Investigating pressure induced conductive states on the nanoscale : A novel route to nano-circuitry

以低成本、高吞吐量和高分辨率转移纳米级金属图案的能力对于削减半导体和数据存储设备的制造成本具有巨大的意义。类似纳米压印光刻的技术允许通过压印抗蚀剂的机械变形和后续工艺来制造这样的纳米尺度图案。尽管该技术被认为是最简单的光刻方法之一，但它在图案转移期间仍然包括几个复杂的步骤。如果转移步骤可以被消除，并且只有压印步骤可以直接导致在所选材料上印刷几个纳米的尖锐电路图案，这将代表在纳米电路图案的生产量和再现性方面的巨大飞跃。为了实现直接压印电路的这一有远见的目标，作为第一步，有必要了解材料中的物理现象，这些物理现象将允许局部压力用作在其他绝缘材料中绘制和控制尖锐导电通道的工具。至少有两种不同的机制可以在绝缘材料中引起局部压力诱导的导电状态。具有导电畴壁的铁电体和经历金属-绝缘体相变的材料是两种主要的材料系统，其中纳米级压力可用于实现材料中的受限导电状态，并可能实现对此类界面的确定性控制。这两种系统允许共存的导电壁或相的散装，但通过局部应力导致在这些材料中的导电界面或通道的形成的机制仍然是很好地理解之前，效果本身可以被充分利用。对于潜在的应用，还需要评估压力下通道形成的难易程度、其稳定性和可重构性。为了解决这些问题，本提案的主要目标是建立局部纳米级导电状态的压力介导控制，并对与此行为相关的物理学进行基本了解，以便可以实现导电界面的可靠控制，作为迈向纳米电路的第一步。通过原子力显微镜（AFM）尖端施加的压力将用于在三种不同的材料中注入导电状态：不适当的铁电体，混合相铁电体和经历金属-绝缘体相变的材料，每种材料都代表通过压力诱导写入产生的独特类型的导电界面。在这三种情况下，将评估尖端压力诱导的导电壁/相的可实现控制程度，并将进行实验，以确定所创建界面的物理起源和导电性机制。通过掌握这些材料中压力诱导导电性的机制，我们的目标是能够精确控制这些受限壁或相的形成和湮灭。将评估压力介导的导电行为控制与其他刺激的互补性，以获得导电通道的最佳可重构性和读取/擦除能力。将对横向电极之间的压力感应传导通道进行概念验证。因此，基于AFM的方法将有助于建立所讨论的材料系统中的压力诱导导电状态的基础物理学，并为开发用于直接写入纳米电路的其他纳米压印方法提供关键见解。

The ability to transfer nanometer scale metallic patterns at low cost, high throughput and high resolution has huge implications for slashing the manufacturing costs of semiconductors and data storage devices. Techniques like nanoimprint lithography allow fabrication of such nanometer scale patterns by mechanical deformation of imprint resist and subsequent processes. Even though the technique is considered one of the simplest lithography approaches, it still comprises of several complicated steps during pattern transfer. If the transfer step could be eliminated and only the imprint step could directly result in the printing of a few nanometer sharp circuit pattern on the chosen material, that would represent a dramatic leap in terms of throughput and reproducibility of patterns for nano-circuitry. In order to achieve this visionary goal of directly imprinting circuitry, it is necessary as a first step to understand the physical phenomena in materials that would allow localised pressure to be used as a tool to sketch and control sharp conductive channels in an otherwise insulating material. There are atleast two different mechanisms that could give rise to local pressure induced conductive states in an insulating material. Ferroelectrics with conducting domain walls and materials undergoing metal-insulator phase transitions are the two primary material systems where nanoscale pressure can be used to realise confined conducting states in the material and potentially achieve deterministic control of such interfaces. Both systems allow co-existence of conducting walls or phases in the bulk but the mechanisms through which localised stress results in the formation of conductive interfaces or channels in these materials remains to be well understood before the effect itself can be fully exploited. For potential applications, it is also necessary to evaluate the ease of channel formation under pressure, their stability and reconfigurability. To address these issues, the primary goal of this proposal is to establish the pressure mediated control of localised nanoscale conductive states and develop a fundamental understanding of the physics associated with this behaviour so that reliable control of conductive interfaces can be achieved as a first step towards nano-circuitry. Pressure applied via an atomic force microscope (AFM) tip will be used to inject conductive states in three different materials : an improper ferroelectric, a mixed phase ferroelectric and a material undergoing metal-insulator phase transition, each representing a unique type of conductive interface created through pressure induced writing. In each of the three cases, the achievable degree of control of tip pressure induced conductive walls/phases will be evaluated and experiments will be performed to identify the physical origin and the mechanisms underlying the conductivity of the created interfaces. With a grasp on the mechanism of pressure induced conductivity in these materials, we aim to be able to precisely control the formation and annihilation of these confined walls or phases. The complementarity of pressure mediated control of conductive behaviour with other stimuli will be evaluated for optimal reconfigurability of conductive channels and read/erase capability. Proof-of-concept demonstration of pressure induced conductive channels between lateral electrodes will be performed. The AFM based approach developed here would thus help establish the underpinning physics of pressure induced conductive states in the discussed material systems and provide key insight for developing other nanoimprint methods for direct writing of nano-circuitry.