Showing papers on "Responsivity published in 1980"

Reference-Free Nonuniformity Compensation For IR Imaging Arrays

Abstract: Multi-detector IR imaging focal plane arrays possess large detector-to-detector dark current (offset) and responsivity (gain) variations which can completely mask the useful thermal signatures in IR scenes. Conventional detector compensation techniques require uniform temperature references of constant radiance over the entire field of view and a mechanical/ electro-optical shutter. This detracts from the mechanical simplicity of multi-detector staring focal planes (which require no scanning). This paper describes a real-time offset and responsivity (gain) compensation technique which dispenses with temperature references and shutters in staring focal planes. The technique makes use of the IR scene itself for calibration and continuously updates the compensation coefficients without interrupting the field of view with a shutter or a temperature reference. The results of real-time simulations of this technique with a number of sensors are presented. Real-time hardware implementation considerations suggest that the technique can be implemented with the addition of very little hardware to a conventional compensation technique requiring temperature references. The technique is also suitable for multi-detector scanning focal planes and for the removal of shading in TV sensors as well.

A Large Area TDI Image Sensor for Low Light Level Imaging

Abstract: A 1030 X 128 element time delay and integration (TDI) CCD image sensor has been developed for low-light-level (L/sup 3/) imaging applications. For L/sup 3/ imaging, output is derived from a high-gain low-noise floating-gate amplifier (FGA). For larger input signal levels, a second, resettable floating-gate amplifier (RFGA) with lower gain and wider dynamic range provides output in parallel to the FGA. The device features four-phase buried-channel construction and a polysilicon gate design tailored to produce optimum broad-band responsivity. Input signal levels of 500 electrons have been successfully imaged and amplifier noise levels of approximately 20 electrons have been observed.

Technology development for InSb infrared imagers

Abstract: InSb semiconductor technology required for infrared-detector-array fabrications is described. High-quality MOS, MOSFET, and linear and two-dimensional (2D) CID devices have been successfully fabricated. Interface-state densities of the MOS capacitors were determined to be less than 5 × 1010cm-2. eV-1, respectively. These results suggest that self-scanned monolithic arrays could be fabricated. The performance of linear and 2D CID arrays were evaluated in terms of detectivity (D*) and responsivity ( R ). The average D*of a 64- element line array was measured to be 3.4 × 1011cm. Hz1/2. W-1which is 70 percent of that of "background-limited-performance" (BLIP) operation. The R was 1 × 10-5V/photon with 10-percent uniformity. The D*and R were also obtained for a 32 × 32 2D array.

Effects of the substrate on the response of pyroelectric detectors

Abstract: In our studies dealing with a theoretical analysis on the response of pyroelectric detectors, it has been found that for substrate-attached pyroelectric detectors, the current responsivity falls off with decreasing frequency below a certain frequency due to the flow of heat out of the pyroelectric crystal into the substrate. The rate of the falloff depends on the thermal conductivity of the substrate. The higher the thermal conductivity, the faster the rate of the falloff. The current responsivity flattens out in a lower intermediate frequency range of 10-2to 102Hz. In this flat plateau region, the smaller the substrate thermal capacity, the higher the current responsivity. The theoretical analysis agrees with the experimental results using LiTaO 3 detectors mounted on silicon substrates.

A large area TDI image sensor for low light level imaging

Abstract: A 1030 × 128 element time delay and integration (TDI) CCD image sensor has been developed for low-light-level (L3) imaging applications. For L3imaging, output is derived from a high-gain low-noise floating-gate amplifier (FGA). For larger input signal levels, a second, resettable floating-gate amplifier (RFGA) with lower gain and wider dynamic range provides output in parallel to the FGA. The device features four-phase buried-channel construction and a polysilicon gate design tailored to produce optimum broad-band responsivity. Input signal levels of 500 electrons have been successfully imaged and amplifier noise levels of approximately 20 electrons have been observed.

Broadband radiometry with spectrally selective detectors.

Abstract: A spectrally selective optical-radiation detector can be normalized to an equivalent detector having unique values for its average responsivity R¯ and its cut-on and cutoff wavelengths λ1 and λ2 It is shown that the radiant power of any source that is described by a second-degree polynomial can be determined exactly between limits λ1 and λ2 Calculations were made for several real detectors and Planckian radiators at several temperatures to demonstrate the low errors inherent in this scheme.

p-i-nf.e.t. hybrid optical receiver for 1.1-1.6 μm optical communication systems

Abstract: The fabrication of low capacitance v.p.e. InGaAs/InP p-i-n photodiodes having a high responsivity up to 1.6 μm wavelength is described. The receiver sensitivities of the p-i-n f.e.t. hybrid receiver for a 280 Mbit/s system, measured at 1.3μm and 1.5 μm are -38.9 dBm and -39.4 dBm,respectively.

