Academic literature on the topic 'Ba0.45Sr0.55TiO3'

Ba(Mg[Formula: see text]Nb[Formula: see text]O3 (BMN) doped and undoped Ba[Formula: see text]Sr[Formula: see text]TiO3 (BST) thin films were deposited via radio frequency magnetron sputtering on Pt/TiO2/SiO2/Al2O3 substrates. The surface morphology and chemical state analyses of the films have shown that the BMN doped BST film has a smoother surface with reduced oxygen vacancy, resulting in an improved insulating properties of the BST film. Dielectric tunability, loss, and leakage current (LC) of the undoped and BMN doped BST thin films were studied. The BMN dopant has remarkably reduced the dielectric loss ([Formula: see text]38%) with no significant effect on the tunability of the BST film, leading to an increase in figure of merit (FOM). This is attributed to the opposing behavior of large Mg[Formula: see text] whose detrimental effect on tunability is partially compensated by small Nb[Formula: see text] as the two substitute Ti[Formula: see text] in the BST. The coupling between [Formula: see text] and V[Formula: see text] charged defects suppresses the dielectric loss in the film by cutting electrons from hopping between Ti ions. The LC of the films was investigated in the temperature range of 300–450[Formula: see text]K. A reduced LC measured for the BMN doped BST film was correlated to the formation of defect dipoles from [Formula: see text], V[Formula: see text] and Nb[Formula: see text] charged defects. The carrier transport properties of the films were analyzed in light of Schottky thermionic emission (SE) and Poole–Frenkel (PF) emission mechanisms. The result indicated that while the carrier transport mechanism in the undoped film is interface limited (SE), the conduction in the BMN doped film was dominated by bulk processes (PF). The change of the conduction mechanism from SE to PF as a result of BMN doping is attributed to the presence of uncoupled Nb[Formula: see text] sitting as a positive trap center at the shallow donor level of the BST.

AbstractThe transfer matrix method (TMM) software (Translight, A. Reynolds [1]) was used to evaluate the photonic band gap (PBG) properties of the periodic arrangement of high permittivity ferroelectric composite (40 wt% Ba0.45Sr0.55TiO3/60 wt% MgO composite, εR = 80, tanδ?= 0.0041 at 10 GHz) in air (or Styrofoam, εR ∼ 1) matrix compared to a lower permittivity material (Al2O3, εR = 11.54, tanδ?= 0.00003 at 10 GHz) in air. The periodic structures investigated included a one-dimensional (1D) stack and a three-dimensional (3D) face centered cubic (FCC) opal structure. The transmission spectrum was calculated for the normalized frequency for all incident angles for each structure. The results show that the bandgaps frequency increased and the bandgap width increased with increased permittivity. The effects of orientation of defects in the opal crystal were investigated. It was found by introducing defects propagation bands were introduced. It was concluded that a full PBG is possible with the high permittivity material.

AbstractThe transfer matrix method (TMM) software (Translight, A. Reynolds [1]) was used to evaluate the photonic band gap (PBG) properties of the periodic arrangement of high permittivity ferroelectric composite (40 wt% Ba0.45Sr0.55TiO3 /60 wt% MgO composite, εR= 80, tanδ = 0.0041 at 10 GHz) in air (or Styrofoam, εR~ 1) matrix compared to a lower permittivity material (Al2O3, εR= 11.54, tanδ = 0.00003 at 10 GHz) in air. The periodic structures investigated included a one-dimensional (1D) stack and a three-dimensional (3D) face centered cubic (FCC) opal structure. The transmission spectrum was calculated for the normalized frequency for all incident angles for each structure. The results show that the bandgaps frequency increased and the bandgap width increased with increased permittivity. The effects of orientation of defects in the opal crystal were investigated. It was found by introducing defects propagation bands were introduced. It was concluded that a full PBG is possible with the high permittivity material.

