Thick Film Capacitors Research Articles

Accurate Real-Time Temperature Measurement Method in Ultra-High Temperature Rotational Environments for Aero Engines/Turbines

This study proposes an innovative method to wirelessly measure the ultra-high temperatures of rotational parts in aero-engines/turbines. The upper measurement limit of this proposed sensor is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1100 ^\circ \text{C}$ </tex-math></inline-formula> . Based on the thick film integration process, the inductor and capacitor are integrated in-situ on the ceramic turntable and ceramic blade. The inductor and capacitor operate in the high temperature and ultra-high temperature areas, respectively, and the temperature signal is transmitted through the electromagnetic coupling between the inductor coil and the antenna. The design of the structure separating the capacitor and inductors is important and can improve the sensor’s high temperature signal reading performance. The designed sensor is tested in the temperature range of 25– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1100 ^\circ \text{C}$ </tex-math></inline-formula> and the rotational speed range of 0–400 rpm. The results show that the minimum sensitivity of the sensor at different rotational speeds is 7.66 kHz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^\circ \text{C}$ </tex-math></inline-formula> , and the minimum sensitivity of the sensor at different rotational speeds is 7.83 kHz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^\circ \text{C}$ </tex-math></inline-formula> . The maximum standard deviation and repeatability of the sensor measured across different temperatures and rotational speeds are 0.11(400 rpm, 900 °C)and 0.389%(400 rpm, 900 °C), respectively. The interference of the rotational speed on the temperature test of the sensor is negligible. The experimental results show that the sensor has strong signal strength in ultra-high temperature rotational environments and is suitable for ultra-high temperature testing.

Multifunctional All-Inorganic Flexible Capacitor for Energy Storage and Electrocaloric Refrigeration over a Broad Temperature Range Based on PLZT 9/65/35 Thick Films.

Multifunctional capacitors can efficiently integrate multiple functionalities into a single material to further down-scale state-of-the-art integrated circuits, which are urgently needed in new electronic devices. Here, an all-inorganic flexible capacitor based on Pb0.91La0.09 (Zr0.65Ti0.35)0.9775O3 (PLZT 9/65/35) relaxor ferroelectric thick film (1 μm) was successfully fabricated on LaNiO3/F-Mica substrate for application in electrostatic energy storage and electrocaloric refrigeration simultaneously. The flexible PLZT 9/65/35 thick film presents a desirable breakdown field of 1998 kV/cm, accompanied by a superior recoverable energy density (Wrec) of 40.2 J/cm3. Meanwhile, the thick film exhibits excellent stability of energy-storage performance, including a broad operating temperature (30-180 °C), reduplicative charge-discharge cycles (1 × 107 cycles), and mechanical bending cycles (2000 times). Moreover, a large reversible adiabatic temperature change (ΔT) of 18.0 °C, accompanied by an excellent electrocaloric strength (ΔT/ΔE) of 22.4 K cm/V and refrigerant capacity (RC) of 11.2 J/cm3, is obtained at 80 °C in the flexible PLZT 9/65/35 thick film under the moderate applied electric field of 850 kV/cm. All of these results shed light on a flexible PLZT 9/65/35 thick film capacitor that opens up a route to practical applications in microenergy-storage systems and on-chip thermal refrigeration of advanced electronics.

Probing effect of temperature on energy storage properties of relaxor-ferroelectric epitaxial Pb0.92La0.08Zr0.52Ti0.48O3 thin film capacitors

The influence of temperature on the energy storage behavior of relaxor-ferroelectric epitaxial Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) thin film capacitors fabricated using pulsed laser deposition was evaluated using cyclic current-voltage measurements from 25°C to 225°C in order to elucidate ferroelectric and dielectric contributions across the Curie temperature (Tc). In the film thickness range of 125nm to 500nm, it has been found that the leakage current through the capacitors increases monotonically with increasing temperature and the effect is more prominent at smaller film thickness, primarily due to a more efficient movement of ferroelectric domains. While these effects prevent thinner PLZT films from maintaining adequate energy storage efficiencies at temperatures above ~100°C, thicker films show promising energy storage properties in a wide temperature range. Specifically, the 500nm thick PLZT film capacitors have a nearly constant energy storage efficiency above ~70% in the temperature range of 25°C to 175°C, with a peak efficiency of 78% at 175°C due to the large dielectric constant exceeding ~2000 as the temperature approaches the PLZT Tc of 200°C. By quantifying the three contributions of the electric conductivity, dielectric capacitance, and relaxor-ferroelectric domain switching polarization to temperature dependent energy storage properties of relaxor-ferroelectric capacitors, this study reveals that the dielectric contribution dominates in the PLZT capacitors with smaller thickness, while even contributions from all three components are present in films of larger thickness. These results suggest that the PLZT relaxor-ferroelectric thin film capacitors are promising for energy storage applications and further improvement of performance may be achieved by optimization of the film/electrode interface.

