Temperature Coefficient Of Dielectric Constant Research Articles

Use of Titanates to Achieve a Temperature‐Stable Low‐Temperature Cofired Ceramic Dielectric for Wireless Applications

A low‐loss and near‐zero temperature coefficient of resonant frequency (Tf) low‐temperature cofired ceramic (LTCC) host dielectric was developed for portable consumer wireless device applications. The low Tf was realized by compensating the Al2O3‐filled‐glass dielectric with admixtures of TiO2 (negative temperature coefficient of dielectric constant (Tɛ)) in the starting formulation. XRD data indicated a portion of the TiO2 in the starting formulation dissolved into the glass, and extensive formation of crystalline titanium compounds was observed via a nucleation and growth mechanism. The dissolution of TiO2 in the glass and subsequent formation of titanium compounds was believed to result in the relatively small amount of TiO2 required to achieve a near‐zero Tf in the final sintered structure.

A Dielectric Bolometer Mode of Infrared Sensor Using a New Ba(Ti 1−x Sn x )O 3 Thin Film with a High Temperature Coefficient of Dielectric Constant

A new Ba(Ti 1 m x Sn x )O 3 (x=0.15) ferroelectric thin film was applied for uncooled infrared (IR) sensor as a sensing material. The film was prepared by metalorganic decomposition (MOD) with final annealing at 800 . The electrical characteristics such as temperature dependence of capacitance and insulation are very good from viewpoints of temperature coefficient of dielectric constant (TCD) and capacitive operation, where TCD is about 3 %/K at 20 and the resistance is about a few Mohms per 200 m square, respectively. The MOD film was applied to our proposed dielectric bolometer (DB) mode of IR detector that has merits in 1) room temperature operation, 2) chopperless, 3) low power dissipation, and 4) high sensitivity. Finally, the DB-mode operation in the sensor was confirmed on a newly developed device structure, and the resultant voltage sensitivity (R v ) and specific detectivity (D*) were observed to be 0.15 kV/W and 3.5 2 10 8 cmHz 1/2 /W with noise voltage (V n ) of 100 nV, respectively, with the detector size mentioned above. Also, a good stability in IR response against thermal cycling is observed.

Synthesis and Dielectric Characterization of Pyrochlore-Free Pb1-xBax(Zn1/3Nb2/3)O3Ceramics

The dielectric properties and synthesis of pyrochlore-free lead zinc niobate ceramics with Ba substituting for Pb were investigated. Ba partial substitution for Pb was effective in stabilizing the perovskite structure in PZN ceramics, where the minimum amount of Ba substitution needed was about 20 mol%. The dielectric loss and the temperature coefficient of dielectric constant of PZN were reduced markedly with Ba substitution, while the dielectric constant was greater than 110. Good dielectric properties were obtained for the composition of Pb0.3Ba0.7(Zn1/3Nb2/3)O3:e = 133.5, tan δ = 0.0009, τe = −811 ppm/°C.

Synthesis and dielectric properties of magnesium niobate-magnesium tantalate solid solutions

Monophasic Oxides of the type MgNb 2−xTa xO 6 (0 ≤ x ≤ 2) have been synthesized by solid-state reactions using Mg(NO 3) 2·6H 2O as the source of Mg. The oxides crystallize in the orthorhombic columbite structure till x = 1.75 and the tetragonal trirutile structure for pure MgTa 2O 6 (x = 2.0). Sintered pellets at 1200°C show dielectric constant varying between 16 to 28 for the entire range of composition at a frequency of 500 kHz. The dielectric loss is nearly constant with frequency, and varies between 0.004 and 0.01 for different compositions. The temperature coefficient of dielectric constant (τ E) is 3 to −3 ppm/C (30 to 300°C). Scanning electron micrographs reveal a gradual decrease in grain size with increase in Ta concentration with size of 7 to 10 microns for the pure Nb phase sintered at 1200°C while the pure Ta phase shows a grain size of approximately 0.5 to 1 microns.

