Thick-film Process Research Articles

Qualification Methodology for the Double Side Printed Substrate for Hybrid Microcircuits Application

Hybrid Microcircuits (HMCs) are always preferred over discrete versions due to small size, less weight, better performance and high reliability for space applications. Double side printed substrates realized using Thick film screen printing and Printed Through Hole (PTH) processes are being used in HMCs in order to achieve further miniaturization. This article details the newly developed innovative Thick film process technology involving drilling of holes and filling the through hole with gold conductive paste to connect the front and rear side of conductor patterns on an alumina substrate. The biggest challenge in the realization of double side printed substrates is creating multiple via holes and filling them with conductor paste. In addition, the limited ability to achieve substrate integration and uniformity pose additional challenges that require optimization of process parameters. A comprehensive test plan created to qualify this innovative method in terms of quality and reliability suitable for the aerospace industry is also presented.

Spontaneous adsorption effect of graphitic carbon nitride nanosheets to improve sintering behavior of yttria-stabilized zirconia microbeads

Yttria-stabilized zirconia (YSZ) is a ceramic material in which the zirconium dioxide structure is stabilized at room temperature by adding yttrium oxide. However, the YSZ formed by the thick film process on a pre-sintered dense substrate suffers from sintering problems such as different sintering shrinkage rates due to phase transitions and thermal conductivity. This in turn can lead to de-bonding, cracking, delamination, and abnormal growth. We prepared a spherical YSZ green body of approximately 38 μm diameter formed by an organic binder based on a sintered YSZ seed with 15 to 20 μm diameter. In addition, the application of two-dimensional g-C3N4 nanosheets that can be adsorbed on the surface and pores of the green body before the sintering process was evaluated. The YSZ green body with adsorbed surface-modified g-C3N4 nanosheets could be synthesized by stable spontaneous adsorption due to zeta-potential attraction onto the surface of zirconia particles in an aqueous solution. Consequentially, the formation of large grains due to abnormal grain growth was reduced as g-C3N4 was adsorbed. The spontaneous adsorption of nanosheets controls the surface diffusion mechanism by sequentially lowering the energy from a high surface energy in the initial stage of sintering. Uniform grain growth thus can be induced according to the activation energy level of the controlled surface diffusion.

Synthesis of a Stable and High-Concentration BaHfxTi1−xO3 Sol–Gel for High Electromechanical Performance of Bulk Ceramics

Lead-based materials are widely used in piezoceramics due to their high electromechanical properties. However, due to environmental protection and sustainable development, the use of the toxic element lead (Pb) in electronic devices is strictly restricted, therefore requiring the rapid development of piezoelectric-based devices with lead-free ceramics. In this context, a lead-free doped barium titanate was studied with a dual objective. First, a new sol–gel method to synthesize Hf4+-doped BaHfxTi1−xO (BHT) with x = 0.05, 0.075, and 0.10 is presented. Such BHT sols were prepared at high concentrations of up to 1 M. Dilution in ethylene glycol allowed parameters (viscosity, colloid sizes, etc.) to be controlled, which ensured a time-stable sol for several months at room temperature. Second, densified bulk ceramics with attrited powders were obtained from these sols and showed very good electromechanical properties, with a thickness coupling factor of kt = 47% (BaHf0.05Ti0.95O3 sintered at 1500 °C/6 h). These results are a first step that will allow the processing of lead-free piezoelectric thick films using a sol–gel composite method for vibrational energy harvesting applications.

A dual-cantilever based MEMS PZT thick-film energy harvester with enhanced internal resonance performance

In this paper, a multi-frequency vibrational piezoelectric energy harvester (PEH) with a dual-microcantilever coupled structure based on the internal resonance effect is proposed. The device consists of a low-frequency cantilever and a high-frequency cantilever with an integer multiple of resonant frequencies connected by a clamped–clamped coupling beam. The internal resonant PEH (IR-PEH) is prepared by the microelectromechanical systems piezoelectric thick-film process based on the flexible thin metal substrate. The output performance of the proposed PEH device is greatly improved by taking advantages of the internal coupling structure and the piezoelectric thick-film microfabrication process. Under the excitation acceleration of 2 g, the maximum power output of IR-PEH reaches 424.6 μW at 190 Hz and 108.8 μW at 365 Hz, which increases by 35% of the power output due to the internal resonance coupling comparing with the PEH without the coupling effect. The corresponding power densities of IR-PEH reach 6.3 and 1.6 mW/cm3, respectively. This IR-PEH configuration induces the competitive advantages of good performance, wide bandwidth, and small volume, which can be potentially employed as a power source for low power wireless sensing nodes.

