Low-temperature Co-Fired Ceramics necessitate low sintering temperatures to enable cofiring with base metals, while dielectric resonator antennas demand temperature-stable dielectric properties; hexagonal perovskite Ba12Zn0.5Zr0.5Nb9O36 (R3̅m) ceramics exhibit excellent microwave dielectric performance but suffer from a high sintering temperature (1475 °C) and undesirably high temperature coefficient of resonant frequency (τf = 26.4 ppm/°C), limiting their practical applications. A synergistic strategy overcomes these critical bottlenecks by integrating BaWO4 (I41/a) for precise τf tuning and BaCu(B4O8) as a sintering aid to enable low-temperature sintering. XRD Rietveld refinement confirms the composites consist exclusively of impurity-free Ba12Zn0.5Zr0.5Nb9O36 and BaWO4 phases, and Raman spectroscopy validates the characteristic vibrational modes of NbO6 octahedra and [WO4]2- groups. The optimal composite at x = 0.89 exhibits exceptional all-around microwave dielectric properties (εr = 19.0, Q × f = 30100 GHz, τf = 3.0 ppm/°C) when sintered at 1000 °C, coupled with excellent chemical compatibility with Cu electrodes during cofiring. The DRA based on this composite delivers a broad 375 MHz bandwidth, 5.13 dBi gain, and 97.17% radiation efficiency at 9.14 GHz, highlighting its great potential for LTCC technology and microwave communication applications.

Abstract The heterogeneous integration of functional substrates with vacuum-sealed microcavities remains a significant challenge in the fabrication of robust microelectromechanical systems (MEMS). Conventional fusion bonding requires elevated thermal budgets, which can compromise the integrity of temperature-sensitive device architectures. To overcome these limitations, this paper presents, to the best of our knowledge, for the first time, an atomic layer deposition (ALD) alumina (Al2O3) enabled wafer-level anodic bonding process for the integration of low-temperature co-fired ceramic (LTCC) and silicon on insulator (SOI) substrates. The bonding mechanism was first optimized at the chip level, where current–time analysis across 150 nm, 250 nm, and 300 nm interlayer thicknesses revealed that the bonding current is inversely proportional to the interlayer thickness. This optimized process was successfully scaled to wafer-level bonding using functional LTCC wafers (with electrical through vias and patterned cavities) and SOI wafers. In this architecture, the 150 nm Al2O3 layer was selected as the optimal trade-off for balancing dielectric insulation and ionic conductivity. This interlayer plays a pivotal dual role, facilitating efficient ion migration for rapid bonding while exhibiting high dielectric breakdown. The bonding integrity and structural stability of the 12 mu-thick suspended membranes over the MEMS cavities were comprehensively characterized using bonding current monitoring, scanning acoustic microscopy (SAM), and 3D surface profilometry. Quantitative yield analysis further demonstrated the high mechanical reliability of the integrated devices after dicing. This work establishes a high-performance, low-temperature alternative to conventional fusion-bonded cavity silicon-on-insulator (Cavity-SOI) architectures, offering a scalable pathway for next-generation integrated MEMS sensors.

Existing spectrum resources can hardly meet the rate and capacity requirements of communication systems, so there is an urgent need to break through these barriers. In order to address the problem in a targeted manner, a novel Ca0.88(Li0.5Sm0.5)0.12MoO4 ceramic material with excellent microwave dielectric properties (εr = 11.3, Q×f = 41,625 GHz, τf = -23.8 ppm/°C) sintered at 950 °C is prepared by the solid-state reaction. The relationships between microwave dielectric properties and microstructure, electronic structure, and lattice vibrations are established through first-principles calculations, Raman spectroscopy, and fundamental characterization. Using this ceramic and silver electrode, an array device for generating vortex beams has been designed and demonstrated. The radiation efficiencies exceed 0.9 and the radiation phase covers 360°. The device converts plane waves into vortex waves with remarkable results and has the opportunity to significantly increase the capacity and efficiency of communications. This functionality is verified by far-field intensity and phase distributions. This work provides new ideas for the design of LTCC devices and broadens the application of microwave dielectric ceramics.

