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1.
Self-compliance resistive random access memory (RRAM) characteristics using a W/TaO x /TiN structure are reported for the first time. A high-resolution transmission electron microscope (HRTEM) image shows an amorphous TaO x layer with a thickness of 7 nm. A thin layer of TiO x N y with a thickness of 3 nm is formed at the TaO x /TiN interface, owing to the oxygen accumulation nature of Ti. This memory device shows 100 consecutive switching cycles with excellent uniformity, 100 randomly picked device-to-device good uniformity, and program/erase endurance of >103 cycles. It is observed that the 0.6-μm devices show better switching uniformity as compared to the 4-μm devices, which is due to the thinner tungsten (W) electrode as well as higher series resistance. The oxygen-rich TaO x layer at the W/TaO x interface also plays an important role in getting self-compliance resistive switching phenomena and non-linear current-voltage (I-V) curve at low resistance state (LRS). Switching mechanism is attributed to the formation and rupture of oxygen vacancy conducting path in the TaO x switching material. The memory device also exhibits long read endurance of >106 cycles. It is found that after 400,000 cycles, the high resistance state (HRS) is decreased, which may be due to some defects creation (or oxygen moves away) by frequent stress on the switching material. Good data retention of >104 s is also obtained.  相似文献   

2.
Comparison of resistive switching memory characteristics using copper (Cu) and aluminum (Al) electrodes on GeOx/W cross-points has been reported under low current compliances (CCs) of 1 nA to 50 μA. The cross-point memory devices are observed by high-resolution transmission electron microscopy (HRTEM). Improved memory characteristics are observed for the Cu/GeOx/W structures as compared to the Al/GeOx/W cross-points owing to AlOx formation at the Al/GeOx interface. The RESET current increases with the increase of the CCs varying from 1 nA to 50 μA for the Cu electrode devices, while the RESET current is high (>1 mA) and independent of CCs varying from 1 nA to 500 μA for the Al electrode devices. An extra formation voltage is needed for the Al/GeOx/W devices, while a low operation voltage of ±2 V is needed for the Cu/GeOx/W cross-point devices. Repeatable bipolar resistive switching characteristics of the Cu/GeOx/W cross-point memory devices are observed with CC varying from 1 nA to 50 μA, and unipolar resistive switching is observed with CC >100 μA. High resistance ratios of 102 to 104 for the bipolar mode (CCs of 1 nA to 50 μA) and approximately 108 for the unipolar mode are obtained for the Cu/GeOx/W cross-points. In addition, repeatable switching cycles and data retention of 103 s are observed under a low current of 1 nA for future low-power, high-density, nonvolatile, nanoscale memory applications.  相似文献   

3.
Resistive switching properties of a self-compliance resistive random access memory device in cross-point architecture with a simple stack structure of Ir/TaO x /W have been investigated. A transmission electron microscope and atomic force microscope were used to observe the film properties and morphology of the stack. The device has shown excellent switching cycle uniformity with a small operation of ±2.5 V and a resistance ratio of >100. The device requires neither any frorming-process nor current compliance limit for repeatable operation in contrast to conventional resistive random access memory devices. The effect of bottom electrode morphology and surface roughness is also studied. The improvement is due to the enhanced electric field at the nanotips in the bottom electrode and the defective TaO x switching layer which enable controlled filament formation/rupture. The device area dependence of the low resistance state indicates multifilament formation. The device has shown a robust alternating current endurance of >105 cycles and a data retention of >104 s.  相似文献   

4.
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.  相似文献   

5.
Enhanced resistive switching phenomena of IrOx/GdOx/W cross-point memory devices have been observed as compared to the via-hole devices. The as-deposited Gd2O3 films with a thickness of approximately 15 nm show polycrystalline that is observed using high-resolution transmission electron microscope. Via-hole memory device shows bipolar resistive switching phenomena with a large formation voltage of -6.4 V and high operation current of >1 mA, while the cross-point memory device shows also bipolar resistive switching with low-voltage format of +2 V and self-compliance operation current of <300 μA. Switching mechanism is based on the formation and rupture of conducting filament at the IrOx/GdOx interface, owing to oxygen ion migration. The oxygen-rich GdOx layer formation at the IrOx/GdOx interface will also help control the resistive switching characteristics. This cross-point memory device has also Repeatable 100 DC switching cycles, narrow distribution of LRS/HRS, excellent pulse endurance of >10,000 in every cycle, and good data retention of >104 s. This memory device has great potential for future nanoscale high-density non-volatile memory applications.  相似文献   