Cover Image, Volume 13, Issue 4

Cover Photograph: Cover photo from Hong Rak Choi et al. Photo of a flexible planar UV‐curable CaCu3Ti4O12 composite thick film capacitor on Cu foil (Fig. 1d). image

Investigation of strain gauges based on interdigitated Ba0.5Sr0.5TiO3 thin film capacitors

The demand for monitoring of strain is growing in high temperature and harsh environment systems. In this work, the thin film interdigitated capacitive strain gauges are fabricated using Ba0.5Sr0.5TiO3 (BST) as the dielectric and palladium-13wt% chromium (PdCr) alloy as the electrodes, and the strain sensing characteristics of the thin film devices are investigated. It was found that the sensors showed low values of dissipation factor and stable capacitance over the frequency range from 15kHz to 500kHz at different temperatures. The temperature coefficient of capacitance (TCC) has been measured for temperature ranging from 25°C to 480°C so that the effect of temperature on the devices is known. At low temperature less than 150°C the TCC is very small within 20ppm/°C. With the temperature increasing, the TCC increased rapidly, and at 480°C, the TCC was measured to be 3100ppm/°C while is obviously less than that of typical thick film capacitors. The gauge factor (GF) of the interdigitated capacitive strain gauge at temperatures ranging from 25°C to 400°C to be about 3. The gauge also exhibits good linearity and sensitivity at applied large strains.

Bi1/2Na1/2TiO3–BaTiO3 based thick-film capacitors for high-temperature applications

Thick films with compositions (1 − x)(0.94Bi1/2Na1/2TiO3–0.06BaTiO3)–x(K0.5Na0.5NbO3) (x = 0, 0.03, 0.09 and 0.18) have been prepared and their structural and electrical properties have been investigated. Dielectric properties show that these films are well suited for high-temperature applications due to their low variance in permittivity (<15%) over large temperature ranges. The thick film with x = 0.18 offers an operational temperature range from room temperature to 350 °C. Films with x = 0.03 and 0.09 also possess a stabile permittivity up to 400 °C. The improvement in the thermal stability of the permittivity is attributed to the addition of K0.5Na0.5NbO3 which leads to breaking of the long-range order in the materials. However, the polarizability of the materials was found to decrease possibly due to the clamping effect of the substrate. The characteristics of each film are discussed based on dielectric and electrical properties.

Inkjet Printing Technology: A Novel Bottom-up Approach for Multilayer Ceramic Components and High Definition Printed Electronic Devices

This paper describes the methodology of thick film and multilayer ceramic capacitor (MLCC) component manufacturing by inkjet printing. The printing unit is a CeraDrop 3D multimaterial inkjet printer. Aqueous conductive and dielectric inks were formulated according to the printhead specifications in terms of viscosity, surface tension, particle size, and sedimentation. Jetting behavior was controlled and optimized to reach the best droplet characteristics with regard to the design. The numerical processing simulation tool helps to control the printing job and to identify potential beneficial issues during the processing. Therefore, printing parameters (droplet spreading, layer thickness, filling strategy, layer drying, etc.) were optimized according to material and component design characteristics. In this way, high definition and thin conductive tracks were achieved on an alumina substrate with good electrical properties. Moreover, two printheads were used to successively build 3D multimaterial MLCC components with thin dielectric and conductive layers (i) with good precision of margins compared with traditional processes, and (ii) with very high complex configurations thanks to the flexibility of the inkjet printing process. For both applications, large area components were accessible in a single batch.

Inkjet Printing Technology: A Novel Bottom-up Approach For Multilayer Ceramic Components and High Definition Printed Electronic Devices

This paper describes the methodology of thick film and Multilayer Ceramic Capacitor (MLCC) components manufacturing by inkjet printing. The printing unit is a CERADROP 3D multimaterial inkjet printer. Aqueous conductive and dielectric inks were formulated according to the printheads specifications in terms of viscosity, surface tension, particles size and sedimentation. Jetting behavior was controlled and optimized to reach the best droplets characteristics with regard to the design. Numerical processing simulation tool helps to control the printing job and to identify beneficial potential issues during the processing. Therefore printing parameters (droplet spreading, layer thickness, filling strategy, layer drying, etc.) were optimized according to material and component design characteristics. By this way, high definition and thin conductive tracks were achieved on alumina substrate with good electrical properties. Moreover, two printheads were used to build successively 3D multimaterial MLCC components with thin dielectric and conductive layers (i) with a good margins precision compared to traditional processes and (ii) with very high complex configurations thanks to the flexibility of the inkjet printing process. For both applications, large area components were accessible in a single batch.

