We report on the fabrication of crossed-dipole resonant filters by direct-write electron-beam and nanoimprint lithographies. Such structures have been used as spectrally selective components at visible, microwave, and infrared wavelengths. Imprinting is accomplished in a modified commercial hot press at 155 °C. The replica is then etched in oxygen plasma and developed in chlorobenzene to selectively dissolve the poly(methylmethacrylate and methacrylic acid) and poly(methylmethacrylate) bilayer resist. This step enhances undercut and improves lift-off metalization. Infrared fourier transform spectroscopy was performed to characterize the transmission response of the frequency selective surfaces (FSSs) fabricated. The resonant behavior for the direct-write FSS was found to be 5.3 μm and for the nanoimprinted FSS to be 6 μm. The shift towards longer wavelengths is consistent with the dimensions obtained for the FSSs elements in both cases.

We report a versatile process for the fabrication of dissimilar metal electrodes with a minimum interelectrode distance of less than 6 nm using electron beam lithography and liftoff pattern transfer. This technique provides a controllable and reproducible method for creating structures suited for the electrical characterization of asymmetric molecules for molecular electronics applications. Electrode structures employing pairs of Au electrodes and non-Au electrodes were fabricated in three different patterns. Parallel electrode structures 300 μm long with interelectrode distances as low as 10 nm, 75 nm wide electrode pairs with interelectrode distances less than 6 nm, and a multiterminal electrode structure with reproducible interelectrode distances of 8 nm were realized using this technique. The processing issues associated with the fabrication of these structures are discussed along with the intended application of these devices.

NEB-22, a chemically amplified negative tone resist has been formulated by Sumitomo for e-beam lithography direct write and mask making applications. The resist has exhibited excellent characteristics which would also make it applicable for use in a SCALPEL exposure tool.^1^,^2 The initial processing results for Sumitomo NEB-22A5 material demonstrated extremely high resolution capabilities with excellent exposure latitude. Although the process worked well for many direct write and mask applications, improvements were needed to address SCALPEL concerns. The process was modified to maintain sensitivity and optimize resolution, exposure latitude and PEB latitude. Excellent results were obtained in a 200 nm film of NEB-22 with new process parameters.

We show that very narrow fin-like periodic nanostructure with 0.1 mu m width, 1 mu m depth, and a few microns length can be fabricated on AlGaAs using Chemically-Assited-Ion-Beam-Etching with oxidized AlGaAs as negative mask. This technique may have applications to nanoscale devices fabrication.

We report on the fabrication of a chirped, phase mask that was used to create a fiber Bragg grating (FBG) device for the compensation of chromatic dispersion in longhaul optical transmission networks. Electron beam lithography was used to expose the grating onto a resist-coated quartz plate. After etching, this phase mask was used to holographically expose an index grating into the fiber core [K. O. Hill, F. Bilodeau, D. C. Johnson, and J. Albert, Appl. Phys. Lett. 62, 1035 (1993)]. The linear increase in the grating period, “chirp,” is only 0.55 nm over the 10 cm grating. This is too small to be defined by computer aided design and a digital deflection system. Instead, the chirp was incorporated by repeatedly rescaling the analog electronics used for field size calibration. Special attention must be paid to minimize any field stitching and exposure artifacts. This was done by using overlapping fields in a “voting” method. As a result, each grating line is exposed by the accumulation of three overlapping exposures at 1/3 dose. This translates any abrupt stitching error into a small but uniform change in the line-to-space ratio of the grating. The phase mask was used with the double-exposure photoprinting technique [K. O. Hill, F. Bilodeau, B. Malo, T. Kitagawa, S. Thériault, D. C. Johnson, J. Albert, and K. Takiguchi, Opt. Lett. 19, 1314 (1994)]: a KrF excimer laser holographically imprints an apodized chirped Bragg grating in a hydrogen loaded SMF-28 optical fiber. Our experiments have demonstrated a spectral delay of −1311 ps/nm with a linearity of +/−10 ps over the 3 dB bandwidth of the resonant wavelength of the FBG. The reflectance, centered on 1550 nm, shows a side-lobe suppression of −25 dB. Fabrication processes and optical characterization will be discussed.

