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Effects of Vanadium Doping on Resistive Switching Characteristics and Mechanisms of SrZrO3-Based Memory Films
(2010-08-01)
Lin, Meng-Han
;
Wu, Ming-Chi
;
Lin, Chen-Hsi
;
Tseng, Tseung-Yuen
;
電子工程學系及電子研究所
The effects of vanadium doping on resistive switching (RS) characteristics and mechanisms of RF-sputtered SrZrO3 (SZO)-based thin films are investigated in this paper. The physical and electrical properties of SZO-based thin films are modulated by vanadium doping due to the Zr4+ ion replaced by V5+, further affecting the RS parameters of SZO-based thin films. The conduction mechanisms of SZO-based thin films are dominated by ohmic conduction (hoping conduction) and Frenkel-Poole emission for the low resistance state (LRS) and the high resistance state (HRS), respectively. The turn-on process might be attributed to the formation of conducting filaments consisting of oxygen vacancies with the effective barrier height (phi(B,eff)) in the range of 0.10-0.13 eV, whereas the turn-off process might result from thermally assisted oxidation of oxygen vacancies by the Joule heating effect. Furthermore, the introduction of the high valence cation (V5+) in a Zr4+ site of SZO crystalline structure can suppress the formation of oxygen vacancies due to the charge neutrality restriction. Such suppression leads to the changes in the forming voltage, turn-on voltage, HRS resistance, dielectric constant, and phi(B,eff) with vanadium doping concentration up to 0.2 mol%, which is within the solid solubility limit based on our measured lattice constants and Vegard's law.
High Device Yield of Resistive Switching Characteristics in Oxygen-Annealed SrZrO3 Memory Devices
(2011-04-01)
Lin, Meng-Han
;
Wu, Ming-Chi
;
Huang, Yi-Han
;
Lin, Chen-Hsi
;
Tseng, Tseung-Yuen
This paper reports the effects of rapid thermal annealing (RTA) on resistive switching (RS) characteristics and mechanisms of SrZrO3 (SZO)-based memory devices. SZO thin films were deposited on LaNiO3 (LNO) (100)/Pt/Ti/SiO2/Si using radio-frequency magnetron sputtering and were followed by an RTA process in N-2, Ar, and O-2 ambients, respectively, at various temperatures for improving RS performance. Experimental results indicate that an SZO device annealed in O-2 at 600 degrees C (O-2-600) exhibits stable RS properties and has a high device yield (similar to 90%), a reliable retention characteristic (up to 1 x 10(6) s at 100 degrees C), and steady nondestructive readout properties (over 1.4 x 10(4) s at 100 degrees C). However, by increasing RTA temperature to more than 700 degrees C, random formation of LNO (110) precipitates on the bottom surface of SZO grains might shorten the effective thickness of the SZO thin films. Furthermore, a strong electric field possibly occurs at the region between Al top electrodes and low-resistivity LNO precipitates. It is speculated that an RS phenomenon, which occurs within SZO grains instead of on grain boundaries, easily leads to RS failure, further resulting in severe degradation of device yield in the O-2-700 and O-2-800 devices. When compared with other devices, O-2-600 SZO memory devices exhibit highly reliable RS characteristics.
Mechanism of Nonlinear Switching in HfO2-Based Crossbar RRAM With Inserting Large Bandgap Tunneling Barrier Layer
(2015-11-01)
Chand, Umesh
;
Huang, Kuan-Chang
;
Huang, Chun-Yang
;
Tseng, Tseung-Yuen
;
電子工程學系及電子研究所
In this paper, the nonlinear switching mechanism of the Ti/HfO2/Al2O3/TiN crossbar structure resistive random access memory device with good reliability is investigated. The nonlinearity of the device can be revealed by inserting a large bandgap of an Al2O3 thin layer between the TiN bottom electrode and the HfO2 switching film. The nonlinear switching mechanism caused by Flower-Nordheim tunneling involves the tunneling barrier of the Al2O3 layer. Besides, the nonlinear behavior is also sensitive to the thickness of the inserting Al2O3 layer. A high nonlinear factor of 37, large endurance more than 10(4), and good retention properties are achieved in the Ti/HfO2/Al2O3 (1-nm)/TiN structure.
