What is a power semiconductor?

What is a power semiconductor? Explanations of its mechanism, characteristics, and applications that are easy to understand

1. The difference between semiconductors and power semiconductors

You probably hear the word “semiconductor” often, but what is the difference between semiconductors and power semiconductors? This section explains the differences between semiconductors and power semiconductors while tracing the history of each.

Semiconductor: A material that has properties of both a conductor and an insulator, and an electronic component made from such a material

As the name implies, a semiconductor is a material that is both an electrical conductor and an insulator (which does not conduct electricity). Electronic components made of this material are also called semiconductors.
Diodes and transistors are electronic components, and integrated circuits (ICs) and large-scale integrated circuits (LSIs), which consist of countless combinations of these components, are also semiconductors, and their main material is silicon. Semiconductors were invented in the United States in 1947, and the development of silicon transistors in 1950 paved the way for their mass production.

Power semiconductor: An electronic component capable of handling high voltages and high currents

Power semiconductors are electronic components that control and convert electric power from the power supply, etc. and the name “power” comes from the fact that it can handle high voltages and high currents. While the main role of semiconductors is information processing, such as operations, memorization, and signal processing, the main role of power semiconductors surrounds the supply, control, and conversion of power supplies and electric power. Power semiconductors can handle high voltages and high currents, so they are used in a wide range of applications that range from common household appliances to electric vehicle (EV) motors and batteries, solar power generation, and more.

The origin of power semiconductors is said to be ICs developed in the 1950s, and their mass production began in the 1960s. A MOSFET, a type of transistor, was developed in 1970, and a MOSFET-based IGBT was developed in the 1980s. Following this power semiconductors with high efficiency and durability were entered practical use.

2. Characteristics of power semiconductors

Semiconductors capable of handling a rated current of 1 A or more are sometimes referred to as power semiconductors. Alternatively, there is the idea that any semiconductor that can handle 1 W or more of electric power is a power semiconductor, but there is no clear definition of what constitutes one.

The main characteristic of power semiconductors is that they can handle high voltages and high currents. Another benefit is that they help to save energy and power because they can be designed to limit power loss during operation and to easily dissipate heat.
There are several types of power semiconductors, including “diodes,” which do not switch, and “power transistors,” which perform high-speed switching.

3. Basic principles and classification of diodes

Diodes are power semiconductors that have the role of making the flow of electricity unidirectional, and have characteristics and functions such as rectification and reverse-current prevention. This section explains the basic principles and classification of diodes.

Basic principles of diodes

Diodes are divided into two types, “PN junction diodes” and “Schottky junction diodes,” according to their structure. The details of each are as follows:

PN junction diode

A PN junction diode has a structure in which two different semiconductors are joined together: a P-type semiconductor, which uses holes as carriers, and an N-type semiconductor, which uses free electrons as carriers. Note that the letter “P” in “P-type” comes from “positive” and the letter “N” in “N-type” comes from “negative.”
P-type semiconductors have an anode terminal, while N-type semiconductors have a cathode terminal. PN junction diodes have the characteristic of allowing current to flow only from the anode to the cathode, with almost no current flowing from the cathode to the anode. Because of these characteristics, PN junction diodes achieve rectification: conducting current in only one direction and converting alternating current to direct current.

Schottky junction diodes

A Schottky junction diode has a structure in which a semiconductor and a metal are joined together. By changing the type and properties of the metal, a Schottky junction diode can be made to conduct current in a certain direction or regulate leakage current that would not normally flow.

Classification of diodes

PN junction diodes are further subdivided into rectifier diodes, Zener diodes, TVS diodes, PIN diodes, and so on. On the other hand, the main type of Schottky junction diode is the Schottky barrier diode.

PN junction diodes are sometimes called “bipolar” diodes, and Schottky junction diodes are sometimes called “unipolar” diodes. The term “bipolar” means “two (“bi”) polarities,” and “unipolar” means “ a single (“uni”) polarity.” These terms are often used to explain the structure and classification of semiconductors, not just diodes.

4. Characteristics and applications of diodes

We have seen that there are different types of diodes, but what are their characteristics? This section is an introduction to the characteristics and applications of typical diodes.

Rectifier diodes

The main purpose of a rectifier diode is to convert alternating-current power to direct current. Rectifier diodes are characterized by their ability to handle particularly high currents and voltages among power semiconductors, and they can easily handle high currents and voltages of 1 A or more and 400 to 600 V. Rectifier diodes are used in primary power supplies supplied by power companies, etc.

Zener diodes

Zener diodes are power semiconductors that provide a constant voltage to a circuit or protect a circuit or IC from overcurrent.
A PN junction diode has the characteristic that when a reverse voltage is applied to it, the current increases but the output voltage remains constant. This characteristic is called the Zener effect, and the voltage that is maintained is called the Zener voltage. Zener diodes take advantage of this characteristic. A Zener diode is also called a “constant-voltage diode” because of its characteristic of maintaining a constant output voltage. For your information, the word “Zener” comes from the American physicist Clarence Zener, who discovered this phenomenon.

TVS diodes

Transient-voltage suppressor (TVS) diodes, like Zener diodes, are also used to protect ICs and circuits from unexpected overvoltages by utilizing the diodes' reverse characteristics.

Specifically, a TVS diode is placed between the circuit or IC to be protected and the power supply. TVS diodes do not operate when the voltage is normal, but when a surge, a sudden overvoltage, is applied, they protect ICs and circuits by conducting a peak pulse current. Static electricity is the main cause of surges.

