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By introducing a thin non-stoichiometric CeO2-x switching layer between the high oxygen affinity metal TaN top electrode and the TiO2 layer in a TaN/CeO2-x/TiO2/Pt bilayer (BL) device, it is possible to enhance the endurance characteristics and overcome the reliability issue. Compared with a single layer device, a BL device significantly enhances the number of direct current overswitching cycles to >1.2 × 104, non-destructive retention (>104 s), and switching uniformity. A TaON interface layer is formed which served as a reservoir of oxygen ions (O2−) in the SET-process and acts as an O2− supplier to refill the oxygen vacancies in the RESET-process and so plays a key role in the formation and rupture of conductive filaments. This study demonstrates that simply introducing a thin non-stoichiometric CeO2-x switching layer into TiO2-based devices can facilitate the enhancement of the endurance property for future nonvolatile memory applications. [ABSTRACT FROM AUTHOR]

In this letter, we report the coexistence of unipolar and bipolar switching in a solution-based nanocrystalline spinel ferrite ZnFe2O4 thin film prepared by the sol-gel method. It is seen that the Au/ZnFe2O4/Pt device could be activated between unipolar and bipolar switching modes just by choosing RESET-voltage polarity. Conversions between unipolar to bipolar switching modes are reversible and controllable. The results show that the SET-voltage of unipolar switching is smaller than that of bipolar switching, while memory windows (ON/OFF ratio) are identical. Furthermore, filaments are induced by the migration of oxygen vacancies (VOs), which are responsible for reducing variations in SET voltages of unipolar switching. By analyzing the current transport conduction mechanism, the electrode-limited Schottky emission mechanism is dominated in the high field region. Temperature dependence of low and high resistance states indicates that conductive filaments are composed of VOs and metallic Zn atoms, involving Joule heating and electrochemical redox reaction effects. Investigation on coexisting both unipolar and bipolar switching modes in a single Au/ZnFe2O4/Pt memory cell would open a pathway for spinel ferrite based low-cost nonvolatile memory. [ABSTRACT FROM AUTHOR]

The threshold energy barrier for hydrogen desorption from the SiO[sub 2]-Si interface has been assumed to be the Si-H bond energy with the value of 3.6 eV. Based on the uniform Si-H bond energy and diffusion-limited degradation, the time-dependent hot-carrier degradation of metal-oxide-semiconductor (MOS) devices has been described by the so-called power law. In this letter, by investigating the degradation of submicron n-channel MOS devices at various stress conditions and over a large time scale (0.01-10000 s), we present experimental evidence that contradicts the uniform bond energy theory and supports the bond energy variation theory proposed recently by Hess and co-workers [Appl. Phys. Lett. 75, 3147 (1999); Physica B 272, 527 (1999)]. We find that, instead of a constant power factor of n=0.5 predicted by the uniform bond/diffusion-limited energy theory, n varies from ∼0.8 at the initial stress stage to ∼0.2 at the final stress stage consistent with the bond energy variation theory. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]