Cosmin Popescu1,Brian Mills1,2,Louis Martin1,Luigi Ranno1,Yifei Zhang1,Qingyang Du1,3,Carlos Ríos4,1,Steven Vitale5,Christopher Roberts5,Paul Miller1,5,Vladimir Liberman5,Hyun Jung Kim6,Kiumars Aryana6,Dennis Callahan2,Myungkoo Kang7,Kathleen Richardson7,Tian Gu1,Juejun Hu1
Massachusetts Institute of Technology1,Charles Stark Draper Laboratory2,Zhejiang Lab3,University of Maryland4,Lincoln Laboratory, Massachusetts Institute of Technology5,NASA Langley Research Center6,University of Central Florida7
Cosmin Popescu1,Brian Mills1,2,Louis Martin1,Luigi Ranno1,Yifei Zhang1,Qingyang Du1,3,Carlos Ríos4,1,Steven Vitale5,Christopher Roberts5,Paul Miller1,5,Vladimir Liberman5,Hyun Jung Kim6,Kiumars Aryana6,Dennis Callahan2,Myungkoo Kang7,Kathleen Richardson7,Tian Gu1,Juejun Hu1
Massachusetts Institute of Technology1,Charles Stark Draper Laboratory2,Zhejiang Lab3,University of Maryland4,Lincoln Laboratory, Massachusetts Institute of Technology5,NASA Langley Research Center6,University of Central Florida7
The ability to reconfigure the optical behavior of a device enables many applications ranging from imaging to sensing and signal control. Such optical devices can be compacted via meta-surfaces, patterned structures with feature sizes below the incident wavelength. Leveraging geometry in addition to material properties and CMOS fabrication techniques has allowed meta-surfaces to operate as lenses, holograms, beam steerers, and more. To incorporate multiple optical functions into one device, various methods of device control have been implemented such as stretching of flexible substrates, tuning the refractive index of the comprising meta-atoms via the electro-optic or the thermo-optic effects, phase transition materials such as VO<sub>2</sub>, and more. Chalcogenide glasses used as optical phase change materials, such as Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub> (GST), have gained increased traction in the optics community for potential use in the NIR and MIR, including the telecom bands. Various chalcogenides such as Sb<sub>2</sub>Se<sub>3</sub>, Sb<sub>2</sub>S<sub>3</sub>, Ge<sub>2</sub>Sb<sub>2</sub>Se<sub>5</sub>, and Ge<sub>2</sub>Sb<sub>2</sub>Se<sub>4</sub>Te (GSST) have been investigated due to their broad NIR or MIR transparency window and large changes in refractive index. In their amorphous phase, these materials usually display a lower refractive index & low absorption when compared to their crystalline state which displays a higher refractive index and typically larger extinction coefficients. The amorphous-crystalline reversible switching can be done on-chip via fast melt-quenching processes triggered by laser heating or electrical impulses, which rely on a substrate as a heat sink. The potential of PCMs in photonic devices can be limited by intrinsic material limitations as well as by device fabrication issues. To explore the cyclability of GSST, a PCM with large refractive index contrast, on-chip electrothermal switching on a silicon-on-insulator platform has been done to analyze potential failure mechanisms from both a material and device perspective. A brief outline of the instrumentation and phase change contrast analysis is provided. Dewetting of the PCM, delamination of and damage to the PECVD SiN<sub>x</sub> protective layer, elemental migration in the PCM, and optical contrast decay have been observed in cycled GSST devices. Guidelines for device performance improvement are proposed and an improved design with greater endurance is shown in this work.