As the communications industry continues to develop, low temperature co-fired ceramics are used as resonators in multilayer chip components of integrated circuits. In order to co-fire with the metal, it is necessary to reduce the sintering temperature of ceramics to below 960 °C. In order to rule out the impact of changes in the operating temperature of the ceramic material, we need to adjust the resonant frequency temperature coefficient to near zero. This paper discusses the application of a temperature-stable low-temperature sintered dielectric material derived from Li 2 ZnSiO 4 (LZS) in low-temperature co-fired ceramics (LTCC). The addition of the low melting point oxide Bi 2 O 3 resulted in a significant reduction of the sintering temperature and improvement of the densification of LZS ceramics, where the sintering temperature was reduced from 1200 °C to 900 °C. The relative density and microwave dielectric properties (dielectric constant ε r , quality factor Q × f and temperature coefficient of resonant frequency τ ƒ ) of LZS- x Bi 2 O 3 ( x = 0, 3, 6, 9, 12 mol%) ceramics sintered at different temperatures increase and then decrease with increasing Bi 2 O 3 content. The best performance was obtained when the Bi 2 O 3 addition was 9 mol% (ε r = 6.87, Q × f = 28,151 GHz, τ ƒ = - 85.2 ppm/°C). By increasing the amount of TiO 2 added to LZS-9 mol%Bi 2 O 3 , the τ ƒ value of the ceramic system can be continuously increased, which is effectively adjusted to near zero. The best integrated dielectric properties of the LZS-Bi 2 O 3 -TiO 2 ceramic system (ε r = 8.9, Q × f = 22.982 GHz, τ ƒ = - 8.34 ppm/°C) are obtained when the TiO 2 addition is 30 wt%. This suggests that LZS-Bi 2 O 3 -TiO 2 ceramics have potential for low-temperature co-fired ceramics (LTCC) applications.
Photothermal sensing is crucial for the creation of smart wearable devices. However, the discovery of luminescent materials with suitable dual-wavelength emissions is a great challenge for the construction of stable wearable optical fibre temperature sensors. Benefiting from the Mn 2+ -Mn 2+ superexchange interactions, a dual-wavelength (530/650 nm)-emitting material Li 2 ZnSiO 4 :Mn 2+ is presented via simple increasing the Mn 2+ concentration, wherein the two emission bands have different temperature-dependent emission behaviours, but exhibit quite similar excitation spectra. Density functional theory calculations, coupled with extended X-ray absorption fine structure and electron-diffraction analyses reveal the origins of the two emission bands in this material. A wearable optical temperature sensor is fabricated by incorporating Li 2 ZnSiO 4 :Mn 2+ in stretchable elastomer-based optical fibres, which can provide thermal-sensitive emissions at dual- wavelengths for stable ratiometric temperature sensing with good precision and repeatability. More importantly, a wearable mask integrated with this stretchable fibre sensor is demonstrated for the detection of physiological thermal changes, showing great potential for use as a wearable health monitor. This study also provides a framework for creating transition-metal-activated luminescence materials.
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