High infrared responsivity Indium-doped silicon detector material compensated by neutron transmutation

Abstract: The use of the neutron transmutation for producing precisely compensated, extrinsic idium-doped, silicon detector material of high infrared responsivity is reported. Highly indium-doped silicon crystals containing (1 to 3) × 1017cm-3indium concentrations and residual acceptors in the low 1012cm-3have been grown by float-zone doping. The high purity obtained by this growth technique enables very low net donor compensation densities to be achieved by neutron irradiation in a reactor. Transmuted phosphorus concentrations ranging from (1 to 20) × 1012cm-3have been investigated and compensation densities, N_{D} - N_{A} , as low as 2 × 1012cm-3have been achieved in irradiated samples after suitable damage annealing. Residual radioactivity due to transmuted indium isotopes approaches negligibly low levels for the neutron fluences required with high purity float-zone Si:In material. Significant improvements in infrared detector performance have been demonstrated with neutron compensated indium-doped silicon. Peak responsivities up to 100 A/W at 50 K and 103-V/cm detector bias have been measured, corresponding to dc photoconductive gains in the 30 to 40 range and mobility-lifetime products > 10-3cm2/V. Additional studies indicate that the detector responsivity, which is adversely affected by high-temperature CCD fabrication processes, can be restored significantly by phosphorus gettering techniques.

Automatic responsivity control for a CCD imager

Abstract: Nearly uniform responsivity in a charge coupled device infrared photodetector array is achieved by a charged coupled device automatic responsivity control circuit, including a subtractor (56), a multiplier (70) and a subtractor (84). The subtractor (56) establishes a reference level which is multiplied with the signal in the multiplier (70), the product being subtracted from a second reference level in the subtractor (84). The resulting signal is free of distortions due to nonuniform responsivities among the detectors in the infrared photodetector array, a significant advantage.

A monolithic thermopile detector fabricated using integrated-circuit technology

Abstract: A thermopile infrared detector fabricated using silicon integrated-circuit technology is described. The device uses a series-connected array of thermocouples whose hot junctions are supported on a thin silicon membrane formed using anisotropic etching and a diffused boron etch-stop. The membrane size and thickness control the speed and responsivity of the structure, which can be designed for a given application. For a membrane measuring 2mm × 2mm × 1µm and containing sixty bismuth-antimony couples, the structure produces a responsivity of 7 volts/watt and a time constant of about 15 msec. Polysilicon couples and the use of slotted membranes can provide further performance improvements while retaining compatibility with on-chip signal processing circuitry.

Temperature dependence of responsivity in closely compensated extrinsic infrared detectors

Abstract: Extrinsic infrared detectors which have closely compensated residual impurities shallower than the major dopant exhibit a large temperature dependence of the responsivity caused by changing occupation of these levels. A model is developed and its behavior is explored using indium-doped silicon as an example. The temperature dependence of the responsivity at low temperatures is found to be a series of plateaus for each overcompensated level. When exact compensation occurs, a unique peak of very high responsivity is predicted. The model is fitted to published Si: In detector data exhibiting such a series of plateaus and good agreement is found.

ZnTe extrinsic photodetector for visible integrated optics

Abstract: Oxygen implantation in ZnTe may be used to obtain optical absorption at wavelengths higher than 0.55 μm, which is the normal absorption edge in this compound semiconductor. Optical waveguides obtained by boron implantation in this material are associated with detectors using that extrinsic absorption effect in the presence of a Schottky barrier depletion layer. The responsivity of the photodetector is about 5×10−2 A/W at 0.61 μm and the rise time is less than 3 ns.

