Showing papers by "Veena Misra published in 2004"

Optoelectronic devices having arrays of quantum-dot compound semiconductor superlattices therein

Abstract: Methods of forming a nano-scale electronic and optoelectronic devices include forming a substrate having a semiconductor layer therein and a substrate insulating layer on the semiconductor layer. An etching template having a first array of non-photolithographically defined nano-channels extending therethrough, is formed on the substrate insulating layer. This etching template may comprise an anodized metal oxide, such as an anodized aluminum oxide (AAO) thin film. The substrate insulating layer is then selectively etched to define a second array of nano-channels therein. This selective etching step preferably uses the etching template as an etching mask to transfer the first array of nano-channels to the underlying substrate insulating layer, which may be thinner than the etching template. An array of semiconductor nano-pillars is then formed in the second array of nano-channels. The semiconductor nano-pillars in the array may have an average diameter in a range between about 8 nm and about 50 nm. The semiconductor nano-pillars are also preferably homoepitaxial or heteroepitaxial with the semiconductor layer.

A capacitance-based methodology for work function extraction of metals on high-/spl kappa/

Abstract: This letter presents a methodology to accurately extract the work function of metal electrodes on high-/spl kappa/ dielectrics with various charge distributions. A mathematical analysis including sources of errors was used to study the effect of charge distribution in gate dielectric stacks on the flatband voltage of the device. The calculations are verified by experimental results obtained for Ru-Ta alloys on HfO/sub 2/ and SiO/sub 2/ gate dielectric stacks. It is shown that accounting for the appropriate charge model is imperative for accurate calculation of workfunction on high-/spl kappa//SiO/sub 2/ gate dielectric stacks.

Porphyrins Bearing Mono or Tripodal Benzylphosphonic Acid Tethers for Attachment to Oxide Surfaces

Abstract: The ability to attach redox-active molecules to oxide surfaces in controlled architectures (distance, orientation, packing density) is essential for the design of a variety of molecular-based information storage devices. We describe the synthesis of a series of redox-active molecules wherein each molecule bears a benzylphosphonic acid tether. The redox-active molecules include zinc porphyrins, a cobalt porphyrin, and a ferrocene-zinc porphyrin. An analogous tripodal tether has been prepared that is based on a tris[4-(dihydroxyphosphorylmethyl)phenyl]-derivatized methane. A zinc porphyrin is linked to the methane vertex by a 1,4-phenylene unit. The tripodal systems are designed to improve monolayer stability and ensure vertical orientation of the redox-active porphyrin on the electroactive surface. For comparison purposes, a zinc porphyrin bearing a hexylphosphonic acid tether also has been prepared. The synthetic approaches for introduction of the phosphonic acid group include derivatization of a bromoalk...

Porphyrins bearing arylphosphonic acid tethers for attachment to oxide surfaces.

Abstract: Synthetic molecules bearing phosphonic acid groups can be readily attached to oxide surfaces. As part of a program in molecular-based information storage, we have developed routes for the synthesis of diverse porphyrinic compounds bearing phenylphosphonic acid tethers. The routes enable (1) incorporation of masked phosphonic acid groups in precursors for use in the rational synthesis of porphyrinic compounds and (2) derivatization of porphyrins with masked phosphonic acid groups. The precursors include dipyrromethanes, monoacyldipyrromethanes, and diacyldipyrromethanes. The tert-butyl group has been used to mask the dihydroxyphosphoryl substituent. The di-tert-butyloxyphosphoryl unit is stable to the range of conditions employed in syntheses of porphyrins and multiporphyrin arrays yet can be deprotected under mild conditions (TMS-Cl/TEA or TMS-Br/TEA in refluxing CHCl3) that do not cause demetalation of zinc or magnesium porphyrins. The porphyrinic compounds that have been prepared include (1) A3B-, trans...

Porphyrin architectures tailored for studies of molecular information storage.

