of the positively charged oxygen vacancies in hafnia, is ∼3 × 1019 cm−3 at the grains, whereas a much higher value of (0.9÷2.1) × 1021 cm−3 is required to reproduce the leakage current through the GBs.

Physical Mechanisms behind the Field‐Cycling Behavior of HfO2‐Based Ferroelectric Capacitors

“…However, it should be noted that the density of defects evaluated from the leakage current corresponds mainly to those located at the grain boundaries, where they contribute the most to the leakage current. [45] Namely, the leakage current thought the grain boundaries is more than tenfold higher than through the grain itself. Thus, the diffusion of the vacancies thought the grain would keep the leakage current constant during the wake-up stage.…”

“…Detailed transport mechanism and dominating trap-assisted-tunneling within the HfO 2 based dielectric were previously reported elsewhere. [43][44][45] Besides the vacancies, that actively assist the electron TAT current, [44] interstitial oxygen ions were considered within the stack. These oxygen vacancies and ions were created by doping the HfO 2 material with Sr as well as by pulling oxygen out of the hafnia during the top electrode deposition process and annealing step.…”

Optoelectronic properties and polar nano-domain behavior of sol–gel derived K0.5Na0.5Nb1−xMnxO3−δnanocrystalline films with enhanced ferroelectricity

“…38 As an example, compared with the KNNM0 film, the KNNM0.06 film has a smoother surface and a smaller interval between two grains with the minimum RMS surface roughness. Generally, extended defects in polycrystalline metal oxide films, such as grains and grain boundaries (GBs), are thought to play an important role in determining their electrical characteristics.…”

Reconfigurable Memristive Device Technologies

“…In poly-crystalline oxide switching layers, such as HfO x , grain boundaries are present that are parallel to the direction of current flow through the device. It has been observed that high densities of oxygen vacancies collect at these grain boundaries, which likely define the location of switching filaments [34]. The details of the switching process in MOxBF cells are still a subject of active research.…”

“…(b) SEM image of a 40 Â 40 Ag/a-Si/SiGe crossbar array integrated on top of a CMOS chip. (c) and (d) Bitmap images of the two sets of data stored and retrieved in the 40 Â 40 crossbar array in (b).Reprinted with permission from[34]. Copyright (2012) American Chemical Society.…”