Semiconductor Revolution (1950–1975)Solid-State Physics & Semiconductors

Bardeen & Brattain's Point-Contact Transistor

US 2,569,347

The Solid-State Semiconductor Amplifier that Replaced Vacuum Tubes and Founded Modern Microelectronics

Inventor(s)John Bardeen, Walter H. Brattain

Grant Date1951-10-03

Filing Date1948-06-17

LocationMurray Hill, New Jersey

Bardeen and Brattain's December 1947 germanium amplifier: two gold points, a few tens of microns apart, minority-hole injection, power gain without a filament. Shockley's junction transistor is the sibling that actually shipped in volume.

USPTO PDF

Engineering Analysis & Physical Principles

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

Before December 1947, all signal amplification required bulky, fragile glass vacuum tubes with glowing red-hot filaments that consumed lots of electricity and burned out frequently. Bardeen and Brattain discovered that two tiny gold contacts touching a crystal of germanium just 50 microns apart could amplify an electrical signal inside a solid crystal at room temperature with zero warmup time.

The Core Breakthrough Mechanism

An n-type germanium crystal has an ohmic base electrode. Two gold-leaf point contacts (emitter and collector) sit on the top surface. Forward-biasing the emitter injects minority 'holes' into the crystal. These holes drift into the reverse-biased collector space-charge depletion zone, modulating the collector current with massive power gain ( $A_p = A_v \cdot A_i$ ).

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Detailed Component Architecture

1Germanium Semiconductor Crystal Base

A crystal block of high-purity n-type germanium with ohmic base contact.

Supplies conduction electrons and supports a surface inversion layer for hole diffusion and drift.

19th-C. Term: Block of semiconductive materialModern: Semiconductor substrate / base region

2Emitter Point-Contact Electrode

A sharp gold foil contact biased in the low-resistance forward direction.

Injects minority carrier holes ( $p$ ) directly into the semiconductor crystal lattice ( $I_E = I_p + I_n$ ).

19th-C. Term: First point electrode / EmitterModern: Transistor emitter terminal

3Collector Point-Contact Electrode

A second sharp contact spaced 50 microns away, biased in reverse direction.

Collects injected holes with high current collection efficiency $\alpha = \Delta I_C / \Delta I_E \approx 1.0$ , producing large output voltage swings across high load resistance.

19th-C. Term: Second point electrode / CollectorModern: Transistor collector terminal

Governing Physical Equations & Principles

Minority Carrier Injection & Transistor Action

\alpha = \left(\frac{\partial I_C}{\partial I_E}\right)_{V_C} \approx 0.98, \quad G_{power} = \alpha^2 \cdot \frac{R_{load}}{R_{in}}

Holes injected by the forward-biased emitter modulate the conductivity of the reverse-biased collector junction, generating substantial power gain.

Ambipolar Carrier Drift & Diffusion

J_p = -q D_p \nabla p + q \mu_p p \vec{E}

Hole current flows through the base region via a combination of concentration gradient diffusion and electric field drift.

Why It Still Matters

The 1947 whisker is in museums. The junction and MOSFET that followed are in everything with a battery. The physics lesson is minority-carrier injection and a surface you can actually control.

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 circuit element which comprises a block of semiconductive material, a base electrode making low-resistance contact with said block, and two point electrodes making rectifier contact with a surface of said block, said point electrodes being spaced apart by a distance of the order of a few mils.”

Plain English Engineering Translation

The master claim defining a three-terminal solid-state circuit element with a semiconductor block, base electrode, and two point-contact electrodes spaced a few thousandths of an inch apart.

Key Protected Innovations:

Three-terminal solid-state amplifierMinority carrier hole injectionPoint-contact emitter/collector spacing

Historical Legal Impact:

Foundational patent that demonstrated the physical transistor effect, leading to the 1956 Nobel Prize in Physics.

The Historical Bottleneck

ENIAC's 18,000 tubes failed by the hour. A long-distance telephone repeater was a rack of hot glass. Shockley's first field-effect attempts at Bell Labs did nothing; surface states trapped the charge. The Labs needed a solid amplifier that did not burn a filament.

Why Prior Art Failed

•de Forest Audions and later pentodes: gain, heat, and a vacuum pump in the supply chain.
•Braun cat's-whisker diodes rectify; they do not amplify.
•Lilienfeld's 1920s FET patents were paper. Nobody could make the surface clean enough.

The Breakthrough Insight

“16 December 1947: two gold contacts, a sliver of n-germanium, a forward-biased emitter injecting holes, a reverse-biased collector a few tens of microns away. Minority-carrier injection, not the FET Shockley had wanted. Brattain and Bardeen had a working point-contact amplifier. Shockley went home furious and invented the junction transistor on paper.”

Patent Wars & Legal Litigations

Vs. William Shockley (inside the same lab)Infringement Challenge

Rival Claim & Defense:

Shockley wanted his name first and a device that was his theory. The attorneys gave the point-contact patent to Bardeen and Brattain (US 2,524,035). Shockley took the junction sandwich (US 2,569,347).

Litigation Conflict:

The personal break never healed. Shockley left to found Shockley Semiconductor; the traitorous eight left him. Bardeen left for Illinois and a second Nobel in superconductivity.

Final Resolution & Judicial Outcome:

The 1956 Nobel went to all three. Bell licensed the transistor package for $25,000 to anyone who would come to the 1952 symposium, which is why the industry is not a single-company museum.

After the Grant

Point-contact transistors were noisy and mechanically fragile. They sold for a few years. The junction and then the silicon planar FET ate them. The 1947 lunch-table demo is still the origin story because it was the first solid gain that worked.

Civilizational Impact

Repeaters shrank. Computers stopped being air-conditioned tube barns. Everything after Noyce assumes this solid-state gain stage.

Historical Fact

They called it a surface-states amplifier until John R. Pierce suggested 'transistor' (transfer + varistor). The lab notebook drawing is a triangle of germanium and two pieces of gold foil on a paper clip.

Further Context

Walter Brattain did the surface physics with his hands. John Bardeen did the theory of the inversion layer and then of the injection. Shockley managed, then competed.
The 1952 Bell transistor symposium's $25,000 ticket is one reason Tokyo and Palo Alto both had a legal starting point.