Ferroelectric $PbTiO_3$ thin film is deposited with rf sputtering at substrate temperature of $100-150^{circ}C$. It is found that this has pyrochlore structure of amorphous type by X-ray diffractive analysis. Thermal annealing has excellent characteristics at $550^{circ}C$ and laser annealing has best crystalline structure in case of scanning with 50 watts. Interface states in MFST and MFOST structure with a $PbTiO_3$ ferroelectric thin film gate have been investigated from analysis of C-V data. The interface states density has been drastically reduced by inserting an oxide layer between ferroelectric and semiconductor. The observed effect increase feasibility of employing ferroelectric thin films such as nonvolatile memory field effect transistor, IR optical FET, and Image Devices with a ferroelectric layer.