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(1 - 9 of 9)
- Title
- INFRARED PHASED-ARRAY ANTENNA-COUPLED TUNNEL DIODES.
- Creator
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Slovick, Brian, Boreman, Glenn, University of Central Florida
- Abstract / Description
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Infrared (IR) dipole antenna-coupled metal-oxide-metal (MOM) tunnel diodes provide a unique detection mechanism that allows for determination of the polarization and wavelength of an optical field. By integrating the MOM diode into a phased-array antenna, the angle of arrival and degree of coherence of received IR radiation can be determined. The angular response characteristics of IR dipole antennas are determined by boundary conditions imposed by the surrounding dielectric or conductive...
Show moreInfrared (IR) dipole antenna-coupled metal-oxide-metal (MOM) tunnel diodes provide a unique detection mechanism that allows for determination of the polarization and wavelength of an optical field. By integrating the MOM diode into a phased-array antenna, the angle of arrival and degree of coherence of received IR radiation can be determined. The angular response characteristics of IR dipole antennas are determined by boundary conditions imposed by the surrounding dielectric or conductive environment on the radiated fields. To explore the influence of the substrate configuration, single dipole antennas are fabricated on both planar and hemispherical lens substrates. Measurements demonstrate that the angular response can be tailored by the thickness of the electrical isolation stand-off layer on which the detector is fabricated and/or the inclusion of a ground plane. Directional detection of IR radiation is achieved with a pair of dipole antennas coupled to a MOM diode through a coplanar strip transmission line. The direction of maximum angular response is altered by varying the position of the diode along the transmission line connecting the antenna elements. By fabricating the devices on a quarter wave layer above a ground plane, narrow beam widths of 35° full width at half maximum and reception angles of ± 50° are achievable with minimal side-lobe contributions. Phased-array antennas can also be used to assess the degree of coherence of a partially coherent field. For a two-element array, the degree of coherence is a measure of the correlation of electric fields received by the antennas as a function of the element separation.
Show less - Date Issued
- 2011
- Identifier
- CFE0003589, ucf:48926
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003589
- Title
- Uncooled Infrared Detector Featuring Silicon based Nanoscale Thermocouple.
- Creator
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Modarres-Zadeh, Mohammad, Abdolvand, Reza, Sundaram, Kalpathy, Yuan, Jiann-Shiun, Malocha, Donald, Cho, Hyoung Jin, University of Central Florida
- Abstract / Description
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The main focus of this dissertation is to improve the performance of thermoelectric (TE)infrared (IR) detectors. TE IR detectors are part of uncooled detectors that can operate at roomtemperature. These detectors have been around for many years, however, their performance hasbeen lower than their contesting technologies. A novel high-responsivity uncooled thermoelectricinfrared detector is designed, fabricated, and characterized. This detector features a single standalonepolysilicon-based...
Show moreThe main focus of this dissertation is to improve the performance of thermoelectric (TE)infrared (IR) detectors. TE IR detectors are part of uncooled detectors that can operate at roomtemperature. These detectors have been around for many years, however, their performance hasbeen lower than their contesting technologies. A novel high-responsivity uncooled thermoelectricinfrared detector is designed, fabricated, and characterized. This detector features a single standalonepolysilicon-based thermocouple (without a supporting membrane) covered by an umbrellalikeoptical-cavity IR absorber. It is proved that the highest responsivity in the developed detectorscan be achieved with only one thermocouple. Since the sub-micrometer polysilicon TE wires arethe only heat path from the hot junction to the substrate, a superior thermal isolation is achieved.A responsivity of 1800 V/W and a detectivity of 2 ? 10^8 (cm. sqrt(Hz)W^?1) are measured from a20?m x 20?m detector comparable to the performance of detectors used in commercial focalplanar arrays. This performance in a compact and manufacturable design elevates the position ofthermoelectric IR sensors as a candidate for low-power, high performance, and inexpensive focalplanar arrays. The improvement in performance is mostly due to low thermal conductivity of thinpolysilicon wires. A feature is designed and fabricated to characterize the thermal conductivity ofsuch a wire and it is shown for the first time that the thermal conductivity of thin polysilicon filmscan be much lower than that of the bulk. Thermal conductivity of ~110nm LPCVD polysilicondeposited at 620C is measured to be ~3.5W/m.K.
Show less - Date Issued
- 2016
- Identifier
- CFE0006537, ucf:51321
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006537
- Title
- An uncooled mid-wave infrared detector based on optical response of laser-doped silicon carbide.
