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采用磁控溅射制备了沿
$\langle100\rangle $ 晶向择优生长的NiO x薄膜, 并与多晶HfO 2薄膜组装成HfO 2/NiO x/HfO 2堆栈器件, 研究其电阻开关特性和导电机制. 微结构分析表明, NiO x薄膜主要成分为NiO和Ni 2O 3, 薄膜整体富含氧空位. HfO 2/NiO x/HfO 2堆栈器件初期呈现两电阻态的双极性电阻开关特性, 高低电阻比约为10 5; 但中后期逐步演变为具有“两级置位过程”的三电阻态开关特性. 器件循环耐受性大于3×10 3个周期, 数据持久性接近10 4s. 器件高低电阻态满足欧姆导电机制, 而中间电阻态遵循空间电荷限制电流导电机制. NiO x薄膜中的氧空位导电细丝和上层HfO 2薄膜中的空间电荷限制电流共同作用使得HfO 2/NiO x/HfO 2堆栈器件表现出稳定的三电阻态开关特性, 有望应用于多级非易失性存储器和类脑神经突触元件.-
关键词:
- HfO2/NiOx/HfO2堆栈/
- 三电阻态/
- 两级置位
With the extensive integration of portable computers and smartphones with “Internet of Things” technology, further miniaturization, high reading/writing speed and big storage capacity are required for the new-generation non-volatile memory devices. Compared with traditional charge memory and magnetoresistive memory, resistive random access memory (RRAM) based on transition metal oxides is one of the promising candidates due to its low power consumption, small footprint, high stack ability, fast switching speed and multi-level storage capacity. Inspired by the excellent resistive switching characteristics of NiO and HfO 2, NiO xfilms are deposited by magnetron sputtering on the Pt $\langle111\rangle $ layer and the polycrystalline HfO 2film, respectively. Their microstructures, resistive switching characteristics and conductive mechanisms are studied. X-ray diffractometer data show the$\langle111\rangle $ preferred orientation for the NiO xfilm deposited on the Pt$\langle111\rangle $ layer but the$\langle100\rangle $ preferred one for the film deposited on the polycrystalline HfO 2layer. X-ray photoelectron depth profile of Ni 2p core level reveals that the NiO xfilm is the mixture of oxygen-deficient NiO and Ni 2O 3. NiO x(111) films show bipolar resistive switching (RS) characteristics with a clockwise current-voltage ( I-V) loop, but its ratio of the high resistance to the low resistance ( R H/ R L) is only ~10, and its endurance is also poor. The NiO x(200)/HfO 2stack exhibits bipolar RS characteristics with a counterclockwise I-Vloop. The R H/ R Lis greater than 10 4, the endurance is about 10 4cycles, and the retention time exceeds 10 4s. In the initial stage, the HfO 2/NiO x(200)/HfO 2stack shows similar bi-level RS characteristics to the NiO x(200)/HfO 2stack. However, in the middle and the last stages, its I-Vcurves gradually evolve into tri-level RS characteristics with a “two-step Setting process” in the positive voltage region, showing potential applications in multilevel nonvolatile memory devices and brain-like neural synapses. Its I-Vcurves in the high and the low resistance state follow the relationship of ohmic conduction ($ I \propto V $ ), while the I-Vcurves in the intermediate resistance state are dominated by the space-charge-limited-current mechanism ($ I \propto V^2 $ ). The tri-level RS phenomena are attributed to the coexistence of the oxygen-vacancy conductive filaments in the NiO x(200) film and the space charge limited current in the upper HfO 2film.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] -
成分 溅射源
(99.99％纯度)生长气氛
流量(比)衬底
温度/℃溅射方式
功率/W, 偏压/V生长
时间/min退火气氛
流量(比)退火
温度/℃退火
时间/minPt金属层 Pt金属靶 2.7 Pa Ar+O2
Ar∶O2= 17∶3700 直流
25, 05 — — — HfO2薄膜 HfO2陶瓷靶 3 Pa Ar
30 sccm350 射频
70, 020 3 Pa O2
30 sccm350 30 NiOx薄膜 Ni金属靶 0.5 Pa Ar+O2
Ar∶O2= 4∶1700 射频
60, 090 0.5 Pa Ar+O2
Ar∶O2= 4∶1700 30 Ag电极 Ag金属靶 0.5 Pa Ar
30 sccm250 直流
25, –10010 — — — 注: sccm为cm3/min. 
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Cell structure Switching type VSet/V VReset/V RH/RL Endurance Retention/s Ref. NiFe/Al2O3/NiO/Pt Unipolar 2.30—4.20 0.55—1.50 ～1×103 >1×102 1×104 [6] Pt/IrO2/NiO/IrO2/Pt Unipolar 1.43 0.41 > 1×102 2×102 — [19] Ag/HfO2/NiO/Pt Bipolar 0.20 –0.20 > 1×103 > 5×103 > 1×103 [20] Pt/NiO/Mg0.6Zn0.4O/Pt Rectifying — 0.54—0.62 ～1×106 1×102 6×104 [21] Au/BaTiO3/NiO/Pt Unipolar 2.00 1.00 — — — [22] Ag/HfO2/nb-NiO/Pt Bipolar 0.16—0.38 –0.19— –0.38 ～1×104 1.2×103 >1×104 [28] Pt/BiFeO3/NiO/Pt Bipolar 1.00—1.50 –0.20— –0.60 > 10 30 — [33] Ag/NiOx/HfO2/Pt Bipolar 0.12—0.18 –0.02— –0.17 > 1×104 ～1×104 > 1×104 Reference cell Ag/HfO2/NiOx/HfO2/Pt Bipolar Set1: 0.13—0.17 –0.03— –0.17 ～1×105 > 3×103 ～1×104 This work Set2: 0.21—0.40 ～1×102 下载:
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