Abstract: A molecular approach to information storage employs redox-active molecules tethered to an electroactive surface. Zinc porphyrins tethered to Au(111) or Si(100) provide a benchmark for studies of information storage. Three sets of porphyrins have been synthesized for studies of the interplay of molecular design and charge-storage properties: (1) A set of porphyrins is described for probing the effect of surface attachment atom on electron-transfer kinetics. Each porphyrin bears a meso-CH2X group for surface attachment where X = OH, SAc, or SeAc. (2) A set of porphyrins is described for studying the effect of surface-charge density in monolayers. Each porphyrin bears a benzyl alcohol for surface attachment and three nonlinking meso substituents of a controlled degree of bulkiness. (3) A set of porphyrins is described that enables investigation of on-chip patterning of the electrolyte. Each porphyrin bears a formyl group distal to the surface attachment group for subsequent derivatization with a molecular entity that comprises the electrolyte. Taken together, this collection of molecules enables a variety of studies to elucidate design issues in molecular-based information storage.

Synthesis of porphyrins bearing hydrocarbon tethers and facile covalent attachment to si(100).

Abstract: The use of redox-active molecules as the active storage elements in memory chips requires the ability to attach the molecules to an electroactive surface in a reliable and robust manner. To explore the use of porphyrins tethered to silicon via carbosilane linkages, 17 porphyrins have been synthesized. Fourteen porphyrins bear a tether at a single meso site, and three porphyrins bear functional groups at two β sites for possible two-point attachment. Two high-temperature processing methods (400 °C under inert atmosphere) have been developed for rapid (minutes), facile covalent attachment to Si platforms. The high-temperature processing conditions afford attachment either by direct deposition of a dilute solution (1 μM−1 mM) of the porphyrin sample onto the Si substrate or sublimation of a neat sample onto the Si substrate. The availability of this diverse collection of porphyrins enables an in-depth examination of the effects of the tether (length, composition, terminal functional group, number of tethers)...

Multiple-bit storage properties of porphyrin monolayers on SiO2

Abstract: Hybrid molecule-silicon capacitors have been fabricated by the self-assembly of a monolayer of porphyrin molecules on a silicon oxide surface. The porphyrin employed [5-(4-dihydroxyphosphorylphenyl)-10,15,20-trimesitylporphinatozinc(II)] attaches to silicon oxide via a phosphonate linkage. Cyclic voltammetry current and capacitance/conductance measurements have been used to characterize the capacitors. The presence of multiple distinct peaks in current density and capacitance/conductance measurements are associated with oxidation and reduction of the molecular monolayer. The charge-storage states of the capacitor indicate applicability for use in multiple-bit memory devices.

In situ patterning of electrolyte for molecular information storage devices

Abstract: This invention pertains to methods assembly of organic molecules and electrolytes in hybrid electronic. In one embodiment, a is provided that involves contacting a surface/electrode with a compound if formula: R-L2-M-L1-Z1 where Z1 is a surface attachment group; L1and L2 are independently linker or covalent bonds; M is an information storage molecule; and R is a protected or unprotected reactive site or group; where the contacting results in attachment of the redox-active moiety to the surface via the surface attachment group; and ii) contacting the surface-attached information storage molecule with an electrolyte having the formula: J-Q where J is a charged moiety (e.g., an electrolyte); and Q is a reactive group that is reactive with the reactive group (R) and attaches J to the information storage molecule thereby patterning the electrolyte on the surface.

High-temperature attachment of organic molecules to substrates

Abstract: This invention provides a new procedure for attaching molecules to semiconductor surfaces, in particular silicon. The molecules, which include, but are not limited to porphyrins and ferrocenes, have been previously shown to be attractive candidates for molecular-based information storage. The new attachment procedure is simple, can be completed in short times, requires minimal amounts of material, is compatible with diverse molecular functional groups, and in some instances affords unprecedented attachment motifs. These features greatly enhance the integration of the molecular materials into the processing steps that are needed to create hybrid molecular/semiconductor information storage devices.

