Charge Transfer Efficiency Degradation Research Articles

Proton Damage Comparison of an e2v Technologies n-channel and p-channel CCD204

Comparisons have been made of the relative degradation of charge transfer efficiency in n-channel and p-channel CCDs subjected to proton irradiation. The comparison described in this paper was made using e2v technologies plc. CCD204 devices fabricated using the same mask set. The device performance was compared over a range of temperatures using the same experimental arrangement and technique to provide a like-for-like comparison. The parallel transfer using the p-channel CCD was then optimized using a trap pumping technique to identify the optimal operating conditions at 153 K.

In-flight calibration of the Cassini imaging science sub-system cameras

We describe in-flight calibration of the Cassini Imaging Science Sub-system narrow- and wide-angle cameras using data from 2004 to 2009. We report on the photometric performance of the cameras including the use of polarization filters, point spread functions over a dynamic range greater than 10 7, gain and loss of hot pixels, changes in flat fields, and an analysis of charge transfer efficiency. Hot pixel behavior is more complicated than can be understood by a process of activation by cosmic ray damage and deactivation by annealing. Point spread function (PSF) analysis revealed a ghost feature associated with the narrow-angle camera Green filter. More generally, the observed PSFs do not fall off with distance as rapidly as expected if diffraction were the primary contributor. Stray light produces significant signal far from the center of the PSF. Our photometric analysis made use of calibrated spectra from eighteen stars and the spectral shape of the satellite Enceladus. The analysis revealed a shutter offset that differed from pre-launch calibration. It affects the shortest exposures. Star photometry results are reproducible to a few percent in most filters. No degradation in charge transfer efficiency has been detected although uncertainties are large. The results of this work have been digitally archived and incorporated into our calibration software CISSCAL available online.

Degradation of a COTS linear CCD induced by proton irradiation

A Commercial Off-The-Shelf (COTS) linear CCD irradiated by protons is examined experimentally in this study. A dummy output voltage, the charge transfer efficiency (CTE) and a dark signal were degraded by 2-, 5-, and 10-MeV proton irradiation for comparison. The CCDs irradiated by 2-MeV protons were damaged most seriously, and the CCDs irradiated by 5-MeV protons were damaged more than those irradiated by 10-MeV protons. Biased CCDs were damaged more seriously than unbiased CCDs with the same proton irradiation conditions. The vacancy density and distribution induced by proton displacement damage and the ionizing energy loss induced by proton ionization damage were calculated using TRIM software. The correlation between CTE degradation and nonionizing energy loss is analyzed.

Experimental analysis of charge transfer efficiency degradation of charge coupled devices induced by proton irradiation

The experiments on charge coupled devices (CCD) irradiated by protons were carried out. The charge transfer efficiency (CTE) of CCD was measured before and after proton radiation. The radiation damage mechanism of CTE degradation was analyzed. The CTE degradation induced by irradiation of protons of different energies was compared. The experimental results were explained by the theoretical analysis based on the calculation by radiation particle transport simulation software.

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.

Electron-Induced Displacement Damage Effects in CCDs

We compare differences in parametric degradation for CCDs irradiated to the same displacement damage dose with 2-MeV, 10-MeV, and 50-MeV electrons. Charge transfer efficiency degradation was observed to not scale well with non-ionizing energy loss (NIEL) for small signals. Short term annealing of mean dark current in a CCD sample irradiated with 2-MeV electrons at -85C is discussed, as well as additional annealing achieved by warming to temperatures up to and including room temperature. In contrast, charge transfer inefficiency was not observed to anneal following room temperature cycling for the sample irradiated at -85C

Proton effects in charge-coupled devices

Basic mechanisms and ground-test data for radiation effects in solid-state imagers are reviewed, with a special emphasis on proton-induced effects on silicon charge-coupled devices (CCDs). For the proton fluxes encountered in the space environment, both transient ionization and displacement damage effects arise from single-particle interactions. In the former case, individual proton tracks will be seen; in the latter, dark-current spikes (or hot pixels) and trapping states that cause degradation in charge-transfer efficiency will be observed. Proton-induced displacement damage effects on dark current and charge transfer are considered in detail, and the practical implications for shielding, device hardening, and ground testing are discussed.