A silicon carbide high gain differential amplifier for extreme temperature applications

In this paper, a high temperature, high gain differential amplifier based on a custom-built silicon carbide (SiC) N-channel junction field effect transistor (JFET) only, without using complementary P-channel devices is proposed. The operation principle of this active load differential amplifier is discussed, and the expression of the differential gain is derived. A prototype circuit is fabricated using thick film process on an alumina substrate and tested from room temperature up to 500 °C to demonstrate the high temperature capability of the proposed differential amplifier. The differential gain of 50.8 dB is achieved with 58.6 dB common-mode rejection ratio (CMRR) and 9.1 MHz gain bandwidth product (GBW) at 500 °C. Excellent linearity and low output impedance of the proposed differential amplifier are also demonstrated at various temperatures. The proposed SiC JFET high gain differential amplifier can serve as a fundamental building block of the signal conditioning circuitry to be integrated with the sensing element for extreme environment applications.

Ultra-Rapid, Physics-Based Development Pathway for Reactor-Relevant RF Antenna Materials

This article presents a rapid, atomistically informed, experimental development pathway for fusion reactor-relevant radio-frequency (RF) antenna materials in the Cu-Cr-(Nb,Al,Zr) composition system, with the goal of improving upon GRCop-84. RF antennas in a tokamak fusion reactor will face a unique set of challenges as both structural and functional materials. The desired material must simultaneously achieve and maintain high electrical conductivity, high strength, high thermal conductivity, resist high temperatures, possess low nuclear activation, and incur low damage due to neutron bombardment. The GRCop-84 alloy serves as a starting point for iterative improvement, with the desire to reduce or eliminate Nb from the material to minimize nuclear activation. The rapid development pathway makes use of a multi-target combinatorial thick-film sputtering process to produce full ternary phase diagrams on a Si wafer substrate. Transient grating spectroscopy (TGS), a laser-ultrasonic method, will determine spatially varying thermoelastic properties, while four terminal electrical conductivity measurements will map out the best performing regions of the sample for in-depth study at larger length scales. High-energy proton and self-ion irradiation emulates the effects of neutron damage on the thermal/electric properties. With rapid turnaround time (~days) in terms of mapping radiation damage-induced material property changes in the full ternary system, these techniques allow rapid iteration toward an optimal material, testing hundreds of nearby compositions in the time it took to test one. Focused testing of larger, single composition samples (produced in an arc furnace or by laser sintering) provides data on structural and high-power RF properties and validates our thick-film-based workflow.

A thermal conductivity sensor based on mixed carbon material modification for hydrogen detection.

In order to overcome the many shortcomings of traditional hot-wire thermal conductivity sensor design, a new design method was proposed in which a graphene-composite carbon nanotube mixed carbon material was used as a thermal conductivity sensor carrier instead of nano-alumina particles. Taking advantage of the large specific surface area and high thermal conductivity of graphene, as well as the characteristics of a large number of gas transport channels modified by carbon nanotubes, a high-efficiency gas heat exchange medium is made. In order to improve the consistency of the product, electrochemical preparation of an aluminum oxide film material is used to make the chip substrate of the thermal conductivity sensor by MEMS process technology, and the heating sensitive electrode of the sensor is made by a thick film process. Experiments show that the sensor prepared by this method has high sensitivity and zero point stability and has greatly improved the detection accuracy and response time. The sensitivity of the sensor to hydrogen detection increases to 3.287 mV/1%H2, and the response time is shorter than 5.4s. The research results have good application prospects.

The Staircase Drive-A Novel Actuator Design Optimised for Daisy-Chaining and Minimum Stress Load Coupling.