6.
Excellent resistive switching memory characteristics were demonstrated for an Al/Cu/Ti/TaOx/W structure with a Ti nanolayer at the Cu/TaOx interface under low voltage operation of ± 1.5 V and a range of current compliances (CCs) from 0.1 to 500 μA. Oxygen accumulation at the Ti nanolayer and formation of a defective high-κ TaOx film were confirmed by high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photo-electron spectroscopy. The resistive switching memory characteristics of the Al/Cu/Ti/TaOx/W structure, such as HRS/LRS (approximately 104), stable switching cycle stability (>106) and multi-level operation, were improved compared with those of Al/Cu/TaOx/W devices. These results were attributed to the control of Cu migration/dissolution by the insertion of a Ti nanolayer at the Cu/TaOx interface. In contrast, CuOx formation at the Cu/TaOx interface was observed in an Al/Cu/TaOx/W structure, which hindered dissolution of the Cu filament and resulted in a small resistance ratio of approximately 10 at a CC of 500 μA. A high charge-trapping density of 6.9 × 1016 /cm2 was observed in the Al/Cu/Ti/TaOx/W structure from capacitance-voltage hysteresis characteristics, indicating the migration of Cu ions through defect sites. The switching mechanism was successfully explained for structures with and without the Ti nanolayer. By using a new approach, the nanoscale diameter of Cu filament decreased from 10.4 to 0.17 nm as the CC decreased from 500 to 0.1 μA, resulting in a large memory size of 7.6 T to 28 Pbit/sq in. Extrapolated 10-year data retention of the Ti nanolayer device was also obtained. The findings of this study will not only improve resistive switching memory performance but also aid future design of nanoscale nonvolatile memory.  相似文献   

7.
Resistive switching memories (RRAMs) are attractive for replacement of conventional flash in the future. Although different switching materials have been reported; however, low-current operated devices (<100 μA) are necessary for productive RRAM applications. Therefore, TaOx is one of the prospective switching materials because of two stable phases of TaO2 and Ta2O5, which can also control the stable low- and high-resistance states. Long program/erase endurance and data retention at high temperature under low-current operation are also reported in published literature. So far, bilayered TaOx with inert electrodes (Pt and/or Ir) or single layer TaOx with semi-reactive electrodes (W and Ti/W or Ta/Pt) is proposed for real RRAM applications. It is found that the memory characteristics at current compliance (CC) of 80 μA is acceptable for real application; however, data are becoming worst at CC of 10 μA. Therefore, it is very challenging to reduce the operation current (few microampere) of the RRAM devices. This study investigates the switching mode, mechanism, and performance of low-current operated TaOx-based devices as compared to other RRAM devices. This topical review will not only help for application of TaOx-based nanoscale RRAM devices but also encourage researcher to overcome the challenges in the future production.  相似文献   

8.
The resistive switching memory of Ge nanowires (NWs) in an IrOx/Al2O3/Ge NWs/SiO2/p-Si structure is investigated. Ge NWs with an average diameter of approximately 100 nm are grown by the vapor–liquid-solid technique. The core-shell structure of the Ge/GeOx NWs is confirmed by both scanning electron microscopy and high-resolution transmission electron microscopy. Defects in the Ge/GeOx NWs are observed by X-ray photoelectron spectroscopy. Broad photoluminescence spectra from 10 to 300 K are observed because of defects in the Ge/GeOx NWs, which are also useful for nanoscale resistive switching memory. The resistive switching mechanism in an IrOx/GeOx/W structure involves migration of oxygen ions under external bias, which is also confirmed by real-time observation of the surface of the device. The porous IrOx top electrode readily allows the evolved O2 gas to escape from the device. The annealed device has a low operating voltage (<4 V), low RESET current (approximately 22 μA), large resistance ratio (>103), long pulse read endurance of >105 cycles, and good data retention of >104 s. Its performance is better than that of the as-deposited device because the GeOx film in the annealed device contains more oxygen vacancies. Under SET operation, Ge/GeOx nanofilaments (or NWs) form in the GeOx film. The diameter of the conducting nanofilament is approximately 40 nm, which is calculated using a new method.  相似文献   

