Chapter 4
Elastic Tunneling Model

It was long believed that NBTI is controlled by the creation of interface dangling bonds as it is the case in numerous variants of the reaction-diffusion and the reaction-limited models. With time, more and more authors[2370] considered trapped oxide charges as a possible cause for NBTI. One of the simplest trapping models has been proposed by Yang et al. [70]. It rests on the assumption that the capture and emission time constants follow certain distributions. Even tough these distributions have been introduced in an ‘ad hoc’ manner and do not rely on any physical profound explanation, the basic concept is still present in each charge trapping model. Therefore, this phenomenological model will be briefly discussed in this chapter.

Tewksbury[23] explained charge trapping as an elastic tunneling process of substrate charge carriers into and out of oxide defects and ascribed the distribution of time constant to a wide range of trap depths. For an evaluation against experiments, his model has been implemented in a device simulator and tested whether it is consistent with the list of experimental findings presented in Section 1.4. In these investigations, a special focus has been put on the temperature dependence of charge trapping, which requires the consideration of quantization effects in the inversion layer. Since the oxide thickness has been reduced to a few nanometers, the model has also been extended to consider charge trapping from and to the gate contact.

 4.1 A Phenomenological Trapping Model
 4.2 Elastic Tunneling
  4.2.1 The Behavior of A Single Trap
  4.2.2 Spatially and Energetically Distributed Traps
  4.2.3 Time Behavior during Stress
  4.2.4 Time Range of Trapping
  4.2.5 Oxide Field Dependence
  4.2.6 Time Behavior during Relaxation
  4.2.7 Investigation of the Temperature Dependence using a Quantum Refinement
  4.2.8 Charge Injection from the Gate
  4.2.9 Width of the Trap Band
 4.3 Conclusion