High-temperature Capacitors Research Articles

Dielectric Properties of Ba0.8Ca0.2TiO3–Bi(Mg0.5,Ti0.5)O3–NaNbO3 Ceramics

Ceramics in the system 0.45Ba0.8Ca0.2TiO3–(0.55−x)Bi(Mg0.5Ti0.5)O3–xNaNbO3, x = 0–0.02 were fabricated by a conventional solid‐state reaction route. X‐ray powder diffraction indicated cubic or pseudocubic symmetry for all samples. The parent 0.45Ba0.8Ca0.2TiO3–0.55Bi(Mg0.5Ti0.5)O3 composition is a relaxor dielectric with a near‐stable temperature coefficient of relative permittivity, εr = 950 ± 10% across the temperature range 80°C–600°C. Incorporation of NaNbO3 at x = 0.2 extends the lower working temperature to ≤25°C, with εr = 575% ± 15% from temperatures ≤25°C to >400°C, and tan δ < 0.025 from 25°C to 400°C. Values of dc resistivity ranged from ~109 Ω·m at 250°C to ~106 Ω·m at 500°C. The properties suggest that this material may be of interest for high‐temperature capacitor applications.

P2IMS depth profile analysis of high temperature boron oxynitride dielectric films

Existing silicon oxynitride (SiON) dielectric can only provide a very near term solution for the metal oxide semiconductor technology. The emerging high-k dielectric materials have a limited thermal stability and are prone to electrical behavior degradation which is associated with unwanted chemical reactions with silicon (Si). We investigated here applicability of amorphous boron oxynitride (BON) thin films as an emerging dielectric for high temperature capacitors. BON samples of thickness varying from 200nm down to 10nm were deposited in a high vacuum reactor using ion source assisted physical vapor deposition (PVD) technique. Plasma profiling ion mass spectrometry (P2IMS) was utilized to specifically determine the interface quality and best capacitor performance as a function of growth temperatures of a graded sample with alternate layers of deposited titanium (Ti) and BON layers on Si. P2IMS depth profiling of these layers were also performed to evaluate the stability of the dielectric layers and their efficacy against B dopant diffusion simulating processes occurring in activated polySi-based devices. For this purpose, BON layers were deposited on boron-isotope 10 (B10) implanted Si substrates and subsequently annealed at high temperatures up to 1050°C for about 10s. Results comparing inter-diffusion of B10 intensities at the interfaces of BON–Si and SiON–Si samples suggest suitability of BON as barrier layers against boron diffusion at high temperature. Stable Ti/BON/Ti capacitor behavior was achieved at optimum growth temperature of 600°C of the BON dielectric layer. Capacitance change with frequency (10kHz to 2MHz) and temperature up to 400°C is about 1% and 10%, respectively.

Diffuse phase transition and electrical properties of lead-free piezoelectric (LixNa1-x)NbO3 (0.04 ≤ x ≤ 0.20) ceramics near morphotropic phase boundary

Temperature-dependent dielectric permittivity of lead-free (LixNa1-x)NbO3 for nominal x = 0.04–0.20, prepared by solid state reaction followed by sintering, was studied to resolve often debated issue pertaining to exactness of morphotropic phase boundary (MPB) location besides structural aspects and phase stability in the system near MPB. Interestingly, a diffuse phase transition has been observed in the dielectric permittivity peak arising from the disorder induced in A-site and structural frustration in the perovskite cell due to Li substitution. A partial phase diagram has been proposed based on temperature-dependent dielectric permittivity studies. The room temperature piezoelectric and ferroelectric properties were investigated and the ceramics with x = 0.12 showed relatively good electrical properties (d33 = 28 pC/N, kp = 13.8%, Qm = 440, Pr = 12.5 μC/cm2, Ec = 43.2 kV/cm, and Tm = 340 °C). These parameter values make this material suitable for piezoelectric resonator and filter applications. Moreover, a high dielectric permittivity (ε′r = 2703) with broad diffuse peak near transition temperature, and low dielectric loss (<4%) over a wide temperature range (50–250 °C) found in this material may also have a potential application in high-temperature multilayer capacitors in automotive and aerospace related industries.

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.