This work presents a novel type of actuator that improves over the standard cantilever by permitting daisy-chaining while minimising stress to the joint connecting to the load. A detailed structural and functional comparison of the proposed device against the cantilever actuator as a baseline is given, led by a brief revision of the cantilever actuator as the state-of-the-art that highlights its limitations with respect to daisy-chaining and the stress it inherently creates within the joint connecting to the load when attempting out-of-plane displacement without rotation. Simulations of both devices’ performance confirm that the newly proposed device yields the targeted displacement profile that both enables the daisy-chaining of such a device into a higher-order actuator for increased displacement and reduce stress in the joint with the load. This comes at the cost of reduced maximum displacement compared to the cantilever, which can be overcome by daisy-chaining. The proposed device’s performance is further evaluated on the basis of manufactured prototypes measured by means of a laser scanning vibrometer. The prototype was manufactured on a 150 m alumina substrate, and both electrodes and piezoelectric layer were deposited in a thick-film printing process.

A Novel Fabricating a Thick Film Cu-Ni Alloy Resistor by Screen Printing an Al Electrode and Galvanic Replacement Reaction

In this study, a thick film Cu-Ni alloy was fabricated by using a novel technique which combing thick film process and galvanic chemical replacement. First, a thick film Al electrode was screen printed and sintered at 600° C on the Al2O3 substrate served as a reactant. Sequentially, the Al electrode on Al2O3 substrate was immersed into a CuSO4 solution at 40° C for 15-30minutes to carry out the first galvanic replacement reactions of partial Al electrode into Cu° After which it was immersed into an NiSO4 solution 80°C for 15 minutes to carry out the second galvanic replacement reactions of remaining Al electrode into Ni to form Cu-Ni layers on the Al2O3 substrate. To make a thick film Cu-Ni alloy, the Cu-Ni layers on Al2O3 substrate was annealed at high temperature for inter-diffusion of Cu and Ni. The results of this study show that when a thick film Al electrode on an Al2O3 substrate is immersed into a CuSO4(aq) solution at 40° C for 15 minutes and sequentially immersed in an NiSO4(aq) solution at 80°C for 15 minutes. Then, after further annealing at 800°C for 30 minutes in a reducing atmosphere, the Cu and Ni composition ratio in the thick film Cu-Ni alloy is approximately 1:1, reflecting Cu-Ni alloy resistor with a very promising TCR performance (115ppm/°C).

Quality Control of Thick Film Hybrid Integrated Circuit Process Design and Manufacturing

With the continuous upgrading of the technological content of electronic products, higher requirements have been put forward for the manufacturing process of thick film hybrid integrated circuits, resulting in the manufacturing process of thick film hybrid integrated circuits. Thick-film hybrid integrated circuits are an important realization method of microelectronic components. They are widely used in many fields such as civil, military, and aerospace satellites. An important reason is that the thick film process has a super high cost performance compared with other process realization methods. Thick film conductive paste is the most core material in the thick film process. Its interconnection performance such as sintering and welding directly affects the performance of the finished thick film components. Therefore, the thick film conductive paste interconnection under specific process conditions is evaluated. Related performance is crucial. In the mass production process of thick film hybrid integrated circuits, it is particularly important to control the quality and increase the product growth rate. This paper introduces the description of the quality management of the rear-film hybrid integrated circuit production line in the aspects of thick-film hybrid integrated circuit quality system construction, raw material procurement, supplier management, project quality management, on-site management, etc. The manufacturing process of the back-film hybrid integrated circuit briefly introduced has stable performance, high reliability and wide application fields in terms of manufacturing characteristics. Studies have shown that the manufacturing process is suitable for mass automated production, and has the advantages of simple process, low investment, and quick results.

Aqueous Thick-Film Ceramic Processing of Planar Solid Oxide Fuel Cells Using La0.20Sr0.25Ca0.45TiO3 Anode Supports

