Marcos V. Puydinger dos Santos

Dielectrophoretic manipulation of individual nickel nanowires for electrical transport measurements

Nanowires (NW) have received much attention due to their high aspect ratio, shape anisotropy, relatively large surface area and particular electron transport properties. In addition, since NW present low current levels and high sensitivity, they can be used as sensor devices for several applications. One of the major challenges when dealing with transport measurements in NW is to trap them between electrodes, which allow electrical characterization and therefore fabrication of nanowire-based devices. Electrically neutral NW can be deposited by dielectrophoresis (DEP) method, which requires the application of an alternating electric field between electrodes. In this work, properly dispersed Ni nanowires (NiNW) (length = 4 ± 1 μm, diameter = 35 ± 5 nm) were deposited on top of Pt electrodes using the DEP method. The effects of electrodes geometry and electric field frequency on DEP efficiency were evaluated. For optimized DEP parameters, the process efficiency is up to 85%. The deposited NiNW exhibit a Schottky-like current versus voltage behavior due to the high contact resistance between NiNW and electrode. Its reduction down to two orders of magnitude, reaching value less than the NiNW resistance (∼6 kΩ), was achieved by depositing a 10 nm-thick Pt layer over the NW extremities. Therefore, this method presents a selection of adequate electrical DEP parameters and electrode geometry, making it a suitable process of NW deposition and electrical characterization. This can be used for investigation of electrical transport properties of individual NW and fabrication of NW-based devices, like sensors and field effect transistors.Nanowires (NW) have received much attention due to their high aspect ratio, shape anisotropy, relatively large surface area and particular electron transport properties. In addition, since NW present low current levels and high sensitivity, they can be used as sensor devices for several applications. One of the major challenges when dealing with transport measurements in NW is to trap them between electrodes, which allow electrical characterization and therefore fabrication of nanowire-based devices. Electrically neutral NW can be deposited by dielectrophoresis (DEP) method, which requires the application of an alternating electric field between electrodes. In this work, properly dispersed Ni nanowires (NiNW) (length = 4 ± 1 μm, diameter = 35 ± 5 nm) were deposited on top of Pt electrodes using the DEP method. The effects of electrodes geometry and electric field frequency on DEP efficiency were evaluated. For optimized DEP parameters, the process efficiency is up to 85%. The deposited NiNW exhibit a Scho...

Influence of Al/TiN/SiO2 structure on MOS capacitor, Schottky diode, and fin field effect transistors devices

Titanium nitride (TiN) films were tested for their suitability as upper electrodes in metal–oxide–semiconductor (MOS) capacitors and Schottky diodes and as metal gate electrodes in fin field effect transistor devices. TiOxNy formation on TiN surfaces was confirmed by x-ray photoelectron spectroscopy and appears to be associated with exposure of the metal electrodes to ambient air. In order to avoid the formation of TiOxNy and TiO2, a layer of aluminum (Al) was deposited in situ after the TiN deposition. TiN work function was calculated for the devices to study how dipole variation at the interface TiN/SiO2 influences TiN work function. TiOxNy and TiO2 formation at the film surface was found to affect the dipole variations at the TiN/SiO2 interface increasing the dipole influence on MOS structure. Furthermore, the estimated values TiN work function are suitable for complementary metal–oxide–semiconductor (CMOS) technology. Finally, this work had shown that Al/TiN structure can be used in CMOS technology, e...

Fabrication of p-type silicon nanowires for 3D FETs using focused ion beam

A Ga+ focused ion beam (GaFIB) from a FIB/scanning electron microscopy (SEM) dual beam system was used for Si milling and p-type local doping of p+-type silicon nanowires (p+-SiNWs). The resulting p+-SiNWs were then used to create pMOS junctionless nanowire transistor (JNT) prototypes for silicon-on-insulator wafer substrates. The electron beam from the FIB/SEM dual beam system was used to deposit SiO2 gate dielectric and Pt source/drain electrodes for JNT transistors. Width, length, and height dimensions of p+-SiNWs were approximately 35 nm, 6 μm, and 15 nm, respectively, and the JNT gate length was 1 μm. Finally, photolithography, Al sputtering deposition, and lift-off processing were conducted to define the Al gate electrode and contacts on Pt source/drain electrodes. Energy dispersive x-ray spectroscopy measurements were taken to confirm the surface composition of p+-SiNWs and Ga doping. Drain–source current (IDS) versus drain–source voltage (VDS) measurements of JNT transistors indicated that the dev...

