As process nodes shrink, random telegraph noise (RTN) and bias temperature instability (BTI) become dominant mechanisms for characteristic variation and reliability degradation. In an article on edn.com, Takuro Nishimura of Agilent Technologies takes a look at how scaled MOSFETs face critical issues, such as characteristic variation and reliability degradation. He discusses methods to set up a measurement apparatus, to explore RTN and BTI, and to solve characteristic variation and reliability degradation issues.
Characteristic variation can fall into several categories like global variation, local variation, systematic variation and random variation. Among them, random variation is a strong contributor to rapid yield loss by causing a significant drop in operating margin or a malfunction of the integrated circuit, which can occur even if each stand-alone device of a circuit works properly. Random dopant fluctuation (RDF) has been a dominant factor of random variation but studies now suggest that beyond the 20-nm process node, random RTN is the main contributor of random variation. Recent research indicates that RTN is related to the BTI, which causes reliability degradation.
In scaled MOSFETs, characteristic variations caused by RTN and BTI are recognized as significant factors to device-level and circuit-level functionality, and reliability degradation, but their measurement methods are not widely understood. This article introduces the phenomena of RTN and BTI, their measurement methods, and their challenges, along with tips for handling those challenges successfully.
The article then takes a deeper dive into random telegraph noise, bias temperature instability, circuit and process design, measuring RTN and BTI, low-current noise measurement, measurement challenges and know-how, and probe techniques.