Types of Power Semiconductors -Reliability and Performance Tests

Types of Power Semiconductors

In our previous column, we discussed how DC power supplies are created from grid connections and AC sources. These power conversions are performed by electronic circuits designed for efficiency. Common examples include inverters in home appliances and power conditioning systems for solar and wind energy. Furthermore, these components are essential for controlling motors in hybrid and electric vehicles, operating efficiently across a wide range of speeds.
Semiconductors used to control and supply power in these circuits are known as "power semiconductors." They are designed to handle a broad spectrum of energy levels, ranging from low-power consumer electronics to high-power industrial applications.

Power semiconductors generally perform four key functions:

1. Converting DC to AC (Inversion)
2. Converting AC to DC (Rectification)
3. Frequency Conversion
4. DC-DC Conversion (Voltage conversion)

Currently, silicon (Si) is the primary material for power semiconductors. However, next-generation materials such as Silicon Carbide (SiC) and Gallium Nitride (GaN) are gaining attention for their higher conductivity and reduced power loss.

MOSFETs and IGBTs
The MOSFET is widely used in low-power applications like mobile devices and computer power supplies due to its high switching speed. For high-power applications requiring higher voltage tolerance, the IGBT (Insulated Gate Bipolar Transistor) is commonly used.

While IGBTs have slower response speeds compared to MOSFETs, they offer superior withstand voltage performance. They also exhibit low conduction loss when handling large currents. These characteristics make IGBTs ideal for electric vehicles (EVs), hybrid vehicles, fuel-cell cars, and industrial machinery.

Following the oil crisis of the 1970s, electric vehicles regained attention. By this time, advancements in transistors and circuit miniaturization had significantly improved component performance. Today, modern power semiconductors are critical to the efficiency and viability of current electric vehicles.

Performance Evaluation and Reliability Testing

Five key requirements define the performance of modern power semiconductors:

1. Higher breakdown voltage
2. Lower leakage current
3. Lower on-state resistance
4. Higher power handling capability
5. Faster switching speeds

The theoretical ideal for a power device involves zero switching time, zero on-state resistance, and zero leakage current loss. While physical limits make perfection impossible, developers strive to come as close to these ideals as possible. To validate these improvements, high-precision testing equipment is essential. Even if a device is capable of high-speed switching, its performance cannot be verified without equally advanced measurement instrumentation.

Reliability and Yield
Reliability is critical, especially for mass production. A low production yield--where only a few units per lot meet specifications--drastically increases device costs. Furthermore, for applications in extreme environments or critical infrastructure (such as satellites, power stations, or automotive systems), failure is not an option.

Therefore, rigorous reliability testing using stable, high-performance power supplies and measurement systems is a crucial phase in power semiconductor development.