- Creator
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Lim, Geunsik, Kar, Aravinda, Coffey, Kevin, Vaidyanathan, Raj, Dhere, Neelkanth, Likamwa, Patrick, University of Central Florida
- Abstract / Description
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This dissertation focuses on an uncooled Mid-Wave Infra-Red (MWIR) detector was developed by doping an n-type 4H-SiC with Ga using the laser doping technique. 4H-SiC is one of the polytypes of crystalline silicon carbide, a wide bandgap semiconductor. The dopant creates an energy level of 0.30 eV, which was confirmed by optical spectroscopy of the doped sample. This energy level corresponds to the MWIR wavelength of 4.21 um. The detection mechanism is based on the photoexcitation of electrons...
Show moreThis dissertation focuses on an uncooled Mid-Wave Infra-Red (MWIR) detector was developed by doping an n-type 4H-SiC with Ga using the laser doping technique. 4H-SiC is one of the polytypes of crystalline silicon carbide, a wide bandgap semiconductor. The dopant creates an energy level of 0.30 eV, which was confirmed by optical spectroscopy of the doped sample. This energy level corresponds to the MWIR wavelength of 4.21 um. The detection mechanism is based on the photoexcitation of electrons by the photons of this wavelength absorbed in the semiconductor. This process modifies the electron density, which changes the refraction index and, therefore, the reflectance of the semiconductor is also changed. The change in the reflectance, which is the optical response of the detector, can be measured remotely with a laser beam such as a He-Ne laser. This capability of measuring the detector response remotely makes it a wireless optical detector. The variation of refraction index was calculated as a function of absorbed irradiance based on the reflectance data for the as-received and doped samples. A distinct change was observed for the refraction index of the doped sample, indicating that the detector is suitable for applications at 4.21 um wavelength. The Ga dopant energy level in the substrate was confirmed by optical absorption spectroscopy. Secondary ion mass spectroscopy (SIMS) of the doped samples revealed an enhancement in the solid solubility of Ga in the substrate when doping is carried out by increasing the number of laser scans. Higher dopant concentration increases the number of holes in the dopant energy level, enabling photoexcitation of more electrons from the valence band by the incident MWIR photons. The detector performance improves as the dopant concentration increases from 1.15(&)#215;1019 to 6.25(&)#215;10^20 cm^-3. The detectivity of the optical photodetector is found to be 1.07(&)#215;10^10 cm?Hz^1/2/W for the case of doping with 4 laser passes. The noise mechanisms in the probe laser, silicon carbide MWIR detector and laser power meter affect the performance of the detector such as the responsivity, noise equivalent temperature difference (NETD) and detectivity. For the MWIR wavelength 4.21 and 4.63 um, the experimental detectivity of the optical photodetector of this study is found to be 1.07(&)#215;10^10 cm?Hz^1/2/W, while the theoretical value is 2.39(&)#215;10^10 cm?Hz^1/2/W. The values of NETD are found to be 404.03 and 15.48 mK based on experimental data for an MWIR radiation source of temperature 25(&)deg;C and theoretical calculation respectively.The doped SiC also has a capability of gas detection since gas emission spectra are in infrared range. Similarly, the sensor is based on the semiconductor optics principle, i.e., an energy gap is created in a semiconductor by doping it with an appropriate dopant to ensure that the energy gap matches with an emission spectral line of the gas of interest. Specifically four sensors have been fabricated by laser doping four quadrants of a 6H-SiC substrate with Ga, Al, Sc and P atoms to detect CO2, NO, CO and NO2 gases respectively. The photons, which are emitted by the gas, excite the electrons in the doped sample and consequently change the electron density in various energy states. This phenomenon affects the refraction index of the semiconductor and, therefore, the reflectivity of the semiconductor is altered by the gas. The optical response of this semiconductor sensor is the reflected power of a probe beam, which is a He-Ne laser beam in this study. The CO2, NO, CO and NO2 gases change the refraction indices of Ga-, Al-, Sc- and Al-doped 6H-SiC, respectively, more prominently than the other gases tested in this study. Hence these doped 6H-SiC samples can be used as CO2, NO, CO and NO2 gas sensors respectively.
Show less - Date Issued
- 2014
- Identifier
- CFE0005519, ucf:50310
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005519
- Title
- ANTENNA-COUPLED INFRARED AND MILLIMETER-WAVE DETECTORS: FABRICATION, MEASUREMENT AND OPTIMIZATION.
