Electron beam direct write of chalcogenide glass integrated optics
AFM images showing the resulting deformation for a linear electron beam exposure: (a) 10 nm Au over-layer, (b) 20 nm Au over-layer. The 10 nm Au over-layer is uneven along its length, showing partial trench and mound formation, whereas the line with the 20 nm Au over-layer is uniform along its length.
Height and width of the deformations for different beam currents and exposure counts vs beam scan rate. For the slowest beam scan rate (3.75 μm/s), highest beam current (355 nA), and greatest number of exposures (3000), deformations greater than three times the original Ge0.2Se0.8 film thickness of 400 nm can be obtained.
(a) Height of the deformations vs exposure count for different film thicknesses. The height increases at a decreasing rate with increasing exposure count, and the relationships are shifted upward for thicker films. (b)Height of the deformations vs film thickness for different exposure counts. The height increases with film thickness with a characteristic s-shape, with the inflection point around 500 nm.
(Color online) (a) AFM scan of two lines exposed close together comprising a directional coupler. The height of the lines is about 150 nm. (b) AFM scan of a ring resonator. The small bump on the upper left of the ring is due to the intersection of the deformation with a film defect and is not caused by the electron beam exposure scheme.
SEM images of gratings directly written onto patterned shallow rib waveguides with a 50 keV electron beam with 322 nA of current, no conductive over-layer, 5 nm beam step size = pixel step size, beam settling time of 3 μs, aperture size of 500 μm, 4 bi-directional exposures per line, and 20 grating periods with width 2.4 μm for a dose of 2.25 C/cm2.
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