With numerous suppliers offering a wide range of semiconductor components, should selection be based solely on individual specifications and characteristics? In reality, circuit designers face multiple challenges throughout the design process. Power circuits, which are integral to nearly all applications, are often prone to issues such as unstable operation caused by parasitic inductance and performance degradation due to overheating. Since no single electric component is ideal for every application, careful selection is essential. Partnering with a supplier that possesses the expertise to address these challenges can greatly reduce the complexity for circuit designers.

• Challenges in Using Power Semiconductors

For engineers working with power semiconductors, development effort can be significantly reduced by choosing a supplier that proactively addresses the challenge of circuit integration, such as minimizing parasitic inductance, ensuring effective heat dissipation, and incorporating protection circuitry.
For instance, selecting a manufacturer that provides pre-designed power modules optimized for low parasitic inductance can significantly reduce trial-and-error during circuit design.
Likewise, companies that develop packages with inherently high thermal performance help ensure stable operation making them valuable partners for designers.
Adopting power modules (IPMs) with built-in protection features such as overcurrent, overvoltage, and thermal shutdown further reduces workload.
An ideal supplier also offers a broad portfolio of device technologies, including silicon, silicon carbide (SiC), and gallium nitride (GaN), proposing the most suitable option based on the application. For example, SiC devices deliver high-efficiency, low-loss power conversion, making them increasingly popular in electric vehicles (EVs) and renewable energy systems. GaN devices, with their excellent high-frequency characteristics, are well-suited for high-speed switching applications, enhancing efficiency in communication equipment and data centers. While SiC and GaN offer superior performance, silicon remains the practical choice for many applications, especially where cost constraints are critical. A supplier offering all three technologies can provide component and topology proposals that strike the optimal balance between performance and cost. Equally important is selecting a manufacturer that guarantees stable product supply through product longevity programs, ensuring worry-free use in long-lifecycle applications like industrial equipment and automotive systems. Additionally, access to a comprehensive library of simulation models allows designers to identify and resolve potential issues in a virtual environment before creating physical prototypes, greatly reducing both design effort and development time.
In short the best partner is a manufacturer whose products, technologies, and services are inherently designed to ease the workload of circuit designers from the very start.

• Differentiation Between Silicon, Silicon Carbide, and Gallium Nitride

ROHM has built extensive expertise in the power semiconductor field over many years, including becoming the first in the world to mass produce SiC (silicon carbide) MOSFETs. ROHM has also led advancements in next-generation materials by successfully mass-producing GaN (Gallium Nitride) devices, which like SiC are gaining significant attention for their performance advantages.
ROHM's Power Eco Family encompasses a complete lineup of silicon, SiC, and GaN power semiconductors, each optimized for a diverse range of applications. By providing devices that accommodate various power capacities and switching frequencies, together with driver ICs designed to unlock their true potential, ROHM enables miniaturization and improved energy efficiency across a broad spectrum of power control applications.

EcoSiC™ is ROHM's brand of silicon carbide (SiC)-based power semiconductors. Compared wot silicon, SiC offers superior voltage and temperature tolerance, making well-suited for high-power applications such as electric vehicles and uninterruptible power supplies (UPS). ROHM's EcoSiC™ lineup comprises a wide range of SiC power semiconductors, including SiC MOSFETs and SiC SBDs (Schottky Barrier Diodes).

EcoSiC™ Products

EcoGaN™ is ROHM's brand of gallium nitride (GaN)-based power semiconductors based. GaN offers higher breakdown voltage and higher-frequency operation than both silicon and SiC. The lineup includes GaN HEMTs (High Electron Mobility Transistors) as well as power stage ICs with integrated controllers. The EcoGaN™ brand focuses on delivering user-friendly GaN devices that reduce power consumption, minimize the size and count of peripheral components, and lower design workload.
Compared to SiC, GaN is better suited for lower power applications that demand higher switching frequencies, such as power adapters, data server power supplies, and PV inverters.

EcoGaN™ Products

EcoIGBT™ is ROHM"s brand of silicon-based Insulated Gate Bipolar Transistors (IGBTs) and Intelligent Power Modules (IPMs). Renowned for their excellent high-voltage tolerance, IGBTs are primarily deployed in high-power applications. While offering high-voltage tolerance comparable to SiC devices, IGBTs are relatively more cost-effective and operate at lower frequencies, making them ideal for large-scale applications such as railway power circuits where miniaturization is not a primary requirement.

