Rishi Maiti

Attojoule-efficient graphene optical modulators

Electro-optic modulation is a technology-relevant function for signal keying, beam steering, or neuromorphic computing through providing the nonlinear activation function of a perceptron. With silicon-based modulators being bulky and inefficient, here we discuss graphene-based devices heterogeneously integrated. This study provides a critical and encompassing discussion of the physics and performance of graphene. We provide a holistic analysis of the underlying physics of modulators including graphenes index tunability, the underlying optical mode, and discuss resulting performance vectors for this novel class of hybrid modulators. Our results show that reducing the modal area and reducing the effective broadening of the active material are key to improving device performance defined by the ratio of energy-bandwidth and footprint. We further show how the waveguides polarization must be in-plane with graphene, such as given by plasmonic-slot structures, for performance improvements. A high device performance can be obtained by introducing multi- or bi-layer graphene modulator designs. Lastly, we present recent results of a graphene-based hybrid-photon-plasmon modulator on a silicon platform and discuss electron beam lithography treatments for transferred graphene for the relevant Fermi level tuning. Being physically compact, this 100u2009u2009aJ/bit modulator opens the path towards a novel class of attojoule efficient opto-electronics.

Towards a 2D printer: a deterministic cross contamination-free transfer method for atomically layered materials (Conference Presentation)

Precision and chip contamination-free placement of two-dimensional (2D) materials is expected to accelerate both the study of fundamental properties and novel device functionality. Current transfer methods of 2D materials onto an arbitrary substrate deploy wet chemistry and viscoelastic stamping. However, these methods produce a) significant cross contamination of the substrate due to the lack of spatial selectivity b) may not be compatible with chemically sensitive device structures, and c) are challenged with respect to spatial alignment. Here, we demonstrate a novel method of transferring 2D materials resembling the functionality known from printing; utilizing a combination of a sharp micro-stamper and viscoelastic polymer, we show precise placement of individual 2D materials resulting in vanishing cross contamination to the substrate. Our 2D printer-method results in an aerial cross contamination improvement of two to three orders of magnitude relative to state-of-the-art dry and direct transfer methods. Moreover, we find that the 2D material quality is preserved in this transfer method. Testing this 2D material printer on taped-out integrated Silicon photonic chips, we find that the micro-stamper stamping transfer does not physically harm the underneath Silicon nanophotonic structures such as waveguides or micro-ring resonators receiving the 2D material. Such accurate and substrate-benign transfer method for 2D materials could be industrialized for rapid device prototyping due to its high time-reduction, accuracy, and contamination-free process.