Showing papers on "Contact resistance published in 1994"

Intermetallic compounds at aluminum-to-copper electrical interfaces: effect of temperature and electric current

Abstract: The effects of intermetallic compounds on the electrical and mechanical properties of bimetallic friction welded Al-Cu joints was studied. The formation and growth of intermetallic compounds was studied in the temperature ranges 200-525/spl deg/C. In addition, the effect of electrical current on the morphology and kinetics of formation of intermetallic compounds of bimetallic friction welded aluminum-copper joints was studied in the temperature ranges 200-500/spl deg/C that was realized by heating Al-Cu joints with an ac current of different intensities (400-1000 A). The contact resistance was found to increase linearly with the thickness of the intermetallics. The presence of an electrical field greatly accelerates the kinetics of formation of intermetallic phases and alters significantly their morphology. The growth kinetics of intermetallic phases under the influence of electrical current is much higher than that under diffusion annealing in furnace. >

Resistance buildup in electrical connectors due to fretting corrosion of rough surfaces

Abstract: A comprehensive model to predict the contact resistance during the nth fretting cycle and the ultimate usable lifetime of the contact has been developed. This model incorporates contact wipe, fretting vibration amplitude and frequency, contaminant chemistry, material properties, plating thickness, asperity deformations, normal load, electrical load, and surface topography. It is assumed that fretting vibrations separate contacting asperities and expose virgin metallic a-spots to environmental contaminant attack. The model calculates the amount of corrosive product produced on the exposed surfaces during the separation phase of a cycle of fretting. As fretting motions pull the exposed corroded asperities back together, a mismatch in size occurs and some of the corrosive product is scraped off and deposited in the valleys. Eventually, the valleys fill and separate the a-spots, resulting in "ultimate" failure. A material balance between amounts produced and scraped off estimates the amount of corrosive product dragged into the contact. Shifting of molecules via plastic deformation mix particles of corrosive product into the asperity metal. Assumptions that correlate mixing to plastic flow and the use of modern composite theory lead to an estimate of the conductivity within the contaminated asperity. Results show a monotonic increase in contact resistance over time. Initial increases are slow, followed by rapid increases. Predicted failure times are consistent with field measurements. >

Resilient electrical interconnect

Abstract: An electrical interconnect is provided for connecting an integrated circuit or other electrical or electronic component to a circuit board or for interconnecting two or more circuit boards. The interconnect comprises a substrate having one or more resilient elements of a non-conductive material and having opposite contact surfaces. A flexible conductive coating is provided on the contact surfaces of the resilient elements and extends between the contact surfaces to provide electrical connection therebetween. In one embodiment each element is integrally formed with a resilient substrate and has electrically conductive contact surfaces which are outward of the respective substrate surfaces and are electrically connected through a conductive surface which extends through vias or openings formed in the substrate. In another embodiment, each element is individually formed and is disposed within a corresponding cavity of a separate substrate. In a further embodiment, each element is individually formed having different sections of different durometers so as to provide intended spring or resilience characteristics. A particulate layer can be provided on the conductive contact surfaces to provide a roughened surface by which an oxide layer on a mating electrical contact is penetrated to minimize contact resistance.

A high-performance self-aligned UMOSFET with a vertical trench contact structure

Abstract: We compare the electrical characteristics of a UMOSFET having a trench contact (TC-UMOS) for the source and the body regions with those of the conventional surface contact UMOSFET (SC-UMOS). For SC-UMOS, there exists an optimum cell pitch which gives the lowest on-resistance. Reducing the cell pitch beyond that point results in increased on-resistance because the source contact resistance increases as the cell pitch is further reduced. On the contrary, for TC-UMOS, the on-resistance decreases as the cell pitch is reduced because the source contact resistance does not change, These results show that TC-UMOS is more effective than SC-UMOS for reducing the on-resistance by scaling down of the cell pitch. The minimum specific on-resistance of TC-UMOS is 0.43 m/spl Omega//spl middot/cm/sup 2/. Furthermore, the critical avalanche current of TC-UMOS is enhanced significantly compared with that of SC-UMOS because the base resistance of the parasitic npn-bipolar transistor of TC-UMOS is lower than that of SC-UMOS. >

Low resistivity (∼10−5 Ω cm2) ohmic contacts to 6H silicon carbide fabricated using cubic silicon carbide contact layer

Abstract: Silicon carbide is a wide band‐gap semiconductor material which exists in more than 170 polytypes. In this work, heteropolytype epitaxy was used to decrease the specific contact resistance of ohmic contacts to the 6H‐SiC polytype (band gap Eg∼3.0 eV). High quality ohmic contacts were produced by metallizing and annealing a thin cap layer of 3C‐SiC (Eg∼2.3 eV) grown by chemical vapor deposition on either n‐ or p‐type 6H‐SiC. The measured specific contact resistance (rc) of the ohmic contacts to n‐type 6H‐SiC was found to be less than 1.7×10−5 and 2×10−5 Ω cm2 for contacts to p‐type 6H‐SiC.