EcoIGBT™ Products

EcoMOS™ is ROHM's brand of silicon MOSFETs. Leveraging silicon, a relatively low-cost material, these devices are widely used in medium-power, medium-frequency applications such as consumer electronics and industrial robots. Beyond cost-effectiveness, EcoMOS™ features an extensive lineup refined through years of R&D, allowing designers to choose the optimal device for each application based on diverse parameters, including noise characteristics and switching performance.

EcoMOS™ Products

Power Eco Family Features

ROHM’s Power Eco Family spans a broad range of power capacities and operating frequencies, addressing the needs of a wide variety of applications. To further ease the challenges faced by circuit designers, ROHM provides a comprehensive lineup of driver ICs and modules.

Power semiconductors are a broad category of semiconductor components designed to control electric power. In this context, the term refers specifically to discrete devices, excluding ICs.
These components are found in a wide range of electrically powered applications, such as industrial equipment, electric vehicles, and household appliances. For instance, they regulate current and voltage to drive motors based on instructions from the CPU.
Common examples of power semiconductors include transistors, diodes, and thyristors used in power supply circuits.

Differences Between Power and Small-Signal Semiconductors

Power semiconductors are critical electronic devices that enable the efficient control and conversion of electrical energy, making them indispensable in all electrically powered applications, from consumer electronics to large-scale industrial power systems. They perform key functions such as rectification, amplification, and switching, acting as the interface between the CPU and actual drive components.
Devices such as transistors, diodes, and thyristors can be classified as power semiconductors, but depending on their specifications and intended use, some may instead be categorized as small-signal semiconductors.
The primary distinction lies in the voltage and current levels they are designed to handle, as well as the nature of their application.

Voltage and Current Capacity

Power Semiconductors: Engineered to handle high voltages and currents (approx. 1W or more).
Small-Signal Semiconductors: Designed for low-voltage, low-current operation.

Applications

Power semiconductors: Used for power conversion and control.
Small-signal semiconductors: Utilized for processing and amplifying low-level signals such as audio.
In other words, transistors may be classified as either as power semiconductors or small-signal semiconductors depending on the voltage and current levels they are designed to handle.

Power semiconductors can be further categorized into rectifying devices and switching devices.
Rectifying devices permit current to flow in only one direction, while switching devices operate as ON/OFF switches. Switching devices further divided into two main types: FETs (Field Effect Transistors) and bipolar transistors.

More specifically, rectifying devices refer to diodes that leverage their rectification ability to convert alternating current (AC) into direct current (DC), and are used in a variety of power control applications.
Switching devices include transistors and thyristors, both capable of turning current flow ON and OFF. The main difference is that thyristors, while more limited in applications than transistors, can handle significantly higher voltages and currents, making them well-suited for large-scale systems such as railway infrastructure and power grids.

In summary, power semiconductors are semiconductor devices designed to control electrical power of 1W or more by leveraging two core functions: rectification and switching.

Diodes

A diode is a semiconductor device that allows current to flow in one direction while blocking it in the opposite direction. When designed to handle power levels of approx. 1W or more, they are classified as power diodes. These devices are widely used in power supplies, motor control circuits, and power conversion systems. Power diodes are available in several types, including rectifier diodes, switching diodes, and Schottky diodes. Rectifier diodes are primarily used to convert AC power into DC power, while switching diodes function as current switches. Schottky diodes, known for their low forward voltage drop, are often selected for applications requiring high efficiency and fast switching performance.

Transistors

A transistor is a semiconductor device that functions either as an amplifier for electrical signals or as a switching element. Devices designed to handle 1W or more of power are classified as power transistors. Capable of both signal amplification and switching in digital circuits, transistors combine compact size with high efficiency, making them essential in a wide range of electronic products, from computers and smartphones to home appliances. They also serve as fundamental building blocks in integrated circuits (ICs).

Bipolar Transistors

A bipolar transistor consists of three layers: the emitter (E), base (B), and collector (C). There are two primary types of bipolar transistors: NPN and PNP.
In an NPN transistor, the emitter is formed from N-type semiconductor material, the base from P-type, and collector from N-type.
〈Characteristics〉
A small base current can control a large collector current, resulting in high current gain but a relatively slow switching speed. The extremely thin base layer allows electrons injected from the emitter to pass through easily, enabling a large collector current and achieving high current amplification.
〈Applications〉
Used in power amplification and audio amps.
Reason: High current gain makes them ideal for amplifying analog signals. However, their relatively slow switching speed limits their suitability for high-speed switching applications.

