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Conduction Mechanisms in Advanced MOS Technologies

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New materials for next-generation transistors

With current silicon-based transistors hitting a wall at around 14 nm, the semiconductor industry is currently on the search for new materials that can prolong Moore's law at smaller scales. An EU-funded project provided further insight into the strengths and limits of using group III-V semiconductors in future complementary metal oxide semiconductor (CMOS) technology.

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Over the last two decades, scaling silicon transistor dimensions has been powering the electronics revolution, with transistors reaching nanometre sizes. However, as CMOS continues to scale down beyond a certain point, reliability problems seem to scale up. To reach beyond the limits of silicon, new channel materials with high carrier velocities are required. With much higher electron mobility than silicon, group III-V semiconductor materials can be fashioned into smaller and faster transistors. Within CONAT (Conduction mechanisms in advanced MOS technologies), scientists significantly improved understanding of the conduction and degradation mechanisms of new transistor structures relying on the use of indium gallium arsenide (InGaAs) as a substrate. Defects and other reliability issues have hitherto prevented this compound semiconductor from making the leap to consumer products. The focus was on transistor structures made of an insulating oxide layer that sits on top of InGaAs, with the topmost layer being the metal gate. Scientists selected a high-κ dielectric to replace the commonly used gate oxide material silicon dioxide. Project results demonstrated that the defects related to the InGaAs substrate play a key role in the degradation characteristics of the transistor structure. In addition, scientists concluded that improvements in the high-κ dielectric/InGaAs interface do not necessarily increase reliability of the MOS structure. Another key area of study was the gate-oxide breakdown for which the CONAT team developed physical models to successfully simulate this failure mechanism in high-κ/III-V transistor structures. The team succeeded in controlling the breakdown growth rate of a number of gate dielectrics choosing a correct combination of voltage, thickness and thermal conductivity values. These efforts were aimed at significantly improving reliability of CMOS circuits. Through a spectroscopic technique, scientists investigated the post-breakdown characteristics of MOS structures consisting of different oxide-semiconductor interfaces. The differences observed in the aluminium oxide-InGaAs and silicon dioxide-silicon interface microstructures under positive and negative voltages were sufficiently explained. Project results and findings are driving a better understanding of degradation and breakdown mechanisms of III-V CMOS technology to continue meeting the demand for increasing transistor performance.


Transistors, silicon, III-V semiconductors, CMOS, electron mobility, indium gallium arsenide

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