Low Current Compliance Research Articles

Diode-like volatile resistive switching properties in amorphous Sr-doped LaMnO3 thin films under lower current compliance

Amorphous Sr-doped LaMnO3 (a-LSMO) thin films can exhibit diode-like volatile resistive switching (RS) properties under lower compliance current (CC). The Ag/a-LSMO/Pt cell exhibits stable volatile RS cycles up to 100 times with rectification ratio above 102. The volatility depends strongly on the temperature as well as the CC-controlled dimension of the Ag nanofilament forming in a-LSMO. The conductive atomic force microscopy current-mapping images confirm the instability of conducting nanofilaments forming under lower CC. The volatile RS behaviors could be explained by the Rayleigh instability of the Ag nanofilament, together with the diffusion of Ag atoms to the a-LSMO matrix. The diode-like volatile RS properties have great application potential in the beyond von-Neumann computers.

Impact of electrically formed interfacial layer and improved memory characteristics of IrOx/high-κx/W structures containing AlOx, GdOx, HfOx, and TaOx switching materials.

Improved switching characteristics were obtained from high-κ oxides AlOx, GdOx, HfOx, and TaOx in IrOx/high-κx/W structures because of a layer that formed at the IrOx/high-κx interface under external positive bias. The surface roughness and morphology of the bottom electrode in these devices were observed by atomic force microscopy. Device size was investigated using high-resolution transmission electron microscopy. More than 100 repeatable consecutive switching cycles were observed for positive-formatted memory devices compared with that of the negative-formatted devices (only five unstable cycles) because it contained an electrically formed interfacial layer that controlled ‘SET/RESET’ current overshoot. This phenomenon was independent of the switching material in the device. The electrically formed oxygen-rich interfacial layer at the IrOx/high-κx interface improved switching in both via-hole and cross-point structures. The switching mechanism was attributed to filamentary conduction and oxygen ion migration. Using the positive-formatted design approach, cross-point memory in an IrOx/AlOx/W structure was fabricated. This cross-point memory exhibited forming-free, uniform switching for >1,000 consecutive dc cycles with a small voltage/current operation of ±2 V/200 μA and high yield of >95% switchable with a large resistance ratio of >100. These properties make this cross-point memory particularly promising for high-density applications. Furthermore, this memory device also showed multilevel capability with a switching current as low as 10 μA and a RESET current of 137 μA, good pulse read endurance of each level (>105 cycles), and data retention of >104 s at a low current compliance of 50 μA at 85°C. Our improvement of the switching characteristics of this resistive memory device will aid in the design of memory stacks for practical applications.

Resistive Switching in a Printed Nanolayer of Poly(4-vinylphenol)

Resistive switching in organic resistive switches fabricated with a sandwich structure of indium tin oxide (ITO)-coated polyethylene terephthalate (PET)/poly(4-vinylphenol) (PVP)/silver (Ag) is reported. A single layer of PVP was used as an active layer in the sandwich structure between the two electrodes. The active layer of the polymer was atomized with the electrohydrodynamic atomization technique on the ITO-coated PET. The film thickness of the PVP polymeric layer on the ITO-coated PET was measured to be 110 nm. The surface morphology was characterized by field-emission scanning electron microscopy, and the purity of the film was examined by x-ray photoelectron spectroscopy analysis. Electrical current–voltage (I–V) measurements confirmed the memristive behavior of the sandwich device. The effect of the current compliance (CC) on resistive switching in the fabricated sandwich structure was also explored. The PVP-based organic resistive switch showed a CC-dependent OFF/ON ratio and memory window. Resistive switching memory effects were prominent at low CC up to nanoamps. The as-fabricated device was operated with low operational voltages for both polarities with OFF/ON ratio greater than 100:1. The robustness of the fabricated memristor was checked with multiple voltage sweeps, and the retention time is reported to be over 100 min.

