  We calculated the frequency dependent dielectric response (electric
susceptibility) of layered ferroelectric-dielectric junction, biased by the
time-dependent harmonic voltage with single frequency $\omega$. Working point
is stabilized, by the charge boundary condition between the layers, in the
region with negative electric capacitance. The static susceptibility $\chi_0$
is negative and relative dielectric constant $\epsilon_r$ smaller than one,
clearly indicating the opposite direction of electric field and polarization in
the ferroelectric layer due to the negative electric capacitance. At finite
frequencies this sign is preserved in real part of susceptibility which gains
the frequency dependence. Also, frequency dependent imaginary part arises due
to the phase shift between electric field and polarization. The type of that
frequency dependence in linear regime is so-called relaxation (Debye) response,
i.e. $\chi'(\omega)=\chi_0/(1+(\tau \omega)^2)$ and $\chi"(\omega)=\chi_0\tau
\omega/(1+(\tau \omega)^2)$, where $\tau$ is polarization switching time
characteristic to ferroelectric material. In particular, we modeled the
junction of ferroelectric BaTiO$_3$ and dielectric Al$_2$O$_3$, taking the
experimental values of material parameters, and addressed the role of
nonlinearity with respect to result of the linear response theory.
