Fabrication of Polycrystalline Ferroelectric Gate FET Memory with an Intermediate Electrode

We fabricated a new ferroelectric gate field-effect transistor memory (F-FET) with an intermediate electrode inserted between the ferroelectric capacitor (C_f) and the metal-oxide-semiconductor field-effect transistor (MOSFET) for writing data. The structure was a RuO₂ top electrode/polycrystalline ferroelectric Pb(Zr_0.52Ti_0.48)O₃ (PZT)/(Pt/RuO₂) intermediate electrode/SiO₂/Si substrate. The basic operation of the new memory was confirmed by a discrete circuit that the Cf was connected serially with the MOSFET. For data writing, two positive or negative square pulses applied between the top electrode and the intermediate electrode induced the positive (Pr⁺) and the negative (Pr^-) remanent polarizations, respectively, for coding memory states. For data reading, an unipolar square pulse train was applied between the top electrode and the source of the MOSFET, and the drain of the MOSFET was biased by a DC voltage. When the memory state corresponded to the Pr⁺ or the P^-, the drain current (I_D) was small or large, respectively. In this study, we used a polycrystalline PZT film to deal with the difficult problems of an epitaxial PZT film such as complicated techniques and high cost of products for commercialization goal.