Photonic non-volatile memories using phase change materials

We propose an all-photonic, non-volatile memory and processing element based on phase-change thin-films deposited onto nanophotonic waveguides. Using photonic microring resonators partially covered with Ge2Sb2Te5 (GST) multi-level memory operation in integrated photonic circuits can be achieved. GST provides a dramatic change in refractive index upon transition from the amorphous to crystalline state, which is exploited to reversibly control both the extinction ratio and resonance wavelength of the microcavity with an additional gating port in analogy to optical transistors. Our analysis shows excellent sensitivity to the degree of crystallization inside the GST, thus providing the basis for non-von Neuman neuromorphic computing

Nanomechanical Resonators towards Single Spin Sensitivity

Ultrasensitive force detectors are required for progress towards single atom imaging using magnetic resonance force microscopy (MRFM). MRFM is a scanned probe imaging technique, with potential for atomic-scale, non-destructive and sub-surface imaging. To achieve the goal of single atom imaging, technical development towards realization of high magnetic field gradients as well as force detectors with very high sensitivity are necessary. Given values of field gradients that can be achieved at present (typically of the order of 10 5 T/m), force sensitivity of an atto-newton (10-18 N/√Hz) at low temperatures (0.3 - 4 K) is required for single spin sensitivity. This has been achieved using optical interferometry; however, optical interferometers corrupt measurements by heating the cantilevers and inducing decoherence of spins in the sample. Thus, there is a need to develop a light-free technique to measure cantilever motion with high sensitivity. In this dissertation, a design for ultrasensitive force detection using capacitive sensing is developed. Thermomechanical noise and position detection sensitivity constraints are addressed. The fabrication of an ultra-thin, nanomechanical force sensing cantilever with an integrated sense electrode for capacitive detection (double cantilever architecture) is accomplished. Gallium Arsenide field effect transistors with potential for integration onto the double cantilever chips are fabricated and characterized at low temperatures. Measurement techniques for capacitive detection are explored and lay the groundwork for future research towards the development of integrated nanomechanical force detectors towards single spin sensitivity for magnetic resonance force microscopy

Casimir probe based upon metallized high Q SiN nanomembrane resonator

We present the instrumentation and measurement scheme of a new Casimir force probe that bridges Casimir force measurements at microscale and macroscale. A metallized high Q silicon nitride nanomembrane resonator is employed as a sensitive force probe. The high tensile stress present in the nanomembrane not only enhances the quality factor but also maintains high flatness over large area serving as the bottom electrode in a sphere-plane configuration. A fiber interferometer is used to readout the oscillation of the nanomembrane and a phase-locked loop scheme is applied to track the change of the resonance frequency. Because of the high quality factor of the nanomembrane and the high stability of the setup, a frequency resolution down to $2\times10^{-9}$ and a corresponding force gradient resolution of 3 $\mu$N/m is achieved. Besides sensitive measurement of Casimir force, our measurement technique simultaneously offers Kelvin probe measurement capability that allows in situ imaging of the surface potentials

Phase change materials in light modulating applications beyond data storage

Invited paper presented at the European\Phase Change and Ovonics Symposium 2015, 2015-09-06, 2015-09-08, AmsterdamThe use of phase change materials in applications that manipulate light reflectivity and transmissivity would appear to be both obvious and completely infeasible at the same time. It is obvious simply because many of these materials were developed with the primary aim of being able to store optically accessible data, which relied on the optical refractive index contrast between the two reversibly accessible solid states of the material. It would appear infeasible upon further consideration because, not only is the change in the refractive index not very large in the visible wavelengths, but also because the absorption of the material in both states resembles a metallic element as opposed to a dielectric, which would greatly reduce contrast. Over the last two and a half years, we have combined thin film optics concepts with phase change materials to essentially enable the use of such materials in light modulation applications such as displays, smart glazing and security markings. In this abstract, we also show some additional work done on two types of phase change materials, demonstrating that new areas of technological development for phase change materials are perhaps in some ways even more exciting than existing ones

Young's modulus and residual stress of GeSbTe phase-change thin films

The mechanical properties of phase change materials alter when the phase is transformed. In this paper, we report on experiments that determine the change in crucial parameters such as Young's modulus and residual stress for two of the most widely employed compositions of phase change films, Ge1Sb2Te4 and Ge2Sb2Te5, using an accurate microcantilever methodology. The results support understanding of the exact mechanisms that account for the phase transition, especially with regard to stress, which leads to drift in non-volatile data storage. Moreover, detailed information on the change in mechanical properties will enable the design of novel low-power nonvolatile MEMS

Accumulation-based computing using phasechange memories with FET access devices

Copyright © 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Phase-change materials and devices have received much attention as a potential route to the realization of various types of unconventional computing paradigms. In this letter, we present non-von Neumann arithmetic processing that exploits the accumulative property of phase-change memory (PCM) cells. Using PCM cells with integrated FET access devices, we perform a detailed study of accumulation-based computation. We also demonstrate efficient factorization using PCM cells, a technique that could pave the way for massively parallelized computations.Engineering and Physical Sciences Research Council (EPSRC

Tunable Nanophotonic circuits based on phase change materials

Paper presented at European\Phase Change and Ovonics Symposium, 2013-09-08, 2013-09-10, BerlinWe present preliminary results of the characterization of the optical response of GeSbTe (GST) thin-films integrated with SiN nanophotonic circuits at telecom wavelengths. Transmission measurements are carried out GST thin-films of varying width deposited on top of ring resonators. The nanophotonics circuits are fabricated and optimized in order to find the best response when GST is placed atop the waveguiding layer. Our results for the absorption/transmission properties at different phase states of GST thin-films paves the way towards a all-photonic non-volatile memories