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The Invention and Early Development of the Transistor

Created on: 2025-02-07

The transistor is one of the most important inventions in modern technology, forming the backbone of nearly all electronic devices today. From its early conceptual roots to its practical implementation, the invention of the transistor involved numerous scientists, intense research, and several controversies. This article explores the invention and early development of the transistor, examining key contributors, technical breakthroughs, commercialization, and the transition from germanium to silicon.

What is a Transistor?

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It plays a crucial role in modern electronics, from radios to computers. Transistors have revolutionized the way we use and interact with electronic devices. Whether you're a hobbyist, student, or professional, understanding the evolution of the transistor is essential for appreciating the world of electronics. This article walks you through its history, from early concepts to its practical applications.

What is a Semiconductor?

A semiconductor is a material with electrical properties that fall between those of a conductor (like copper) and an insulator (like rubber). It can conduct electricity under certain conditions but not others. This unique property makes semiconductors essential to modern electronics, including transistors. The most commonly used semiconductor materials are silicon (Si) and germanium (Ge).

Semiconductors are typically crystalline solids, and their ability to conduct electricity can be controlled by introducing impurities through a process called doping. Doping adds tiny amounts of other elements, like phosphorus or boron, to the semiconductor material, creating either an excess of electrons (n-type) or a shortage of electrons (p-type). These modifications allow semiconductors to act as a switch or amplifier, which is the fundamental role of a transistor in electronic devices.

In essence, the semiconductor's ability to switch between being a conductor and an insulator is what makes it the backbone of modern electronics. Transistors rely on these properties to amplify signals or control the flow of current, allowing them to perform crucial tasks in devices like computers, radios, and smartphones.

Early Concepts and Precursors to the Transistor

Ferdinand Braun and the Solid-State Rectifier (1874)

In 1874, German physicist Ferdinand Braun discovered the rectifying properties of certain crystals, a phenomenon later applied in early radio detectors. This was one of the earliest observations of solid-state electronics.

Oleg Lossev and the First Known Amplification (1920s)

Russian scientist Oleg Lossev conducted experiments in the 1920s that demonstrated amplification using semiconductor materials. His research on negative resistance in zinc oxide and silicon carbide laid an important foundation for later developments.

Julius Lilienfeld and the Field-Effect Transistor Patent (1926)

In 1926, Austrian-Hungarian physicist Julius Edgar Lilienfeld patented the concept of a field-effect transistor (FET), a device that controlled current using an electric field rather than direct current flow. However, there is no evidence that Lilienfeld successfully built a working prototype. Some claims suggest he constructed a working radio based on his FET concept, but there is no verifiable documentation to support this.

Robert Pohl and Rudolf Hilsch's Germanium Experiments (1930s)

During the 1930s, Robert Pohl and Rudolf Hilsch experimented with the electrical properties of germanium, a material that would later become central to early transistor technology.

Bell Labs and the Push for Solid-State Research (1940s)

In the 1940s, Bell Labs formed a solid-state physics research group led by William Shockley. This group aimed to develop a replacement for bulky and inefficient vacuum tubes used in telecommunications and computing.

The First Working Transistor: Point-Contact Transistor (1947)

Invention at Bell Labs

On December 16, 1947, John Bardeen and Walter Brattain, working under William Shockley at Bell Labs, successfully demonstrated the first working transistor. This was a point-contact transistor, which functioned similarly to a vacuum tube but in a much smaller form factor.

What is a Point-Contact Transistor?

A point-contact transistor consists of two closely spaced metal contacts (emitter and collector) placed onto a small germanium crystal. These contacts introduce minority carriers into the material, allowing the transistor to amplify electrical signals. The key difference between a point-contact transistor and a later bipolar junction transistor (BJT) is that the former relied on fragile mechanical contacts, making it unstable for mass production.

Specifications of the First Transistor

  • Material: Germanium
  • Power Rating: Approximately 1 milliwatt
  • Frequency Response: Up to a few kilohertz (limited compared to vacuum tubes)
  • Primary Use: Demonstration of amplification capabilities

The Bipolar Junction Transistor (BJT) and Commercialization

William Shockley and the Junction Transistor (1950)

Although Bardeen and Brattain built the first working transistor, William Shockley was dissatisfied with their approach. In 1950, he invented the bipolar junction transistor (BJT), which had a much more reliable and manufacturable design.

How BJTs Differ from Point-Contact Transistors

  • BJT: Uses a sandwich-like structure of semiconductor layers (NPN or PNP) to control current flow.
  • Point-Contact Transistor: Uses physical metal contacts to control current, making it less stable.

Early Commercial Applications

The transition from experimental to commercial use took a few years. By 1952, Bell Labs licensed the transistor for $25,000, leading to broader adoption.

First Commercial Use (1954)

The first practical application of transistors appeared in hearing aids in the early 1950s. Texas Instruments and Regency produced the first commercial transistor radio, the Regency TR-1, in 1954.

The Regency TR-1 Radio Features

The Regency TR-1 was the first commercially available portable transistor radio, a groundbreaking device that introduced the world to the convenience of personal, battery-operated radios.

