Today, semiconductor chips can be found in almost every electrical device. Cellphones contain dozens; cars, over a thousand. Now that even simple objects such as car keys or LED lamps are controlled via chips, many electrical devices are easier to use and offer numerous additional functions – such as car keys that allow drivers to open the windows remotely on hot days in order to cool the car down before they get in. With the growing number of chips, however, comes a greater risk that the technology will fail. A defective chip can cause a device to break down even though the other components are still in working order. There is generally no technical provision for replacing an individual chip, and it is far too expensive in any case. Accordingly, many products prematurely end up as electronic waste, thereby squandering valuable raw materials.

Testing the key element of electronics

Dr. Katrin Ortstein works on making electronics more durable and therefore more sustainable. With this in mind, the physicist and manager of the “Quality and Reliability” group at Fraunhofer IIS in Dresden starts right at the beginning of chip production – with the transistors, the tiny structures that make up the electronic circuits on chips. Ortstein and her team at the Engineering of Adaptive Systems division specialize in testing new transistor types and technologies before they enter large-scale use in industry. “We receive requests to test new transistor technologies not only from semiconductor manufacturers but also from car manufacturers and developers of consumer electronics,” says Ortstein. In the Dresden laboratory, the transistors are subjected to different stresses for many hours. This includes being cooled to minus 40 degrees Celsius and heated to up to 200 degrees, as well as exposure to high electrical voltages.

Combination of testing and modeling

The idea is to expose transistors to short-term loading that mimics the natural aging experienced over many years. Since this one-off loading is not an exact comparison for the many different loads that a component experiences over its life, the team also develops mathematical models based on the measured values. “We or our partners use these models to simulate the behavior of transistors under typical operating conditions over longer periods of time. This combination of technical testing and modeling is what sets our work apart,” says Ortstein. At a later stage, chip developers can then use these computer models for the design, optimization, or validation of new circuits and chips made up of the transistors. “It’s therefore possible to identify circuit designs during the design phase that would prematurely fail in subsequent use – long before preseries production begins,” says Ortstein. “This is a particularly sustainable approach, because it avoids the unnecessary consumption of energy and raw materials.”

Extremely fast measurements

At Fraunhofer IIS, transistors are scrutinized using various different tests. This usually includes exposing them to a specific form of stress, such as an increased voltage and an increased temperature, over a period of several hours. In the meantime, measurements are taken repeatedly to determine how the transistor’s properties change with increasing stress duration. The trick is to keep the measurement phases as short as possible, because they interrupt the stress phase and therefore influence the transistor’s aging. With the technique used at the Engineering of Adaptive Systems division, a measurement phase lasts just five microseconds. This makes Ortstein’s team significantly faster than similar test procedures carried out according to the usual standards. Such measurements are usually performed on the millisecond scale – and therefore several hundred times slower.

Ortstein’s team is also in a position to precisely address specific customer requirements in testing and modeling. Among other special features, the tests can apply stress to the transistor in such a way that it corresponds to real-world conditions in subsequent use. For example, the testing applies alternating stresses that increase and decrease according to a certain rhythm. Ortstein says: “Overall, we want to allow circuit developers to make an efficient assessment, helping them to achieve their reliability objectives.”