MUE Lecture 17: A very brief history of MOSFETs

Summary

This lecture provides a brief history of MOSFETs, tracing the evolution of amplification devices from the early 1900s. It begins with the invention of the vacuum tube amplifier in 1907, followed by the introduction of bipolar junction transistors (BJTs) in the 1950s. The discussion then moves to junction field-effect transistors (JFETs) and the eventual development of MOSFETs in the 1960s. The lecture explains how these devices, which control current flow via a third terminal, led to significant advancements in power efficiency and miniaturization in amplifiers and electronic devices, eventually replacing BJTs in most applications.

Takeaways

• 😀 The first vacuum tube amplifier was invented around 1907-1910 by Lee De Forest, marking the beginning of amplification technology.
• 😀 Vacuum tube amplifiers dominated the industry for several decades, especially in radio and long-distance telephone communications.
• 😀 The major drawbacks of vacuum tube amplifiers included their bulky size and high power consumption due to the heating process involved in thermionic emission.
• 😀 In the 1950s and 1960s, the introduction of Bipolar Junction Transistors (BJTs) offered a significant shift, reducing the size and power consumption of amplifiers.
• 😀 BJTs allowed for higher frequency operations compared to vacuum tube amplifiers and consumed much less power, making them a practical choice for many applications.
• 😀 The development of the Junction Field-Effect Transistor (JFET) and the Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) followed the BJT's success, based on similar principles of controlling current flow through a third terminal.
• 😀 The shift from vacuum tube amplifiers to BJTs was a clear improvement, but the transition to MOSFETs was more complex due to the superior analog performance of BJTs in certain applications.
• 😀 The MOSFET was invented in the late 1950s-1960s, introducing silicon dioxide between the metal gate and the semiconductor to address earlier issues with FETs.
• 😀 The fundamental principle of all amplifiers—whether vacuum tube, BJT, FET, or MOSFET—is that they are three-terminal devices controlling current flow between two terminals via a third terminal, with minimal current draw at the control terminal.
• 😀 The main goal of these devices is to achieve power gain, where a large amount of power is delivered to a load while the control terminal draws little or no current, enabling amplification.
• 😀 BJTs and MOSFETs both serve as amplifiers but are used in different contexts due to their respective advantages, with MOSFETs being more common in digital and analog RF integrated circuits today.

Q & A

What was the first discovery related to amplifiers, and when did it occur?

The first discovery related to amplifiers was the invention of the vacuum tube amplifier, which occurred around 1907 to 1910.

Why were vacuum tube amplifiers replaced by bipolar junction transistors in the 1950s?

Vacuum tube amplifiers were replaced by bipolar junction transistors because BJTs were more compact, consumed less power, and did not require the heating process that vacuum tube amplifiers did.

What is a key difference between vacuum tube amplifiers and bipolar junction transistors?

The main difference is that vacuum tube amplifiers require thermionic emission and large amounts of power to heat coils, whereas bipolar junction transistors are smaller, require less power, and do not need heating.

In what applications were vacuum tube amplifiers used?

Vacuum tube amplifiers were used in telephone communications, radio communications, radios, long-distance telephone communications, and first-generation computers during World War II.

What is the fundamental principle behind all amplifying devices, including vacuum tube amplifiers and MOS amplifiers?

The fundamental principle is that these amplifying devices are three-terminal devices where the current flow between two terminals is controlled by the application of voltage at a third terminal.

What was a significant drawback of vacuum tube amplifiers?

A significant drawback was their large size, high power consumption due to heating, and the need for vacuum environments, making them bulky and inefficient.

What major advantage did the bipolar junction transistor offer over vacuum tube amplifiers?

The bipolar junction transistor offered smaller size, significantly reduced power consumption, and no need for heating, making it more efficient and practical compared to vacuum tube amplifiers.

Why did engineers in the 1920s consider building a field-effect transistor (FET)?

Engineers in the 1920s considered building a field-effect transistor to control the flow of electrons between two terminals by applying a voltage at a third terminal, with the goal of creating an amplification device.

How did the invention of the MOSFET improve upon previous transistor designs?

The MOSFET improved upon previous designs by introducing a silicon dioxide layer between the semiconductor and the metal gate, resolving earlier issues and making the device more practical and efficient for amplification.

What is the significance of the term 'MOSFET'?

MOSFET stands for Metal-Oxide-Semiconductor Field-Effect Transistor. It refers to a field-effect transistor with a metal oxide semiconductor structure, which was developed in the late 1950s and 60s to replace bipolar junction transistors in most applications.