Scientific Charge Coupled Devices

James Janesick

SPIE PRESS Vol. PM83 * Published January 2001
920 pages * Hardcover
List price $88; SPIE Members $70 

Published by SPIE--The International Society for Optical Engineering

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The invention of the charge-coupled device over 30 years ago marked the
beginning of a remarkable image capture technology that has changed the
course of imaging in disciplines ranging from astronomy to biotechnology.
This book presents a comprehensive history, tutorial, and state-of-the-art
description of the CCD. James R. Janesick, an early proponent of the
scientific CCD at Jet Propulsion Laboratory, provides invaluable reference
information for scientists, engineers, and hardware managers involved with
imaging CCDs and high-performance camera systems, and others who may need a
detailed introduction to the subject.

This book began from a series of lecture notes for courses held on
charge-coupled devices and digital camera systems at UCLA Extension and SPIE
meetings in the mid-1980s. These sessions were well attended and met with
great enthusiasm by the scientific and commercial imaging communities. The
courses, and the enthusiasm, continue today after 15 years. 

The courses are intended for scientists, engineers, and hardware managers
involved with CCD imaging sensors and camera systems. The material details
advances made in pixel count (arrays as large as 10,000 by 10,000 pixels),
quantum efficiency (spectral coverage of 1 to 11,000  ), charge transfer
efficiency (99.9999% efficient per pixel transfer), read noise (less than 1
e  rms), large dynamic range (greater than 106), and high-speed operation
(diffusion-limited). The CCD technologies used to achieve such high levels
of performance are discussed. The courses also review the electronic design
of slow-scan and fast-scan CCD imaging camera systems. Applications include
near-IR, visible, UV, EUV, x-ray, and particle cameras. The success of these
courses prompted us to bring these notes together, along with additional
detailed discussions, into a single comprehensive reference manual and
tutorial. It is a timely collection, as the CCD has recently celebrated its
thirtieth birthday.

This book is written for a wide audience from the novice to the advanced CCD
user. The level of the book's presentation is suitable for students in
physics and engineering who have received a standard preparation in modern
solid state physics and electronic circuits. Numerous examples throughout
the text provide valuable exercises for students and perspective for the
professional imaging engineer in terms of modern CCD performance. The text
captures 30 years of experimentation with the technology, giving the
less-experienced engineer the benefit of the lessons learned during the
development of the CCD. Although the book focuses on scientific devices, it
is also of interest to other imaging engineers who work with commercial CCDs
for broadcasting and photography. Other areas of overlap include CMOS, CID,
and photodiode imaging arrays. The book can be used as a reference for
participants in educational short courses organized by SPIE and
other educational institutions as well.

Scientific Charge-Coupled Devices contains more than 500 figures and
illustrations which present experimental and modeling data products taken
from many scientific CCDs in operation. The majority of these sensors are
found in space imaging cameras that are currently generating new and
exciting facts about the universe in which we live. The book provides
hundreds of modeling equations used to support the data presented. It has
been
very important that theory and experiment work hand-in-hand to bring about a
sensor that is nearly textbook perfect. This intimate connection also shows
us the physical limitations of device performance and what potential
advances might be made in the future. Also, the CCD has inspired its own
language to describe its unique characteristics and operational features.
Therefore, we have included a glossary of CCD terms to which the reader can
refer. 

The book is organized into eight chapters. 

Chapter 1 reviews historical aspects of the scientific CCD as taken from the
author's perspective and experiences. As with most celebrated technologies,
the CCD of today was not born overnight; the technical and political
climates that gave rise to the CCD imaging revolution was complex and
interesting. Chapter 1 also includes a review of the basics of CCD operation
and performance which serve as the book's skeleton charge generation, charge
collection, charge transfer and charge measurement as well as performance
characteristics and related specifications. The chapter will also acquaint
the reader with different CCD architectures and how the sensors are designed
and fabricated. Presented is basic solid state CCD theory, which is
necessary to understand and support the experimental findings presented in
subsequent chapters. In particular the potential well, which is responsible
for collecting and transferring charge, is studied in detail.

Chapter 2 introduces standard tests and absolute units used to characterize,
optimize, and calibrate CCD performance, presented in the form of transfer
curves. For example, an important transfer curve called photon transfer
produces a multitude of critical performance data products: read noise, full
well, dynamic range, linearity, signal-to-noise, etc. The chapter will also
take the reader through a CCD clock and bias optimization procedure using
transfer curves as a guide. The material in this section is considered
advanced but it is critically important in order to achieve the high and
reliable performance results that CCD camera users demand. 

Chapter 3 discusses the first major operation performed by the CCD: charge
generation. It is shown that the charge generation process is capable of
covering an enormous wavelength range, from the IR to the hard x ray,
covering more than four decades of spectral range (i.e., 1 to 11,000). We
will review several loss mechanisms that prevent incoming photons from
interacting with the CCD. Discussions are then given to high- performance
frontside-illumination CCDs whose design features reduce interaction loss.
We then discuss the highest-sensitivity device available to the imaging
community, the backside-illuminated CCD. Detailed studies are given on the
backside accumulation process required by this technology. 

Chapter 4 on charge collection explores the ability of the CCD to form an
image after charge is generated. Three performance parameters associated
with charge collection efficiency are elaborated: well capacity, pixel
nonuniformity, and charge diffusion. The modulation transfer function (MTF)
is discussed in considerable detail in quantifying charge diffusion effects
and limiting performance. 

Chapter 5 deals with charge transfer, the third basic CCD operation.
Discussions include a review of the charge transfer efficiency (CTE)
requirements for high-performance large-area arrays and physical
descriptions responsible for high-speed charge movement. This chapter
discusses several CTE measurement techniques in characterizing charge traps
that limit CTE performance. Numerous operational, process and design
solutions are given to solve CTE problems when encountered. We close the
chapter with a short discussion on the power dissipated behind the charge
transfer process.

Chapter 6 discusses charge measurement, the last major CCD operation.
Discussions here are devoted to the sensor's output amplifier and off-chip
signal processing electronics. We will describe the progress that has been
achieved in the areas of design, processing and operation to achieve
ultralow-noise performance. The chapter discusses other amplifier
characteristics such as loading, output impedance, frequency response,
sensitivity,
linearity, and power consumption. The technique of correlated double
sampling (CDS) is reviewed in detail, an important video processing circuit
that delivers optimum S/N performance. The last section reviews a floating
gate amplifier that allows subelectron noise performance.

Chapter 7 focuses on noise sources other than the CCD's output amplifier.
The sources are grouped into two major categories: on-chip and off-chip.
This chapter familiarizes the reader with the multitude of known noise
sources, which can be reduced below that of the noise generated by the
output amplifier. Important noise sources include dark current, spurious
charge, fat-zero, residual image, luminescence, cosmic rays, cosmetic
defects,
quantizing noise, clock jitter, electromagnetic interference, grounding
noise and other sources.

Chapter 8 is on the subject of CCD damage. The majority of the chapter is
devoted to the damage induced by high-energy radiation sources that take
place within the gate dielectric and bulk silicon. Numerous design,
processing, and operational solutions are given to address and alleviate the
problem. Discussions on transient events produced by high-energy particles
and photons are also provided. A technique that converts a complicated
radiation environment into a single energy that produces the same damage is
described. The last subject of this chapter is on electrical, thermal and
ESD damage mechanisms.
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