- Creator
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Middleton, Charles, Boreman, Glenn, University of Central Florida
- Abstract / Description
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Antenna-coupled detectors provide uncooled, cost-effective solutions for infrared and millimeter-wave imaging. This work describes the design, fabrication, measurement, and optimization of several types of antenna-coupled detectors for LWIR (8 - 12 µm) and 94 GHz radiation. Two types of millimeter-wave antenna-coupled detectors were fabricated and tested: a slot antenna coupled to a bolometer, and a patch antenna coupled to a SiC Schottky diode. Electromagnetic modeling of the antennas...
Show moreAntenna-coupled detectors provide uncooled, cost-effective solutions for infrared and millimeter-wave imaging. This work describes the design, fabrication, measurement, and optimization of several types of antenna-coupled detectors for LWIR (8 - 12 µm) and 94 GHz radiation. Two types of millimeter-wave antenna-coupled detectors were fabricated and tested: a slot antenna coupled to a bolometer, and a patch antenna coupled to a SiC Schottky diode. Electromagnetic modeling of the antennas helped guide the design of antennas with better impedance matching to the detectors. Schottky diodes are discussed as detectors for millimeter-wave and infrared radiation, with the goal of increasing the cutoff frequency to allow infrared detection. The magnitude of response of antenna-coupled bolometric detectors to infrared radiation is affected by the thermal-conduction properties of the sensor structure. Two fabrication processes were developed to improve the thermal isolation of the antenna-coupled bolometer from its substrate. The first process creates a membrane beneath the device. Measured results show a factor of 100 increase in responsivity over an identical device without a membrane. The second process thermally isolates the device from its substrate by suspending the metallic structure in air. Several factors for optimization of infrared antenna-coupled detectors are investigated. The complex dielectric function of the metal from which the antenna is constructed can affect the performance of the device. The use of a ground plane and dielectric standoff layer beneath the antenna can increase the sensor responsivity. Dielectric material properties and thicknesses are considered, and incorporated in device simulations. Finally, a potential fabrication process is presented for via connections from the antenna-coupled detector through a ground plane to bond pads to mitigate the effect of bias lines on antenna behavior.
Show less - Date Issued
- 2006
- Identifier
- CFE0001242, ucf:46908
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001242
- Title
- Frequency Selective Detection of Infrared Radiation in Uncooled Optical Nano-Antenna Array.
- Creator
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Modak, Sushrut, Chanda, Debashis, Schoenfeld, Winston, Fathpour, Sasan, University of Central Florida
- Abstract / Description
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Mid-infrared (mid-IR) detection and imaging over atmospheric transparent 3-5 ?m and 8-12 ?m bands are increasingly becoming important for various space, defense and civilian applications. Various kinds of microbolometers offer uncooled detection of IR radiation. However, broadband absorption of microbolometers makes them less sensitive to spectrally resolved detection of infrared radiation and the fabrication is also very tedious involving multiple complex lithography steps. In this study, we...
Show moreMid-infrared (mid-IR) detection and imaging over atmospheric transparent 3-5 ?m and 8-12 ?m bands are increasingly becoming important for various space, defense and civilian applications. Various kinds of microbolometers offer uncooled detection of IR radiation. However, broadband absorption of microbolometers makes them less sensitive to spectrally resolved detection of infrared radiation and the fabrication is also very tedious involving multiple complex lithography steps. In this study, we designed an optical nano-antenna array based detector with narrow frequency band of operation. The structure consists of a two-element antenna array comprised of a perforated metallic hole array coupled with an underneath disk array which trap incident radiation as dipole currents. The energy is dissipated as electron plasma loss on the hole-disk system inducing close to ~100% absorption of the incident radiation. This near perfect absorption originates from simultaneous zero crossing of real component of permittivity and permeability due to the geometrical arrangement of the two antenna elements which nullifies overall charge and current distributions, prohibiting existence of any propagating electromagnetic modes at resonance. Moreover, the continuous perforated film allows probing of the induced (")micro-current(") plasma loss on each nano hole-disk pair via a weak bias current. Such optical antenna design enables flexible scaling of detector response over the entire mid-infrared regime by change in the antenna dimensions. Furthermore, the development of simple nanoimprint lithography based large area optical antenna array fabrication technique facilitates formation of low cost frequency selective infrared detectors.
