The proliferation of electronic control and electronic power conversion into a variety of industries (e.g., energy generation, industrial motor drives and control, transportation, and IT) has made efficient power semiconductor device design and test more critical than ever. To demonstrate technology improvements, new device capabilities must be compared with those of existing devices. The use of semiconductor materials other than silicon demands the use of new processes. To be sustainable, these new processes must be tuned to deliver consistent results and high production yield. As new device designs are developed, reliability measurements must be performed on many devices over long periods. Therefore, test engineers must identify test equipment that is not only accurate, but scalable and cost-effective.
Power module design engineers — the consumers of the discrete power semiconductor components — work at the other end of the semiconductor device testing spectrum from the device test engineers. They integrate the discrete components into designs for DCDC converters, inverters, LED controllers, battery management chips, and many other devices. Driven by demands for higher energy efficiency, these engineers need to qualify the devices they receive from their vendors to ensure that they can withstand use in the application, predict how the efficiency of the power modules may be affected by the device, and validate the performance of the end product.
Source Measure Units (SMUs) give both types of engineers the tools they need to characterize new devices quickly. This article highlights some of the most commonly performed tests, the challenges associated with them, and the advantages the newest generation of high-power SMUs offer for characterizing new high-power semiconductors based on both silicon and new widebandgap materials.
Power Semiconductor Product Circuit Elements
The switching power supply is one circuit element commonly used in power management products. Its main components include a semiconductor such as a power MOSFET, a diode, and some passive components, including an inductor and a capacitor (Figure 1). Many also include a transformer for electrical isolation between the input and output. The semiconductor switch and diode alternatively switch on and off at a controlled duty cycle to produce the desired output voltage.
When evaluating a device’s energy efficiency, engineers need to understand both its switching loss (which occurs when the device is changing states) and conduction loss (which occurs when the device is either on or off). This article focuses on conduction loss. Although curve tracers were once the instruments of choice for device characterization, engineers are increasingly turning to solutions that configure one or more SMUs into parametric curve tracer systems to evaluate the device parameters that affect conduction loss. SMUs integrate the capabilities of a precision power supply with those of a high-performance digital multimeter in a single instrument. For example, they can simultaneously source or sink voltage while measuring current, and source or sink current while measuring voltage. They can also be used as pulse generators, as waveform generators, and as automated current-voltage (I-V) characterization systems. The newest SMUs offer higher power capabilities (up to 3kV) to support power semiconductor characterization and test.
Semiconductor devices like thyristors are often employed for overvoltage protection. To achieve that objective, such devices must trigger at the appropriate voltage and current, must withstand the intended voltage, and must behave in circuit with minimal current draw. Highpower instrumentation (including the latest generation of SMUs) is essential to qualify these devices properly.
Static power device parameters can be divided into two broad categories: those that determine a device’s performance in its ON state and those that determine the performance in its OFF state.
ON-state characterization is typically performed using a high-current instrument capable of sourcing and measuring low voltages. If the device has three terminals, a second SMU is used at the device control terminal to place the device in the ON state. Figure 2 illustrates a typical configuration for characterizing the ON-state parameters of a power MOSFET.
Let’s examine the configuration details and measurement challenges of a few ON-state parameters.
A semiconductor device’s data sheet normally includes a plot of its output characteristics that depicts the relationship between the output voltage and current. For a gated power semiconductor switch such as a MOSFET, IGBT, or BJT, output characteristics are commonly referred to as the “family of curves.” Figure 3 shows the results for a commercially available power IGBT.