Temperature-stable high-energy-density capacitors using complex perovskite thin films

Chemical-solution-derived thin film synthesis and dielectric characterizations of (1 - x)BaTiO(3-x)Bi(Mg,Ti) O(3) complex perovskites with compositions x <0.15 have been explored for temperature-stable high-energy-density capacitor applications. Solution chemistry has been optimized to synthesize and stabilize the precursor solution. Solution-derived (1 - x)BaTiO(3-x)Bi(Mg,Ti)O(3) thin film samples in thicknesses ranging from 250 to 500 nm were fabricated by repeated spinning and subsequent crystallization processes. These thin films showed nearly linear polarization response with high relative dielectric permittivity exceeding 900, which is beneficial for high-capacitance-density and high-energy-density capacitors. Average dielectric breakdown strengths of the dense films were as high as 2.08 MV/cm. The BaTiO(3)-Bi(Mg,Ti) O3 samples showed very low leakage current densities of the order of 10-8 A/cm(2) even at temperatures of 200°C. Based on the structural stability at high temperatures of the pseudocubic perovskite, the high dielectric permittivity and the typical P-E behaviors of the BaTiO(3)-Bi(Mg,Ti)O(3) thin films were also maintained at such high temperatures. Resulting energy density of the 500-nm-thick 0.88BaTiO(3)-0.12Bi(Mg,Ti) O(3) thin film was as high as 37 J/cm(3) at 1.9 MV/cm. The high energy density and excellent temperature stability of the Ba- TiO(3)-Bi(Mg,Ti)O(3) complex perovskite show promise for use in high-temperature pulse power capacitor applications.

High temperature electronic properties of BaTiO3 – Bi(Zn1/2Ti1/2)O3 – BiInO3 for capacitor applications

Solid solutions xBaTiO3 – (1-x)(0.5Bi(Zn1/2Ti1/2)O3 – 0.5BiInO3), where x = 0.95–0.60, were prepared by conventional mixed oxide method. The single phase perovskite structure was obtained for the composition with x ≥ 0.75. Phase transformation from tetragonal to pseudocubic was observed from x-ray diffraction patterns when x decreased from 0.95 to 0.75. In tetragonal phase region, x ≥ 0.90, the increase of Bi(Zn1/2Ti1/2)O3 – BiInO3 content decreased the tetragonality and the temperature at which the relative permittivity is maximum (Tmax). The increase in lattice parameter and Tmax were observed in the pseudocubic phase region, x < 0.90. Additionally, a highly broad and diffuse phase transition was observed from the dielectric data in the pseudocubic phase region. The introduction of Ba vacancies in compositions with x = 0.80 and 0.75 also improved dielectric loss at high temperatures. The incorporation of BiInO3 into the BaTiO3 – Bi(Zn1/2Ti1/2)O3 compound was also found to improve the temperature coefficient of the relative permittivity, with values as low as approximately −1,000 ppm/K. Overall, ternary perovskite solid solutions based on adding Bi(Zn1/2Ti1/2)O3 – BiInO3 to BaTiO3 shows excellent potential for high temperature capacitor applications

Structural, dielectric, and piezoelectric properties of BaTiO3-Bi(Ni1/2Ti1/2)O3 ceramics

Undoped and Mn-doped (1−x)BaTiO3–xBi(Ni1/2Ti1/2)O3 (x = 0.03–0.7) ceramics were synthesized by a conventional solid state route. X-ray diffraction patterns revealed that the crystal structure was a tetragonal perovskite at x = 0.03, a pseudo-cubic perovskite at x = 0.1 and 0.3, and mixed phases at x = 0.5–0.7. The dielectric and piezoelectric responses were ferroelectric at x = 0.03 and relaxor-like at x = 0.1–0.7. The polarization–electric field and strain–electric field responses were suppressed at the relaxor compositions, and the large-field piezoelectric constant was 25–40 pm/V at x = 0.3–0.7. As x increased, the temperature of the maximum dielectric constant decreased compared to the Curie temperature of BaTiO3 at x ≤ 0.1, and then it increased and reached 325°C at x = 0.7. At x = 0.3–0.7, the dielectric constant was less temperature dependent. These results suggest that the samples may be suitable for high temperature capacitor application.

High Temperature Performance of Coiled Glass Capacitors

Alkali-free flat panel display glass is produced in large quantity and has excellent electrical insulating properties at high temperature. Aluminum borosilicate glass with alkaline-earth modifier has low sodium content and low dielectric loss (tan δ &amp;lt;0.1 at 250°C), high dielectric breakdown strength (109 V/m) and excellent high temperature stability. In addition, roll-to-roll processing of thin glass sheet has been demonstrated and glass capacitors that are configured in a coil. Excellent high power capability of these glasses was confirmed by analytical, finite element, and finite difference modeling. The modeling work indicates that a combination of hybrid electrode design and effective heat loss at the interface can further extend power capability of glass capacitors. Alkali-free glass is an ideal candidate material for high temperature capacitors.

