Thin films of (Ba,Sr)TiO3 on Pt/SiO2/Si substrates were deposited using rf magnetron sputtering at various substrate temperatures and O2/(Ar+O2) mixing ratios (OMR). The crystallinity of the films improved significantly as the OMR increased. The dielectric constant increased with increasing OMR and reached a maximum value at 50% OMR. The leakage current density decreased with increasing oxygen flow, but had a minimum value at 40% OMR. The results for the dielectric constant and the leakage current were interpreted in terms of polarization effect and loss theory. The film deposited at 450 °C and 50% OMR exhibited good surface morphology and had a dielectric constant of 375, a tangent loss of 0.074 at 100 kHz, a leakage current density of 7.35×10−9 A/cm2 at an electric field of 100 kV/cm with a delay time of 30 s, and a charge storage density of 49 fC/μm2 at an applied field of 150 kV/cm. The 10 yr lifetime of time-dependent dielectric breakdown studies indicate that a 50% OMR sample has a longer lifetime than the 0% OMR sample.

Effect of oxygen to argon ratio on properties of (Ba,Sr)TiO3 thin films prepared by radio-frequency magnetron sputtering

Finite difference quasielectrostatic modeling is used to predict the complex dielectric permittivity of barium titanium oxide (BTO)—polymer composites of interest for capacitor applications. The simulations explore the effects of the microstructural arrangement of spherical ceramic particles, the volume filling fraction of ceramic, and the type of polymer on the composite permittivity. For composites with randomly positioned ceramic particles, a soft percolation regime is found between volume filling fractions of 0.35 and 0.5 that leads to a more gradual growth in permittivity compared to ordered arrangements of particles. For BTO dispersed in a representative relaxor ferroelectric polymer, dielectric constants as high as 300 are predicted at a filling fraction of 0.45. Electric field statistics inside the composites are also computed, and localized intensification factors in the range of three to eight times the applied field are predicted, with an incrementally linear growth in high-field probability wi...

Finite difference simulations of permittivity and electric field statistics in ceramic-polymer composites for capacitor applications

By employing a deep level transient spectroscopy (DLTS) technique, this work investigates the deep trap levels of rf-sputtered (Ba0.4Sr0.6)TiO3 (BST) thin films deposited at various temperatures. Arrhenius plots of DLTS spectra detect a single trap located at 0.45 eV in 450 °C deposited films, whereas two traps located at 0.2 and 0.40 eV appear in 550 °C deposited films. On the other hand, examining the I–V characteristics of the films at the temperature range of 298–403 K reveals the presence of two conduction regions in the BST film capacitors, having ohmic behavior at low voltage ( 6 V). The barrier height and trapped level are, respectively, estimated to be 0.46 and 0.51 eV, corresponding to the trap activation energy 0.4–0.45 eV obtained from our DLTS measurements. Compared with previous published reports, the trap distributed at 0.4–0.5 eV should be an intrinsic defect of BST and possibly ascribed to be oxygen vacancies. Meanwhi...

Electronic defect and trap-related current of (Ba0.4Sr0.6)TiO3 thin films

The structure and electrical properties of multi-ion beam reactive sputter (MIBERS) deposited barium strontium titanate (BST) films were characterized in terms of Ba/Sr ratio, substrate temperature, annealing temperature and time, film thickness, doping concentration, and secondary low-energy oxygen ion bombardment. Films deposited onto unheated substrates, followed by annealing at 700 °C showed lower dielectric constant (<200), compared to a dielectric constant of about 560 for those deposited at elevated temperatures, probably due to reduced voids. Two types of microstructures (type I and type II) were observed depending on the incipient phase of the as-grown films, which also led to two types of time domain dielectric response, Curie-von Schweidler and Debye type, respectively. The current-voltage (I-V) characteristics of type II films doped with high donor concentration showed a bulk space-charge-limited conduction (SCLC) with discrete shallow traps embedded in a trap-distributed background at high electric fields. The I-V characteristics of bombarded films deposited at higher substrate temperatures showed promising results of lower leakage currents and trap densities.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400077359

Structures and electrical properties of barium strontium titanate thin films grown by multi-ion-beam reactive sputtering technique

A low dielectric constant material for an intermetal dielectric (IMD) is imperative to reduce power dissipation, cross talk, and interconnection delay in the deep submicron device regime. SiO2 aerogel is one of the possible candidate with an inherent low dielectric constant. This article reports on the results of the successful fabrication of a SiO2 aerogel film as well as its material properties and electrical properties. Fundamental physical, chemical, and electrical material properties were evaluated for a SiO2 aerogel film before and after thermal treatment. An inherent low dielectric constant of 2.0 was realized for about 70% porosity of the SiO2 aerogel film and the leakage current density held at a level of 10−7 A/cm2. Preliminary results of the SiO2 aerogel film investigated in our study represent a very positive prospective to IMD applications.

SiO2 aerogel film as a novel intermetal dielectric

Leakage currents in new and degraded (typically at twice rated voltage, 125°C) ZSU and X7R types Of multilayer ceramic (MLC) capacitors show both ohmic and space charge limited current behavior. The near 3/2 power voltage characteristic (la V3/2) of new devices can be attributed to electron emission from electrode points. The quadratic behavior (I \alpha V2) seen for moderately degraded devices represents space charge limited emission from near planar electrodes. This emission may evolve from the point emission due to resistivity decreases that occur in the emission region as a result of ion movement. For these currents, electrons are believed to be the dominant charge carriers. Neither Schottky or Poole-Frenkel currents were identified. Thermal activation energies decrease from ~1.3 eV for new X7R devices, to zero for degraded ones, corresponding to resistivity decreases from ~ 1013 \Omega -cm to 105 \Omega -cm or less (at 125°C). Carrier concentrations and mobilities have been estimated from thermoelectric measurements on new and reduced nonelectroded X7R chips, which exhibit n-type conduction. These parameters both increase substantially with reduction, with mobility dominating the thermal activation energy. These measurements are consistent with a small polaron hopping mode for electron transport in the ceramic.

Kyo-Chol Lee

Papers

Leakage Currents in Multilayer Ceramic Capacitors