Switchable Persistent Spin Helix Devices

功耗和能耗是制约当前基于硅场效应晶体管的计算技术未来可扩展性的关键因素。由于它们具有低开关能量的潜力，利用电子自旋来携带信息而不是电荷的自旋电子器件长期以来一直被作为数字计算和模拟设备的替代方法。然而，实现自旋电子器件的潜力需要克服一些基本的挑战。首先，传统自旋电子材料（如砷化镓）中的弱自旋轨道耦合需要在大型设备上传输电子以控制自旋。相比之下，使用具有高自旋-轨道耦合的材料来制造较小的器件会导致自旋信息由于失相而快速丢失：自旋快速旋转并且彼此失相。pi们提出利用具有特殊自旋行为的材料来解决这两个挑战，这种自旋行为被称为持续自旋螺旋，其中电子自旋即使在快速旋转时也保持相，使自旋信息即使在高自旋轨道材料中也能保留更长时间。具体来说，通过在具有强自旋-轨道耦合的范德华固体中使用电场可调谐的持续自旋螺旋，pi建议为自旋电子器件提供一类新的材料，其中自旋行为可以由电场敏感地控制，并且由于明显更强的自旋-轨道耦合，器件尺寸可以减少两到三个数量级。这将有助于创新具有竞争力的自旋场效应晶体管的设计，用于高性能和低功耗计算。该奖项还旨在促进在快速发展的自旋电子材料和器件领域中历史上代表性不足的群体的研究培训，从而为未来微电子技术的发展提供技术知识和劳动力。研究人员提出了解电场调谐对称性和哈密顿量对自旋电子器件中具有强自旋轨道耦合的方形范德华晶体的自旋织构、自旋动力学和自旋输运的影响。根据所选材料基平面的方对称性和天然量子阱结构，当外加电场沿所期望的晶体取向施加时，可以得到持续的自旋螺旋型自旋轨道场。凭借持续的自旋螺旋态和强自旋轨道耦合，pi有望实现电场/电压可切换的对称保护远程相干自旋输运。模型材料包括空气稳定，光刻友好的范德华晶体Bi2O2Se和BiOI，模型器件包括持续自旋螺旋自旋场效应晶体管。所提出的启用和调整持续自旋螺旋的方法不需要在III-V中常见的Rashba和Dresselhaus场之间进行仔细的平衡。这使得所提出的模型系统成为探索自旋场效应晶体管的强大平台。pi将生长单晶取向控制的自旋电子四方范德华半导体，并制造持久的自旋螺旋型场效应晶体管。pi将通过计算和实验揭示模型材料和器件中自旋极化带结构、持续自旋螺旋的动力学和波长。pi还将演示基于持续自旋螺旋的场效应晶体管的概念验证，并揭示器件结构/尺寸、栅极介质、外部电压/极化和温度对自旋场效应晶体管特性和性能的影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Power dissipation and energy consumption are a key limiting factor in the future scalability of present computing technologies based on silicon field-effect transistors. Due to their potential for a low switching energy, spintronic devices that leverage the spin of electrons to carry information instead of their charge have long been pursued as an alternative approach, both for digital computing and analog devices. However, realizing the potential of spintronic devices requires overcoming a few basic challenges. First, weak spin-orbit coupling in conventional spintronic materials such as GaAs necessitates transport of electrons over large devices to allow control of the spin. In contrast, using a material with high spin-orbit coupling to make smaller devices leads to rapid loss of spin information due to dephasing: spins rapidly rotating and becoming out of phase with each other. The PIs propose to address these two challenges by leveraging materials with a special class of spin behavior called the persistent spin helix, where electron spins remain in phase even when rotating rapidly, enabling spin information to be retained longer even in high spin-orbit materials. Specifically, by using electric-field tunable persistent spin helix in van der Waals solids with strong spin-orbit coupling, the PIs propose to enable a new class of materials for spintronic devices, where the spin behavior can be sensitively controlled by electric fields and where the device dimensions can be reduced by two to three orders of magnitude due to the significantly stronger spin-orbit coupling. This would help innovate the design of competitive spin field-effect transistors for high-performance and low-power computing. This award also aims to promote research training to historically underrepresented groups in the rapidly growing field of spintronic materials and devices, and thereby contribute to both the technical knowhow and workforce for the development of future microelectronics.The PIs propose to understand the effect of electric field-tuned symmetry and Hamiltonian on the spin texture, spin dynamics, and spin transport of square van der Waals crystals with strong spin-orbit coupling for spintronic devices. With the square symmetry of the basal plane and natural quantum well structures of selected materials, when an external electric field is applied along desired crystallographic orientations, persistent spin helix-type spin-orbit field is expected. With persistent spin helix states and strong spin-orbit coupling, the PIs expect to achieve electric field/electric voltage-switchable symmetry-protected long-range coherent spin transport. The model materials include air-stable, lithography-friendly van der Waals crystals Bi2O2Se and BiOI, and the model devices include persistent spin helix-based spin field effect transistors. The proposed approach for enabling and tuning persistent spin helix does not require careful balance between Rashba and Dresselhaus fields commonly seen in III-V. This makes the proposed model systems a robust platform for exploring spin field effect transistor. The PIs will grow single crystalline orientation-controlled spintronic tetragonal van der Waals semiconductors and fabricate persistent spin helix-based field effect transistors. The PIs will computationally predict and experimentally reveal the spin-polarized band structure, and dynamics and wavelength of persistent spin helix in the model materials and devices. The PIs will also demonstrate the proof-of-concept persistent spin helix-based field effect transistors and reveal the effects of device structure/dimension, gate dielectrics, external voltage/polarization, and temperature on the characteristics and performance of the spin field effect transistor.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.