Low-Permittivity and Low-Temperature Cofired BaSO4-BaF2 Microwave Dielectric Ceramics for High-Reliability Packaged Electronics.

In developing low-temperature cofired ceramic (LTCC) technology for high-density packaging or advanced packaged electronics, matching the coefficient of thermal expansion (CTE) among the packaged components is a critical challenge to improve reliability. The CTEs of solders and organic laminates are usually larger than 16.0 ppm of °C1-, while most low-permittivity (εr) dielectric ceramics have CTEs of less than 10.0 ppm °C1-. Therefore, a good CTE match between organic laminates and dielectric ceramics is required for further LTCC applications. In this paper, we propose a high-CTE BaSO4-BaF2 LTCC as a potential solution for high-reliability packaged electronics. The BaSO4-BaF2 ceramics have the advantages of a wide low-temperature sintering range (650-850 °C), low loss, temperature stability, and Ag compatibility, ensuring excellent performance in LTCC technology. The 95 wt %BaSO4-5 wt %BaF2 ceramic has a εr of 9.1, a Q × f of 40,100 GHz @11.03 GHz (Q = 1/tan δ), a temperature coefficient of the resonant frequency of -11.2 ppm °C1-, a CTE of +21.8 ppm °C1-, and a thermal conductivity of 1.3 W mK-1 when sintered at 750 °C. Furthermore, a dielectric resonant antenna using BaSO4-BaF2 ceramics, a typically packaged component of LTCC and laminate, was designed and used to verify the excellent performance by a gain of 6.0 dBi at a central frequency of 8.97 GHz and a high radiation efficiency of 90% over a bandwidth of 760 MHz. Good match and low thermal stress were found in the packaged components of BaSO4-BaF2 ceramics, organic laminates, and Sn-based solders by finite element analysis, proving the potential of this LTCC for high-reliability packaged electronics.

Novel Method to Achieve Temperature-Stable Microwave Dielectric Ceramics: A Case in the Fergusonite-Structured NdNbO4 System.

Microwave dielectric ceramics with permittivity (εr) ∼ 20 play an important role in massive multiple-input multiple-output (MIMO) technology in 5G. Although fergusonite-structured materials with low dielectric loss are good candidates for 5G application, tuning the temperature coefficient of resonant frequency (TCF) remains a problem. In the present work, smaller V5+ ions (rV = 0.355 Å, with coordination number (CN) = 4) were substituted for Nb5+ (rNb = 0.48 Å with CN = 4) in the Nd(Nb1-xVx)O4 ceramics, which, according to in situ X-ray diffraction data, lowered the fergusonite-to-scheelite phase transition (TF-S) to 400 °C for x = 0.2. The thermal expansion coefficient (αL) of the high-temperature scheelite phase was +11 ppm/°C, whereas for the low-temperature fergusonite phase, it was + 14 < αL < + 15 ppm/°C. The abrupt change in αL, the associated negative temperature coefficient of permittivity (τε), and the minimum value of εr at TF-S resulted in a near-zero TCF ∼ (+7.8 ppm/°C) for Nd(Nb0.8V0.2)O4 (εr ∼ 18.6 and Qf ∼ 70,100 GHz). A method to design near-zero TCF compositions based on modulation of τε and αL at TF-S is thus demonstrated that may also be extended to other fergusonite systems.

ARPP-19 Mediates Herceptin Resistance via Regulation of CD44 in Gastric Cancer.

PURPOSE: As the first-line drug for treatment of HER2-positive metastatic gastric cancer (GC), Herceptin exhibits significant therapeutic efficacy. However, acquired resistance of Herceptin limits the therapeutic benefit of gastric cancer patients, in which the molecular mechanisms remain to be further determined. METHODS: Quantitative real-time polymerase chain reaction was performed to detect the mRNA levels of ARPP-19 and CD44 in GC cells. Protein levels were determined using Western blot and IHC staining. MTT and soft agar colony formation assays were used to measure cell proliferation. Xenograft model was established to verify the functional role of ARPP-19 in Herceptin resistance in vivo. Sphere formation assay was conducted to determine cell stemness. RESULTS: We observed ARPP-19 was up-regulated in Herceptin resistance gastric cancer cells NCI-N87-HR and MKN45-HR. The forced expression of ARPP-19 promoted, whereas the silencing of ARPP-19 impaired Herceptin resistance of HER2-positive gastric cancer cells both in vitro and in vivo. Moreover, ARPP-19 significantly enhanced the sphere formation capacity and CD44 expression, CD44 was also a positive factor of Herceptin resistance in HER2-positive gastric cancer cells. In addition, high level of ARPP-19 was positively associated with Herceptin resistance and poor survival rate of gastric cancer patients. CONCLUSION: We have demonstrated that ARPP-19 promoted Herceptin resistance of gastric cancer via up-regulation of CD44, our study suggested that ARPP-19 could be a potential diagnostic and therapeutic candidate for HER2-positive gastric cancer.