Despite its small size, the Regency TR-1 was capable of receiving AM radio broadcasts, which was standard for radios of that time. The TR-1 was primarily designed as an AM receiver, offering users access to the popular AM broadcast bands. It had the following key features:

  • AM Radio Reception: The TR-1 was designed for AM radio, offering a range of frequencies typically between 540 kHz and 1600 kHz.
  • Four Germanium Transistors: The radio used four germanium transistors, which helped reduce the size and power consumption while improving audio quality.
  • Compact Design: The Regency TR-1 was small and lightweight, making it portable and easy to carry around, a major step forward in personal radio devices.
  • Battery Operated: It ran on a 22.5V battery, allowing users to take the radio anywhere without needing a power outlet.
  • Volume and Tuning Controls: The TR-1 featured basic controls for adjusting the volume and tuning into different AM stations.
  • Plastic Housing: The TR-1 had a plastic casing, which contributed to its lightweight design and durability, with a distinctive mid-century aesthetic.

The Regency TR-1 was a pioneering product in portable consumer electronics, with only about 150,000 units produced. Despite its innovation, the TR-1 faced competition from other emerging portable radios, most notably the Zenith Royal 500, which was released shortly after. The Royal 500 offered similar features but with improved reception and a more refined design, contributing to its own success in the market.

The Regency TR-1 played a pivotal role in sparking the development of portable radios, laying the groundwork for the widespread adoption of portable music and news in the years to come. While only 150,000 units were produced, it was a major innovation that influenced later, more widely adopted portable radios. While it was eventually overshadowed by competitors, its contribution to the electronics industry and the world of portable radios remains significant.

Transition to Silicon (Late 1950s)

Early transistors were made from germanium due to its high carrier mobility. However, germanium had drawbacks:

  • Thermal instability: Germanium transistors failed at temperatures above 85°C.
  • Higher leakage currents: Making them less efficient for complex circuits.

Silicon, pioneered by Gordon Teal at Texas Instruments, overcame these issues. By the late 1950s, silicon BJTs dominated the market.

What is a Valve or Vacuum Tube?

Before the invention of the transistor, vacuum tubes (also known as valves) were used to amplify electrical signals. These glass tubes contained a vacuum and controlled the flow of electricity via an electrode called the cathode, which emitted electrons when heated, and a plate that attracted the electrons.

Vacuum tubes were integral to many electronic devices, including:

  • Radios
  • Television sets
  • Early computers
  • Audio amplifiers

However, vacuum tubes were large, fragile, power-hungry, and prone to failure, which made them inefficient for portable devices. They were eventually replaced by transistors in most applications.

Early Radio Technologies

Now that we know that one of the early uses of transistors was in transistor radios, let's look at some early radio technology that was replaced by transistor circuits in radios.

Crystal radios, also known as crystal sets, using a cat's whisker and crystal, as well as vacuum tube radios were being used before transistors were available.

What is a Cat's Whisker?

A cat's whisker refers to a thin wire used as a contact in crystal radios—a type of radio receiver. The whisker was placed against a mineral crystal (often galena) to create a point contact, which rectified the radio signal. The name “cat's whisker” came from the similarity in shape to a cat's sensitive whiskers, which are used for tactile sensing. These radios were called crystal sets because they used these crystals to detect radio signals, and they were the simplest form of radio receivers.

Who Used Crystal Sets?

Crystal sets were widely used in the early 20th century, especially before the mass adoption of vacuum tube radios. They were popular among hobbyists and people with limited access to commercial radios. They required no external power source, other than the radio waves they received, making them ideal for use in areas where power was scarce. Crystal sets were often homemade and represented a significant step in the evolution of personal electronics.

How Could Someone Listen to a Crystal Set's Audio?

Crystal sets did not drive speakers. Instead, they used a headphone or ear piece to listen to the audio. The reason was that crystal sets produced very weak audio signals due to the lack of amplification. To hear the sound, the user needed a high-impedance headphone with an earphone or a high-impedance earpiece that could pick up and convert the small audio signals into sound. Crystal sets, therefore, were mostly suited for personal listening with headphones, rather than larger audio systems.

How Did Crystal Sets Compare to Valve Radios?

Compared to valve radios (which used vacuum tubes to amplify the radio signal), crystal sets were much simpler and did not require any power other than the incoming radio waves. However, they also had limitations:

  • Audio quality: Crystal sets produced weaker sound and required headphones for listening.
  • Range: They could only receive strong local stations due to the lack of amplification.

In contrast, valve radios provided amplified audio, a greater range, and were suitable for home use with speakers. Crystal sets, while a fascinating part of early radio history, were eventually replaced by more powerful vacuum tube radios in the late 1920s and 1930s.

Evolution of Radio Receivers and the Transistor's Impact

Early Radio Technologies

  • Vacuum Tube Radios: Large, power-hungry, and required frequent maintenance.
  • Crystal Sets (Cat's Whisker Detectors): Passive, unpowered radios that required careful tuning and produced weak audio.
  • Transistor Radios: Small, portable, and battery-powered, revolutionizing consumer electronics.

