Temperature Coefficient Of Capacitance Research Articles

Structural, Dielectric and AC Conduction Studies on Vacuum Evaporated BaTiO<SUB>3</SUB> Nano Thin Films Prepared from BaTiO<SUB>3</SUB> Nano Particles

BaTiO3 nanoparticles prepared by using wet chemical method were thermally grown onto well cleaned glass substrates between aluminium electrodes to form the MIM structure under the vacuum of 2 × 10 −5 torr, using 12A4 Hind Hivac coating unit. The thickness of the film was measured by quartz crystal monitor. From X-ray analysis, it has been found that BaTiO3 nanoparticles possess tetragonal structure and deposited films has a polycrystalline in nature, whereas the crystallinity of film increases with increase of temperature. Surface morphology of fabricated thin film observed that very homogeneous and uniform size. The transport mechanism in these films under a.c. fields was studied in the frequency range 12 Hz to 100 kHz, at different temperatures (303–483 K). The dependence of capacitance and loss factor on frequency, for different temperatures was investigated and results are discussed. The process of a.c. conduction has been explained on the basis of hopping conduction mechanism. The dielectric constant ( � ), temperature co-efficient of capacitance (TCC) and temperature co-efficient of permitivity (TCP) were estimated. The dependences of activation energy on frequency also studied.

Polymorphic Phase Transition and Temperature Coefficient of Capacitance of Alkaline Niobate Based Ceramics

<TEX>$0.95(Na_{0.5}K_{0.5})NbO_3-0.05BaTiO_3+0.2wt%\;Ag_2O$</TEX> (hereafter, No excess NKN) ceramics and <TEX>$0.95(Na_{0.5}K_{0.5})NbO_3-0.05BaTiO_3+0.2wt%\;Ag_2O$</TEX> with excess <TEX>$(Na_{0.5}K_{0.5})NbO_3$</TEX> (hereafter, Excess NKN) were fabricated by the conventional solid state sintering method, and their phase transition properties and dielectric properties were investigated. The crystalline structure of No excess NKN ceramics and Excess NKN ceramics were shown characteristics of polymorphic phase transition (hereafter, PPT), especially shift from the orthorhombic to tetragonal phase by increasing sintering temperature range from <TEX>$1,100^{\circ}C$</TEX> to <TEX>$1,200^{\circ}C$</TEX>. Also, the temperature coefficient of capacitance (hereafter, TCC) of No excess NKN ceramics and Excess NKN ceramics from <TEX>$-40^{\circ}C$</TEX> to <TEX>$100^{\circ}C$</TEX> was measured to evaluate temperature stability for applications in cold regions. The TCC of No excess NKN and Excess NKN ceramics showed positive TCC characteristics at a temperature range from <TEX>$-40^{\circ}C$</TEX> to <TEX>$100^{\circ}C$</TEX>. Especially, Excess NKN showed a smaller TCC gradient than those of Excess NKN ceramics in range from <TEX>$-40^{\circ}C$</TEX> to <TEX>$100^{\circ}C$</TEX>. Therefore, NKN piezoelectric ceramics combined with temperature compensated capacitor having negative temperature characteristics is desired for usage in cold regions.

Effects of extra Ba2+ and two-step sintering on the crystal structure, microstructure, and dielectric properties of (Ba, Ca)(Ti, Zr)O3

Abstract This study investigated how extra Ba 2+ and two-step sintering affect the crystal structure, microstructure, and dielectric properties of (Ba, Ca)(Ti, Zr)O 3 (BCTZ). XRD results indicate that no secondary phase formed in any of the BCTZ samples after sintering. Raman spectra reveal that Ca 2+ ions were pushed from the Ba-site to the Ti-site when extra Ba 2+ was added after sintering. The Curie temperatures of all BCTZ samples decreased due to the smaller tetragonality caused by the addition of extra Ba 2+ . SEM micrographs revealed that two-step sintering decreased the grain size from 5.0 μm to 0.5 μm compared with normal sintering. Furthermore, samples with fine-grain microstructures exhibited flat curves for the temperature coefficient of capacitance.

Electrical properties of (Na0.5Bi0.5)(Zr0.75Ti0.25)O3ceramic

Lead-free compound <TEX>$(Na_{0.5}Bi_{0.5})(Zr_{0.75}Ti_{0.25})O_3$</TEX> was prepared using conventional ceramic technique at <TEX>$1070^{\circ}C$</TEX>/4h in air atmosphere. X-ray diffraction analysis showed the formation of single-phase orthorhombic structure. Permittivity data showed low temperature coefficient of capacitance (<TEX>$T_{CC}{\approx}5%$</TEX>) up to <TEX>$100^{\circ}C$</TEX>. Complex impedance studies indicated the presence of grain boundary effect, non-Debye type dielectric relaxation and evidences of a negative temperature coefficient of resistance. The ac conductivity data were used to evaluate the density of states at Fermi level and apparent activation energy of the compound.

