Omega Ldr Research Articles

Analytical and Finite-Element Modeling of a Cross Kelvin Resistor Test Structure for Low Specific Contact Resistivity

Various test structures have been employed to determine the specific contact resistivity (rho <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> ) of ohmic contacts, and cross Kelvin resistor (CKR) test structures are most suitable for estimating low rho <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> values. The value determined by CKRs includes error due to parasitic resistances that have been difficult to account for when rho <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> is low (< 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> Omega ldr cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). In this paper, an analytical technique for determining the error in measurements from CKR test structures is presented. The analytical model described for circular contacts is based on Bessel function expressions. Using several contacts of different diameter ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> ) with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</i> les 0.4 ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</i> is the width of the CKR arms), the parasitic resistance can be accurately accounted for by extrapolation of experimental data to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</i> rarr 0. Finite-element modeling and experimental results for metal-to-silicide contacts are used to validate the analytical expressions presented.

Fabrication of Titanium-Doped Indium Oxide Films for Dye-Sensitized Solar Cell Application Using Reactive RF Magnetron Sputter Method

To develop high-efficiency transparent conductive oxide glass in a longer wavelength zone for dye-sensitized solar cell (DSC) application, we fabricate titanium-doped indium oxide (ITiO) films on a soda-lime glass substrate by an RF magnetron sputtering. The ITiO films showed a minimum resistivity of 1.25 times 10-3 Omega ldr cm. The transmittance increases from 80% at 450 nm to 90% at 700 nm in the visible spectrum. From the atomic force microscopy result, the surface roughness of the sample showed a change from 10 to 50 nm with annealing temperature. From the XPS result, the concentration ratio (%) for In, Ti, and O was 27 : 2 : 42. The annealing treatment on the ITiO films improves the photovoltaic characteristics of the ITiO-based DSCs, and energy conversion efficiency (eta) is 5.79% (FF: 0.62, Voc: 0.71 V, Jsc: 13.23 mA/cm2) at 100-mW/cm2 light intensity.

Interfacial Oxidation Enhanced Perpendicular Magnetic Anisotropy in Low Resistance Magnetic Tunnel Junctions Composed of Co/Pt Multilayer Electrodes

Low-resistance magnetic tunnel junctions utilizing perpendicular magnetic anisotropy of Co/Pt multilayer electrodes have been investigated. In these junctions, AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> tunnel barrier has been prepared by repeated natural oxidation processes. Each natural oxidation process has been optimized by varying the thickness of pre-oxidized Al layer prior to oxidation. The perpendicular magnetic anisotropy of Co/Pt multilayer has been found to be dependent on the degree of oxidation at the interface of tunnel barrier and Co adjacent layer. It has been observed that magnetization of Co/Pt multilayer is tilted when Co layer adjacent to tunnel barrier is relatively thick, which is attributed to the lack of interfacial anisotropy contribution near the interface of Co adjacent layer and AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> barrier. Interfacial oxidation treated on the monolayer thick Co adjacent layer has enhanced perpendicular magnetic anisotropy of the entire Co/Pt multilayer electrodes, enabling sharp transition between well-defined parallel and anti-parallel states at micro-fabricated perpendicular magnetic tunnel junctions of ~100 Omega ldr mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> resistance-area product.

Induction of Long Gap Discharge by Water Jet

This paper presents the images of a long gap discharge induced by a water jet. Spherical metal balls of 5-cm diameter were used as high-voltage, ground, and guiding electrodes. The distance between the high-voltage electrode and the ground one was 50 cm, and the distance between the high-voltage electrode and the guiding one was set to 75 cm. A tap water of 50 Omega ldr m resistivity was jetted from behind the guiding electrode toward the high-voltage electrode. A lightning impulse voltage of 1/40 mus generated with an impulse generator was applied to the high-voltage electrode. The leader discharge developed from the tip of the water jet toward the high-voltage electrode. After the discharge bridged between the water jet and the high-voltage electrode, the discharge developed along the water jet.

