53 research outputs found
Radiation Tolerance of Fully-Depleted P-Channel CCDs Designed for the SNAP Satellite
Thick, fully depleted p-channel charge-coupled devices (CCDs) have been
developed at the Lawrence Berkeley National Laboratory (LBNL). These CCDs have
several advantages over conventional thin, n-channel CCDs, including enhanced
quantum efficiency and reduced fringing at near-infrared wavelengths and
improved radiation tolerance. Here we report results from the irradiation of
CCDs with 12.5 and 55 MeV protons at the LBNL 88-Inch Cyclotron and with 0.1-1
MeV electrons at the LBNL Co60 source. These studies indicate that the LBNL
CCDs perform well after irradiation, even in the parameters in which
significant degradation is observed in other CCDs: charge transfer efficiency,
dark current, and isolated hot pixels. Modeling the radiation exposure over a
six-year mission lifetime with no annealing, we expect an increase in dark
current of 20 e/pixel/hr, and a degradation of charge transfer efficiency in
the parallel direction of 3e-6 and 1e-6 in the serial direction. The dark
current is observed to improve with an annealing cycle, while the parallel CTE
is relatively unaffected and the serial CTE is somewhat degraded. As expected,
the radiation tolerance of the p-channel LBNL CCDs is significantly improved
over the conventional n-channel CCDs that are currently employed in space-based
telescopes such as the Hubble Space Telescope.Comment: 11 pages, 10 figures, submitted to IEEE Transaction
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Improved Spatial Resolution in Thick, Fully-Depleted CCDs withEnhanced Red Sensitivity
The point spread function (PSF) is an important measure of spatial resolution in CCDs for point-like objects, since it affects image quality and spectroscopic resolution. We present new data and theoretical developments for lateral charge diffusion in thick, fully-depleted charge-coupled devices (CCDs) developed at Lawrence Berkeley National Laboratory (LBNL). Because they can be over-depleted, the LBNL devices have no field-free region and diffusion is controlled through the application of an external bias voltage. We give results for a 3512 x 3512 format, 10.5 {micro}m pixel back-illuminated p-channel CCD developed for the SuperNova/Acceleration Probe (SNAP), a proposed satellite-based experiment designed to study dark energy. The PSF was measured at substrate bias voltages between 3 V and 115 V. At a bias voltage of 115 V, we measure an rms diffusion of 3.7 {+-} 0.2 {micro}m. Lateral charge diffusion in LBNL CCDs will meet the SNAP requirements
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Quantum efficiency characterization of back-illuminated CCDs Part 2: reflectivity measurements
The usual quantum efficiency (QE) measurement heavily relies on a calibrated photodiode (PD) and the knowledgeof the CCD s gain. Either can introduce significant systematic errors. But reflectivity can also be used to verify QE measurements. 1 - R >_ QE, where R is the reflectivity, and over a significant wavelength range, 1 - R = QE. An unconventional reflectometer has been developed to make this measurement. R is measured in two steps, using light from the lateral monochromator port via an optical fiber. The beam intensity is measured directly with a PD, then both the PD and CCD are moved so that the optical path length is unchanged and the light reflects once from the CCD; the PD current ratio gives R. Unlike traditional schemes this approach makes only one reflection from the CCD surface. Since the reflectivity of the LBNL CCDs might be as low as 2 percent this increases the signal to noise ratio dramatically. The goal is a 1 percent accuracy. We obtain good agreement between 1 - R and the direct QE results
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Measurement of lateral charge diffusion in thick, fully depleted, back-illuminated CCDs
Lateral charge diffusion in back-illuminated CCDs directly affects the point spread function (PSF) and spatial resolution of an imaging device. This can be of particular concern in thick, back-illuminated CCDs. We describe a technique of measuring this diffusion and present PSF measurements for an 800x1100, 15 mu m pixel, 280 mu m thick, back-illuminated, p-channel CCD that can be over-depleted. The PSF is measured over a wavelength range of 450 nm to 650 nm and at substrate bias voltages between 6 V and 80 V
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Integrating Signal Processing and A/D Conversion in one Focal-Plane Mounted ASIC