Investigation into real-time pressure sensing properties of SnO2, TiO2, and TiO2/ZnO thick films with interdigitated electrodes

Abstract The pressure sensing properties of nanocomposite SnO 2 , TiO 2 , and TiO 2 /ZnO thick film capacitors with interdigitated electrodes are investigated. To form the dielectric layers, the metal oxides powders were respectively mixed with isopropanol, wet ball milled for 24 h, then the mixtures were dried at 120 °C and further the powders were placed under 2 tonnes of pressure to form pellets, which were fired at 1250 °C (rate of 5 °C/min) in a vacuum of 6 × 10 −3 mbar for 5 h, followed by cooling (rate of 3 °C/min). After firing, the resultant nanopowders were mixed with 7 wt.% of polyvinyl butyral (binder) and suitable amount of ethylenglycolmonobutylether (solvent) to form the pastes. These were screen-printed over the Ag electrodes on alumina substrates to form SnO 2 , TiO 2 , and TiO 2 /ZnO capacitor pressure sensors accordingly. The evaluation of pressure sensing properties of these sensors was performed using a HP 4192A Impedance Analyser, which recorded the changes in the values of the capacitances under different mechanical stresses. At the applied load of 5 kPa, the response times of 2.5 s, 5.6 s and 4 s were recorded for SnO 2 , TiO 2 , and TiO 2 /ZnO sensors, respectively. In addition to instant response times, these pressure sensors have the advantage of being reusable, as their electrical properties were restored to the original value after annealing for 2 h at 80 °C. Moreover, one year later after the initial testing, the sensors were still operational and produced similar time responses to pressure.

Laser micro-cladding electronic pastes for fabrication of MIM thick film capacitors

Two direct-write processing methods - direct material deposition by microPen and Nd:YAG laser micro-cladding - are integrated with computer-aided design/computer-aided manufacturing (CAD/CAM) technology for the fabrication of passive electronic components. A basic two-step procedure of the laser micro-cladding electronic paste (LMCEP) process for thick film pattern preparation is presented. In particular, metal-insulatormetal (MIM) type thick film capacitors are fabricated on ceramic substrates by the LMCEP process. Multilayer structures of the MIM thick film capacitors are demonstrated and discussed. Results of the frequency characteristics test show that the MIM thick film capacitors fabricated by the LMCEP process have excellent direct current (DC) voltage stability (<2.48%), excellent frequency stability (<2.6%) and low dissipation factor (<0.6%), which are sufficient for many megahertz applications.

Dielectric behavior of Bi2/3Cu3Ti4O12 ceramic and thick films

The paper reports on synthesis, sintering and microstructure of Bi2/3Cu3Ti4O12, a lead-free, high-permittivity material with internal barrier layer capacitor behavior. Complex impedance and capacitance of the ceramic and thick films were studied as a function of frequency (10 Hz–2 MHz) and temperature (−170 to 400°C). Dc electrical conductivity of the samples was measured in the temperature range 20–400°C. Broad and high maxima of dielectric permittivity versus temperature plots were observed reaching 60,000 for ceramic and 5,000 for thick films. The maxima decrease and shift to higher temperatures with increasing frequency. Two arcs ascribed to grains and grain boundaries were found in the plots of imaginary part versus real part of impedance. Analysis of the impedance spectra indicates that Bi2/3Cu3Ti4O12 ceramic could be regarded as electrically heterogeneous system composed of semiconducting grains and less conducting grain boundaries. The developed thick film capacitors with dielectric layers based on Bi2/3Cu3Ti4O12 exhibit dense microstructure, good cooperation with Ag electrodes, high permittivity up to 5,000 and relatively low temperature coefficient of capacitance in the temperature range 100–300°C. Broad maxima in the dielectric permittivity versus temperature curves may be attributed to Maxwell–Wagner relaxation.