Research into the use of Rh and Ce0.80Gd0.20O1.90 (CGO20) co-impregnated La0.20Sr0.25Ca0.45TiO3 (LSCTA-) anodes for electrolyte-supported Solid Oxide Fuel Cells (SOFC) has yielded extremely impressive durability and robustness at industrial short stack scales over the past decade. These anodes have exhibited the ability to rival the degradation and RedOx/thermal/thermo-RedOx cycling tolerance of state-of-the-art SOFC anodes at short stack scales, in addition to providing the ability to operate under sulfur-laden fuel gas streams and high fuel utilisation/overload conditions. (1)Given the success of implementation of LSCTA- anodes into Electrolyte Supported Cells (ESC) and the reasonable mechanical strength of LSCTA- as a support material, (2,3) successful attempts have also been made to employ LSCTA- as an anode support for SOFC at button cell scales, (4,5) in addition to appraisal of the upscaling of thick-film ceramic processing techniques used to prepare larger (20 cm by 20 cm) SOFC anode supports. (3) These studies performed by Lu et al., Ni et al. and Verbraeken et al. (3-5) focussed upon production of LSCTA- anode supports by aqueous tape casting followed by either co-casting or screen printing of a 8 mol. % yttria-stabilised-zirconia (8YSZ) electrolyte layer.Therefore, using these studies as a basis for the current research, we present results concerning the ceramic processing of Anode Supported Cells (ASC) that employ LSCTA- anode ‘backbone’ microstructures, with the ultimate aim of testing SOFC whose anodes have been decorated with Rh and CGO20 catalysts through wet impregnation. Here, we detail a thermal compatibility study of a variety of electrode and electrolyte material sets using dilatometric analysis, leading to the conclusion that the shrinkages of LSCTA- and 8YSZ are sufficiently matched to allow co-sintering of the anode support and electrolyte layers. Subsequently, the thick-film aqueous ceramic processing of LSCTA- anode supports, via tape casting, is discussed in addition to an appraisal of the most appropriate method to produce dense 8YSZ electrolyte layers (i.e., electrolyte deposition by co-casting or screen printing), with the aim of co-sintering the structure up to 1400 °C in air. Finally, an evaluation of the microstructural characteristics of LSCTA − supports, prepared using a typical graphite pore former (commonly used with organic solvent systems) or without the use of a pore former, will be provided, in comparison to microstructures resulting from the incorporation of poly(ethyl/methyl methacrylate) pore formers that are compatible with the aqueous solvent system employed. References R. Price, M. Cassidy, J. G. Grolig, G. Longo, U. Weissen, A. Mai and J. T. S. Irvine, Adv. Energy Mater., 2003951, 1 (2021).V. Vasechko, M. Ziegner and J. Malzbender, Ceram. Int., 40, 13179 (2014).M. C. Verbraeken, B. R. Sudireddy, V. Vasechko, M. Cassidy, T. Ramos, J. Malzbender, P. Holtappels and J. T. S. Irvine, J. Eur. Ceram. Soc., 38, 1663 (2018).L. Lu, C. Ni, M. Cassidy and J. T. S. Irvine, J. Mater. Chem. A, 4, 11708 (2016).C. Ni, L. Lu, D. N. Miller, M. Cassidy and J. T. S. Irvine, J. Mater. Chem. A, 6, 5398 (2018).

Aqueous Thick-Film Ceramic Processing of Planar Solid Oxide Fuel Cells Using La0.20Sr0.25Ca0.45TiO3 Anode Supports

Recent research into the upscaling and implementation of Rh/Ce0.80Gd0.20O1.90 co-impregnated La0.20Sr0.25Ca0.45TiO3 (LSCTA-) anodes in electrolyte-supported SOFC at short-stack industrial scales has resulted in extremely robust performance under realistic operation and tolerance to harsh conditions. Furthermore, evaluation of the mechanical strength of LSCTA- and incorporation of this material into anode-supported SOFC also yielded promising performance at the button cell scale (using Ni and CeO2 catalyst impregnates). The knowledge on ceramic processing obtained during these previous research campaigns may be used to develop anode-supported SOFC with LSCTA- ‘backbones’ that have been optimised for high mechanical strength, high ‘effective’ electronic conductivity and sufficient porosity. Therefore, this manuscript details the preparation of anode-supported SOFC using the thick-film ceramic processing technique of aqueous tape casting, the optimisation of anode microstructure through addition of aqueous solvent-compatible graphitic and methacrylate polymer pore formers and the co-sintering of a LSCTA- support with a typical SOFC electrolyte material.