Structural and dielectric characterization of Ba4Nd2Ti4+xTa6−xO30−x/2 nonstoichiometric ceramics

Ba4Nd2Ti4Ta6O30 dielectric ceramics with high-Ε and low dielectric loss were modified to improve the temperature coefficient of dielectric constant. Through partial substitution of Ti4+ for Ta5+, a significantly reduced temperature coefficient of dielectric constant (tΕ = –664p pm/°C) combined with a dielectric constant above 110 and a low dielectric loss (tanδ–0.0005 to 0.0006 at 1 MHz) resulted in the nonstoichiometric dielectric ceramics with nominal compositions Ba4Nd2Ti4+xTa6-xO30?x/2 (x = 0.8–1.2).

Dielectric properties of La-substituted Pb0.5Ca0.5[(Mg1/3Nb2/3)0.5Ti0.5]O3 ceramics

Modification of Pb0.5Ca0.5[(Mg1/3Nb2/3)0.5Ti0.5]O3 dielectric ceramics was performed by up to 20 mol% La substitution for Pb and Ca. The temperature coefficient of dielectric constant was significantly reduced by the present approach, while an increased Qf factor was achieved. Good microwave dielectric properties were obtained in a composition Pb0.425Ca0.425La0.1[(Mg1/3Nb2/3)0.5Ti0.5]O3: ε = 125; Qf = 3150 GHz; calculated temperature coefficient of resonant frequency δf = +253 ppm/°C.

Modified Ba3Sm3Ti5Ta5O30 dielectric ceramics

Abstract Dielectric ceramics of Ba 3 Sm 3 Ti 5 Ta 6 O 30 were modified by introducing the nonstoichiometric composition Ba 3−3 x Sm 3+2 x Ti 5 Ta 5 O 30 and the sintering characteristics, microstructures and dielectric properties of Ba 3−3 x Sm 3+2 x Ti 5 Ta 5 O 30 ceramics were investigated as a function of the composition. Ba 3−3 x Sm 3+2 x Ti 5 Ta 5 O 30 dense ceramics, sintered at 1400–l430°C, have complex phase constitutions, containing the tungsten–bronze major phase and the pyrochiore secondary phase. With increasing x , the temperature coefficient of dielectric constant ( τ e ) was pronouncedly improved from −l050 to −610 ppm/°C without considerable increase of dielectric loss, but the dielectric constant ( e ) decreased considerably.

Fine-tuning of temperature coefficients of capacitance (TCC) and dielectric constant (TCK) of Mg2SnO4 via second phase addition

Fine-tuning of the temperature coefficients of capacitance and dielectric constant of magnesium orthostannate (Mg2SnO4) has been attempted by means of Sn (IV) and Zr (IV) oxide incorporation as a second phase. The additives were also employed to enhance the density and minimize or eliminate porosity at lower sintering temperatures. Phase-pure magnesium stannate powder was synthesized via conventional solid-state reaction. It was mixed with ZrO2 and/or SnO2 and sintered in the temperature range 1500°–1600°C for up to 6 h. Electrical measurements using an AC immittance spectroscopic technique over the temperature range 25°–300°C, on Mg2SnO4 compacts containing 5 wt.% of additives and sintered at 1500 °C/ 6 h, were carried out. Data analyses revealed that the capacitance and the derived dielectric constant remained invariant over more than 3 decades of frequency in the kilo to megahertz regime. It was also found that addition of ZrO2 and SnO2 has a benign effect on both temperature coefficient of capacitance (TCC) and temperature coefficient of dielectric constant (TCK) as it resulted in smaller dependence of capacitance and dielectric constant compared to pure Mg2SnO4. Typically, the TCC values were 5 and 30 ppm/°C and TCK values were 20 and 30 ppm/°C for 5 wt.% ZrO2- and 5 wt.% SnO2- added Mg2SnO4, respectively, in the temperature range 25°–300°C.

