Characteristics of Au/SBT/LZO/Si MFIS structure forferroelectric-gate field-effect transistors

Non-volatile memories using ferroelectric-gate field-effect transistors (Fe-FETs) with metal/ferroelectric/semiconductor gate stack (MFS-FETs) have superior advantages such as non-destructive read operation and high density. However, the interfacial reactions between ferroelectric materials and Si substrates make it difficult to obtain good electrical properties of MFS-FETs. As an alternative solution, Fe-FETs with a metal/ferroelectric/insulator/ insulator/semiconductor gate stack (MFIS-FETs) have been proposed. We prepared SrBi₂Ta₂O₉ (SBT) film as a ferroelectric layer and LaZrO_x (LZO) film as the insulating buffer layer, and then fabricated the n-channel Fe-FETs with the Au/SBT/LZO/Si structure. The thickness of the LZO buffer layer and SBT film deposited by a sol-gel method were about 35 nm and 450 nm, respectively. From the electrical properties of the LZO film on Si, no hysteresis was observed in the C-V curve and the leakage current density was about 1.4 × 10^-7 A/cm² at 5 V. SBT film on the LZO/Si structure was crystallized in a polycrystalline phase with a highly preferred (115) orientation. The C-V characteristics of Au/SBT/LZO/Si structure showed a clockwise hysteresis loop and the memory window width increased as the bias voltage increased. The fabricated Fe-FETs showed typical n-channel MFIS-FETs C-V characteristics and the current on/off ratio was about 10₃ Also, the memory window width was about 0.7 V.