Showing papers on "Contact resistance published in 2006"

An experimental study of contact effects in organic thin film transistors

Abstract: We report on parasitic contact effects in organic thin film transistors (OTFTs) fabricated with pentacene films. The influence on the OTFT performance of the source and drain contact metal and the device design was investigated. Top contact (TC) and bottom contact (BC) gated transmission line model (gated-TLM) test structures were used to extract the combined parasitic contact resistance as a function of gate voltage swing and drain-source voltage for OTFTs with gold source and drain contacts. For comparison BC test structures with palladium contacts were studied. Differences in the bias dependence of the contact resistance for TC and BC OTFTs indicate that charge injection and device performance are strongly affected by the device design and processing. The results from this investigation show that TC and BC device performances may be contact limited for high mobility OTFTs with channel lengths less than 10μm.

Electrical Contacts: Fundamentals, Applications and Technology

Abstract: FUNDAMENTALS OF ELECTRICAL CONTACTS Introduction to Electrical Contacts . Introduction . Summary of Basic Features Contact Mechanics . Surface of Solids . Surface Topography . Modern Techniques of Measuring Surface Parameters . Contact of Smooth Surfaces . Contact between Rough Surfaces Tribology . Friction . Wear . Lubrication . Current Trends in Tribology Contact Materials . Metallic Contact Materials . Coatings for Electrical Contacts . Composite Contact Materials . Nanostructured Materials Current and Heat Transfer across the Contact Interface . Contact Resistance . Interfacial Heating Reliability Issues in Electrical Contacts . Significance of Electrical Contacts Reliability . Electrical Contact Requirements . Factors Affecting Reliability . Connection Degradation Mechanisms . Impact of Connection Degradation APPLICATIONS OF ELECTRICAL CONTACTS Power Connections . Types of Power Connectors . Design Features and Degradation Mechanisms . Mitigating Measures . Installation Procedures Electronic Connections . Types of Electronic Connections . Materials for Electronic Connections . Degradation Mechanisms in Electronic Connections . Mitigating Measures Sliding Contacts . Tribology of Electrical Contacts . Dry Metal Contacts . Lubricated Metal Contacts . Composite Contacts DIAGNOSTIC AND MONITORING TECHNOLOGIES Electrical Methods in Tribology . Surface Characterization . Diagnosis of Contact Area and Friction Regimes . Evaluation of Tribological Performance of Materials and Lubricants Monitoring Technologies . Thermal Measurements . Resistance Measurements . Monitoring Contact Load (Pressure) . Ultrasonic Measurements . Wireless Monitoring . Cost Benefits of Monitoring and Diagnostics Techniques Appendix 1: Methods of Description of Rough Surface Appendix 2: Shape-Memory Materials Appendix 3: Electrical Contact Tables References Index

Programmable resistive RAM and manufacturing method

Abstract: Programmable resistive RAM cells have a resistance that depends on the size of the contacts. Manufacturing methods and integrated circuits for lowered contact resistance are disclosed that have contacts of reduced size.

Film and contact resistance in pentacene thin-film transistors: Dependence on film thickness, electrode geometry, and correlation with hole mobility

Abstract: We describe variable temperature contact resistance measurements on pentacene organic thin-film transistors via a gated four-probe technique. The transistors consist of Au source and drain electrodes contacting a pentacene film deposited on a dielectric/gate electrode assembly. Additional voltage sensing leads penetrating into the source-drain channel were used to monitor potentials in the pentacene film while passing current between the source and drain electrodes during gate voltage sweeps. Using this device structure, we investigated contact resistance as a function of film thickness (60–3000A), deposition temperature (25 or 80°C), gate voltage, electrode geometry (top or bottom contact), and temperature. Contact resistance values were approximately 2×103–7×106Ωcm, depending on film thickness. In the temperature range of 77–295K, the contact resistance displayed activated behavior with activation energies of 15–160meV. Importantly, it was observed that the activation energies for the source and drain r...