MOSFETs

A MOSFET has three terminals: gate (G), drain (D), and source (S), and is classified into two types: P-channel (Pch) and N-channel (Nch). In an Nch MOSFET, the source and drain regions are composed of N-type semiconductor material.
〈Characteristics〉
A voltage-controlled device, the MOSFET regulates the current between the drain and source according to the voltage applied between the gate and source. It offers high-speed switching capability and low ON-resistance, although ON-resistance tends to increase at higher voltages.
When voltage is applied to the gate, an electric field forms in the semiconductor layer beneath the insulating film, causing electrons to gather and form a conductive channel. This channel allows current flow from the source to the drain. Because the channel is controlled by the gate voltage, adjusting this voltage provides precise current regulation, enabling exceptionally high-speed switching. Due to this capability, MOSFETs are widely used in applications such as inverters and switching power supplies.
〈Applications〉
Switching power supplies, inverters, motor control, and more.
Reason: High-speed switching and low ON-resistance allow efficient power control, while voltage-driven operation makes the gate is easy to drive.

*Low ON resistance
Once a conductive channel is formed, current flows from the source to the drain with minimal resistance. The low ON-resistance allows current to pass efficiently, reducing power loss and enabling highly efficient power control.

ROHM MOSFET Lineup

IGBTs (Insulated Gate Bipolar Transistors)

An IGBT is a transistor that combines the advantages of both MOSFETs and bipolar transistors. It features three terminals: gate (G), collector (C), and emitter (E). A P+ collector layer is added to the drain side of the MOSFET, forming a P-N-P-N junction. IGBTs are well-suited for high-voltage applications.
〈Characteristics〉
High-speed switching: The gate structure of the MOSFET enables rapid ON/OFF current control.
High current drive: Leveraging the properties of a bipolar transistor, IGBTs can conduct large currents, making them ideal for applications such as power conversion and motor drive. (Note: small-signal IGBTs do not exist) Voltage control: Operates as a voltage-driven transistor.
High breakdown voltage: The combination of P+ collector layer and N- drift layer allows the device to withstand high voltages. Low ON resistance: Conductivity modulation reduces resistance during conduction, improving efficiency.
Long turn-OFF time: Due to bipolar operation, excess carriers must be cleared when switching OFF, resulting in a longer transition from conduction to non-conducting states.
〈Applications〉
High-voltage, high-current switching; electric vehicle inverters; industrial motor control; and similar uses.
Reason: IGBTs combine the high-speed switching capability of MOSFETs with the high-current handling and high breakdown voltage of bipolar transistors. However, their relatively long turn-OFF time limits suitability for ultra-high speed switching applications.

ROHM IGBT Lineup

In the past, silicon was the sole material used for semiconductors, but today multiple materials are selectively employed, each chosen for its unique characteristics.

Silicon (Si)

Silicon remains the widely used semiconductor material due to its abundance, ease of processing, and relatively low cost. It has the ability to either conduct or block electricity depending on specific conditions, making it ideal for ON/OFF switching in semiconductor devices.
In addition, silicon offers excellent thermal dissipation and chemical stability, enabling reliable performance even under heat-generating conditions while providing resistance to oxidation and corrosion, ensuring consistent operation over long periods.

Silicon Carbide (SiC)

A compound of silicon and carbon, SiC has emerged as a next-generation power semiconductor material thanks to its significantly higher voltage and heat tolerance compared to silicon, as well as lower power losses. These advantages make it increasingly popular in applications such as electric vehicles (EVs) and solar power systems. SiC’s superior properties are largely due to its wide bandgap - 3.2eV compared to silicon's 1.1eV. A wider bandgap means electrons require more energy to transition from the valence band to the conduction band, enabling the material to handle higher voltages. SiC also features high thermal conductivity that allows for efficient heat dissipation and stable operation in high-temperature environments. However, SiC is extremely hard and therefore difficult to process. Growing single crystals requires advanced technology and precise control to minimize crystal defects. Scaling wafer size while maintaining quality remains challenging, contributing to higher manufacturing costs.
For low-voltage, cost-sensitive applications, silicon remains the more practical choice, while SiC is better suited for high-power, high-efficiency designs.