We show how to integrate a vitreous carbon ion-absorbing coating with current silicon stencil mask technology to create a mask for ion beam lithography with dramatically improved radiation resistance. The masks were formed by first sputtering a graphitic carbon film onto the nonplanar side of a patterned silicon stencil mask. The carbon film was subsequently vitrified by He+ ion implantation and patterned by O2 reactive ion etching using the silicon mask itself as an etching template. In the example reported herein, the thicknesses of the silicon mask and carbon film were 0.7 and 1.0 μm, respectively. Silicon mask openings as small as 80 nm were faithfully replicated in the carbon, making a 20:1 aspect ratio in the bilayer mask. The mean stress of these multilayer masks is extremely stable when lithography ions are stopped within the carbon layer: stress change is less than experimental error (0.5 MPa) for at least 500 000 proximity exposures. Compared to silicon stencil masks, which wrinkle after only 100 exposures, these masks represent a breakthrough in nanostructure manufacturing.

We report the measurement of cavity propagation losses in nearly single-mode semiconductor waveguide-coupled ring and disk microcavity optical resonators. Using a novel 10.5-/spl mu/m-diameter ring resonator, we measure transverse electric (TE) and transverse magnetic (TM) field intensity losses in 0.35-/spl mu/m-wide ring waveguide cavities in the 1.55-/spl mu/m-wavelength region. We present the experimental results for nanofabricated AlGaAs-GaAs 10.5-/spl mu/m-diameter ring and disk resonators to quantify cavity losses and to show the feasibility of these promising and robust submicron-scale devices.

We report the realization and demonstration of novel semiconductor waveguide-coupled microcavity ring and disk resonators. For a 10.5-microm-diameter disk resonator, we measure a finesse of 120, a resonant linewidth of 0.18 nm, and a free-spectral range of 21.6 nm in the 1.55-mum-wavelength region. We present the nanofabrication methods and the experimental results for 10.5- and 20.5-mum-diameter ring and disk resonators to show the feasibility of such devices.

A superconducting ring, biased in an external flux Phi(0)/2, can be in either of two energetically degenerate fluxoid states. In one state, the supercurrent hows in a clockwise direction with a resulting downward magnetic moment; the current in the other state flows in a counterclockwise direction and its moment points up. There is thus a strong analogy between such a ring and an Ising spin. Two nearby but electrically isolated rings can interact magnetically; this interaction favors an antiparallel alignment of moments and is thus analogous to an antiferromagnetic spin-spin interaction. Regular arrays of such rings may thus be expected to exhibit effects of lattice geometry and geometrical frustration. To study these issues, we have fabricated arrays containing up to 2.4 x 10(5) aluminum rings, each approximately 1.6 mu m across. We have used a sensitive superconducting quantum interference device-based magnetometer to probe the global magnetic properties of the arrays; local information about particular spin configurations was obtained using a high-resolution scanning Hall probe microscope. The magnetic measurements show that individual rings do indeed behave as Ising spins, showing a paramagnetic susceptibility which freezes out only a few milliKelvin below the critical temperature T-c. This illustrates that the ring dynamics is dominated by an energy barrier between the two states which rises rapidly as the temperature is lowered below T-c. The magnetic measurements also show a hysteretic field dependence of the susceptibility which can be quantitatively interpreted in terms of an antiferromagnetic interaction between the rings. To explore possible ordering of the spins, we have used the Hall microscope to directly image specific configurations of spins. We find significant antiferromagnetic nearest-neighbor correlations, but no evidence for any long-range ordering. We attribute this to a significant degree of disorder in the system related to small fluctuations in the areas of the aluminum rings. The effective disorder may be increased by working at higher fractions of Phi(0). The observed short-range correlations drop rapidly at these higher fractions.

We report the first realization of waveguide-coupled AlGaAs/GaAs ring and disk microcavity resonators with 21.6-nm free spectral range and finesse of 120, We present the nanofabrication methods and the experimental results.

