Ever since the introduction of the metal-oxide-silicon field-effect-transistor (MOSFET), the nature of mobile and trapped charge in the oxide layer has been studied in great detail. For example, contamination with alkali ions such as sodium, causing instability of the flat-band voltage, was a major concern in the early days of MOS fabrication. Another SiO2 impurity of particular interest is hydrogen, because of its beneficial property of passivating charge traps. In this work we show that annealing of Si/SiO2/Si structures in forming gas (Ar:H2; 95:5) above 400 °C can introduce mobile H+ ions into the SiO2 layer. These mobile protons are confined within the oxide layer, and their space-charge distribution is well controllable and easily rearrangeable by applying a gate bias, making them potentially useful for application in a reliable nonvolatile MOSFET memory device. We present speed, retention, endurance, and radiation tolerance data showing that this non-volatile memory technology can be competitive with existing Si-based non-volatile memory technologies such as Flash.

The chemical kinetics of mobile-proton reactions in the SiO2 film are also analyzed in greater detail. Our data show that the initial buildup of mobile protons during hydrogen annealing is limited by the rate of lateral hydrogen diffusion into the buried SiO2 films. The final density of mobile protons is determined by the cooling rate which terminates the annealing process and, in the case of subsequent anneals, by the temperature of the final anneal. To explain the observations, we propose a dynamical equilibrium model. Based on these insights, the incorporation of the proton generation process into standard semiconductor process flows is discussed.

In this work we show that annealing of silicon/silicon‐dioxide/silicon structures in forming gas (N2:H2; 95:5) above 500°C leads to spontaneous incorporation of mobile H+ ions in the buried SiO2 layer. We demonstrate that, unlike the alkali ions feared as killer contaminants in the early days, the space charge distribution of these mobile protons within the buried oxide layer can be very well controlled and easily rearranged with relatively high speed at room temperature. The hysteresis in the flat band voltage shift provides a unique vehicle to study proton kinetics in silicon dioxide thin films. It is further shown how this effect has great potential as the basis for a reliable nonvolatile FET memory device that is expected to be competitive with state‐of‐the‐art Si‐based memory technologies. The power of this novel device is its simplicity; it requires few processing steps, all of which are standard in Si integrated‐circuit fabrication.

We review the processes and mechanisms by which voltage offsets occur in the hysteresis loop of ferroelectric materials. Simply stated, voltage shifts arise from nearinterfacial charge trapping in the ferroelectric. We show that the impetus behind voltage shifts in ferroelectric capacitors is the net polarization, with the net polarization being determined by the perovskite and the aligned defect-dipole components. Some common defect-dipoles in the PZT system are lead vacancy-oxygen vacancy complexes. One way to change the net polarization in the ferroelectric is to subject the PZT capacitor to a dc bias at elevated temperature; this process is spectroscopically shown to align defect-dipoles along the direction of the applied electric field. The alignment of defect-dipoles can strongly impact several material properties. One such impact is that it can lead to enhanced voltage shifts (imprint). It is proposed that the net polarization determines the spatial location of the asymmetrically trapped charge that are the cause for the voltage shifts. An enhanced polarization at one electrode interface can lead to larger voltage shifts since it lowers the electrostatic potential well for electron trapping, i.e., more electron trapping can occur. Defect-dipole alignment is also shown to increase the UV sensitivity of the ferroelectric.

We have performed electron spin resonance and electrical measurements on SiO2/Si structures subjected to anneals in 5% H2/N2 or 5% D2/N2 gases and subsequently injected with electrons using corona ions and ultra‐violet radiation. Threshold voltage and transconductance measurements have also been made on 0.25 μm metal‐oxide‐semiconductor transistors subjected to 400 °C anneals in the same gases and subsequently aged by hot electron injection. The electrical data on SiO2/Si structures indicates that the density of interface states increases as a result of electron injection but that there are only minor differences between H and D passivated interfaces. The data on Pb, trivalent Si dangling bond, centers at the same interfaces observed by electron spin resonance is insufficiently accurate to enable us to observe any significant differences. The hot electron injection experiments on transistors, consistent with other authors, indicate that, for the limited number of measurements we have made, the transistor ageing resulting from the generation of interface states is significantly reduced for devices annealed in the D containing gas as compared to those annealed in the H containing gas. The origins of some potential differences in annealing behaviour between the SiO2/Si structures and the 0.25 μm transistors are suggested.

We apply a number of complementary characterization techniques including electron paramagnetic resonance, optical absorption, and photoluminescence spectroscopies to characterize a wide range of different ZnO phosphor powders. We generally observe a good correlation between the 510-nm green emission intensity and the density of paramagnetic isolated oxygen vacancies. In addition, both quantities are found to peak at a free-carrier concentration ne, of about 1.4 × 1018 cm-3. We also find that the green emission intensity can be strongly influenced by free-carrier depletion at the particle surface, especially for small particles and/or low doping. Our data suggest that the green PL in ZnO phosphors is due to the recombination of electrons in singly occupied oxygen vacancies with photoexcited holes in the valence band.

Ab initio Hartree-Fock and second-order Möller-Plesset theory calculations have been performed to investigate the stability of triply-coordinated 0+ centers in the Si-O-Si network of amorphous SiO2. The calculations reveal that the H+ ion binds with a bridging O center to form a very stable (De > 6 eV) trivalent O complex. Capture of an electron by the positively charged protonated complex, however, is predicted to immediately lead to the dissociation of the O-H bond. A relatively weaker, but stable bond is also formed between the bridging O atom and a +SiH3 ion.

Low temperature electron spin resonance (ESR) measurements were carried out on a broad range of separation by implantation of oxygen (SIMOX) substrates. The post-implantation forming anneal (T 1325°C) was observed to induce a donor in the SIMOX structure, more specifically, a shallow effective mass donor in Si of axial symmetry and preferential alignment along [001], likely an oxygen-related heat-treatment donor. Controlled etching back experiments revealed that the donor defects reside in an interfacial Si layer of at least 600$$A thick at both sides of the buried oxide layer reaching a local volume density of about 1018 cm−3. In the flat band situation, the donor was observed to be in a diamagnetic, ESR non-active state. Downward sweeping of the Si energy bands near the buried oxide interfaces, relative to the Fermi level, either by in situ positive ate biasing of large area metal-oxide-silicon capacitors fabricated on the buried oxide or γ7-irradiation induced positive charging of the buried oxide, was observed to alter the ionization state of part of the donors into an ESR-active state.

Oxygen-vacancy defects (E') generated at the surface of buried SiO2 layers formed by O+ implantation during the separation by implantation of oxygen (SIMOX) process have been studied by electron spin resonance (ESR) at 4.2 K. The E' damage was generated during exposure to a dc Ar glow discharge that produces defects predominantly in a surface layer of ≈100 Å thick, reaching local volume densities at the surface up to 8 × 1019 cm−3. This glow discharge exposure, alternated with step-by-step etch back, allowed mapping of a defect generation sensitivity depth profile of the buried oxide (BOX) layer, revealing a fairly uniform sensitivity with a strong decline towards the BOX/substrate interface. Besides the usual E' γ signal, the E'δj center — a delocalized variant of the E' center — has been newly observed in the BOX. Reoxidation of the BOX was observed to reduce the E' sensitivity close to that of regular dry thermal oxide (≥ 29 times lower), while the E'γ signal could no longer be generated, again similar to conventional thermal oxide. These data suggest a revision of the model for the E' defect. In general, the results strongly suggest that the buried oxide contains excess Si, exceedingly so near the BOX/substrate interface.