New Publication: Tunable Volatility of Ge2Sb2Te5 in Integrated Photonics

Congratulations to third year CDT PGR Emanuele Gemo , co-author of a paper, Tunable Volatility of Ge2Sb2Te5 in Integrated Photonics, which was recently published in the prestigious journal Advanced Functional Materials. His co-authors include his supervisors Dr Anna Baldycheva and Prof C David Wright.

This work was led by researchers from the labs of Prof Harish Bhaskaran at Oxford University and Prof Dr Wolfram Pernice at Muenster University. It was carried under the auspices of the EU H2020 project Fun-COMP .


The operation of a single class of optical materials in both a volatile and nonvolatile manner is becoming increasingly important in many applications. This is particularly true in the newly emerging field of photonic neuromorphic computing, where it is desirable to have both volatile (short‐term transient) and nonvolatile (long‐term static) memory operation, for instance, to mimic the behavior of biological neurons and synapses. The search for such materials thus far have focused on phase change materials where typically two different types are required for the two different operational regimes.

In this paper, a tunable volatile/nonvolatile response is demonstrated in a photonic phase‐change memory cell based on the commonly employed nonvolatile material Ge2Sb2Te5 (GST). A time‐dependent, multiphysics simulation framework is developed to corroborate the experimental results, allowing us to spatially resolve the recrystallization dynamics within the memory cell. It is then demonstrated that this unique approach to photonic memory enables both data storage with tunable volatility and detection of coincident events between two pulse trains on an integrated chip. Finally, improved efficiency and all‐optical routing with controlled volatility are demonstrated in a ring resonator. These crucial results show that volatility is intrinsically tunable in  normally nonvolatile GST which can be used in both regimes interchangeably.


Figure 1
Phase‐change photonic device. a) Illustration of device and measurement scheme. Optical WRITE pulses are used to switch the GST to a partial amorphous state while a counter propagating, variable‐power optical probe is used to control the recrystallization dynamics. b) Optical image of single device with input grating coupler (center), reference waveguide and output coupler (left), and device waveguide and input/output coupler (right). (Scale bar is 50 µm) c) False‐color SEM image of the GST vertical strip overlaying the Si3N4 waveguide. (Scale bar is 1 µm) d) FDTD simulations of the power flow from left to right through the region of GST (outlined by white dashed lines) when GST is in both the amorphous and crystalline states. e) Experimental optical transmission of device with increasing optical probe power. At low probe powers (black line), the device remains in the amorphous state for nonvolatile operation, while increasing the probe power causes recrystallization of the GST. f) Simulated optical transmission and crystallization dynamics of the device during volatile operation.


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