Structure and microwave dielectric characteristics of Hf_1‐xTi_xO₂ ceramics

Abstract

Hf 1-x Ti x O 2 dense ceramics were prepared by a standard solid-state reaction process, and the microwave dielectric properties in a wide frequency range were determined together with structure evolution. With increasing x, the structure gradually changed from HfO 2 -based solid solution (monoclinic in space group P2 1 /c, x ≤ 0.05) to HfTiO 4 (orthorhombic in space group Pbcn, x = 0.5), and the two phase regions were determined for 0.1 ≤x < 0.5 and x = 0.55. The microwave dielectric properties of HfO 2 ceramics at 10 GHz were determined as ε r = 14, Qf = 24 500 GHz, τ f = -50 ppm/°C. With Ti-substitution, the microwave dielectric characteristics, especially the Qf value, could be significantly improved, and the best combination of microwave dielectric characteristics was achieved at x = 0.05: ε r = 17, Qf = 84 020 GHz (at 7.8 GHz) and 151 260 GHz (at 27.9 GHz), and τ f = -47 ppm/°C. The smallest temperature coefficient of resonance frequency (τ f = -4.8 ppm/°C) was obtained for x = 0.55 together with a Qf value of 52 370 GHz at 5.0 GHz and 60 390 GHz at 17.9 GHz, where the dielectric constant was 40. Moreover, Hf 1-x Ti x O 2 microwave dielectric ceramics might be very competitive in the future of mobile communication technology due to their excellent compatibility with Si.

(Ni1/3Nb2/3)4+-Improved High-K Ba3Ti4Nb4O21 Microwave Dielectric Ceramics for Miniaturized All-Ceramic Radomes with 5G Beam-Splitting Function

“…With the increase of (Ni 1/3 Nb 2/3 ) 4+ substitution (0.03 ≤ x ≤ 0.15), the bulk densities at all temperatures reach the maximum value at x = 0.09 (4.748 g/cm 3 ∼ 1190 °C, 4.992 g/cm 3 ∼ 1250 °C, and 4.952 g/cm 3 ∼ 1310 °C). Calculations based on eqs S1 and S2 , show that the relative densities also reach their highest values at x = 0.09 (90.9% ∼ 1190 °C, 95.6% ∼ 1250 °C, and 94.8% ∼ 1310 °C). These phenomena indicate that the internal structure of the BTN ∼ NN ceramics is densest at x = 0.09 (4.992 g/cm 3 , 94.88% ∼ 1250 °C).…”

Improvement of τf in HfTiO4 microwave dielectric ceramics with Zr‐ and Sn‐substitution

“…[1][2][3] As an important promising material in electronic devices, HfO 2 has received the increasing scientific attention due to its interesting physicochemical properties, such as the good thermal stability, suitable dielectric constant, good compatibility with Si, as well as unique ferroelectricity in HfO 2 -based thin films. [4][5][6][7] Moreover, the excellent microwave dielectric characteristics in HfO 2 -TiO 2 ceram-ics have been reported, where the superior microwave dielectric characteristic of Hf 1-x Ti x O 2 was reported for x = 0.5 (HfTiO 4 ): ε r = 37, Qf = 53,600 GHz at 6.0 GHz and τ f = −28 ppm/ • C. 8 The important issue remained in this composition is that the temperature coefficient of resonant frequency τ f needs to be modified into near-zero without apparent damage in Q value and ε r .…”

Structure evolution and adjustment of τf in (Ba, Sr)HfO3 and (Sr, Ca)HfO3 microwave dielectric ceramics

“…As the key materials for resonators and filters, microwave dielectric ceramics are required to possess an appropriate dielectric constant ε r to balance smaller device size and working frequency, high-quality factor Q to obtain excellent frequency selectivity and near-zero temperature coefficient of resonant frequency τ f to ensure the temperature stability. [1][2][3] Although a number of microwave dielectric ceramics have been developed, [4][5][6] pursuing the optimum combination of these three parameters is still a big challenge. Generally, tuning and improving the Q value and τ f are considered to be the crucial task for obtaining the microwave dielectric ceramics with a specific ε r .…”