Stability of Ru- and Ta-based metal gate electrodes in contact with dielectrics for Si-CMOS

Abstract: The Ru-Ta-Si-O, Ta-Si-N-O, and Ru-Ta-Zr-O phase diagrams are important for predicting reactions at interfaces between SiO2 and ZrO2 gate dielectrics and novel Ru and Ta-based metal gate electrodes. Simplified quaternary phase diagrams of the Ru-Ta-Si-O, Ta-Si-N-O, and Ru-Ta-Zr-O systems at 900 degreesC were constructed from known and estimated Gibbs free energy data, respectively. Ru is predicted to be stable in contact with ZrO2 and SiO2, whereas Ta is not stable in contact with SiO2 at temperatures around 900 degreesC. Stoichiometric RuTa and TaN compounds were estimated to be stable in contact with both dielectrics at 900 degreesC. Experimental observations of gate electrode/dielectric interfaces are discussed. They are consistent with the thermodynamic predictions within the limitations of these phase diagrams. Metastable phases, often found in TaN, films, and diffusion of species from the vapor (e.g., oxygen), in particular along grain boundaries in columnar gate electrodes, may lead to reactions not predicted by the equilibrium phase diagrams. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Characteristics of TaSixNy thin films as gate electrodes for dual gate Si-complementary metal-oxide-semiconductor devices

Abstract: Reactively sputtered TaSixNy films have been investigated as gate electrodes for dual gate Si-complementary metal-oxide-semiconductor devices. The as-deposited TaSixNy films were amorphous over a wide range of compositions. After annealing at 1000 °C, Ta30Si33N37 film became crystalline, however Ta26Si28N52 film remained amorphous. The x-ray photoelectron spectroscopy shows a significant increase of Si–N bonding in the TaSixNy films with increasing N content. The presence of Si–N bonds is attributed to cause the amorphous nature of the high N containing TaSixNy films. The work functions of TaSixNy films were extracted by capacitance–voltage analysis. The work function values for TaSixNy films with varying N contents range from 4.26 to 4.35 eV after forming gas annealing at 400 °C for 30 min, suggesting that TaSixNy films have work functions appropriate for n-type metal-oxide-semiconductor devices. However, it was observed, after 1000 °C anneals, that the work function of TaSixNy films increased to ∼4.8 eV...

Evaluation of Fermi level pinning in low, midgap and high workfunction metal gate electrodes on ALD and MOCVD HfO/sub 2/ under high temperature exposure

Abstract: The workfunction behavior and stability of several candidate metal gate electrodes on HfO/sub 2/ was carefully examined and correlated with processing parameters such as anneal temperatures and oxygen exposures. Transition metals and their nitrides, binary metal alloys and refractory metals were studied on MOCVD HfO/sub 2/ dielectrics of varying thicknesses. Binary low work function Mo-Ta alloys were also investigated on HfO/sub 2/.

Modulation of drain current by redox-active molecules incorporated in Si MOSFETs

Abstract: Redox-active molecular monolayers were incorporated in MOSFETs to modulate the device characteristics. The discrete molecular states were manifested in the drain current characteristics indicating the presence of distinct energy levels at room temperature.

Porphyrins Bearing Mono or Tripodal Benzylphosphonic Acid Tethers for Attachment to Oxide Surfaces.

Abstract: The ability to attach redox-active molecules to oxide surfaces in controlled architectures (distance, orientation, packing density) is essential for the design of a variety of molecular-based information storage devices. We describe the synthesis of a series of redox-active molecules wherein each molecule bears a benzylphosphonic acid tether. The redox-active molecules include zinc porphyrins, a cobalt porphyrin, and a ferrocene-zinc porphyrin. An analogous tripodal tether has been prepared that is based on a tris[4-(dihydroxyphosphorylmethyl)phenyl]-derivatized methane. A zinc porphyrin is linked to the methane vertex by a 1,4-phenylene unit. The tripodal systems are designed to improve monolayer stability and ensure vertical orientation of the redox-active porphyrin on the electroactive surface. For comparison purposes, a zinc porphyrin bearing a hexylphosphonic acid tether also has been prepared. The synthetic approaches for introduction of the phosphonic acid group include derivatization of a bromoalk...