Show less - Date Issued
- 2014
- Identifier
- CFE0005845, ucf:50932
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005845
- Title
- RESPONSE-CALIBRATION TECHNIQUES FOR ANTENNA-COUPLED INFRARED SENSORS.
- Creator
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Krenz, Peter, Boreman, Glenn, University of Central Florida
- Abstract / Description
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Infrared antennas are employed in sensing applications requiring specific spectral, polarization, and directional properties. Because of their inherently small dimensions, there is significant interaction, both thermal and electromagnetic, between the antenna, the antenna-coupled sensor, and the low-frequency readout structures necessary for signal extraction at the baseband modulation frequency. Validation of design models against measurements requires separation of these effects so that the...
Show moreInfrared antennas are employed in sensing applications requiring specific spectral, polarization, and directional properties. Because of their inherently small dimensions, there is significant interaction, both thermal and electromagnetic, between the antenna, the antenna-coupled sensor, and the low-frequency readout structures necessary for signal extraction at the baseband modulation frequency. Validation of design models against measurements requires separation of these effects so that the response of the antenna-coupled sensor alone can be measured in a calibrated manner. Such validations will allow confident extension of design techniques to more complex infrared-antenna configurations. Two general techniques are explored to accomplish this goal. The extraneous signal contributions can be measured separately with calibration structures closely co-located near the devices to be characterized. This approach is demonstrated in two specific embodiments, for removal of cross-polarization effects arising from lead lines in an antenna-coupled infrared dipole, and for removal of distributed thermal effects in an infrared phased-array antenna. The second calibration technique uses scanning near-field microscopy to experimentally determine the spatial dependence of the electric-field distributions on the signal-extraction structures, and to include these measured fields in the computational electromagnetic model of the overall device. This approach is demonstrated for infrared dipole antennas which are connected to coplanar strip lines. Specific situations with open-circuit and short-circuit impedances at the termination of the lines are investigated.
Show less - Date Issued
- 2010
- Identifier
- CFE0003177, ucf:48606
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003177
- Title
- Vanadium Oxide Microbolometers with Patterned Gold Black or Plasmonic Resonant Absorbers.
- Creator
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Smith, Evan, Peale, Robert, Khondaker, Saiful, Dove, Adrienne, Boreman, Glenn, University of Central Florida
- Abstract / Description
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High sensitivity uncooled microbolometers are necessary to meet the needs of the next generation of infrared detectors, which seek low power consumption and production cost without sacrificing performance. Presented here is the design, fabrication, and characterization of a microbolometer with responsivity enhanced by novel highly absorptive coatings. The device utilizes a gold-doped vanadium oxide film in a standard air bridge design. Performance estimations are calculated from current...
Show moreHigh sensitivity uncooled microbolometers are necessary to meet the needs of the next generation of infrared detectors, which seek low power consumption and production cost without sacrificing performance. Presented here is the design, fabrication, and characterization of a microbolometer with responsivity enhanced by novel highly absorptive coatings. The device utilizes a gold-doped vanadium oxide film in a standard air bridge design. Performance estimations are calculated from current theory, and efforts to maximize signal to noise ratio are shown and evaluated. Most notably, presented are the experimental results and analysis from the integration of two different absorptive coatings: a patterned gold black film and a plasmonic resonant structure.Infrared-absorbing gold black was selectively patterned onto the active surfaces of the detector. Patterning by metal lift-off relies on protection of the fragile gold black with an evaporated oxide, which preserves gold black's near unity absorptance. This patterned gold black also survives the dry-etch removal of the sacrificial polyimide used to fabricate the air-bridge bolometers. Infrared responsivity is improved 70% for mid-wave IR and 22% for long-wave IR. The increase in the thermal time constant caused by the additional mass of gold black is a modest 15%. However, this film is sensitive to thermal processing; experimental results indicate a decrease in absorptance upon device heating.Sub-wavelength resonant structures designed for long-wave infrared (LWIR) absorption have also been investigated. Dispersion of the dielectric refractive index provides for multiple overlapping resonances that span the 8-12 ?m LWIR wavelength band, a broader range than can be achieved using the usual resonance quarter-wave cavity engineered into the air-bridge structures. Experimental measurements show an increase in responsivity of 96% for mid-wave IR and 48% for long-wave IR, while thermal response time only increases by 16% due to the increased heat capacity. The resonant structures are not as susceptible to thermal processing as are the gold black films. This work suggests that plasmonic resonant structures can be an ideal method to improve detector performance for microbolometers.
