ELECTRONICS

Exploration into transistor reliability leads to new discoveries

According to imec, its research has spawned breakthroughs in self-learning chips, new data security technology and biosensors. The investigations explore the reliability of transistors and electrical characterisation, observing what happens when transistors operate properly and when they fail.

Guido Groeseneken of imec, said: “We’ve been doing this in terms of circuits, devices and materials – and sometimes right down to the level of atoms. The insights that we gather from this work help us to provide the right feedback to the process technologists, who in turn are able to make the transistors more reliable. It is particularly interesting to note that in recent years the knowledge we have gained about these failure mechanisms can also be applied to other areas. These insights no longer only serve to solve problems, but are the basis for innovative and surprising solutions in very diverse domains.”

Self-learning chips

Last year, imec’s work focused on self-learning chips, data security codes, FinFET biosensors and computer systems that can correct themselves.

imec has said the development of the self-learning chip is based on pre-existing knowledge of resistive RAM, which use the breakdown of an oxide to switch a memory bit on or off (0 or 1). The oxide breakdown occurs due to the filament that occurs during this process and this can cause problems.

imec however, says it has demonstrated the ability to control the strength of the filament – a similar process to the brain. The connections between neurons in the brain can become stronger or weaker according to the occurrence they are processing or the learning process they use. Due to this similarity, imec has suggested the possibility of using RRAM filaments in chips that work like our brains.

“It was this insight that provided us with the foundation for the development of imec’s neuromorphic chip, which – as has been demonstrated – can even compose music,” Groeseneken explained.

Data security

imec has also been working with COSIC, exploring the possibilities of computer security and physically unclonable functions. imec say that transistor breakdown mechanisms can be used to create and read out a fingerprint that is unique for each chip and unpredictable through the means of random telegraph noise. This, imec says, makes it possible to ascertain the identity of chips in data exchanges, offering a solution to rogue chip hacking.

Biosensors

imec has also looked at FinFET transistors and their failure mechanisms, which has led to the possibility of using them as biosensors.

Groeseneken said: “Biomolecules have a certain charge and when that charge comes into the vicinity of a FinFET, the current in the FinFET will be influenced. As a result, there is the potential that the presence of a single biomolecule can be detected by such a FinFET.”

Self-healing chips

The team are also working on producing reliable chips, even with transistors that are no longer reliable.

“Extremely small transistors with dimensions smaller than 5nm can be very variable and the way they behave is unpredictable. For that reason, we are working with system architects on solutions such as self-healing chips, based among other things on the existing models of the failure mechanisms that we provide them with.

“These self-healing chips will contain monitors that detect local errors. A smart controller then interprets this information and decides how to solve the problem, after which actuators are directed by the controller to carry out the task required,” Groeseneken explained.

The near and distant future

Ways to ensure transistors can still be miniatursed and improved for as long as possible are also being explored.

“To do so, the classic transistor architecture has already been replaced by a FinFET architecture and in the future, this will evolve even to nanosheets or nanowires,” Groeseneken said. “Materials other than silicon, with greater mobility, are also being looked at, such as III-V materials (germanium for pMOS and InGaAs for nMOS).”

According to imec, failure mechanisms and the reliability of the new solutions is a vital exploration when it comes to future architectural decisions.

imec’s work into III-V transistor last year, revealed that although mobility was optimal, their stability remains a challenge and will prevent steps being taken towards manufacturing.

Groeseneken explained that the insulation layers within the III-V transistors contain a lot of traps, which result in this ‘instability in transistor characteristics’. He believes that it is vital to gauge a better understanding of this if a solution is ever to be found.

On the distant future, Groeseneken says it is difficult to predict, but the strong interest in quantum computers that was seen in 2017 will continue into 2018, with imec itself planning to launch a program.

He concludes: “In the past, quantum computing has been considered more as a purely academic field of research – something of value for physicists at universities, but not for engineers and companies. So perhaps the breakthrough of industrial quantum computing will be the next milestone in the history of electronics. Or perhaps this milestone will come from a totally unexpected angle – by combining knowledge and people from entirely different disciplines, creating totally new ideas and concepts.”

Author
Bethan Grylls

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