Temperature Capacitance Research Articles

Influence of Composition on Properties of Medium Temperature Sintering (Ba, Sr)TiO 3 Series Capacitor Ceramics

The influence of the composition (Yb 2O 3, MgO, CeO 2, Li 2CO 3) on the dielectric properties of medium temperature sintering (Ba,Sr)TiO 3(BST) series capacitor ceramics was investigated by means of conventional technology process and orthogonal design experiments. The major secondary influencing factors and the influencing tendency of various factor's levels for the dielectric properties of BST ceramics were obtained. The optimum formula for maximum dielectric constant ɛ and for minimum dielectric loss (tanδ) was obtained under the experimental conditions. The BST ceramics with optimum comprehensive properties was obtained by means of orthogonal design experiments, with the sintering temperature at 1200 °C, the dielectric constant 5239, the dielectric loss 0.0097, withstand electric voltage over 6 MV · m −1, capacitance temperature changing rate (Δ C/C) − 75.67%, and suited for Y5V character. The mechanism of the influence of various components on the dielectric properties of medium temperature sintering BST ceramics was studied, thus providing the basis for preparation of multilayer capacitor ceramics and single-chip capacitor ceramics.

Capacitance Temperature Sensor Using Ferroelectric (Sr0.95Ca0.05)TiO3 Perovskite

Thermometric properties of the capacitance temperature sensor with polycrystalline (Sr1−x Cax)TiO3 (x = 0.05) have been investigated at cryogenic temperatures. Ferroelectric state appeared at 31.8 K due to Ca doping. Temperature sensitivity S and dimensionless temperature sensitivity Sd at 2.5 K were 90 pF/K and 0.045, respectively. This capacitance temperature sensor could improve the accuracy of temperature sensing at cryogenic temperatures due to its large dimensionless temperature sensitivity.

Optimisation of amorphous and polymorphous thin silicon layers for the formation of the front-side of heterojunction solar cells on p-type crystalline silicon substrates

In this study, we investigate the properties of n-doped amorphous silicon layer a-Si:H(n) combined with intrinsic thin silicon film deposited on high quality p-type CZ crystalline silicon, aiming at developing high performance heterojunction solar cells. The interface characteristics are analysed using Transmission Electron Microscopy TEM and capacitance measurements versus temperature and frequency. The insertion of a thin silicon film at the interface deposited under conditions of polymorphous material drives to a different structure of the interface. Our best front side heterojunction solar cells achieve 15% efficiency on 25 cm 2 , with an open-circuit voltage of 634 mV. A maximum open-circuit voltage of 676 mV has also been obtained on polymorphous/crystalline heterojunctions with a high quality rear local BSF, indicating the excellent interface passivation achieved with the intrinsic layer deposited in conditions of polymorphous silicon. This experimental study reveals the clear potential of p-type substrates for the development of amorphous/crystalline heterojunctions solar cells.

Capacitance temperature sensor using epitaxial SrTiO 3 film with a single-crystal-like behavior

A parallel capacitor of epitaxially grown YBa 2Cu 3O 7− δ /SrTiO 3/YBa 2Cu 3O 7− δ was fabricated by a chemical mechanical planarization method and its characteristics as a capacitance thermometer were investigated. The capacitance, temperature sensitivity, and dimensionless temperature sensitivity of the elements were found to be 1.7 nF, 10 pF/K, and 0.01 at 2.2 K, respectively. These values are of the same order as that of a commercially available bulk doped-SrTiO 3 capacitance temperature sensor. These results reveal that the parallel capacitor with quantum paraelectric SrTiO 3 film has potential for use in capacitance thermometers for monitoring cryogenic temperatures under high magnetic fields.

Daily Variations in Skin Surface Properties Using Mixed Model Methodology

In order to explore the variations over the course of a day in certain skin biophysical properties, a study was conducted on 8 female volunteers. An assessment of several skin biophysical properties was carried out on the face and the volar forearm every 4 h over a period of 48 h. The biophysical parameters were assessed on the face for sebum secretion, skin surface pH, skin colour, transepidermal water loss, capacitance and skin surface temperature. The same parameters were measured on the volar forearm (excepted for sebum secretion). A statistical analysis based on mixed effect models was conducted. Four models, with different covariance structures, were successively tested. The analysis allowed us to identify a structure that repeated itself over time in the same way over each 24-hour period for capacitance on the forearm and for sebum secretion, skin surface pH and skin colour (L* and a* parameters) on the face. Mixed effect methodology is a powerful tool to analyse longitudinal data involving correlations among repeated measurements made on the same subject.