Direct Electron Beam Writing of Silver-Based Nanostructures

Direct writing utilizing a focused electron beam constitutes an interesting alternative to resist-based techniques, as it allows for precise and flexible growth onto any conductive substrate in a single-step process. One important challenge, however, is the identification of appropriate precursors which allow for deposition of the material of choice, e.g., for envisaged applications in nano-optics. In this regard the coinage metal silver is of particular interest since it shows a relatively high plasma frequency and, thus, excellent plasmonic properties in the visible range. By utilizing the precursor compound AgO2Me2Bu, direct writing of silver-based nanostructures via local electron beam induced deposition could be realized for the first time. Interestingly, the silver deposition was strongly dependent on electron dose; at low doses of 30 nC/μm2 a dominant formation of pure silver crystals was observed, while at higher electron doses around 104 nC/μm2 large carbon contents were measured. A scheme for the enhanced silver deposition under low electron fluxes by an electronic activation of precursor dissociation below thermal CVD temperature is proposed and validated using material characterization techniques. Finally, the knowledge gained was employed to fabricate well-defined two-dimensional deposits with maximized silver content approaching 75 at. %, which was achieved by proper adjustment of the deposition parameters. The corresponding deposits consist of plasmonically active silver crystallites and demonstrate a pronounced Raman signal enhancement of the carbonaceous matrix.

How to Characterize Cylindrical Magnetic Nanowires

Cylindrical magnetic nanowires made through the help of nanoporous alumina templates are being fabricated and characterized since the beginning of 2000. They are still actively investigated nowadays, mainly due to their various promising applica‐ tions, ranging from high-density magnetic recording to high-frequency devices, passing by sensors, and biomedical applications. They also represent suitable systems in order to study the dimensionality effects on a given material. With time, the development in fabrication techniques allowed to increase the obtained nanowire complexity (control‐ led crystallinity, modulated composition and/or geometry, range of materials, etc.), while the improvements in nanomanipulation permitted to fabricate system based either on arrays or on single nanowires. On the other side, their increased complexity requires specific physical characterization methods, due to their particular features such as high anisotropy, small magnetic volume, dipolar interaction field between them, and interesting electronic properties. The aim of this chapter was to offer an ample overview of the magnetic, electric, and physical characterization techniques that are suitable for cylindrical magnetic nanowire investigation, of what is the specific care that one needs to take into account and which information will be extracted, with typical and varied examples.

Comparative study of post-growth annealing of Cu(hfac)2, Co2(CO)8 and Me2Au(acac) metal precursors deposited by FEBID

Non-noble metals, such as Cu and Co, as well as noble metals, such as Au, can be used in a number modern technological applications, which include advanced scanning-probe systems, magnetic memory and storage, ferroelectric tunnel junction memristors, metal interconnects for high performance integrated circuits in microelectronics and nano-optics applications, especially in the areas of plasmonics and metamaterials. Focused-electron-beam-induced deposition (FEBID) is a maskless direct-write tool capable of defining 3-dimensional metal deposits at nanometre scale for above applications. However, codeposition of organic ligands when using organometallic precursors is a typical problem that limits FEBID of pure metal nanostructures. In this work, we present a comparative study using a post-growth annealing protocol at 100, 200, and 300 °C under high vacuum on deposits obtained from Co2(CO)8, Cu(II)(hfac)2, and Me2Au(acac) to study improvements on composition and electrical conductivity. Although the as-deposited material was similar for all precursors, metal grains embedded in a carbonaceous matrix, the post-growth annealing results differed. Cu-containing deposits showed the formation of pure Cu nanocrystals at the outer surface of the initial deposit for temperatures above 100 °C, due to the migration of Cu atoms from the carbonaceous matrix containing carbon, oxygen, and fluorine atoms. The average size of the Cu crystals doubles between 100 and 300 °C of annealing temperature, while the composition remains constant. In contrast, for Co-containing deposits oxygen release was observed upon annealing, while the carbon content remained approximately constant; the cobalt atoms coalesced to form a metallic film. The as-deposited Au-containing material shows subnanometric grains that coalesce at 100 °C, maintaining the same average size at annealing temperatures up to 300 °C. Raman analysis suggests that the amorphous carbonaceous matrix of the as-written Co, Cu and Au deposits turned into nanocrystalline graphite with comparable crystal sizes of 12–14 nm at 300 °C annealing temperature. However, we observed a more effective formation of graphite clusters in Co- than in Cu- and Au-containing deposits. The graphitisation has a minor influence on the electrical conductivity improvements of Co–C deposits, which is attributed to the high as-deposited Co content and the related metal grain percolation. On the contrary, electrical conductivity improvements by factors of 30 and 12 for, respectively, Cu–C and Au–C deposits with low metal content are mainly attributed to the graphitisation. This relatively simple vacuum-based post-growth annealing protocol may be useful for other precursors as it proved to be efficient in reliably tuning the electrical properties of as-deposited FEBID materials. Finally, a H2-assisted gold purification protocol is demonstrated at temperatures around 300 °C by fully removing the carbon matrix and drastically reducing the electrical resistance of the deposit.