Particle sputtering and deposition mechanism for material transfer in breaking arcs

Abstract: A novel mechanism called particle sputtering and deposition is proposed based on the facts that the arced contact morphology, mass transfer, and arc durations in the metallic phase and the gaseous phase undergo transition phenomena with increasing load current. The mechanism is used satisfactorily as an explanation of the material transfer process and the contact resistance degradation of Pd and Ag contacts during the breaking of dc circuits.

Method and device for detecting and measuring pressure and coordinates in pressure-sensitive pads

Abstract: A data input resistance pad for measuring coordinates and pressure of a stylus pressed on the pad has X and Y-coordinate resistance boards The X and Y-coordinate resistance boards are connectable by respective switches to high and low voltage sources at opposite ends of each board By measuring the voltage at either side of a contact resistance with a high impedance voltage measuring device, a voltage drop across the contact resistance is calculated This voltage drop represents the contact resistance and therefore the pressure of the stylus The X position is calculated by measuring the voltage drop from an end of the X-coordinate resistance board to the point of contact The Y position is calculated by measuring the voltage drop from an end of the Y-coordinate resistance board to the point of contact

Elastic behavior of contacting surfaces under normal loads: A computer simulation using three-dimensional surface topographies

Abstract: It is very important to understand the potential and limitation of the contact theories in order to apply them to geophysical problems. Using three-dimensional topographies, a computer simulation concerning the behavior of contacting surfaces under normal loads was performed to examine the contact models previously proposed. Two models, the Brown and Scholz (B&S model) and the Yamada et al. (Y model), were compared in detail. It is found that the Y model neglects the contacts between asperities and valleys or shoulders, which results in a smaller area of contact and smaller stiffness than with the B&S model. The contact area formed between asperities and shoulders or valleys is estimated at about 20% of the total contact area, a value that does not depend on either normal stress or surface roughness. The real area of contact is proportional to normal load even under purely elastic conditions, as originally proposed by Archard, and it is much smaller than 1% of the total area of contact up to the normal stress of 30 MPa. Average area of contact, contact density, mean contact pressure, and maximum contact pressure were also calculated as a function of normal stress, which revealed the detailed process of contact mechanics under normal loads.

Thermal stability of ti/pt/au nonalloyed ohmic contacts on inn

Abstract: Extremely low contact resistance of nonalloyed Ti/Pt/Au metallization on n‐type InN is demonstrated. The contacts were annealed at different temperatures up to 420 °C to investigate their thermal stability. A low contact resistivity of 1.8×10−7 Ω cm2 was measured at room temperature using the transmission line method. This was due to the extremely high doping level (5×1020 cm−3) in the InN. After 300 °C annealing, the contact resistivity increased to 2.4×10−7 Ω cm2. For 360 °C annealing, the contact morphology showed some degradation, but the contact resistivity was almost the same as at 300 °C. There was serious degradation of the contacts after 420 °C annealing. The morphology became very rough, and the contact and sheet resistances increased by factors of 3–5 times. This degradation is believed due to the decomposition of the InN film. The contact resistivities between n‐type epitaxial GaAs and InN were also investigated, and showed values around 10−4 Ω cm2.

0.1 /spl mu/m Schottky-collector AlAs/GaAs resonant tunneling diodes

Abstract: The Schottky-collector resonant tunneling diode (RTD) is an RTD with the normal N+ collector and ohmic contact replaced by a Schottky contact, thereby eliminating the associated parasitic resistance. With submicron Schottky contact dimensions, the remaining components of the parasitic series resistance can be greatly reduced, resulting in an increased maximum frequency of oscillation, f/sub max/. AlAs/GaAs Schottky-collector RTDs were fabricated using 0.1 /spl mu/m T-gate technology developed for high electron mobility transistors. From their measured dc and microwave parameters, and including the effect of the quantum well lifetime, f/sub max/=900 GHz is computed. >

Pt and Zn based ohmic contacts to p-type InP

Abstract: Interest in InP as a material for electronic and photonic devices such as junction field effect transistors (JFET) and laser diodes has increased rapidly over the last decade. Low resistance, reliable ohmic contacts play an essential role in the performance of these devices. Solar cells and LEDs require contacts to p-type InP, however, the large (/spl sim/0.8 eV) barrier height for metals on this material makes their formation difficult. This paper presents the fabrication and characteristics of a new Zn based metallisation for ohmic contacts to p-InP, achieving a lowest specific contact resistance of 2/spl times/10/sup -5/ /spl Omega/ cm/sup 2/. >