Frequency characteristics of the MIM thick film capacitors fabricated by laser micro-cladding electronic pastes

With rapid development of the electronic industry, how to respond the market requests quickly, shorten R&D prototyping fabrication period, and reduce the cost of the electronic devices have become a challenge work, which need flexible manufacturing methods. In this work, two direct write processing methods, direct material deposition by microPen and Nd:YAG laser micro-cladding, are integrated with CAD/CAM technology for the hybrid fabrication of passive electronic components. Especially, the metal–insulator–metal (MIM) type thick film capacitors are fabricated on ceramic substrates by this method. A basic two-step procedure of laser micro-cladding electronic pastes (LMCEPs) process for the thick film pattern preparation is presented. For a better understanding of the MIM thick film capacitor characterization, equivalent circuit models at low-frequency and high-frequency domains are introduced, respectively. The frequency characteristics tests up to 1.8 GHz of capacitance stability, equivalent series resistance (ESR), equivalent series inductance (ESL) and impendence are performed, and the results show good DC voltage stability (<2.48%), good frequency stability (<2.6%) and low dissipation factor (<0.6%) of the MIM thick film capacitors, which may get application to megahertz regions. The further developments of the LMCEP process for fabricating MIM thick film capacitors are also investigated.

Thick Film Capacitors with Variable Tc on Cu Foils

ABSTRACTHigh k dielectric thick films, consisting of BaTiO3, a low softening glass and fluoride compounds, were studied to apply them as potential low temperature N2-fireable capacitors on commercially-available Cu foils. Different additive combinations of LiF, ZnF2 and BaF2 were specifically compared in terms of dielectric constant, dielectric loss and Curie temperature (Tc) for the purpose of optimizing dielectric performance. The thick film consisting of 95BaTiO3-1.5LiF-1.5ZnF2-2 bismuth borosilicate glass exhibited the best performance, i.e., a dielectric constant of 2,382 and a dissipation factor of 0.021 at Tc of 27°C at the firing temperature of 950°C. This result can be regarded as one of the best performance, compared to literature reported on embedded capacitors in Cu-PCB applications. No apparent Cu-diffusion was detected across the Cu-thick film-Cu foil structure.

Radiation-induced changes in the electrical properties of carbon filled PVDF thick films

The electrical properties of PVDF thick film capacitors under gamma radiation are investigated. To increase the conductivity of the films, they were filled with 4 and 6 wt.% of carbon, which is close to the percolation threshold. Screen-printing was used for film fabrication. All films were exposed to a disk-type 137Cs source with an activity of 370 kBq. Changes in I– V characteristics were measured after each exposure dose. A tenfold increase in the values of current was recorded after a dose of 228 μGy for C-PVDF films with a thickness of 23.97 μm and 6 wt.% carbon doping. A higher dose of 342 μGy resulted a decrease in the values of current. Thicker films showed an increase in the values of current with irradiation to a dose of 798 μGy. PVDF + carbon system has potential applications in low-dose radiation dosimetry. The high current induced by radiation caused heating and electroforming of the device, due to the metal inclusions from the Ag contact material. It was noticed that as-printed films of 23.97 μm in thickness, tend to electroform at about 12 V, whereas films irradiated with 171 μGy showed a strong electroforming effect at a lower voltage of 5 V. For that reason, proper design of dosimetry systems is essential to eliminate such effects. Gamma radiation sensitivity of counterpart PVDF thick films with 4 wt.% carbon doping was studied via capacitance-dose measurements in real time, since these samples were less conductive. Irradiation of this sensor with doses from 1.15 to 2.5 mGy caused a considerable monotonic increase in the values of its capacitance from 2.92 to 12.37 pF. Accordingly, sensors with 4 wt.% of carbon could sustain higher radiation doses, but had poor sensitivity to radiation of lower level.

Wireless real time compact radiation detector based on Bi 2O 3/Nb 2O 5 thick film capacitors

A novel cost-effective gamma radiation monitoring system based on metal oxide thick films is presented. The changes in Bi 2O 3/Nb 2O 5 thick film capacitors were monitored in real time under the influence of gamma radiation using miniaturized, low power, bi-directional wireless communication system. The capacitive interface circuitry was based on a Delta-sigma (ΣΔ) modulator using switched capacitor (SC) circuit architecture with integrated on-chip temperature sensor.

Study on the structure and properties of thick-film capacitors fabricated by laser micro-cladding and rapid prototype

With the development of thick-film capacitors for miniaturization, high frequency and low dissipation, thick-film capacitors fabricated by traditional thick-film technology have many shortcomings such as limited sizes, low capacity and high dissipation, which have limited their applications in industry. In this paper, thick-film capacitors were fabricated on ceramic substrate by a novel technology of laser micro-cladding and rapid prototype. Compared with traditional sintering, the electrode film and dielectric film were rapidly fabricated in a manner of a layer by layer and without mask and sintering, therefore, capacitors had different properties. The structure and properties of the capacitors fabricated by different methods were studied. Detailed experimental results were demonstrated as following: compared with traditional sintering techniques, the structure of capacitors fabricated by laser micro-cladding and rapid prototype was found to be compact and even without the composition diffuseness between interfaces. Its dielectric constant and insulation resistance are high and the dissipation is low. Obviously, its reliability and stability are high, with higher capacity and good repeatability.