Effect of Bi2O3 doping on the dielectric properties of medium-temperature sintering BaTiO3-based X8R ceramics

Medium-temperature sintering X8R ceramics were fabricated based on BaTiO3-based ceramics with Bi2O3 additives. The effects of sintering aids Bi2O3 on crystalline structure and electrical properties of BaTiO3-based ceramics were investigated. The sinterability of BaTiO3 ceramics was significantly improved by adding Bi2O3, whose densification sintering temperature reduced from 1,260 to 1,130 °C. However, the dielectric constant (e) of BaTiO3-based ceramics doped with Bi2O3 was decreased dramatically. Both low e phase Bi4Ti3O12 and the decrease of the tetragonality (c/a ratio), which are demonstrated by XRD pattern, are resulted in the decrease of e. The e of samples doped with 5.5 wt% Bi2O3 was higher than the other doped samples. The substitution of Bi3+ for the Ba2+ in BaTiO3 resulted in the increase of electrovalence (from +2 to +3) of A-site ion, so the attractive force between A and B (Ti4+) sites becomes stronger. Thus Ti4+’s polarization enhances, then e was increased to some extent. The X8R BaTiO3-based ceramics could be sintered at as low as 1,130 °C by doping 5.5 wt% Bi2O3 additives into the BaTiO3-based ceramics, with a e greater than 2,430 at 25 °C, dielectric loss lower than 1.3 % and temperature coefficient of capacitance <±15 % (−55–150 °C).

Electrical Properties of Amorphous BaTi4O9 Films Grown on Cu/Ti/SiO2/Si Substrates Using RF Magnetron Sputtering

Amorphous BaTi4O9 (BT4) films for use as capacitors embedded in PCB substrates were grown on Cu electrodes at low temperatures (≤ 200°C). The dielectric constant (k) of the amorphous BT4 film grown at room temperature (RT) was 38, and its dissipation factor was 3.2% at 100 kHz. A similar k value was obtained at radio‐frequency ranges, with a quality factor of 143 at 1.0 GHz. The films showed a capacitance density of 200 nF/cm2, a temperature coefficient of capacitance of 296 ppm/°C at 75 kHz, and a breakdown voltage of 42.5 V. This film therefore satisfies the requirements of the International Technology Roadmap for Semiconductors for 2016 for capacitors grown on organic substrates. In addition, the leakage current mechanism of the amorphous BT4 films was found to be Schottky emission, and the Schottky barrier height was calculated as 2.26 eV.

Morphology, Structural and Dielectric Properties of Vacuum Evaporated V2O5 Thin Films

Vanadium pentoxide (V2O5) thin films were deposited on well cleaned glass substrate using evaporation technique under the pressure of 10-5 Torr. The thickness of the films was measured by the multiple beam interferometry technique and cross checked by using capacitance method. Metal-Insulator-Metal (MIM) structure was fabricated by using suitable masks to study dielectric properties. The dielectric properties were studied by employing LCR meter in the frequency range 12 Hz to 100 kHz for various temperatures. The temperature co- efficient of permittivity (TCP), temperature co-efficient of capacitance (TCC) and dielectric constant (ɛ) were calculated. The activation energy was calculated and found to be very low. The activation energy was found to be increasing with increase in frequency. The obtained low value of activation energy suggested that the hopping conduction may be due to electrons rather than ions.

Fabrication of CaCu3Ti4O12 Multilayer Capacitors, Their Microstructure and Dielectric Properties

The high-permittivity material CaCu3Ti4O12, being a naturally formed internal barrier layer capacitor, was utilized for preparation of slurries for tape casting and fabrication of multilayer ceramic capacitors. The dielectric properties of capacitors were studied in a wide frequency range of 0.1 Hz – 2 MHz and in the temperature range from −55 to 400°C. The dominant response recorded at low frequency range and at temperatures above 150°C was assigned to grain boundaries. The dielectric response at low temperatures and/or high frequencies was attributed to grains. SEM and EDS studies showed heterogeneous microstructure and composition of ceramic layers. The fabricated multilayer capacitors exhibit low sintering temperature, good compatibility of ceramic layers with the applied commercial conductive pastes, high specific capacitance and a relatively low temperature coefficient of capacitance.

