In this paper, for the first time, we clarified the multidomain dynamics of ferroelectric polarization in the Negative Capacitance Field-Effect Transistors (NCFETs) by an in-house Technology Computer-Aided Design (TCAD) module. It enables self-consistent simulations among the time-dependent Landau-Khalatnikov equation and the other equations that govern operation of FETs. Our simulation reveals that domain-wall thickness T dw, which reflects a correlation strength between domains predominates coherency of the NC polarization. In a strong correlation (large T dw) case, a coherent NC polarization is realized at least to a degree of T dw. On the other hand, in a weak correlation (small T dw) case, perturbation from peripherals easily leads to incoherence of polarization, where a uniform polarization is split into multiple spontaneous polarization domains. This coherency breaking found to give rise to deteriorated voltage amplification of NC. Design methodology to maintain the NC coherency is also proposed.