Unipolar resistive switching behaviors and mechanisms in an annealed Ni/ZrO2/TaN memory device
(2015-01-28)
Tsai, Tsung-Ling
;
Ho, Tsung-Han
;
Tseng, Tseung-Yuen
;
電子物理學系
;
Department of Electrophysics
The effects of Ni/ZrO2/TaN resistive switching memory devices without and with a 400 degrees C annealing process on switching properties are investigated. The devices exhibit unipolar resistive switching behaviors with low set and reset voltages because of a large amount of Ni diffusion with no reaction with ZrO2 after the annealing process, which is confirmed by ToF-SIMS and XPS analyses. A physical model based on a Ni filament is constructed to explain such phenomena. The device that undergoes the 400 degrees C annealing process exhibits an excellent endurance of more than 1.5 x 10(4) cycles. The improvement can be attributed to the enhancement of oxygen ion migration along grain boundaries, which result in less oxygen ion consumption during the reset process. The device also performs good retention up to 10(5) s at 150 degrees C. Therefore, it has great potential for high-density nonvolatile memory applications.
Unipolar Resistive Switching Characteristics of a ZrO2 Memory Device With Oxygen Ion Conductor Buffer Layer
(2012-06-01)
Lee, Dai-Ying
;
Tseng, Tseung-Yuen
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Oxygen ion migration is an important factor in the formation and rupture of a conducting filament to cause resistive switching (RS) behavior. A calcium oxide-doped zirconium oxide (CaO:ZrO2) oxygen ion conductor buffer layer is introduced between the Ti/ZrO2 interface of conventional Ti/ZrO2/Pt memory devices to improve their unipolar RS properties. Increasing the CaO doping concentration to 2 mol% introduces higher oxygen vacancy content within the CaO:ZrO2 buffer layer, leading to higher oxygen ion conductivity. This allows more oxygen ions to migrate from the oxygen reservoir laterally and vertically across the 2-mol% CaO:ZrO2 buffer layer to the region where the conducting filament forms and ruptures. Therefore, the Ti/2-mol% CaO:ZrO2/ZrO2/Pt device in this letter exhibits good endurance, high-speed switching (50 ns) without soft errors, stubborn nondestructive readout, and stable retention at 150 degrees C.
Resistive switching mechanisms of V-doped SrZrO3 memory films
(2006-09-01)
Lin, Chun-Chieh
;
Tu, Bing-Chung
;
Lin, Chao-Cheng
;
Lin, Chen-Hsi
;
Tseng, Tseung-Yuen
The resistive switching behaviors of sputtered V-doped SrZrO3 (V:SZO) memory films were investigated in this letter. The current states of the memory films were switched between high current state (H-state) and low current state (L-state). The resistance ratio of the two current states was over 1000 at a read voltage. The switching mechanism from L- to H-state corresponds to the formation of current paths. However, this mechanism from H- to L-state is thought to be due to the fact that the defects present in the V:SZO film randomly trap electrons, and hence, the current paths are ruptured. The conduction mechanism of the H-state is dominated by ohmic conduction, whereas the L-state conduction is dominated by Frenkel-Poole emission. The polarity direction of the resistive switching is an intrinsic property of the SrZrO3 oxides. The V:SZO films with high uniformity and good stability are expected to be used in nonvolatile memory.
