Electrical Programmable Low-loss high cyclable Nonvolatile Photonic Random-Access Memory

Abstract

The retention-of-state functionality provided by memories is fundamental to any Turing machine and neural network, hence is critical for any information system today. While emerging optical machine learning accelerators and photonic neuromorphic computing paradigms provide promising signal processing and computing performance, the lack of a photon-photon force in the universe makes storing optical information challenging. Fortunately, phase change materials provide such a missing memristive nonvolatile function via their reconfigurable crystalline structure and allow for rapid optical READ paradigms. However, demonstrations of photonic memory are limited by high optical loss, low state-cyclability, and rely on cumbersome non-CMOS like optical programmability. To overcome all three shortcomings and unlock the full potential of optical information storage and access, here we introduce a photonic random-access memory featuring vanishing low optical loss, demonstrate more than half a million switching cycles, a 100x improvement over state-of-art, and realize electrical programmability on-chip. The exceedingly low optical absorption (0.0015 dB/μm) is achieved via a novel broadband transparent phase change material, Ge2Sb2Se5 integrated atop a nanophotonic waveguide of a silicon chip. We show a highly efficient signal modulation (0.2 dB/μm) achieved by realizing a newly designed paired micro-heaters along both sides of waveguide, which allows for electronic-standard programmability of these photonic memories. When interrogated by an optical beam, they offer picosecond-short memory READ latency. Furthermore, we demonstrate a partial amorphization scheme realizing multi-state memory levels on a single heater enhancing footprint efficiency. Lastly, we verify the energy and switching speed and show how each trades-off with heater-to-waveguide proximity and signal strength, respectively. Such as CMOS-near electronically programmed and optical read photonic random-access memory with low-optical loss yet efficient programmability can become a crucial building block for network edge AI system of the looming industry 4.0 era.

Broadband Nonvolatile Electrically Controlled Programmable Units in Silicon Photonics

“…47−50 However, we note that the choice of GST is preferred for compatibility with existing high-volume manufacturing because this material has been extensively studied in electronic memories and is technologically mature. 17,51 Although our 2 × 2 programmable unit displayed the highest reported cyclability among electrically controlled PCM-based photonic devices (we note a work came out during the review of this study shows half million cycles operations using a tungsten heater 52 ), it is still significantly lower than the records obtained for electronic memories (∼10 12 cycles, potentially scale up to 10 15 cycles). 17,51 The cyclability of our device is mainly limited by thermal reflowing and material ablation because of the large GST volume (Supplementary, Section S7).…”

Opportunities and Challenges for Large-Scale Phase-Change Material Integrated Electro-Photonics

“…Early works reported limited cyclability (around 10 cycles) 84 and low optical contrast (less than 1 dB). 82 Recently, high endurance (over half a million cycles 85 ) and large contrast switching (more than 10 dB contrast) have been achieved using external heaters 45,83,85,86 with high-quality encapsulation.…”

“…There are predominantly two types of electrical heaters: (1) doped intrinsic semiconductor, such as silicon, on which the PICs are fabricated; 45,83,87 and (2) extrinsic heaters, such as metal, 85 graphene, 88,89 indium-doped tin oxide (ITO), 84,86 or fluorine-doped tin oxide (FTO). 90 A detailed simulation study of different heaters revealed that graphene heaters are much more electrical energy-efficient than doped semiconductors (such as PIN diode-based silicon heaters) or ITO heaters, 91 primarily because of graphene's much smaller active volume.…”

“…Optical amplitude switches 83,85,86 and phase shifters 45 are demonstrated with electrical control using doped silicon heaters. Additionally, electrically controlled tunable 2 × 2 beam splitters switching between cross and bar ports over more than 2800 cycles have been reported with GST and PIN heaters.…”

Reconfigurable Application-Specific Photonic Integrated Circuit for solving Partial Differential Equations

“…The spectrum plotted indicates that the absorption is 8 dB, which implies a 0.08 dB/µm absorption coefficient of the GSSe onchip. Significantly, the imaginary part of the effective refractive index in the amorphous state is 2.18 × 10 −5 , leading to an exceedingly small unit of passive insertion loss (16).…”