3D integration by Cu-Cu thermo-compression bonding of extremely thinned bulk-Si die containing 10 μm pitch through-Si vias

Abstract: Using standard single damascene type techniques on bulk-Si, combined on one hand with extreme wafer thinning and on the other with Cu-Cu thermo-compression bonding technology, the paper demonstrate yielding 10k through-wafer 3D-via chains with a via pitch of 10μm for a via diameter of 5μm. The bonded contacts exhibit shear strengths exceeding 40MPa. Measurements indicate there is no significant contact resistance at the Cu-Cu bonded interface: within measurement accuracy, the 4-point via chain resistance is consistent with bulk Cu resistivity

Evaluating the impact of resistance in carbon nanotube bundles for VLSI interconnect using diameter-dependent modeling techniques

Abstract: Single-walled carbon nanotube (SWCNT) bundles have the potential to provide an attractive solution for the resistivity and electromigration problems faced by traditional copper interconnects. This paper discusses the modeling of nanotube bundle resistance for on-chip interconnect applications. Based on recent experimental results, the authors model the impact of nanotube diameter on contact and ohmic resistance, which has been largely ignored in previous bundle models. The results indicate that neglecting the diameter-dependent nature of ohmic and contact resistances can produce significant errors. Using the resistance model, it is shown that SWCNT bundles can provide up to one order of magnitude reduction in resistance when compared with traditional copper interconnects depending on bundle geometry and individual nanotube diameter. Furthermore, for local interconnect applications, an optimum nanotube diameter exists to minimize the resistance of the carbon nanotube bundle

Interface resistance switching at a few nanometer thick perovskite manganite active layers

Abstract: We have studied the transport and resistance switching properties of Ti∕Sm0.7Ca0.3MnO3 (n unit cells)/La0.7Sr0.3MnO3 [Ti∕SCMO(n)∕LSMO] layered structures. The metal-to-metal contact of the Ti/LSMO junction (n=0) does not exhibit resistance switching effect, while the insertion of a very thin insulating SCMO layer (n⩾1) induces resistance switching effect. As the SCMO layer thickness (n) increases, the resistance switching amplitude grows and the response gets faster. This indicates that the SCMO layer as thin as several u.c. adjacent to the interface works as an active source for the resistance switching effect.

Thermal Contact Resistance and Thermal Conductivity of a Carbon Nanofiber

Abstract: It has been suggested that CNTs and carbon nanofibers CNFs can be used as thermal interface materials to enhance contact thermal conductance for electronic packaging applications. Several groups have reported mixed experimental results from no improvements to large improvements in the thermal contact conductance due to the CNTs and CNFs 8‐12. These mixed results can be caused by the difference in surface coverage and perpendicular alignment of the CNTs or CNFs. Moreover, the results can be affected by two other factors. First, the CNTs and CNFs grown using different methods possess different defect densities and different intrinsic thermal conductivities. Secondly, the contact thermal resistance of the nanometer scale point and line contacts between a CNT or CNF and a planar surface can be high due to enhanced phonon-boundary scattering at the nanocontacts. We have used a microfabricated device to measure the thermal resistance of an individual CNF from a vertically aligned CNF film for applications as thermal interface materials. The measurement was conducted before and after a platinum Pt layer was deposited on the contacts between the CNF and the microdevice so as to investigate the thermal contact resistance between the CNF and a planar surface. The contact resistance was reduced by the platinum coating for about 9‐13% of the total thermal resistance of the nanofiber sample before the Pt coating. At temperature 300 K, the obtained axial thermal conductivity of the carbon nanofibers was about three times smaller than that of graphite fibers grown by pyrolysis of natural gas prior to high-temperature heat treatment.

Fabrication and electrical characterization of circuits based on individual tin oxide nanowires

Abstract: Two- and four-probe electrical measurements on individual tin oxide (SnO2) nanowires were performed to evaluate their conductivity and contact resistance. Electrical contacts between the nanowires and the microelectrodes were achieved with the help of an electron- and ion-beam-assisted direct-write nanolithography process. High contact resistance values and the nonlinear current–bias (I–V) characteristics of some of these devices observed in two-probe measurements can be explained by the existence of back-to-back Schottky barriers arising from the platinum–nanowire contacts. The nanoscale devices described herein were characterized using impedance spectroscopy, enabling the development of an equivalent circuit. The proposed methodology of nanocontacting and measurements can be easily applied to other nanowires and nanometre-sized materials.

Effect of Ag Particle Size in Thick-Film Ag Paste on the Electrical and Physical Properties of Screen Printed Contacts and Silicon Solar Cells