Effect of top electrode material on resistive switching properties of ZrO2 film memory devices
(2007-05-01)
Lin, Chih-Yang
;
Wu, Chen-Yu
;
Wu, Chung-Yi
;
Lee, Tzyh-Cheang
;
Yang, Fu-Liang
The influence of top electrode material on the resistive switching properties of ZrO2 -based memory film using Pt as a bottom electrode was investigated in this letter. In comparison with Pt/ZrO2/Pt and Al/ZrO2/Pt devices, the Ti/ZrO2/Pt device exhibits different resistive switching current-voltage (I-V) curve, which can be traced and reproduced by a dc voltage more than 1000 times only showing a little decrease of resistance ratio between high and low resistance states. Furthermore, the broad dispersions of resistive switching characteristics in the Pt/ZrO2/Pt and Al/ZrO2/Pt devices are generally observed during successive resistive switching, but those dispersions are suppressed by the device using Ti as a top electrode. The reliability results, such as cycling endurance and continuous readout test, are also presented. The write-read-erase-read operations can be over 104 cycles without degradation. No data loss is found upon successive readout after performing various endurance cycles.
Voltage-polarity-independent and high-speed resistive switching properties of v-doped SrZrO3 thin films
(2007-12-01)
Lin, Chun-Chieh
;
Lin, Chih-Yang
;
Lin, Meng-Han
;
Lin, Chen-Hsi
;
Tseng, Tseung-Yuen
In this paper, nonpolar resistive switching behavior is reported for the first time in a SZO-based memory device. The electrode materials used which have different conductivities affect the resistive switching properties of the device. The A1/V:SZO-LNO/Pt device shows nonpolar switching behavior, whereas the A1/V:SZO/LNO device has bipolar switching property. The resistance ratios of these two devices are quite distinct owing to the difference between the resistance of low resistance states. The A1/V:SZO-LNO/Pt device with lower resistive switching voltages (+/- 7 V turn on and 2 V turn off) and higher resistance ratio (10(7)) is more suitable for practical applications compared to the A1/V:SZO/LNO device. The switching speed of the A1/V:SZO-LNO/Pt device is 10 ns, which is the fastest speed that has ever been reported. The conduction mechanisms, nondestructive readout property, retention time, and endurance of this device are also reported in this paper.
Improvement of resistive switching characteristics in SrZrO3 thin films with embedded Cr layer
(2008-10-01)
Lin, Chih-Yang
;
Lin, Meng-Han
;
Wu, Ming-Chi
;
Lin, Chen-Hsi
;
Tseng, Tseung-Yuen
The stabilization of the resistive switching properties is necessary to realize the memory application of the SrZrO3 (SZO)-based resistive switching devices. During continuous resistive switching cycle, broad variations of the resistive switching parameters of the SZO-based memory devices can be improved by a thin embedded Cr layer. The Cr metal layer is proposed to diffuse into and dope the SZO thin film to produce the space charge region, further reducing the effective resistive switching region. Hence, the good stabilization of the resistive switching properties can be obtained in the SZO films with embedded Cr layer.
Resistive switching properties of SrZrO(3)-based memory films
(2007-04-01)
Lin, Chun-Chieh
;
Lin, Chao-Cheng
;
Tu, Bing-Chung
;
Yu, Jung-Sheng
;
Lin, Chen-Hsi
The resistive switching properties of the sputter-deposited SrZrO(3) (SZO) memory films were investigated in this study. The resistive switching behaviors of the SZO film can be improved by doping with vanadium oxide. The conduction mechanisms of the high and low current states of the 0.3% V-doped SZO (V:SZO) film are ohmic conduction and Frenkel-Poole emission, respectively, which implies the bulk effect of the memory film. The resistive ratio of two current states of the 0.3% V:SZO film remains 1000 times after applying 100 voltage sweeping cycles. Furthermore, the 0.3% V:SZO film shows stable resistive switching properties when measurement is performed at 100 degrees C. The band modulation of the SZO/LNO interface is proposed to explain the forming process of the SZO films. The 0.3% V:SZO memory film has excellent properties, such as high stability, good endurance, and long retention time, which make it a good candidate for next-generation nonvolatile memory application.

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