Phase Change Dynamics and Two-Dimensional 4-Bit Memory in Ge₂Sb₂Te₅ via Telecom-Band Encoding

Abstract

As modern computing gets continuously pushed up against the von Neumann Bottleneck -limiting the ultimate speeds for data transfer and computation-new computing methods are needed in order to bypass this issue and keep our computer's evolution moving forward, such as hybrid computing with an optical co-processor, all-optical computing, or photonic neuromorphic computing. In any of these protocols, we require 1 arXiv:1911.03536v1 [physics.app-ph] 7 Oct 2019 an optical memory: either a multilevel/accumulator memory, or a computational memory. Here, we propose and demonstrate a 2-dimensional 4-bit fully optical non-volatile memory using Ge 2 Sb 2 Te 5 (GST) phase change materials, with encoding via a 1550 nm laser. Using the telecom-band laser, we are able to reach deeper into the material due to the low-loss nature of GST at this wavelength range, hence increasing the number of optical write/read levels compared to previous demonstrations, while simultaneously staying within acceptable read/write energies. We verify our design and experimental results via rigorous numerical simulations based on finite element and nucleation theory, and we successfully write and read a string of characters using direct hexadecimal encoding.

Combining Switchable Phase‐Change Materials and Phase‐Transition Materials for Thermally Regulated Smart Mid‐Infrared Modulators

“…[36,37] The spectral tuning via the PCM layer can also be realized continuously with a much faster, well-defined, multilevel switching by applying electrical or optical methods. [7,38,39] In principle, very fast electrical and optical switching in the ns-range has been shown for memory applications, [6,40] mostly on sub-micron length scales. In these applications, the speedlimiting factor is normally the crystallization speed and the size of the devices.…”

Ultra‐Thin Switchable Absorbers Based on Lossy Phase‐Change Materials

“…It is however well-known that intermediate crystallization states can be accessed by short-time annealing [72][73][74] or optical switching. [48,51,75,76] Thus, the whole absorptance tuning ranges marked in Figure 3b should be accessible with these intermediate states. To investigate the effect of partial crystallization on the absorptance of an ultrathin lossy PCM absorber, we first fabricated a sample consisting of 20 nm GeTe on a sapphire substrate.…”

Multilevel Switching in Phase‐Change Photonic Memory Devices

“…As a result, 16 multilevel states between SET and RESET have been realized in both nucleation dominated GST and growth dominated AIST materials. [ 51,62,64 ] Similarly, optical tuning capability has also been observed in integrated phase‐change photonic memory devices by using single‐shot laser pulses. The single‐shot pulses are used to tune different amorphous levels in integrated circuits, whereas multishot pulses are required for attaining different crystalline levels.…”

“…To overcome this problem, single‐shot laser pulses of variable fluence have been introduced to produce multilevel states with higher optical contrast. [ 53,61–63 ] There is a linear rise in the optical contrast between the SET and RESET process with an increase in the laser fluence (performed in free‐space optics), as shown in Figure . [ 64 ] By carefully tuning the laser fluence, the optical contrast can be increased significantly, which enables precise tunability of amorphous/crystalline volumetric fraction.…”