Multibit/analog artificial synapses are in demand for neuromorphic computing systems. A problem hindering the utilization of memristive artificial synapses in commercial neuromorphic systems is the rigidity of their functional parameters, plasticity in particular. Here, we report fabricating polycrystalline rutile-based memristive memory segments with Ti/poly-TiO₂/Ti structures featuring multibit/analog storage and the first use of a tunable DC-biasing for synaptic plasticity adjustment from short- to long-term. The unbiased device is of short-term plasticity, positive biasing increases the remanence of the recorded events and the device gains long-term plasticity at a specific biasing level determined from the device geometry. The adjustability of the biasing field provides an additional degree of freedom allowing performance tuning; the paired-pulse facilitation index of the device is tuned by the biasing level adjustment providing further functional versatility. An appropriately biased segment provides more than 10 synaptic weight levels linearly depending on the number and duration of the stimulating spikes. The relationship with spike magnitude is exponential. The experimentally determined nonlinearity coefficient of the biased device for 50 potentiating spikes is comparable to the best published data. The spike-timing-dependent plasticity determined experimentally for the biased device in its long-term plasticity mode fits the mathematical relationship developed for biological synapses. Fabricated on a titanium metal foil, the produced memristors are sturdy and flexible making them suitable for wearable and implantable intelligent electronics. Our findings are anticipated to raise the potential of forming artificial synapses out of polycrystalline metal oxide thin films.

中文翻译：

---

直流场偏置多位/模拟人工突触，具有额外的性能调整自由度


神经形态计算系统需要多比特/模拟人工突触。阻碍忆阻人工突触在商业神经形态系统中利用的一个问题是其功能参数的刚性，尤其是可塑性。在这里，我们报告了制造具有 Ti/poly-TiO2/Ti 结构的基于多晶金红石的忆阻存储器段，具有多位/模拟存储，并首次使用可调谐直流偏置进行从短期到长期的突触可塑性调整。无偏置器件具有短期可塑性，正偏置增加记录事件的剩磁，并且器件在由器件几何形状确定的特定偏置水平上获得长期可塑性。偏置场的可调节性提供了额外的自由度，允许进行性能调整;该器件的双脉冲促进指数通过偏置电平调整进行调节，从而提供进一步的功能多功能性。适当偏倚的片段根据刺激性尖峰的数量和持续时间线性提供超过 10 个突触权重水平。与尖峰幅度的关系是指数级的。实验确定的偏置器件对 50 个增强尖峰的非线性系数与已发表的最佳数据相当。在其长期可塑性模式下，通过实验确定的偏置器件的尖峰时间依赖性可塑性与为生物突触开发的数学关系相吻合。生产的忆阻器在钛金属箔上制造，坚固耐用且灵活，使其适用于可穿戴和植入式智能电子产品。 我们的发现有望提高从多晶金属氧化物薄膜形成人工突触的潜力。