Alumina Ceramic Substrate Research Articles

Influence of casting-warm pressing process on the thermal conductivity of micro–nano-Al2O3 substrate

Alumina substrates are increasingly used for high-power integrated circuits due to their high thermal conductivity, low thermal expansion coefficient, and excellent insulation properties. However, pores in the green tape from the tape casting process reduce the thermal conductivity and permittivity of the sintered ceramic substrate. Researchers have attempted to minimize ceramic porosity with chemical additives or by sintering pure alumina at temperatures above 1650 °C, but these methods often degrade thermal conductivity or quality of substrate evenness. This study proposes a low-cost casting-warm pressing process to densify pure alumina ceramic substrates using micro–nano-mixed alumina powders and sintering at relatively low temperatures. The results indicate that the relative density of the pure alumina ceramic substrate prepared at 1500 °C is 93%, a 4.4% improvement over the tape casting process. Additionally, the thermal conductivity of the alumina substrate from the casting-warm pressing process reaches 15.89 W/(m K), which is 1.4 times higher than that of the tape casting process. Microstructure analysis shows that the casting-warm pressing process with micro- and nano-multi-scale mixed alumina powders forms a novel thermal conduction enhancement mechanism. Large particles in the green tape overlap, while small particles fill the spaces between the large particles. The connected micrometer-sized particle skeletons form high thermal conduction net channels in the substrate, improving the thermal conductivity for heat transfer.

Achieving high sheet resistance and near-zero temperature coefficient of resistance in NiCr film resistors by Al interlayers

Thin film resistive materials with low temperature coefficients of resistance (TCR) and high sheet resistances are essential for various electronic applications, such as embedded resistors. In this study, Al inserting layers and NiCr resistive layers were sequentially deposited on alumina ceramic substrates via DC magnetron sputtering to fabricate Al/NiCr bilayer resistive materials. The electrical properties of the bilayer films were adjusted by varying the thicknesses of the Al inserting layers and annealing conditions. When the thickness of the Al inserting layer varied from 5 to 7.5 nm, and post-annealing treatments ranging from 200℃ to 400℃ were applied, evident Al-NiCr interdiffusion occurred, forming intermediate layers at the interfaces and oxides on the film surfaces. A mixture of partial crystalline phases and amorphous phases was also observed in the cross-sectional high-resolution transmission electron microscope (HRTEM) images. The formation of intermediate layers and surface oxides and the balance between partial crystalline phases and amorphous phases collectively enhanced the electrical performance of bilayer film resistors, achieving thin film resistors with a remarkably low TCR of −6.61 ppm/K and a sheet resistance of up to 265.95 Ω/sq. By rational design of Al layers, NiCr layers and thermal treatment, thin film resistors with near zero TCRs and extremely wide sheet resistance range of 93.34–1439.01 Ω/sq can be obtained.

Growth of thick amorphous carbon films on alumina for improved tribological properties

Alumina, as a pivotal ceramic material extensively utilized in contemporary applications, the surface modification and enhancement of tribological properties are crucial. In this study, reactive magnetron sputtering was employed to deposit Ti, Si co-doped hydrogen-free (TiSi/a-C), and hydrogenated amorphous carbon films (TiSi/a-C:H) with a thickness exceeding 7 μm onto the surface of alumina ceramic substrates. Utilizing the design of the film structure, the difficulty of film-substrate adhesion was resolved by controlling the deposition time to influence the growth rate of the film, thereby enabling the reliable fabrication of thick films. The adhesion of the TiSi/a-C film exhibits the highest value, with an Lc1 value of 36.7 N. The hardness of the TiSi/a-C:H reaches a maximum of 15.2 GPa, and the hardness is closely correlated with the reaction gas utilized during its depositional process. The wear rate of amorphous carbon film decreases by 34 times compared to alumina substrate. During the dissociation of CH4 at a high hydrogen-to-carbon ratio, more hydrogen atoms are involved in the chemical reaction. The introduction of hydrogen elevates the H/E and sp3/sp2 ratios within the film, thereby favoring the generation of low-friction surfaces and refining the tribological performance of alumina ceramics.