We report the realization and demonstration of novel semiconductor waveguide-coupled microcavity ring and disk resonators. For a 10.5-microm-diameter disk resonator, we measure a finesse of 120, a resonant linewidth of 0.18 nm, and a free-spectral range of 21.6 nm in the 1.55-mum-wavelength region. We present the nanofabrication methods and the experimental results for 10.5- and 20.5-mum-diameter ring and disk resonators to show the feasibility of such devices.

This paper describes coupling and switching of optical radiation using metal-semiconductor- metal (MSM) structures, specifically in a metal-on-silicon waveguide configuration. These structures have the special advantage of being VLSI-compatible. Three different designs were successfully used to examine modulation and optical switching based upon nonlinear interactions in the silicon waveguide; a traditional Bragg reflector design and a phase-shifted structure were used to observe thermally-tunable switching of nanosecond-regime Nd:YAG pulses. Finally, a normal-incidence structure was examined which exhibited nonlinear reflectivity modulation.

We report on the fabrication and characterization of broadband Bragg filters in microfabricated AlGaAs waveguides. Electron-beam lithography and chemically assisted ion-beam etching were used to fabricate first-order gratings with 250 nm period. Bragg filters with rejection bandwidth ∼15 nm and centered at ∼1.6 μm are demonstrated.

Self-assembled monolayers of octadecylsiloxane and octadecylthiol have been modified by high-resolution electron beam lithography. Focused electron beams from 1 to 50 keV and scanning tunneling microscopy at ∼10 eV have been used as patterning tools. The patterns have been transferred into many substrates by wet, dry, and combinations of wet and dry etches. Wet etching almost always results in a positive tone, but reactive ion etching of GaAs with Cl2 at very low dc biases (<10 V) results in a negative tone. The effect of electron beam damage on the monolayers and the subsequent etching reactions has been explored through x-ray photoelectron spectroscopy.

Image contrast in proximity ion beam lithography is limited by scattered ions which enter the opaque regions of the mask and exit through the sidewalls of the mask windows. The scattering angles are widely distributed resulting in a ‘‘proximity effect’’ whose range is on the order of the mask-to-wafer gap. This problem becomes more severe with increasing pattern density and sets the resolution limit for high density patterns such as interdigital transducers. The only way to counteract this effect is to limit the ion range to a fraction of the mask thickness so that the scattered ions can be recaptured by adjacent sidewalls. This article explores the dependence of image contrast on resolution, pattern density, and beam energy in proximity ion beam lithography. Patterns with feature sizes in the range from 20 to 50 nm and 0.4 μm pitch have been printed with a linewidth change of only 3 nm for a 10% change in dose.

A strongly-guided one-dimensional (1-D) waveguide called a photonic wire has high spontaneous emission coupling efficiency, enabling one to realize low-threshold lasers. Combined with the use of 1-D photonic bandgap structures consisting of arrays of holes etched within the photonic wire, novel microcavity lasers can be realized, We report the nanofabrication of a photonic bandgap structure for 1.5 mu m wavelength along a InGaAsP photonic wire, and discuss numerical simulations for its electrodynamics.

We have obtained directional light output from a recently realized InGaAsP photonic-wire microcavity ring lasers. The output was achieved by fabricating a 0.45-/spl mu/m-wide U-shape waveguide next to a 10-/spl mu/m diameter microcavity ring laser. The laser has a threshold pump power of around 124 /spl mu/W when optically pumped at 514 nm. It is comparable to the former structure without output coupling. The output coupling efficiency can be controlled carefully by choosing the spacing between the laser cavity and the waveguide.

An investigation of optical switching in phase-shifted metal–semiconductor–metal Bragg gratings is presented. A silicon-on-insulator waveguide with aluminum interdigitated surface gratings and an amorphous silicon overcoat provided high-contrast, tunable switching characteristics. This structure is one of many potential realizations of a novel class of metal–semiconductor switching devices currently under investigation. We discuss switching dynamics, tuning mechanisms, and potential applications.