High-resistance-state tunneling in 25 nm TiOx/Y-doped HfO2/Pt nanocrossbar ferroelectric tunnel junctions.

We report nanocrossbar-type ferroelectric tunnel junctions (FTJs) with a Ti/TiOx/7% yttrium-doped HfO2 (YHO7)/Pt structure integrated on thermally oxidized Si substrates, which exhibit clear direct tunneling conduction even in the high-resistance state (HRS) and a tunneling electroresistance ratio exceeding 103. The nanocrossbar FTJs were fabricated using a double-exposure electron-beam lithography (EBL) process with lateral dimensions scaled down to 25 nm. The temperature dependence of the TER effect measured at 9 and 300 K confirms that both low- and high-resistance states are dominated by the direct tunneling conduction. A maximum TER ratio of 2.2 × 103 was obtained in a 3 nm-thick YHO7 nanocrossbar FTJ with an effective area of 26 × 24 nm2. The FTJ area was reduced from 42 000 to 255 nm2, and the scaling behavior of the TER effect in 3 nm-thick YHO7 devices closely resembles that in 2 nm-thick devices. The OFF-state current decreased with a slope of 1.1 between 42 000 and 2600 nm2, followed by a steeper reduction below 2600 nm2, whereas the ON-state current decreased more gradually with a slope of 0.30. These contrasting area dependences are attributed to the suppression of leakage pathways along grain boundaries in the OFF state and to uniformly aligned remanent polarization within a limited number of grains in the ON state. The demonstrated nanocrossbar FTJs highlight a promising route toward high-density, energy-efficient, and CMOS-compatible integration of ferroelectric memory.