AM vs. FM Radio

  • AM (Amplitude Modulation): The dominant radio technology before the 1960s.
  • FM (Frequency Modulation): Introduced better sound quality but required more complex circuitry, which became feasible with transistor advancements.

Transistors in Hobby Electronics

Transistors first became widely available to hobbyists in the late 1950s and early 1960s. Early hobbyist transistors included:

  • CK722 (1953): A germanium PNP transistor, used in small-signal amplification, radios, and audio circuits.
  • OC71 (1954): A popular germanium audio transistor.
  • 2N107 (1955): A germanium PNP transistor, used in simple amplifiers.
  • 2N2222 (1962): One of the most widely used silicon NPN transistors, capable of handling 800mA and 500mW.
Transistor Type Max Voltage Max Current Power Rating Application
CK722 (1953) PNP Germanium 40V 100mA 500mW Small-signal amplification, radios, audio circuits
OC71 (1954) PNP Germanium 45V 30mA 500mW Audio amplification
2N107 (1955) PNP Germanium 50V 20mA 500mW Simple amplifiers
2N2222 (1962) NPN Silicon 40V 800mA 500mW General-purpose amplifiers, switching circuits

One of the most iconic transistors of the early hobbyist era was the CK722, introduced by Raytheon in 1953. Priced at $7.60 each, it was a small-signal PNP germanium transistor used in various audio and radio applications. The CK722 played an important role in hobbyist electronics projects during the 1950s and 1960s, with hundreds of DIY electronics projects being published in popular books and magazines during that time.

Types of Transistors

There are several types of transistors, each with unique characteristics and applications. Over the decades, different transistor technologies have evolved, enabling advancements in electronics, computing, and communication.

  • BJT (Bipolar Junction Transistor) – Invented in 1947: A current-controlled device that uses a sandwich-like structure of semiconductor materials (either NPN or PNP) to control current flow. BJTs are commonly used for amplification in audio circuits, radio frequency applications, and switching operations.
    • NPN Transistor: In an NPN transistor, current flows from the collector to the emitter when a small current is applied to the base. These are more commonly used than PNP transistors due to better electron mobility.
    • PNP Transistor: In a PNP transistor, current flows from the emitter to the collector when a small current is applied to the base. These are often used in complementary circuits with NPN transistors.
  • JFET (Junction Field-Effect Transistor) – Invented in 1945, commercialized in the 1960s: A voltage-controlled transistor that offers high input impedance and low noise, making it ideal for analog signal applications and sensitive measuring instruments.
    • N-Channel JFET: In an N-channel JFET, electrons are the majority charge carriers, offering faster operation and lower resistance.
    • P-Channel JFET: In a P-channel JFET, holes are the majority charge carriers, but these devices typically have higher resistance and slower operation compared to N-channel JFETs.
  • MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) – Invented in 1959: A voltage-controlled transistor widely used in modern computing, power electronics, and digital circuits due to its low power consumption, high efficiency, and fast switching speed.
    • N-Channel MOSFET (First introduced in 1960): The first MOSFETs were N-channel devices, which are faster and more efficient due to higher electron mobility.
    • P-Channel MOSFET: These MOSFETs operate with hole carriers, typically having higher resistance and slower speeds than N-channel MOSFETs. They are used in complementary MOS (CMOS) circuits along with N-channel MOSFETs.

MOSFET and the Rise of Silicon Computing

While BJTs enabled early electronics, the invention of the metal-oxide-semiconductor field-effect transistor (MOSFET) by Mohamed Atalla and Dawon Kahng in 1959 revolutionized computing.

The following table gives a basic comparison between BJT vs. MOSFET transistors as used in computing.

Feature BJT MOSFET
Power Consumption High Low
Switching Speed Slower Faster
Integration Density Lower Higher
Stability Good Excellent

MOSFETs became the backbone of modern microprocessors, enabling high-speed and low-power computing.

Future Trends and Final Notes

Did Germanium Disappear?

Although silicon dominates, germanium is still used in specialized applications such as:

  • High-frequency RF transistors
  • Infrared detectors
  • High-speed optical communication

Modern Applications of Transistors

Transistors are the building blocks of modern electronics, playing an essential role in devices like computers, mobile phones, and other digital devices. One of the most significant advancements in transistor technology has been the development of MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), which are crucial for creating highly efficient processors used in virtually all modern computing devices. In addition, BJTs (Bipolar Junction Transistors) continue to be used in power supplies and other high-power applications due to their ability to handle large currents and provide high gain.

Transistor technology continues to evolve with new materials like graphene and quantum dots, which could make transistors even smaller and more efficient in the coming decades. These advancements could lead to further miniaturization of electronic devices while improving their performance and energy efficiency.

Conclusion

The invention of the transistor transformed technology forever. From its roots in the 1920s to its full realization in 1947, transistors have enabled the digital revolution. As research continues, transistors will remain the foundation of electronics for the foreseeable future. Whether you’re a hobbyist, student, or professional, understanding the transistor’s history and impact is essential for advancing in the world of electronics.