Oxygen diffusion barriers for epitaxial thin-film heterostructures with highly conducting SrMoO3 electrodes

Abstract

Transition metal perovskite oxide SrMoO3 with a Mo4+ 4d2 electronic configuration exhibits a room-temperature resistivity of 5.1 μΩcm in a single-crystal form and, therefore, is considered a prominent conducting electrode material for all-oxide microelectronic devices. Stabilization of the unfavorable Mo4+ valence state in SrMoO3 thin films necessitates reductive growth conditions that are often incompatible with a highly oxidative environment necessary to grow epitaxial heterostructures with fully oxygenated functional layers (e.g., tunable dielectric BaxSr1−xTiO3). Interestingly, only a few unit cells of the perovskite titanate capping layers SrTiO3, BaTiO3, and Ba0.5Sr0.5TiO3 act as an efficient oxygen barrier and minimize SrMoO3 oxidation into electrically insulating SrMoO4 in the broad range of the thin-film growth parameters. The Mo valence state in SrMoO3, determined by x-ray photoelectron spectroscopy, is used to analyze oxygen diffusion through the capping layers. The lowest level of oxygen diffusion is observed in Ba0.5Sr0.5TiO3. A Ba0.5Sr0.5TiO3 film with a thickness of only 6 unit cells preserves the Mo4+ oxidation state in the SrMoO3 underlayer up to the oxygen partial pressure of 8 mTorr at the temperature of 630 °C. Results, therefore, indicate that SrMoO3 films covered with atomically thin Ba0.5Sr0.5TiO3 remain conducting in an oxygen environment and can be integrated into all-oxide thin-film heterostructures with other functional materials.

Microwave Liquid Crystal Enabling Technology for Electronically Steerable Antennas in SATCOM and 5G Millimeter-Wave Systems

“… in semiconductor technologies [5][6][7][8][9][10], in particular silicon technologies (Complementary Metal-Oxide-Semiconductor (CMOS) and Bipolar CMOS) that offer much lower cost as compared to Indium Phosphide (InP) or Gallium Arsenide (GaAs) technologies, and can address consumer applications,  with RF MicroElectroMechanical Systems (RF-MEMS) [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25], and  by using functional materials such as ferrites [26][27][28], ferroelectrics, mainly Barium Strontium Titanate (BST) capacitors, filters, and phase shifters in thin or thick-film technology [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] and the Microwave Liquid Crystal (MLC) technology beyond optics.…”

Modifying Metastable Sr1–xBO3−δ (B = Nb, Ta, and Mo) Perovskites for Electrode Materials

“…However, in the case of SNO and STaO, the ρ is higher than what has been reported in literature. , From these results, it is evident that the defect stability in these metastable crystals follows the order of Mo < Nb < Ta. This trend is closely correlated with the descending sequence of electronegativity observed for the B-site ions (Mo ∼ 2.2; Nb ∼ 1.6; Ta ∼ 1.5). , Therefore, as the electronegativity of the B–O bond increases, it presumably becomes more challenging to stabilize defects during the H 2 /Ar treatment, thus facilitating the crystal formation. , However, the identity of these deep defect states, and their impact on the electronic structure, is not immediately clear based on these experiments.…”

“…60,61 Therefore, as the electronegativity of the B−O bond increases, it presumably becomes more challenging to stabilize defects during the H 2 /Ar treatment, thus facilitating the crystal formation. 8,62 However, the identity of these deep defect states, and their impact on the electronic structure, is not immediately clear based on these experiments.…”

Heteroepitaxial Hexagonal (00.1) CuFeO2 Thin Film Grown on Cubic (001) SrTiO3 Substrate Through Translational and Rotational Domain Matching

“…The cubic perovskite SrTiO 3 doped with Nb is the only commercially available conductive single crystal metal oxide substrate widely used for growing epitaxial oxide thin films. Alternatively, epitaxial layers of cubic perovskite oxides, such as SrRuO 3 , [20][21][22] La x Sr 1-x MnO 3 , [23,24] LaNiO 3 , [25][26][27] and SrMoO 3 , [27][28][29][30] are commonly used as conductive buffer layers. The epitaxial growth of CuFeO 2 thin film has been only demonstrated with a (00.1) out-of-plane crystallographic orientation on insulating hexagonal (00.1) sapphire substrates using pulsed laser deposition.…”