Investigation of defect properties in Cu(In,Ga)Se 2 solar cells by deep-level transient spectroscopy

The performance of the chalcopyrite material Cu(In,Ga)Se 2 (CIGS) used as an absorber layer in thin-film photovoltaic devices is significantly affected by the presence of native defects. The deep-level transient spectroscopy (DLTS) technique is used in this work to characterize the defect properties, yielding relevant information about the defect types, their capture cross-sections, and energy levels and densities in the CIGS cells. Three solar cells developed using different absorber growth technologies were analyzed using DLTS, capacitance–voltage ( C– V), and capacitance–temperature ( C– T) techniques. It was found that CIS cells grown at the University of Florida exhibits a middle-gap defect level that may relate to the cell's low fill factor and open-circuit voltage values observed. A high efficiency ( η c>18%) CIGS cell produced by the National Renewable Energy Laboratory (NREL) was found to contain three minority-carrier (electron) traps and a 13% CIGS cell produced by the Energy Photovoltaics Inc. (EPV) exhibited one majority (hole) trap. The approach followed using the DLTS technique serves as a paradigm for revealing the presence of significant defect levels in absorber materials, and may be used to support the identification of remedial processing operations.

Dermal toxicity and microscopic alterations by JP-8 jet fuel components in vivo in rabbit

In this study, we investigated the skin irritation, macroscopic and microscopic barrier alteration in vivo in rabbits from aliphatic and aromatic components of jet propellant-8 (JP-8) jet fuel. Macroscopic barrier properties were evaluated by measuring transepidermal water loss (TEWL), skin capacitance, and skin temperature; microscopic changes were observed by light microscopy. Draize visual scoring system was used to measure skin irritation. We found significant ( P<0.05) increase in temperature at the site of all chemically saturated patches immediately after patch removal in comparison to the control site. Tridecane (TRI) produced a greater increase in temperature and capacitance at all time points than all the other components of JP-8. Both the aliphatic and aromatic components increased the TEWL at all time points. Tridecane produced greater increase in TEWL followed by naphthalene (NAP), 1-methylnaphthalene (1-MN), 2-metylnaphthalene (2-MN), tetradecane (TET), and dodecane (DOD). All of the above components of JP-8 caused moderate to severe erythema and edema, which were not resolved to the baseline even after 24 h of patch removal. Light microscopy revealed an increase in epidermal thickness (ET), and decrease in length and thickness of collagen fibers’ bundle by the above components of JP-8. These results suggest potential dermatotoxicity from the JP-8 components.

Development of Dielectric Ceramics for Nickel Electrode Multilayer Capacitors

Calcium-doped BaTiO3-based dielectrics have a high resistance to reduction. This can be explained by taking the following three factors into account: 1) decrease in conduction electron density caused by acceptor Ca ions at the Ti site, 2) low freezing temperature of the equilibrium reaction by Ca ions at the Ti site, and 3) large enthalpy change in the reduction reaction by Ca ions at the Ba site. Fine-grained BaTiO3 ceramics can be prepared using the tetragonal BaTiO3 powder using ultra-fine starting BaTiO3 powder synthesized by hydrolysis method. The non-uniform distortion is caused in the grains during sintering, which is attributed to the surface tension and clamping stress from the thin grain boundary layer. This suppresses the tetragonality symmetry of the grains and provides the BaTiO3 ceramics with a high dielectric constant, low loss, and flat capacitance temperature characteristics. The Ca-doped ultra-thin dielectric layer compatible with nickel electrode can realize the nickel electrode multilayer capacitors of large capacitance and large volumetric efficiency, which is competitive with the Ta and Al-electrolytic capacitors and as reliable as conventional precious metal electrode multilayer capacitors.

Phase transitions in gallium nanodroplets detected by dielectric spectroscopy

Both theoretical and experimental works give evidence that gallium exhibits solid phases labelled β, γ, δ, e besides the stable α phase strongly dependent both on the size and the confinement conditions. An experimental technique was used based on capacitance and conductance measurements vs. temperature in the audiofrequency range. This technique is particularly sensitive to the conditions of the investigated particle surface that plays a fundamental role in the melting and more generally in the phase transition processes. In particular the strict relation between the derivative of the capacitance with respect to the temperature, dC/dT, and the entropy of the system is considered. In gallium nanoparticles 20 nm in radius, only the δ phase is shown to occur. Further the transition to liquid phase was detected. The melting process was found to start about 65 K below the full melting temperature value. In the case of particles 10 nm in radius, where different metastable phases may occur, the capacitance vs. temperature curve was found to display abrupt changes of the slope. The singularities are associated to a well defined transition temperature.

