Search

Uncooled pyroelectric infrared detectors based on semiconducting Y–Ba–Cu–O have been investigated. Samples with four different structures were characterized. Two of the pyroelectric detectors were thermally isolated from the substrate by micromachining techniques for high optical sensitivity. Pyroelectricity was observed by the methods of optical illumination and direct substrate heating. A wide range of the values of pyroelectric coefficients was obtained with the maximum close to 20 μC/cm2 K in one device. Detectivities up to 108 cm Hz1/2/W were measured. The temperature dependence of these pyroelectric sensors was investigated. It was found that one device showed a fairly constant optical response with respect to temperature over a wide range around 300 K. However, responsivity of another device of a different geometry decreased sharply at ∼304 K. The spectral study of these devices showed that the wavelength-dependent response decreased when the silicon transmission increased. In addition, frontside i...

We have explored the charge transport mechanisms in six different YBaCuO semiconducting thin films in the temperature range of 70 K to room temperature. Two of the samples were deposited on LaAlO 3 substrate and were tetragonal with the composition of YBa 2 Cu 3 O 6.5 and YBa 2 Cu 3 O 6.3 . The other four were amorphous as-deposited on Si substrate with and without a MgO buffer layer, and on an oxidized Si substrate with and without a MgO buffer layer. All tested films exhibited semiconductor-type resistance vs. temperature characteristics with increasing resistance as the temperature was decreased. Around room temperature all six samples had thermally activated transport characteristics that was interpreted as activation of hole-like carriers from localized states around the Fermi level to extended states. As the temperature was decreased, two tetragonal samples went through a transition to a variable range hopping-like conduction. The amorphous ones remained within the thermally-activated transport regime in the temperature range of 253 K to 318 K, with E A ≈ 0.2 eV.

The characteristics of infrared (IR) microbolometer arrays utilizing semiconducting YBaCuO and operating at room temperature are presented. Surface-micromachined structures in the form of 1/spl times/10 arrays of pixel size 40 /spl mu/m/spl times/40 /spl mu/m and 60 /spl mu/m/spl times/60 /spl mu/m as well as single pixels of various geometries were constructed. Using the chopped radiation from a broad-band IR source, the responsivity R/sub V/ of the sensor was measured to be as high as 10/sup 4/ V/W and detectivity D* to be /spl sim/2/spl times/10/sup 7/ cm Hz/sup 1/2//W for a thermal conductance G/spl sim/10/sup -5/ W/K between the detector and the substrate. The spectral response was found to be uniform over a range of 1-12 /spl mu/m. Silicon micromachining and ambient-temperature processing were employed to ensure compatibility and, therefore, potential integration with CMOS-based signal processing circuitry. Methods of enhancing the figures of merit are discussed.

Thermal infrared detectors require thermal isolation to permit the infrared-sensitive material to integrate the incident photon energy and thereby obtain high responsivity and detectivity. This paper describes the fabrication of semiconducting YBaCuO microbolometer arrays into thermal isolation structures by employing Si surface-micromachining techniques. An isotropic HF:HNO/sub 3/ etch was used to remove the underlying Si substrate from the front-side of the wafer and suspend SiO/sub 2/ membranes into 1/spl times/10 pixel-array structures. The infrared-sensitive material, YBaCuO, was subsequently deposited onto the thermal isolation structures and patterned to form the detector arrays. The high-temperature coefficient of resistance and low noise of semiconducting YBaCuO at room temperature is attractive for uncooled infrared detection. The fabrication process was conducted entirely at room temperature. In this manner, infrared detectors are fabricated in a process that is compatible with CMOS technology to allow for the integration with on-chip signal processing circuitry. The end result is low-cost infrared-detector arrays for night vision in a variety of applications including transportation and security. Preliminary results show a temperature coefficient of resistance above 3%, voltage responsivity close to 10/sup 4/ V/W, and detectivity over 10/sup 7/ cm/spl middot/Hz/sup 1/2//W at a bias current of 0.79 /spl mu/A.

