A FORMing-Free HfO₂-/HfON-Based Resistive-Gate Metal-Oxide-Semiconductor Field-Effect-Transistor (RG-MOSFET) Nonvolatile Memory with 3-Bit-Per-Cell Storage Capability

We present a nonvolatile resistive-gate metal-oxide-semiconductor-field-effect transistor (RG-MOSFET). An RG-MOSFET comprises a MOSFET and dielectric layers sandwiched between the top and bottom electrode metal-dielectric-metal (MDM). The gate of the MOSFET is electrically connected to the bottom electrode of MDM in series. Dielectric layers of MDM are composed of a resistance-switching layer made by hafnium oxynitride (HfON) and a resistance-nonswitching layer by hafnium dioxide (HfO2). RG-MOSFET as a memory can be achieved by resistance changes in the HfON. Eight distinguishable resistance values can be programmed randomly, which is performed as a 3 bit per cell through the edge Fowler-Nordheim (FN) mechanism between the top electrode metal and the drain of RG-MOSFET. The external voltage applied to the top electrode is divided by the MDM and the gate dielectric, and the threshold voltage ( ${V}_{\text {th}}$ ) of an RG-MOSFET is modulated by different resistance values of MDM. Therefore, states stored in MDM can be read out from the drain-current level of an RG-MOSFET. FORMing-free characteristic of MDM is required for bipolar operation. A ratio of drain current between the high-resistance state (HRS) and the low-resistance state (LRS) is $10^{{5}}$. Gradual SET/RESET is executed to tune the drain current by pulse operations; $10^{{5}}$ endurance cycles of RG-MOSFETs are demonstrated, and a retention test can be passed for more than ${5} \times 10^{{6}}$ (35 days) at 125 °C.