Preparation of BST Ferroelectric Thin Film by Metal Organic Decomposition for Infrared Sensor

Barium Strontium Titanate (Ba1-xSrxTiO3) ferroelectric thin films have been prepared by Metal Organic Decomposition (MOD) on Pt/Ti/SiO2/Si and on micromachined Pt/Ti/NSG/Si3N4/SiO2/Si wafer with an aim to fabricate dielectric bolometer type infrared sensor. The XRD pattern and D-V hysteresis curve of the film have been measured in order to investigate the effects of the final annealing temperature and annealing time on the property of the film. The results show that the films annealed at 700 or 800°C all have good perovskite structure, while the film annealed at 800°C has better ferroelectric loops. Films annealed at 800°C with different annealing time from 5 to 60 minutes show a similar perovskite structure, among which films annealed at 30 and 60 minutes condition have the better ferroelectric loops. Temperature Coefficient of Dielectric constant (TCD) of the MOD made BST thin film on micromachined substrate is about 1%/K. The uniformity of the BST film on micromachined Si wafer also has been confirmed to be well enough for operation of sensor array.

Effect of NiO additive on structure and dielectric properties of Bi2O3-ZnO-Nb2O5 based ceramics

The effect of NiO additive on structure and dielectric properties of Bi2O3-ZnO-Nb2O5 based ceramics was investigated. All the samples were obtained at lower sintering temperature between 960°C∽1020°C. With the aids of XRD analyses the structure of these samples was recognized. It shows that although the structure at small amount additive (NiO≤2wt%) is still made of cubic pyrochlore α phase and monoclinic pyrochlore β phase as that of the reference composition, the proportion of each phase has been changed. With increasing of NiO doping, dielectric constant and loss rises at room temperature, and temperature coefficient of dielectric constant is declined to negative. The result of dielectric behaviors indicates that certain NiO additive can be an effective way to improve the value of dielectric constant and adjust temperature coefficient in Bi2O3-ZnO-Nb2O5 based ceramics.

Dielectric properties and microstructure of Ca5Nb2TiO12 and Ca5Ta2TiO12

The 1 MHz dielectric properties of Ca 5 Nb 2 TiO 12 and Ca 5 Ta 2 TiO 12 compounds were reported recently. Both compounds have a common characteristic dependence of the temperature coefficient of dielectric constant (TCK) and dielectric constant ( ϵ r ) on sintering temperature. For both compounds a TCK<5 ppm/deg can be achieved by selecting the right processing conditions. It was suggested that an order–disorder transition among the B-site ions in these perovskite-based compounds plays a major role in the determination of TCK. Since X-ray powder diffraction does not appear to be a good technique to detect the structural changes, transmission electron microscopy (TEM) was applied in this work. It was found that different types of ordering between (111) planes, namely 1:1, 1:2 and 1:3, as well as distortions by tilting of octahedra, are involved in the formation of a microstructural state at an ambient temperature. The compounds in the as-sintered conditions both have a microdomain structure but with a different type of ordering, 1:3 for Ca 5 Nb 2 TiO 12 and 1:2 for Ca 5 Ta 2 TiO 12 . Both compounds have a tilting phase transition from the disordered Pm 3 m to distorted Pnma (with the a − b + a − tilt of octahedra) structures at temperatures that coincide with the observed kinks at T A1 and T A2 in the TCK( T S ) and K ( T S ) curves.

Bismuth titanium indium antimony oxide: A low-temperature-coefficient, high-K dielectric material

The 1 MHz dielectric properties for mixed-phase polycrystalline ceramics in the system Bi4Ti3O12–Bi(InxSb1x)O3 were reported. In the vicinity of ambient temperature, the dielectric constants for the Sb and In end-members were approximately 430 and 160, respectively, and the temperature coefficients of dielectric constant (TCKs) were approximately -7600 and +430 ppm/deg. At an overall composition of Bi4Ti3O12:Bi(In0.37Sb0.63)O3 a dielectric constant of 144 and a low TCK were found. Powder x-ray diffraction and electron microscopy analyses indicated that the optimal composition contained three major phases. Deviation of any of the elements from the above ratio leads to degradation of the properties.

