Joseph Shappir

Trap generation and occupation dynamics in SiO2 under charge injection stress

The effect of enduring charge injection on the physical properties of the SiO2 layer of a metal‐oxide‐semiconductor structure is studied by means of a novel characterization method. It is based on the observation reported previously, that under charge injection conditions the density of occupied oxide traps reaches a value which is only a fraction of the total trap density. This trap occupation level is strongly dependent on the oxide electric field. The oxide trap density can be evaluated by measuring this field dependence, using a relatively small amount of charge injection. This method is used to distinguish between the process of trap generation and electron trapping in the generated traps, under conditions of continuous charge injection up to levels of more than 50 C/cm2. The trap generation rate is found to be proportional to the flux of the injected charge, and to increase exponentially with the oxide electric field. At high oxide field only a small fraction of the newly generated traps are occupie...

Locally Oxidized Silicon Surface-Plasmon Schottky Detector for Telecom Regime

We experimentally demonstrate an on-chip nanoscale silicon surface-plasmon Schottky photodetector based on internal photoemission process and operating at telecom wavelengths. The device is fabricated using a self-aligned approach of local-oxidation of silicon (LOCOS) on silicon on insulator substrate, which provides compatibility with standard complementary metal-oxide semiconductor technology and enables the realization of the photodetector and low-loss bus photonic waveguide at the same fabrication step. Additionally, LOCOS technique allows avoiding lateral misalignment between the silicon surface and the metal layer to form a nanoscale Schottky contact. The fabricated devices showed enhanced detection capability for shorter wavelengths that is attributed to increased probability of the internal photoemission process. We found the responsivity of the nanodetector to be 0.25 and 13.3 mA/W for incident optical wavelengths of 1.55 and 1.31 μm, respectively. The presented device can be integrated with other nanophotonic and nanoplasmonic structures for the realization of monolithic opto-electronic circuitry on-chip.

Analysis and modeling of floating-gate EEPROM cells

Floating-gate MOS devices using thin tunnel oxide are becoming an acceptable standard in electrically erasable nonvolatile memory. Theoretical and experimental analysis of WRITE/ERASE characteristics for this type of memory cell are presented. A simplified device model is given based on the concept of coupling ratios. The WRITE operation is adequately represented by the simplified model. The ERASE operation is complicated due to formation of depletion layers in the transistors channel and under the tunnel oxide. Experimental investigation of these effects is described, and they are included in a detailed cell model. In certain cell structures, a hole current can flow from the drain into the substrate during the ERASE oepration. This effect is shown to be associated with positive charge trapping in the tunnel oxide and threshold window opening. An experimental investigation of these phenomena is described, and a recommendation is made to avoid them by an appropriate cell design.

Dynamic model of trapping‐detrapping in SiO2

The field and time dependence of charge carriers trapping under different charge injection conditions, is studied in this work, using the dc hot electron injection technique. It is shown that the trapping characteristics converge to field‐dependent quasisaturation values. Variation of the trapping levels, due to change of the oxide field magnitude, are obtained in both directions and exhibit complete reversibility. These results, which cannot be explained by the first‐order conventional trapping model, are consistent with a dynamic trapping‐detrapping model. According to this model, quasisaturation of trapping characteristics is obtained when the trapping and detrapping processes are balanced. The occupation of the traps under steady‐state conditions is therefore field dependent. The same model also describes the generation of positive charge under high‐field injection conditions. This phenomenon is shown to be related to ionization of localized states in the SiO2 forbidden gap. The implications of the dy...

High‐field and current‐induced positive charge in thermal SiO2 layers

The generation of a bulk positive charge in SiO2 layers of silicon gate metal‐oxide‐silicon (MOS) devices, under the conditions of high‐field and charge injection is studied. The time dependence of the positive charge and its spatial distribution as a function of the oxide thickness and electric field are all consistent with an impact ionization‐recombination model which takes into account both the spatial and the field dependence of the ionization probability. The nature of the ionization, either band‐to‐band, or traps ionization, is still unknown. Bulk positive charge of the same nature is also formed in Al gate oxides. Nevertheless, it was not always observed in previous works since a much larger Si‐SiO2 interfacial positive charge is also generated in these samples.

