Molecular Bridges Link Monolayers of Hexagonal Boron Nitride during Dielectric Breakdown
Journal article, 2023

We use conduction atomic force microscopy (CAFM) to examine the soft breakdown of monocrystalline hexagonal boron nitride (h-BN) and relate the observations to the defect generation and dielectric degradation in the h-BN by charge transport simulations and density functional theory (DFT) calculations. A modified CAFM approach is adopted, whereby 500 × 500 nm2 to 3 × 3 μm2 sized metal/h-BN/metal capacitors are fabricated on 7 to 19 nm-thick h-BN crystal flakes and the CAFM tip is placed on top of the capacitor as an electrical probe. Current-voltage (I-V) sweeps and time-dependent dielectric breakdown measurements indicate that defects are generated gradually over time, leading to a progressive increase in current prior to dielectric breakdown. Typical leakage currents are around 0.3 A/cm2 at a 10 MV/cm applied field. DFT calculations indicate that many types of defects could be generated and contribute to the leakage current. However, three defects created from adjacent boron and nitrogen monovacancies exhibit the lowest formation energy. These three defects form molecular bridges between two adjacent h-BN layers, which in turn "electrically shorts"the two layers at the defect location. Electrical shorting between layers is manifested in charge transport simulations, which show that the I-V data can only be correctly modeled by incorporating a decrease in effective electrical thickness of the h-BN as well as the usual increase in trap density, which, alone, cannot explain the experimental data. An alternative breakdown mechanism, namely, the physical removal of h-BN layers under soft breakdown, appears unlikely given the h-BN is mechanically confined by the electrodes and no change in AFM topography is observed after breakdown. High-resolution transmission electron microscope micrographs of the breakdown location show a highly localized (<1 nm) breakdown path extending between the two electrodes, with the h-BN layers fractured and disrupted, but not removed.

conduction AFM

h-BN

gate dielectric

and reliability

2D layer breakdown

Author

Alok Ranjan

Singapore University of Technology and Design

Chalmers, Physics, Nano and Biophysics

Sean J. O'Shea

Agency for Science, Technology and Research (A*STAR)

Andrea Padovani

University of Modena and Reggio Emilia

Tong Su

Singapore University of Technology and Design

Paolo La Torraca

University of Modena and Reggio Emilia

Yee Sin Ang

Singapore University of Technology and Design

Manveer Singh Munde

Philipps University Marburg

Chenhui Zhang

King Abdullah University of Science and Technology (KAUST)

Xixiang Zhang

King Abdullah University of Science and Technology (KAUST)

Michel Bosman

National University of Singapore (NUS)

Agency for Science, Technology and Research (A*STAR)

Nagarajan Raghavan

Singapore University of Technology and Design

Kin Leong Pey

Singapore University of Technology and Design

ACS Applied Electronic Materials

26376113 (eISSN)

Vol. 5 2 1262-1276

Subject Categories

Materials Chemistry

Other Physics Topics

Condensed Matter Physics

DOI

10.1021/acsaelm.2c01736

More information

Latest update

3/16/2023