Guy Zummo

First THz and IR characterization of nanometer-scaled antenna-coupled InGaAs/InP Schottky-diode detectors for room temperature infrared imaging

Nanometer high performance InP Schottky detectors are scaled to IR wavelengths. The increased cutoff frequency of the Schottky detector was accomplished by both reducing its capacitance to attofarad range and also by reducing the contact resistance. The Schottky detectors were fabricated on InGaAs/InP substrates with the doping level as high as 1 x 1019 cm-2. The typical Schottky detector anode size was 0.1 x 1 μm2. Planar broadband antennas were designed for LWIR wavelengths to couple the radiation into the nanometer size detector. Several different IR antenna designs were evaluated, including complimentary square spirals, bow ties and crossed dipoles. A 6 × 7 array of antenna-coupled Schottky detectors was characterized at DC, yielding a 20 KΩ zero-bias resistance and a responsivity of 6 A/W for the entire array. The arrays were characterized at 2.5 THz, as well as in the IR (3-5μm and 10.6 μm). The current results for polarization sensitivity confirm that an antenna-coupled mechanism is responsible for the measured responsivity with the highest value measured at the THz range.

Design, fabrication, and characterization of antenna-coupled metal-oxide-metal diodes for dual-band detection

Two designs for antenna-coupled Ni-NiO-Ni diodes are fabricated and tested for dual-band detection in the millimeter-wave (MMW), 94-GHz, and infrared (IR), 28.3-THz, frequencies. The detector noise, antenna receiving properties, and noise equivalent power (NEP) are measured. The simultaneous dual-band response is verified.

Fabrication of periodic microstructures on flexible polyimide membranes

Periodic metallic microstructures were fabricated on polyimide membranes. Techniques were developed to maintain flatness of the membrane during processing while still allowing for flexibility in the final structure. For proper functionality of the structures, it was necessary to first fabricate a continuous metallic film and a continuous dielectric layer on top of the flexible substrate, which underlaid the periodic microstructure. Flexibility of the overall structure was maintained by using a polymer as the dielectric layer, which was constrained to have high optical transmission over the infrared wavelength range of 6–14μm. Three candidate polymers were evaluated, and their measured optical properties are presented. Benzocyclobutene was found to be the best choice for this application. The final structure fully populated a 10cm (4in.) diameter flexible membrane with microstructures of excellent uniformity.

Direct-write electron-beam lithography of an IR antenna-coupled microbolometer onto the surface of a hemispherical lens

This article describes a method for performing direct-write lithography of an IR antenna-coupled microbolometer onto the surface of a hemispherical lens. Antennas on a dielectric half-space receive power more efficiently from the substrate side than from the air side. The use of a hemispherical lens facilitates reception through the substrate as well as elimination of trapped surface waves that would normally occur in the substrate. Using direct-write lithography onto the surface of the hemispherical lens eliminates the potential of an air gap between the antenna and lens. Additionally, the accuracy of alignment between the antenna and the center of the lens is controlled at the lithographic step. As a result, there is increased responsivity is observed in the antenna-coupled microbolometer when illuminated from the substrate-side compared to air-side illumination.

Antenna-coupled MOM diodes for dual-band detection in MMW and LWIR

An antenna-coupled metal-oxide-metal (MOM) diode for dual-band Infrared (IR)-millimeter wave (MMW) detection is presented. Electron-beam lithography and conventional sputtering techniques were used to fabricate a Ni-NiO-Ni diode coupled to an Infrared slot antenna at 28 THz and a coplanar waveguide (CPW)-fed MMW twin slot antenna at 94 GHz; simultaneous dual-band detection was tested and verified.

Thin-film, wide-angle, design-tunable, selective absorber from near UV to far infrared

We experimentally demonstrate a structured thin film that selectively absorbs incident electromagnetic waves in discrete bands, which by design occur in any chosen range from near UV to far infrared. The structure consists of conducting islands separated from a conducting plane by a dielectric layer. By changing dimensions and materials, we have achieved broad absorption resonances centered at 0.36, 1.1, 14, and 53 microns wavelength. Angle-dependent specular reflectivity spectra are measured using UV-visible or Fourier spectrometers. The peak absorption ranges from 85 to 98%. The absorption resonances are explained using the model of an LCR resonant circuit created by coupling between dipolar plasma resonance in the surface structures and their image dipoles in the ground plane. The resonance wavelength is proportional to the dielectric permittivity and to the linear dimension of the surface structures. These absorbers have application to thermal detectors of electromagnetic radiation.

Passive millimeter-wave focal plane array

We built and tested a low-cost 8-by-8 millimeter-wave focal plane array using antenna-coupled micro-bolometers. The array consists of slot antennas coupled to nickel bolometers and was fabricated using optical lithography on high-resistivity silicon wafers. The measured noise equivalent temperature difference (NETD) of an individual element was 450 K. Simulation results corresponded with observed device performance. An improved design was then implemented using a square spiral antenna. We discuss the fabrication of this type of array element, including some modeling results, and present the methods and results of our measurements.

DMD-based infrared scene projection: comparison of MWIR and LWIR modulation transfer function

We compare modulation-transfer-function (MTF) measurements for both mid-wave (MWIR) and long-wave IR (LWIR) bands for an IR-laser scene projector based on the digital micro-mirror device (DMD). We evaluate MTF for both IR-CO2 (10.6 micron) and IR-HeNe (3.39 micron) laser systems. This gives a quantitative image-quality criterion for verifying system performance using identical configurations of the DMD, lens, and screen. Different angles of illumination for the MWIR and LWIR were used, to give an output beam always perpendicular to the DMD. For this experiment a set of bar-target images was used to measure the residual modulation depth at the fundamental spatial frequency of the bars. As expected, the MWIR projector system has better MTF than the LWIR system because of diffraction effects occurring at the 17-micron pixels of the DMD.

Wavelength tuning of an antenna-coupled infrared microbolometer

Wavelength tuning is demonstrated in an antenna-coupled infrared microbolometer. With a 300-mV control voltage, we observed a tuning range of 0.15 μm near 10 μm. A metal-oxide-semiconductor capacitor underneath the antenna arms causes the shift of resonance wavelength with applied voltage. We develop a device model that agrees with measured results.

Characterization of a wavelength-tunable antenna-coupled infrared microbolometer

Wavelength tuning is demonstrated in an antenna-coupled infrared microbolometer. With a 300-mV control voltage, we observed a tuning range of 0.5 µm near 10 µm. A metal-oxide-semiconductor capacitor underneath the antenna arms causes the shift of resonance wavelength with applied voltage. We develop a device model that agrees well with measured results.