Francisco J. Gonzalez

Measurement of the resonant lengths of infrared dipole antennas

The resonant lengths of infrared dipole antennas at 10.6 and 3.39 lm are experimentally investigated. For this purpose, submicron-sized microbolometers coupled to dipole antennas with lengths between 0.7 and 20 lm were fabricated on a SiO2-on-Si substrate. The response of the detector to 10.6 lm radiation shows a first resonance for an antenna length between 1.0 and 2.5 lm. A subsequent zero and a second attenuated resonance are observed as the antenna length increases. Similar behavior is observed for illumination at 3.39 lm, with a first resonance occurring at a length shorter than 1 lm. The results permit evaluation of an eAective dielectric permittivity and shows the eAect of the surface impedance of the metal on the propagation of current-wave on the antenna. The resonance behavior is further studied by changing the irradiation conditions of the detectors. Air-side and substrate-side illumination exhibit identical resonant antenna lengths, but diAerent eAciencies of power collection. The antenna patterns as a function of incident angle have also been measured at 10.6 lm, showing a transition from a primary broadside lobe to the development of side lobes for longer antennas. Finally, an antenna response is measured at visible frequencies. Our measurements point out similarities, as well as diAerences, between infrared antennas and their counterparts at microwave frequencies, and provide insights useful for the design optimization of planar infrared antennas. ” 2000 Elsevier Science B.V. All rights reserved.

Detection mechanisms in microstrip dipole antenna-coupled infrared detectors

We compare the detection mechanisms employed in microstrip dipole antenna-coupled infrared detectors. The electrical currents induced along the antenna arms are detected by a rectangular niobium (Nb) microsensor placed at the center of the antenna. The ohmic nature of the Au–Nb contact determines the detection mechanism. Devices with linear contacts between the Au antenna arms and the Nb microsensor exhibit bolometric response. A nonlinear Au– insulator–Nb junction rectifies the induced antenna currents. Devices with nonlinear contacts also exhibit a bolometric response. The devices with nonlinear contacts are 1=f noise limited while the devices with linear contacts are Johnson noise limited. The rectification mechanism is 5.3 times faster than the thermal detection. The current–voltage ðI–V Þ characteristic of the devices exhibiting bolometric response is linear, while that of the rectifying devices is cubic. For devices with nonlinear contacts excellent agreement is obtained between the measured detector response and the ratio between the second and the first derivative of the I–V characteristic. 2003 Elsevier Science B.V. All rights reserved.

THERMAL IMPEDANCE MODEL OF ELECTROSTATIC DISCHARGE EFFECTS ON MICROBOLOMETERS

In this paper, we have presented a new design method for a coaxially fed circularly polarized rectangular microstrip an- tenna using a GA. The usefulness of a GA for the compli- cated object function was illustrated by designing the circu- larly polarized microstrip antenna. The size and the feeding point were optimized for the given substrate properties and the operating frequency. The computed return loss was 27.6 . dB, the bandwidth was 52 MHz 2.3% , and the operating frequency showed a 1.7% error for the measured data. The . axial ratio bandwidth was 13 MHz 0.51% , and showed a 0.04% difference for the simulated data using Ensemble. ABSTRACT: The small thermal mass of microbolometers, used in antenna-coupled infrared detectors, makes them especiallyulnerable to () electrical stress caused by electrostatic discharge ESD . In this paper, an empirical thermal model, which is independent of the deice geometry, is used to characterize the behaior of microbolometers under ESD conditions. The parameters of this thermal model are fitted to measure- ments made on the microbolometers, and a power-to-failureersus time-to-failure cure is obtained. Q 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 26: 291)293, 2000.

Antenna-coupled microbolometer arrays with aerogel thermal isolation

Abstract Uncooled bolometric detectors used in infrared imaging systems have slow response times (∼10 ms) which makes them impractical for fast-frame-rate applications. Antenna-coupled microbolometer arrays have been shown to have fast response times (∼130 ns) and can be used as picture elements in infrared imaging systems but lack sufficient responsivity. Thermal isolation of antenna-coupled microbolometer arrays will increase its responsivity but will also increase its response time. Thermal isolation can be achieved using silica aerogel as a substrate, and its porosity can be used to modify the thermal conductivity down to values lower than air. In this paper antenna-coupled microbolometer arrays were fabricated on a substrate coated with a thin film of aerogel, noise, response and radiation characteristics were measured and compared to similar devices fabricated on a SiO2 substrate. The measured signal-to-noise ratio of devices fabricated on aerogel were one order of magnitude higher than devices fabricated on SiO2 and had time constants around 5 μs.

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.

Fabrication of infrared antennas using electron-beam lithography

The methods of fabricating infrared antennas using electron beam lithography will be investigated. For this purpose, a process using a bi-layer lift off process and a single layer of resist has been developed. The bi-layer lift off process used allowed for antenna arm resolution of 200nm. The single layer resist process enhanced the resolution of the antenna arms to 90nm by using a Chlorine based reactive ion etcher with Chrome as an etch mask. An alignment scheme using a set of global and local marks allowed for an overlay accuracy of 25nm. An improved process was developed to further improve device yield and uniformity of the infrared detectors by sputtering the bolometer and using an oxygen descum to remove residual resist between antenna and bolometer. Two separate methods of fabrication of air-bridge microstrip antenna-coupled microbolometers using both a critical point dryer and an isotropic reactive ion etcher will also be introduced.

Wave propagation in planar antennas at THz frequencies

Waves along metals at an air-dielectric interface tend to propagate at a velocity that is intermediate between the velocity of waves in the air and the velocity of waves in the dielectric; at frequencies below a few GHz the quasistatic approximation to the effective permittivity can be used to find the effective wavelength that propagates in the antenna. Above these frequencies the frequency dispersion of the effective permittivity must be taken into account. In order to find the effective permittivity and the effective wavelength of propagation at THz frequencies a numerical simulation of a planar dipole antenna is performed and compared to measurements made on similar devices. From the numerical results an empirical formula for the effective permittivity is obtained which accounts for the effect of the complex surface impedance of metals at THz frequencies.