  We report a tunable optical filter based on phase change material
$Ge_{2}Sb_{2}Te_{5}$ embedded in a silicon microring resonator. The high
thermo-optic coefficient of $Ge_{2}Sb_{2}Te_{5}$ in amorphous phase enables
tuning of resonance wavelength in broad range with a very small active volume.
The low-loss indium-tin-oxide electrodes are employed to induce Joule heating
in $Ge_{2}Sb_{2}Te_{5}$-Si active waveguide region. The electrically induced
heating in the active region alters the effective refractive index of hybrid
microring resulting in a wavelength tuning of 1.04 nm for an applied voltage of
only 3V. The device exhibits high extinction ratios in the range of 20-41 dB
and a compact active footprint 0.96 $\mu m^{2}$ only and is suitable for the
large scale reconfigurable integrated photonic circuits.
