Article
Breakdown voltage and dielectric constant measurements
The current density–voltage (J–V) and capacitance–frequency (C–f)
characteristics of the films in metal/a-BN/n-Si stacks were measured
using a Tektronics K4200A-SCS parameter analyser system and a Karl
Suss PA-200DS semi-automatic probe station. a-BN-based capacitors
were fabricated on BN films directly deposited or transferred onto n-Si
substrates. To prevent polymer contamination during device fabrica-
tion, a shadow mask with a 200-μm-diameter pattern was used, and a
100-nm-thick Cu electrode was deposited over the a-BN/Si stack. After
the device fabrication, capacitance–voltage units in the parameter
analyser system were used to perform the C–f measurements. We car-
ried out the C–f measurements in the frequency range 1 kHz–10 MHz
with a hold bias of 0.5 V and an a.c. drive of ±30 mV. The measured
capacitance values did not change substantially as a function of the
applied voltage of 0.5 V. Therefore, the relative dielectric constant was
evaluated using the relation κ = Ct/Aε 0 , where t denotes the a-BN film
thickness, A represents the area and ε 0 denotes the dielectric constant
of vacuum. At high frequencies exceeding 5 MHz, considerable noise
levels were observed in the capacitance, probably owing to the low
impedance of the a-BN capacitor. Subsequently, the J–V characteristics
of both film samples were determined using source measurement units
of the parameter analyser system. The applied voltage was swept from
0 to 10 V with a resolution of 1 pA and a compliance current of 10 mA.
Additionally, measurements were carried out at 50-mV voltage steps
over 10 power line cycles to prevent degradation due to bias stresses.
Diffusion barrier performance
To evaluate the performance of the films as diffusion barriers,
~3-nm-thick samples of a-BN and TiN (deposited by radiofrequency
sputtering) were deposited on Si substrates. Subsequently, the samples
were coated with 80-nm-thick Co layers using d.c. sputtering. After
deposition, the samples were placed inside a furnace for annealing.
The furnace temperature was ramped up at a rate of 40 °C min−1 in a
vacuum of less than 10−4 torr. During annealing, thermally activated
diffusion is expected to occur at the interface between Co and the
dielectric barrier materials.
Data availability
The datasets generated and/or analysed during the current study are
available from the corresponding authors on reasonable request.
Code availability
The code used to generate the figures is available from the correspond-
ing authors on reasonable request.
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Acknowledgements We thank UNIST Central Research Facilities (UCRF) and Y. K. Kim for the
cross-sectional high-resolution TEM images. This work was supported by Samsung Electronics
(Samsung-SKKU Graphene/2D Center), the research fund (NRF-2017R1E1A1A01074493 and
NRF-2019R1A4A1027934), the IBS (IBS-R-019-D1) and a grant (CASE-2013M3A6A5073173) from
the Centre for Advanced Soft Electronics under the Global Frontier Research Program via the
National Research Foundation of the Ministry of Science and ICT, South Korea. The NEXAFS
experiments performed at the 4D, 6D and 10A2 beamlines of the Pohang Accelerator
Laboratory (PAL) were supported in part by the Ministry of Science and ICT, POSTECH and
UNIST. M.C. acknowledges support from Leverhulme Trust Research Grant RPG-2019-227. S.R.,
A.A. and M.C. acknowledge the European Union Horizon 2020 research and innovation
programme for grant number 785219 and 881603 (Graphene Flagship). A.A. is supported by
Project MECHANIC (PCI2018-093120) funded by Ministerio de Ciencia, Innovación y
Universidades. The Catalan Institute of Nanoscience and Nanotechnology is funded by the
CERCA Programme/Generalitat de Catalunya and supported by the Severo Ochoa Centres of
Excellence programme, funded by the Spanish Research Agency (grant number SEV-2017-
0706).Author contributions H.S.S. and H.-J.S. planned and supervised this project. S.H., K.Y.M.,
G.K, S.I.Y. and H.S.S. performed the growth and characterization experiments. C.-S.L.,
M.-H.L. and H.-J.S. fabricated the electrical devices. S.W.K. performed and analysed the
ellipsometry measurements. H.-I.L. obtained and analysed the RBS data. Y.L. and Z.L.
obtained the TEM data. K.I., K.-J.K. and T.J.S. measured the NEXAFS data. E.-c.J., H.J. and
J.-Y.K measured the mechanical properties and adhesion. A.A. and S.R. performed the
molecular dynamics simulations. M.C. suggested key experiments and measurements and
helped with the interpretation of results. M.C. wrote and edited the manuscript with H.S.S.
All authors contributed to the writing of the manuscript and agreed on the contents of
the paper.Competing interests The authors declare no competing interests.Additional information
Correspondence and requests for materials should be addressed to M.C., H.-J.S. or H.S.S.
Peer review information Nature thanks Francesca Iacopi, Lain-Jong Li and Junhao Lin for their
contribution to the peer review of this work.
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