InAsSb Hybrid Imager Evaluation

Abstract: Current research on infrared hybrid focal planes is directed toward devices in whichdetection occurs in a p -n junction formed in an intrinsic narrow energy bandyap semi-conductor, and signal processing is accomplished in a Si CCD multiplexer which is electri-cally interfaced to the detector array. A hybrid array such as this, where the detectorformat is a 32 x 32 matrix, has been fabricated. The active material is backside-illumi -nated InAsSb which has been planar processed and fully passivated. The cutoff wavelengthis 4.0 pm at the operating temperature of 77K. The CCD is four phase with a two levelpolysilicon yate structure. The signal input is via direct injection with an option for dcsuppression. Operation of the focal plane in a staring mode that uses dc suppression isdiscussed. Data derived from the video output is presented; this includes responsivity anddetectivity. Off focal plane non -uniformity compensation is also discussed. Displays ofthermal images utilizing processed data from the hybrid focal plane array will be shown.IntroductionA demand for high performance, high density, nigher operating temperature imaging arrayswhich can be produced in quantity exists. In order to address these needs, a "common"detection technology approach has been adopted; this permits a variety of system require-ments to be satisfied with a maximum of overlap in the technology used. This approach usesa hybrid structure that consists of three components: a photovoltaic detector, which isbackside - illuminated through a transparent substrate; a Si CCD multiplexer, which alsoserves to integrate the signal; and an In interconnect technology, which electrically andphysically joins the detector array to the multiplexer.Changes in detector material and CCD multiplexer input cell allow operation in anyportion of the 3 - 12 pm spectral region for both high and low background. Both epitaxialInAsl_xSbx /GaSb and Hgl_xCdxTe /CdTe are under intensive development for use in this commonapproach; the former for applications in the 3 - 5 um spectral band, the latter for bothmid and far IR spectral bands. Details of current detector performance for these systemshas been given elsewhere (1,2). Photocurrent from the detector is injected into an induceddrain FET (which may be the CCD itself if no "front end" signal processing is desired).The signal may then be processed according to the application, including dc suppression,gain reduction, and ac coupling. This paper reports on the construction and imaging with acommon focal plane array that has InAsSb as the detector material. The focal plane geome-try is a 32 x 32 matrix which is operated in a staring mode.Hybrid ComponentsDetectorsDetectors were fabricated from InAsl_XSbx/ GaSb, grown by liquid phase epitaxy withx = 0.11 (lattice matched system). Fabrication of the detectors is a planar process thatuses Be ion implantation with CVD SiO2 as an insulator (3). The spectral response of thesedetectors is from 1.6 (cut -on of the transparent GaSb substrate) to 3.95 um at 77K, with aquantum efficiency of about 80 percent. At this tpemperature the RoA of at least ninetypecent of the 1024 detectors is in excess of 10

Evaluation of composite bolometers at 0.4 kelvin

Abstract: Composite bolometer structures have provided the most sensitive IR detectors for operation at helium-4 temperatures of 1.5K. Below 1.5K the electrical and thermal properties change significantly and the performance characteristics cannot be accurately extrapolated for composite bolometers at helium-3 temperatures of 0.4K. The paper deals with experimentally assessed performance of composite bolometers at 0.4K. It is found that sensitivity estimates derived from electrical or load curve properties can overestimate the responsivity to radiation by several orders of magnitude depending upon a particular material behavior. For many near-millimeter applications background power levels are several nanowatts and the associated photon noise plus Johnson and phonon noise components impose a fundamental detection limit of about 5 x 10 to the -15thW/Hz to the -1/2. We have successfully fabricated composite bolometers which at 0.4 K and millimeter wavelengths achieve a noise equivalent power of 7 x 10 to the -15thW/Hz to the -1/2 coupled with a large absorbing area (0.3 sq cm) and a fast response time (2 msec.).

Thermal Imaging Systems Utilizing Pyroelectric Detector Arrays Coupled With Solid-State Readout Techniques

Abstract: Pyroelectric detectors have the advantage of being inherently accoupled to the target scene and they are therefore ideally suited for use in high-background and/or long-wavelength thermal imaging systems. This paper presents the results of a study to determine the feasibility and to predict the performance of focal planes employing very thin pyroelectric detector arrays together with solid-state readout circuitry. Detectivities within a factor of two of the radiation-limited performance have been achieved by wire bond connecting pyroelectric detectors to a Hughes CCD with a modulating gate input. It is shown that the voltage responsivity is symmetric with respect to the thermal and electrical time con-stants; the traditional role of these time constants (Tpc < Til) can be reversed to that Tw. becomes greater than Tth. The lumped parameter analysis creaks down for very thin detectors when the thermal time constant must be severely adjusted and for detector arrays in the absence of adequate thermal isolation between elements; in this case, thermal spreading must be accounted for. A more extensive treatment utilizing a thermal diffusion analysis allows such cases to be considered.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Video Detection of Far Infrared Radiation by Nb Thin Film Microbridges under Vortex Flux Flow

Abstract: Video detection of far infrared radiation in the spectral region of 10-35 cm-1 was carried out at 4.2 K using Nb thin film microbridges (1×1 µm2 in area and 1000 A thick) in which vortex flux flow existed. A structureless response spectrum with a broad peak at 13 cm-1, very different from those observed previously in Nb-Nb point-contact junctions, was obtained. Some discussions are given on the responsivity of a microbridge operating under vortex flux flow.

Thermal IR imaging System Using A Self-Scanned HgCdTe/CCD Detector Array

Abstract: It is likely that future high resolution earth observation imaging systems will utilize self-scanned IR detectors. In an initial step toward this goal, an IR imaging system operating in the 10 to 12 micron spectral region has been developed. This system uses a 9-element HgCdTe/CCD linear array operating in the photoconductive mode, nine pre-amplifiers and a silicon CCD multiplexer integrated into a focal plane assembly. Opto-mechanical techniques are used to scan the scene and images are produced in real time. The imaging performance of this system is described and measurements of noise, responsivity, specific detectivity, and detector sensitivity profiles are presented. The requirements for more advanced detector arrays for use in future NASA remote sensing missions are also discussed.