Low-loss on-chip transmission lines with micro-patterned artificial dielectric shields

Low-loss coplanar waveguide (CPW) transmission lines integrated on a standard (5 -10 Omega ldr cm) silicon substrate are realised by using an artificial dielectric shield with a very high in-plane dielectric constant. The shield consists of a 30 nm-thick Al 2 O 3 film sandwiched by two 100 nm-thick aluminium layers patterned into lattices of mum-size elements. The individual metallic elements are micro-patterned to suppress the flow of eddy currents at microwave frequencies. Inserted below the CPW, the shield blocks the electric field of the line from entering the silicon substrate. The resulting line attenuation (measured up to 25 GHz) is comparable to that of identical CPWs built on a high-resistivity silicon wafer.

Label-Free DNA Sensor on Nanoporous Silicon-Polypyrrole Chip for Monitoring Salmonella Species

Label-free DNA sensors based on nanoporous silicon (nPS) substrate were fabricated and electrochemically characterized. A low resistivity (0.01-0.02 Omega ldr cm) p-type silicon wafer (100 orientation) was electrochemically anodized in an ethanoic hydrofluoric acid (HF) solution containing ethanol to construct the nPS layer with pore diameter of about 10 nm. This nano structure is compatible with organic polymeric conductors. Polypyrrole (PPy) film was directly electropolymerized on the nPS substrate without pre-deposition of any metallic thin-film underlayer. The rough surface of the nPS layer was favorable for strong adsorption of the PPy film. The intrinsic negative charge of the DNA backbone was exploited to adsorb 26 base pairs of probe DNA (pDNA) into the PPy film by applying positive bias forming the nPS/PPy+pDNA layer. DNA from salmonella enterica serovar enteritidis (tDNA) was extracted using standard protocol and, subsequently, amplified by polymerase chain reaction (PCR). Salmonella species are classified as bioterrorism threat agents by the centers for disease control and prevention (CDC). Results from the scanning electron microscopy (SEM) image of the cross section of the nPS/PPy multilayered film shows successful direct electropolymerization of PPy on the nPS substrate. Results also show that the tDNA concentration is inversely related to the peak current (i <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> ) at 0.2 V versus Ag/AgCl. The plot of i <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> versus incubation time showed that current density (J) decreases by 29 muA ldr cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> per hour. The sensitivity obtained from the plot of i <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> versus tDNA concentration is -166.6 muA ldr cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ldr muM <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . Current density decreases with increasing incubation time and tDNA concentration. These results demonstrate that the nPS substrate with PPy+pDNA+tDNA film has been successfully developed for a label-free DNA sensor in rapidly and specifically detecting select and threat agents.

Accurate Estimation of Low $( ≪ \hbox{10}^{-8}\ \Omega \cdot \hbox{cm}^{2})$ Values of Specific Contact Resistivity

Advancements in nanotechnology have created the need for efficient means of communication of electrical signals to nanostructures, which can be addressed using low resistance contacts. In order to study and estimate the resistance of such contacts or the resistance posed by the interface(s) in such contacts, accurate test structures and evaluation techniques need to be used. The resistance posed by an interface is quantified using its specific contact resistivity (SCR), and although multiple techniques have been utilized, inaccuracies of such techniques in measuring values of SCR lesser than ( < 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> Omega ldr cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) have been reported. In this letter, an approach for estimating very low values of SCR (lower than the previously limiting ( < 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> Omega ldr cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> )) using a cross Kelvin resistor test structure is demonstrated using aluminum to titanium silicide ohmic contacts, with a minimum estimated SCR value of 6.0 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> Omega ldr cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

High Performance Inductors on CMOS-Grade Trenched Silicon Substrate

This paper reports on a new implementation of high-quality factor copper inductors on CMOS-grade silicon substrates (p = 10-20 Omega ldr cm) using a CMOS-compatible process. A low-temperature fabrication sequence (<300degC) is used to reduce the loss in silicon at RF frequencies by trenching the silicon substrate. The high aspect-ratio (30:1) trenches are subsequently bridged over or refilled with a low-loss dielectric to close the open areas and create a rigid low-loss island, referred to as Trenched Si Island. This method does not require air suspension of the inductors, resulting in mechanically-robust structures that are compatible with any packaging technology. A one-turn 0.8 nH inductor fabricated on a Trenched Silicon Island exhibits a very high peak quality factor of 71 at 8.75 GHz with a self-resonant frequency larger than 15 GHz.

