  Among the various kinds of spin defects in hBN, the negatively charged boron
vacancy ($\rm V_B^-$) spin defect that can be deterministically generated is
undoubtedly a potential candidate for quantum sensing, but its low quantum
efficiency restricts its %use in practical applications. Here, we demonstrate a
robust enhancement structure with advantages including easy on-chip
integration, convenient processing, low cost and suitable broad-spectrum
enhancement for $\rm V_B^-$ defects. %Improved photoluminescence (PL) intensity
and optically detected magnetic resonance (ODMR) contrast of $\rm V_B^-$ defect
arrays. In the experiment, we used a metal reflective layer under the hBN
flakes, filled with a transition dielectric layer in the middle, and adjusted
the thickness of the dielectric layer to achieve the best coupling between the
reflective dielectric cavity and the hBN spin defect. Using a reflective
dielectric cavity, we achieved a PL enhancement of approximately 7-fold, and
the corresponding ODMR contrast achieved 18\%. Additionally, the oxide layer of
the reflective dielectric cavity can be used as an integrated material for
micro-nano photonic devices for secondary processing, which means that it can
be combined with other enhancement structures to achieve stronger enhancement.
This work has guiding significance for realizing the on-chip integration of
spin defects in two-dimensional materials.