PIN diodes

A PIN diode is a device that combines an I-type semiconductor (intrinsic semiconductor) with a high resistance value in between a P-type semiconductor and an N-type semiconductor. When a forward voltage is applied, PIN diodes act like variable resistors, but when a reverse voltage is applied, they act like capacitors, storing electrical charge. PIN diodes are also called “high-frequency diodes” because of their high-frequency characteristics.

PIN diodes are used in attenuators that reduce the strength of radio signals sent to TVs, audio equipment, etc. to an appropriate level, as well as in high-frequency signal mobile devices and variable resistance elements for AGC circuits.

Schottky barrier diodes

Schottky barrier diodes (SBD) have a structure in which a metal such as molybdenum and an N-type semiconductor are joined together, and they are characterized by faster switching than PN junction diodes. Due to this characteristic, Schottky barrier diodes are widely used for rectification on the power supply (secondary power supply) side, which is directly connected to electronic devices and the like.

5. Basic principle and classification of transistors

A transistor is a semiconductor device that has amplification and switching functions. In particular, transistors that can handle high voltages and currents are called power transistors, and are classified as power semiconductors.

The “amplification” function, which is one of the functions of a transistor, is used in situations such as when you want to make the audio signal from a radio louder so you can hear it through a speaker. Transistors can also turn the current and voltage on and off. Another function of a transistor is “switching,” which is used in situations such as moving and stopping components such as motors.

In this section, we will take a closer look at the basic principles and classifications of transistors.

Basic principle of transistors (NPN type)

This section explains how transistors perform the two functions of amplification and switching, using the NPN transistor as an example.

An NPN transistor has a structure in which a P-type semiconductor is sandwiched between two N-type semiconductors, and has a total of three terminals: the “emitter” and “collector” terminals from the N-type semiconductor, and the “base” terminal from the P-type semiconductor.

The three terminals also comprise the basic structure of a transistor. When a small current is passed through the base terminal of an NPN-type transistor, several hundred times the current of the input current flows from the collector to the emitter.

On the other hand, the switching function is very simple. When a certain voltage or more is applied to the base terminal and a small current flows, the transistor is turned on. When the voltage at the base is less than a certain level, no current flows and the transistor is turned off, fulfilling its role as a switching device.

Classification of transistors

The three main types of transistors are the bipolar transistor, the unipolar transistor, and the insulated gate bipolar transistor (IGBT).
The typical bipolar transistor is called a “BJT,” and the typical unipolar transistor is called an “FET.”

6. Characteristics and applications of transistors

There are many different types of transistors, and they have different characteristics. In this section, we will introduce some of the types that have attracted attention in recent years and look at their applications.

BJTs

One type of bipolar transistor is the bipolar junction transistor (BJT). A major characteristic of BJTs is that although they can generate a large current from a small input current, their switching speed is not very fast and their power consumption during switching is high.
There are two types of BJTs: NPN-type and PNP-type BJTs, and they are used in amplifiers, oscillators, low-voltage switching, and so on.

FETs

Whereas the BJT is current driven, the field-effect transistor (FET) is a type of unipolar transistor that is voltage driven. An FET has the same role as a BJT as a transistor, but is characterized by fast switching and low power consumption.

FETs are further subdivided into “junction FETs,” “MOSFETs,” and “GaAs FETs.” Junction FETs are used in analog circuits in audio equipment, etc., MOSFETs are used in digital ICs such as microcomputers, etc., and GaAs FETs are used to amplify microwaves for satellite broadcasting reception and other applications.

Insulated gate bipolar transistors (IGBTs)

An insulated gate bipolar transistor (IGBT) is a power transistor that combines the characteristics of MOSFETs and bipolar transistors. Specifically, it can operate at high voltages from 600 to 1,200 V and has the characteristic of amplifying a current to a large current from 5 to 1,000 A.

Due to these characteristics, IGBTs have a wide range of applications and are used in various inverter devices, air conditioners, IH rice cookers, electric power grids, large-scale transportation equipment such as railways, data centers, medical and healthcare equipment such as heavy ion beam therapy and MRI, industrial equipment, machine tools, and automotive power semiconductors, including EV motor control.

7. New materials for power semiconductors

As mentioned at the beginning of this article, conventional power semiconductors are generally made of silicon. However, recent times have seen the need for more active power saving to further expand applications and achieve carbon neutrality, so power semiconductors using new materials have been developed and are steadily entering practical use.

In recent years, silicon carbide (SiC) and gallium nitride (GaN) have attracted attention as materials for semiconductors. SiC is synthesized from silicon (Si) and carbon (C), and GaN is synthesized from gallium (Ga) and nitrogen (N). Unlike Si, which is a single material, these are semiconductor materials comprise multiple compounds.

SiC is increasingly finding use in EVs and solar power generation due to its excellent stability at high temperatures, high voltage resistance, and low power loss during operation.
GaN has traditionally been employed in blue LEDs and laser devices. It is used in semiconductors especially for smartphone chargers and AC adapters for PCs because it has excellent voltage resistance and can perform high-voltage and large-capacity conversion. This material is expected to be used in the future in scenarios such as power supplies for data center servers.

8. When it comes to your power semiconductor needs, talk to MinebeaMitsumi. We can integrate all processes from development to production.

We deal with a wide variety of precision components, and are expanding our power semiconductor business not only by developing our chip business, but also by improving our packaging and modularization technologies and production capacity.

In the future, we will provide innovative power semiconductors capable of handling high currents by integrating the systems from development to production of power semiconductors, and by combining power semiconductors with our power supply-related products—a niche in the market where we have an advantage.
We are also involved in the development and manufacture of next-generation power semiconductors such as SiC. If you have questions or would like to discuss anything related to power semiconductors, please feel free to contact us.