A new model for the discharge behaviour of metal-nitride-oxide-silicon (MNOS) non-volatile memory devices

A new model is presented for the discharge mechanism of MNOS memory devices. For moderate and large charge contents the discharging effect can actually be ascribed to the compensation of the stored charge by the injection from the silicon into the nitride of carriers of the opposite type.     

Towards an understanding and control of cavitation activity in 1 MHz ultrasound fields

Various industrial processes such as sonochemical processing and ultrasonic cleaning strongly rely on the phenomenon of acoustic cavitation. As the occurrence of acoustic cavitation is incorporating a multitude of interdependent effects, the amount of cavitation activity in a vessel is strongly depending on the ultrasonic process conditions. It is therefore crucial to quantify cavitation activity as a function of the process parameters. At 1 MHz, the active cavitation bubbles are so small that it is becoming difficult to observe them in a direct way. Hence, another metrology based on secondary effects of acoustic cavitation is more suitable to study cavitation activity. In this paper we present a detailed analysis of acoustic cavitation phenomena at 1 MHz ultrasound by means of time-resolved measurements of sonoluminescence, cavitation noise, and synchronized high-speed stroboscopic Schlieren imaging. It is shown that a correlation exists between sonoluminescence, and the ultraharmonic and broadband signals extracted from the cavitation noise spectra. The signals can be utilized to characterize different regimes of cavitation activity at different acoustic power densities. When cavitation activity sets on, the aforementioned signals correlate to fluctuations in the Schlieren contrast as well as the number of nucleated bubbles extracted from the Schlieren Images. This additionally proves that signals extracted from cavitation noise spectra truly represent a measure for cavitation activity. The cyclic behavior of cavitation activity is investigated and related to the evolution of the bubble populations in the ultrasonic tank. It is shown that cavitation activity is strongly linked to the occurrence of fast-moving bubbles. The origin of this “bubble streamers” is investigated and their role in the initialization and propagation of cavitation activity throughout the sonicated liquid is discussed. Finally, it is shown that bubble activity can be stabilized and enhanced by the use of pulsed ultrasound by conserving and recycling active bubbles between subsequent pulsing cycles.     

Band alignment at the interfaces of Al2O3 and ZrO2-based insulators with metals and Si

Internal photoemission of electrons was used to determine the band alignment in metal (Mg, Al, Ni, Cu, Au)-oxide-silicon structures with Al₂O₃- and ZrO₂-based insulators. For Al₂O₃- and ZrO₂ layers grown on Si by atomic layer deposition the barrier height between the Si valence band and the oxide conduction band was found to be 3.25 and 3.1 eV, respectively. Thermal oxidation of the Si/oxide stacks results in a barrier height increase to ≈4 eV for both cases due to formation of a silicate interlayer. However, there is a significant sub-threshold electron emission both from silicon and metals, indicating a high density of states in the band gap of the insulators. These states largely determine the electron transport across metal oxides and may also account for a significant dipole component of the potential barrier at the metal/ZrO₂ and metal/Al₂O₃ interfaces.     

Spectrophotometric determination of the first protonation constant of orthovanadate

The first protonation constant for VO(3-)(4) has been determined spectrophotometrically at 25 degrees in 1M sodium chloride and found to have the value log K = 13.29 +/- 0.01. Individual absorption spectra for VO(3-)(4) and HVO(2-)(4) have been calculated (for the range 218-350 nm) from experimental absorbance measurements.     

The statistics of dielectric breakdown in MOS capacitors under static and dynamic voltage stress

The statistics of dielectric breakdown at fields 8 MV/cm has been studied under both static (constant voltage) and dynamic (ramped voltage) conditions. MOS capacitors of the same size and from the same wafer were used for all measurements. Data from both types of test conformed to a Weibull distribution. The Weibull parameters a and b, which determine the time and field dependence of breakdown, were calculated from static tests at various applied fields and independently from dynamic tests at various ramp-rates. The values of a and b were: a 0.24; b 6.89 and a 0.34; b 6.55, from static and dynamic tests respectively. The similarity of the values for the two pairs of Weibull parameters suggests that breakdown proceeds by the same mechanism in both types of test.