A novel sensor with excellent high-temperature performance for in-situ temperature measurement

Real-time access to critical information about system temperature variations is essential for evaluating system performance in some of the high-temperature and harsh environments. Given the technical difficulty of accurately obtaining the temperature of a high-temperature and harsh environment, a new sensor package structure is proposed. Combining ceramic sintering and isostatic pressure molding methods, the thermal junction is fixed in the temperature measurement end face of the alumina ceramic substrate, while the shell design threads play a role in fixing the sensor and preventing loosening. This paper conducted repeatability, upper-temperature limit, and high-temperature serviceability assessment tests on the sensor. The results show that the sensor maximum repeatability error is 2.4%. The sensor can continue to operate at 1200°C for more than 6 hours with no signal interruption and the upper limit of temperature measurement is 1307°C. The results demonstrate the feasibility and practicality of temperature measurement by this sensor in high-temperature and harsh environments.

Laser drilling of alumina ceramic substrates: A review

Laser drilling of alumina ceramic substrates: A review

High-Linearity Wireless Passive Temperature Sensor Based on Metamaterial Structure with Rotation-Insensitive Distance-Based Warning Ability.

A wireless passive temperature sensor based on a metamaterial structure is proposed that is capable of measuring the temperature of moving parts. The sensor structure consists of an alumina ceramic substrate with a square metal double split-ring resonator fixed centrally on the ceramic substrate. Since the dielectric constant of the alumina ceramic substrate is temperature sensitive, the resonant frequency of the sensor is altered due to changes in temperature. A wireless antenna is used to detect the change in the resonant frequency of the sensor using a wireless antenna, thereby realizing temperature sensing operation of the sensor. The temperature sensitivity of the sensor is determined to be 205.22 kHz/°C with a strong linear response when tested over the temperature range of 25-135 °C, which is evident from the R2 being 0.995. Additionally, the frequency variation in this sensor is insensitive to the angle of rotation and can be used for temperature measurement of rotating parts. The sensor also has a distance warning functionality, which offers additional safety for the user by providing early warning signals when the heating equipment overheats after operating for extended durations.

Ultra-Thin Ceramic Substrates for Improved Heatsinking for microLEDs.

MicroLEDs provide unrivaled luminance and operating lifetime, which has led to significant activity using devices for display and non-display applications. The small size and high power density of microLEDs, however, causes increased adverse heating effects which can limit performance. A new generation of electrically insulating high thermal conductivity materials, such as alumina, has been proposed to mitigate these thermal effects when used as a substrate as an alternative to glass. This strategy then could be used as a method of passive heatsinking to improve the overall performance of the microLED. In this work, a newly available material, an 80 micron thick alumina ceramic substrate, is shown to yield a 30 % improvement on average in the maximum current drive over a glass substrate.

Design, Preparation, and Performance Study of a Miniaturized High-Temperature Thick-Film Heat Flux Sensor

Solving heat transfer problems in high-temperature and temperature-changing environments is critical in a variety of applications, including modern turbines, aerospace, and nuclear power plants. However, most current thin-film-type heat flow sensors operate at approximately 1000 °C. Thus, we fabricated a kind of platinum–platinum/rhodium thick-film thermopile-type heat flux sensor which can work stably at 1200 °C based on an alumina ceramic substrate. The entire electrode layer was prepared by screen printing process. The surface morphology of the Pt electrode and the material in thermal resistance layer at different stages were investigated using scanning electron microscopy. The steady-state characteristics of the sensor were evaluated by using a high-temperature test platform. The experiments show that the peak voltage of the sensor is 1.4126 mV at the temperature of 1200 °C and the heat flow density of 283.3 kW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Moreover, the repeatability of sensor at 1200 °C and high temperature holding for 4 h experiments were performed, verifying that the sensor has good consistency and durability. Therefore, we infer that the designed sensor can be applied for a long time under high temperature and large heat flow conditions, such as aerospace, mechanical metallurgy and energy construction fields.

Nano cone ITO thin films prepared by pulsed laser deposition for surface measurement of high-temperature components

Semiconductor thin-film thermocouples (TFTCs) are widely used for temperature measurement of aero-engine components due to their large output and fast response. As a thermoelectric material, indium tin oxide (ITO) makes the device have very good thermoelectric merit because of its low resistivity, which is very suitable for the preparation of thin-film thermocouples. In this study, Pt-ITO thin-film thermocouple was fabricated on alumina ceramic substrate by pulsed laser deposition (PLD), and the microstructure and electrical properties of TFTCs prepared under different deposition conditions and annealing conditions were investigated. The results show that the ITO thin films prepared by PLD have a new type of nano cone structure and the resistivity of ITO thin films was only 2.76 × 10−4 Ω·cm when the substrate temperature was 600 °C. The Pt-ITO thin-film thermocouples can stable work for at 25–1300 °C and work in a short time at 1400 °C, and the average Seebeck coefficient is more than 50 µV/°C at 1300 °C. The response time of the prepared TFTC tested by pulsed laser is no more than 435 μs. These results provide an important basis for a potential application prospect of Pt-ITO TFTCs in the field of high-temperature measurement. It is further confirmed that the preparation of superior thermoelectric semiconductor materials by PLD is a promising method.

