(a) Fabrication process flow of the three types of Ti/HfO2/Pt devices. Type A is the pure HfO2 device, type B is the Al layer doped device and type C is the Al local doped device. (b) The surface AFM image shows that the as-prepared film is polycrystalline HfO2 with the grain size ∼40 nm and the surface roughness ∼7 nm.
(a) Schematics of the device structure of the three types. (b)-(c) The different switching characteristics under DC sweep mode of the undoped, Al layer doped, and Al local doped HfO2 devices, respectively. The current compliance keeps at 0.5 mA in set process to avoid a hard breakdown.
(a) The cycle-to-cycle distributions of HRS/LRS resistance of the three devices. (b) The cycle-to-cycle distributions of Vset and (c) Vreset of the three devices. (d) The average forming voltage and largest reset current of the three devices. The Al local doped device demonstrates a lower forming voltage and reduced reset current.
The cycle-to-cycle uniformity of the multiple states in one device (50cycles for each parameter). (a) The multiple LRS is controlled by the set current compliance. The LRS resistance decreases with the enhanced set current. The reset voltage keeps at −3 V. (b) The multiple HRS obtained by modulating the maximal reset volatege. The HRS increases with the larger Vmax . The set current compliance keeps at −2 mA.
(a) The endurance and uniformity properties of the undoped HfO2 device operated by +2.5 V/−2.5 V 5 μs pulses. (a) The endurance and uniformity properties of the Al local doped HfO2 device operated by +2.5 V/−2 V 5 μs pulses. The read pulses of +0.1 V are applied during the switching cycles to measure the HRS and LRS resistance. (c) Four multiple states achieved by different reset pulses. The retention time of each state is larger than 5 × 104 s.
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