The CRIC (CCD Readout IC) ASIC has been designed to meet the power, space and radiation requirements of the SNAP satellite. It incorporates four channels consisting of a pre-amplifier, double correlated sampler and pipeline A/D converter with integrated voltage reference. The CRIC chip has been specifically designed to operate both at room temperature and at typical focal plane temperatures down to 130K. This minimizes wiring complexity while maintaining signal integrity on complex focal planes. CRIC is half of a two ASIC CCD readout system; the other ASIC in development is a bias and clock voltage generator. Also in development, are 16 and 32 channel versions of CRIC for use with hybrid photodiode and near infrared pixel arrays
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Integrating Signal Processing and A/D Conversion in one Focal-Plane Mounted ASIC
The CRIC (CCD Readout IC) ASIC has been designed to meet the power, space and radiation requirements of the SNAP satellite. It incorporates four channels consisting of a pre-amplifier, double correlated sampler and pipeline A/D converter with integrated voltage reference. The CRIC chip has been specifically designed to operate both at room temperature and at typical focal plane temperatures down to 130K. This minimizes wiring complexity while maintaining signal integrity on complex focal planes. CRIC is half of a two ASIC CCD readout system; the other ASIC in development is a bias and clock voltage generator. Also in development, are 16 and 32 channel versions of CRIC for use with hybrid photodiode and near infrared pixel arrays
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Quantum efficiency characterization of LBNL CCD's Part 1: the Quantum Efficiency Machine
Instrumentation was developed in 2004 and 2005 to measure the quantum efficiency of the Lawrence Berkeley National Lab (LBNL)total-depletion CCD's, intended for astronomy and space applications. This paper describes the basic instrument. Although it is conventional even to the parts list, there are important innovations. A xenon arc light source was chosen for its high blue/UV and low red/IR output as compared with a tungsten light. Intensity stabilization has been difficult, but sinceonly flux ratios matter this is not critical. Between the light source andan Oriel MS257 monochromator are a shutter and two filter wheels. High-bandpass and low-bandpass filter pairs isolate the 150-nm wide bands appropriate to the wavelength, thus minimizing scattered light and providing order blocking. Light from the auxiliary port enters a 20-inch optical sphere, and the 4-inch output port is at right angles to the input port. An 80 cm drift space produces near-uniform illumination on the CCD. Next to the cold CCD inside the horizontal dewar is a calibrated reference photodiode which is regulated to the PD calibration temperature, 25 C. The ratio ofthe CCD and in-dewar reference PD signals provides the QE measurement. Additional cross-calibration to a PD on the integrating sphere permitslower-intensity exposures
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A low noise CMOS camera system for 2D resonant inelastic soft X-ray scattering
Resonant Inelastic X-ray Scattering (RIXS) is a powerful spectroscopic technique to study quantum properties of materials in the bulk. A novel variant of RIXS, called 2D RIXS, enables concurrent measurement of the scattered X-ray spectrum for a wide range of input energies, improving on the typically low throughput of 1D RIXS. In the soft X-ray domain, 2D RIXS demands an X-ray camera system with small pixels, large area, high quantum efficiency and low noise to limit the false detection rate in long duration exposures. We designed and implemented a 7.5 Megapixel back-illuminated CMOS detector with 5 μm pixels and high quantum efficiency in the 200–1,000 eV X-ray energy range for the QERLIN 2D RIXS spectrometer at the Advanced Light Source. The QERLIN beamline and detector are currently in commissioning. The camera noise from in-situ 3 s long dark exposures is 7e− or less and the leakage current is 6.5 × 10−3 e−/(pixel ∙ s). For individual 500 eV X-rays, the expected efficiency is greater than 75% and the false detection rate is ∼1 × 10−5 per pixel
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Improved Spatial Resolution in Thick, Fully-Depleted CCDs with Enhanced Red Sensitivity
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