High field current induced‐positive charge transients in SiO2

The formation of bulk positive charge in SiO2 induced by charge injection and high field conditions is studied in this work, utilizing new experimental methods. Using a dc hot electron injection technique it is shown that the presence of electrons in the SiO2 conduction band is a necessary condition for the positive charge formation. This result rules out field (only) induced mechanisms as possible explanations of high field positive charge generation in SiO2. The positive charge formation and annihilation are found to be governed by the same rate equation, and, therefore, exhibit similar behavior as a function of time. This behavior is consistent with an impact ionization‐recombination model, with a recombination cross section σ=2×10−16 cm2 and ionization rate α which is in agreement with previous published values. However, other collision activated mechanisms cannot be ruled out.

Spine-shaped gold protrusions improve the adherence and electrical coupling of neurons with the surface of micro-electronic devices

Interfacing neurons with micro- and nano-electronic devices has been a subject of intense study over the last decade. One of the major problems in assembling efficient neuro-electronic hybrid systems is the weak electrical coupling between the components. This is mainly attributed to the fundamental property of living cells to form and maintain an extracellular cleft between the plasma membrane and any substrate to which they adhere. This cleft shunts the current generated by propagating action potentials and thus reduces the signal-to-noise ratio. Reducing the cleft thickness, and thereby increasing the seal resistance formed between the neurons and the sensing surface, is thus a challenge and could improve the electrical coupling coefficient. Using electron microscopic analysis and field potential recordings, we examined here the use of gold micro-structures that mimic dendritic spines in their shape and dimensions to improve the adhesion and electrical coupling between neurons and micro-electronic devices. We found that neurons cultured on a gold-spine matrix, functionalized by a cysteine-terminated peptide with a number of RGD repeats, readily engulf the spines, forming tight apposition. The recorded field potentials of cultured Aplysia neurons are significantly larger using gold-spine electrodes in comparison with flat electrodes.

Waveguide based compact silicon Schottky photodetector with enhanced responsivity in the telecom spectral band

We experimentally demonstrate an on-chip compact and simple to fabricate silicon Schottky photodetector for telecom wavelengths operating on the basis of internal photoemission process. The device is realized using CMOS compatible approach of local-oxidation of silicon, which enables the realization of the photodetector and low-loss bus photonic waveguide at the same fabrication step. The photodetector demonstrates enhanced internal responsivity of 12.5mA/W for operation wavelength of 1.55µm corresponding to an internal quantum efficiency of 1%, about two orders of magnitude higher than our previously demonstrated results [22]. We attribute this improved detection efficiency to the presence of surface roughness at the boundary between the materials forming the Schottky contact. The combination of enhanced quantum efficiency together with a simple fabrication process provides a promising platform for the realization of all silicon photodetectors and their integration with other nanophotonic and nanoplasmonic structures towards the construction of monolithic silicon opto-electronic circuitry on-chip.

Investigation of MOS capacitors with thin ZrO 2 layers and various gate materials for advanced DRAM applications

Thin ZrO2layers were used to realize MOS capacitors with aluminum, polysilicon, and molybdenum gate electrodes. The layers, 300-600 Å in thickness, were obtained by metal organic chemical vapor deposition. The effects of various high-temperature treatments as well as gate material deposition conditions on the MOS capacitor properties were studied. Processing conditions compatible with standard silicon technology were established to obtain capacitors suitable for advanced DRAM application. Relative dielectric constant ∈ ≥ 16, breakdown fieldE_{B} \ge 3MV/cm, and leakage currents at applied voltage of 5V around 10-8A/cm2enable the realization of capacitors with dielectric layer equivalent to 35 Å of SiO2.

A model for silicon‐oxide breakdown under high field and current stress

A recently developed self‐consistent model for gate‐oxide degradation due to charge injection, described in a companion paper, is expanded to include electrical ‘‘wear out’’ breakdown. In the present work, gate‐oxide breakdown is defined to occur when the density of generated neutral trapping sites reaches a critical threshold value at the anode. Breakdown experimental results obtained under constant tunneling current are treated and simulated. The new model deals successfully with oxide breakdown dependence on: injection history, gate‐oxide thickness, charge‐injection current density, injection polarity reversal, gate electrode material, and oxide anneal temperatures.