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Preface xiii

1 History, Operation, Performance, Design, Fabrication and Theory. 3

1.1 Scientific CCD History........................ 3

1.2 Operation and Performance......................22

1.2.1 Operation...........................22

1.2.2 Performance Functions...................25

1.2.3 Performance Specifications.................36

1.3 Architecture, Design, Photolitography and Fabrication....... 37

1.3.1 Architecture.........................37

1.3.2 Design and Photolithography................ 42

1.3.3 Processing and Fabrication................. 51

1.4 CCD Theory..............................61

1.4.1 MOS Capacitor........................61

1.4.2 Surface-Channel Potential Well............... 65

1.4.3 Buried-Channel Potential Well............... 70

References..................................92

FurtherReading............................93

2 CCD Transfer Curves and Optimization................95

2.1 CCD Transfer Curves.........................95

2.1.1 CCD Performance......................9

2.1.2 CCD Camera Performance................. 96

2.1.3 CCD Camera Calibration..................97

2.2 Photon Transfer............................97

2.2.1 Photon Transfer Derivation................. 98

2.2.2 Photon Transfer Curve....................101

2.2.3 Camera Gain Constants...................105

2.2.4 Camera Gain Histogram...................108

2.2.5 Camera Gain Uncertainty..................110

2.2.6 Dynamic Range.......................113

2.2.7 Linearity...........................117

2.2.8 Flat-Field Signal-to-Noise..................120

2.2.9 Contrast Signal-to-Noise..................121

2.2.10 High-Speed Photon Transfer Generation..........125

2.2.11 Photon Transfer Simulation.................130

2.3 X-Ray Transfer.............................131

2.3.1 X-ray Characteristics and Use................131

2.3.2 Fe55..............................132

2.3.3 X-ray Images.........................139

2.3.4 X-ray Transfer........................141

2.3.5 X-ray Histograms......................143

2.3.6 Fano-Noise-Limited Performance..............147

2.3.7 Cadmium XRays......................151

2.4 QE Transfer..............................151

2.5 CCD Clock and Bias Optimization..................156

2.5.1 Clock and Bias........................156

2.5.2 Set-point Transfer Curves..................160

References..................................165

3 Charge Generation.............................167

3.1 Charge Generation...........................167

3.2 QE Formulas..............................170

3.2.1 Backside Illumination....................170

3.2.2 Frontside Illumination....................173

3.2.3 Miscellaneous QE Losses..................174

3.2.4 Monte Carlo Simulation...................177

3.3 Frontside Illumination.........................178

3.3.1 Phosphor Coatings......................178

3.3.2 Virtual Phase.........................183

3.3.3 Open Pinned Phase......................188

3.3.4 Thin Gate...........................190

3.3.5 Transparent Gate.......................194

3.3.6 Poly Hole Gate........................194

3.4 Backside Illumination.........................195

3.4.1 Thinning...........................195

3.4.2 Quantum Efficiency Hysteresis...............196

3.4.3 Accumulation and QE Pinning...............199

3.4.4 Self-Accumulation......................201

3.4.5 Accumulation Theory....................214

3.4.6 Passive Accumulation....................227

3.4.7 Active accumulation.....................256

3.4.8 Antireflection coatings....................266

References..................................268

4 Charge Collection..............................273

4.1 Charge Collection...........................273

4.2 Well Capacity.............................274

4.2.1 Bloomed Full Well......................275

4.2.2 Surface Full Well.......................277

4.2.3 Optimum Full Well.....................277

4.2.4 Clocking Modes.......................280

4.2.5 Full Well Transfer......................280

4.2.6 Full Well Data........................283

4.2.7 Self-induced Emission and Thermionic Emission.....289

4.2.8 Clocked Antiblooming....................293

4.2.9 Antiblooming Structures...................300

4.2.10 High-Speed Erasure.....................305

4.2.11 Window Clocking......................310

4.2.12 Multipinned Phase(MPP)..................310