Improving bonding strength between Ni/Cu/Ag coatings and MgTiO3 ceramic resonator by alumina thin-film grown by atomic layer deposition

A layer of nano-sized alumina thin-film was grown on MgTiO3 based ceramic resonator using atomic layer deposition (ALD) to improve the bonding between resonator and electroless plated and/or electroplated metal coatings. The hydroxylation of resonator surface ensures the strong bonding between alumina film and ceramic substrate, indicating by the bonding score to 10 from 0. However, it will not result in the degradation of the insertion loss of metalized resonators. The signal insertion loss of metalized ceramic resonator with alumina thin-film intermediate layer is significantly lower than that of resonators treated by traditional HF solution corrosion and/or laser scanning to achieve strong bonding between resonator and metalized coatings. It could be promising to metalize ceramic resonators with highly complex intricate geometric shape.

Wireless High Temperature Sensing Chipless Tag Based on a Diamond Ring Resonator

A passive wireless sensor is designed for real-time monitoring of a high temperature environment. The sensor is composed of a double diamond split rings resonant structure and an alumina ceramic substrate with a size of 23 × 23 × 0.5 mm3. The alumina ceramic substrate is selected as the temperature sensing material. The principle is that the permittivity of the alumina ceramic changes with the temperature and the resonant frequency of the sensor shifts accordingly. Its permittivity bridges the relation between the temperature and resonant frequency. Therefore, real time temperatures can be measured by monitoring the resonant frequency. The simulation results show that the designed sensor can monitor temperatures in the range 200~1000 °C corresponding to a resonant frequency of 6.79~6.49 GHz with shifting 300 MHz and a sensitivity of 0.375 MHz/°C, and demonstrate the quasi-linear relation between resonant frequency and temperature. The sensor has the advantages of wide temperature range, good sensitivity, low cost and small size, which gives it superiority in high temperature applications.

Novel lead-connection technology for thin-film temperature sensors with arbitrary electrode lengths

Traditional thin-film thermocouples (TFTCs) have limitations in measuring real surface temperature changes in aircraft because the connection between the nanofilm and the leads can easily fail. Despite this, how to improve this weak connection has rarely been addressed in previous studies. In this study, a lead-embedded alumina ceramic substrate is proposed to improve the durability of TFTCs. Multi-layer two-dimensional nanofilms with different thin-film electrode lengths were prepared on a substrate using DC-pulsed magnetron sputtering. Furthermore, the effect of the thin-film electrode length on the sensitivity, response time and measurement error of the sensor was investigated. The electrode length did not affect the sensitivity and response time; however, as it was increased, the temperature measurement error decreased. In addition, the static and dynamic performance, repeatability, measurement accuracy and service lifetime of the developed sensor were verified. The results show that the sensor has high sensitivity and linearity and good repeatability, with the response time being in microseconds. The sensor can continue to operate at 500 °C for more than 2 h with no signal interruption. The sensor’s reported accuracy is 0.43% at 300 °C.

Design of a metamaterial chipless RFID sensor tag for high temperature

A high temperature sensor based on a metamaterial is proposed as a chipless radio frequency identification sensor tag that can measure temperature wirelessly. The metamaterial, based on a double circular split ring resonator (SRR), is highly frequency selective and has negative permittivity. The double circular SRR is fabricated on the alumina ceramic substrate, which acted as the temperature sensing material. The permittivity of the material varies with the temperature parameter, resulting in a shift of backscattered resonant frequency of the sensor tag. Simulations verify the feasibility of this sensor tag in the microwave band under electromagnetic stimuli. When the temperature increases from 200 to 1000 °C, the resonant frequency monotone decreases from 6.64 to 6.26 GHz with an average sensitivity of 0.475 MHz/°C. The sensor tag has features such as high temperature, being wireless, passive, of comparatively low-cost, and miniature, with diversified application potential, allowing it to compete with other sophisticated temperature devices in terms of performance.

