Device reliability issues originating from Interface traps or Bias Temperature Instability (BTI), has been of great concern in emerging devices like Negative Capacitance (NC) FinFET, GAA-FET etc. Exploration of interface trap study at the different interfaces of such 3-dimensional devices, is of much importance to predict the reliability of the device behaviour. In the proposed analysis, for the first time, we have demonstrated the individual and the overall impact of trap densities at the various practical interfaces present in the gate and spacer stack of the Ferroelectric (FE)-Dielectric (DE) spacer NC-FinFET. The trap states in the proposed device alters the polarization dynamics and improves sub-threshold characteristics especially the off-state current (IOFF) thus, revealing excellent short channel characteristics. We have further evaluated the degree of performance degradation occurring due to interface traps, by means of optimized capacitance matching (FE parameters), hysteretic window, output transconductance (gds) and voltage gain (AV) etc. Furthermore, we have also studied the impact of trap states on the mixed-mode characteristics of the spacer based NC-FinFET Inverter design.