Behavior of TiN and Ti Barrier Metals in Al‐Barrier‐Al Via Hole Metallization

Abstract: The behavior of TiN and Ti barrier metals in Al-barrier-Al via structures was investigated. When a reactive-sputtered TiN film is deposited onto an Al-1 weight percent (w/o) Si-0.5 w/o Cu surface, AlN is formed at the TiN/Al interface due to the reaction of N 2 to Al, and causes an increase in via contact resistance. To suppress the increase in via contact resistance, it is crucial to interpose a Ti buffer layer at the TiN/Al interface

Contact resistance of superconductor‐semiconductor interfaces: The case of Nb‐InAs/AlSb quantum‐well structures

Abstract: The contact resistances of widely spaced (≫1 μm) superconducting Nb contacts to InAs‐AlSb quantum wells indicate a resistive behavior of the interface, with a positive electron transfer length, while narrow‐spaced contacts (≤1 μm) exhibit a strong conductance enhancement at low bias with pronounced subgap features. The data are interpreted in terms of a model in which the current across the interface is carried by Andreev reflections. From the measured transfer lengths, we estimate a single‐event Andreev reflection probability of about 3.5%, but with a high backplane‐enhanced overall reflection probability.

Low specific resistance (<6×10−6 Ω cm2) TiC ohmic contacts to n‐type β‐SiC

Abstract: An array of transfer length measurement (TLM) structures was formed on an electrically isolated n+β=SiC (111) epilayer. The n+β‐SiC epilayer was in situ doped with a nitrogen concentration of 2×1019 cm−3. The specific contact resistance (pc), sheet resistance (Rs), contact resistance (Rc), and transfer length (LT) were calculated from resistance (RT) versus contact spacing (d) measurements obtained from 10 TLM structures. The linear curves used for these calculations were fit to the RT versus d data by calculating the standard error of linear regression of RT on d; where, the average correlation coefficient with a straight line was 1.0000 and the average standard error of linear regression of RT on d was 0.26 Ω. The resulting average values were: pc=5.4×10−6 Ω cm2, Rs=22 Ω/⧠, Rc=1.45 Ω, and LT=5.0 μm. The TiC contacts, epitaxially grown by chemical vapor deposition, could not be scratched with a tungsten carbide scriber, nor could they be delaminated from the β‐SiC surface.

Au/Ge/Ni ohmic contacts to n-type InP

Abstract: The relationship between the electrical properties and microstructure for annealed Au/Ge/Ni contacts to n-type InP, with an initial doping level of 1017 cm-3, have been studied. Metal layers were deposited by electron beam evaporation in the following sequence: 25 nm Ni, 50 nm Ge, and 40 nm Au. Annealing was done in a nitrogen atmosphere at 250-400‡C. The onset of ohmic behavior at 325‡C corresponded to the decomposition of a ternary Ni-In-P phase at the InP surface and the subsequent formation of Ni2P plus Au10In3, producing a lower barrier height at the InP interface. This reaction was driven by the inward diffusion of Au and outward diffusion of In. Further annealing, up to 400‡C, resulted in a decrease in contact resistance, which corresponded to the formation of NiP and Au9ln4 from Ni2P and Au10In3,respectively, with some Ge doping of InP also likely. A minimum contact resistance of 10-7 Ω-cm2 was achieved with a 10 s anneal at 400‡C.

Influence of metal/n‐InAs/interlayer/n‐GaAs structure on nonalloyed ohmic contact resistance

Abstract: We have investigated in detail the influence of interlayer structures on nonalloyed ohmic contact resistance (ρc), in terms of the crystalline defects and the potential barrier at the interlayer/GaAs interface. The interlayer structures are a graded‐band‐gap InAs/GaAs strained‐layer superlattice (graded SLS), a graded‐band‐gap InGaAs, and conventional SLSs without graded band gaps. A two‐layer transmission line model indicates that the barrier resistance in the interlayer highly depends on the interlayer structure: ≤5×10−8 Ω cm2 for the graded SLS and graded InGaAs interlayers and 10−5–10−6 Ω cm2 for the conventional SLS interlayers. To explain the large dependence of the interlayer structure, first, the density and distribution of the misfit dislocations and stacking faults caused by the large lattice mismatch between InAs and GaAs have been investigated in detail by high‐resolution transmission electron microscopy. In the graded SLS and conventional SLS interlayers, the influence of the high‐density dep...

