In Solid-State Electronics Journal a new article on VO2 was published in a joint work of the consortium, here between:IBM Zurich-EPFL Lausanne-Cambridge University-Nov. 2019
The article "Density Functional Theory Studies of the Metal–Insulator Transition in Vanadium Dioxide Alloys" was published in Phys. Status Solidi B
Abstract: Vanadium dioxide (VO2) is of great interest because it has a metal–insulator transition involving a change in structure and electronic structure. For certain applications, it is useful to vary the bandgap and the transition temperature. Although strain can be used, another method is to alloy VO2 with oxides such as GeO2 or MgO. Herein, density functional supercell calculations are carried out on these alloys. The bandgap of the alloys does not change because the band edges of the M1 phase consist of V 3d bands, where V is sixfold bonded. However, there is also a fivefold VO2/MgO structure with a much larger bandgap of up to 2.1 eV. For Ge alloying, the structure reverts to the rutile phase but with a bandgap, because GeO2 has a rutile phase. It is also found that hydrogen doping varies the oxide gap between 0 to 1 eV. The result is consistent with experimental observations and it gives an important view to explain the mechanism of alloying.
Oscillator networks are known for their interesting collective behavior such as frequency locking, phase locking, and synchronization. Compared to other artificial neural network implementations, timing rather than amplitude information is used for computation. We have fabricated and simulated small networks of coupled VO2 oscillators and investigated the electrical behavior. It is demonstrated experimentally and through simulations that the coupled oscillators lock in frequency and the phase relation can be adjusted by the coupling resistance. Pattern recognition was simulated in resistor-coupled networks with up to nine oscillators (pixels), demonstrating the possibility of implementation of this task with compact VO2 circuits.
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The article was presented in November 2018 at 2018 IEEE International Conference on Rebooting Computing (ICRC)
The chemical bonding and band edge line-up of several gate insulators on monoclinic (M1) phase VO2arestudied based on hybrid density functional calculations. High dielectric constant HfO2and ZrO2, wide band gapoxide Al2O3, and narrower band gap oxide TiO2are considered. The insulating interface supercells with a cleanbandgap are built and adapted to analysis the band alignment. All the gate insulators show the type-I bandalignment with VO2. The valence band offsets are all larger than 1 eV. The calculated conduction band offsets forHfO2, ZrO2and Al2O3are all larger than 2 eV. In terms of the band alignment, these three insulators can work assuitable gate dielectrics for VO2-based device application, but more accurate line-up analysis on TiO2/VO2in-terface is still needed.
More infos on the article homepage -Aug 2019