Nathan’s second NSF proposal entitled, “High-endurance phase-change devices for electrically reconfigurable optical systems” was funded! Our lab will be working in collaboration with co-PI Feng Xiong at Pitt to investigate the mechanisms limiting the endurance and cyclability of electrically-controlled, phase-change photonic memory. See the following technical abstract for more information:

Technical abstract: Phase-change materials, such as Ge2Sb2Te5 and GeTe, are particularly promising for reconfigurable optical devices owing to their fast, dramatic, non-volatile, and reversible change in refractive index. Experimental demonstrations of reconfigurable smart windows, reflective displays, metasurfaces, and photonic devices for memory and computing have reignited interest in these materials. For phase-change devices with dimensions greater than the optical wavelength, an electro-thermal approach to switching is most promising, but limited prior work shows poor endurance and cyclability (1000 cycles or less) compared to the high endurances (greater than 10 million cycles) demonstrated for phase-change data storage. The team proposes that the endurance is limited by poorly matched thermal properties of materials within these devices, while the degrading optical contrast often observed is due to phase segregation and void formation in the phase-change layer. To test this hypothesis, the project has three aims:

(1) improve the lifetime of electro-thermal phase-change devices by properly matching the thermal expansion coefficients of the materials within the device layers;

(2) reduce the cycling-induced degradation of optical contrast by reducing thermal gradients within the device and improving deposition conditions; and

(3) identify the effects and limitations of scaling on phase-change optical devices.

The proposed approach will overcome the limited cyclability of prior electro-thermally switched phase-change devices by studying the thermal response of the device layers through complementary thermal-mechanical modelling, dynamic optoelectronic measurements, and advanced nano-characterization techniques. The insights gained by understanding and addressing the current limitations of electro-thermally controlled optical phase-change films are expected to be broadly applicable to such fields as tunable optical coatings, non-von Neumann computing, electrical-optical conversion, and reconfigurable photonic and RF systems.

Link to NSF funding page here.