Enhanced nanoscale resistive switching memory characteristics and switching mechanism using high-Ge-content Ge0.5Se0.5 solid electrolyte

We demonstrate enhanced repeatable nanoscale bipolar resistive switching memory characteristics in Al/Cu/Ge0.5Se0.5/W, as compared with Al/Cu/Ge0.2Se0.8/W structures, including stable AC endurance (>105 cycles), larger average SET voltage (approximately 0.6 V), excellent data retention (>105 s) at 85°C, and a high resistance ratio (>104) with a current compliance of 8 μA and a small operation voltage of ±1.5 V. A small device size of 150 × 150 nm2 and a Cu nanofilament with a small diameter of 30 nm are both observed by high-resolution transmission electron microscope in the SET state. The GexSe1 − x solid electrolyte compositions are confirmed by both energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The switching mechanism relies on the smaller barrier heights for holes rather than for electrons; the positively charged Cuz+ ions (i.e., holes) migrate through the defects in the GexSe1 − x solid electrolytes during SET/RESET operations. Hence, the Cu nanofilament starts to grow at the Ge0.5Se0.5/W interface, and starts to dissolve at the Cu/Ge0.5Se0.5 interface, as illustrated in the energy band diagrams. Owing to both the higher barrier for hole injection at the Cu/Ge0.5Se0.5 interface than at the Cu/Ge0.2Se0.8 interface and greater thermal stability, the resistive switching memory characteristics of the Al/Cu/Ge0.5Se0.5/W are improved relative to the Al/Cu/Ge0.2Se0.8/W devices. The Al/Cu/Ge0.5Se0.5/W memory device can also be operated with a low current compliance of 1 nA, and hence, a low SET/RESET power of 0.61 nW/6.4 pW is achieved. In addition, a large memory size of 1,300 Pbit/in2 is achieved with a small nanofilament diameter of 0.25 Å for a small current compliance of 1 nA.

Impact of TaOx nanolayer at the GeSex/W interface on resistive switching memory performance and investigation of Cu nanofilament

The impact of a TaOx nanolayer at the GeSex/W interface on the performance of resistive switching memory in an Al/Cu/GeSex/TaOx/W structure has been examined. All materials and the memory structure have been investigated using high-resolution transmission electron microscopy, energy dispersive x ray spectroscopy, and x ray photo-electron spectroscopy analyses. A conically shaped crystalline Cu (111) nanofilament with a diameter of around 17 nm in the TaOx nanolayer after a current compliance (CC) of 500 μA has been observed, and this has been also characterized by fast Fourier transform. The low resistance state (LRS) decreases as the current compliances (CCs) increased from 1 nA to 1 mA, since the nanofilament diameter increased from 0.04 to 23.4 nm. This is also estimated by bipolar resistive switching characteristics. The resistivity of this crystalline Cu nanofilament is approximately 2300 μΩ.cm. The nanofilament has a cylindrical shape, with CCs ranging from 1 nA to 10 μA and a conical shape with CCs ranging from 50 μA-1 mA. The resistive switching mechanism has been explained successfully under SET and RESET operations. Improved resistive switching parameters, such as SET voltage, LRS, and high resistance state with consecutive switching cycles are obtained and compared to those of pure GeSex and TaOx materials. Extrapolated, long program/erase endurance of > 106 cycles, attributed to the Al/Cu/GeSex/TaOx/W structure design, is observed. This resistive switching memory structure shows extrapolated 10 years data retention with a resistance ratio of > 10 at a low CC of 0.1 μA at 50 °C. A large memory size of ∼ 6 Pbit/sq. in. is obtained, considering the nanofilament diameter at a low CC of 0.1 μA. This study is important not only for improving the performance of low-power resistive switching memory, but also helpful for designing other nonvolatile memory devices.

High-κ Al2O3/WOx Bilayer Dielectrics for Low-Power Resistive Switching Memory Applications

A bipolar resistive switching memory device using high-κ Al2O3/WOx bilayer dielectrics in an IrOx/Al2O3/WOx/W structure with a small device area of 8 ×8 µm2 is investigated for the first time. A high hole trapping density of ∼1.76 ×1018 cm-3 in a high-κ Al2O3 film with a thickness of 5 nm is investigated using IrOx/Al2O3/SiO2/p-Si capacitors. The thickness and chemical bonding of the high-κ Al2O3/WOx films in a resistive memory device are investigated by both high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The resistive switching memory device with a low power operation of 0.7 mW and a low current compliance of 500 µA has a reasonable SET/RESET voltage of -1.4 V/+1.0 V, a high resistance ratio of >103, an excellent read endurance of >105 times at a large read voltage of -0.5 V, and 10 years of data retention at 85 °C.

