β-Ga2O3: ultralow-loss and low-permittivity dielectric ceramic for high-frequency packaging substrate

Abstract

As the core carrier of integrated circuits, packaging substrates usually respond in time to the evolution of electronic products. Among which, ceramic substrate materials are desired to have excellent dielectric and voltage-resistant properties, high reliability, and good thermal and chemical stability. The β-Ga₂O₃ ceramic prepared in this work has excellent microwave dielectric properties with a Q × f value of ∼133 140 GHz (Q = 1/tan δ), ε_r of ∼9.57, and temperature coefficient of resonant frequency (TCF) value of ∼−58.2 ppm °C⁻¹, which meet the requirements of high-frequency packages. Another highlight is that the β-Ga₂O₃ ceramic has a higher dielectric strength of ∼30 kV mm⁻¹ compared with conventional ceramic substrates, such as Al₂O₃, AlN, etc., allowing it to be used in higher-power circuits. Meanwhile, a flexural strength of ∼110 MPa, a thermal expansion of ∼+8.9 ppm °C⁻¹ and a thermal conductivity of ∼15 W m⁻¹ K⁻¹ have been achieved in the β-Ga₂O₃ ceramic. In addition, a patch antenna for sub-6 GHz applications was designed and fabricated using the Ga₂O₃ ceramic substrate, showing good performance with a wide bandwidth of ∼140 MHz, a return loss S₁₁ of ∼−21 dB at the center frequency, a radiation efficiency of ∼92% and a gain of ∼5 dBi. The stated results guarantee that the Ga₂O₃ ceramic shows great potential in applications towards high-frequency and high-power fields.