Anomalous random telegraph noise in nanoscale transistors as direct evidence of two metastable states of oxide traps

Shaofeng Guo,Dongyuan Mao,Ru Huang,Yangyuan Wang,Runsheng Wang

doi:10.1038/s41598-017-06467-7

Shaofeng Guo, Dongyuan Mao + Show 3 more

Open Access

https://doi.org/10.1038/s41598-017-06467-7

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Abstract

In this paper, a new pattern of anomalous random telegraph noise (RTN), named “reversal RTN” (rRTN) induced by single oxide trap, is observed in the drain current of nanoscale metal-oxide-semiconductor field-effect transistors (MOSFETs) with high-k gate dielectrics. Under each gate voltage, the rRTN data exhibit two zones with identical amplitudes but reversal time constants. This abnormal switching behavior can be explained by the theory of complete 4-state trap model (with two stable states and two metastable states), rather than the simple 2-state or improved 3-state trap model. The results provide a direct experimental evidence of the existence of two metastable states in a single oxide trap, contributing to the comprehensive understanding of trap-related reliability and variability issues in nanoscale transistors.

Highlights

With the metal-oxide-semiconductor field-effect transistor (MOSFET) dimension downscaling, oxide traps in the gate dielectric have drawn much attention due to their serious impacts on the device reliability and variability[1,2,3,4,5,6,7,8,9,10,11]
Devices characterized in this work are planar high-k/metal-gate n-type MOSFETs with length L = 60 nm, width W = 300 nm and ultra-thin HfO2 gate dielectrics
The experimental results of the anomalous random telegraph noise (RTN) in drain current under different gate voltages VG are shown in Fig. 2, with the drain voltage kept at VD = 50 mV, and temperature T = 25 °C

Summary

Experimental Results

The expanded detail shows that the capture time constant is smaller than the emission time constant in zone A, while it has the reversal feature in zone B. It is named “reversal RTN” (rRTN) here. The RTN induced by N traps in a single device should be corresponding to 2N current levels. The time constants τc and τe in each zone are extracted as shown, and the extraction details are shown in Fig. S2 of the supplementary materials. Both τc and τe in two zones have the similar VG dependence, respectively.

Discussions on Physical Mechanism

Conclusion

Author Contributions

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