固体撮像とその関連技術 単層メタル電極ＣＣＤイメージセンサの検討

A single-layer metal-electrode CCD image sensor was studied with the purpose of simplifying the steps in the production process with the aim of achieving low-cost sensors and supplressing smear noise. The inter-electrode gap of the single-layer electrode was decreased to 0.3 micrometer to achieve charge-transfer efficiency of unity. Boron ion-implantation which is self-aligned to the interelectrode gap was introduced to suppress degradation in charge-transfer efficiency. A reduction in the number of process steps needed to fabricate a 1/3-inch-format 360K-pixel interline transfer CCD image sensor was achieved. Vertical resolution was 350 TV lines. Low smear noise of-108dB was obtained.

Radiation hardness of pn-CCDs for X-ray astronomy

Results of all extensive radiation hardness test of a full depletion pn-Charge Coupled Device (pn-CCD) detector are presented. The pn-CCD is a new type of Charge Coupled Device designed for X-ray spectroscopy in ESA's cornerstone X-ray Multi Mirror (XMM) satellite mission. The devices were irradiated with 10 MeV-protons with fluences up to 6.5/spl middot/10/sup 9/ cm/sup -2/. This is more than one order of magnitude higher than the equivalent proton radiation environment expected for the 10 year mission. The only effect to the device was a degradation of charge transfer efficiency (CTE) at temperatures around 120 K. At XMM's operating temperature between 140 K and 170 K the performance of the detector will not significantly change during the 10 year mission. The degradation of the CTE was studied, and a method to improve it is described.

A technique to measure trap characteristics in CCD's using X-rays

An important type of radiation damage in CCD's used for X-ray spectroscopy is the degradation of charge transfer efficiency (CTE). Traps associated with radiation-induced defects are the basic cause of the damage. Here, we describe a method to extract trap characteristics using small charge packets produced by individual X-ray photon interactions in rectangular imaging CCD's. The method applies the principles of trap occupancy to the framestore CCD configuration, and uses data from CCD's operating in their normal transfer mode. We have measured trap characteristics in radiation damaged CCD's in a range of operating temperatures from 170-200 K, and have found that these data compare well to the expected phosphorus-vacancy (P-V) trap characteristics.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Displacement damage effects in mixed particle environments for shielded spacecraft CCDs

Analysis of monoenergetic proton test data reveals displacement damage degradation of charge transfer efficiency in state-of-the-art charge coupled devices (CCDs). New measurements, in combination with literature data, demonstrate good agreement between the energy dependencies of proton damage and the nonionizing energy loss (NIEL) for protons in Si. Massive shields being considered to preserve CCD performance in satellites are analyzed using the transport code BRYNTRN, which quantifies both primary and secondary particle production. Using NIEL to combine the cumulative effects of both protons and neutrons reaching the CCD. Al and Ta shield approaches are compared for both trapped and flare proton environments. In general, massive Ta shields have diminished benefit owing to damage from large secondary neutron fluxes. Analysis with Shockley-Read-Hall theory demonstrates the importance of CCD operating conditions and transfer efficiency measurement techniques in evaluating flight performance and comparing results between devices and laboratories.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effects of soft X-ray irradiation on solid-state imagers

The visible effects of soft X-ray damage in solid-state imagers are changes in the flat-band voltages, degradation in charge transfer efficiency and increased dark current. Details of these effects, and possible underlying mechanisms, are discussed. Deep level transient spectroscopy is introduced as a useful tool for identifying existing and radiation-induced trapping centres in charge-coupled devices. The effects of various annealing methods for charge-coupled and photodiode imagers are presented.

A resistive-gate Al/sub 0.3/Ga/sub 0.7/As/GaAs 2DEG CCD with high charge-transfer efficiency at 1 GHz

The fabrication and performance of an Al/sub 0.3/Ga/sub 0.7/As/GaAs modulation-doped resistive-gate charge-coupled device (CCD) are reported. The two-dimensional electron gas (2DEG) CCD, implemented as a 32-stage four-phase delay line, was tested at both low (1-13-MHz) and high (0.6-1.0-GHz) frequency. It exhibits a room-temperature charge-transfer efficiency (CTE) of better than 0.999 at clock frequencies from 10 MHz up to 1 GHz without a fat-zero signal and is limited by dark current below 10 MHz. The high-frequency test showed no CTE degradation up to 1-GHz operation. The CTE degraded at frequencies lower than approximately 5 MHz due to dark current. The charge-handling capability and minimum clock swing of the resistive-gate 2DEG CCD are calculated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>