0.25 $\mu\hbox{m}$ Self-Aligned AlGaN/GaN High Electron Mobility Transistors

Self-aligned AlGaN/GaN high electron mobility transistors grown on semiinsulating SiC substrates with a 0.25 mum gate-length were fabricated using a single-step ohmic process. Our recently developed Mo/Al/Mo/Au-based ohmic contact requiring annealing temperatures between 500degC and 600degC was utilized. Ohmic contact resistances between 0.35-0.6 Omega ldr mm were achieved. These 0.25 mum gate-length devices exhibited drain current density as high as 1.05 A/mm at a gate bias of 0 V and a drain bias of 10 V. A knee voltage of less than 2 V and a peak extrinsic transconductance (gm ) of 321 mS/mm were measured. For their microwave characteristics, a unity gain cutoff frequency (fT ) of 82 GHz and maximum frequency of oscillation (f max) of 103 GHz were measured.

Contactless Measurements of Resistivity of Semiconductor Wafers Employing Single-Post and Split-Post Dielectric-Resonator Techniques

Complementary single- and split-post dielectric- resonator techniques were used for contactless absolute resistivity measurements of semiconductor wafers and for onwafer resistivity mapping in the range of 10-5 to 105 Omega ldr cm. Uncertainties of the resistivity measurements employing both techniques are in the range of 2%-4%. Permittivities of high-resistivity semiconductors were measured with uncertainties of approximately 0.5%. Several Silicon, GaAs, and SiC wafers were tested at room and at elevating temperatures, showing excellent repeatability of measurements.

Optimal Conditions for Micromachining $\hbox{Si}_{1 - { \rm x}}\hbox{Ge}_{\rm x}$ at 210 $^{\circ}\hbox{C}$

This paper investigates the possibility of reducing the deposition temperature of silicon-germanium (Si1-xGex) thin films to 210degC and tuning the physical properties of the film locally to achieve optimal mechanical and electrical properties that are suitable for a wide range of microelectromechanical systems that can be postprocessed on top of standard prefabricated electronics or onto more exotic substrates, such as polymer films. First, the effect of the Ge content, layer thickness, and deposition pressure on the mechanical properties of as-deposited Si1-xGex films, which are deposited at 210degC, is analyzed in detail, and the optimal deposition conditions are experimentally determined. Then, the possibility of using pulsed excimer laser annealing to control the electrical and mechanical properties of such films is demonstrated. It is shown that the low deposition temperature imposes many constraints on the laser-annealing conditions, particularly for optimizing the mechanical properties. Moreover, the Ge content and the film thickness have a significant influence on the optimal laser-annealing conditions. It is illustrated that eliminating stress gradient implies very shallow crystallization, which is accompanied by relatively high electrical resistivity. Using the optimal laser-annealing conditions, the stress gradient can be as low as 1 times 10-6 mum-1 for a 0.3-mum-thick film. The optimal electrical resistivity, on the other hand, depends on the Ge content. For 70% Ge, the minimum resistivity is 80 mOmega ldr cm; decreasing the Ge content to 30% results in a resistivity of 3 Omega ldr cm.

Monolithic Integration of a Folded Dipole Antenna With a 24-GHz Receiver in SiGe HBT Technology

The integration of an on-chip folded dipole antenna with a monolithic 24-GHz receiver manufactured in a 0.8-mum SiGe HBT process is presented. A high-resistivity silicon substrate (1000 Omega ldr cm) is used for the implemented circuit to improve the efficiency of the integrated antenna. Crosstalk between the antenna and spiral inductors is analyzed and isolation techniques are described. The receiver, including the receive and an optional transmit antenna, requires a chip area of 4.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and provides 30-dB conversion gain at 24 GHz with a power consumption of 960 mW.