Effect of tungsten doping on the variability of InZnO conductive-bridging random access memory.

The characteristics of conductive-bridging random access memory (CBRAM) with amorphous indium-tungsten-zinc-oxide (a-InWZnO) switching layer and copper (Cu) ion-supply layer were prepared by sputtering. It was found that the doping ratio of tungsten has a significant effect on the memory characteristics of the CBRAM, and the doping of tungsten acts as a suppressor of oxygen vacancies in the InWZnO film. The O 1s binding energy associated with the oxygen-deficient regions in the α-InWZnO thin film decreases with increasing tungsten doping ratio, which can be demonstrated by x-ray photoelectron spectroscopy. When the tungsten doping ratio is 15%, the a-InWZnO CBRAM can achieve the excellent memory characteristics, such as high switching endurance (up to 9.7 × 103 cycling endurance), low operating voltage, and good retention capability. Moreover, the electrical uniformity and switching behavior of InWZnO device are evidently improved as the doping ratio of tungsten in the switching layer increases. These results suggest that CBRAM based on novel material InWZnO have great potential to be used in high-performance memory devices.

Oxygen Concentration Effect on Conductive Bridge Random Access Memory of InWZnO Thin Film.

In this study, the influence of oxygen concentration in InWZnO (IWZO), which was used as the switching layer of conductive bridge random access memory, (CBRAM) is investigated. With different oxygen flow during the sputtering process, the IWZO film can be fabricated with different oxygen concentrations and different oxygen vacancy distribution. In addition, the electrical characteristics of CBRAM device with different oxygen concentration are compared and further analyzed with an atomic force microscope and X-ray photoelectron spectrum. Furthermore, a stacking structure with different bilayer switching is also systematically discussed. Compared with an interchange stacking layer and other single layer memory, the CBRAM with specific stacking sequence of bilayer oxygen-poor/-rich IWZO (IWZOx/IWZOy, x < y) exhibits more stable distribution of a resistance state and also better endurance (more than 3 × 104 cycles). Meanwhile, the memory window of IWZOx/IWZOy can even be maintained over 104 s at 85 °C. Those improvements can be attributed to the oxygen vacancy distribution in switching layers, which may create a suitable environment for the conductive filament formation or rupture. Therefore, it is believed that the specific stacking bilayer IWZO CBRAM might further pave the way for emerging memory applications.

Highly durable and flexible gallium-based oxide conductive-bridging random access memory.

The flexible conductive-bridging random access memory (CBRAM) device using a Cu/TiW/Ga2O3/Pt stack is fabricated on polyimide substrate with low thermal budget process. The CBRAM devices exhibit good memory-resistance characteristics, such as good memory window (>105), low operation voltage, high endurance (>1.4 × 102 cycles), and large retention memory window (>105). The temperature coefficient of resistance in the filament confirms that the conduction mechanism observed in the Ga2O3 layer is similar with the phenomenon of electrochemical metallization (ECM). Moreover, the performance of CBRAM device will not be impacted during the flexibility test. Considering the excellent performance of the CBRAM device fabricated by low-temperature process, it may provide a promising potential for the applications of flexible integrated electronic circuits.

Performance Enhancement for Tungsten-Doped Indium Oxide Thin Film Transistor by Hydrogen Peroxide as Cosolvent in Room-Temperature Supercritical Fluid Systems.

In this study, hydrogen peroxide (H2O2) cosolvent, which was dissolved into supercritical-phase carbon dioxide fluid (SCCO2), is employed to passivate excessive oxygen vacancies of the high-mobility tungsten-doped indium oxide without any essential thermal process. With the detailed material analysis, the internal physical mechanism of the cosolvent effect or the interaction between the cosolvent solution and supercritical-phase fluid is well discussed. In addition, the optimized result has been applied for the thin film transistor device fabrication. As a result, the device with SCCO2 + H2O2 treatment exhibits the lowest subthreshold swing of 82 mV/dec, the lowest interface trap density of 8.76 × 1011 eV-1 cm-2, the lowest hysteresis of 47 mV, and an excellent reliability and uniformity characteristic compared with any other control groups. Besides, an extremely high field-effect mobility of 98.91 cm2/V s can also be observed, while there is even a desirable positive shift for the threshold voltage. Notably, compared with the untreated sample, the highest on/off current ratio of 5.11 × 107 can be achieved with at least four orders of magnitude enhancement by this unique treatment.

Mobility enhancement for high stability tungsten-doped indium-zinc oxide thin film transistors with a channel passivation layer.

This study investigates the electrical characteristics and physical analysis for an amorphous tungsten-doped indium-zinc oxide thin film transistor with different backchannel passivation layers (BPLs), which were deposited by an ion bombardment-free process. A 10 times increase in mobility was observed and attributed to the generation of donor-like oxygen vacancies at the backchannel, which is induced by the oxygen desorption and Gibbs free energy of the BPL material. The mechanism was well studied by XPS analysis. On the other hand, a HfO2 gate insulator was applied for the InWZnO TFT device to control the extremely conductive channel and adjust the negative threshold voltage. With both a HfO2 gate insulator and a suitable BPL, the InWZnO TFT device exhibits good electrical characteristics and a remarkable lifetime when exposed to the ambient air.