Abstract: The impact of the Ag particle (metal powder in the screen printed paste) size on the quality of Ag thick-film ohmic contacts to high-sheet-resistance emitters of Si solar cells is investigated. Spherical particle size wasvaried in the range of 0.10-10 μm (ultrafine to large). Even though ultrathin glass regions are achieved for the large particle paste, giving low specific contact resistance (ρ c ), secondary ion mass spectroscopy measurements showed a higher Ag concentration (>10 1 5 cm - 3 ) at the p-n junction that increased the junction leakage current (J o 2 ) and decreased the V o c by ∼7 mV and fill factor (FF) by ∼0.02. Pastes with ultrafine Ag particles generally produced a thick glass layer at the Ag-Si contact interface, which increased ρ c and series resistance (R s ) (≥ 1 Ω cm 2 ), and lowered the FF by ∼0.03. Small to medium size Ag particles in the paste produced thin glass regions and many regularly distributed Ag crystallites at the contact interface. This resulted in low R s (< 1 Ω cm 2 ), high shunt resistance (60,558 Ω cm 2 ), low J o 2 (∼20 nA/cm 2 ), and high FF (0.781). Cell efficiencies of ∼17.4% were achieved on untextured float zone Si with 100 Ω/□ emitter by rapid firing of screen printed contacts in a lamp-heated belt furnace.

High-performance low-cost organic field-effect transistors with chemically modified bottom electrodes.

Abstract: The characteristics of organic field-effect transistors (OFETs) were dramatically improved by chemically modifying the surface of the bottom-contact Ag or Cu source−drain (D−S) electrodes with a simple solution method. The contact resistance and energetic mismatch typically observed with Ag D−S electrodes in pentacene bottom-contact OFETs can be properly eliminated when modified by the Ag-TCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane). The pentacene transistors with low-cost Ag-TCNQ-modified Ag bottom-contact electrodes exhibit outstanding electrical properties, which are comparable with that of the Au top-contact devices. It thus provides a novel way toward high-performance low-cost bottom-contact OFETs.

Transistor with improved tip profile and method of manufacture thereof

Abstract: Embodiments are an improved transistor structure and the method of fabricating the structure In particular, a wet etch of an embodiment forms source and drain regions with an improved tip shape to improve the performance of the transistor by improving control of short channel effects, increasing the saturation current, improving control of the metallurgical gate length, increasing carrier mobility, and decreasing contact resistance at the interface between the source and drain and the silicide

Thermal properties of carbon nanotube array used for integrated circuit cooling

Abstract: Carbon nanotubes (CNTs), owing to their exceptionally high thermal conductivity, have a potential to be employed in micro- and optoelectronic devices for integrated circuit (IC) cooling. In this study we describe a photothermal metrology intended to evaluate the thermal conductivity of a vertically aligned CNT array (VCNTA) grown on a silicon (Si) substrate. Plasma-enhanced chemical vapor deposition, with nickel (Ni) as a catalyst, was used to grow CNT. The experimentally evaluated thermal conductivity of the VCNTA and the thermal contact resistance at the interface between the VCNTA and the “hot” surface was found to be in a satisfactory agreement with theoretical predictions. The measured effective thermal resistance is measured to be 0.12∼0.16cm2∙K∕W. This resistance was compared to the measured resistance of commercially available thermal grease. Based on this comparison, we conclude that, although the thermal resistance of CNTs might not be as low as it might be desirable, there exists a definite inc...

Enhanced thermal contact conductance using carbon nanotube array interfaces

Abstract: Heat-conduction interfaces that employ carbon nanotube (CNT) arrays have been fabricated and studied experimentally using a reference calorimeter testing rig in a vacuum environment with infrared temperature measurements. Arrays of multiwalled CNTs are grown directly on silicon substrates with microwave plasma-enhanced chemical vapor deposition. Iron and nickel were used as CNT catalysts. CNT arrays grown under different synthesis conditions exhibit different pressure-contact conductance characteristics. The thermal contact resistance of CNTs with a copper interface exhibits promising results with a minimum value of 19.8mm2K/W at a pressure of 0.445MPa

Characterization of metal and metal alloy films as contact materials in MEMS switches

Abstract: This study presents a basic step toward the selection methodology of electric contact materials for microelectromechanical systems (MEMS) metal contact switches. This involves the interrelationship between two important parameters, resistivity and hardness, since they provide the guidelines and assessment of contact resistance, wear, deformation and adhesion characteristics of MEMS switches. For this purpose, thin film alloys of three noble metals, platinum (Pt), rhodium (Rh) and ruthenium (Ru) with gold (Au), were investigated. The interrelationship between resistivity and hardness was established for three levels of alloying of these metals with gold. Thin films of gold (Au), platinum (Pt), ruthenium (Rh) and rhodium (Ru) were also characterized to obtain their baseline data for comparison. All films were deposited on silicon substrates. When Ru, Rh and Pt are alloyed with Au, their hardness generally decreases but resistivity increases. This decrease or increase was, in general, dependent upon the amount of alloying.