9.
La1 − x Al x FeO3 (x = 0.0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5) nanopowders were prepared by polymerization complex method. All prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and UV-vis spectrophotometry (UV-vis). The magnetic properties were investigated using a vibrating sample magnetometer (VSM). The X-ray results of all samples show the formation of an orthorhombic phase with the second phase of α-Fe2O3 in doped samples. The crystallite sizes of nanoparticles decreased with increasing Al content, and they are found to be in the range of 58.45 ± 5.90 to 15.58 ± 4.64 nm. SEM and TEM images show the agglomeration of nanoparticles with average particle size in the range of 60 to 75 nm. The FT-IR spectra confirm the presence of metal oxygen bonds of O-Fe-O and Fe-O in the FeO6 octahedra. The UV-vis spectra show strong absorption peaks at approximately 285 nm, and the calculated optical band gaps are found to be in the range of 2.05 to 2.09 eV with increasing Al content. The M-H loop of the pure sample is antiferromagnetic, whereas those of the doped samples tend to be ferromagnetic with increasing Al content. The magnetization, remanent magnetization, and coercive field of the Al-doped sample with x = 0.5 are enhanced to 1.665 emu/g, 0.623 emu/g, and 4,087.0 Oe, respectively.  相似文献   

10.
A simplified one-diode one-resistor (1D1R) resistive switching memory cell that uses only four layers of TaN/ZrTiO x /Ni/n+-Si was proposed to suppress sneak current where TaN/ZrTiO x /Ni can be regarded as a resistive-switching random access memory (RRAM) device while Ni/n+-Si acts as an Schottky diode. This is the first RRAM cell structure that employs metal/semiconductor Schottky diode for current rectifying. The 1D1R cell exhibits bipolar switching behavior with SET/RESET voltage close to 1 V without requiring a forming process. More importantly, the cell shows tight resistance distribution for different states, significantly rectifying characteristics with forward/reverse current ratio higher than 103 and a resistance ratio larger than 103 between two states. Furthermore, the cell also displays desirable reliability performance in terms of long data retention time of up to 104 s and robust endurance of 105 cycles. Based on the promising characteristics, the four-layer 1D1R structure holds the great potential for next-generation nonvolatile memory technology.  相似文献   

11.
We report on the out-of-plane thermal conductivities of epitaxial Fe3O4 thin films with thicknesses of 100, 300, and 400 nm, prepared using pulsed laser deposition (PLD) on SiO2/Si substrates. The four-point probe three-omega (3-ω) method was used for thermal conductivity measurements of the Fe3O4 thin films in the temperature range of 20 to 300 K. By measuring the temperature-dependent thermal characteristics of the Fe3O4 thin films, we realized that their thermal conductivities significantly decreased with decreasing grain size and thickness of the films. The out-of-plane thermal conductivities of the Fe3O4 films were found to be in the range of 0.52 to 3.51 W/m · K at 300 K. For 100-nm film, we found that the thermal conductivity was as low as approximately 0.52 W/m · K, which was 1.7 to 11.5 order of magnitude lower than the thermal conductivity of bulk material at 300 K. Furthermore, we calculated the temperature dependence of the thermal conductivity of these Fe3O4 films using a simple theoretical Callaway model for comparison with the experimental data. We found that the Callaway model predictions agree reasonably with the experimental data. We then noticed that the thin film-based oxide materials could be efficient thermoelectric materials to achieve high performance in thermoelectric devices.  相似文献   

12.
A novel idea by using copper (Cu) pillar is proposed in this study, which can replace the through-silicon-vias (TSV) technique in future three-dimensional (3D) architecture. The Cu pillar formation under external bias in an Al/Cu/Al2O3/TiN structure is simple and low cost. The Cu pillar is formed in the Al2O3 film under a small operation voltage of <5 V and a high-current-carrying conductor of >70 mA is obtained. More than 100 devices have shown tight distribution of the Cu pillars in Al2O3 film for high current compliance (CC) of 70 mA. Robust read pulse endurances of >106 cycles are observed with read voltages of −1, 1, and 4 V. However, read endurance is failed with read voltages of −1.5, −2, and −4 V. By decreasing negative read voltage, the read endurance is getting worst, which is owing to ruptured Cu pillar. Surface roughness and TiO x N y on TiN bottom electrode are observed by atomic force microscope and transmission electron microscope, respectively. The Al/Cu/Al2O3/TiN memory device shows good bipolar resistive switching behavior at a CC of 500 μA under small operating voltage of ±1 V and good data retention characteristics of >103 s with acceptable resistance ratio of >10 is also obtained. This suggests that high-current operation will help to form Cu pillar and lower-current operation will have bipolar resistive switching memory. Therefore, this new Cu/Al2O3/TiN structure will be benefited for 3D architecture in the future.  相似文献   