Structure and dielectric behavior of TlSbS2

A comparison of structure and dielectric properties of TlSbS2 thin films, deposited in different thicknesses (400–4100 A) by thermal evaporation of TlSbS2 crystals that were grown by the Stockbarger–Bridgman technique and the bulk material properties of TlSbS2 are presented. Dielectric constant e1 and dielectric loss e2 have been calculated by measuring capacitance and dielectric loss factor in the frequency range 20 Hz–10 KHz and in the temperature range 273–433 K. It is observed that at 1 kHz frequency and 293 K temperature the dielectric constant of TlSbS2 thin films is e1=1.8–6 and the dielectric loss of TlSbS2 thin films is e2=0.5–3 depending on film thickness. In the given intervals, both of dielectric constant and dielectric loss decrease with frequency, but increase with temperature. The maximum barrier height Wm is calculated from the dielectric measurements. The values of Wm for TlSbS2 films and bulk are obtained as 0.56 eV and 0.62 eV at room temperature, respectively. The obtained values agree with those proposed by the theory of hopping over the potential barrier. The temperature variation of ac conductivity can be reasonably interpreted in terms of the correlated barrier hopping model since it obeys the ωs law with a temperature dependent s (s<1) and going down as the temperature is increased. The temperature coefficient of capacitance (TCC) and permittivity (TCP) are evaluated for both thin films and bulk material of TlSbS2.

A new SrBi4Ti4O15/CaBi4Ti4O15 thin-film capacitor for excellent electric stability

SrBi(4)Ti(4)O(15) (SBTi) and CaBi(4)Ti(4)O(15) (CBTi) dielectric films of bismuth layered-structure dielectrics (BLSD) are prepared on Pt(100) film for constructing stacked-type dielectric capacitors; it is observed that they are c-axis singleoriented crystalline films. Compared with the perovskite barium titanate family of (Ba,Sr)TiO(3) (BST), it is observed that the SBTi film keeps a low leakage of 10(-7) A/cm(2) at 250 kV/ cm, which is smaller by an order of magnitude than the BST film, even with thinner SBTi film. The temperature coefficient of capacitance (TCC) of the SBTi or CBTi film is about 100 to 250 ppm/K and is much smaller than that of the perovskite BST film. Because the SBTi and CBTi films have opposite polarities of TCC in this experiment, they are expected to cancel out the temperature dependence in the SBTi/CBTi composite capacitor. These results indicate that the BLSD films of SBTi and CBTi are effective for application in high-temperature and high-permittivity capacitors with the practical barium perovskite oxide family.

Extremely High Tunability and Low Loss in Nanoscaffold Ferroelectric Films

There are numerous radio frequency and microwave device applications which require materials with high electrical tunability and low dielectric loss. For phased array antenna applications there is also a need for materials which can operate above room temperature and which have a low temperature coefficient of capacitance. We have created a nanoscaffold composite ferroelectric material containing Ba(0.6)Sr(0.4)TiO(3) and Sm(2)O(3) which has a very high tunability which scales inversely with loss. This behavior is opposite to what has been demonstrated in any previous report. Furthermore, the materials operate from room temperature to above 150 °C, while maintaining high tunability and low temperature coefficient of tunability. This new paradigm in dielectric property control comes about because of a vertical strain control mechanism which leads to high tetragonality (c/a ratio of 1.0126) in the BSTO. Tunability values of 75% (200 kV/cm field) were achieved at room temperature in micrometer thick films, the value remaining to >50% at 160 °C. Low dielectric loss values of <0.01 were also achieved, significantly lower than reference pure films.

Preparation of Nano BaTiO&lt;sub&gt;3&lt;/sub&gt;-Based Dielectric Ceramics by Different Sintering Methods

Microstructure control in thin-layer multilayer ceramic capacitors (MLCCs) is one of the nowaday challenges for increasing capacitive volumetric efficiency and high voltage dielectric properties. In this paper, the ultrafine-grained BaTiO3 dielectric ceramics with uniform grain size distribution were prepared by chemical coating approach. The doping effects of rare-earth element (Ho) on the microstructures and dielectric properties of the ceramics were investigated. The addition of Ho in nano BaTiO3-based ceramics was found to improve the temperature coefficient of capacitance (TCC) performance, which could be attributed to a significant reduction in the grain size. Moreover, the effects of two-step sintering (TSS) method on the microstructures and dielectric properties, compared with conventional sintering (CS) method, were also discussed. The dielectric constant of ceramics sintered by the TSS method was higher than that of ceramics prepared by CS method. The results reveal that the adoption of TSS method could control the grain size and suppress the abnormal grain growth more effectively, which improves the TCC characteristics.

