Maciej Sobocinski

Multilayer low-temperature co-fired ceramic systems incorporating a thick-film printing process

Abstract: Since the first application of low-temperature co-fired ceramics (LTCC) – a radar chip manufactured by DuPont and Hughes – in the 1980s, LTCC has gone through many changes, evolving from a simple multilayer substrate technology to a complex microelectronic system suitable for ‘intelligent’ packages with buried passive components, heat sinks, sensors, actuators, energy harvesters and even microsystems. Moreover, novel materials and enhanced processes have been introduced constantly. This chapter presents LTCC technology, starting from material development followed by processing steps and proposed applications. Future trends and challenges are discussed, and literature containing more detailed descriptions is listed.

Low temperature co-fired ceramic packaging of CMOS capacitive sensor chip towards cell viability monitoring

Cell viability monitoring is an important part of biosafety evaluation for the detection of toxic effects on cells caused by nanomaterials, preferably by label-free, noninvasive, fast, and cost effective methods. These requirements can be met by monitoring cell viability with a capacitance-sensing integrated circuit (IC) microchip. The capacitance provides a measurement of the surface attachment of adherent cells as an indication of their health status. However, the moist, warm, and corrosive biological environment requires reliable packaging of the sensor chip. In this work, a second generation of low temperature co-fired ceramic (LTCC) technology was combined with flip-chip bonding to provide a durable package compatible with cell culture. The LTCC-packaged sensor chip was integrated with a printed circuit board, data acquisition device, and measurement-controlling software. The packaged sensor chip functioned well in the presence of cell medium and cells, with output voltages depending on the medium above the capacitors. Moreover, the manufacturing of microfluidic channels in the LTCC package was demonstrated.

A piezoelectric active mirror suspension system embedded into low-temperature cofired ceramic

Low-temperature cofired ceramic (LTCC) has proven to be a cost-effective, flexible technology for producing complicated structures such as sensors, actuators, and microsystems. This paper presents a piezoelectric active mirror suspension system embedded into LTCC. In the structure, the LTCC was used as a package, for the passive layers of piezoelectric monomorphs, as support for the mirrors, and as a substrate for the conductors. The active mirror structure, 17 mm in diameter, was made by compiling 20 LTCC layers using common LTCC processing techniques. Each sample contained a laser-micromachined bulk lead zirconate titanate (PZT) structure which formed a monomorph with the LTCC during the firing process. A mirror substrate (diameter 4 mm) was mounted in the middle of the monomorph arms for evaluation of the positioning performance, where each of the three arms had independent signal electrodes and a common ground electrode. Electrical and electromechanical properties were investigated with an LCR meter, network analyzer, and laser vibrometer for the different arms and the mirror. The active mirror structure exhibited more than 1 μm dc displacement for mirror leveling and also allowed small changes in mirror angle up to 0.06°. The first bending resonance frequency of the structure with the mirror was detected at 11.31 kHz with 4.0 μm displacement; 13.02 kHz and 2.7 μm were obtained without the mirror. The structure exhibited characteristics feasible for further utilization in tunable Fabry-Perot filter applications, allowing the mounting of active mirrors on both sides with distance and angle control.

Piezoelectric active mirror suspension embedded into Low Temperature Co-fired Ceramic

Low Temperature Co-fired Ceramic (LTCC) has proven to be a cost effective and flexible technology for producing complicated structures: sensors, actuators and microsystems. In this paper, piezoelectric active mirror suspension embedded into LTCC is presented. In the structure the LTCC was used as a package, passive layers of piezoelectric monomorphs, support for the mirrors and substrate for conductors. Active mirror structure, 17 mm in diameter, was made by compiling 20 layers using standard LTCC processing techniques. Each sample contained a laser micromachined bulk PZT structure which formed a monomorph with LTCC during the firing process. A mirror substrate (Ø 4mm) was mounted in the middle of the monomorph arms for evaluation of positioning performance where each of the three arms had independent signal electrodes and a common ground electrode. Electrical and electromechanical properties were investigated with LCR meter, network analyser and laser vibrometer for different arms and the mirror. Active mirror structure exhibited over 1 µm DC displacement for mirror leveling allowing also small changes in mirror angle up to 0.06°. First bending resonance frequency of the structure with the mirror was detected at 11.31 kHz with 4.0 µm displacement while 13.02 kHz and 2.7 µm was obtained without the mirror. The structure exhibited feasible characteristics for further utilization as tunable Fabry-Perot filter applications, allowing mounting of two active mirrors on both sides with distance and angle control.