Effects of barrier height (/spl Phi//sub B/) and the nature of bi-layer structure on the reliability of high-k dielectrics with dual metal gate (Ru & Ru-Ta alloy) technology

Abstract: In this work, we present the effects of barrier height on the reliability of HfO/sub 2/ with dual metal gate technology in terms of Weibull slope, soft breakdown characteristics, defect generation rate, critical defect density and charge-to-breakdown. It was found that the lower Weibull slope of high-k dielectrics (compared to SiO/sub 2/) is partially attributed to the lower barrier height of high-k dielectrics which in turn results in larger current increase. Thus, defect generation rate increases and charge-to-break down decreases, while critical defect density remains constant. In addition, it has been found that there is distinct bi-modal defect generation rate for high-k/SiO/sub 2/ stack. Two-step breakdown process was clearly observed; and Weibull slope of soft breakdown (1/sup st/ breakdown) shows lower /spl beta/ value compared to that of hard breakdown (2/sup nd/ breakdown). Soft breakdown characteristics were dependent on the barrier heights. The bi-modal defect generations are believed to be resulted from the breakdown in interface and bulk layer.

Effects of gate electrodes and barrier heights on the breakdown characteristics and Weibull slopes of HfO/sub 2/ MOS devices

Abstract: In this work, we present the effect of gate electrodes and barrier heights on the breakdown characteristics and Weibull slopes of HfO/sub 2/ MOS devices. Higher Weibull slope (/spl beta/) of Ru gate electrode has been observed when compared that of Ru-Ta alloy. The higher /spl beta/ in Ru devices is due to smaller charge fluence which results from relatively higher barrier height. Varying SiO/sub 2/ and HfO/sub 2/ were investigated in order to understand ultra-thin HfO/sub 2/ gate stack structure. We found that there is bi-modal defect generation rate on High-k/SiO/sub 2/ stack. Two-steps breakdown process was clearly observed and Weibull slope of soft breakdown (1st breakdown) shows lower /spl beta/ value compared to that of hard breakdown (2/sup nd/ breakdown). Soft breakdown characteristics were dependent on the barrier heights. The bi-modal defect generations are believed to be resulted from the breakdown in interface and bulk layer. Weibull slope of high-k gate stacks is a strong function of the inter-face layer thickness and the barrier height by gate electrode workfunction, whereas it is a weak function of high-k layer thickness.

Porphyrins Bearing Arylphosphonic Acid Tethers for Attachment to Oxide Surfaces.

Abstract: Synthetic molecules bearing phosphonic acid groups can be readily attached to oxide surfaces. As part of a program in molecular-based information storage, we have developed routes for the synthesis of diverse porphyrinic compounds bearing phenylphosphonic acid tethers. The routes enable (1) incorporation of masked phosphonic acid groups in precursors for use in the rational synthesis of porphyrinic compounds and (2) derivatization of porphyrins with masked phosphonic acid groups. The precursors include dipyrromethanes, monoacyldipyrromethanes, and diacyldipyrromethanes. The tert-butyl group has been used to mask the dihydroxyphosphoryl substituent. The di-tert-butyloxyphosphoryl unit is stable to the range of conditions employed in syntheses of porphyrins and multiporphyrin arrays yet can be deprotected under mild conditions (TMS-Cl/TEA or TMS-Br/TEA in refluxing CHCl3) that do not cause demetalation of zinc or magnesium porphyrins. The porphyrinic compounds that have been prepared include (1) A3B-, trans...