Abstract Based on shared-via low temperature cofired ceramic (LTCC) technology, a heterogeneously integrated chain-type micro thermoelectric generator ( µ TEG) is proposed in this work. The multilayer LTCC process enables a vertically interwoven thermoelectric arm configuration based on a shared hot–cold metal layout, which increases lateral integration density and reduces the effective thermal transport length. Large-aperture metallized vias are implemented as combined vertical thermal pathways and electrical interconnects, facilitating coupled transverse electrical conduction and longitudinal heat flow. The thermoelectric performances are experimentally characterized using cavity aluminum plate to regulate heat-flux distribution. The fabricated µ TEG incorporating 64 pairs of interwoven thermocouples achieves a voltage factor of 2.35 × 10 − 1 mVcm − 2 K − 1 and a power factor of 1.87 × 10 − 2 μ W cm − 2 K − 2 under temperature difference of 90 K . Relative to a bilayer transverse thermoelectric generator fabricated with the same LTCC process, the power generation capability of the proposed structure is increased by 70.1%. This work presents an effective method for capturing thermal energy in high-density integrated power components.

ABSTRACT A miniaturized ultra‐wideband band‐pass filter with wide out‐of‐band suppression based on low‐temperature cofired ceramic (LTCC) technology is presented, which works from 0.74 GHz to 6.5 GHz, consisting of a highpass filter and a lowpass filter. Because of utilizing advanced LTCC technology, the big multilayer capacitors and helical‐shape inductors can be realized in multiple thin layers to overcome the large circuit size, so the size of the proposed filter is miniaturized with 6 mm × 4 mm × 2 mm (0.19λ g × 0.12λ g × 0.06λ g ). The high frequency interferences are able to be eliminated by introducing small capacitors in the lowpass part of the proposed filter to realize wide stopband performance. Therefore, the fractional bandwidth of the proposed passband filter is 160% with return loss better than 10 dB, insertion loss less than 2 dB, and 20 dB out‐of‐band suppression arrival at 4.4 f 0 ( f 0 is the center frequency 3.6 GHz). The measured results have a good agreement with simulated results to verify the design theory.

New glass-free low-temperature co-fired microwave dielectric composites with compositions (1-4x/3)Ba3(VO4)2-xBaWO4-(2x/3)Li3VO4 (x = 0.3-0.7) were fabricated by reactive liquid-phase sintering of (1-x)Ba3(VO4)2-xLi2WO4 mixtures at 850 °C. During sintering, Li2WO4 is fully consumed by reacting with Ba3(VO4)2 to form BaWO4 and Li3VO4 while providing a transient liquid phase that promotes densification. As a result, the sintered ceramics achieve high relative densities of ≈94-98% at 850 °C. The relative fractions of Ba3(VO4)2, BaWO4, and Li3VO4 can be systematically tailored by adjusting the initial Li2WO4 content, enabling effective control of the temperature coefficient of the resonant frequency (τf) and the quality factor (Q × f). With increasing Li2WO4 content, the τf values shift from +23.97 to -45.48 ppm/°C, owing to the increasing contributions of the negative τf phases BaWO4 and Li3VO4, while the Q × f values increase moderately from 44,300 to 47,300 GHz. The optimal microwave dielectric properties are obtained for x = 0.5, meaning εr = 9.19, Q × f = 45,900 GHz, and τf = -1.15 ppm/°C when sintering at 850 °C for 1 h. Chemical compatibility tests confirmed that the composites exhibit no detectable reaction with Ag electrodes, indicating that the Ba3(VO4)2-BaWO4-Li3VO4 system is a promising glass-free dielectric for LTCC applications requiring low firing temperature, near-zero thermal drift, and reliable electrode compatibility.