A novel copper precursor for electron beam induced deposition

A fluorine free copper precursor, Cu(tbaoac)2 with the chemical sum formula CuC16O6H26 is introduced for focused electron beam induced deposition (FEBID). FEBID with 15 keV and 7 nA results in deposits with an atomic composition of Cu:O:C of approximately 1:1:2. Transmission electron microscopy proved that pure copper nanocrystals with sizes of up to around 15 nm were dispersed inside the carbonaceous matrix. Raman investigations revealed a high degree of amorphization of the carbonaceous matrix and showed hints for partial copper oxidation taking place selectively on the surfaces of the deposits. Optical transmission/reflection measurements of deposited pads showed a dielectric behavior of the material in the optical spectral range. The general behavior of the permittivity could be described by applying the Maxwell–Garnett mixing model to amorphous carbon and copper. The dielectric function measured from deposited pads was used to simulate the optical response of tip arrays fabricated out of the same precursor and showed good agreement with measurements. This paves the way for future plasmonic applications with copper-FEBID.

Electrical Manipulation of a Single Nanowire by Dielectrophoresis

Nanowires (NWs), due to their unique highly anisotropic characteristics, hold a great promise to be used in wide technological fields, such as building blocks for data storage and memory, advanced scanning probes, and biotechnological applications. In addition, given the high sensitivity to their environment, NWs can be used as sensor for a number of applications. The fabrication and electrical characterization of NW‐based devices can be achieved after proper placing of NWs between electrodes, which represents one of the major challenges in this field. The dielectrophoresis (DEP) method can be used to trap electrically neutral NWs by the application of an alternating electric field between a pair of electrodes. Here, we present a systematic study of DEP parameters as well as electrodes geometry for NW deposition. This method presents a suitable protocol for deposition in a useful and coherent fashion of post‐growth electrodeposited NWs and further electrical characterization. This can be used for investigation of the fundamental transport properties of individual NWs and fabrication of NW‐based devices, such as sensors and field‐effect transistors.

Ga+ focused ion beam lithography as a viable alternative for multiple fin field effect transistor prototyping

A novel method for fast and flexible fin field effect transistor (FinFET) prototyping using a Ga+ focused ion beam is presented. The fin width and height control is explored, aiming for the successful fabrication of prototypes. This method results in fins with negligible Ga incorporation, when compared to traditional focused ion beam milling techniques. Our method for multiple fin FinFET prototyping enables advanced device fabrication and great flexibility regarding both the number of fins and fin width. Working FinFET prototypes have been fabricated using the proposed fin definition method, and the electrical characterization is discussed.

Formation and characterization of tin layers for metal gate electrodes of CMOS capacitors

In this study, ultrathin films (thickness of less than 20 nm) of titanium nitride (TiN) to be used as gate electrodes for CMOS (Complementary Metal Oxide Semiconductor) technology were obtained. These ultrathin films were obtained by electron beam evaporation of ultrathin layers (1 or 2 nm thick) of titanium (Ti) followed by ECR (Electron Cyclotron Resonance) plasma nitridation of nitrogen (N2). After deposition and nitridation of the titanium, in order to prevent oxidation of the films, in the same nitriding ECR reactor, a-Si:H (hydrogenated amorphous silicon) films were deposited by CVD (Chemical Vapor Deposition) using SiH4/Ar plasma. These films of a-Si:H were implanted with phosphorus (P+) and annealed by rapid thermal annealing to turn them n+ dopped and polycrystalline. Thus, MOS metal gate electrodes were formed with n+ Poly-Si/TiN structures.