The High Tech Tribune

June 2025

Transistors are the fundamental building blocks of modern electronics, enabling the operation of everything from microprocessors to memory chips, to networking all the way to advanced AI systems. The IC transistor technology follows Moore’s Law (1965) guidelines pressing the IC transistor technology to advance, and it is leading to the exponential increase in computing power and the decrease in size and relative cost. Over As transistor sizes approach atomic scales in recent years, novel transistor architectures have evolved from conventional planar FET suited upto 28 nm nodes, to modern FinFET that is suited for upto 7nm nodes, and to the more recent and advanced Gate-All-Around FET (GAAFET) that is suited for all the way to sub 2nm nodes.

In this article, we intuitively explore the evolution of IC chip transistor technology. We ramp up starting from the PN junction as a fundamental block, and then we develop a preceptive understanding to the basic operation of the field effect transistor (FET), before exploring the progression of the FETs technology from planar FET, to FinFET, and finally to GAAFET. We will highlight the reasons for each transition, the differences in fabrication processes, and the current state-of-the-art fabrication manufacturers.

The PN Junction Is A Fundamental Block

The PN junction is a diode that is formed by joining p-type and n-type semiconductor materials. A depletion region is created at the area of interface that acts as a barrier that blocks the current in one direction (reversed biased) from the n-type to the p-type material, but it passes the current in the other direction (forward biased) from the p-type to the n-type material. When a forward voltage is applied, the barrier region is reduced, allowing the current to flow. when reverse biased, the barrier width increases preventing the current from flow in the opposite direction. Simply, the PN junction is uncontrolled switch allowing the current to flow in one direction. This rectifying behavior is essential in making FETs.

Two Back-to-Back Diodes

Now, let’s look at two back-to-back diodes by stacking three layers of npn material in consecutive order. This is assembled as three consecutive material are jointed together (i.e. npn or pnp). By joining two back-to-back pn junctions, there is not any current flowing the material, as each of pn junctions blocks the current in one of the two opposite directions. For example, if a voltage is applied from one end to the other, the current will now flow as one diode will be reversed biased. If the middle material can be controlled to flip its type, such as the p type is flipped into n type in the npn, then the current would flow from one end to the other.

Basic Concept of The Field Effect Transistor (FET)

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Now, let’s look at two back-to-back diodes by stacking three layers of npn material jointed in consecutive order. This is assembled as three consecutive material are jointed together (i.e. npn or pnp). By joining two back-to-back pn junctions, there is not any current flowing the material, as each of pn junctions blocks the current in one of the two opposite directions. For example, if a voltage is applied from one end to the other, the current will now flow as one diode will be reversed biased. If the middle material can be controlled to flip its type, such as the p type is flipped into n type in the npn, then the current would flow from one end to the other.

The Eletric Field Within the Back-to-Back Diodes

One end of the back-to-back diodes are called Source, and the other end is called Drain. Electric field is applied from the middle p-type material to the Source.

The electric field attracts free electrons from the Source (n-type) to the middle p-type material creating an n-channel from the drain to the source. Now, the current may flow from the Drain to the Source.

The middle p-type material is covered by a sheet of insulator (high K material) and a sheet of conductor (polysylicon). The conduction is called the gate termial. The insulator does not allow the current to flow from the gate the p-material . A capacitor is created from the gate to the source as an insulator is inserted between the two conducting material.

If the voltage from the Gate to the source above a threshold value, an electric field is created from the gate (p-type material) to the Source (n-type material). The electric field attracts the electronics from the heavily doped n-material to the gate. Thus, creating a channel from the Drain to the Source that allows the current to flow.

The Planar FETs

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