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Orthogonal-Transfer Charge-Coupled Devices and Low-Noise Charge-Coupled Devices Readout Circuits*

Orthogonal-Transfer Charge-Coupled Devices and Low-Noise Charge-Coupled Devices Readout Circuits*. Barry E. Burke.

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Orthogonal-Transfer Charge-Coupled Devices and Low-Noise Charge-Coupled Devices Readout Circuits*

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  1. Orthogonal-Transfer Charge-Coupled Devices and Low-Noise Charge-Coupled Devices Readout Circuits* Barry E. Burke *The MIT Lincoln Laboratory portion of this work was performed under a Collaboration Agreement between MIT Lincoln Laboratory and The University of Hawaii, Institute for Astronomy (IfA). Opinions, interpretations, conclusions, and recommendations are those of the authors, and do not necessarily represent the view of the United States Government.

  2. Outline • Review of Orthogonal-Transfer Charge-Coupled Devices (OTCCD) • Development of the orthogonal transfer array (OTA) • Low-noise CCD readout circuits • Summary

  3. Conventional vs. Orthogonal-Transfer CCDs

  4. Application Areas Videoout • Compensation of platform motion • Imaging from unstable and/or moving platforms • TDI (time delay and integrate) with variable scan direction • Compensation of scene motion • Ground-based astronomy Output register Frame store Imaging area OTCCD can noiselessly compensate for scene motion across sensor during image integration

  5. Application of OTCCDs in Astronomy Star-cluster imagery (M71) • Use OTCCD to remove blurring due random motion of star images (electronic tip-tilt) No motion compensation, =0.73" With motion compensation, =0.50” SNR increase: 1.7

  6. Outline • Review of Orthogonal-Transfer Charge-Coupled Devices (OTCCD) • Development of the orthogonal transfer array (OTA) • Low-noise CCD readout circuits • Summary

  7. Pan-STARRS(Panoramic Survey Telescope and Rapid Response System) • Four 1.8-m telescopes viewing same sky sector • 3˚ FOV, 24 mv sensitivity • High-cadence, wide-field surveys • Detect variable or moving objects • 1.4-Gpixel CCD focal-plane array on each telescope Proposed Pan-STARRS telescope configuration Gigapixel focal-plane array (64 CCDs) First Pan-STARRS telescope on Haleakala (PS1)

  8. Orthogonal-Transfer Array 2.38 arc min • Wide field-of-view (FOV) imaging • Wavefront tilt decorrelates over FOV > few arc minutes • Need 2D array of OTCCDs, each independently clocked to track local wavefront tilt (“rubber focal plane”) • OTA is a new CCD architecture • Requires on-chip switching logic • More complex layout and processing than conventional CCDs

  9. Orthogonal Transfer Array Four-phase OTCCD pixels OTA: 88 array of OTCCD cells OTA cell with I/O control • New device paradigm • 2D array of independent OTCCDs • Independent clocking and readout of OTCCDs • Advantages • Enables spatially varying tip-tilt correction • Isolated defective cells tolerable (higher yield)

  10. OTA Operation • Subset (4 – 5) of cells chosen to image guide stars • Map of wavefront tilt constructed from guide-star data and applied to science cells • Four redundant views of every patch of sky used to fill gaps due to • Guide-star cells • Dead cells • Cosmic rays • Dead areas between cells and devices

  11. Device Fabrication • Four OTAs on 150-mm wafer (die size 49.550.1 mm) • Four-poly, n-buried-channel process • Fabricated on 5 000 Ω·cm float-zone silicon wafers • Back-illuminated devices thinned to 75 µm 150-mm wafer with four OTAs Photo of pixel array

  12. Sample Imagery • First devices were fully functional but with some issues (noise, logic “glow”) • Device redesign resolved issues with prototype devices • Redesigned devices have been fabricated and most of them packaged Image from back-illuminated OTA 10-µm pixel, 22.6 Mpixels Image from OTA cell with fixed light spot and CCD gates clocked

  13. Substrate Bias • Substrate bias enables thick, fully depleted devices: • High quantum efficiency, 800-1000 nm • Small charge point-spread function

  14. Quantum Efficiency • Back-surface p+ using ion-implant/laser anneal • Two-layer anti-reflection coating with reflection null at 850 nm for reduced fringing • Thicker device clearly superior beyond 800 nm

  15. OTA Focal Planes • TC3 focal plane assembled from 16 prototype devices; on-sky tests in February • GPC1 assembled from lots 2 and 3 (summer 2007)

  16. Outline • Review of Orthogonal-Transfer Charge-Coupled Devices (OTCCD) • Development of the orthogonal transfer array (OTA) • Low-noise CCD readout circuits • Summary

  17. CCD Output Circuits

  18. Output Circuit Comparison Sense-node capacitance is lower (higher responsivity) for JFET than MOSFET Noise spectral voltage is lower for JFET than MOSFET

  19. Noise Comparison 2000-fps, 160160-pixel imager, 20 ports with JFET output circuits Best MOSFET noise vs. preliminary JFET noise

  20. Summary • OTCCD developed for astronomical applications but has a potentially much broader range of uses • OTA development for Pan-STARRS is new OTCCD concept, also with other applications • Recent work with JFETs shows noise levels better than BCMOSFETs and nearing 1 e-

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