A-Site (MCe) Substitution Effects on the Structures and Properties of CaBi4Ti4O15 Ceramics

We investigated the effect of A-site compound substitution on the structures and properties of Ca0.8(MCe)0.1Bi4Ti4O15 (M denotes Li, Na and K) ceramics. The samples were prepared by the conventional ceramic technique. Sintering characteristics of Ca0.8(MCe)0.1Bi4Ti4O15 and CaBi4Ti4O15 ceramics were discussed. X-ray powder diffraction patterns of the three modified CBT-based compounds show a single phase of bismuth oxide layer type structure with m=4. The hysteresis loops of polarization versus electric field of the four compounds were also measured. A-site compound substitution improves the piezoelectric properties and the high-temperature resistivity of these materials. A-site (LiCe) and (KCe) substitution not only improves the Curie temperature but also decreases the temperature coefficient of dielectric constant (TKε). Among the three modified ceramics, only the Curie temperature of Ca0.8(NaCe)0.1Bi4Ti4O15 is lower than that of CaBi4Ti4O15; however, its TKε is the lowest. As a result, all the three modified CBT-based ceramics were found to be excellent high-temperature piezoelectric materials.

A Dielectric Bolometer Behavior of BST Thin Film Prepared by Metal-Organic-Decomposition with Excellent Reproducibility in Thermal Cycling Test

AbstractWe have proposed a new type of simple detector pixel circuit and device structure for application of dielectric bolometer mode (DB) of infrared (IR) image sensor. The DB mode has merits such as uncooled room temperature operation, chopperless, low power dissipation, and high-sensitivity. A stable Ba1划xSrxTiO3 (BST) thin film has been successfully developed as a dielectric bolometer material for IR detector by Metal-Organic-Decomposition (MOD) method. The film was prepared on both Pt/Ti/SiO2/Si-bulk and Pt/Ti/NSG/Si3N4/SiO2 membrane structures, where an IR light is detected at the membrane as a change in dielectric constant (ε). So, the important issue for realizing a reliable IR sensor with high-sensitivity has been achieved to have a good thermal stability in ε against change in the detector temperature. XRD patterns and D-E hysteresis curves were measured and revealed that the BST film has a good perovskite structure and shows an adequate ferroelectric loops, especially for final annealing temperature higher than 700 °C. Temperature Coefficient of Dielectric constant (TCD), which decides the IR sensitivity, of the MOD made BST film is about 1 %/K. The reproducibility in ε, namely IR detector capacitance, was found to be very good in temperature ranging from about 10 to 80 °C within a relative change of 2 %. Finally, the stabilities in both the temperature dependence of ε and the output level have been obtained with a fairly large IR detectivity, where voltage sensitivity(Rv) and specific detectivity(D*) were about 1.2 kV/W and 2.9e8 cmHz 1/2/W, respectively.

Modification of Ba 4 Sm 2 Ti 4 Ta 6 O 30 dielectric ceramics

Modification of promising tungsten bronze-type dielectric ceramic Ba4Sm2Ti4Ta6O30 has been investigated by adjusting the composition in Ba4-3xSm2+2xTi4Ta6O30. The temperature coefficient of dielectric constant has been significantly improved by such modification together with the suppressed dielectric loss, but the dielectric constant decreased significantly. © 2000 Kluwer Academic Publishers

Application of Ferroelectric BST Thin Film Prepared by MOD for Uncooled Infrared Sensor of Dielectric Bolometer Mode

