Resistive switches (RRAM) and memristive behaviour in silicon-rich silicon oxides

该项目的主要目标是发展对富硅氧化物中电阻开关的基本理解和应用。这可能会导致硅微电子器件在电阻随机存取存储器（RRAM）器件的低成本片上集成方面取得突破。为此，我们将进行详细的开关实验研究；开发物理切换模型；将该模型应用于演示器件的设计和制造；表征器件，并为包含Si RRAM的系统开发电路级模型，从而将Si微电子的功能扩展到新的领域和应用。RRAM器件是其电阻可以通过施加适当的电压来改变的元件。它们是下一代电子存储器的有希望的候选者，与传统的闪存相比，它们具有许多显著的优势，包括：非常高的封装密度；快速切换;低能量开关；3D集成，进一步增加内存容量；易于处理。现有的RRAM技术主要基于金属氧化物材料。然而，硅基器件具有许多优点，包括易于与硅CMOS处理技术集成，以及通过改变编程电压脉冲来定制其电性能的可能性。RRAM设备在内存之外还有潜在的应用：如果设备电阻可以连续变化，它们的行为可能与神经元类似，因此可能用于新型神经网络或其他处理架构。此外，由于电阻开关在CMOS器件中具有许多氧化物失效的特征，因此对RRAM的研究结果将产生有价值的信息，可能有助于减少器件故障，甚至恢复损坏的器件。我们最近开发了一种Si/SiO2 RRAM。与竞争技术不同，它不依赖于金属离子的扩散，只能由Si和SiO2制成，并且在环境条件下运行。电阻对比度高达1,000,000，开关时间<90ns，开关能量低于1pJ/bit。扫描隧道显微镜显示单个开关元件小至10nm。器件可以循环数千次，可以在单极或双极模式下工作，每种模式都具有不同的特性：在前者中，可以实现离散电平之间的二进制切换，而在后者中，我们能够连续改变器件电阻，从而开辟了模拟器件如忆阻器的可能性。我们的设备是现有的金属氧化物基设备的替代品。Si/SiO2系统是Si CMOS技术的基石-我们的设备不需要其他材料。我们发现，在SiOx器件中，金属氧化物系统中可靠的电阻开关所需的外部设定电流顺应性是不必要的——结构的不对称掺杂产生了内在的自限制。此外，我们基于半导体的RRAM器件固有的高度非线性减轻了RRAM器件阵列中寄生漏电流的问题。我们的项目将比Si/SiO2 RRAM器件的实验研究更进一步。我们还将开发电阻开关过程的综合理论模型，以及电路级模型来研究我们的RRAM器件在实际系统中的应用。我们的方法是新颖而独特的，因为它从材料的原子建模和电气特性，以及电阻开关中涉及的基本电子和离子过程，到实验设备的模拟和制造，再到它们在技术上的优化和潜在实现。这只能通过伦敦大学学院和格拉斯哥大学的专业知识的协同作用来实现。

The main goal of this project is to develop a fundamental understanding and applications of resistive switching in silicon-rich oxide. This may lead to a breakthrough in low-cost on-chip integration of Resistive Random Access Memory (RRAM) devices with Si microelectronics. To achieve that we will carry out detailed experimental studies of switching; develop a physical switching model; apply this model to design and fabricate demonstrator devices; characterise the devices, and develop circuit-level models for systems incorporating Si RRAM and hence extend the capabilities of Si microelectronics into new domains and applications.RRAM devices are components whose electrical resistance can be varied by applying an appropriate voltage. They are promising candidates for next generation electronic memories, offering a number of significant advantages over conventional Flash memory, including: very high packing density; fast switching; low energy switching; 3D integration to further increase memory capacity; ease of processing. Existing RRAM technologies are primarily based on metal oxide materials. However, Si- based devices have a number of advantages, including ease of integration with silicon CMOS processing technology, along with the possibility to tailor their electrical properties by varying programming voltage pulses.RRAM devices have potential applications beyond memory: if the device resistance can be continuously varied they may behave in a similar way to neurons, and may therefore be used in novel neural networks or other processing architectures. Also, as resistive switching shares many of the features of oxide failure in CMOS devices, the results from a study of RRAM will yield valuable information that may help reduce device failure, or even recovering damaged devices.We have recently developed a Si/SiO2 RRAM. Unlike competing technologies, it does not rely on the diffusion of metal ions, can be fabricated only from Si and SiO2, and operates in ambient conditions. Resistance contrast is up to 1,000,000, switching time <90ns, and switching energy 1pJ/bit or lower. Scanning Tunnelling Microscopy suggests individual switching elements as small as 10nm. Devices can be cycled thousands of times and can be operated in either unipolar or bipolar modes, with different characteristics in each: in the former, binary switching between discrete levels can be achieved, while in the latter we are able to continuously vary the device resistance, opening up the possibility of analogue devices such as memristors.Our devices are an alternative to existing metal oxide-based devices. The Si/SiO2 system is the building block of Si CMOS technology - our devices require no other material. We have found that the externally-set current compliance required for reliable resistive switching in metal oxide systems is not necessary in SiOx devices - asymmetric doping of the structure produces intrinsic self-limiting. In addition, the high degree of nonlinearity inherent in our semiconductor-based RRAM devices mitigates the problem of parasitic leakage currents in arrays of RRAM devices.Our project will go further than experimental studies of Si/SiO2 RRAM devices. We will also develop comprehensive theoretical models for the resistance switching process, and circuit-level models to investigate the application of our RRAM devices in real systems. Our approach is novel and unique in that it goes all the way from the atomistic modelling and electrical characterization of materials and fundamental electronic and ionic processes involved in resistive switching, through the simulation and fabrication of experimental devices to their optimisation and potential implementation in technology. This can only be achieved via synergy of expertise available at UCL and Glasgow.