Infrared ROIC for very low flux and very low noise applications

Fièque, B.; Martineau, L.; Sanson, E.; Chorier, Philippe; Boulade, O.; Moreau, Vincent; Geoffray, Hervé

doi:10.1117/12.898987

Cited by 15 publications

(11 citation statements)

References 7 publications

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“…One can measure the pixel capacitance by changing the reference voltage in the middle of an acquisition. The pixel capacitance is then given by: (6) where C f is the fixed capacitance of the test pixel, ΔVin is the voltage difference applied on the reference voltage and ΔVout is the difference between the two measured signals. With this test method we obtained a 5.6fF ROIC capacitance which is noticeably small and fairly close to the expected design value.…”

Section: Test Resultsmentioning

confidence: 99%

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ROIC development at CEA for SWIR detectors: pixel circuit architecture and trade-offs

Guellec

Boulade²,

Cervera

et al. 2017

International Conference on Space Optics — ICSO 2014

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I. INTRODUCTIONInfrared detection is widely used in astrophysics and plays a key role in several space missions aiming for example at scanning the sky to discover new objects (coolest stars, dust-obscured galaxies, exo-planets …) or studying the evolution of the universe, where light is redshifted in the infrared range. In many cases the space telescope involves an HgCdTe infrared detector operating at low frame rate over long integration time. Due to the very low input signal, dark current and readout noise are essential figures that must be minimized to get the best detector sensitivity. This kind of application also requires very large focal plane array (FPA) often relying on a butting arrangement of large detectors [1]. The trend is to increase the single detector format from 1Kx1K to 2Kx2K and 4Kx4K. For very large formats, material quality and detector process may affect the production yield and the global infrared FPA cost. As a result the detector format could result from a trade-off taking into account producibility.In the first part, we review three common pixel circuits and discuss their characteristics with respect to these application needs. In the second part we describe a ROIC based on SFD pixel that we have developed at CEA-LETI. Then we provide in the third part test results and electrical performances of the ROIC.

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Section: Test Resultsmentioning

confidence: 99%

“…III. SFD ROIC DEVELOPMENT Following a previous development [6] from our partner, Sofradir, we designed a 640x512 ROIC with 15µm pixel-pitch in a standard 0.18µm CMOS process. It has been hybridized with a SWIR HgCdTe photodiode array in the perspective of astrophysics applications.…”

Section: Capacitive Trans-impedance Amplifiermentioning

confidence: 99%

ROIC development at CEA for SWIR detectors: pixel circuit architecture and trade-offs

Guellec

Boulade²,

Cervera

et al. 2017

International Conference on Space Optics — ICSO 2014

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“…The ROIC design is detailed in a dedicated paper from Sofradir within the same conference [ 9 ]. Briefly, it is a 384x288 array with a 15µm pitch.…”

Section: Read Out Circuit Designmentioning

confidence: 99%

Ultra low dark current CdHgTe FPAs in the SWIR range at CEA and Sofradir

et al. 2011

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We report here first results carried out at CEA and Sofradir to build ultra low dark current focal plane arrays (FPA) in the short wave infrared range (SWIR) for space applications. Those FPAs are dedicated to very low flux detection in the 2µm wavelength range. In this purpose, Sofradir has designed a source follower per detector readout circuit (ROIC), 384x288, 15µm pitch. This ROIC has been hybridized on different HgCdTe diode configurations processed at CEA-LETI and low flux characterisations have been carried out at CEA-SAp at low temperature (from 60 to 160K). Both p/n and n/p structures have been evaluated. The metallurgical nature of the absorbing layer is also examined and both molecular beam epitaxy (MBE) and liquid phase epitaxy (LPE) have been processed. Dark current measurements are discussed in comparison with previous results from the literature. State of the art dark currents are recorded for temperatures higher than 120K. At temperatures lower than 100K, the decrease in dark current saturates for both technologies. In this regime, currents between 0.4 and 0.06 e/s/pixel are reported. IntroductionSpace based observatories for astrophysics are very demanding in ultra low flux detection in the IR spectrum. Such low flux levels represent the detection of a few photons only during long integration times (typically 1e-/s during several minutes) and therefore require ultra low dark current photodiodes coupled to a very high performance ROIC stage in terms of noise and leakage. To meet these requirements, a very attractive structure is a source follower per detector (SFD) where the charge integration is carried out on the diode capacitance itself, minimising the integration capacitance thus optimizing the charge conversion factor, without any injection efficiency issue. Another advantage of such a structure is the fact that it usually allows non destructive readings, enabling different sampling strategies to minimise read out noise such as correlated double sampling, Fowler sampling or follow up the ramp. Up to now, this type of architecture has been mostly developed by US companies leading to very large format focal plane arrays (FPA) involving p/n Mercury Cadmium Telluride (MCT) diodes, InSb diodes and Si:As diodes [ 1 , 2 , 3 ]. In the case of the MCT material system, the choice of p/n polarity is generally driven by dark current considerations. n/p diodes lead usually to larger dark currents because of the presence of Hg vacancies in the p base layer degrading the minority carrier lifetime. However, this is only true in the case of a diffusion limited diode. Nevertheless, to meet ultra low dark current requirements, diodes have to be cooled down to very low temperatures. The thermal evolution of these data suggests that in these conditions [ 4 ], the diode limiting mechanisms are not diffusion current from the absorbing layer but more likely generation-recombination (GR) from the diode depletion region. This GR phenomenon being material and technology dependant, it appeared instructive to explore bot...

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“…Those various datasets have been measured with different read out input circuits (ROIC). The first two were based on a source follower per detector (SFD) input stage well suited for very low flux values [ 6 ]. The last one was a capacitive trans-impedance amplifier per pixel (CTIA), dedicated for ultra-fast measurement (RAPID ROIC, [ 7 ]), less suited for very low fluxes.…”

Section: Nir Arrays For Astrophysicsmentioning

confidence: 99%