Embedding of bulk piezoelectric structures in low temperature co-fired ceramic

Abstract It has been over a century since the Curie brothers discovered the piezoelectric effect. Since then our knowledge about this phenomena has been constantly growing, accompanied by a vast increase in its applications. Modern piezoelectric devices, especially those meant for use in personal equipment, can often have complicated shapes and electric circuits; therefore, a suitable and cost effective packaging method is needed. The recent introduction of self-constrained Low Temperature Co-fired Ceramic (LTCC) characterized by virtually no planar shrinkage has pushed the limits of this technology a step further. The practical lack of dimension change between “green” state and sintered ceramic has not only improved the design of multilayer smart packages but also allowed the embedding of other bulk materials within the LTCC and their co-firing in one sintering process. This thesis introduces a novel method of seamlessly embedding piezoelectric bulk structures in LTCC by co-firing or bonding with adhesive. Special attention is paid to the multistage lamination and post-firing poling of the piezoelectric ceramics. Examples of several structures from the main areas of piezoelectric applications are presented as proof of successful implementation of the new technique in the existing production environment. The performance of the structures is investigated and compared to structures manufactured using other methods. Integration of bulk piezoelectric structures through co-firing is a new technique with a wide area of applications, suitable for mass production using existing process flow.Tiivistelmä Curien veljekset havaitsivat pietsosähköisen ilmiön jo yli sata vuotta sitten. Ilmiöön liittyvä tutkimustieto ja erityisesti siihen perustuvien sovellusten määrä on nykyisin valtava. Uusissa pietsosähköisissä komponenteissa ja varsinkin niissä, jotka on tarkoitettu henkilökohtaisissa laitteissa käytettäviksi, muodot samoinkuin elektroniikapiirit voivat olla monimutkaisia. Siksi tarvitaan tarkoituksenmukaista ja hinnaltaan edullista laitteen pakkausmenetelmää. Hiljattain kehitetyt itseohjautuvat matalan lämpötilan yhteissintattavat keraamit (LTCC), joiden planaarinen kutistuma on lähes olematon, ovat lisänneet LTCC-teknologian sovellusmahdollisuuksia. Muotoon valmistetun sintraamattoman ja lopullisen sintratun keraamin dimensioiden yhtäsuuruus ei ole ainoastaan parantanut älykkäiden monikerrospakkausten suunnittelua, vaan mahdollistanut myös erilaisten materiaalien ja komponenttien upottamisen LTCC-rakenteisiin ja niiden yhteissintrauksen. Väitöstyössä esitetään uusi menetelmä pietsosähköisten bulkrakenteiden upottamiseksi saumattomasti LTCC-rakenteisiin yhteissintrauksella tai liimaliitoksella. Erityistä huomiota on kiinnitetty monivaiheiseen laminointiin ja sintrauksen jälkeiseen pietsosähköisten keraamien polarisointiin. Työssä on esitetty esimerkkejä useista rakenteista pietsosähköisten sovellusten pääalueilta osoituksena uuden tekniikan onnistuneesta käyttöönottamisesta nykyisessä valmistusympäristössä. Tutkittujen uusien rakenteiden ja muilla menetelmillä valmistettujen rakenteiden ominaisuuksia on verrattu keskenään. Pietsosähköisten bulkrakenteiden integroiminen yhteissintrauksella on uusi tekniikka, joka mahdollistaa lukuisia sovelluksia ja soveltuu massatuotantoon olemassa olevilla prosseintilaitteistoilla

Multilayer functional tapes cofired at 450 °C:beyond HTCC and LTCC technologies

Abstract 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

3D printed dielectric ceramic without a sintering stage

Abstract 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

Electromechanical properties of PZT/P(VDF-TrFE) composite ink printed on a flexible organic substrate

Abstract The fabrication and electromechanical properties of composite inks consisting of 30–70 vol.% of piezoceramic PZT powder and piezoelectric co-polymer P(VDF-TrFE) are presented. Samples were stencil-printed on a commercial PET film and printable silver ink was used for the electrodes thus allowing a maximum process temperature of 130 °C. The relative permittivity at 1 kHz varied between 33 and 69 depending on poling and composite composition. The highest remanent polarization, up to 4.8 μC/cm², with 34 MV/m electric field and piezoelectric coefficient d₃₁ up to 17 pm/V, was obtained with a 50 vol.% PZT loading level. The mechanical and electrical results indicate that the developed composite ink enables fully printable and flexible sensor applications with an increased level of integration

Linearly polarized 64-element antenna array for mm-wave mobile backhaul application

Abstract The paper presents simulated and measured results of a large millimeter-wave antenna array, designed by keeping mind the particular interests for proof of concepts in 5G demonstrations in South-Korean Winter Olympics 2018. The array consist of 16 (2×8) unit cells, each having four (2×2) linearly polarized patch elements exited with the same amplitude and phase. The desired −10 dB impedance bandwidth for the array is from 25.65 GHz to 27.50 GHz, and the proposed structure achieves lower than −30 dB mutual coupling between the unit cells. The presented simulation and measurement results show good match with each other, as well as with the specifications. The radiation pattern is measured element by element at 27 GHz, and the results are summed in post-processing to perform the array factor. Sidelobe levels are 15 dB below the maximum gain, whereas the measured maximum gain is around 20 dB as the numerical results predicted 21.5 dB

Dual-polarized 2x2 element sub-array at 15 GHz with high port isolation

Abstract 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

SiC MOSFET soot sensor in a co-fired LTCC package

Abstract A novel method for soot detection based on SiC MOSFET devices with a dual suspended/ floating gate configuration in a co-fired LTCC package has been investigated. Response to different concentrations of soot was measured through the application of an electric field between the two gate electrodes to attract charged soot onto the sensor surface. Results are promising with application areas from automotive and transportation to air pollution control

Tape casting system for ULTCCs to fabricate multilayer and multimaterial 3D electronic packages with embedded electrodes

Abstract A 3D multilayer structure built by two ultra‐low temperature co‐fired ceramic (ULTCC) compositions with silver embedded electrodes are co‐fired at a temperature of 450°C. The 3D multilayer module is prepared by laminating the ULTCC green tapes with a new binder system, which organics can be completely burned out at temperature of 250°C before the sintering of the ULTCC 3D modulus. High‐density microstructures are achieved for the sintered module. In this study, the ULTCC feasible binder system is introduced. Also, ULTCC multilayers and multimaterial structures with surface and embedded silver electrodes are fabricated. This research opens up a new horizon for fabrication of electroceramic devices with embedded electrodes in multimaterial devices

Wide band frequency measurements of fungal species using laser patterned finger electrodes on LTCC

Abstract High frequency measurements at 50 MHz – 10 GHz were performed for the first time using interdigitated electrodes on a low temperature co-fired ceramic substrate to analyze fungal spores. Wet and dry spore generation methods were evaluated and tested with two different fungal species. The dry generation method was found feasible for RF measurements, since the component capacitance increased 14–21% in the 2–6 GHz range, but for the wet generation method the capacitance decreased only slightly (<1%). Based on these initial results the RF measurements have the capacity to evaluate the quantity of fungal spores but not to identify their species

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

Abstract 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