Statistical sampling of new semiconductors

For example, typical drain leakage currents on a silicon carbide power FET might be less than one nano-amp, but an automated power device tester is often limited to hundreds of nano-amps or even micro-amp capability. One solution is for the power device manufacturer to configure their own automated solutions using higher performance instrumentation, such as the latest high power SMUs, which now offer numerous features designed to simplify the development of automated systems, including built-in scripting capability, and virtual backplane capability for synchronising multiple instruments for more complex solutions. Keithley even offers software specifically designed to control and manage automated testers. Automated Characterisation Suite (ACS) software was specifically designed to manage data acquisition and data management across multiple devices undergoing multiple tests.

Once a designer is satisfied that a statistical sample of the devices perform as required, the next step is a production qualification run. From these wafers, a Long Term Life Test can be set up to validate the reliability of the devices under different conditions designed to emulate the real world. This is normally done in large parallel batches, with many devices installed in thermally controlled environments. Many hundreds of devices are tested for hundreds or thousands of hours under various electrical and environmental stress conditions. In most cases, the designer has specific conditions that he wants life-tested, which makes it essential that the test equipment be flexible and readily reconfigurable. Creating and maintaining parallel test resources and monitoring and managing the masses of data acquired during this phase can easily become overwhelming. Typical parameters tested here include leakage current (IDSS and IGSS), ON resistance (RDS(ON)), and threshold voltage drift (delta VTH).

Correlating the results of tests performed in various test environments has always been complicated due in no small part to the very different test systems (each with its own unique set of capabilities and sources of error) often used in different test environments. Today, a growing number of device manufacturers are striving to consolidate on a uniform set of instrumentation, so that, for example, the leakage current measurements made in the early stages of the device design process can be correlated with those from devices being produced in the fab.

Characterising power devices has always been a challenging task. The combination of new, higher performance power devices, coupled with traditional test equipment often no longer up to the job, imposes a growing burden on power device designers. Fortunately, test equipment companies are starting to see the light and bring out new products optimised specifically for power device characterisation and test.

You can read the rest of this article in the September issue of Electronic Specifier Design by clicking here.