EAGER: RF Switches Using 2D Phase Change Materials

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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.