CAREER: Melting-free Photonic Memory with Layered Chalcogenide Materials

University Of Delaware, Newark DE

Investigators

Abstract

Nonvolatile memories, which retain their device status (resistance or refractive index change) after removing the external drive (such as heat, electric field, current, or illumination), are indispensable components in many stand-alone systems. Nonvolatile electronic memories have a rich history, and they can be broadly categorized into three primary groups: phase change material (PCM), memristor, and ferroelectric memory, operating through thermal-induced atomic restructuring, current-driven ionic dynamics, and electric field-oriented polarization, respectively. Over the past half-century, electronic memory technologies have witnessed significant growth, achieving a high level of maturity in terms of scalability, endurance, and CMOS integration. Being able to perform uniform phase transitions over a subwavelength scale makes PCMs particularly suitable for photonic applications. For switching between amorphous and crystalline states, the chalcogenide PCMs are brought to a melting temperature to break the covalent bonds. The cooling rate determines the final state. The high melting temperature sets the upper limit of clock rate, integration density, and the device lifetime. The proposed works will explore alternative optical reversible tuning mechanisms, address a few myths and challenges in the new material platform, and locate proper photonic memory device schematics. The CAREER project will be carried out by graduates, with the involvement of undergraduates and high school interns. Through local society-organized summer camps, our undergraduate and high school interns will share their initiatives and motivations for choosing STEM with the younger generations. The proposed projects bridge the fields of layered material physics, semiconductor manufacturing, and photonic technologies, and strengthen multidisciplinary education among quantum mechanics, nanofabrication, optoelectronics, and photonic system engineering. The proposed work explores melting-free mechanisms in layered chalcogenide materials for nonvolatile tuning and switching in integrated photonics, enabled by the unique atomic structures in these materials. The small energy barrier facilitates low temperature reversible phase transitions, which reduces the chance of element segregation-associated device failure. This material search started with In2Se3. Its layered structures are convertible and stable at room temperature. In addition, loss-invariant large refractive index tuning in layered chalcogenide through photochemistry will be explored in ambient conditions. Through in-situ probing of the material and device responses, a physical framework will be developed for describing the complex interplay between the thermal and mechanical processes in the phase transition process, understand the details of transient dynamics at atomic scale, and optimize device geometric design and fabrication steps towards selected photonic applications, from high contrast coherent optical modulator, phase array to integrated multi-layer metasurface system for photonic computing. This project is jointly funded by the Electrical, Communications and Cyber Systems division(ECCS), and the Established Program to Stimulate Competitive Research (EPSCoR). 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.