ROHM SiC Lineup

Gallium Nitride (GaN)

GaN offers both high breakdown voltage and low ON resistance, with an even wider bandgap than SiC (approx. 3.4eV), enabling superior voltage tolerance. GaN devices are typically designed as high electron mobility transistors (HEMTs) using an AlGaN/GaN heterostructure that delivers exceptionally fast switching speeds through high electron mobility. These characteristics make GaN ideal for high-frequency, high-efficiency applications.
However, GaN devices also introduce challenges. Their high-frequency operation can increase noise, requiring precise gate drive voltage control for suppression, adding design complexity. Additionally, GaN is difficult to crystallize and process, demanding advanced manufacturing techniques. As a result, only a limited number of suppliers can product GaN devices at scale.

ROHM GaN Lineup

Material Selection by Application

• Silicon
  Cost-effective and widely used in consumer electronics and relatively low-voltage power control devices
• SiC
  Ideal for high-voltage, high-temperature environments and applications demanding high efficiency, such as electric vehicles (EVs) and renewable energy systems
• GaN
  Best suited for sets where high-speed switching is advantageous, including communication infrastructure and data centers
  
  These materials are applied selectively to leverage their unique characteristics.
  Understanding which materials are best for a given applications enables more efficient and reliable power control.

Summary
Power semiconductor devices regulate and convert electrical energy across a broad range of applications, functioning as compact, non-mechanical switches that deliver high reliability and efficiency. Key growth sectors, such as electric vehicles, data centers, solar power systems, and inverters, are driving demand for these devices, supporting the advancement of AI and the achievement of a sustainable society.

As the role of power semiconductors continues to grow, several technical challenges must be addressed to ensure optimal performance and reliability.

Reducing Parasitic Inductance

Parasitic inductance refers to the unintended inductive effect that occurs in a circuit when current flows. When the current changes rapidly, this inductance generates a force opposing the change, which can cause voltage fluctuations (surges). Such effects can compromise circuit performance and reliability.
Power devices that manage large amounts of electrical energy are particularly sensitive to parasitic inductance, so minimizing this is important for efficient operation.
This can be achieved by shortening wiring lengths, optimizing component placement, and using low-inductance packing and layout techniques.

Thermal Design and Heat Dissipation

Power semiconductors handle higher voltages and larger currents, generating significant heat during operation. Without proper thermal management, overheating can lead to performance degradation, malfunction, or even device failure. Effective thermal design maintains operating temperature within a safe range, improving both performance stability and product longevity. Solutions include:
• Heat sinks to absorb and dissipate heat
• Cooling methods such as natural convection, forced-air, or liquid cooling
• Thermal interface materials (TIMs) like silicone grease or pads to enhance heat transfer
• Heat pipes to transport heat efficiently over longer distances
• Optimized PCB design with improved copper thickness and strategic component placement for better thermal conduction

Implementing Protection Circuits

Power semiconductors handle higher voltages and larger currents, making them more vulnerable to abnormal conditions such as overcurrent, overvoltage, and overheating. Protection circuits safeguard both the devices and and overall system by detecting these conditions and taking corrective action. Common protection mechanisms include:
• Overcurrent protection using fuses, circuit breakers, or detection circuits
• Overvoltage protection with Zener diodes, varistors, or surge absorbers
• Overheat protection via thermistors or temperature sensors to trigger shutdown when temperatures exceed safe limits
• Short-circuit protection to quickly interrupt current flow
Some integrated solutions, such as IPMs, include built-in protection circuits, reducing design time and complexity.

Device Selection

Selecting the right power semiconductor starts with determining the maximum voltage and current requirements. For switching devices, switching speed and efficiency are key considerations. High-speed devices like MOSFETs enable efficient energy conversion but may require advanced cooling solutions due to increased heat generation. Other factors include:
• Operating temperature range to ensure reliable performance in varying environments
• Material durability for long service life in high temperature or harsh conditions
• Cost-performance balance, since advanced devices with the latest technologies tend to be more expensive

Modeling involves representing a device's behavior using mathematical equations or equivalent circuits, enabling accurate virtual reproduction of its operation. Once created, models can be reused across multiple design projects, improving efficiency.

Simulation uses these models to verify operation in a virtual environment before building physical prototypes. This approach allows:
• Early identification and resolution of design issues
• Optimization of parameters before hardware fabrication
• Reduction in prototype iterations, lowering development costs
• Shortened time-to-market
Accurate modeling and simulation not only streamline the design process, but also enhance the reliability of the final system.