4.3 Fixed-pattern Noise..........................318

4.3.1 Pixel Nonuniformity.....................318

4.3.2 Flat Fielding.........................321

4.3.3 Fixed-pattern Sources....................325

4.4 Charge Diffusion............................332

4.4.1 Charge Diffusion.......................332

4.4.2 Measurement and Modeling Techniques..........338

4.4.3 Aliasing and Beating.....................373

References..................................383

5 Charge Transfer..............................387

5.1 Charge Transfer............................387

5.2 Transfer Mechanisms.........................390

5.2.1 Diffusion Drift........................393

5.2.2 Self-induced Drift......................395

5.2.3 Fringing Field Drift.....................396

5.2.4 High-Speed Data.......................400

5.2.5 Clock Propagation......................405

5.2.6 Substrate Bounce.......................408

5.3 CTE Measurement Techniques....................418

5.3.1 X-ray Transfer........................418

5.3.2 Extended Pixel Edge Response(EPER)..........423

5.3.3 First Pixel Edge Response..................429

5.3.4 Pocket Pumping.......................430

5.3.5 Charge Injection.......................433

5.4 Traps..................................433

5.4.1 Design Traps.........................434

5.4.2 Process traps.........................439

5.4.3 Bulk Traps..........................453

5.4.4 Radiation-induced Traps...................466

5.4.5 Proportional and Fixed Loss.................466

5.4.6 Fat-zero............................469

5.4.7 Notch Channel CCD.....................472

5.5 Transfer Power.............................476

5.5.1 Charge Motion Power....................478

5.5.2 Potential Power........................482

5.5.3 Reactive Power........................482

References..................................486

6 Charge Measurement...........................489

6.1 Charge Measurement.........................489

6.2 Output Amplifier Characteristics...................490

6.2.1 Operation...........................490

6.2.2 Voltage Gain.........................498

6.2.3 Loading............................499

6.2.4 Output Impedance......................503

6.2.5 Time Response........................504

6.2.6 Frequency Response.....................504

6.2.7 Bias..............................507

6.2.8 Sensitivity..........................509

6.2.9 Linearity...........................516

6.2.10 Temperature Characteristics.................519

6.2.11 Lightly Doped Drain.....................520

6.2.12 Amplifier Luminescence...................523

6.2.13 Multistage Amplifiers....................527

6.2.14 Power Consumption.....................531

6.3 Output Amplifier Noise........................532

6.3.1 Johnson Noise........................532

6.3.2 Reset Noise..........................537

6.3.3 White Noise.........................541

6.3.4 Flicker Noise.........................543

6.3.5 Shot Noise..........................553

6.3.6 Contact and Popcorn Noise.................555

6.3.7 Output Amplifier Noise Equation..............555

6.4 Correlated Double Sampling.....................556

6.4.1 Correlated Double Sampling Circuit Elements.......557

6.4.2 Correlated Double Sampling Circuits............558

6.4.3 Camera Gain Constant....................561

6.4.4 Correlated Double Sampling Transfer Function......563

6.5 Dual Slope Processor.........................578

6.5.1 Dual Slope Circuit Elements................578

6.5.2 Dual Slope Transfer Function................579

6.6 Remnant Signal and Noise......................582

6.6.1 Remnant Signal.......................582

6.6.2 Remnant Noise........................583

6.7 Skipper Amplifier...........................585

6.7.1 Introduction.........................585

6.7.2 Operation...........................586

6.7.3 Performance.........................588

6.7.4 Design............................592

6.7.5 Signal-to-Noise(Extended Images).............595

6.7.6 Signal-to-Noise(Point Images)...............599

References..................................602

7 Noise Sources................................605

7.1 On-chip Noise Sources........................605

7.1.1 Dark Current.........................605

7.1.2 Spurious Charge.......................649

7.1.3 Fat-zero............................654

7.1.4 Transfer Noise........................656