Show less - Date Issued
- 2015
- Identifier
- CFE0006004, ucf:51026
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006004
- Title
- Characterization of gold black and its application in un-cooled infrared detectors.
- Creator
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Panjwani, Deep, Peale, Robert, Chow, Lee, Del Barco, Enrique, Schoenfeld, Winston, University of Central Florida
- Abstract / Description
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Gold black porous coatings were thermally evaporated in the chamber backfilled with inert gas pressure and their optical properties were studied in near-far-IR wavelengths. The porosities of coatings were found to be extremely high around ~ 99%. Different approaches of effective medium theories such as Maxwell-Garnett, Bruggeman, Landau-Lifshitz-Looyenga and Bergman Formalism were utilized to calculate refractive index (n) and extinction coefficient (k). The aging induced changes on...
Show moreGold black porous coatings were thermally evaporated in the chamber backfilled with inert gas pressure and their optical properties were studied in near-far-IR wavelengths. The porosities of coatings were found to be extremely high around ~ 99%. Different approaches of effective medium theories such as Maxwell-Garnett, Bruggeman, Landau-Lifshitz-Looyenga and Bergman Formalism were utilized to calculate refractive index (n) and extinction coefficient (k). The aging induced changes on electrical and optical properties were studied in regular laboratory conditions using transmission electron microscopy, Fourier transform infrared spectroscopy, and fore-probe electrical measurements. A significant decrease in electrical resistance in as deposited coating was found to be consistent with changes in the granular structure with aging at room temperature. Electrical relaxation model was applied to calculate structural relaxation time in the coatings prepared with different porosities. Interestingly, with aging, absorptance of the coatings improved, which is explained using conductivity form of Bergman Formulism. Underlying aim of this work was to utilize gold blacks to improve sensitivity in un-cooled IR sensors consist of pixel arrays. To achieve this, fragile gold blacks were patterned on sub-mm length scale areas using both stenciling and conventional photolithography. Infrared spectral imaging with sub-micron spatial resolution revealed the spatial distribution of absorption across the gold black patterns produced with both the methods. Initial experiments on VOx-Au bolometers showed that, gold black improved the responsivity by 42%. This work successfully establishes promising role of gold black coatings in commercial un-cooled infrared detectors.
Show less - Date Issued
- 2015
- Identifier
- CFE0005680, ucf:50197
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005680
- Title
- ANTENNA-COUPLED TUNNEL DIODES FOR DUAL-BAND MILLIMETER-WAVE/INFRARED FOCAL-PLANE ARRAYS.
- Creator
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Abdel Rahman, Mohamed, Boreman, Glenn, University of Central Florida
- Abstract / Description
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The infrared and millimeter-wave portions of the spectrum both have their advantages for development of imaging systems. Because of the difference in wavelengths, infrared imagers offer inherently high resolution, while millimeter-wave systems have better penetration through atmospheric aerosols such as fog and smoke. Shared-aperture imaging systems employing a common focal-plane array that responds to both wavebands are desirable from the viewpoint of overall size and weight. We have...
Show moreThe infrared and millimeter-wave portions of the spectrum both have their advantages for development of imaging systems. Because of the difference in wavelengths, infrared imagers offer inherently high resolution, while millimeter-wave systems have better penetration through atmospheric aerosols such as fog and smoke. Shared-aperture imaging systems employing a common focal-plane array that responds to both wavebands are desirable from the viewpoint of overall size and weight. We have developed antenna-coupled sensors that respond simultaneously at 30 THz and at 94 GHz, utilizing electron-beam lithography. Slot-antenna designs were found to be particularly suitable for coupling radiation into metal-oxide-metal (MOM) tunnel diodes at both frequencies. The MOM diodes are fabricated in a layered structure of Ni-NiO-Ni, and act as rectifying contacts. With contact areas as low as 120 nm × 120 nm, these diodes have time constants commensurate with rectification at frequencies across the desired millimeter-wave and infrared bands. One challenge in the development of true focal-plane array imagers across this factor-of-300 bandwidth is that the optimum spatial sampling interval on the focal plane is different in both bands. We have demonstrated a focal plane with interleaved infrared and millimeter-wave sensors by fabricating infrared antennas in the ground plane of the millimeter-wave antenna. Measured performance data in both bands are presented for individual antenna-coupled sensors as well as for devices in the dual-band focal-plane-array format.
Show less - Date Issued
- 2004
- Identifier
- CFE0000305, ucf:46309
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000305