Effect of the Gas Temperature on Agglomeration of Au Nanoparticles Synthesized by Spark Discharge and Their Application in Surface-Enhanced Raman Spectroscopy

In this work, we have, for the first time, experimentally verified the hypothesis of reducing the agglomeration rate of aerosol nanoparticles produced by spark discharge upon decreasing the carrier gas temperature in the range of 24 °C to –183 °C. The synthesis of nanoparticles was implemented as a result of spark ablation of electrodes manufactured from Au with a purity of 99.998% installed in a specially designed gas chamber dipped into liquid nitrogen (−196 °C) to cool down the carrier gas supplied through one of hollow electrodes. It follows from the analysis of transmission electron microscopy images that both the average size of primary nanoparticles and the degree of their sintering become lower if the gas is cooled. For example, in the case of using nitrogen as a carrier gas, the average size of primary nanoparticles decreases from 9.4 nm to 6.6 nm as the gas temperature decreases from 24 °C to –183 °C. This also causes the aggregates to become more branched, manifested by the reduction in their solidity from 92% to 76%. The agglomeration model of Feng based on Smoluchowski theory was employed to calculate particle size distributions that were found to be consistent with the experimental data. The gold nanoparticles synthesized at room and cryogenic temperatures of the carrier gas (N₂, Ar + H₂, He) were used to pattern plasmonic nanostructures on ceramic alumina substrates by using aerosol jet printing technology for the purpose of demonstrating the possibility of their application in surface-enhanced Raman spectroscopy (SERS). The SERS enhancement factor was estimated at 2 × 106 from the analysis of SERS and normal Raman spectra of 1,2-bis(4-pyridyl)ethylene used as an analyte.

Core-Shell Structured Carbon@Al2O3 Membrane with Enhanced Acid Resistance for Acid Solution Treatment.

Ceramic membrane has an important application prospect in industrial acid solution treatment. Enhancement of the acid resistance is the key strategy to optimize the membrane treatment effect. This work reports a core-shell structured membrane fabricated on alumina ceramic substrates via a one-step in situ hydrothermal method. The acid resistance of the modified membrane was significantly improved due to the protection provided by a chemically stable carbon layer. After modification, the masses lost by the membrane in the hydrochloric acid solution and the acetic acid solution were sharply reduced by 90.91% and 76.92%, respectively. Kinetic models and isotherm models of adsorption were employed to describe acid adsorption occurring during the membrane process and indicated that the modified membrane exhibited pseudo-second-order kinetics and Langmuir model adsorption. Compared to the pristine membrane, the faster adsorption speed and the lower adsorption capacity were exhibited by the modified membrane, which further had a good performance with treating various kinds of acid solutions. Moreover, the modified membrane could be recycled without obvious flux decay. This modification method provides a facile and efficient strategy for the fabrication of acid-resistant membranes for use in extreme conditions.

Preparation and Application of Nanocomposite Thin-Film Temperature Sensor during the Milling Process.

During the titanium alloy milling process, high temperatures in the tool-chip contact area will affect the tool life and precision of titanium alloy machining. Therefore, it is essential to measure the temperature of the tool-chip contact area continuously. In this paper, a finite element simulation model of the milling process was established using ABAQUS2020 to obtain the highest temperature location in the tool-chip contact area when milling titanium alloy. The integration of the wire with the alumina ceramic substrate formed an integrated wire substrate. Furthermore, NiCr, NiSi, and SiO2 films were deposited on the substrate sequentially using the DC pulsed magnetron sputtering technique. Finally, its microscopic morphology and static and dynamic performance were tested. The results show that the developed thin-film thermocouple temperature sensor has a Seebeck coefficient of 40.72 μV/°C and a dynamic response time of 0.703 ms. The application of the sensor to our titanium alloy milling experiments showed that the sensor can monitor the transient temperature in the tool-chip contact area, and its temperature measurement performance showed no detrimental effect from wearing. The effect of each milling parameter on the milling temperature was analyzed using ANOVA, and a regression model with an R-sq of 96.76% was obtained for the milling temperature.

Design, Simulation, and Fabrication of Multilayer Al2O3 Ceramic Micro-Hotplates for High Temperature Gas Sensors.

