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Ouyang et al. Microstructures 2023;3:2023027 https://dx.doi.org/10.20517/microstructures.2023.22 Page 3 of 10

maximum applicable electric field. By using a thick LaNiO buffer layer (~110 nm) on platinized Si and a
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fast deposition rate, we successfully suppressed the growth of randomly-oriented, discontinuous columnar
grains in the BaTiO film directly deposited on the Pt electrode. Instead, we achieved a (001)-textured,
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continuous columnar nanograin structure. This structure is similar to those obtained at low deposition
temperatures [9,10] but with an increased average grain size (~50-60 nm vs. 10-20 nm), resulting in an
enhanced dielectric response. In comparison to the unbuffered films, the LaNiO -buffered BaTiO films
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exhibited a higher dielectric polarization under the same applied electric field (320 MV/m), leading to a
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~40% boost in the recyclable energy density of a film capacitor (81.0 J/cm vs. 57.1 J/cm @3.2 MV/cm).
Furthermore, to break down the aspect-ratio conservation of the continuous columnar nanograin
[13]
microstructure and its associated thickness scalable energy storage performance , we went back to the
classic random polycrystalline BaTiO film directly deposited on platinized Si. The rapid growth of its grain
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size with deposition time led to an increasing polarizability/relative dielectric permittivity with the film
thickness. Consequently, an enhanced energy storage density close to 50 J/cm was achieved in device-level
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thick BaTiO films (46.6 J/cm @300 V on a 1.3 μm thick film and 48.8 J/cm @460 V on a 2.6 μm thick film).
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These values are ~25 times higher than those of the BaTiO ceramics and serve as an important benchmark
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for the future development of multilayer ceramic capacitors (MLCCs).
MATERIALS AND METHODS
For the preparation of the platinized Si substrate, a Pt/Ti bilayer bottom electrode was used. The Ti layer,
with a thickness of ~10 nm, is the adhesion layer to bond with the Si substrate. The deposition process was
carried out on a (100) Si substrate at 300 °C via dc magnetron sputtering in a pure Ar atmosphere. The
resulting Pt layer showed a high degree of (111) texture. It is noteworthy that these platinized Si substrates
are also commercially available for this purpose. The (100) Si substrates (10 mm × 10 mm) and ceramic
targets of BaTiO and LaNiO (Φ = 50 mm, t = 5 mm, 99.9% purity) were purchased from the Anhui
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Institute of Optics, Chinese Academy of Science. The Pt and Ti sputtering targets (Φ = 50 mm, t = 3 mm,
99.99% purity) were purchased from Zhongnuo Advanced Material Technology Co. Limited (Beijing,
China). The key deposition parameters of the LaNiO -buffered and unbuffered BaTiO film heterostructures
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are summarized in Table 1. Dot-shaped Au top electrodes (Φ = 0.2 mm) were sputtered through a masked
plate at room temperature for electrical measurements.

The microstructure of the two types of BaTiO thin film heterostructures was characterized by using X-ray
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diffraction (XRD) θ-2θ scans in a commercial Rigaku Dmax-rc XRD diffractometer equipped with a Ni-
filtered Cu K radiation source. The surface morphologies were analyzed via atomic force microscopy (AFM)
on a MicroNano D-5A scanning probe microscope (Shanghai, China). The layer thicknesses and
nanostructures of the BaTiO thin film heterostructures were analyzed via transmission electron microscopy
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(TEM) using a JEM-2010 microscope (JEOL, Japan). The room temperature FE hysteresis loops (P-V) were
measured at 100 Hz via a commercial Multiferroic FE tester (Radiant Technology, USA). The voltage-
TM
dependent capacitance (C-V) curves, from which the relative dielectric permittivity and loss tangent as
functions of the applied voltage/field were obtained, were measured by using a B1505A impedance analyzer
(Agilent Technologies, USA) at 5 kHz by applying a small ac signal of 50 mV. The voltage was swept from
negative maximum to positive maximum and vice versa during the measurements.

RESULTS AND DISCUSSION
Figure 1 shows the XRD θ-2θ scan patterns of the BaTiO /Pt/Ti/Si [Figure 1A] and BaTiO /LaNiO / Pt/Ti/Si
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[Figure 1B] thin film heterostructures, respectively. It can be clearly seen that while the unbuffered BaTiO
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film showed a typical polycrystalline structure, the LaNiO buffered BaTiO film was (001)-textured, as
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reported in our previous publications [13-15] . Furthermore, the degree of crystallinity was significantly