7.1.5 Residual Image........................657

7.1.6 Luminescence........................665

7.1.7 Cosmic Rays and Radiation Interference..........670

7.1.8 Excess Charge........................674

7.1.9 Cosmetic Defects.......................678

7.1.10 Blem Spillover........................679

7.1.11 Seam Noise..........................680

7.2 Off-chip Noise Sources........................684

7.2.1 Light Leak..........................684

7.2.2 Preamplifier Noise......................684

7.2.3 ADC Quantizing Noise...................686

7.2.4 Clock-Jitter Noise......................697

7.2.5 Electromagnetic Interference................699

7.2.6 Grounding..........................706

7.2.7 Image Cross Talk.......................711

7.2.8 Noise-Reduction Techniques................714

7.2.9 Noise-Reduction Summary.................716

References..................................719

8 Damage....................................721

8.1 Radiation Damage...........................721

8.1.1 Introduction.........................721

8.1.2 Near-Earth Radiation Environment.............723

8.1.3 Radiation Units........................726

8.1.4 Transient Events.......................736

8.1.5 Ionization Damage Equivalence...............749

8.1.6 Ionization Damage......................750

8.1.7 Clock and Bias for Minimum Ionization Damage

and Control............................759

8.1.8 IonizationDamage Measurements.............761

8.1.9 Bulk Damage.........................773

8.2 Electrical, Thermal and ESD Damage................837

8.2.1 Electrical Damage......................837

8.2.2 Thermal Damage.......................838

8.2.3 Electrostatic Discharge (ESD) Damage...........839

References..................................841

Appendixes 847

Glossary of CCD Terms 871

Index 889

PREFACE

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. The 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. _____________

In the course of the writing this book, many people have assisted me and offered their support. I would like to express my appreciation to the management of NASA's Jet Propulsion Laboratory for providing the rich environment for the research and investigation of CCDs from their conception; without their support this book could have not been written. I also thank Pixel Vision for the R&D environment directed toward high-speed backside-illuminated CCDs discussed in Chapter 5. I wish to express my gratitude to Tom Elliott for being my partner for nearly 15 years in generating the majority of the data products presented in this book. His artistic skills and ingenuity in conjunction with his natural curiosity about CCDs reflects upon the figures presented. Special thanks go to Jeff Pinter and Jim McCarthy, who through countless hours of CCD discussions on the black board brought excitement into the book. I have benefitted significantly from technical discussions with Stewart Collins, Taner Dosuoglu, Morley Blouke, Denis Heidtman, Dick Bredthauer, George Soli, Jim Westphal, Fred Landauer, Jim Gunn, Bob Locke, Mark Wadsworth, Michael Lesser, Bob Hlivak, Lloyd Robinson, Barry Burke, Willard Boyle, Jim Early, Albert Theuwissen, George Smith, Gene Weckler, Rudy Dyck, Ken Klaasen , Charles Chandler, Kurt Liewer, Dave Burrows, Gorden Garmire, Paul Vu, Dick Savoye, Rusty Winzenread, Andrew Holland, David Lumb, Fred Harris, Russ Schaefer, Taher Daud, Jerry Hynecke, Dave Norris, Robert Groulx, Raymond Frost, Arsham Dingzian, Gorden Hopkinson, Bev Oke, Terrence Lomheim, Gary Sims, Walter Kosonocky, Nelson Saks, Cheryl. Dale, Paul Marshall, Fred Pool, Loren Acton, Bob Lockart, Dave Swenson, John Geary, Jim Beletic, Alice Reinheimer, Larry Hovland, Sandra Faber, Bedabrata Pain, John Flemming, and Harry Marsh.

Special thanks goes to Shouleh Nikzad in writing the section of MBE delta doping and Steve Holland on his biased ohmic contact on high-resistivity substrate, both included in Chapter 3. I am also grateful to Gloria Putnam who encouraged and helped me finish the book. Also, her valuable contributions on theoretical aspects of CCD physics were enlightening and insightful. I am further indebted to Steve Holland, Peter Hughes, Gloria Putnam, Sharon Streams, and Rick Hermann for technical and copy editing of the entire manuscript. Finally, I wish especially to thank my wife Linda Janesick, daughter Amanda, sister Barb, and Mom and Dad for their assistance in many ways.