This work presents a new method for the enhancement of
sensitivity
in Terahertz (THz) spectroscopy on metamaterial (MM) in terms of its
resonance frequency shift (ΔF), by attaching
the dielectric back plate to the MM’s silicon (Si) wafer. The
dielectric back plates are designed to minimize the Fresnel reflections
at the backside of the substrate, identical to a broadband antireflective
(AR) plate tailored for THz. Utilizing broadband AR technology, we
demonstrate the concept of decoupling MM resonance from the substrate’s
Fabry–Pérot (FP) oscillations. This is done by effectively
coupling the THz light out of the high-permittivity substrate, resulting
in the improved quality factor of the MM resonance and overall plasmonic
enhancement on the metasurface. The back plate acts as a surface plasmonic
enhancer to the THz MM by increasing the field intensity on the front
metasurface, leading to enhancement of dielectric response (MM’s
ΔF). This makes the MM resonance ultrasensitive
to the minor changes of particle size/concentration under test spread
on the metasurface, contributing to enhanced resonance ΔF. The plate also makes the Si substrate optically lossless,
enabling the full effect of MM resonance shift and increasing the
resonance ΔF by 8-fold compared with MM’s
fabricated on conventional Si substrates. This research is backed-up
with system-level CST simulations and experimental THz impedance spectroscopy
of the MM. This method and chip structure is CMOS compatible having
potential applications for any resonant MM fabricated on a substrate
aimed to maximize dielectric sensitivity for biosensing and nanoparticle
THz spectroscopy.