Effect of Nitrogen Passivation on the Performance of MIM Capacitors With a Crystalline- $\hbox{TiO}_{2}/\hbox{SiO}_{2}$ Stacked Insulator

TiO2/SiO2 stacked dielectric-based metal-insulator-metal capacitors with different thermal and nitrogen plasma treatments (NPTs) were explored in this letter. As the TiO2 dielectric crystallizes from amorphous phase after a thermal treatment, capacitance density increasing from 7.7 to 11.9 fF/m2 was obtained at the price of aggravating leakage current and wider distribution in device characteristics. With NPT to well passivate grain-boundary-related defects in the crystalline TiO2 film, devices still keep a satisfactory capacitance level of 11.2 fF/μm2 while exhibiting suppressed leakage current by a factor of 53, a lower quadratic voltage coefficient of capacitance (VCC-α) of 30 ppm/V2, near frequency dispersion-free capacitance, a better temperature coefficient of capacitance of 82 ppm/°C, and more controllable device uniformity. The mechanism for the improved electrical characteristics was further confirmed by atomic force microscope. These results suggest that NPT paves a new avenue to further advance the performance of crystalline dielectric-based devices.

Dielectric and piezoelectric properties of low temperature synthesized iso-valent modified BT ceramics

Ba(1−x)YxTiO3 (where Y=Ca, Mg and Sr, x=0.02, 0.04, 0.06 and 0.08) ferroelectric ceramic samples were synthesized in single perovskite phase by modified solid state reaction (MSSR) route. For single perovskite phase formation and dense grain morphology, 900°C and 1300°C were optimized as calcination and sintering temperatures. With the increase of substitutions% of Ca in BCT ceramic samples, the position of Tc increases slightly, whereas with the increase of Mg and Sr substitution% in BMT and BST systems, the position of Tc decreased but remains above RT. Decreased processing temperature with low temperature coefficient of capacitance made BCT ceramic samples useful for dielectric applications. Symmetric nature of the S–E loops indicated the increase of piezoelectric nature with the increase of Ca substitution% in BCT system.

Electrical Characterization of Advanced MIM Capacitors With ${\rm ZrO}_{2}$ Insulator for High-Density Packaging and RF Applications

This paper deals with the electrical and wideband frequency characterizations of metal-insulator-metal (MIM) capacitors integrating the medium-k material ZrO2. First, the in situ material electrical properties are characterized in a frequency range from dc up to 5 GHz by using a microstrip waveguide method. The loss tangent and the permittivity are extracted with frequencies up to 5 GHz. We then investigate the evolution with frequency of the electrical parameters, such as capacitance density, quality factor, temperature coefficient of capacitance, voltage coefficient of capacitance, and cut-off frequency for MIM capacitors which incorporate ZrO2 dielectric layers with thickness from 10 to 45 nm.

Crystal Structures and Dielectric Properties of Bi2((Zn1/3Nb2/3)1−xTix)2O7 Ceramics

Bi2((Zn1/3Nb2/3)1−xTix)2O7 ceramics with 0 ≤ x ≤ 0.4 were synthesized using solid-state reaction method. The crystal structure is pure zirconolite type for the compositions with 0 ≤ x ≤ 0.15, single weberite type for the compositions with 0.3 ≤ x ≤ 0.4, and mixture of zirconolite and weberite for the compositions with 0.15 < x < 0.3. The weberite ceramics with only Bi as the A-site cation are first reported. A possible correlation between the crystal structure transformation and Ti content in system of Bi2((Zn1/3Nb2/3)1−xTix)2O7 with 0 ≤ x ≤ 0.4 was suggested. Dielectric constant (e), dielectric loss (tan δ) and temperature coefficient of capacitance (TCC) are ~85, ~0.001, and ~200 ppm/°C for the zirconolite solid solutions, ~140, 0.004, and between −120 and −200 ppm/°C for the weberite solid solutions, respectively, at 1 MHz. Ceramics with a near zero TCC consisting of the zirconolite and weberite phases were obtained. High e, low tanδ, and low sintering temperatures (~950°C) make the novel ceramic system of Bi2((Zn1/3Nb2/3)1−xTix)2O7 potential dielectrics for applications in low-temperature co-fired ceramic and multiplayer ceramic capacitors.

