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Author

Alessandro C. Callegari

Other affiliations: GlobalFoundries
Bio: Alessandro C. Callegari is an academic researcher from IBM. The author has contributed to research in topics: Layer (electronics) & High-κ dielectric. The author has an hindex of 35, co-authored 130 publications receiving 5750 citations. Previous affiliations of Alessandro C. Callegari include GlobalFoundries.


Papers
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Journal ArticleDOI
05 Feb 1999-Science
TL;DR: An all-room-temperature fabrication process sequence was used, which enabled the demonstration of high-performance organic IGFETs on transparent plastic substrates, at low operating voltages for organic devices.
Abstract: The gate bias dependence of the field-effect mobility in pentacene-based insulated gate field-effect transistors (IGFETs) was interpreted on the basis of the interaction of charge carriers with localized trap levels in the band gap. This understanding was used to design and fabricate IGFETs with mobility of more than 0.3 square centimeter per volt per second and current modulation of 10 5 , with the use of amorphous metal oxide gate insulators. These values were obtained at operating voltage ranges as low as 5 volts, which are much smaller than previously reported results. An all-room-temperature fabrication process sequence was used, which enabled the demonstration of high-performance organic IGFETs on transparent plastic substrates, at low operating voltages for organic devices.

822 citations

Journal ArticleDOI
TL;DR: In this paper, an experimental and modeling study of charge trapping related threshold voltage shifts in Al2O3 and HfO2 n-type field effect transistors (nFET) is reported.
Abstract: An experimental and modeling study of charge trapping related threshold voltage shifts in Al2O3 and HfO2 n-type field effect transistors (nFET) is reported. The dependence of threshold voltage, subthreshold slope, and gate leakage currents on stressing time and injected charge carrier density are investigated as a function positive bias stress voltage and temperature. Based on experimental data, a model for trapping of charges in the existing traps is developed. The model is similar to SiO2 charge trapping models with one exception. Unlike SiO2 models, the model assumes a continuous distribution in trapping capture cross sections. The model predicts that threshold voltage would increase with a power law dependence on stressing time and injected charge carrier density (Ninj) in the initial stages of stressing. The model calculates threshold voltage shifts as a function of stress time and Ninj, thereby provides estimates of threshold voltage shifts after 10 years lifetime. It also provides insights into the...

300 citations

Journal ArticleDOI
22 Jun 2001-Science
TL;DR: This work uses near-edge x-ray absorption fine structure (NEXAFS) spectroscopy to link the orientational bond order at three carbonaceous surfaces with the direction of liquid crystal (LC) alignment on these surfaces, showing that LC alignment can be created on any carbonaceous substrate by inducing orientational order at its surface.
Abstract: We used near-edge x-ray absorption fine structure (NEXAFS) spectroscopy to link the orientational bond order at three carbonaceous surfaces-rubbed polyimide, ion beam-irradiated polyimide, and ion beam-irradiated diamondlike carbon films-with the direction of liquid crystal (LC) alignment on these surfaces. We show that, in general, LC alignment can be created on any carbonaceous substrate by inducing orientational order at its surface. Our results form the scientific basis for LC alignment layers consisting of amorphous carbon films in which orientational order near the surface is induced by a directional low-energy ion beam.

288 citations

Journal ArticleDOI
TL;DR: Hafnium oxides and hafnium silicate films were investigated as a possible replacement for the SiO2 gate dielectric in this article, where they were formed by reactive sputtering from a single Hf oxide target in a predominantly oxygen atmosphere.
Abstract: Hafnium oxides and hafnium silicate films were investigated as a possible replacement for the SiO2 gate dielectric. Hafnium oxide films were formed by reactive sputtering from a single Hf oxide target in a predominantly Ar atmosphere containing small additions of oxygen. Hafnium silicates were made by adding a He-diluted silane gas for Si incorporation. By changing the silane gas flow, different Si atomic concentrations were incorporated into the Hf oxide films. Depositions were performed with the substrate held at temperatures of 22 °C and 500 °C. The chemical composition of the films was determined with nuclear techniques. Optical reflectivity was used to measure the optical band gap. The film morphology was investigated by transmission electron microscopy (TEM) and the electrical properties were measured with capacitance–voltage and current–voltage measurements using aluminum gate capacitors. TEM and electrical measurement showed that a SiO2 interfacial layer of about 3 nm formed at the Si interface du...

270 citations

Patent
09 Jul 1998
TL;DR: In this paper, a method to achieve a very low effective dielectric constant in high performance back end of the line chip interconnect wiring and the resulting multilayer structure are disclosed.
Abstract: A method to achieve a very low effective dielectric constant in high performance back end of the line chip interconnect wiring and the resulting multilayer structure are disclosed. The process involves fabricating the multilayer interconnect wiring structure by methods and materials currently known in the state of the art of semiconductor processing; removing the intralevel dielectric between the adjacent metal features by a suitable etching process; applying a thin passivation coating over the exposed etched structure; annealing the etched structure to remove plasma damage; laminating an insulating cover layer to the top surface of the passivated metal features; optionally depositing an insulating environmental barrier layer on top of the cover layer; etching vias in the environmental barrier layer, cover layer and the thin passivation layer for terminal pad contacts; and completing the device by fabricating terminal input/output pads. The method obviates issues such as processability and thermal stability associated with low dielectric constant materials by avoiding their use. Since air, which has the lowest dielectric constant, is used as the intralevel dielectric the structure created by this method would possess a very low capacitance and hence fast propagation speeds. Such structure is ideally suitable for high density interconnects required in high performance microelectronic device chips.

