Metal–ferroelectric–insulator–Si devices using HfTaO buffer layers

Metal–ferroelectric–insulator–Si (MFIS) diodes and transistors using Pt/Sr0.8Bi2.2Ta2O9 (SBT)/HfTaO/Si gate structures were fabricated. HfTaO films were deposited at room temperature by electron beam evaporation under a background vacuum of ~1.5 × 10−9 Torr. By process optimization of post-deposition annealing, a small effective oxide thickness of 1.6 nm, a small leakage current of 2.4 × 10−4 A cm−2 at a voltage shifted from the flat band voltage by 1 V and a negligible hysteresis loop were obtained for Al/HfTaO (4 nm)/Si diodes. The MFIS diodes were fabricated by the deposition of SBT films on the HfTaO (4 nm)/Si substrate using chemical solution deposition. A memory window of 0.62 V was obtained for Pt/SBT (300 nm)/HfTaO (4 nm)/Si diodes for a voltage sweep between +4 V and −4 V. P-channel ferroelectric-gate transistors were fabricated using the same gate structure, which showed a memory window of 0.6 V and good long-term retention characteristics. A drain current ON/OFF ratio as high as 103 was attained at a fixed reading voltage of −0.7 V even after over 104 s has elapsed.