We explore the application of the semiconducting phases of YBaCuO thin films as a bolometer for uncooled infrared detection. For this study, four different structures were built with different types of buffer layers: YBaCuO on a Si substrate with and without a MgO buffer layer, and on an oxidized Si substrate with and without a MgO buffer layer. These films were all amorphous without a detectable long range order. For comparison, crystalline tetragonal YBa 2 Cu 3 O 6.5 and YBa 2 Cu 3 O 6.3 thin films on a LaAlO 3 substrate were included into the study. All six films exhibited semiconducting resistance versus temperature characteristics. The bolometer figures of merit, responsivity, and detectivity were calculated from the measured temperature coefficient of resistance ~TCR! and the inherent noise characteristics of the temperature sensing element. The room temperature TCRs for all four amorphous films were greater than 2.5% K 21 . The highest TCR of 4.02% K 21 was observed on the amorphous YBaCuO thin film deposited on MgO/Si without a SiO2 layer. The TCR of the tetragonal films, on the other hand, remained 2% K 21 or less in the same temperature range. Noise measurements performed in the 1‐100 Hz frequency range revealed a quadratic dependence on the bias current as would be expected from ohmic electrical characteristics. The Johnson and 1/f regions were clearly identified in the noise spectrum. From TCR and noise measurements, we estimated the amorphous semiconducting YBaCuO bolometers would have a responsivity as high as 3.8310 5 V/W and a detectivity as high as 1.6310 9 cm Hz 1/2 /W for 1 mA bias current and frame frequency of 30 Hz if integrated with a typical air-gap thermal isolation structure. © 1996 American Institute of Physics.@S0021-8979~96!02924-6#

A pyroelectric infrared detector operating at room temperature and based on semiconducting Y-Ba-Cu-O was fabricated. The capacitor structure consisting of semiconducting Y-Ba-Cu-O layer sandwiched between two Nb electrodes was fabricated on top of a thermally isolated SiO2 bridge. The polycrystalline Y-Ba-Cu-O layer was deposited by ambient-temperature sputtering while standard Si micromachining techniques were used to etch the silicon under the oxide bridge. The pyroelectric response of the material is characterized by the temperature coefficient of polarization (p=dP/dT) which was measured to be as high as 65 nC/K cm2 without an externally applied electric field. The pyroelectric figure of merit Fd for the material was estimated to be 0.032 (cm3/J)1/2. Employing a radiometric infrared source, the room-temperature voltage responsivity RV and specific detectivity D* of the unbiased detector were measured to be over 103 V/W and 108 cm Hz1/2/W, respectively. This letter discusses the characteristics of this...

The integration of optoelectronic devices with conventional electronics will ultimately enable free space optical interconnects (FSOI) for high speed switching applications. Specifically, the development of smart pixels allows compact integration of optics and electronics for use in various systems and applications. OptiComp has integrated these smart pixel arrays into a high performance optoelectronic computing (HPOC) module which is composed of an array of 850 nm VCSELs, laser drivers, diffractive optical interconnect elements (DOIEs), detectors, and receivers. The HPOC module was used to implement a 4 /spl times/ 4 crossbar switch for ATM by exploiting global (N/sup 4/) FSOI.

Linear arrays of 40 X 40 micrometers 2 to 60 X 60 micrometers 2 microbolometers utilizing a semiconducting YBaCuO thin film as the IR sensitive material were fabricated and tested. This material displays a high temperature coefficient of resistance at room temperature, which makes it very attractive as an uncooled IR detector. The compatibility of semiconducting YBaCuO with Si micromachining techniques and CMOS technology and its ease of fabrication into thin films is attractive to the fabrication of inexpensive, high performance infrared detectors and imaging arrays. The room temperature responsivity, Rv, of the detectors was measured using 100 Hz chopped broad band infrared radiation to be as high as 104 V/W at 0.8 (mu) A current bias, providing a detectivity of 107 cm Hz1/2/W. The thermal conductance, G, of the isolation structure was measured to be a relatively high 10-5 W/K which limited the responsivity of the detector. Since Rv varies as 1/G, the responsivity and hence detectivity may be increased by up to two orders of magnitude by improving the thermal isolation. Zero bias responsivity was also observed on the structures, which was interpreted as pyroelectric IR detection. This was confirmed with independent pyroelectric current measurements.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Semiconducting YBaCuO thin films are a candidate for infrared bolometers operating at room temperature without the need for temperature control. Semiconducting YBaCuO thin films were fabricated by rf magnetron sputtering onto silicon substrates at room temperature. Room temperature deposition provides compatibility with CMOS technology to allow for the fabrication of low cost infrared imaging arrays with focal plane signal processing. The temperature coefficient of resistance (TCR) of the thin films was measured to be as high as 4% K-1 over a wide temperature range near 300 K. In this respect, amorphous YBaCuO thin films provided a higher TCR than epitaxial, tetragonal YBa2Cu3O6+x films. The noise voltage at 30 Hz was measured to be typically less than 1 (mu) V/Hz1/2. If the thin films are integrated into a typical air-gap thermal isolation structure, the projected responsivity Rv would be as high as 3.8 multiplied by 105 V/W with 1 (mu) A of current bias providing an estimated detectivity D* of 1.6 multiplied by 109 cm Hz1/2/W at a frame frequency of 30 Hz.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.