Digital Frequency-Domain Multiplexing (DfMux) is a technique that uses MHz superconducting resonators and Superconducting Quantum Interference Device (SQUID) arrays to read out sets of transition ...edge sensors. DfMux has been used by several Cosmic Microwave Background experiments, including most recently POLARBEAR-2 and SPT-3 G with multiplexing factors as high as 68, and is the baseline readout technology for the planned satellite mission
LiteBIRD
. Here, we present recent work focused on improving DfMux readout noise, reducing parasitic impedance, and improving sensor operation. We have achieved a substantial reduction in stray impedance by integrating the sensors, resonators, and SQUID array onto a single-carrier board operated at 250 mK. This also drastically simplifies the packaging of the cryogenic components and leads to better-controlled crosstalk. We demonstrate a low readout noise level of 8.6
pA
/
Hz
1
1
/
2
, which was made possible by operating the SQUID array at a reduced temperature and with a low dynamic impedance. This is a factor of two improvement compared to the achieved readout noise level in currently operating Cosmic Microwave Background experiments using DfMux and represents a critical step toward maturation of the technology for the next generation of instruments.
We describe improvements in CCD performance that have been achieved on 4k×4k, (15 μm)2-pixel, fully depleted CCDs for the Dark Energy Spectroscopic Instrument (DESI) 1. With respect to our previous ...work on CCDs for the Dark Energy Camera and the Baryon Oscillation Spectroscopic Survey, our goals for the DESI CCD development were to improve read noise and quantum efficiency, improve the astrometric precision, and decrease pixel-size variations. We report experimental results on recently fabricated CCDs to be used in DESI.
Physics of fully depleted CCDs Holland, S E; Bebek, C J; Kolbe, W F ...
Journal of instrumentation,
03/2014, Letnik:
9, Številka:
3
Journal Article
Recenzirano
In this work we present simple, physics-based models for two effects that have been noted in the fully depleted CCDs that are presently used in the Dark Energy Survey Camera. The first effect is the ...observation that the point-spread function increases slightly with the signal level. This is explained by considering the effect on charge-carrier diffusion due to the reduction in the magnitude of the channel potential as collected signal charge acts to partially neutralize the fixed charge in the depleted channel. The resulting reduced voltage drop across the carrier drift region decreases the vertical electric field and increases the carrier transit time. The second effect is the observation of low-level, concentric ring patterns seen in uniformly illuminated images. This effect is shown to be most likely due to lateral deflection of charge during the transit of the photo-generated carriers to the potential wells as a result of lateral electric fields. The lateral fields are a result of space charge in the fully depleted substrates arising from resistivity variations inherent to the growth of the high-resistivity silicon used to fabricate the CCDs.
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 60 Co 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 3 times 10 -6 and 1 times 10 -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.
Lateral charge diffusion in charge-coupled devices (CCDs) dominates the device point-spread function (PSF), which can affect both image quality and spectroscopic resolution. We present new data and ...theoretical interpretations for lateral charge diffusion in thick, fully depleted CCDs developed at Lawrence Berkeley National Laboratory (LBNL). Because they can be overdepleted, the LBNL devices have no field-free region and diffusion is controlled through the application of an external bias voltage. Recent improvements in CCD design at LBNL allow the application of bias voltages exceeding 200 V. We give results for a 3512times3512 format, 10.5 mum pixel back-illuminated p-channel CCD developed for the SuperNova/Acceleration Probe (SNAP), a proposed satellite-based experiment designed to study dark energy. Lateral charge diffusion, which is well described by a symmetric two-dimensional (2-D) Gaussian function, was measured at substrate bias voltages between 3 and 115 V. At a bias voltage of 115 V, we measure a root-mean square (rms) diffusion of 3.7plusmn0.2mum. Lateral charge diffusion in LBNL CCDs will meet the SNAP requirements
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 800/spl times/1100, 15 /spl mu/m pixel, 280 /spl 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.
Observation of B → φ K and B → φ K Briere, R. A.; Chen, G. P.; Ferguson, T. ...
Physical review letters,
04/2001, Letnik:
86, Številka:
17
Journal Article
P-channel backside illuminated silicon charge-coupled devices (CCDs) were developed and fabricated on high-resistivity n-type silicon. The devices have been exposed up to 1 /spl times/ 10/sup 11/ ...protons/cm/sup 2/ at 12 MeV. The charge transfer efficiency and dark current were measured as a function of radiation dose. These CCDs were found to be significantly more radiation tolerant than conventional n-channel devices. This could prove to be a major benefit for space missions of long duration.
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