TEMPERATURE-INDEPENDENT DIELECTRIC PROPERTIES OF 0.82[0.94Bi0.5Na0.5TiO3–0.06BaTiO3]–0.18K0.5Na0.5NbO3 CERAMICS

In order to explore the high temperature stability of ceramic capacitor, we present temperature-independent dielectric properties of 0.82[0.94Bi0.5Na0.5TiO3–0.06BaTiO3]–0.18K0.5Na0.5NbO3 (BNT–BT–18KNN) ceramics. For different sintered temperature and annealing treatment, the pseudoternary system showed a εr of 2265 at 1 kHz at 35°C with a normalized permittivity ε/ε35°C varying less than ±15% from 11°C to 382°C. This pure perovskite phase with slimmer and heat proof P–E loops possessed energy density of 0.616 J/cm3 with a tolerance of about ±3% in a temperature interval ranging from 20°C to 120°C, which is higher and more temperature stable than most ceramic capacitors, such as PLZST and 0.89BNT–0.06BT–0.05KNN. This relaxor ferroelectric (at room temperature) with parabolic bipolar strain–electric (S(E)) curve showed a quite low temperature dependence of positive strain with less than ±6.5% tolerance from the average value of 0.091% between 20°C and 120°C, which is also more temperature stable than the same composition Zhang et al. reported. These merits demonstrate that the newly produced BNT–BT–18KNN ceramics should be a promising candidate for the development of high-temperature capacitor and actuator materials.

High-K (Ba0.8Bi0.2)(Zn0.1Ti0.9)O3ceramics for high-temperature capacitor applications

Solid solutions of BaTiO(3)-Bi(Zn(1/2)Ti(1/2))O(3) were investigated for high-temperature capacitor applications. Compositions close to 0.8BaTiO(3)-0.2Bi(Zn(1/2)Ti(1/2))O(3) revealed pseudo-cubic symmetry and showed a linear dielectric response. The existence of a nearly flat temperature dependence of the relative permittivity over the temperature range of 100 to 350°C was also obtained. In this study, the effects of cation non-stoichiometry and doping were investigated in an attempt to optimize the insulation resistance for high-temperature applications. The dielectric response of (Ba(0.8)-xBi(0.2))(Zn(0.1)Ti(0.9)) O(3) ceramics where 0 ≤ X ≤ 0.08, as well as ZrO2- and Mn(2)O(3)-doped ceramics were studied. The optimum compositions exhibited a relative permittivity in excess of 1150 with a low loss tangent (tan δ < 0.05) that persisted up to a temperature of 460δC. The temperature dependence of resistivity also revealed the improved insulation resistance of Ba-deficient compositions. Additionally, we suggest that an ionic conduction mechanism is responsible for the degradation of resistivity at high temperatures. The temperature coefficient of permittivity ((τ)K) and the RC time constant were also investigated.

Effects of ZnO and CeO2 additions on the microstructure and dielectric properties of Mn-modified (Bi0.5Na0.5)0.88Ca0.12TiO3 ceramics

The effects of ZnO and CeO2 on the microstructure and dielectric temperature characteristics of the Mn-modified (Bi0.5Na0.5)0.88Ca0.12TiO3 ceramics were investigated to develop temperature-stable dielectric ceramics. By adding 1–2 wt% ZnO, the overall dielectric constant increased. With further increasing the amount of ZnO, the dielectric constant at temperatures lower than 25 °C decreased, whereas the dielectric constant at temperatures higher than 75 °C increased. The temperature characteristic of capacitance became flatter when more than 4 wt% ZnO was doped. By adding CeO2, the dielectric constant decreased and a flat temperature characteristic of permittivity was obtained. X-ray diffraction analysis revealed that the perovskite BNT phase formed for all the compositions and the secondary phases Zn2TiO4 and Bi2Ti2O7 occurred, respectively when ZnO and CeO2 was added. Scanning electron microscope indicated that an inhomogeneous microstructure comprising fine and rectangle grains was observed in the ZnO-free sample. ZnO less than 2 wt% could inhibit the grain growth and decrease long grains. However, the grain growth was promoted as more than 8 wt% ZnO was added. The dielectric loss with different contents of ZnO and CeO2 were characterized as the function of temperatures for potential use at high temperature. The dielectric loss at 25 °C was independent of the amounts of ZnO and CeO2. However, the dielectric loss at 250 °C decreased by adding 1 wt% ZnO and then increased with increasing ZnO. This system is considered to be a potential material for high-temperature capacitors.