LTCC Packaged Ring Oscillator Based Sensor for Evaluation of Cell Proliferation

A complementary metal-oxide-semiconductor (CMOS) chip biosensor was developed for cell viability monitoring based on an array of capacitance sensors utilizing a ring oscillator. The chip was packaged in a low temperature co-fired ceramic (LTCC) module with a flip chip bonding technique. A microcontroller operates the chip, while the whole measurement system was controlled by PC. The developed biosensor was applied for measurement of the proliferation stage of adherent cells where the sensor response depends on the ratio between healthy, viable and multiplying cells, which adhere onto the chip surface, and necrotic or apoptotic cells, which detach from the chip surface. This change in cellular adhesion caused a change in the effective permittivity in the vicinity of the sensor element, which was sensed as a change in oscillation frequency of the ring oscillator. The sensor was tested with human lung epithelial cells (BEAS-2B) during cell addition, proliferation and migration, and finally detachment induced by trypsin protease treatment. The difference in sensor response with and without cells was measured as a frequency shift in the scale of 1.1 MHz from the base frequency of 57.2 MHz. Moreover, the number of cells in the sensor vicinity was directly proportional to the frequency shift.

3D printed dielectric ceramic without a sintering stage

This paper presents for the first time the fabrication of dielectric ceramic parts by 3D printing without sintering. The printable paste was prepared by mixing a carefully selected amount of water-soluble Li2MoO4 powder with water. A viscous mixture of solid ceramic particles and saturated aqueous phase was formed with a solid content of 60.0 vol.%. Printing of the sample discs was conducted with material extrusion using a low-cost syringe-style 3D printer. The consolidation and densification of the printed parts occurred during both printing and drying of the paste due to extrusion pressure, capillary forces, and recrystallization of the dissolved Li2MoO4. Complete drying of the paste was ensured by heating at 120 °C. The microstructure showed no delamination of the printed layers. Relatively high densities and good dielectric properties were obtained, especially when considering that no sintering and only pressure from the extrusion was employed. This approach is expected to be feasible for similar ceramics and ceramic composites.

Multilayer Functional Tapes Cofired at 450 °C: Beyond HTCC and LTCC Technologies

This paper reports the first ultralow sintering temperature (450 °C) cofired multifunctional ceramic substrate based on a commercial lead zirconium titanate (PZ29)-glass composite, which is fabricated by tape casting, isostatic lamination, and sintering. This substrate was prepared from a novel tape casting slurry composition suitable for cofiring at low temperatures with commercial Ag electrodes at 450 °C. The green cast tape and sintered substrate showed a surface roughness of 146 and 355 nm, respectively, suitable for device-level fabrication by postprocessing. Additionally, the ferroelectric and piezoelectric studies disclosed low remnant polarization due to the dielectric glass matrix with average values of piezoelectric coefficient (+ d33) and voltage coefficient (+ g33) of 17 pC/N and 30 mV/N, respectively. The dielectric permittivity and loss value of the sintered substrates were 57.8 and 0.05 respectively, at 2.4 GHz. The variation of relative permittivity on temperature dependence in the range of -40 to 80 °C was about 23%, while the average linear coefficient of thermal expansion was 6.9 ppm/°C in the measured temperature range of 100-300 °C. Moreover, the shelf life of the tape over 28 months was studied through measurement of the stability of the dielectric properties over time. The obtained results open up a new strategy for the fabrication of next-generation low-cost functional ceramic devices prepared at an ultralow temperature in comparison to the high-temperature cofired ceramic and low-temperature cofired ceramic technologies.

Dual-polarized 2×2 element sub-array at 15 GHz with high port isolation

This paper presents simulation results of a dual-polarized 2×2 element sub-array antenna element at 15 GHz center frequency. The basic idea is to use two waveguides stacked on in a right-angle configuration to excite the orthogonal polarizations by using radiating slots. Above the slots, 4 parasitic patches are set to a form of 2×2 element sub-array. Antenna presents −10 dB impedance bandwidth from 14.3 to 15.6 GHz with better than 68 dB isolation between the excitation ports. At the aforementioned bandwidth, the total efficiency is better than −0.7 dB (> 85%). Antenna shows very good polarization properties and difference between ϕ, θ components is greater than 45 dB. Also the radiation patterns and surface current distributions at 15 GHz center frequency are presented and compared.

Development of planar dielectric passive microwave circuits and antennas

In this paper we propose an approach for designing compact all-dielectric passive microwave/mm-wave components. Our design is based on an extremely thin layer of high-permittivity dielectric which creates a large permittivity contrast with its adjacent dielectric/substrate and can be built using two-dimensional printing fabrications. Couplers, transmission lines, and various antennas such as multimode, multisegment, and wideband antennas are investigated, fabricated, and discussed.