High-κ Al2O3/WOxBilayer Dielectrics for Low-Power Resistive Switching Memory Applications

A bipolar resistive switching memory device using high-κ Al2O3/WOx bilayer dielectrics in an IrOx/Al2O3/WOx/W structure with a small device area of 8 ×8 µm2 is investigated for the first time. A high hole trapping density of ∼1.76 ×1018 cm-3 in a high-κ Al2O3 film with a thickness of 5 nm is investigated using IrOx/Al2O3/SiO2/p-Si capacitors. The thickness and chemical bonding of the high-κ Al2O3/WOx films in a resistive memory device are investigated by both high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The resistive switching memory device with a low power operation of 0.7 mW and a low current compliance of 500 µA has a reasonable SET/RESET voltage of -1.4 V/+1.0 V, a high resistance ratio of >103, an excellent read endurance of >105 times at a large read voltage of -0.5 V, and 10 years of data retention at 85 °C.

Coexistence of the bipolar and unipolar resistive switching behaviours in Au/SrTiO3/Pt cells

The bipolar and unipolar resistive switching (BRS and URS) modes are first observed to coexist in the Au/SrTiO3/Pt cell fabricated by pulsed laser deposition. These two switching modes can be activated separately depending on the different current compliance (CC) during the electroforming process: with a lower CC (1 mA) the asymmetric BRS behaviour is measured in the voltage range −1.2 to +1 V, while the URS behaviour is observed with a higher CC (10 mA). On the basis of current–voltage characteristics, the switching mechanisms for the BRS and URS modes are considered as a change in Schottky-like barrier height and/or width at the Au/SrTiO3 interface and the formation and disruption of conduction filaments, respectively. The conversion between BRS and URS is reversible. Because each switching mode has a specific advantage, selecting the desired switching mode can broaden the application scope of the cell and enable large flexibility in terms of memory architecture.

Low power resistive switching memory using Cu metallic filament in Ge 0.2Se 0.8 solid-electrolyte

Bipolar resistive switching memory device using Cu metallic filament in Au/Cu/Ge 0.2Se 0.8/W memory device structure has been investigated. This resistive memory device has the suitable threshold voltage of V th > 0.18 V, good resistance ratio ( R High/ R Low) of 2.6 × 10 3, good endurance of >10 4 cycles with a programming current of 0.3 mA/0.8 mA, and 5 h of retention time at low compliance current of 10 nA. The low resistance state ( R Low) of the memory device decreases with increasing the compliance current from 1 nA to 500 μA for different device sizes from 0.2 μm to 4 μm. The memory device can work at very low compliance current of 1 nA, which can be applicable for extremely low power-consuming memory devices.

Effect of the top electrode material on the resistive switching of TiO2 thin film

Effect of the top electrode (TE) metal on the resistive switching of (TE)/TiO2/Pt structure was investigated. It was confirmed that the potential barrier height between the metal and TiO2 is an important factor on the resistive switching characteristics. When high Schottky barrier was formed with the TiO2 film, using Pt or Au as a top electrode, both stable URS (unipolar) and BRS (bipolar resistive switching) characteristics were observed depending on the current compliance level. In the case of Ag, which forms a relatively low Schottky barrier, only BRS characteristics were observed, regardless of the current compliance level. In the case of Ni and Al, which have similar work function as Ag, unstable URS and BRS at very low current compliance levels were observed due to a chemical reaction at the interface. For the Ti electrode, resistive switching was not observed, because the work function of Ti is lower than that of TiO2 and TiO phase was formed at the interface (Ti/TiOx contact is ohmic).

The Effect of Current Compliance on the Resistive Switching Behaviors in TiN/ZrO2/Pt Memory Device

In this paper, TiN/ZrO2/Pt sandwiched resistive switching memory devices were fabricated. The effect of set current compliance on the resistive switching behaviors in TiN/ZrO2/Pt memory device was studied. The different dependence of low resistance state on the set current compliance were observed under the different magnitudes of set current compliance: 1) the average read current was linearly dependent on the set current compliance in the magnitude of low set current compliance; 2) then a weaker dependence of the average read current on the set current compliance was observed in the magnitude of higher set current compliance; 3) when the current compliance is high enough, the unipolar resistive switching behaviors instead of the bipolar resistive switching was shown. A physical model based on oxygen vacancy conducting filamentary paths is proposed to explain the effect of set current compliance on the resistive switching behaviors in TiN/ZrO2/Pt memory device.