CO 2 Transversely Excited Atmospheric (TEA) Laser Rangefinder

Abstract: The system described here uses a CO2-TEA-laser that operates at 2pps with a pulse peak power greater than 300KW. Independent optical trains are used with a transmitted beam divergence of 0.5 mrad and 5-inch diameter receiving optics. A high-speed HgCdTe photodiode with a responsivity of a D* = 1.34 x 10 'cm Hz 2/W is used in the straight detection mode for detecting the leading edge of the pulse return from the target. The unit has been field-tested and range data from many natural and man-made targets has been obtained.

HgCdTe Charge-Coupled Detectors (CCD)

Abstract: CCD shift registers have been investigated in 4.4 pm HgCdTe for time delay and integrate (TDI) enhancement of responsivity and signal to noise ratio and for multiplexing a number of TDI shift registers. CCD linear arrays and area arrays have been operated from 77K to 140K cooling and from 50 kHz to above 1 MHz. Charge transfer efficiency (CTE) has been measured to 0.9999 on a 32 stage four phase p channel device. Infrared sensitivity measure-ments show, D* values above 1012 cmHz1/2/W for full TDI enhancement of32. TDI has been demonstrated utilizing focused laser illumination scanned synchronously with the clocked charge. Sensitivity and noise analyses have been made to show limits of detection for multiplexed arrays.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Performance of hybrid silicon focal planes

Abstract: Infrared hybrid silicon focal planes offer the advantage of combining excellent performance with high cost-effectiveness. It will be shown that an extrinsic indium-doped detector array interconnected to 32 × 32 direct injection multiplexer exhibits an interconnect yield of 99.6 percent. Furthermore, radiometric performance data such as detectivity and responsivity will be presented in addition to operational characteristics such as the effect of bias voltage, integration time, and skimming on signal output.

Comparison of the responsivity of W-Ni point contact MBM diodes with W-Si point contact Schottky diodes

Abstract: The responsivities of the W-Ni point contact MBM diode and the W-Si point contact Schottky diode (commercial 1N23B diode) are compared at 9.5 GHz under identical conditions. The MBM diode has almost half the responsivity of the Schottky diode and was measured to be ≃20 V/W for a 550 Ω termination. The responsivity of the MBM diode decreases with an increase of the frequency. However, this is not due to the RC time constant of MBM diodes, but due to the antenna properties of the whisker and the relaxation behavior of the metallic whisker antenna.

Fast-response photodiode based on a surface-barrier Au-n-n/+/-GaAs structure

Abstract: A fast-response photodiode was constructed from a surface-barrier Au–n-n+-GaAs structure. The active n-type region was a film grown by vapor epitaxy and characterized by a free-electron density n = 1014–1015cm−3. The photodiode was highly sensitive in a wide spectral range of 0.25–0.9 μ. The monochromatic current responsivity was 0.5 A/W at λ = 0.8 μ. The rise time of the photoresponse signal was 100 psec when the bias voltage was up to 50 V.

New Microwave Detector Employing Nb/GaAs Super-Schottky Contact

Abstract: A super-Schottky contact diode made of Nb on heavily doped p-GaAs has been fabricated by electron-beam deposition under high vacuum, resulting in a long life and very reliable characteristics with estimated detector current responsivity S?1500 V?1 and NEP ? 1.2 × 10?15 w/?HZ at 4.2 K under optimum bias conditions.

Design considerations on high sensitivity mos area image sensor

Abstract: By clarifying the design approach of the photoelectric conversion of the two-dimensional MOS solid-state image sensor, a 320 × 244 element high responsivity MOS sensor has been fabricated and characterized. In the design of the photodiode design formulas for sensing capacity, responsivity and spectral response are presented and are in good agreement with the measurement. In order to suppress blooming without lowering the responsivity, the threshold voltage of the vertical switch transistor is raised and the photodiode whose n+-diffusion layer of the signal wire is surrounded by the p+-layer is proposed. In the horizontal switch transistor design, the signal reading residue is obtained and a simple formula describing the vertical resolution affected by the residue is also obtained. The main features of the MOS sensor developed by this design approach are: (1) high responsivity; (2) high resolution; and (3) strong blooming. The main characteristics are: for 1.4 μA saturation signal current, 71x saturation faceplate illumination (by Tungsten source) at 550 nm, the responsivity is 0.22 μA/μW, horizontal resolution is 240 TV lines, vertical resolution 190 TV lines and dissipation power is 30 mW.