Suspended silicon nitride thin films with enhanced and electrically tunable reflectivity

Abstract

We report on the realization of silicon nitride membranes with enhanced and electrically tunable reflectivity. A high contrast grating is directly patterned using electron beam lithography on suspended 200 nm-thick, high stress commercial films. We show that the grating transverse profile can be measured in situ using localized cuts of the suspended film with a Focused Ion Beam. A Fano resonance is observed at 937 nm in the transmission spectrum of TM polarized light impinging on the membrane at normal incidence, leading to an increase in its reflectivity from 10% to 78%. By mounting membrane chip on a ring piezoelectric transducer and applying a compressive force to the corners of the film we subsequently show that it is possible to shift the transmission spectrum by 0.23 nm.

Polarization-independent optical spatial differentiation with a doubly-resonant one-dimensional guided-mode grating

“…5(c) shows the result of an AFM scan of one part of the patterned area. The observed profile is close to trapezoidal, as observed with similar structures fabricated using Electron Beam Lithography and chemical etching [25,63,66,67], the main difference being the increased film thickness (∼ 315 nm versus 200 nm) in order to achieve polarization-independent resonances in the wavelength range of 915-985 nm of the laser available for the sample characterization. Another slight difference is a more pronounced curvature at the bottom of the grooves.…”

“…Let us further note that piezoelectric tuning of the optical response as demonstrated in Ref. [66] could also be applied in order to extend the tuning range of the spatial differentiation.…”

“…The light transmitted by beamsplitter BS 2 is collected by a 75 mm-focal length and a CMOS camera in order to provide an image of the transverse profile of the transmitted beam at the grating position with a magnification of approximately 3. The transmission of the sample under various incidence angles and incident polarizations is obtained by scanning the laser wavelength and normalizing the referenced transmitted photodetector signal by that without sample [47,66]. As discussed in Sec.…”

Collimation and finite-size effects in suspended resonant guided-mode gratings

“…The gratings are fabricated following the recipe detailed in [32,55] and structurally characterized using AFM profilometry [56]. In brief, commercial (Norcada Inc., Canada), high tensile stress (∼GPa) stoichiometric silicon nitride films suspended on a silicon frame are patterned with subwavelength grating structures using Electron Beam Lithography and dry etching.…”

Mechanical investigations of free-standing SiN membranes patterned with one-dimensional photonic crystal structures

“…In this work, we report on investigations of mechanical properties of prestressed silicon nitride membranes patterned with one-dimensional photonic crystal structures 37 . Atomic Force Microscopy (AFM) scans are applied to evaluate the tensile stress-related deformation of the structure in the vicinity of the patterned area 38 , which essentially depend on the ratio of the elasticity modulus and the pretension level of the membrane.…”