One typical characteristic of conventional all-dielectric terahertz metamaterials is their thickness, which is designed to be dozens of, or even one hundred microns, to reduce the leakage of the resonant field to the substrate. In the frequency range of 2 THz to 3 THz, we propose a substrate-free ultra-thin all-dielectric terahertz metamaterial (UATM) composed of a silicon (Si) dual-ellipse array and silicon dioxide (SiO2) supporting layer with thicknesses of 5 μm and 2 μm, respectively. The UATM exhibits quasi-bound state in the continuum (quasi-BIC) modes related to the tilt angle and period parameters. Moreover, due to the strong electromagnetic field near the interfaces and large interaction area, the UATM exhibits a high refractive index sensitivity exceeding 1.00 THz per RIU. Furthermore, at oblique incident angles ranging from 0° to 25°, the resonant quality factor (Q-factor) of the UATM remains higher than 100, and the sensitivities to the incident angle are 22.53 and 26.17 GHz per degree with a linear range of 0.498 THz and 0.438 THz, respectively. These properties indicate the potential applications of the UATM in high sensitivity biochemical sensing and multifunctional narrowband filtering fields.