In gas sensors composed of semiconductor metal oxides and two-dimensional materials, the gas-sensitive material is deposited or coated on a metallic signal electrode and must be selective and responsive at a specific temperature. The microelectromechanical devices hosting this material must keep it at the correct operating temperature using a micro-hotplate robust to high temperatures. In this study, three hotplate designs were investigated: electrodes arranged on both sides of an AlN substrate, a micro-hotplate buried in an alumina ceramic substrate, and a beam structure formed using laser punching. The last two designs use magnetron-sputtered ultra-thin AlN films to separate the upper Au interdigital electrodes and lower Pt heating resistor in a sandwich-like structure. The temperature distribution is simulated by the Joule heat model, and the third design has better energy consumption performance. This design was fabricated, and the effect of the rough surface of the alumina ceramic on the preparation was addressed. The experimental results show that the micro-hotplate can operate at nearly 700 °C. The micro-hotplate heats to nearly 240 °C in 2.4 s using a power of ~340 mW. This design makes ceramic-based micro-hotplates a more practical alternative to silicon-based micro-hotplates in gas sensors.

Layered metal oxides loaded ceramic membrane activating peroxymonosulfate for mitigation of NOM membrane fouling

Catalytic membrane can achieve sieving separation and advanced oxidation simultaneously, which can improve the effluent water quality while reducing membrane fouling. In this study, the catalytic membranes (M2+Al@AM) were fabricated by loading different binary layered metal oxides (M2+Al-LMO: MnAl-LMO, CuAl-LMO and CoAl-LMO) on alumina ceramic substrate membranes (AM) via vacuum filtration followed by calcination process. The performance of the catalytic membranes was investigated by filtering actual surface water. It was found that the presence of peroxymonosulfate (PMS) could mitigate membrane fouling effectively, as evidenced by the increase of normalized flux from 0.28 to 0.62 in CoAl@AM/PMS system, from 0.25 to 0.52 in CuAl@AM/PMS system, and from 0.22 to 0.31 in MnAl@AM/PMS system, respectively. Correspondingly, the CoAl@AM exhibited the highest removal for UV254, TOC and fluorescent components in the surface water, followed by CuAl@AM and MnAl@AM. Quenching effect of phenol and furfuryl alcohol proposed the surface-bound radicals and singlet oxygen were the major reactive oxygen species in the M2+Al@AM/PMS systems. Interface free energy calculations confirmed the in-situ PMS activation could enhance the repulsive interactions between NOM and the membranes, thus mitigating membrane fouling. This work provides an original but simple strategy for catalytic ceramic membrane preparation and new insights into the mechanism of membrane fouling mitigation in catalytic membrane system.

Submicron Cu@glass core-shell powders for the preparation of conductive thick films on ceramic substrates

Coating Cu powders with glasses to form a core-shell structure provides an important route to achieve uniform distribution of glass components in Cu pastes for the fabrication of various electronic devices. In this study, submicron Cu powders are synthesized via a chemical solution method at first, and then coated with Bi-Si-B-Zn-Al glass by a sol-gel method to form submicron Cu@glass core-shell powders which are then prepared into Cu pastes with different glass contents. The Cu@glass pastes are printed on alumina ceramic substrates and sintered at temperatures ranging from 600 to 800 °C to form conductive thick films. Enhanced anti-oxidation properties are observed for the Cu@glass core-shell powders. The Cu pastes can be sintered into conductive films with a good electric conductivity and adhesion strength on alumina substrate at a relatively low temperature of 600 °C. A low resistivity of 3.0 µΩ cm is achieved for the sintered Cu film with a glass content of 6 wt%. The glass shells are observed to transform into uniformly distributed glass phases which provide advantages for the formation of Cu-grain conductive pathway at a low sintering temperature.

Preparation of PdO-decorated NiO porous film on ceramic substrate for highly selective and sensitive H2S detection

This work is to develop high-performance thin film gas sensors on the alumina ceramic substrate. Here, porous NiO films of about 2 μm were obtained by the simple electrochemical deposition technique. The NiO gas sensing thin films obtained by the in-situ growth overcomes the disadvantages of great thickness, material agglomeration, and uneven size of the conventional device structure. The films exhibit good uniformity, consistency, and reproducibility. The composition of the films and their porous morphological characteristics were demonstrated by SEM, XRD, AFM, and XPS characterization. The doping of PdO significantly enhanced the sensitivity and specificity selection of the NiO films for H2S gas. 2 wt% PdO/NiO thin film sensor exhibited a high response (515.27) and fast dynamic process at 155 °C for 10 ppm H2S. The outstanding gas-sensing performance of the thin film sensor is due to the doping of PdO and the porous structure of the film.