HfO₂–ZrO₂ Superlattice HZO Ultrathin Poly-Si Channel (3.5 nm) Junctionless FeTFTs Exhibiting Superior Endurance and Robust Retention

Abstract

In this study, HfO2–ZrO2 superlattice (SL) HfZrO2 (HZO) 3.5-nm ultrathin poly-Si channel (UTPC) junctionless (JL) ferroelectric thin-film transistors (FeTFTs) with the two types of HfO2/ZrO2 nanolamination (NL) thicknesses (0.5 and 1.0 nm) and a 1.0-nm ZrO2 seed layer were experimentally investigated and discussed their ferroelectricity and reliability for the first time. Compared with the conventional HZO UTPC JL FeTFTs, the SL HZO UTPC JL FeTFTs with a HfO2 and ZrO2 NL thickness of 1 nm achieved a relatively large pristine/residual pulsed memory window (MW) up to 1.09/1.06 V under a very low pulse height $\times $ pulse width down to $0.8~\mu $ Vs and nearly zero MW degradation rate ( $\Delta $ MW/MW $_{,\text {pristine}}$ ) down to 2.8% after the endurance test up to $10^{{7}}$ cycles. Furthermore, the SL HZO UTPC JL FeTFTs with an NL thickness of 1 nm exhibited a robust 10/298/423 K retention characteristic for 25 h with a sufficiently large pulsed MW of 1.30/1.38/0.65 V, and the synaptic behavior with a maximum channel conductance over 1400 nS. According to pulsed characteristic and reliability viewpoints, the HfO2–ZrO2 SL HZO UTPC JL FeTFTs are greatly promising candidates for 3-D nand nonvolatile memories (NVMs) and neuromorphic systems.