Low-Temperature Co-Fired Ceramic (LTCC)-based mechanical sensors are inherently limited by the thickness and rigidity of multilayer ceramic stacks, which restrict miniaturization and mechanical compliance. To overcome these constraints, this work presents a hybrid LTCC/Kapton® platform enabling high-sensitivity mechanical sensing through mechanically tunable RF passive components. The proposed approach integrates a flexible polyimide membrane, bonded onto an LTCC substrate at low temperatures using selectively electroplated indium pillars that simultaneously define the air gap and provide mechanical fixation. Inductance tuning is achieved via metal-shielding proximity effects, whereas capacitance tuning relies on force-controlled air-gap modulation in a metal-insulator-metal configuration. The fabrication process ensures precise gap control, high compliance, and structural robustness without requiring deformable ceramic membranes. Experimental characterization, including three-dimensional surface profiling and impedance measurements, demonstrates a 48% inductance tuning range with a sensitivity of 0.715 nH/mN and a 36% capacitance tuning range with a sensitivity of 47.3 fF/mN at 1 MHz. The proposed hybrid platform provides a compact and scalable solution for high-sensitivity sensors and mechanically reconfigurable RF components suitable for harsh-environment and adaptive electronics applications.

Buried cavities in low temperature co-fired ceramic (LTCC) substrates, whether completely blind or fabricated with ports, are often utilized in industry in areas such as microelectronics packaging, microfluidic sensor fabrication, and microwave resonant chamber creation. These applications often have stringent requirements for cavity volume, parallelism, and wall planarity that are critical for the performance of a given device. While there has been significant research and reporting on the fabrication and functionality of these structures, there is a lack of available literature regarding methods used to mitigate deformation of these structures during the fabrication process while providing for precise dimensional control of the final structure. Although essential processes in the fabrication of LTCC structures, the lamination and sintering steps both pose challenges to creating uniform and precise buried cavities in LTCC substrates: deformation due to high pressure on unsupported green tape during lamination, as well as volume loss and deformation during the sintering process. This paper will report on methods, technologies, and processes used to mitigate deformation and allow for precise and repeatable dimensional control of buried cavities in LTCC substrates. Specifically, fugitive materials and rigid cavity inserts will be used in conjunction with the manipulation of lamination pressures and sintering profiles to understand and control the forces resulting in the deformation of these buried cavity structures. The results of these technologies and processes will be examined through cross sectioning and optical inspection as well as through optical profilometry.

With an increased number of wireless applications at microwave frequencies, a frequency spectrum became crowded. Microwave filters, as an essential part of any microwave circuitries, enable selection of target wavelengths for further processing. Performance of filters strongly depend on properties of dielectrics materials used for filter construction. The choice of dielectric materials defines center frequency of the filter, insertion loss, filter selectivity, and other key parameters. As an example, lower losses of the dielectric enable higher filter quality factor which translates to lower passband insertion loss and sharper transitions from passband to stopband. Another level of improvements can be achieved when a filter simultaneously utilizes several dielectrics having different dielectric constant. This design approach assists with optimization of each section of the filter and promotes better microwave performance with higher volumetric efficiency. Low temperature co-fired ceramic (LTCC) has become an enabling technology for a variety of wireless applications at microwave frequencies as it provides cost-effective and efficient solution suitable for high-volume production. To meet the market demands for higher performance and lower cost, Vibrantz has developed both low-K (K~7) and high-K (K~50) co-fireable low loss LTCC dielectrics, MW7U and MW50U. Both LTCC dielectrics are fully compatible between each other and with 100% Ag electrodes, can be fired at 900°C for 30 minutes, and offer a set of excellent dielectric properties: MW7U: K=7.0; Q=1,780; Q*f=27,790GHz; Τf=-27.0ppm/C; MOR=250MPa. MW50U: K=51.8; Q=1,650; Q*f=10,560GHz; Τf=204.0ppm/C; MOR=170MPa. In addition, MW7U and MW50U offer high resistance to chemical attacks during plating which is the critical parameter for a chip component manufacturing. Properties of both LTCC dielectrics are comprehensively evaluated and considered for microwave filter applications.

