3 research outputs found
Lanthanum Aluminum Oxide Thin-Film Dielectrics from Aqueous Solution
Amorphous LaAlO<sub>3</sub> dielectric
thin films were fabricated
via solution processing from inorganic nitrate precursors. Precursor
solutions contained soluble oligomeric metal-hydroxyl and/or -oxo
species as evidenced by dynamic light scattering (DLS) and Raman spectroscopy.
Thin-film formation was characterized as a function of annealing temperature
using Fourier transform infrared (FTIR), X-ray diffraction (XRD),
X-ray reflectivity (XRR), scanning electron microscopy (SEM), and
an array of electrical measurements. Annealing temperatures ≥500
°C result in thin films with low leakage-current densities (∼1
× 10<sup>–8</sup> A·cm<sup>–2</sup>) and dielectric
constants ranging from 11.0 to 11.5. When incorporated as the gate
dielectric layer in a-IGZO thin-film transistors (TFTs), LaAlO<sub>3</sub> thin films annealed at 600 °C in air yielded TFTs with
relatively low average mobilities (∼4.5 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup>) and high turn-on voltages
(∼26 V). Interestingly, reannealing the LaAlO<sub>3</sub> in
5%H<sub>2</sub>/95%N<sub>2</sub> at 300 °C before deposition
of a-IGZO channel layers resulted in TFTs with increased average mobilities
(11.1 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup>) and lower turn-on voltages (∼6 V)
Effects of Oxygen Incorporation on the Physical Properties of Amorphous Metal Thin Films
Incorporated
oxygen is known to affect amorphous metal thin film
(AMTF) mechanical properties, but comparatively little is known about
how it affects their structural characteristics and electrical transport
properties. In this study, AMTFs are produced by using sputter deposition.
Chemical composition, average interatomic spacing, surface roughness,
and electrical transport properties are examined using electron probe
microanalysis (EPMA), X-ray diffraction (XRD), atomic force microscopy
(AFM), spectroscopic ellipsometry (SE), and variable-temperature resistivity.
ZrCuAlNi amorphous metal thin films exhibit a temperature dependence
that is characteristic of <i>d</i>-electron conduction and
electrical resistivity that increases substantially with increasing
oxygen content. TiAl and ZrCuB are found to be <i>sp</i>-electron conductors with electrical resistivity that decreases with
increasing oxygen content. The surface roughness of all films increases
with oxygen content, whereas interatomic spacing is relatively insensitive
to incorporated oxygen content. The relationships among amorphous
metal composition, structural characteristics, and electrical transport
properties are discussed
Amorphous In–Ga–Zn Oxide Semiconducting Thin Films with High Mobility from Electrochemically Generated Aqueous Nanocluster Inks
Solution processing
is a scalable means of depositing large-area electronics for applications
in displays, sensors, smart windows, and photovoltaics. However, solution
routes typically yield films with electronic quality inferior to traditional
vacuum deposition, as the solution precursors contain excess organic
ligands, counterions, and/or solvent that leads to porosity in the
final film. We show that electrolysis of aq. mixed metal nitrate salt
solutions drives the formation of indium gallium zinc oxide (IGZO)
precursor solutions, without purification, that consist of ∼1
nm radii metal–hydroxo clusters, minimal nitrate counterions,
and no organic ligands. Films deposited from cluster precursors over
a wide range of composition are smooth (roughness of 0.24 nm), homogeneous,
dense (80% of crystalline phase), and crack-free. The transistor performance
of IGZO films deposited from electrochemically synthesized clusters
is compared to those from the starting nitrate salt solution, sol–gel
precursors, and, as a control, vacuum-sputter-deposited films. The
average channel mobility (μ<sub><i>AVE</i></sub>)
of air-annealed cluster films (In:Ga:Zn = 69:12:19) at 400 °C
was ∼9 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, whereas those of control nitrate salt and sol–gel precursor
films were ∼5 and ∼2 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, respectively. By incorporating an ultrathin
indium–tin–zinc oxide interface layer prior to IGZO
film deposition and air-annealing at 550 °C, a μ<sub><i>AVE</i></sub> of ∼30 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> was achieved, exceeding that of sputtered
IGZO control films. These data show that electrochemically derived
cluster precursors yield films that are structurally and electrically
superior to those deposited from metal nitrate salt and related organic
sol–gel precursor solutions and approach the quality of sputtered
films