Backside-illuminated Charge-coupled Device Research Articles

Modeling the Wavelength Dependence of Pixel Response Nonuniformity of a CCD Sensor

Precision measurements in astronomy require stringent control of systematics such as those arising from imperfect correction of sensor effects. In this work, we develop a parametric method to model the wavelength dependence of pixel response nonuniformity (PRNU) for a laser-annealed backside-illuminated charge-coupled device. The model accurately reproduces the PRNU patterns of flat-field images taken at nine wavelengths from 290 to 950 nm, leaving the rms residuals no more than 0.2% in most cases. By removing the large-scale nonuniformity in the flat fields, the rms residuals are further reduced. This model fitting approach gives more accurate predictions of the PRNU than cubic-spline interpolation does with fewer free parameters. It can be applied to make PRNU corrections for individual objects according to their spectral energy distribution to reduce the photometry errors caused by the wavelength-dependent PRNU, if sub-percent level precision is required.

A New Method for Suomi-NPP VIIRS Day–Night Band On-Orbit Radiometric Calibration

The Suomi National Polar-orbiting Partnership Visible Infrared Imaging Radiometer Suite (S-NPP VIIRS) instrument contains a visible imaging band designed to produce imagery during both daytime and nighttime, which is called the day-night band (DNB). The DNB is a three-gain-stage backside-illuminated charge-coupled device (CCD) with four detector arrays that aggregate the individual CCD pixels into 32 different aggregation modes across scan, yielding imagery with a roughly constant horizontal sampling interval. The highest gain stage is over 100 000 times more sensitive than the lowest gain stage; the combination of the three gain stages allows for imagery with radiances ranging from 10 -10 to 10 -2 W · cm -2 · sr -1 . The initial DNB on-orbit calibration relies on monthly sensor special operations. This offline calibration approach results in discrete calibration and the loss of some science data. In this paper, we will present a new calibration method based solely on VIIRS onboard calibrators (OBCs). The calibrator data collected on the nighttime side of an orbit are used to determine the dark offset and the data collected over the daytime side of the orbit, and the day-night terminators are used to compute the cross-stage gain ratios. The results showed that the dark offset and the gain ratio derived from the initial method could be biased up to ten digital numbers (DN) and 12%, respectively, due to nighttime airglow and Earth scene stray light. The calibration is also continuous as calibrator data are recorded for each scan. Because no special operation and offline analysis are required, this method was approved for VIIRS operational implementation to improve the DNB radiometric calibration and sensor on-orbit operations.

Long-Range Reconnaissance Imager on New Horizons

The LOng-Range Reconnaissance Imager (LORRI) is the high resolution imaging instrument for the New Horizons mission to Pluto, its giant satellite Charon, its small moons Nix and Hydra, and the Kuiper Belt, which is the vast region of icy bodies extending roughly from Neptune's orbit out to 50 astronomical units (AU). New Horizons launched on January 19, 2006 as the inaugural mission in NASA's New Frontiers program. LORRI is a narrow angle (field of view=0.29 deg), high resolution (4.95 microrad pixels), Ritchey-Chretien telescope with a 20.8 cm diameter primary mirror, a focal length of 263 cm, and a three lens field-flattening assembly. A 1024 x 1024 pixel (optically active region), thinned, backside-illuminated charge-coupled device (CCD) detector is used in the focal plane unit and is operated in frame transfer mode. LORRI provides panchromatic imaging over a bandpass that extends approximately from 350 nm to 850 nm. LORRI operates in an extreme thermal environment, situated inside the warm spacecraft with a large, open aperture viewing cold space. LORRI has a silicon carbide optical system, designed to maintain focus over the operating temperature range without a focus adjustment mechanism. Moreover, the spacecraft is thruster-stabilized without reaction wheels, placing stringent limits on the available exposure time and the optical throughput needed to satisfy the measurement requirements.

Exploration of X-ray and charged-particle spectroscopy with CCDs and PSDs

Two alternative detector types have been studied for use in the Eindhoven Scanning Ion Microprobe set-up. First, the applicability of a Charge Coupled Device (CCD) system for X-ray spectroscopy has been explored. Second, some properties of the SiTek type 1L30 Position Sensitive Detector (PSD) for charged-particle spectroscopy have been studied. A literature survey shows that excellent X-ray spectroscopy with a CCD system is feasible, particularly with a deep-depletion backside-illuminated CCD and low speed read-out. If, however, high-speed CCD read-out is required, such as for scanning microprobe experiments, a CCD system cannot be used for spectroscopy due to excess read-out noise. For the PSD, noise theory calculations are presented, which result in a noise shaping time for optimal energy and position resolution. In practice, however, a much longer time is needed to obtain sufficient energy and position linearity. Characterization measurements of the PSD using our 4 MeV He + microprobe are also described. A position resolution of 0.47 mm and a position linearity of better than 0.15% detector length are found. In addition, an energy linearity better than 0.3% and an energy resolution of 36 keV are measured. The latter will have to be improved, to make the PSD suitable for charged-particle spectroscopy applications.

Vacuum-ultraviolet quantum efficiency of a thinned, backside-illuminated charge-coupled device

The UV quantum efficiency of a Scientific Imaging Technologies (SITe, Beaverton, Ore., formerly Tektronix) 1024 pixel by 1024 pixel thinned and backside-illuminated charge-coupled device has been measured in the wavelength band from 1164 to 5200 Å. The 24-µm-pixel device, which does not have an antireflective coating, has an average quantum efficiency of more than 40% in the band from 1164 to 4000 Å and a read noise of 15 e(-)/pixel.

CELESTIAL GAMMA RAY BURSTS DETECTOR DEVELOPMENT AND MODEL SIMULATIONS

CELESTIAL GAMMA RAY BURSTS DETECTOR DEVELOPMENT AND MODEL SIMULATIONS

Characteristics of thinned backside-illuminated charge-coupled device imagers

A linear 500×1 charge-coupled device (CCD) surface channel imager is thinned to less than 30 μm, with the thinned back surface accumulated to reduce the surface recombination velocity. Photoresponsivity is measured to be 90 mA/W of incident wide-band power from a 2854-K blackbody light source. This sensitivity is a factor of 3 higher than previously reported values. Spectral responsivity reaches a peak of 90% quantum efficiency at 7000-Å wavelength, and over 50% quantum efficiency for the spectral range from 5000 to 9000 Å. A 32% square wave amplitude response at the Nyquist limit is obtained at a location 150 resolution elements from the output diode. Optical imager resolution obtained by using the backside-illuminated device is illustrated.