EAGER: RF Switches Using 2D Phase Change Materials

非技术：随着连接到世界无线基础设施的人员和设备数量的增长，电信体系结构变得越来越复杂。多用途、高性能系统的一个关键特征是可重构性，即调整无线电工作频带的能力。开关是构成可重构射频（RF）前端电路主干的器件，因此是研究的热点。相变开关是一项特别有前途的技术。这些装置依赖于通过施加电压或热量来改变纳米材料的晶体结构，从而改变其导电性。前几代的相变开关依赖于几十纳米厚的薄膜。这个EAGER项目旨在展示第一个原子厚度（1nm）的相变开关。这种开关将以碲化钼（MoTe2）为基础，这是一种原子级薄的半导体，属于一类被称为过渡金属二硫化物的材料。原子薄材料，通常被称为二维材料，提供了许多有趣的好处。这包括柔性电子器件的高应变极限和比竞争薄膜技术更高的电子迁移率。不同的二维材料也可以垂直堆叠，形成具有独特性能的新材料。对于射频开关性能至关重要的是，原子厚相变材料已经被预测为需要更低的电压来诱导相变。这将降低开关本身的能耗，以及它们所内置的整个系统的能耗。总体而言，低能量可重构射频电路可能对便携式、柔性或透明无线系统的发展产生深远的影响。它们的发展还可能导致新的应用，如便携式纳米无线电、电信远程节点和健康监测传感器。技术：拟议工作的目标是演示在射频（RF）频率下低压二维材料相变开关的操作。在具有多波段发射/接收能力的无线系统中，需要开关来实现可重构RF前端电路。与固态或机电开关相比，相变开关具有低损耗、高截止频率、高隔离和快速开关的优点。二维（2D）碲化钼（MoTe2）已被证明具有相变特性，其理论预测电压要求显著低于传统薄膜相变材料。低电压开关，加上灵活性和透明度，使二维相变开关成为下一代移动纳米系统的有吸引力的候选者。提出的工作将实验验证和表征大面积，2D MoTe2 RF开关。这将涉及器件的制造，以及低压和频率响应性能极限的实验探索。这些结果将是未来相变器件发展、预测模型建立和可重构纳米电路演示的关键。该EAGER提案的智力优点包括：(1)探索并建立对应用于2D MoTe2和相关器件的相位控制技术（如热量和电压）之间权衡的基本理解，以便建立行为模型并实现低能量开关器件；(2)解锁2D相变膜的大面积化学气相沉积（CVD），特别注意低能相变的厚度控制，以及高频操作的迁移率增加；(3)建立第一批使用二维相变材料的射频开关的基本设计程序，这将通过制造和表征进行验证。所提出的工作结果将对低功耗无线电路产生巨大影响，并加速物联网内外无线传感器节点的出现。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。

Non-technical:Telecommunications architectures have become increasingly more complex as the number of people and devices connected to the world's wireless infrastructure grows. One key characteristic of multi-purpose, high performance systems is reconfigurability--the ability to tune the frequency band at which a radio operates. Switches are the devices that form the backbone of reconfigurable radio-frequency (RF) front-end circuits and are therefore the subject of intense research. Phase change switches are a particularly promising technology. These devices rely on changing electrical conductivity of a nanomaterial by changing the crystal structure through the application of voltage or heat. Previous generations of phase change switches have relied on films that are tens of nanometers thick. This EAGER project aims to demonstrate the first atomically thick ( 1 nm) phase change switch. The switch will be based on molybdenum telluride (MoTe2), an atomically thin semiconductor that belongs to a class of materials known as transition metal dichalcogenides. Atomically thin materials, often referred to as two-dimensional materials, offer a number of interesting benefits. These include high strain limits for flexible electronics and higher electron mobilities than competing thin film technologies. Different two-dimensional materials can also be stacked vertically to form new materials with unique properties. Critical to RF switch performance, atomically thick phase change materials have been projected to require lower voltages to induce a phase change. This will lower the energy consumption of the switches themselves, as well as the overall systems that they are built into. Overall, low-energy reconfigurable RF circuits could have a profound impact in the development of portable, flexible or transparent wireless systems. Their development could also lead to new applications such as portable nano-radios, remote nodes for telecommunications and sensors for health monitoring.Technical:The objective of the proposed work is to demonstrate the operation of low voltage, 2D material-based phase change switches at radio-frequency (RF) frequencies. Switches are required for reconfigurable RF front-end circuits in wireless systems with multi-band transmit/receive capabilities. Compared to solid-state or electro-mechanical, phase change switches promise low loss, high cut-off frequencies, high isolation and rapid switching. Two-dimensional (2D) molybdenum telluride (MoTe2) has been shown to demonstrate phase change properties, with theoretically projected voltage requirements significantly lower than traditional thin film phase change materials. Low voltage switching, coupled with flexibility and transparency make 2D phase change switches attractive candidates for next-generation, mobile nanosystems. The proposed work will experimentally validate and characterize large area, 2D MoTe2 RF switches. This will involve fabrication of the devices, as well as experimental exploration of the low-voltage and frequency response performance limits. These results will be key to the future development of phase change devices, the establishment of predictive models and the demonstration of reconfigurable nano-circuits. The intellectual merit of this EAGER proposal comprises of the following: (1) exploring and establishing a fundamental understanding of trade-offs between phase control techniques, such as heat and voltage, applied to 2D MoTe2 and related allows in order to establish behavioral models and achieve low-energy switching devices; (2) unlocking large-area chemical vapor deposition (CVD) of 2D phase change films, paying particular attention to thickness control for low-energy phase transitions, as well as increased mobility for high-frequency operation; and (3) establishing basic design procedures for the first RF switches using 2D phase change materials, which will be validated through fabrication and characterization. This results of proposed work stand to have immense implications for low-power wireless circuits and accelerate the advent of wireless sensor nodes within the Internet of Things and beyond.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.