A self-consistent characterization methodology for Schottky-barrier diodes and ohmic contacts

Abstract: Based on the simple interfacial-layer theory, the extraction methods for the interface parameters of the metal-semiconductor contact have been developed and applied to characterize both the Schottky-barrier diodes and the ohmic contacts in a self-consistent manner. It has been shown that the physical parameters at the metal-semiconductor interface can be extracted from the I-V characteristics of the Schottky-barrier diodes and the degradation of the thermal-equilibrium barrier height due to the thermal cycle can be directly modeled in terms of the extracted interface parameters. Besides, using the extracted parameters, the specified surface-treatment process can be evaluated by the extracted thermal-equilibrium barrier height, and thus the strongly process-dependent specific contact resistivity /spl rho//sub c/ of the ohmic contacts can be theoretically calculated by a modified tunneling model considering the impurity band. Furthermore, by comparing the simulated results and the measured /spl rho//sub c/ data deduced from the Al and Ti contacts on both doping types of the Si-substrate, satisfactory agreements have been obtained. >

Formation of metal silicide‐silicon contact with ultralow contact resistance by silicon‐capping silicidation technique

Abstract: Ultralow contact resistance of metal silicide‐n+‐Si contact has been achieved by a novel contact metallization process employing Ta silicidation of a n+‐Si contact surface by a Si‐capping silicidation technique. The Si‐capping silicidation has been employed to realize an ultraclean silicidation. The as‐deposited Ta surface is in situ covered with a very thin Si protection layer in order to prevent the metal surface from being oxidized or contaminated. By combining the oxide‐layer‐free Si/metal on Si deposition process and an ultraclean ion implantation for mixing, metal silicide‐n+Si structure has been formed by low temperature thermal annealing in an ultraclean Ar gas. As a result, an ultralow contact resistivity of 5.8×10−9 (Ω cm2) has been achieved.

Low emitter resistance GaAs based HBT's without InGaAs caps

Abstract: Low emitter resistance is demonstrated for AlGaAs/GaAs heterojunction bipolar transistors using Pd/Ge contacts on a GaAs contact layer. The contact resistivity to 2-10/spl times/10/sup 18/ cm/sup -3/ n-type GaAs is 4-1/spl times/10/sup -7/ /spl Omega/-cm/sup 2/. These are comparable to contact resistivities obtained with non-alloyed contacts on InGaAs layers. The non-spiking Pd/Ge contact demonstrates thermal stability and area independent resistivity suitable for scaled devices. The substitution of Pd/Ge for AuGe/Ni GaAs emitter and collector contacts reduced by an order of magnitude the emitter-base offset voltage at high current densities and increased f/sub t/ by more than 15% with significantly improved uniformity for devices with 2 and 2.6 /spl mu/m wide emitters having lengths two, four and six times the width. >

Pt/ti/ge/pd ohmic contacts to gaas : a structural, chemical, and electrical investigation

Abstract: Interface morphology, phase composition, and elemental diffusion of Pt/Ti/Ge/Pd ohmic contacts to both n+‐ and p+‐GaAs have been investigated as a function of annealing temperature. Structural and chemical results were correlated with specific contact resistances (ρc) measured for each thermal treatment in an attempt to determine how the indiffusion of contact metal and the out‐diffusion of Ga and As affect specific contact resistance, and how effective Ti is as a diffusion barrier. Annealing at 450 °C yielded the lowest ρc, ∼6.4×10−7 Ω cm2. The interface was observed to be smooth and abrupt, and there was little As out‐diffusion and Pt indiffusion. Two interface phases were detected; a primary phase, PdGe, and a secondary, Ga rich Pd–Ga–As ternary phase. The presence of this ternary phase is believed to be critical to contact formation on n‐type GaAs. The Ti and Pt layers remained pristine. Annealing at 550 °C resulted in a slightly higher ρc,∼2.1×10−6Ω cm2. There was significant elemental diffusion within the contact metal and minor diffusion into the GaAs substrate. The interface possessed limited areas of spiking with uniform composition. Annealing at 600 °C proved to have a detrimental effect on the ρc, ∼10−4Ω cm2. This electrical degradation was accompanied by strong chemical intermixing between the contact and substrate, resulting in a continuous nonplanar interface with deep multiphase protrusions, and the Ti layer no longer was effective as a diffusion barrier.

