An official website of the United States government
Abstract This study employs a data‐driven machine learning approach to investigate specific ferroelectric properties of Al1−xScxN thin films, targeting their application in next‐generation nonvolatile memory (NVM) devices. This approach analyzes a vast design space, encompassing over a million data points, to predict a wide range of coercive field values that are crucial for optimizing Al1−xScxN‐based NVM devices. We evaluated seven machine learning models to predict the coercive field across a range of conditions, identifying the random forest algorithm as the most accurate, with a testR2value of 0.88. The model utilized five key features: film thickness, measurement frequency, operating temperature, scandium concentration, and growth temperature to predict the design space. Our analysis spans 13 distinct scandium concentrations and 13 growth temperatures, encompassing thicknesses from 9–1000 nm, frequencies from 1 to 100 kHz, and operating temperatures from 273 to 700 K. The predictions revealed dominant coercive field values between 3.0 and 4.5 MV/cm, offering valuable insights for the precise engineering of Al1−xScxN‐based NVM devices. This work underscores the potential of machine learning in guiding the development of advanced ferroelectric materials with tailored properties for enhanced device performance.
more »
« less
Epitaxial Sc x Al 1− x N on GaN exhibits attractive high-K dielectric properties
Epitaxial Sc x Al 1− x N thin films of ∼100 nm thickness grown on metal polar GaN substrates are found to exhibit significantly enhanced relative dielectric permittivity (ε r ) values relative to AlN. ε r values of ∼17–21 for Sc mole fractions of 17%–25% ( x = 0.17–0.25) measured electrically by capacitance–voltage measurements indicate that Sc x Al 1− x N has the largest relative dielectric permittivity of any existing nitride material. Since epitaxial Sc x Al 1− x N layers deposited on GaN also exhibit large polarization discontinuity, the heterojunction can exploit the in situ high-K dielectric property to extend transistor operation for power electronics and high-speed microwave applications.
more »
« less
- Award ID(s):
- 1719875
- PAR ID:
- 10325442
- Date Published:
- Journal Name:
- Applied Physics Letters
- Volume:
- 120
- Issue:
- 15
- ISSN:
- 0003-6951
- Page Range / eLocation ID:
- 152901
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
We present a thermodynamic analysis of the recently discovered nitride ferroelectric materials using the classic Landau–Devonshire approach. Electrostrictive and dielectric stiffness coefficients of Al 1− x Sc x N with a wurtzite structure ( 6 mm) are determined using a free energy density function assuming a hexagonal parent phase (6/ mmm), with the first-order phase transition based on the dielectric stiffness relationships. The results of this analysis show that the strain sensitivity of the energy barrier is one order of magnitude larger than that of the spontaneous polarization in these wurtzite ferroelectrics, yet both are less sensitive to strain compared to classic perovskite ferroelectrics. These analysis results reported here explain experimentally reported sensitivity of the coercive field to elastic strain/stress in Al 1− x Sc x N films and would enable further thermodynamic analysis via phase field simulation and related methods.more » « less
-
null (Ed.)A systematic study of (1− x )Pb(Fe 0.5 Nb 0.5 )O 3 – x BiFeO 3 ( x = 0–0.5) was performed by combining dielectric and electromechanical measurements with structural and microstructural characterization in order to investigate the strengthening of the relaxor properties when adding BiFeO 3 into Pb(Fe 0.5 Nb 0.5 )O 3 and forming a solid solution. Pb(Fe 0.5 Nb 0.5 )O 3 crystalizes in monoclinic symmetry exhibiting ferroelectric-like polarization versus electric field ( P–E ) hysteresis loop and sub-micron-sized ferroelectric domains. Adding BiFeO 3 to Pb(Fe 0.5 Nb 0.5 )O 3 favors a pseudocubic phase and a gradual strengthening of the relaxor behavior of the prepared ceramics. This is indicated by a broadening of the peak in temperature-dependent permittivity, narrowing of P–E hysteresis loops and decreasing size of ferroelectric domains resulting in polar nanodomains for x = 0.20 composition. The relaxor behavior was additionally confirmed by Vogel–Fulcher analysis. For the x ≥ 0.30 compositions, broad high-temperature anomalies are observed in dielectric permittivity versus temperature measurements in addition to the frequency-dispersive peak located close to room temperature. These samples also exhibit pinched P–E hysteresis loops. The observed pinching is most probably related to the reorganization of polar nanoregions under the electric field as shown by synchrotron X-ray diffraction measurements as well as by piezo-response force microscopy analysis, while in part affected by the presence of charged point defects and anti-ferroelectric order, as indicated from rapid cooling experiments and high-resolution transmission electron microscopy, respectively.more » « less
-
We determine the composition dependence of the transverse and longitudinal optical infrared-active phonon modes in rhombohedral α-(Al x Ga 1− x ) 2 O 3 alloys by far-infrared and infrared generalized spectroscopic ellipsometry. Single-crystalline high quality undoped thin-films grown on m-plane oriented α-Al 2 O 3 substrates with x = 0.18, 0.37, and 0.54 were investigated. A single mode behavior is observed for all phonon modes, i.e., their frequencies shift gradually between the equivalent phonon modes of the isostructural binary parent compounds. We also provide physical model line shape functions for the anisotropic dielectric functions. We use the anisotropic high-frequency dielectric constants for polarizations parallel and perpendicular to the lattice c axis measured recently by Hilfiker et al. [Appl. Phys. Lett. 119, 092103 (2021)], and we determine the anisotropic static dielectric constants using the Lyddane–Sachs–Teller relation. The static dielectric constants can be approximated by linear relationships between those of α-Ga 2 O 3 and α-Al 2 O 3 . The optical phonon modes and static dielectric constants will become useful for device design and free charge carrier characterization using optical techniques.more » « less
-
Determination of anisotropic optical properties of MOCVD grown m-plane α-(Al x Ga 1−x ) 2 O 3 alloysAbstract The anisotropic dielectric functions (DF) of corundum structured m -plane α -(Al x Ga 1− x ) 2 O 3 thin films (up to x = 0.76) grown on m -plane sapphire substrate by metalorganic CVD have been investigated. IR and visible–UV spectroscopic ellipsometry yields the DFs, while X-ray diffraction revealed the lattice parameters ( a , m , c ), showing the samples are almost fully relaxed. Analysis of the IR DFs from 250 to 6000 cm −1 by a complex Lorentz oscillator model yields the anisotropic IR active phonons E u and A 2 u and the shift towards higher wavenumbers with increasing Al content. Analyzing the UV DFs from 0.5 to 6.6 eV we find the change in the dielectric limits ε ∞ and the shift of the Γ-point transition energies with increasing Al content. This results in anisotropic bowing parameters for α -(Al x Ga 1− x ) 2 O 3 of b ⊥ = 2.1 eV and b ∣∣ = 1.7 eV.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1063/5.0075636
