Improvement in Long-Term and High-Temperature Retention Stability of Ferroelectric Field-Effect Memory Transistors With Metal-Ferroelectric-Metal-Insulator-Semiconductor Gate-Stacks Using Al-Doped HfO2 Thin Films

Nonvolatile memory characteristics of the ferroelectric field-effect transistors (FeFETs) were investigated by introducing the metal-ferroelectric-metal-insulator-semiconductor (MFMIS) gate-stacks, employing Al-doped HfO 2 (Al:HfO 2 ) ferroelectric thin films. The obtained memory window (MW) of the MFMIS FETs increased from 1.0 to 2.8 V by increasing the areal ratios of the metal-insulator-semiconductor (MIS) to the metal-ferroelectric-metal (MFM) (S I /S F ) from 8 to 32. The device with an S I /S F ratio of 16 exhibited a 3-order-of-magnitude on/off memory margin even with a program pulse duration of 500 ns. The long-term data retention was also verified by improving the tolerance against the depolarization field by introducing the MFMIS gate-stacks, which can use fully saturated polarization. The temperature-dependent memory performance and operational reliabilities of the MFMIS-FETs were also investigated at high temperatures to exploit fully the thermal stability of the Al:HfO 2 . The obtained MWs were not markedly degraded for a retention time of 10 4 s from room temperature (RT) to 80 °C.