Semiconductor Revolution (1950–1975)Digital Imaging & Optoelectronics

Boyle & Smith's Charge-Coupled Device (CCD Sensor)

US 3,923,554

The Solid-State Imaging Sensor that Eliminated Chemical Photographic Film and Enabled Digital Cameras

Inventor(s)Willard S. Boyle, George E. Smith

Grant Date1975-12-02

Filing Date1974-06-28

LocationMurray Hill, New Jersey

The Digital Eye of Humanity: Willard Boyle and George Smith's Charge-Coupled Device (CCD) at Bell Labs, which stores photo-generated charge packets in silicon potential wells and shifts them across the chip with three-phase clocking, replacing chemical photographic film with digital pixels.

USPTO PDF

Engineering Analysis & Physical Principles

How It Works: Step-by-Step Mechanical & Physical Breakdown

For over a century, photography required messy chemical silver-halide film that could not be transmitted electronically or viewed immediately. Boyle and Smith conceived a solid-state electronic analog of photographic film: light hitting silicon creates tiny packets of electrical charge, which are trapped in microscopic potential 'buckets' and shifted across the surface of the chip like a bucket brigade to create digital images.

The Core Breakthrough Mechanism

Photons generate electrons in silicon ( $n_e = \eta \Phi$ ). These electrons collect in potential wells under MOS gate electrodes. Applying a 3-phase clock voltage sequence ( $\phi_1, \phi_2, \phi_3$ ) lowers potential under adjacent electrodes, shifting each pixel charge packet step-by-step to a floating diffusion amplifier node at the edge of the chip ( $V_{out} = Q / C_{sense}$ ).

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Detailed Component Architecture

1MOS Potential Well Storage Array

An array of metal-oxide-semiconductor electrodes over p-type silicon.

Positive gate voltages create surface depletion potential wells ( $V_s \propto V_G$ ) that collect and store photo-generated electrons with minimal dark-current leakage.

19th-C. Term: Depletion potential well arrayModern: CCD pixel photo-gate array

23-Phase Charge Transfer Shift Register

Overlapping gate electrodes clocked in 3-phase sequence.

Dynamically translates charge packets along silicon channels with Charge Transfer Efficiency exceeding 99.999% ( $\text{CTE} > 0.99999$ ).

19th-C. Term: Sequential multi-phase clockingModern: Charge-transfer shift register

3Floating Diffusion Readout Node

On-chip diode and source follower converting charge to voltage.

Translates minute femtocoulomb charge packets into low-noise video signals ( $S = Q / C$ ).

19th-C. Term: Output sensing diodeModern: Sense amplifier charge-to-voltage readout

Governing Physical Equations & Principles

Internal Photoelectric Effect & Charge Integration

Q_{pixel} = q \cdot \eta_{QE} \int_0^{T_{int}} I(x, y, t) \, dt

Incident photons generate electron-hole pairs in silicon, accumulating a linear charge packet proportional to light intensity and exposure time.

Charge Transfer Efficiency (CTE)

Q_{out} = Q_{in} \cdot (\text{CTE})^N, \quad \text{CTE} = 1 - \epsilon

Extremely high charge transfer efficiency preserves crisp image contrast after thousands of sequential transfers across the pixel array.

Why It Still Matters

The CCD sensor eliminated film, launched the digital photography and video revolution, made the Hubble Space Telescope possible, and paved the way for CMOS sensors in billions of smartphones today.

Legal Claims Decoder (1 Numbered Claims)

Compare dense legalistic claims directly with decoded plain-English functional specifications.

Claim #1Independent Master Claim

Verbatim Historical Legal Text

“A charge coupled device comprising a semiconductor substrate, an insulating layer overlying a surface of said substrate, an array of closely spaced electrodes overlying said insulating layer and forming a plurality of three-electrode charge transfer stages, and means for applying three-phase clock voltages to said electrodes to cause sequential transfer of charge packets through said substrate.”

Plain English Engineering Translation

The master claim covering a 3-phase charge coupled device with a semiconductor substrate, dielectric layer, electrode array, and 3-phase clocking means to transfer charge packets across the chip.

Key Protected Innovations:

Charge packet bucket-brigade transfer3-phase overlapping gate clockingMonolithic solid-state digital imaging sensor

Historical Legal Impact:

Foundational patent that founded digital photography and earned Boyle and Smith the 2009 Nobel Prize in Physics.

The Historical Bottleneck

A 1969 camera was either silver halide (hours in a darkroom) or a vidicon (a hot glass bottle that burned in highlights). Photodiode arrays needed an amplifier per pixel, which did not scale.

Why Prior Art Failed

•Film: beautiful, slow, wet.
•Vidicons and plumbicons: bulky, laggy, burn-in.
•XY-addressed photodiodes: a transistor budget that exploded with resolution.

The Breakthrough Insight

“17 October 1969, one hour at a Bell Labs blackboard: store photocharge in MOS potential wells and march it to a single output amplifier by clocking the gates, a bucket brigade. No per-pixel amp.”

Patent Wars & Legal Litigations

Vs. Fairchild, TI, and the later CMOS crowdInfringement Challenge

Rival Claim & Defense:

Fairchild and TI shipped frame-transfer and interline CCDs and argued architecture, not the transfer idea.

Litigation Conflict:

Bell kept the charge-coupling claim. The commercial cameras came from Japan and from Fairchild's space line. CMOS active-pixel sensors (Fossum and others, 1990s) later took the phone market by putting the amplifier back at the pixel, cheaply.

Final Resolution & Judicial Outcome:

Boyle and Smith received the 2009 Nobel Prize in Physics. Hubble's WFPC and a generation of camcorders were CCD.

After the Grant

Bell Labs did not become a camera company. Kodak, Sony, and later every phone vendor did. Boyle retired to Nova Scotia; Smith stayed in device physics.

Civilizational Impact

Astronomy went digital first (you cannot develop a plate on Mauna Kea as fast as you can read a chip). Then camcorders, then, after CMOS, everyone's pocket.

Historical Fact

The chalkboard session is well attested. They were supposed to be thinking about magnetic bubble memory. They walked out with an imager.

Further Context

A CCD is a shift register that happens to be light-sensitive. That is why early video cameras had 'smear': the charge had to walk through other pixels.
Hubble's original WFPC used Texas Instruments CCDs. The 1993 repair mission swapped in WFPC2, still CCD.