Critical Trap Density Research Articles

Breakdown and degradation of ultrathin Hf-based (HfO2)x(SiO2)1−x gate oxide films

Ultrathin films of hafnium oxide (HfO2) and hafnium silicate (HfO2)x(SiO2)1−x gate stacks (∼3nm) have been subjected to localized electrical stress with a conductive atomic force microscope (C-AFM) in ultrahigh vacuum. The nanoscale current-voltage (I-V) characteristics, prebreakdown temperature dependent I-V measurements on large area metal-insulator-semiconductor capacitors, postbreakdown (BD) topography, current maps, and AFM tip-surface contact force are used to interpret the progressive degradation of the oxide under electrical stress. For the pre-BD phase, trap-assisted tunneling and Fowler–Nordheim tunneling were found to be dominant current transport mechanisms in Hf-based gate stacks contributing to oxide leakage current. For the post-BD phase, an overall effect of barrier limited tunneling current on the charge propagation is confirmed and related to post-BD conductivity features observed by constant voltage scanning. A critical trap density required to trigger a BD event of the ultrathin (HfO2)x(SiO2)1−x∕SiO2 gate stacks is postulated.

Conductive atomic force microscopy studies of thin SiO2 layer degradation

The dielectric degradation of ultrathin (∼2nm) silicon dioxide (SiO2) layers has been investigated by constant and ramped voltage stresses with the conductive atomic force microscopy (CAFM). CAFM imaging shows clearly the lateral degradation propagation and its saturation. Current-voltage characteristics, performed at nanometer scale, show the trap creation rate in function of the stress condition. The critical trap density has been found.

Electron traps in organic light-emitting diodes

This work presents the effects of electron traps in organic light-emitting diodes using a model which includes charge injection, transport, and recombination. For electron-only devices, the electron current is reduced by the traps for several orders of magnitude at fixed voltage, and the traps strongly increase the transient time. For bipolar devices, due to negative trapped charges, traps enhance the hole current and the total current, opposite to the electron-only devices. The traps also make the recombination region close to the cathode. There is a voltage-dependent critical trap density beyond which the quantum efficiency decreases and transient time rises dramatically. The quantum efficiency is doubled if the hole traps are added to balance the electron and hole injections. Finally, the trap effect can be used in a bilayer light-emitting diode to make the emission color-tunable.

Impact of temperature and breakdown statistics on reliability predictions for ultrathin oxides

ABSTRACTThis paper discusses the evolution in the degradation and breakdown behaviour of ultra-thin oxides when scaling the oxide thickness into the sub-4 nm range for future CMOS technology generations. It will be shown that changes in the breakdown statistics, which can be explained by a percolation model for breakdown, lead to an increased area dependence of the time-tobreakdown. This has to be taken into account when predicting the oxide reliability. Also the impact of the test methodology, the relevance of a so-called polarity gap in the charge-tobreakdown and its consequences for reliability testing, are highlighted. Moreover, a strong increase in the temperature dependence of breakdown, especially for sub-3 nm oxides, is demonstrated and the impact of temperature on trap generation and critical trap density at breakdown is discussed. Finally it is shown that the combined effects of all these phenomena might lead to oxide reliability becoming a potential showstopper for further technology scaling.

Oxide and interface degradation and breakdown under medium and high field injection conditions: A correlation study

Oxide degradation and breakdown are studied using Substrate Hot Electron (SHE) and Fowler-Nordheim (FN) injection techniques. It is shown that the generation of electron traps during stress and breakdown are identical with both techniques and therefore SHE-injection can be used to study breakdown mechanisms at medium oxide fields that are not accessible with FN-injection. Breakdown is found to occur when a critical electron trap density is reached. In the high field range, it is shown that this critical trap density corresponds to a critical hole fluence, linking the models based on electron trap generation and on hole fluence together.

Impact of thermal NH3-nitridation on dielectric properties of ultrathin Sio2 films

The dielectric properties of rapid thermally NH/sub 3/-nitrided (RTN) ultrathin ( approximately=5 nm) SiO/sub 2/ films have been investigated. High-field endurance characteristics indicate that after Fowler-Nordheim electron injection, both the low-field leakage current and electron trap density increase. Moreover, the oxide leakage is strongly dependent on the NH/sub 3/-nitridation time. These results indicate that in ultrathin SiO/sub 2/ the oxide leakage is a result of trap-assisted tunnelling, leading to a breakdown event when a critical trap density is reached. >