This work introduces a dual-polarized (DP) slot-excited dielectric-filled cavity antenna phased array designed for 5G and beyond AiP solutions using low-temperature co-fired ceramic (LTCC) technology. The primary challenge is to maximize a two-dimensional (2-D) beamsteering range with a compact form factor in a DP operation. Most reported LTCC AiP arrays have ≤ 55° beamsteering range at 5G mmWave frequencies and lack experimental validation for DP 2-D beamsteering operation. In contrast, the proposed antenna element in the infinite array enables ±60° 2-D beamsteering in the 5G n261 (27.5-28.35 GHz) band with the form factor as small as 5mm×5mm×1.3mm. This performance is achieved by introducing a wide-angle impedance matching (WAIM) structure directly at the antenna aperture, comprising a dual-layer metasurface formed by periodically arranged electrically small patches in a staggered configuration. The antenna is jointly optimized with a DP feeding network to minimize parasitics in the multilayer LTCC stack and a co-integrated printed circuit board (PCB) carrier to mitigate package-carrier coupling often neglected in previous works. It is fabricated in a single LTCC process without air gaps to ensure precise layer-to-layer alignment and eliminate losses from additional support structures inherent to conventional air-gap WAIM stacks. A custom equivalent-circuit model enables efficient analysis of scan-dependent impedance matching for the optimization. A 128-element AiP prototype employs 4×4 subarrays of four DP elements on the PCB carrier and is packaged with ball grid arrays (BGAs) to facilitate integration. This modular approach allows scaling to large arrays while considering the critical effects of the package stack-up and DP feeding. The simulated active reflection coefficient is < -8.5 dB within ±60° (with a scan loss marginally above 3 dB) at 27.5-29.5 GHz. Measurements confirm simulations for all relevant performance metrics in ±60° 2D-range.

Heatsink antennas perform dual functions of both radiation and heat dissipation. Thus, their electrical and thermal performance should be considered carefully in a codesign procedure, especially in the high-frequency range. In this paper, the electrical and thermal design of a millimeter-wave high-gain heatsink antenna array is presented. The radiation is generated by the laminated resonator antenna (LRA) in the low temperature co-fired ceramic (LTCC) substrate, and then enhanced by the specially designed heatsink structure. To facilitate the independent control of electromagnetic and thermal performance, the vertical structure of the heatsink element is divided into two parts: the upper fins are utilized to enlarge the effective radiation area and thus improve the gain, while the lower fins are designed to satisfy the heat dissipation demand, which has a negligible impact on the radiation performance. The element gain achieves 11.5 dBi at 60 GHz by loading the proposed heatsink structure, and the element spacing reaches 1.25 λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the wavelength in free space at 60 GHz) for a 4×4 heatsink antenna array. In measurement, the peak gain and aperture efficiency are 21 dBi and 48.6% at 61.1 GHz, respectively. The impedance bandwidth is 19.1%, from 56.3 GHz to 68.2 GHz. A heatsink antenna array prototype with multiple chips is fabricated to demonstrate its thermal performance. The overall thermal resistance is reduced by about 38% with the proposed design. Under the forced-air cooling condition, the hotspot temperature is lower than 85 ℃, with an input power of 2.5 W.

We report the development of a large area cold atmospheric plasma (CAP) array. The device consists of a parallel stack of 43 linear-discharge plasma elements that create a 10 cm × 10 cm treatment area. The CAP device is fabricated using low temperature co-fired ceramic (LTCC) layers to create 10 cm long linear discharge channels (1.1 mm discharge gap) with embedded opposing silver metal electrodes. A 21 kHz AC voltage of 1.55 kVrms applied to the electrodes generates an Ar plasma between the plates, with the gas flow directing the reactive species toward the intended biological sample (bacteria biofilms, etc.) to affect the antimicrobial treatment. Internal ballast resistors (20 kΩ) were used on each side of the two electrode elements to improve discharge uniformity and to prevent large filamentary discharges. Typical element discharge currents were 3.5-4 mA with the total array current tested at 178 mA (rms) to provide optimal device uniformity at a 1.55 kV (rms), and an argon flow rate of 130 lpm. Further, the gas flow system was optimized to obtain a uniform plasma. Treatment of Ps. fluorescence bacterial biofilms on stainless steel coupons demonstrated a 91% decrease in colony forming units after 150 s of treatment with a 1.5 cm gap.