Resistive switching in a Pt/TiO 2/Pt thin film stack – a candidate for a non-volatile ReRAM

In Pt/27 nm thick TiO2/Pt stacks bipolar and unipolar resistive switching (BRS, URS) behavior of were investigated. Depending on the current compliance during electroforming process, BRS or URS could be observed: With a lower current compliance (<0.1mA) asymmetric current-voltage (I-V) curves (BRS) were measured in the voltage range −1.6V to +1.1V, while with a higher current compliance (1 to 10mA) the URS behavior was observed. Furthermore, the permanent transition from BRS to URS was investigated by applying voltage with a higher current compliance (∼3 mA). Preliminary results of microstructural investigations show heavily damaged regions in the stacks.

Coexistence of Bipolar and Unipolar Resistive Switching Behaviors in a Pt∕TiO[sub 2]∕Pt Stack

Bipolar resistive switching (BRS) as well as unipolar resistive switching (URS) behaviors in Pt/27 nm thick TiO 2 /Pt stacks were investigated. Depending on the current compliance during the electroforming process, either BRS or URS was observed. With a lower current compliance (<0.1 mA) during electroforming, asymmetric current-voltage curves showing BRS were observed in the voltage range -1.6 to +1.1 V, while with a higher current compliance (1-10 mA) URS behavior was observed. Furthermore, the permanent transition from BRS to URS was investigated by applying a voltage with a higher current compliance (∼3 mA).

Raman study of electric-field-induced first-order metal-insulator transition in VO2-based devices

An abrupt first-order metal-insulator transition (MIT) as a current jump has been observed by applying a dc electric field to Mott insulator VO2-based two-terminal devices. The size of the jumps was measured to be asymmetrical depending on the direction of the applied voltage due to heating effects. The structure of VO2 is investigated by micro-Raman scattering experiments. An analysis of the Raman-active Ag modes at 195 and 222cm−1, explained by pairing and tilting of V cations, and 622cm−1, shows that the modes below a low compliance (restricted) current do not change when the MIT occurs, whereas a structural phase transition above the low compliance current is found to occur secondarily, due to heating effects in the device induced by the MIT. The MIT has applications in the development of high-speed and high-gain switching devices.

Physical analysis of hard and soft breakdown failures in ultrathin gate oxides

The physical analysis of the ultrathin gate oxides (33 and 25 Å) after the electrical stressing, under constant voltage stress, reveals that the damage is not only limited to the oxide layer, but also to the entire gate structure. The hard breakdown failure makes catastrophic damage to the structure, whereas the analysis of soft breakdown failure reveals many of the hidden damages in the device structure. In Ti-silicided structures, the predominant failure mechanism is Ti migration to form a leakage path, as well as localized re-crystallisation of poly-Si or Si substrate near to the gate oxide. Co migration is so far not seen in Co-silicided devices. However, even for the very low current compliance levels and devices which do not show any electrical degradation after the SBD stress, localized epitaxy formation in the gate or Si substrate is observed, which could be a reliability concern.

Soft breakdown at all positions along the N-MOSFET

We observe soft breakdowns at all positions along the gates of N-MOSFETs when testing is performed at low voltage or with low current compliance. Devices whose breakdown spots are at or near the gate–drain overlap region have the highest off-currents, although not high enough to be fatal to device operation.

Intraventricular conduction defects: Hübener, G.: Deutsche med. Wchnschr. 64: 1222, 1938

Bipolar resistive switching memory device using Cu metallic filament in Au/Cu/Ge0.2Se0.8/W memory device structure has been investigated. This resistive memory device has the suitable threshold voltage of Vth > 0.18 V, good resistance ratio (RHigh/RLow) of 2.6 × 103, good endurance of >104 cycles with a programming current of 0.3 mA/0.8 mA, and 5 h of retention time at low compliance current of 10 nA. The low resistance state (RLow) of the memory device decreases with increasing the compliance current from 1 nA to 500 μA for different device sizes from 0.2 μm to 4 μm. The memory device can work at very low compliance current of 1 nA, which can be applicable for extremely low power-consuming memory devices.