Nonlinear dielectric ceramics and their applications to capacitors and tunable dielectrics

Nonlinear ceramics that provide the basis for high-energy-density and high-temperature capacitors, as well as tunable microwave dielectrics, and their applications are discussed in this article.

High temperature capacitors using a BiScO3-BaTiO3-(K1/2Bi1/2)TiO3 ternary system

BiScO3-BaTiO3 with (K1/2Bi1/2)TiO3 [BSBT-KBTx] in the perovskite solid solution system were prepared by conventional ceramic processing for potential high temperature capacitors. The effect of KBT on the dielectric properties of BSBT was investigated as a function of temperature and frequency. The BSBT-KBT20 exhibited high dielectric permittivity and low dielectric loss over the temperature range from 100°C to 300°C with flat coefficients of temperature (TCɛs). In addition, BSBT-KBTx were observed to possess dielectric relaxation behavior at temperatures (> RT) as observed in lead-based relaxors. Furthermore, the E-field polarization behavior was investigated showing high energy density of 1.28 J/cm3 at 100 kV/cm for the BSBT-KBT20.

Lead-free high-temperature dielectrics with wide operational range

The dielectric, electrical and structural properties of (1–x)(0.94Bi1/2Na1/2TiO3–0.06BaTiO3)–xK0.5Na0.5NbO3 (BNT–BT–xKNN) with x=0.09, 0.12, 0.15, and 0.18 were investigated as potential candidates for high-temperature capacitors with a working temperature far beyond 200 °C. Temperature dependent dielectric permittivity (ε) showed two local broad maxima that at the optimal composition of KNN (x=0.18) are combined to form a plateau. This then results in a highly temperature-insensitive permittivity up to ∼300 °C at the expense of a small reduction in absolute permittivity values. High-temperature in situ x-ray diffraction study showed pseudocubic symmetry without obvious structural changes, which implies that the dielectric anomalies observed could only be a consequence of a slight change in space group. BNT–BT–0.18KNN showed a permittivity of ∼2150 at the frequency of 1 kHz at 150 °C with a normalized permittivity ε/ε150 °C varying no more than ±10% from 43 to 319 °C. With very good electrical properties persisting up to 300 °C, i.e., a resistivity on the order of magnitude of 108 Ω m and the RC constant of about 1 s, the examined BNT–BT–xKNN compositions present a good starting point for the development of high-temperature capacitor materials.

High Stability of Dielectric Permittity for K0.5Na0.5NbO3-Based Lead Free Piezoelectric Ceramics

A new perovskite ferroelectric, Bi(Mg2/3Nb1/3)O3, was proposed to develop Na0.5K0.5NbO3(KNN)-based lead-free piezoelectric ceramics by an conventional preparation technique. Dielectric stability properties of lead-free K0.5Na0.5NbO3- Bi(Mg2/3Nb1/3)O3 ceramics were studied. The addition of BMN leads to a polymorphic phase transition between ferroelectric orthorhombic and rhombohedral phases(x = 0.01). 0.03BMN-0.97KNN ceramics show a broad and stable permittivity maximum near 1450 from 25 to 400°C and lower dielectric loss(≤5%) at broad temperature usage range 25–400°C for diffusion phase transition. The results indicate that this material may have great potential for high temperature capacitors in automobile applications.

High-Temperature Capacitor Based on Ca-Doped Bi0.5Na0.5TiO3-BaTiO3 Ceramics

High-temperature capacitors were prepared by the conventional oxide method based on Bi0.5Na0.5TiO3-BaTiO3-CaTiO3 (BNT-BT-CT) lead-free piezoelectric ceramics. BNT-BT is one of the promising candidates as a high-temperature relaxor, and has a high Curie temperature and broadened dielectric constant. The addition of CT increases the dielectric constant at lower temperatures and decreases the dielectric constant at higher temperatures, so that the variation of capacitance is decreased. The effect of BT on the temperature characteristic of dielectric constant is contrary to that of CT. A single-phase rhombohedral perovskite and square grains were obtained in this study. With the proper amount of BT and CT additions, the high-temperature specification can be met: from −55°C to 200°C, the variation of capacitance is within ±15% of room-temperature capacitance.