Nanocrystalline SrTiO3 was synthesized using a single-step modified combustion process, producing phase-pure perovskite powder suitable for low-temperature ceramic processing. Remarkably, the material achieved a high relative density of 99.2% at a sintering temperature of only 890 °C, without the use of any sintering additives. Structural analysis by X-ray diffraction confirmed a cubic perovskite phase with an average crystallite size of 16 nm, which was consistent with the TEM observations showing uniformly distributed nanoparticles with clear lattice fringes, indicating high crystallinity. XPS analysis verified the expected oxidation states of Ti4+ and Sr2+ and revealed oxygen-vacancy-related components in the O 1s spectrum, correlating well with the material's optical behavior. The optical band gap was determined to be 3.07 eV, and the strong blue photoluminescence emission originated from vacancy-induced defect states within the TiO6 octahedra. Thermal stability assessed through DTA–TGA showed no significant weight loss up to 900 °C, confirming robust thermochemical behavior. The sintered ceramics exhibited a dielectric constant of εᵣ ≈ 50, a loss factor of tan δ ≈ 0.3 at 5 MHz, and a low temperature coefficient of permittivity (TCK ≈ 0.505 ppm °/C). The combination of nanoscale features, excellent densification at reduced temperature, oxygen-vacancy-driven luminescence, and favorable dielectric properties highlights nanocrystalline SrTiO3 as a strong candidate for advanced LTCC (Low-Temperature Co-fired Ceramic) devices.

To develop high-performance W–Cu conductor pastes for high-temperature co-fired ceramics (HTCC), graded particle-size design and ball-milling modification were systematically investigated. The particle-size distribution and powder morphology were changed, resulting in pastes with improved rheological stability and electrical conductivity. Rheological analysis combined with microstructural characterization revealed that powder size and morphology jointly controlled rheological behavior, sintering densification, and electrical conductivity. The optimized pastes exhibited improved flowability and dense sintered films. Electrical testing showed that resistivity decreased significantly, from 57.77 ± 2.41 mΩ·cm for coarse mixed powders to 5.80 ± 0.37 mΩ·cm for ball-milled powder s. Inspired by previous studies on W–Cu bulk composites, ball milling was employed to induce lamellar particle morphologies, which facilitated interparticle contact, promoted the formation of conductive networks. As a result, dense W–Cu films with reduced resistivity were successfully fabricated, demonstrating the feasibility of W–Cu pastes as advanced metallization materials for HTCC.

With the advancement of wireless communication technologies into high-frequency millimeter wave and sub-THz bands, conventional transmission lines such as microstrip and stripline face significant limitations. Under the circumstances, along with the increased application of new transmission lines such as substrate-integrated waveguides (SIWs), the design of transition structures between different transmission lines has become a practical requirement in modern signal transmission systems. This paper presents a novel stripline to SIW transition structure. Drawing inspiration from the classical microstrip probe techniques in metal waveguides, the proposed design employs Low-Temperature Co-fired Ceramic (LTCC) technology for both device fabrication and SIW implementation. The developed structure demonstrates a stable performance, structural simplicity, and manufacturing feasibility. Through fabrication and testing, the transition structure can achieve a return loss below -10 dB across the 89-100 GHz frequency range, with an insertion loss of approximately 0.75 dB.

This paper presents a compact four-beam dual-polarized phased array with the high performance front-end module based on system-in-package (SiP) technology. By employing high-temperature co-fired ceramic (HTCC) substrates, the proposed design achieves efficient thermal management and high level of integration within a tile-type architecture. The front-end module based on SiP can simultaneously generate four independent beams with switchable left- and right-hand circular polarizations, providing flexible beam control. To verify the proposed method, a Ku-band 256-element phased array receiver with four beams has been designed and experimentally verified using HTCC and SiP process. Operating in 14–14.5 GHz, the proposed low-profile array demonstrates stable radiation characteristics, beam pointing accuracy and excellent beam consistency across the entire frequency range. The measurement results confirm that the SiP-based phased array maintains efficient thermal management, high polarization purity and robust beam-scanning capability, validating its suitability for mobile satellite communication.