Enhancement-Mode AlGaN/AlN/GaN High Electron Mobility Transistor with Low On-State Resistance and High Breakdown Voltage

Abstract: A low on-resistance and high-breakdown-voltage enhancement-mode (E-mode) AlGaN/AlN/GaN high electron mobility transistor (HEMT) was fabricated without the recessed-gate process. A thin AlGaN barrier layer (4.5 nm) was used for the normally-off operation. In order to decrease the on-state resistance, two different techniques are used. One is the side-ohmic contact, which has a low contact resistance, due to the direct contact with the two-dimensional electron gas (2DEG). The other is SiO2 passivation, which induces the sheet carriers and decreases the sheet resistance. As a result, an on-state resistance of 1.9 mΩcm2 and an off-state breakdown voltage of 610 V were achieved for the E-mode HEMT within a threshold voltage of approximately -0.1 V.

Method for forming an integrated circuit

Abstract: A method is described for manufacturing an n-MOS semiconductor transistor. Recesses are formed in a semiconductor substrate adjacent a gate electrode structure. Silicon is embedded in the recesses via a selective epitaxial growth process. The epitaxial silicon is in-situ alloyed with substitutional carbon and in-situ doped with phosphorus. The silicon-carbon alloy generates a uniaxial tensile strain in the channel region between the source and drain, thereby increasing electron channel mobility and the transistor's drive current. The silicon-carbon alloy decreases external resistances by reducing contact resistance between source/drain and silicide regions and by reducing phosphorous diffusivity, thereby permitting closer placement of the transistor's source/drain and channel regions.

Effects of metal penetration into organic semiconductors on the electrical properties of organic thin film transistors

Abstract: To investigate the effects of metal penetration into organic semiconductors on the electrical properties of organic thin film transistors, gold was deposited onto pentacene films at various deposition rates. The sharp interface between the gold electrode and the pentacene film that results from a fast deposition rate was found to produce lower contact resistance and an increase in the field-effect mobility.

Micron-scale organic thin film transistors with conducting polymer electrodes patterned by polymer inking and stamping

Abstract: We report organic thin film transistors (OTFTs) with conductive polymer poly (3,4-ethylenedioxythiophene)/poly(4-styrenesulphonate) (PEDOT) electrodes that are fabricated by a simple polymer inking and stamping technique. An OTFT channel length of 2μm has been achieved. This patterning technique is a purely additive process, which does not affect the functionality of the conductive polymers, and is fully compatible for patterning on a flexible substrate. Electrical characteristics of top contact (TC) pentacene TFTs with PEDOT electrodes is superior to those with gold electrodes due to a lower carrier injection barrier. Extracted contact resistance shows that the channel length of TC OTFTs can be further reduced to increase the drain current.

Microswitches with sputtered Au, AuPd,Au-on-AuPt, and AuPtCu alloy electric contacts

Abstract: This paper is the first to report on a new analytic model for predicting microcontact resistance and the design, fabrication, and testing of microelectromechanical systems (MEMS) metal contact switches with sputtered bimetallic (i.e., gold (Au)-on-Au-platinum (Pt), (Au-on-Au-(6.3at%)Pt)), binary alloy (i.e., Au-palladium (Pd), (Au-(3.7at%)Pd)), and ternary alloy (i.e., Au-Pt-copper (Cu), (Au-(5.0at%)Pt-(0.5at%)Cu)) electric contacts. The microswitches with bimetallic and binary alloy contacts resulted in contact resistance values between 1-2Omega. Preliminary reliability testing indicates a 3times increase in switching lifetime when compared to microswitches with sputtered Au electric contacts. The ternary alloy exhibited approximately a 6times increase in switch lifetime with contact resistance values ranging from approximately 0.2-1.8Omega

Review of Thermal Joint Resistance Models for Nonconforming Rough Surfaces

Abstract: The thermal contact resistance (TCR) in a vacuum is studied. The TCR problem is divided into three different parts: geometrical, mechanical, and thermal. Each problem includes a macroand microscale subproblem; existing theories and models for each part are reviewed. Empirical correlations for microhardness, and the equivalent (sum) rough surface approximation, are discussed. Suggested correlations for estimating the mean absolute surface slope are summarized and compared with experimental data. The most common assumptions of existing thermal analyses are summarized. As basic elements of thermal analyses, spreading resistance of a circular heat source on a half-space and flux tube are reviewed; also existing flux tube correlations are compared. More than 400 TCR data points collected by different researchers during the last 40 years are grouped into two limiting cases: conforming rough and elastoconstriction. Existing TCR models are reviewed and compared with the experimental data at these two limits. It is shown that the existing theoretical models do not cover both of the above-mentioned limiting cases. This review article cites 58 references. DOI: 10.1115/1.2110231