Recent development of high energy density polymers for dielectric capacitors

High energy density dielectric materials are desirable for capacitors and other energy storage systems. Two approaches were developed to achieve high electric energy density: explore high dielectric constant (K) materials and improve high operation electric field. Relaxor ferroelectric polyvinylidene fluoride (PVDF) based copolymers P(VDF-HFP), P(VDF-CTFE) and terpolymer P(VDF-TrFE-CFE) have been proven to possess high electric energy density. An energy density of over 25 J/cm3 has been achieved in PVDF-based polymers, which represents the state of art in high energy density polymers. Aromatic polyurea thin films were developed through vapor phase deposition, exhibiting relatively high dielectric constant, low loss, high breakdown field (>800 MV/m) and consequently high energy density (>12 J/cm3). Its thermal stability up to 200°C and high charge-discharge efficiency (>90%) make it attractive for high temperature capacitors. Investigation through SEM, AFM and other experiments indicated unbalanced aromatic polyurea could exhibit apparent high-K (~15) due to the non-uniformity of film thickness and surface morphology. This article reviews the recent development of these high performance polymers.

High-temperature stable dielectrics in Mn-modified (1-x) Bi0.5Na0.5TiO3-xCaTiO3 ceramics

In the current work, the bulk (1-x) Bi0.5Na0.5TiO3-xCaTiO3 [BNCT100x] system was synthesized via solid-state route. CaTiO3 in solid solution with Bi0.5Na0.5TiO3 was observed to decrease the dielectric constant at higher temperature and raise the dielectric constant at lower temperature. Polarization hysteresis measurements indicated that the ferroelectricity of Bi0.5Na0.5TiO3 was weakened with an increase of CaTiO3, resulted in the shift of the depolarization temperature (T d) toward lower temperatures. X-ray diffraction analysis revealed that TiO2 was produced as a secondary phase due to the losses of Bi and Na during milling and sintering processes. Moreover, the addition of Ca promoted the segregation of Ti out of BNT grains. Dielectric properties of BNCT12 ceramics with different dopant levels of Mn were characterized as a function of temperature for potential use of high-temperature capacitors. Modification of BNCT12 materials with Mn improved the temperature characteristic of capacitance (−55°C to 250°C, △C/C25°C ≤ ±15%). Finally, by doping 1.5 wt% Mn, the dielectric constant at room temperature could reach over 900, with a low dielectric loss below 1% and a high insulation resistivity about 1012 Ω•cm. Furthermore, a small amount of Mn influenced the microstructure in the way to inhibit the long grains and grain growth of BNCT solution ceramics. However, excess Mn caused abnormal grain growth, and therefore, rectangle grains appeared again.

A brief introduction to ceramic capacitors

A century of diligent R&D has resulted in a wide range of ceramic dielectrics and processing technologies. The technology used to manufacture an MLCC (multilayer ceramic capacitors) that costs pennies was unimaginable 30 years ago. The present trends of enhanced mobility, connectivity, and reliability in consumer, industrial, and military electronics will continue to drive future innovations in ceramic capacitor technology. In addition, power electronics applications are an emerging market in which ceramic capacitors will play an increasing role through improved breakdown strength, enhanced dielectric stability in harsh environments, and innovative packaging. The investment made by the US government to develop high energy density and high temperature capacitor technology will also contribute to the advancement of dielectric materials technology for pulse and power electronic capacitors.

High Temperature Capacitors Based on [0001] and [1120] Sapphire Dielectrics

The test results of the dielectric properties of [0001] (C-plane) and [1120] (A-plane) sapphire (single crystalline Al2O3) at high temperatures indicate that these materials have very stable dielectric constants and low dielectric losses (compared with polycrystalline alumina) at low frequencies in the temperature range from room temperature to 550°C. Therefore, sapphire materials have become likely candidate dielectric materials for high temperature capacitors. This paper reports prototype low-volume (∼100pF) capacitors based on sapphire dielectrics for high temperature and low frequency applications. Low-volume parallel-plate capacitors using C-plane and A-plane sapphire as dielectric material were fabricated by stacking metallized sapphire substrates. These prototype capacitors were characterized in the temperature range from room temperature to 550°C by measuring the capacitance and parallel resistance of these devices at 120Hz, 1kHz, 10kHz, 100kHz, and 1MHz. The capacitance and equivalent parallel resistance of these capacitors were all directly measured by an AC LCZ impedance meter in controlled temperature environments. These prototype devices demonstrate stable capacitances over a wide temperature range, and therefore, have the potential to be integrated with silicon carbide (SiC) devices to enable high temperature electronics. The needs of thin-film metallization and encapsulation for these sapphire substrates are also discussed.