To measure temperature and pressure parameters in harsh environments such as those with high temperature and high pressure, a wireless and passive multi-grid Complementary Split-Ring Resonator and substrate integrated waveguide (MG-CSRR-SIW) structure for a temperature and pressure sensor based on microwave scattering principles and high-temperature co-fired ceramic (HTCC) technology is proposed. It can measure temperature within 25–1200 °C and pressure within 0–300 kPa. The structural design of the sensor by using high-frequency electromagnetic simulation software contributes to a linear relationship between the measured parameters and the sensor’s return loss (S11). Furthermore, the performance validation of the proposed sensor is implemented by sensor fabrication and experimentation. The test results show that the proposed sensor exhibits good performance of reliability and linearity. The temperature sensitivity is 199.33 kHz/°C and 379.75 kHz/°C in the temperature ranges of 25–475 °C and 475–1200 °C, respectively. In addition, the pressure sensitivity reaches 235.5 kHz/kPa at 800 °C. The maximum relative measurement error is 2.2% and 1.45% in regard to temperature and pressure, respectively.

Low-temperature co-fired ceramics (LTCC) with unique multilayer interconnection architectures are indispensable for electronic communication devices and high-density integrated packaging, facing stringent demands in millimeter-wave and higher-frequency applications. This review highlights recent advances in optimizing the comprehensive performance of LTCCs and proposes strategies for further enhancement to meet the ever-growing demands of high-performance microwave devices and systems. Specifically, LTCC material designs tailored to achieve desirable properties are discussed, including appropriate permittivity, low dielectric loss, a near-zero temperature coefficient of resonant frequency, high thermal conductivity, matched coefficient of thermal expansion, and excellent mechanical strength. Additionally, innovations in sintering technologies are highlighted, such as ultra-low temperature co-fired ceramic (ULTCC) technology and cold sintering process (CSP). These approaches further reduce sintering temperatures, enabling LTCCs to integrate with a broader range of materials (e.g., silicon chips, aluminum electrodes, 2D materials, and polymers) that were previously incompatible with traditional high-temperature processes. Finally, this review offers insights into the future development directions of LTCCs in emerging applications, including 3D integration and advanced packaging, integrated communication and sensing systems, and millimeter-wave/terahertz integrated miniaturized devices for next-generation electronics.

High-temperature co-fired ceramics (HTCC) exhibit great potential for sensing and monitoring applications in extreme environments. This paper presents an integrated metamaterial sensor utilizing a HTCC substrate, capable of real-time measurement of harsh environment conditions by tracking the resonance frequencies between the antenna and the sensor. A multi-resonance design was developed, featuring three distinct resonance frequencies ranging from 7 GHz to 9 GHz, allowing for the separate monitoring of temperature, pressure, and strain. The temperature-pressure-strain (TPS) sensor was shown to operate steadily between 25-1200 °C, 0-700kPa and -400 to +400με. Utilizing metamaterial technology, the sensor offers high stability, compact dimensions, which provides a reliable solution for improving the robustness of direct environmental monitoring of industrial systems in extreme environments.

In this article, we propose a synthesis method for wideband high-selectivity bandpass filters (BPFs) based on the tri-mode lumped-element resonator in heterogeneous low-temperature co-fired ceramic (LTCC) substrates. The tri-mode lumped-element resonator is analyzed to generate three resonances and two controllable transmission zeros without using cross couplings, showing a simple topology. A Remez-like numerical iterative algorithm is adopted to construct the polynomials of the tri-mode resonator in the bandpass domain, which can eliminate the need for complex transmission-function polynomial derivations and high-order iterations, allowing direct calculation of lumped-element values by the polynomials without optimization. Furthermore, the extracted-pole technique is used to expand the filter design. A comprehensive synthesis workflow is proposed for high-order filtering responses by integrating the extracted-pole technique and the tri-mode lumped-element resonator. The resultant filter is capable of achieving the desired responses with a wide bandwidth and multiple transmission zeros in a simple and practically achievable topology. For demonstration, a BPF covering 5G-n77 band (3.3–4.2 GHz) is implemented using a heterogeneous LTCC substrate. The measured result shows a low loss of 0.76dB and the circuit size is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.3\times 1.09\times 0.53$</tex-math> </inline-formula> mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (or <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.016\lambda _{{0}} \times 0.014\lambda _{{0}} \times 0.007\lambda _{{0}}$</tex-math> </inline-formula>), which is suitable for 5G applications.