E.D. Characterization - Low Voltage Hot Electrons

Hot carrier effects at low applied voltage

Present day low-voltage low-power circuits operate at supply voltages of 3.3V or less, comparable to the critical thresholds for injection over the Si-SiO2 energy barrier, and for impact ionization. As a consequence, additional energy gain mechanisms other than the potential drop inside the device are expected to turn on the substantial hot-carrier effects observed.

In this framework, the present research is aimed to study the role of these additional mechanisms (phonon absorption, electron-electron scattering, impact ionization feedback) by means of experiments and device simulations. The implications on the reliability of MOSFETs and non-volatile memory cells are also analyzed.

In particular, a thorough device characterization of gate and substrate currents, and photon emission at low voltages has been performed that revealed significantly different behaviors in channel and substrate injection conditions. The analysis of the results, supported by extensive Monte Carlo simulations, allowed a model to be developed for the substrate injection experiments. This model also revealed the severe limitations of the conventional lucky carrier model in explaining hot carriers at low voltages.

Low-voltage hot carrier induced soft-programming of scaled Flash memory cells has also been analysed to assess its impact on the reliability of these devices.

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