Le déploiement de la technologie 5G a soulevé des préoccupations significatives concernant la consommation d'énergie. Celle-ci peut être minimisée en ajustant l'impédance de l'antenne à 50 ohms. Pour répondre aux exigences de la 5G et du NFC, un circuit d'adaptation d'impédance contrôlable en tension avec une capacité hautement modulable (varactor) est nécessaire. Plus précisément, un rapport de réglage d'au moins 5 et de faibles pertes diélectriques dans la bande 5G (2-5 GHz) sont essentiels pour préserver l'efficacité énergétique (courant de fuite ~1 nA). Les condensateurs paraélectriques (PE) à commande de tension répondent à ce besoin grâce à leur permittivité relative dépendante du champ électrique εᵣ (E).Le pérovskite Ba₁₋ᵧSrᵧTiO₃ (BST) est largement utilisé dans les varactors 4G pour son excellent compromis entre la réglabilité et les pertes, offrant des facteurs de qualité supérieurs par rapport aux autres technologies. Cependant, une fréquence de résonance acoustique fᵣ de 3 GHz due à l'électrostriction limite les applications 4G actuelles. Ainsi, la 5G et le NFC nécessitent des varactors améliorés, spécifiquement avec fᵣ > 5 GHz et une tension de fonctionnement < 3 V. Une épaisseur de BST inférieure à 50 nm, déplaçant fᵣ au-delà de 6 GHz, peut répondre à ces spécifications. Cependant, ces varactors minces présentent une réglabilité dégradée et un courant de fuite plus élevé, en raison de la permittivité diélectrique réduite près des électrodes causée par des charges de polarisation non compensées et une fuite statique par transport limité au volume. L'augmentation de la hauteur de barrière de Schottky (SBH) à l'interface électrode/BST par alignement de bande peut réduire considérablement les fuites en empêchant l'injection de porteurs dans le diélectrique. Les calculs ab initio soulignent l'importance d'incorporer une couche de contrôle d'interface pérovskite (ICL) de quelques nanomètres de films conducteurs ou diélectriques entre l'électrode inférieure et le BST dans les varactors. Des facteurs tels que le gauchissement, la discontinuité polaire et l'asymétrie de l'environnement des cations sur le site B de l'interface peuvent améliorer la polarisabilité de l'interface et la hauteur de barrière de Schottky (SBH).Comprendre les mécanismes contrôlant les interfaces électrode/PE est crucial pour les applications 5G et NFC, révélant des modifications chimiques et électrostatiques de la SBH et du potentiel chimique. Nous proposons d'étudier les états électroniques et chimiques de ces interfaces à l'échelle sub-micrométrique, comparés aux calculs DFT.La Déposition Combinatoire par Laser Pulsé a été utilisée pour varier les compositions chimiques et les épaisseurs de manière orthogonale sur un seul substrat. Une discontinuité polaire variable a été induite à l'interface LSMO/BST en insérant une ICL de 3 u.c. d'épaisseur de La₁₋ₓSrₓMnO₃ (une discontinuité polaire entre 1 et 0 e⁻).Nous avons étudié la polarisation de l'interface en fonction de l'épaisseur de BST. La spectroscopie de photoémission a montré une modulation de la fonction de travail φ, de la densité de porteurs à l'interface au niveau de Fermi, et de la polarisation de l'interface, démontrant l'impact de l'ICL chimiquement modifiée de 1,2 nm d'épaisseur. Enfin, nous avons fabriqué des varactors BST réglables en tension en utilisant l'ingénierie ICL. Nous avons étudié la SBH en fonction de la discontinuité polaire à l'interface. La HAXPES en mode opératoire a permis d'accéder aux interfaces supérieures et inférieures, nous permettant d'estimer la structure de bande électronique et de quantifier la SBH. L'induction d'une discontinuité polaire à l'interface a entraîné une réduction du courant de fuite. Pour des varactors BST de 10x10 μ m², le courant de fuite est attendu à environ 1 nA, une amélioration de deux ordres de grandeur par rapport aux varactors des téléphones 4G actuels
The deployment of 5G technology has raised significant issues of energy consumption. This can be minimized by adjusting the antenna impedance to 50 ohms. Impedance matching is also crucial for Near Field Communications (NFC) to ensure energy-efficient contactless communications. To meet 5G and NFC requirements, a voltage-controllable impedance matching circuit with highly tunable capacitance (varactor) is needed. Specifically, a tuning ratio of at least 5 and low dielectric losses in the 5G band (2-5 GHz) are essential to preserve energy efficiency (leakage current ~1 nA). Voltage-tunable paraelectric (PE) capacitors meet this need due to their field-dependent relative permittivity εᵣ (E). The perovskite Ba₁₋ᵧSrᵧTiO₃ (BST) is widely used in 4G varactors for its excellent tunability/losses compromise, offering superior quality factors compared to other technologies. However, an acoustic resonance frequency fᵣ of 3 GHz due to electrostriction limits current 4G applications. Thus, 5G and NFC require improved varactors, specifically with fᵣ > 5 GHz and an operating voltage < 3 V. A BST thickness below 50 nm, shifting fᵣ above 6 GHz, can meet these specifications. However, these thin varactors exhibit degraded tunability and higher leakage current, due to reduced dielectric permittivity near electrodes from uncompensated polarization charges and static leakage through bulk-limited transport. Enhancing the Schottky Barrier Height (SBH) at the electrode/BST interface through band alignment can significantly reduce leakage by preventing carrier injection into the dielectric. Ab initio calculations highlight the importance of incorporating a perovskite Interface Control Layer (ICL) of a few nanometers of conductive or dielectric films between the bottom electrode and the BST in varactors. Factors such as rumpling, polar discontinuity, and interfacial B-site cation environment asymmetry can enhance interface polarizability and the Schottky Barrier Height (SBH). Understanding the mechanisms controlling electrode/PE interfaces is crucial for 5G and NFC applications, revealing chemical and electrostatic modifications of SBH and chemical potential. We propose investigating the electronic and chemical states of these interfaces at the sub-micrometric scale, compared with DFT calculations. Combinatorial Pulsed Laser Deposition (CPLD) was used to vary chemical compositions and thicknesses orthogonally on a single substrate. Chemical modulation at the Ba atoms and Ba diffusion into the dielectric STO up to the surface, driven by strain release to reduce system energy. Second, a variable polar discontinuity was induced at the LSMO/BST interface by inserting a 3 u.c. thick ICL of La₁₋ₓSrₓMnO₃ (a polar discontinuity between 1 and 0 e⁻). We investigated the interface polarization relative to BST thickness. Photoemission spectroscopy showed modulation of the work function φ, interface carrier density at the Fermi level, and interface polarization, demonstrating the impact of the 1.2 nm thick chemically modulated ICL. Finally, we fabricated voltage-tunable BST varactors using ICL engineering. We investigated the SBH versus polar discontinuity at the interface. Operando HAXPES provided access to both top and bottom interfaces, allowing us to estimate the electronic band structure and quantify the SBH. Inducing a polar discontinuity at the interface resulted in a reduction of leakage current. For 10x10 µm² BST-engineered varactors, the leakage current is expected to be close to 1 nA, an improvement by two orders of magnitude compared to current 4G cellphone varactors