These semiconductor materials offer superior properties compared to silicon (Si), whose physical limits are now almost exhausted. By enabling higher switching speeds and processing higher voltages and currents over longer temperature ranges, WBG devices increase the energy efficiency and reliability of current designs while saving space. Developers need to know more about them to get the full potential out of these devices and make successful end products out of it, as indicated in the datasheets.
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Modeling and parametric measurements
In power applications that demand energy efficiency, high power density, high switching frequency, and temperature resistance, WBG semiconductors are superior to silicon because of their exceptional material properties. When evaluating WBG power devices, consider their extended operating ranges (voltage, current, and temperature) compared to traditional devices. At the same time, sufficient measuring accuracy must be ensured even under these aggravating conditions.
The overall power loss of a MOSFET is made up of three quantities: progressive loss, driver loss, and switching loss. Driver losses are due to gate charging / discharging during switching and are dependent on gate capacitance, gate drive voltage and switching frequency. The switching loss is due to various capacities and depends among other things on the gate resistance and the switching frequency. In the context of the characterization of a MOSFET, it is, therefore, necessary to measure other parameters besides the IU characteristic such as capacitance and gate charge.
Due to the high switching frequencies, operating voltages and operating currents of components based on WGB semiconductors, some special features must be taken into account when measuring these parameters. For example, the gauges used must be able to measure on-resistance in the sub-milliohm range. To measure junction capacitances, the device under test must be stimulated with a small millivolt AC signal, with voltages of several kilovolts and currents of several hundred amperes. The challenges are even greater if the characterization of the component is to take place over a wide temperature range.
Parametric (electrical) measurements are the first step in understanding component properties. Based on the measured values, a behavioral model of the component can be developed, which is then used for circuit simulation. Component behavioral models enable designers to simulate, optimize, and validate designs before production starts. Manufacturing and process engineers can use simulation tools and models to maximize manufacturing yield. The development of accurate behavioral models requires a comprehensive characterization of many static and dynamic component parameters under both normal and extreme operating conditions. Besides, other aspects have to be taken into consideration, such as test throughput.
Test solutions for power components
Keysight offers two solutions that meet the parametric measurement requirements outlined above: the power component analyzers B1505A and B1506A. These devices can measure all the parameters necessary to characterize WBG semiconductor devices fully. The B1505A is the more versatile and adaptable of the two solutions and can be optimized for current and future production requirements.
Numerous modules are available for the B1505A, which cover different requirements for output voltage and output current (Figure 2). The most powerful of these modules provide output currents up to 1500 A and output voltages up to 10 kV. Also, the B1505A can measure minute sub-picoampere currents at high voltages. The device is suitable for on-wafer measurements as well as for measurements on thinned components. However, the maximum amperage for on-wafer measurements is limited by the load capacity of the probe’s probe card.
Dynamic parameters such as gate charge and capacitance are particularly important for WBG devices because their dynamic losses are greater than the static losses. With the B1505A, these parameters can be measured at DC operating voltages up to 3000V. The analyzer supports automated temperature cycle measurements over the range of -50 to 250 ° C and allows the analysis of resistance in the micro-ohm range at currents of up to several hundred amperes. B1505A can perform high-power pulsed measurements with pulse width from 10 μs. Such measurements minimize the self-heating of the test object and are therefore particularly accurate. In combination with the high voltage / high current fast switch option, the B1505A is also suitable for characterizing the current collapse phenomenon of AlGaN / GaN HEMTs.
With the analyzer, materials and process engineers can quickly and accurately capture all the data sets they need to optimize the manufacturing process. Recorded datasets can also be imported into part modeling and simulation tools such as Keysight’s IC-CAP part modeling software. Precise part models enable circuit and system designers to validate and optimize their designs before production starts, to improve the performance of their products, and to increase manufacturing yield.
Extension for component production test
Keysight, Agilent and Hewlett-Packard have been offering parametric production test systems since the early 1980s. The most recent model is the 4080 family, which is the standard for component production test systems used by most semiconductor manufacturers worldwide. The systems enable a high test throughput and can perform very high precision measurements in a short time.