A Self-Consistent Scheme for Understanding Particle Impact and Adhesion in the Aerosol Deposition Process

Aerosol deposition (AD) is a thick-film deposition process that can produce films tens to hundreds of micrometers thick with densities greater than 95% of the bulk at room temperature. However, the precise mechanisms of bonding and densification are still under debate. To better understand and predict deposition, a self-consistent approach is employed that combines computational fluid dynamics (CFD), finite element (FE) modeling, and experimental observation of particle impact to improve the understanding of particle flight, impact, and adhesion in the AD process. First, deposition is performed with a trial material to form a film. The process parameters are fed into a CFD model that refines the particle flow and impact velocity for a range of sizes. These values are in turn used to inform the FE parameters to model the fracture and adhesion of the particle on the substrate. The results of FE modeling are compared to SEM images of fractured particles to complete a self-consistent numerical and experimental understanding of the AD process. Additional FE and CFD simulations are used to study how process parameters, materials, and particle parameters affect the deposition process and how the developed tools can be used to optimize deposition efficiency.

Novel Ballistic Processing of Thick Films: Structural Evolution and Mechanical Behavior

Ballistic processing (BP) is a new process that promises almost instantaneous processing of thick and thin films, through the acceleration of a carrier through a molten metal stream. The mechanisms by which such films are produced are difficult to study due to the ultrarapid processing speeds involved. In this article, we use the thermal properties of the carrier to reveal the mechanisms of formation of these films. High-speed imaging and extensive postprocessing characterization were used to arrive at a fundamental understanding of the microstructural evolution of thick films in BP. Results show that the thermal characteristics of the carrier material play a role in the morphology, topography, structure, and mechanical behavior of the processed films. An increase in carrier thermal conductivity generally resulted in an increase in film thickness and apparent elastic modulus. Increasing the carrier speed beyond the current limit is forecasted to decrease the thickness and improve the properties.

Polarization Parameters and Scaling Matter—How Processing Environment and Shape Factor Influence Electroactive Nanocomposite Characteristics

Polymeric-ceramic smart nanocomposite piezoelectric and dielectric materials are of interest due to their superior mechanical flexibility and ability to leverage characteristics of constituent materials. A great deal of work has centered on development of processes for manufacturing 0–3 continuity composite piezoelectric materials that vary in scale ranging from bulk, thick and thin film to nanostructured films. Less is known about how material scaling effects the effectiveness of polarization and electromechanical properties. This study elucidates how polarization parameters: contact versus corona, temperature and electrical voltage field influence the piezoelectric and dielectric properties of samples as a function of their shape factor, i.e., bulk versus thick film. Bulk and thick film samples were prepared via sol gel/cast-mold and sol gel/spin coat deposition, for fabrication of bulk and thick films, respectively. It was found that corona polarization was more effective for both bulk and thick film processes and that polarization temperature produced higher normalized changes in samples. Although higher electric field voltages could be achieved with thicker samples, film samples responded the most to coupled increases in temperature and electrical voltage than bulk samples.

Impact of Pressure and Temperature on the Compaction Dynamics and Layer Properties of Powder-Pressed Methylammonium Lead Halide Thick Films

While halide perovskite X-ray detectors based on single crystals could achieve extraordinary sensitivities, detectors based on polycrystalline thick films lag behind in efficiency. This is unfortunate since the processing methods for producing polycrystalline thick films, especially by pressure treatment of powders, are suitable for upscaling. Here, we investigate in detail the pressing of readily prepared powders of methylammonium lead halide perovskites MAPbI3 and MAPbBr3 to thick layers. By time-dependent pressure measurements, we monitor the occurring compaction dynamics, identifying two relaxation processes with different timescales. When pressing at elevated temperatures from room temperature (RT) to 100 °C, the pressure relaxations change drastically. While the layer properties such as relative density and surface roughness only improve to a certain degree by increasing the pressure at RT, we observe relative densities >97%, considerable reduction in surface roughness, and a significant increase in grain size with tempered pressing. Analyses regarding time-dependent pressure relaxations of tempered pressing allow attributing the dynamics to a sintering process, where we find the sinter onset to be surprisingly low at about 30 °C, mainly independent of the applied pressure (10–100 MPa). Our results will allow for an improved and more targeted powder processing of halide perovskite thick films as they are promising candidates for efficient X-ray detectors.

