Tuomo Siponkoski

Ferroelectric, pyroelectric, and piezoelectric properties of a photovoltaic perovskite oxide

A perovskite solid-solution, (1-x)KNbO3-xBaNi1/2Nb1/2O3-δ (KBNNO), has been found to exhibit tunable bandgaps in the visible light energy range, making it suitable for light absorption and conversion applications, e.g., solar energy harvesting and light sensing. Such a common ABO3–type perovskite structure, most widely used for ferroelectrics and piezoelectrics, enables the same solid-solution material to be used for the simultaneous harvesting or sensing of solar, kinetic, and thermal energies. In this letter, the ferroelectric, pyroelectric, and piezoelectric properties of KBNNO with x = 0.1 have been reported above room temperature. The investigation has also identified the optimal bandgap for visible light absorption. The stoichiometric composition and also a composition with potassium deficiency have been investigated, where the latter has shown more balanced properties. As a result, a remanent polarization of 3.4 μC/cm2, a pyroelectric coefficient of 26 μC/m2 K, piezoelectric coefficients d33 ≈ 23 p...

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.