A semiconductor device is a component that controls the flow of electrons in order to process and store information.

Such devices are present in virtually every electronic product, including smartphones, computers, automobiles, and medical equipment.

In electrical circuits, semiconductor devices are known as active devices, in contrast to passive components such as resistors, capacitors, and coils.

Semiconductor devices serve three main roles:

1.Switching (ON/OFF control): Stopping or allowing the flow of electrons, converting information into the digital states of “0” and “1.”

2.Amplification: Boosting a weak signal, used for applications such as audio, radio waves, and sensor outputs.

3.Storage: Holding an electrical charge for a set period of time — or permanently — to record data.

By combining these functions, sophisticated electronic systems capable of computation, communication, and control become possible.

Semiconductor devices can be classified based on how they are controlled:

・Current-controlled devices: Such as bipolar junction transistors (BJTs). The base current controls the collector current, and these devices are mainly used for analog amplification and power control.

・Voltage-controlled devices: Such as MOSFETs and JFETs. Gate voltage controls the channel current, and these devices are used in digital circuits and switching applications.

・Light-controlled devices: Such as photodiodes and phototransistors. These convert light into electrical signals and are used in optical communications and sensors.

・Magnetically controlled devices: Such as MRAM and spintronic devices. These use electron spin to retain information and are applied in non-volatile memory and AI devices.

Components used in electrical circuits fall broadly into two categories:

・Passive devices: Components that only consume external energy, such as resistors, capacitors, and inductors.

・Active devices: Components capable of controlling, amplifying, or converting an external input, such as transistors, diodes, and ICs.

Semiconductor devices form the core of this category of active devices.

Semiconductor devices can also be classified based on the type of signal they handle:

・Analog devices: Handle continuous signals such as voltage and current. Representative examples include BJTs and operational amplifiers.

・Digital devices: Handle discrete signals represented as 0s and 1s. Representative examples include MOSFETs, CMOS, logic ICs, and memory.

In modern electronic devices, analog and digital technologies coexist. In a smartphone, for example, audio and video (analog signals) are integrated with communication and computation (digital signals).

Semiconductor devices can be understood through the following hierarchical structure:

・Device level: The stage of understanding the behavior of basic physical elements, such as PN junctions and MOS structures.

・Circuit level: The stage of combining multiple devices to form logic circuits and amplifier circuits.

・System level: The stage of integrating multiple circuits into complex functional modules, such as CPUs, memory, and communication chips.

In the early stages of training, it’s important to focus first on understanding devices at the device level.

Semiconductor technology has evolved as follows:

・1970s: BJTs were the dominant technology.

・1980s onward: MOSFETs became the mainstream technology.

・2000s: FinFET structures drove a shift toward 3D device architectures.

・2020s: Research has advanced into GAA structures, nanosheet structures, and even quantum devices.

Throughout this evolution, the consistent direction has been toward devices that are smaller, faster, and more energy-efficient.

・Semiconductor devices are active components that control the flow of electrons in order to process signals.

・Devices are classified as current-controlled, voltage-controlled, light-controlled, or magnetically controlled.

・Transistors can be considered the heart of virtually every electronic device.

・The central driver of this evolution has been miniaturization and the application of new physical principles.

1.What are the three basic functions of a semiconductor device?

2.What is the difference between a BJT and a MOSFET?

3.What is the difference between analog and digital devices?

 

Column Supervisor: Koji Kakumoto (Otis Group Co., Ltd.)

After studying abroad and working in planning and development at a trading company, he joined Otis Group Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as Representative Director, working to drive business growth and strengthen the organization.

 

This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.