Dielectric properties of the BaTiO3-AlN-additive system

The mixed system of BaTiO3 and AlN has been investigated in terms of dielectric properties and microstructure. Two different types of additives, bismuth oxide and bismuth borosilicate glass, were used to lower sintering temperature. First, the addition of a fixed content (3 wt.%) of Bi2O3 provided densification at 1200∘C where monotonous decreases of dielectric constant were found with increasing the content of AlN. On the other hand, the bismuth borosilicate glass was effectively used to decrease firing temperature to 850∘C, which is suitable for thick film capacitor applications. A practical demonstration of thick film capacitors using a Ag electrode on a 96% alumina substrate indicated that the optimum composition of 76BaTiO3-20AlN-4glass may be adequate for generating k of 79.4 and tan δ of 0.014 at 1 MHz as a result of the low temperature firing of 850∘C in air atmosphere.

Development of oxide thick film capacitors for a real time pressure monitoring system

Accurate pressure readings are essential tools in a wide range of applications. For example in monitoring intracranial pressure for patients with head injuries or tyre pressure to improve automobile safety. With this in mind, a real time monitoring system, which displays the change in sensor capacitance with pressure on a PC, has been developed. Thick film capacitors with an oxide dielectric layer formed using niobium pentoxide (Nb2O5), titanium dioxide (TiO2) and cerium dioxide (CeO2) are investigated using this system. SEM was used to examine the morphology and particle size of the thick films. To aid in the development of a suitable interface circuitry, the frequency and temperature dependence of each device is investigated. Each sensor was then subjected to pressures in the region of 0–100 kPa. The results show that capacitors with an Nb2O5 dielectric layer were most sensitive. It is thought that this is due to its particle size.

Investigation of TiO 2 thick film capacitors for use as strain gauge sensors

In this work the strain sensing properties of interdigitated and sandwich thick film capacitors, using titanium dioxide as the dielectric, are investigated. By pre-firing the TiO 2 powder and forming a polymer thick film paste the use of expensive paste ingredients, such as ruthenium or palladium oxide, was avoided. After firing, XRD was used to verify the composition and crystallite size of the TiO 2 powder, while SEM allowed the particle sizes of the powder to be examined. It was found that the powder has a crystallite and particle size, which is less than 1 μm. Following this, the sensors were fabricated by screen-printing onto glass substrates and placed in a cantilever beam arrangement so that the change in their capacitance with strain could be measured. The gauge factor, which demonstrates the devices sensitivity, was found by dividing the fractional change in capacitance by the applied strain. A gauge factor of 5 and 30 was recorded for interdigitated and sandwich capacitors, respectively. In the case of sandwich capacitors, this gauge factor is higher than normally achieved using oxide films (3–15). Furthermore, the sensors showed a high degree of linearity with low hysteresis. The TCC has been measured for temperatures ranging from 25 to 70 °C so that the effect of temperature on the devices is known. Values, typical of thick film capacitors (876–2834 ppm/°C) have been recorded for temperatures up to 60 °C. Finally, ac electrical measurements have been used to shown that tunnelling is the dominant conduction mechanism within the TiO 2 film.

Embedding Ceramic Thick-Film Capacitors into Printed Wiring Boards

ABSTRACTEmbedding passives into printed wiring boards have numerous advantages that show up in different segments of the market. For example, the ability to locate decoupling capacitors within a couple hundred microns of semiconductor I/Os greatly improves response time and signal integrity leading to product performance improvements. One crucial need, however, is high capacitance density. High capacitance density can only be readily achieved by ceramic technology. Therefore, the focus of this work has been the development of ceramic thick-film capacitor technology that can be used to bury high capacitance density components within an organic substrate. This allows high value decoupling capacitors to be buried for chip packaging or related applications in spaces available within any layer of the substrate.The dielectric paste is based on doped barium titanate composition and works together with a cofired copper electrode paste. The capacitor system is designed to be screen printed on copper foil in the locations desired in the circuit and fired in nitrogen at 900°C to form the ceramic components. Following this, the foil is laminated, component face down, to the organic laminate using standard prepreg and the inner layer etched to reveal the components in an organic matrix. The system has a dielectric constant of approximately 3000 and achieves a capacitance density of ∼1.5 nF/mm2. In the following sections, issues that we encountered when making embedded capacitors with this first generation system are presented.