Abstract
Over the past 30 years or more, chalcogenide phase-change materials and devices have generated much scientific and industrial interest, particularly as a platform for non-volatile optical and electronic storage devices. More recently, the combination of chalcogenide phase-change materials with photonic integrated circuits has begun to be enthusiastically explored, and among many proposals, the all-photonic phase-change memory brings the memristor-type device concept to the integrated photonic platform, opening up the route to new forms of unconventional (e.g., in-memory and neuromorphic) yet practicable optical computing. For any memory or computing device, fast switching speed and low switching energy are most attractive attributes, and approaches by which speed and energy efficiency can be improved are always desirable. For phase-change material-based devices, speed and energy consumption are both enhanced the smaller the volume of phase-change material that is required to be switched between its amorphous and crystalline phases. However, in conventional integrated photonic systems, the optical readout of nanometric-sized volumes of phase-change material is problematic. Plasmonics offers a way to bypass such limitations: plasmonic resonant structures are inherently capable of harnessing and focussing optical energy on sub-wavelength scales, far beyond the capabilities of conventional optical and photonic elements. In this work, we explore various approaches to combine the three building blocks of Si-photonics, resonant plasmonic structures, and phase-change materials to deliver plasmonically enhanced integrated phase-change photonic memory and computing devices and systems, underlining the inherent technical and theoretical challenges therein.
Highlights
Silicon photonics is a relatively mature and established technology, and one that is at the very center of the scientific community’s attention[1,2,3,4,5,6] One of the main reasons for this is the inherent energy efficiency and wider bandwidth of the optical signal transport channels, as compared to electrical interconnects
We aim to underline the as yet untapped potential for the realization of fast, energy-efficient photonic memory and computing devices arising from the union of the energy-efficient silicon photonics platform, the sub-wavelength light-squeezing and field-enhancing capability of plasmonic resonant structures, and the intrinsic tuneability functionality brought by PCMs
From the results presented and in the related literature,[54–56] it is clear that plasmonic enhancement has the potential to drastically improve the energy and speed performance of the conventional integrated phase-change photonic memory devices
Summary
Silicon photonics is a relatively mature and established technology, and one that is at the very center of the scientific community’s attention[1,2,3,4,5,6] One of the main reasons for this is the inherent energy efficiency and wider bandwidth of the optical signal transport channels, as compared to electrical interconnects. The basic concept of the integrated phase-change optical memory device is shown in Fig. 1; a thin chalcogenide PCM layer is fabricated on the top surface of a conventional photonic integrated waveguide [see Fig. 1(a)]. 512 bit memory device has been successfully fabricated and tested.[12] multi-state PCM cells of the type shown in Fig. 1 have been used to provide arithmetic functionality,[15,18] have been incorporated into novel photonic crossbar arrays to deliver ultra-fast matrix-vector multipliers,[17] and have been used to realize synaptic and neuronal “mimics”[10] and even small-scale neuromorphic processors.[14]. We aim to underline the as yet untapped potential for the realization of fast, energy-efficient photonic memory and computing devices arising from the union of the energy-efficient silicon photonics platform, the sub-wavelength light-squeezing and field-enhancing capability of plasmonic resonant structures, and the intrinsic tuneability functionality brought by PCMs
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