The effects of neutron transmutations on the low-temperature dielectric properties of solid tantalum capacitors

The method of neutron transmutation doping (NTD) was used to modify the composition of the tantalum pentoxide (Ta 2O 5) dielectric of commercial solid tantalum electrolytic capacitors. The dielectric properties of these isotopically engineered capacitors were measured in the temperature range 90–300 K. Neutron irradiation periods of 30 and 120 days resulted in shifts in the capacitance–temperature and dielectric loss–temperature profiles with increasing irradiation dose. The 10 μF 35 V rated tantalum capacitors showed a good radiation hardness.

Development of composite dielectrics with high specific capacitance and stable temperature characteristics

A new alternative of tailoring the dielectric characteristics of a BaTiO3-based ceramic is established in this study. The ceramic dielectrics were made by either two or three constituents having a composition of (Ba0.96Ca0.04)(Ti1.0−xZr x Mn0.01)O3 (BCTZ), where x ranges from 0 to 0.22, and sintered with Ni inner electrodes at 1300°C for 4 h in a reducing atmosphere. Both alternative stacking, i.e., layer-by-layer of different compositions, and bulk stacking configurations were prepared by screen-printing, resulting in a composite dielectric of different characteristics. It is obtained that the Curie temperature (Tc) of the BCTZ ceramics decreases with an increase of Zr in the dielectrics, i.e., −8°C per mole of Zr. In addition, the stacking configuration, the proportion and the number of constituents in the composite materials control the dielectric characteristics of the multilayer ceramic capacitors. On the basis of the principles outlined, a multilayer ceramic dielectric having k-value in excess of 8000 with the X7R specification (−55 ∼ +125°C, ±15%), which consists of two BCTZ ceramics with Curie temperatures of −20 and 100°C, was successfully developed.

Influence of sintering temperature on the properties of high Tc bismuth layer structure ceramics

Bismuth layer structure Ca 0.82(NaCe) 0.09Bi 4Ti 4O 15 piezoelectric ceramics were prepared by the conventional ceramic technique. Sintering characteristic of Ca 0.82(NaCe) 0.09Bi 4Ti 4O 15 was discussed. The X-ray powder diffraction pattern showed a single phase of bismuth oxide layer structure having general formula (Bi 2O 2) 2+(A m−1 B m O 3 m+1 ) 2− with m=4. Scanning electron microscope (SEM) micrographs of the natural surface of ceramic samples indicated that the anisotropy of growth of grains becomes stronger with the increase in the sintering temperature. With the increase in the sintering temperature, the resistivity and piezoelectric constant d 33 increased to a maximum value and then decreased, but the dielectric constant ε 33 T / ε 0 decreased. The Curie temperature and the capacitance temperature stability of the ceramics were improved with the increase in the density.

A capacitance temperature sensor for the liquid nitrogen region

A capacitance temperature sensor based on commercial manufactured ceramic condensers was found, satisfying most of the demands for absolute temperature measurement at 77 K. Beside linear, relatively good sensitivity in liquid nitrogen (LN 2) temperature range and virtually no magnetic field dependence, the sensor could be simply fixed to a specimen using thermally conductive glue. The self-heating of the sensor is negligibly small, of the order of nW. The sensitivity of capacity measurement provides 0.02 K resolution.

Analysis characterisation and optimisation of temperature coefficient parameters in capacitive pressure sensors

The literal expression of the temperature coefficient is derived in the case of plane sensing cells. It states that the thermal behaviour of the capacitance depends on the cell dimensions and the temperature coefficients of the fixed plate and the internal cavity. Measurements carried out in a set of sensors, constituted of aluminium fixed plates and thin silicon membranes bonded to Pyrex substrates, show that the amplitude of the capacitance thermal coefficient is very sensitive to the bonded length and the fixed plate thickness. Analyses of experimental results indicate that, very often, thermo-mechanical deformations of the internal cavity determine the amplitude of the capacitance temperature coefficient. Nevertheless, they also demonstrate the feasibility of sensing cells in which the capacitance temperature coefficient is very small and practically equal to the temperature coefficient of the fixed plate. In these cells, the fabrication of the fixed plate from ultra thin films and/or metals featuring small thermal expansion coefficients should give capacitance temperature coefficient lower than 44 ppm/°C. Finally it is shown that analyses of isomorphous sensors allow to separate the contributions of the fixed plate and the cell structure and in addition to withdraw the effects of packaging and parasitic capacitors.