232 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the authors present new insight into conduction mechanisms and performance characteristics, as well as opportunities for modeling properties of organic thin-film transistors (OTFTs) and discuss progress in the growing field of n-type OTFTs.
Abstract: Organic thin-film transistors (OTFTs) have lived to see great improvements in recent years. This review presents new insight into conduction mechanisms and performance characteristics, as well as opportunities for modeling properties of OTFTs. The shifted focus in research from novel chemical structures to fabrication technologies that optimize morphology and structural order is underscored by chapters on vacuum-deposited and solution-processed organic semiconducting films. Finally, progress in the growing field of the n-type OTFTs is discussed in ample detail. The Figure, showing a pentacene film edge on SiO2, illustrates the morphology issue.

4,804 citations

Journal ArticleDOI
TL;DR: Electronic Coupling in Oligoacene Derivatives: Factors Influencing Charge Mobility, and the Energy-Splitting-in-Dimer Method 3.1.
Abstract: 2.2. Materials 929 2.3. Factors Influencing Charge Mobility 931 2.3.1. Molecular Packing 931 2.3.2. Disorder 932 2.3.3. Temperature 933 2.3.4. Electric Field 934 2.3.5. Impurities 934 2.3.6. Pressure 934 2.3.7. Charge-Carrier Density 934 2.3.8. Size/molecular Weight 935 3. The Charge-Transport Parameters 935 3.1. Electronic Coupling 936 3.1.1. The Energy-Splitting-in-Dimer Method 936 3.1.2. The Orthogonality Issue 937 3.1.3. Impact of the Site Energy 937 3.1.4. Electronic Coupling in Oligoacene Derivatives 938

3,635 citations

Journal ArticleDOI
05 Feb 2009-Nature
TL;DR: A highly soluble and printable n-channel polymer exhibiting unprecedented OTFT characteristics under ambient conditions in combination with Au contacts and various polymeric dielectrics is reported and all-printed polymeric complementary inverters have been demonstrated.
Abstract: Printed electronics is a revolutionary technology aimed at unconventional electronic device manufacture on plastic foils, and will probably rely on polymeric semiconductors for organic thin-film transistor (OTFT) fabrication. In addition to having excellent charge-transport characteristics in ambient conditions, such materials must meet other key requirements, such as chemical stability, large solubility in common solvents, and inexpensive solution and/or low-temperature processing. Furthermore, compatibility of both p-channel (hole-transporting) and n-channel (electron-transporting) semiconductors with a single combination of gate dielectric and contact materials is highly desirable to enable powerful complementary circuit technologies, where p- and n-channel OTFTs operate in concert. Polymeric complementary circuits operating in ambient conditions are currently difficult to realize: although excellent p-channel polymers are widely available, the achievement of high-performance n-channel polymers is more challenging. Here we report a highly soluble ( approximately 60 g l(-1)) and printable n-channel polymer exhibiting unprecedented OTFT characteristics (electron mobilities up to approximately 0.45-0.85 cm(2) V(-1) s(-1)) under ambient conditions in combination with Au contacts and various polymeric dielectrics. Several top-gate OTFTs on plastic substrates were fabricated with the semiconductor-dielectric layers deposited by spin-coating as well as by gravure, flexographic and inkjet printing, demonstrating great processing versatility. Finally, all-printed polymeric complementary inverters (with gain 25-65) have been demonstrated.

2,769 citations

Journal ArticleDOI
29 Oct 1999-Science
TL;DR: A thin-film field-effect transistor having an organic-inorganic hybrid material as the semiconducting channel was demonstrated and molecular engineering of the organic and inorganic components of the hybrids is expected to further improve device performance for low-cost thin- film transistors.
Abstract: Organic-inorganic hybrid materials promise both the superior carrier mobility of inorganic semiconductors and the processability of organic materials A thin-film field-effect transistor having an organic-inorganic hybrid material as the semiconducting channel was demonstrated Hybrids based on the perovskite structure crystallize from solution to form oriented molecular-scale composites of alternating organic and inorganic sheets Spin-coated thin films of the semiconducting perovskite (C(6)H(5)C(2)H(4)NH(3))(2)SnI(4) form the conducting channel, with field-effect mobilities of 06 square centimeters per volt-second and current modulation greater than 10(4) Molecular engineering of the organic and inorganic components of the hybrids is expected to further improve device performance for low-cost thin-film transistors

1,887 citations

Journal ArticleDOI
TL;DR: Integration of organic transistors and rubber pressure sensors, both of which can be produced by low-cost processing technology such as large-area printing technology, will provide an ideal solution to realize a practical artificial skin.
Abstract: It is now widely accepted that skin sensitivity will be very important for future robots used by humans in daily life for housekeeping and entertainment purposes Despite this fact, relatively little progress has been made in the field of pressure recognition compared to the areas of sight and voice recognition, mainly because good artificial “electronic skin” with a large area and mechanical flexibility is not yet available The fabrication of a sensitive skin consisting of thousands of pressure sensors would require a flexible switching matrix that cannot be realized with present silicon-based electronics Organic field-effect transistors can substitute for such conventional electronics because organic circuits are inherently flexible and potentially ultralow in cost even for a large area Thus, integration of organic transistors and rubber pressure sensors, both of which can be produced by low-cost processing technology such as large-area printing technology, will provide an ideal solution to realize a practical artificial skin, whose feasibility has been demonstrated in this paper Pressure images have been taken by flexible active matrix drivers with organic transistors whose mobility reaches as high as 14 cm2/V·s The device is electrically functional even when it is wrapped around a cylindrical bar with a 2-mm radius

1,804 citations