Method for determining the resistance and carrier profile of a semiconductor element using a scanning proximity microscope

Abstract: A method for measuring the resistance or conductivity between two or more conductors which are placed against a semiconductor element, the conductors are placed either in contact with the top surface or one conductor is placed in contact with the top surface and the other conductor is in the form of a large ohmic contact applied to the bottom surface of the semiconductor element. In order to bring the contact resistance between the top conductor(s) and the element to, and hold it at, a predetermined value during measuring, the conductor(s) are held at a constant distance and/or under constant pressure relative to the semiconductor element by use of a scanning proximity microscope. The top conductor may have a boron implanted diamond tip. The carrier profile of the semiconductor element is determined from previously derived calibration curves.

Assessment of fretting failure models of electrical connectors

Abstract: Two competing models of the effects of fretting corrosion on contact resistance have been investigated. The asperity contamination model explored corrosion product mixing into asperity metals: asperity metals evolved into a metal/salt composite with elevated resistance at the asperities. The valley filling mechanism assumed wear debris dropped into surface valleys: after valleys filled, surfaces separated and contact resistance escalated. Both mechanisms predicted correct orders of magnitude for the number of cycles to high resistance failure. Each mechanism was based on a material balance and incorporated fretting vibration amplitude and frequency, changes in material properties induced by corrosion, plating thickness, loads, and asperity deformations. In this paper the models are extended to include other important factors such as imperfect packing of wear debris dropping into in valleys, wear of asperities, plating deterioration, effect of asperity contamination on further asperity corrosion, effect of normal force on debris wear, contact healing via fritting, and second stage resistance fluctuations.

Contact resistance characteristics of Ag material in breaking low-load DC arcs

Abstract: Contact resistance of Ag contacts was determined from nonload to 4 A under switching inductive load conditions. The tested results show that three characteristic contact resistance variations corresponding to three types of contact morphologies exist, and there are a critical transition load current and a critical transition operation cycle. When the load current is less than 0.2 A, which is called critical transition current, the contact resistance at the beginning of the operation, which is less than critical transition operation cycle, is like that in nonload condition, i.e., low and stable. If the load current is larger than this critical value, the contact resistance is, however, high and unstable during the whole test process. It is demonstrated that this phenomenon is attributable to arc occurrence probability and arc duration. Both mechanical factors (wear and mechanochemical reaction) and electrical factors (arc erosion and heat corrosion) are considered to be dominant in different load currents and different operation periods. >

NiGe‐based ohmic contacts to n‐type GaAs. II. Effects of Au addition

Abstract: Our efforts have been continued to improve the electrical properties of NiGe ohmic contacts by adding a small amount of a third element to the NiGe contacts without deteriorating thermal stability and surface smoothness. In the present study, Au was chosen as the third element, and the optimum conditions to produce thermally stable, low resistance ohmic contacts were determined by preparing a variety of contacts with different thickness ratios of the Ni, Ge, and Au layers. The best ohmic contact was prepared by depositing sequentially Ni (40 nm), Au (5 nm), and Ge (100 nm) onto the n‐type GaAs substrate, and annealing at 450 °C for 5 s. This contact provided the contact resistance of about 0.2 Ω mm, which is lower than that of the NiGe(In) contacts. The present contact had smooth surface after contact formation and showed excellent thermal stability during isothermal annealing at 400 °C. The cross‐sectional observation using high‐resolution electron microscopy indicated that the GaAs/metal interface was uniform and the diffusion depth of the contact metal to the GaAs substrate was shallow (∼20 nm). These contact properties are desirable for future GaAs very large scale integration devices.

Method for fabricating a bipolar transistor with reduced base resistance

Abstract: A semiconductor device manufacturing method according to the present invention includes forming an outer base region in a collector layer. The outer base region connects an intrinsic base layer and a base electrode so that base contact resistance between them is decreased.

Alloyed and Non-Alloyed Ohmic Contacts for AlInAs/ InGaAs High Electron Mobility Transistors

Abstract: AuGe/Ni/Au alloyed and WSi non-alloyed ohmic contacts are investigated for AlInAs/InGaAs high electron mobility transistors (HEMTs). For the alloyed contact, a contact resistance (R c) lower than 0.03 Ω mm is obtained at an alloy temperature of 300°C. The value of R c drastically increases with alloy temperatures above 300°C and exceeds 0.15 Ω mm at 380°C. Auger analysis and analytical cross-sectional transmission electron microscopy have revealed significant outdiffusion of In in the epitaxial layer into the top Au layer and the formation of polycrystalline GaAs in the epitaxial layer, which cause the increase of R c with alloy temperature. For the refractory WSi non-alloyed ohmic contact, R c remains lower than 0.1 Ω mm under annealing temperatures up to 380°C. The extrinsic maximum transconductance (g m) of 600 mS/mm is obtained for the HEMT device with the WSi ohmic contact.