Orthogonal transfer charge coupled devices and low noise charge coupled devices readout circuits
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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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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

*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.


Outline

Outline

  • Review of Orthogonal-Transfer Charge-Coupled Devices (OTCCD)

  • Development of the orthogonal transfer array (OTA)

  • Low-noise CCD readout circuits

  • Summary


Conventional vs orthogonal transfer ccds

Conventional vs. Orthogonal-Transfer CCDs


Application areas

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


Orthogonal transfer charge coupled devices and low noise charge coupled devices readout circuits

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


Outline1

Outline

  • Review of Orthogonal-Transfer Charge-Coupled Devices (OTCCD)

  • Development of the orthogonal transfer array (OTA)

  • Low-noise CCD readout circuits

  • Summary


Pan starrs panoramic survey telescope and rapid response system

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)


Orthogonal transfer array

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


Orthogonal transfer array1

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)


Ota operation

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


Device fabrication

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


Sample imagery

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


Substrate bias

Substrate Bias

  • Substrate bias enables thick, fully depleted devices:

    • High quantum efficiency, 800-1000 nm

    • Small charge point-spread function


Quantum efficiency

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


Ota focal planes

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)


Outline2

Outline

  • Review of Orthogonal-Transfer Charge-Coupled Devices (OTCCD)

  • Development of the orthogonal transfer array (OTA)

  • Low-noise CCD readout circuits

  • Summary


Ccd output circuits

CCD Output Circuits


Output circuit comparison

Output Circuit Comparison

Sense-node capacitance is lower (higher responsivity) for JFET than MOSFET

Noise spectral voltage is lower for JFET than MOSFET


Noise comparison

Noise Comparison

2000-fps, 160160-pixel imager, 20 ports with JFET output circuits

Best MOSFET noise vs. preliminary JFET noise


Summary

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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