Microstructure evolution and electromechanical properties of (K,Na) NbO3‐based thick films

ABSTRACTThis study investigated an unconventional method of electrophoretic deposition (EPD) for the processing of environmentally benign (K0.5Na0.5)0.99Sr0.005NbO3 (KNNSr) thick films on Pt/alumina substrate. EPD allows rapid, economical, and low‐waste processing of thick films and thus offers an integration advantage for electronics manufacturing. To understand the functional response of the KNNSr thick films, the effect of the sintering temperature and atmosphere on their structure, microstructure, and electromechanical properties was investigated. KNNSr thick films densify in constrained conditions in a very narrow temperature range only a few 10°C below the melting temperature of 1140°C. Up to 1100°C the relative density increases to 80%, upon further heating to 1110°C we observed only the grain growth and pore coalescence. The densification is not affected significantly by the atmosphere. The local domain structure of 25‐33 μm thick KNNSr films was similar, while the dielectric and electromechanical properties increased with the increasing sintering temperature. KNNSr thick film sintered at 1100°C has a thickness‐coupling factor kt of 0.4, comparable to that of bulk. The results reveal that the EPD enables the economic processing of high‐performance thick films on complex‐shape substrates that are difficult to fabricate using conventional thick‐film methods.

Hybrid Stacking Integration of Multi-Sensor Navigation Module with WLFO and Thick Film Process

A hybrid stacking integration of multi-sensor navigation module with WLFO and thick film process was demonstrated. With wafer level fan-out packaging and stacked LTCC substrates, the GNSS, MEMS IMU, magnetometer and altimeter were integrated in one single module, the MEMS inertial sensors and ASIC chips were overlapping integrated with WLFO process as a multilayer wafer and diced, then the diced MEMS-ASIC modules, as well as the accessory circuits were pattered and mounted on several LTCC substrates as a drawer structure to accomplish the final system. The size of inertial sensor module is 10mm×5mm, and the entire navigation module is with size of 26.7cm3 and weight of 36g, meanwhile, with a high performance, the multi-sensor module can achieve low cost and high performance simultaneously. This module can be utilized for reliable navigation and gesture perception of micro UAV/UUV, automotive and other minimized platforms.

New Opportunities in Metallization Integration in Cofired Electroceramic Multilayers by the Cold Sintering Process

Metallization with high conductivities is critical in the design of high performance multilayer electroceramic devices. Cold sintering offers exciting new opportunities in the integration of different material classes; here we explore novel metal chemistries and demonstrate their integration into ceramic multilayers. The processing is enabled due to the cosintering of both the ceramic and metal powders in fast times and at extremely low sintering temperatures. Metal powders are printed as pastes and formed into multilayers that can be cosintered with the ceramic ZnO; these specific metals include Cu, Fe, and Al. The multilayer structures are assembled and fabricated under a thick film process and enabled by using a polypropylene carbonate binder system that can be removed at low temperatures under N2–H2 forming gas, permitting control of oxidation of the Cu, Fe, and Al. As a result, extremely high conductivity electrodes are fabricated and quantified through the equivalent series resistance (ESR). In addi...

A Catalytic Carrier Gas Sensor Based on a Nanotube Array

To effectively monitor methane in coal mine environments, a new type of catalytic carrier gas sensor based on a nanotube array was designed and fabricated. The sensor consists of a catalytic carrier based on a nanotube array, a sensitive Pt electrode, leading wires made from Ag/Pd alloy, a standard two-pin tube shell, powder metallurgy sheets and other components. The metallurgical copper powder sheets make the sensor explosion-proof. The desired catalytic carrier based on a Al2O3 nanotube array was prepared by chemical deposition on a nanoporous carrier film. The sensitive Pt electrode was prepared by a thick-film printing process via impregnation with a chloroplatinic acid and palladium chloride solution to form the noble metal catalyst. The results show that for methane concentrations in the range of 0% to 3%, the measured output is approximately 73 5 mV, the response time is 6 seconds, and the recovery time is 5 seconds. When the CH4 concentration is in the range of 0~3.81%, the response voltage of the sensor and the concentration of CH4 exhibit a good linear relationship. The stability of the sensor was examined in a 2% CH4 environment, and the stability of the sensor drifted 0.15% after 60 days.