13.
The structures, processes of shrinkage, and phase composition of the compact system ZrO2-WC, obtained by hot pressing with the transmission of high current, are considered in the article. We found that as a result of compaction, the ZrO2-WC-ceramics have uniform density distribution, with the following optimal mode consolidation values T = 1,350°C, P = 30 MPa and t = 2 min. These conditions allow us to achieve the best combination of ceramic properties by criteria density and strength.  相似文献   

14.
A new nanosensor composed of laminated samarium borate and immobilized laccase was developed for phenol determination. The laminated samarium borate was synthesized by a mild solid-state-hydrothermal (S-S-H) method without any surfactant or Template. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were used to characterize the samples. The morphology of the as-prepared materials was characterized by SEM, which shows that laminated samarium borate are uniform nanosheets with a layer-by-layer self-assembled single-crystal structure. These laminated samarium borate have typical diameters of 3 ~ 5 μm and the thickness of each layer is in the range of 10 ~ 80 nm. And then, these SmBO3 multilayers were used to immobilize the laccase. The proposed nanosensor composed of laminated samarium borate and immobilized laccase was successfully developed for phenol determination. Cyclic voltammetry were used to study the nanosensor. The proposed nanosensor displayed high sensitivity toward phenolic compounds. The linearity of the nanosensor for the detection of hydroquinone was obtained from 1 to 50 μM with a detection limit of 3 × 10-7 M (based on the S/N = 3).  相似文献   

15.
In this study, we fabricated thin films of SexTe100 − x (x = 0, 3, 6, 9, 12, and 24) nanoparticles using thermal evaporation technique. The results obtained by X-ray diffraction show that the as-synthesized nanoparticles have polycrystalline structure, but their crystallinity decreases by increasing the concentration of Se. They were found to have direct bandgap (Eg), whose value increases by increasing the Se content. These results are completely different than those obtained in the films of SexTe100 − x microstructure counterparts. Photoluminescence and Raman spectra for these films were also demonstrated. The remarkable results obtained in these nanoparticles specially their controlled direct bandgap might be useful for the development of optical disks and other semiconductor devices.  相似文献   

16.
Molybdenum disulfide (MoS2)/cadmium sulfide (CdS) heterojunction solar cells were successfully synthesized via chemical bath deposition (CBD) and chemical vapor deposition (CVD). The as-grown CdS film on a fluorine tin oxide (FTO) substrate deposited by CBD is continuous and compact. The MoS2 film deposited by CVD is homogeneous and continuous, with a uniform color and a thickness of approximately 10 nm. The optical absorption range of the MoS2/CdS heterojunction covers the visible and near-infrared spectral regions of 350 to 800 nm, which is beneficial for the improvement of solar cell efficiency. Moreover, the MoS2/CdS solar cell exhibits good current-voltage (I-V) characteristics and pronounced photovoltaic behavior, with an open-circuit voltage of 0.66 V and a short-circuit current density of 0.227 × 10-6 A/cm2, comparable to the results obtained from other MoS2-based solar cells. This research is critical to investigate more efficient and stable solar cells based on graphene-like materials in the future.  相似文献   

