Figure 3.

Typical I-V characteristics with different voltage sweeping sequences measured at two pristine cells on the MIM structures with Ti fluence of 5 × 10¹⁵ cm⁻² (a), 1 × 10¹⁶ cm⁻² (b), and 5 × 10¹⁶ cm⁻² (c).The insets show the I-V characteristics with the same voltage sweeping sequences but different maximum voltage measured at the same cell on the MIM structures. Note that to avoid a hard breakdown of the devices, the maximum current was limited to be 100 μA. The sets of the maximum voltages are [8.0 V, 9.0 V, 10.0 V], [8.0 V, 8.5 V, 9.0 V] and [6.0 V, 7.0 V, 8.0 V] for the MIM structures with Ti fluence of 5 × 10¹⁵ cm⁻², 1 × 10¹⁶ cm⁻², and 5 × 10¹⁶ cm⁻², respectively. The numbers (1)–(4) and the arrows indicate the voltage sweeping sequences and the voltage sweeping directions, respectively.