Influence of carrier concentration on the resistive switching characteristics of a ZnO-based memristor

Sandwich-style memristor devices were synthesized by electrochemical deposition with a ZnO film serving as the active layer between Al-doped ZnO （AZO） and Au electrodes. The carrier concentration of the ZnO films is controlled by adding HNO3 during the growth process. A resulting increase in carrier concentration from 10^17 to 10^19 cm^-3 was observed, along with a corresponding drop in the on--off ratio from 6,437% to 100%. The resistive switching characteristics completely disappeared when the carrier concentration was above 1029 cm-3, making it unsuitable for a memory device. The decreasing switching ratio is attributed to a reduction in the driving force for oxygen vacancy drift. Systematic analysis of the migration of oxygen vacancies is presented, including the concentration gradient and electrical potential gradient. Such oxygen vacancy migration dynamics provide insight into the mechanisms of the oxygen vacancy drift and provide valuable information for industrial production of memristor devices.

Effect of carrier screening on ZnO-based resistive switching memory devices

The carrier screening effect occurs commonly in dielectric materials. It reduces the electric potential gradient, thus negatively affecting the functionality of resistive random access memory （RRAM） devices. An Au/ZnO film/Al-doped ZnO device fabricated in this work exhibited no resistive switching （RS）, which was attributed to the carrier screening effect. Therefore, annealing was used for alleviating the screening effect, significantly enhancing the RS property. In addition, different on/off ratios were obtained for various bias values, and the screening effect was accounted for by investigating electron transport mechanisms. Furthermore, different annealing temperatures were employed to modulate the free carrier concentration in ZnO films to alleviate the screening effect. The maximal on/off ratio reached 10s at an annealing temperature of 600 ℃, yielding the lowest number of free carriers and the weakest screening effect in ZnO films. This work investigates the screening effect in RS devices. The screening effect not only modulates the characteristics of memory devices but also provides insight into the mechanism of RS in these devices.

Neoantigen vaccine and neoantigen-specific cell adoptive transfer therapy in solid tumors:Challenges and future directions

The phenomenon of tumor hierarchy and genetic instability can be explained by the“two-hits theory”and results in the occurrence of many somatic mutations.The expression of nonsynonymous mutations results in the production of mutant proteins from tumor cells,namely tumor-specific antigens called neoantigens.Because neoantigens do not exist in healthy cells,they have the potential to stimulate antitumor immune responses by CD4+and CD8+T-cell activation without jeopardizing normal tissues.Immunotherapy has reshaped the cancer treatment paradigm in recent decades with the introduction of immune-checkpoint blockade therapy and transgenic Tcell receptor/chimeric antigen receptor T cells.However,these strategies performed poorly in solid tumors because of the obstacles of the immunosuppressive microenvironment caused by regulatory T cells and other suppressor cells.Therefore,other immunotherapeutic strategies are under development,such as personalized vaccines,to trigger de novo T-cell responses against neoantigens and lead to the amplification of tumorspecific T-cell subclones.Neoantigen epitope prediction algorithms have enabled the detection of neoantigens and the creation of tailored neoantigen vaccines as a result of the fast development of next-generation sequencing and cancer bioinformatics.Here we provide an overview of the current neoantigen cancer vaccines and adoptive T-cell transfer therapy with neoantigen-specific lymphocytes.We also discuss the challenges in developing neoantigentargeted immunotherapeutic strategies for cancer.