17.
A method for situ preparing a hybrid material consisting of silica nanoparticles (SiO2) attached onto the surface of functionalized graphene nanoplatelets (f-GNPs) is proposed. Firstly, polyacrylic acid (PAA) was grafted to the surface of f-GNPs to increase reacting sites, and then 3-aminopropyltriethoxysilane (APTES) KH550 reacted with abovementioned product PAA-GNPs to obtain siloxane-GNPs, thus providing reaction sites for the growth of SiO2 on the surface of GNPs. Finally, the SiO2/graphene nanoplatelets (SiO2/GNPs) hybrid material is obtained through introducing siloxane-GNPs into a solution of tetraethyl orthosilicate, ammonia and ethanol for hours'' reaction. The results from Fourier transform infrared spectroscopy (FTIR) showed that SiO2 particles have situ grown on the surface of GNPs through chemical bonds as Si-O-Si. And the nanostructure of hybrid materials was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). All the images indicated that SiO2 particles with similar sizes were grafted on the surface of graphene nanoplatelets successfully. And TEM images also showed the whole growth process of SiO2 particles on the surface of graphene as time grows. Moreover, TGA traces suggested the SiO2/GNPs hybrid material had stable thermal stability. And at 900°C, the residual weight fraction of polymer on siloxane-GNPs was about 94.2% and that of SiO2 particles on hybrid materials was about 75.0%. However, the result of Raman spectroscopy showed that carbon atoms of graphene nanoplatelets became much more disordered, due to the destroyed carbon domains during the process of chemical drafting. Through orthogonal experiments, hybrid materials with various sizes of SiO2 particles were prepared, thus achieving the particle sizes controllable. And the factors’ level of significance is as follows: the quantity of ammonia > the quantity of tetraethyl orthosilicate (TEOS) > the reaction time.  相似文献   

18.
Thermal atomic layer-deposited (ALD) aluminum oxide (Al2O3) acquires high negative fixed charge density (Qf) and sufficiently low interface trap density after annealing, which enables excellent surface passivation for crystalline silicon. Qf can be controlled by varying the annealing temperatures. In this study, the effect of the annealing temperature of thermal ALD Al2O3 films on p-type Czochralski silicon wafers was investigated. Corona charging measurements revealed that the Qf obtained at 300°C did not significantly affect passivation. The interface-trapping density markedly increased at high annealing temperature (>600°C) and degraded the surface passivation even at a high Qf. Negatively charged or neutral vacancies were found in the samples annealed at 300°C, 500°C, and 750°C using positron annihilation techniques. The Al defect density in the bulk film and the vacancy density near the SiOx/Si interface region decreased with increased temperature. Measurement results of Qf proved that the Al vacancy of the bulk film may not be related to Qf. The defect density in the SiOx region affected the chemical passivation, but other factors may dominantly influence chemical passivation at 750°C.  相似文献   

19.
In this work, we report the structural, morphological, and optical properties of TiO2 thin films synthesized by the electro phoretic deposition technique. The TiO2 film was formed on a doped fluorine tin oxide (SnO2:F, i.e., FTO) layer and used as a photo electrode in a dye solar cell (DSC). Using spectroscopic ellipsometry measurements in the 200 to 800 nm wavelengths domain, we obtain a thickness of the TiO2 film in the range of 70 to 80 nm. Characterizations by X-ray diffraction and atomic force microscopy (AFM) show a polycrystalline film. In addition, AFM investigation shows no cracks in the formed layer. Using an ultraviolet–visible near-infrared spectrophotometer, we found that the transmittance of the TiO2 film in the visible domain reaches 75%. From the measured current–voltage or I-V characteristic under AM1.5 illumination of the formed DSC, we obtain an open circuit voltage Voc = 628 mV and a short circuit current Isc = 22.6 μA, where the surface of the formed cell is 3.14 cm2.  相似文献   

20.
Cu2ZnSnSe4 (CZTSe) thin films are prepared by the electrodeposition of stack copper/tin/zinc (Cu/Sn/Zn) precursors, followed by selenization with a tin source at a substrate temperature of 530°C. Three selenization processes were performed herein to study the effects of the source of tin on the quality of CZTSe thin films that are formed at low Se pressure. Much elemental Sn is lost from CZTSe thin films during selenization without a source of tin. The loss of Sn from CZTSe thin films in selenization was suppressed herein using a tin source at 400°C (A2) or 530°C (A3). A copper-poor and zinc-rich CZTSe absorber layer with Cu/Sn, Zn/Sn, Cu/(Zn + Sn), and Zn/(Cu + Zn + Sn) with metallic element ratios of 1.86, 1.24, 0.83, and 0.3, respectively, was obtained in a selenization with a tin source at 530°C. The crystallized CZTSe thin film exhibited an increasingly (112)-preferred orientation at higher tin selenide (SnSe x ) partial pressure. The lack of any obvious Mo-Se phase-related diffraction peaks in the X-ray diffraction (XRD) diffraction patterns may have arisen from the low Se pressure in the selenization processes. The scanning electron microscope (SEM) images reveal a compact surface morphology and a moderate grain size. CZTSe solar cells with an efficiency of 4.81% were produced by the low-cost fabrication process that is elucidated herein.  相似文献   

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