Measurement of the low temperature electrical properties of solid tantalum capacitors

Highly reproducible capacitance–low temperature and dissipation factor–low temperature curves were obtained for commercial solid tantalum electrolytic capacitors in the range 90–310 K. A description of a design of a cryostat used to test radial wire ended tantalum bead capacitors at low temperatures is given. The tantalum capacitors showed excellent capacitance–temperature linearity between 220 and 310 K for test frequencies of 120 Hz and 1 kHz. Some evidence is given for the presence of dielectric relaxation at ∼210 K.

Determination of the 2D-Electron Gas Density in a Quantum Well from C–T and C–V Measurements

The 2D-electron gas (2DEG) carrier density in AlGaAs–GaAs–AlGaAs Schottky-gate quantum well structures prepared by MBE has been determined from capacitance–temperature (C–T) and capacitance–voltage (C–V) characteristics. The achieved results are in remarkable agreement with the values of the 2DEG carrier density determined from simulation, Shubnikov-de Haas oscillations and quantum Hall effect (QHE) measurements.

Determination of the 2D-Electron Gas Density in a Quantum Well from C-T and C-V Measurements

The 2D-electron gas (2DEG) carrier density in AlGaAs-GaAs-AlGaAs Schottky-gate quantum well structures prepared by MBE has been determined from capacitance-temperature (C-T) and capacitance-voltage (C-V) characteristics. The achieved results are in remarkable agreement with the values of the 2DEG carrier density determined from simulation, Shubnikov-de Haas oscillations and quantum Hall effect (QHE) measurements.

A corrected 3D Ewald calculation of the low effective temperature properties of the electrochemical interface

The corrected 3D Ewald method is used to verify charged sheets method results that show increasing double-layer capacitance with increasing temperature in the low effective temperature region. The restricted primitive model is used where ions are represented as charged hard spheres and the solvent is represented by a uniform dielectric constant. It is shown that the capacitance temperature plot for the test system exhibits increasing capacitance with increasing temperature in the low effective temperature region, which contradicts common theories of the electrochemical interface. For this system, the corrected 3D Ewald method results coincide well with the charged sheets method results.

Hole-transporting polyimide for organic electroluminescent display

The thermal stability of newly synthesized hole-transporting polyimide, poly[ N,N′–diphenyl– N,N′–bis(4–aminobiphenyl)–(1,1′–biphenyl)–4,4′–diamine pyromellitimide] (PMDA-DBABBD PI), via vapor deposition polymerization was investigated with the aid of the capacitance–temperature ( C– T) measurement technique. Prior to the examination of the complete organic electroluminescent device (OELD), the single layer devices with the individual materials including tris(8-hydroxyquinolinato) aluminum (Alq 3), N,N′-diphenyl- N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD), N,N′-diphenyl- N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB), copper phthalocyanine (CuPc), and PMDA-DBABBD PI were subjected to the C– T measurement. The relaxation temperatures of the single layer devices with Alq 3, TPD, NPB, CuPc, and PMDA-DBABBD PI were 180, 76, 110, 125, and more than 200°C, respectively. The OELD with PMDA-DBABBD PI and Alq 3 as a hole-transporting layer and emissive layer was not relaxed up to 150°C, while those containing CuPc/TPD and NPB thin films were catastrophically damaged at ca. 76 and 110°C, respectively. The OELD with the small organic hole-transporting molecule has almost the same relaxation temperature as the single layer device with the respective molecules. The rectifying and electroluminescent characteristics disappeared for the annealed OELD with the small organic hole-transporting molecules, whereas the OELD with the hole-transporting polyimide did still show the rectifying behavior with the green light emission even though the current density and the light intensity became largely reduced.

Characterization of Si-doped Ga 0.52In 0.48P grown by solid source molecular beam epitaxy using deep level transient spectroscopy

The defect properties of Si-doped Ga 0.52In 0.48P layers grown by solid source molecular beam epitaxy (SSMBE) have been studied by deep-level transient spectroscopy (DLTS), temperature-dependent electron concentration, and capacitance–temperature ( C– T) measurements. The persistent photoconductivity (PPC) effect was observed in highly Si-doped samples. The same samples showed a linear relationship, and changes of almost the same order of magnitude between the trap concentration and electron concentration. There is evidence to suggest that these donor-related levels can be attributed to the presence of DX centers. This defect exhibits ionization energies from ∼358 to 435 meV, but is located at only ∼11–13 meV below the conduction band. The energy level, capture barrier, and ionization energy characteristics are typical of those for a donor-related DX center. The electric field effect (Poole–Frenkel effect) on the emission rate strongly suggests that the defect is shallow.