Showing papers by "Qi Liu published in 2008"

Nonpolar Nonvolatile Resistive Switching in Cu Doped $\hbox{ZrO}_{2}$

Abstract: In this letter, the unique reproducible nonpolar resistive switching behavior is reported in the Cu-doped ZrO2 memory devices. The devices are with the sandwiched structure of Cu/ZrO2:Cu/Pt. The switching between high resistance state (OFF-state) and low resistance state (ON-state) does not depend on the polarity of the applied voltage bias and can be achieved under both voltage sweeping and voltage pulse. The ratio between the high and low resistance is on the order of 106. Set and Reset operation in voltage pulse mode can be as fast as 50 and 100 ns, respectively. No data loss is found upon continuous readout for more than 104 s. Multilevel storage is considered feasible due to the dependence of ON-state resistance on Set compliance current. The switching mechanism is believed to be related with the formation and rupture of conducting filamentary paths.

Resistive switching memory effect of ZrO2 films with Zr+ implanted

Abstract: The Au∕Cr∕Zr+-implanted-ZrO2∕n+-Si sandwiched structure exhibits reversible bipolar resistive switching behavior under dc sweeping voltage. The resistance ratio (Rratio) of high resistive state and low resistive state is as large as five orders of magnitude with 0.5V readout bias. Zr+-implanted-ZrO2 films exhibit good retention characteristics and high device yield. The impact of implanted Zr+ ions on resistive switching performances is investigated. Resistive switching of the fabricated structures is explained by trap-controlled space charge limited current conduction.

On the resistive switching mechanisms of Cu/ZrO2:Cu/Pt

Abstract: We use convincing experimental evidences to demonstrate that the nonpolar resistive switching phenomenon observed in Cu/ZrO2:Cu/Pt memory devices conforms to a filament formation and annihilation mechanism. Temperature-dependent switching characteristics show that a metallic filamentary channel is responsible for the low resistance state (ON state). Further analysis reveals that the physical origin of this metallic filament is the nanoscale Cu conductive bridge. On this basis, we propose that the set process (switching from OFF state to ON state) and the reset process (switching from ON to OFF state) stem from the electrochemical reactions in the filament, in which a thermal effect is greatly involved.

Resistance switching of Au-implanted-ZrO2 film for nonvolatile memory application

Abstract: The resistive switching characteristics and switching mechanisms of the Au-implanted-ZrO2 film are extensively investigated for nonvolatile memory applications. Reversible resistance-switching behavior from a high resistance to low resistance state can be traced by dc voltage and pulse voltage. After more than 200 dc switching cycles, the resistance ratio between the high and low resistance states is more than 180 times under 0.7 V readout bias. In the voltage pulse test, the “write” and “erase” speeds can be as fast as 50 and 100 ns, respectively. No data loss is observed for more than 106 s. The formation and rupture of conducting filamentary paths related to the implanted Au ions are suggested to be responsible for the resistive switching phenomenon. The dependence of resistance on temperature indicates that the variable-range hopping conduction mechanism is dominated in the low-resistance state, while the current characteristics are governed by the trap-controlled space limited conduction mechanism in...

Role of metallic cobalt in room temperature dilute ferromagnetic semiconductor Zn0.95Co0.05O1−δ

Abstract: Using two suitably designed thin film systems, the impact of metallic cobalt nanodots on the mechanism of ferromagnetism (FM) in ZnO thin films was studied. At a relatively higher oxygen partial pressure, Co nanodots embedded ZnO thin films no longer show FM, as compared to Co-doped ZnO dilute magnetic semiconductor (DMS). The structural and magnetic properties of these two systems support the hypothesis that (1) the FM of DMS thin films is due to bound magnetic polarons instead of cobalt nanoclusters and (2) the critical defect concentration is the key parameter which controls the FM properties in DMS thin films.

Comparison of discrete-storage nonvolatile memories: advantage of hybrid method for fabrication of Au nanocrystal nonvolatile memory

Abstract: In this paper, the memory characteristics of two kinds of metal-oxide-semiconductor (MOS) capacitors embedded with Au nanocrytals are investigated: hybrid MOS with nanocrystals (NCs) fabricated by chemical syntheses and rapid thermal annealing (RTA) MOS with NCs fabricated by RTA. For both kinds of devices, the capacitance versus voltage (C–V) curves clearly indicate the charge storage in the NCs. The hybrid MOS, however, shows a larger memory window, as compared with RTA MOS. The retention characteristics of the two MOS devices are also investigated. The capacitance versus time (C–t) measurement shows that the hybrid MOS capacitor embedded with Au nanocrystals has a longer retention time. The mechanism of longer retention time for hybrid MOS capacitor is qualitatively discussed.

Excellent resistive switching characteristics of Cu doped ZrO 2 and its 64 bit cross-point integration

Abstract: Excellent nonpolar resistive switching behavior is reported in the Cu doped ZrO2 memory devices with the sandwiched structure of Cu/ZrO2:Cu/Pt. The ratio between the high and low resistance is in the order of 106. Set and Reset operation in voltage pulse mode can be as fast as 50 ns and 100 ns, respectively. Multilevel storage is considered feasible due to the dependence of ON-state resistance on Set compliance current. The switching mechanism is demonstrated to be related with the formation and rupture of Cu conductive bridge. Based on this working cell, 64 bit cross-point array is fabricated and tested.