Metal Organic Decomposition (MOD) has been applied to prepare Barium Strontium Titanate (Ba1-xSrxTiO3) ferroelectric thin film on micromachined Si wafer with an aim to fabricate dielectric bolometer(DB) type infrared image sensor. The detector pixel circuit is a capacitor-capacitor serially connected circuit, with one capacitor of BST film on Si membrane structure and the other on Si bulk structure. When exposed to IR radiation, the capacitance of the IR detecting capacitor on membrane structure changed as a result of the change in dielectric constant against temperature of BST ferroelectric film. Temperature Coefficient of Dielectric constant (TCD) of the MOD made BST (x=0.25, Ba/Sr=75/25) thin film is about 1%/K. Uniform and reproducible capacitance behavior in the BST ferroelectric thin film capacitor on micromachined Si substrate has been confirmed. Chopperless operation has been attained and IR responses of the fabricated sensor also have been obtained with Rv of 0.4kV/W and D* of 1×108 cmHz1/2/W, respectively.

Dielectric properties of sintered materials prepared from glass-ZrO 2 -SrTiO 3 mixtures

(Ca,Sr,Ba)O-Al2O3-SiO2-TiO2 glass powder was mixed with 6.7 mol % ZrO2 and 0–11.96 mol % SrTiO3. The mixtures were sintered at 850 °C, 900 °C or 950 °C. Most of the glass phase changed to crystalline phases of (Ca,Sr,Ba)2TiSi2O6TS, (Ca,Sr,Ba)Si2O6AS, ZrO2 and SrTiO3 during sintering. The dielectric properties of samples sintered at 900 °C were measured at 1 MHz using silver electrodes. With increasing SrTiO3 content, the dielectric constant increased from 12 to 19 and the temperature coefficient of dielectric constant, TCD, changed from -30 ppm ^C-1 to -400ppm^C-1. Using mixture equations, dielectric constants and TCD values were estimated for the samples and these values were compared with experimental results.

Stabilization of the low temperature coefficient of dielectric constant of Ca 5Nb 2TiO 12 by Zr doping

The effects of small amounts of Zr substitution for Ti in the low loss, low temperature coefficient dielectric material Ca 5Nb 2TiO 12 are reported. Substitutions at the 1–5% level significantly increase the range of possible firing temperatures at which polycrystalline ceramics with low temperature coefficients can be obtained. This low temperature coefficient state is at the borderline between ordered and disordered states of the Ca, Nb, and Ti ions in the B sites of the perovskite lattice. The kinetics for ordering is apparently enhanced by the Zr substitutions.

Dielectric ceramics of Ba6-3xNd8 2x(Zr,Ti)18O54

The sintering characteristics, microstructures and microwave dielectric properties of Ba-3XNd8+2X(Zr,Ti)18O54 ceramics were investigated. By substitution of Zr for Ti in BaNd2Ti4O12 ceramics, the density and the densification temperatures increased. Meanwhile, both the dielectric constants and the Qf values decreased as the amount of Zr increased. Moreover, a solid solution limit (between 25mol% and 50mol%) of Zr for Ti in BaNd2Ti4O12 was suggested by the XRD analysis, and the temperature coefficient of dielectric constant could be improved when Ti was substitution by Zr within this solid solution limit.

Temperature-stable dielectric ceramics in Ba4Nd2Ti4Ta6O30/(La0.1Bi0.9)2Ti2O7 biphase system

Biphase dielectric ceramics in the system of (1 − x)Ba4Nd2Ti4Ta6O30/ x(La0.1Bi0.9) 2Ti2O7 were investigated to obtain a near-zero temperature coefficient of dielectric constant. With the increase in x, the dielectric constant increased slightly, and the temperature coefficient changed from negative to positive. High dielectric constant of ε = 143 and good temperature stabibility (τ ε = −48 ppm/ °C) were achieved in a composition of x = 0.45, and the increased dielectric loss became the new problem.