This study investigates the effects of ferroelectric thickness scaling in a bilayer-structured ferroelectric tunnel junction. It was found that both the remnant polarization and the transport mechanisms exhibit a correlation with the thickness of the ferroelectric film. While variations in ferroelectric thickness influence the tunneling current in the Off state, the magnitude of the remnant polarization significantly affects the current during the On state. Considering that the On-Off ratio serves as an important figure of merit, an analysis of the optimal memory window is provided, accounting for the impact of reading voltage and cycling conditions. Moreover, investigation of the polarization decay observed at different delay times after the writing reveals the direct correlation between the depolarization field and thickness scaling. Retention studies further indicate that tunneling current decay induced greater vulnerability to the On state, primarily attributed to the asymmetry of the stack structure, which results in imperfect screening of polarization charges. Our investigation into the scaling of ferroelectric thickness emphasizes its critical importance by examining both ferroelectric properties and device performance. These findings indicate that the optimization of FTJ for low operation voltage, long data retention, and high on-current density necessitates a coordinated optimization of the layer stack structure, establishing a direct relationship crucial for the future development of hafnia-based FTJ devices.