Dielectric Properties of (Ba,Ca)(Ti,Zr)O3 Based MLCC Novel Cofired with Ni by Free and Constrained Sintering

In this paper, the (Ba,Ca)(Ti,Zr)-MLCCs with nickel electrodes by free sintering and constrained sintering as different heating rate have been investigated as different heating rate with 200°C/hr, 1500°C/hr and 3000°C/hr, respectively. The BaTiO3 was adopted as constraining layer due to the tensile stress of generation resulted from the different onset temperature. The electrical characteristics were closely related to the microstructure change including electrode overlap areas and grain size by free and constrained sintering with different heating rate. The variation of dielectric constant and insulation resistance can be explained by grain size change. The variation of dielectric loss can be explained by the curve of the temperature coefficient of capacitance. To compare with the free sintering, the capacitance value of constrained sintering of MLCCs has increased regardless of the heating rates. The high capacitance, high electrode continuity (>98%) and high insulation resistance (>1010Ω) of BCTZ-based MLCC with nickel electrode can be attained by using a rapid constrained sintering technique.

Application of High Permittivity Bismuth Copper Titanate in Multilayer Capacitors

A nonferroelectric high permittivity compound with the perovskite structure, Bi2/3Cu3Ti4O12, was synthesized at 900 ◦C. The ceramic powder and appropriate organic additives were used for preparation of a slurry for tape casting. The obtained green tapes were smooth, flexible, and with a uniform thickness of 25 μm after drying at 50 ◦C. Ag electrodes were screen printed on green rectangular sheets cut by a laser. Subsequent operations were screen printing of Ag internal electrodes, stacking of green sheets, isostatic lamination, cutting, deposition of external terminations and co-firing of dielectric and conductive layers at 850 ◦C. Scanning electron microscopy observations showed well sintered, dense, fine-grained microstructure of ceramic layers and good cooperation with the electrodes made of commercial Ag paste. Capacitance and dissipation factor of multilayer capacitors were examined in the temperature range from −55 to 330 ◦C at frequencies 10 Hz–2 MHz. The fabricated multilayer capacitors exhibit high capacitance and relatively low temperature coefficient of capacitance in the temperature range from −55 to 110 ◦C. The obtained lead-free high permittivity nonferroelectric material Bi2/3Cu3Ti4O12 is a spontaneously formed internal barrier capacitor. This material seems to be a promising alternative for conventional lead-based relaxor dielectrics in multilayer ceramic capacitors.

Dielectric properties of DC reactive magnetron sputtered Al2O3 thin films

Alumina (Al2O3) thin films were sputter deposited over well-cleaned glass and Si <100> substrates by DC reactive magnetron sputtering under various oxygen gas pressures and sputtering powers. The composition of the films was analyzed by X-ray photoelectron spectroscopy and an optimal O/Al atomic ratio of 1.59 was obtained at a reactive gas pressure of 0.03Pa and sputtering power of 70W. X-ray diffraction results revealed that the films were amorphous until 550°C. The surface morphology of the films was studied using scanning electron microscopy and the as-deposited films were found to be smooth. The topography of the as-deposited and annealed films was analyzed by atomic force microscopy and a progressive increase in the rms roughness of the films from 3.2nm to 4.53nm was also observed with increase in the annealing temperature. Al-Al2O3-Al thin film capacitors were then fabricated on glass substrates to study the effect of temperature and frequency on the dielectric property of the films. Temperature coefficient of capacitance, AC conductivity and activation energy were determined and the results are discussed.

Phase equilibria and electrical properties of pyrochlore and zirconolite phases in the Bi2O3–ZnO–Ta2O5 system

The complete subsolidus phase diagram of the system Bi2O3–ZnO–Ta2O5, including cubic pyrochlore and monoclinic zirconolite phases, has been determined at 950–1050 °C. Through systematic heat treatment and X-ray diffraction of over 100 compositions, the layout of compatibility triangles (both 2-phase and 3-phase) and single phase solid solution areas has been determined. Pyrochlore and zirconolite phases have ideal nominal compositions Bi1.5Zn1.0Ta1.5O7 and Bi2(Zn1/3Ta2/3)2O7 respectively, but both form solid solution areas. The sintering condition of pyrochlore pellets has been optimised to obtain high density ceramics with minimal weight loss: optimised condition is 1100 °C for pellets covered with sacrificial powder. Permittivity, ɛ′ dielectric loss and temperature coefficient of capacitance, TCC, of single phase materials were measured using impedance spectroscopy; ɛ′ and TCC show little variation with composition but the losses are higher for Zn-deficient compositions.