Showing papers on "Contact resistance published in 1993"

Metal contacts to gallium nitride

Abstract: We report measurements on the nature of aluminum and gold contacts to GaN. The GaN films were deposited onto the R‐plane of sapphire substrates by molecular beam epitaxy and are autodoped n‐type. Metal contacts were deposited by evaporation and were patterned photolithographically. Current‐voltage characterization shows that the as‐deposited aluminum contacts are ohmic while the as‐deposited gold contacts are rectifying. The gold contacts become ohmic after annealing at 575 °C, a result attributed to gold diffusion. The specific contact resistivity of the ohmic aluminum and gold contacts were found by transfer length measurements to be of device quality (10−7–10−8 Ω m2). The results of these studies suggest a direct correlation between barrier height and work function of the metal, consistent with the strong ionic character of GaN.

Flat ceramic heater having discrete heating zones

Abstract: A plurality of resistive heating elements and conductive elements are screenprinted onto a ceramic substrate to form a heater having multiple resistive heating elements. Slots formed between adjacent resistive heating elements members provide air gaps to thermally insulate each heating element from neighboring elements. Gold-plated leads provide low contact resistance for receiving power from a battery for energizing each of the resistive heating elements.

Contact resistance measurements on p‐type 6H‐SiC

Abstract: Specific contact resistance measurements are reported for Al‐Ti ohmic contacts to epitaxial p‐type 6H‐SiC as a function of epitaxial doping The circular transmission line method was used to measure the specific contact resistance including the sheet resistance of the epitaxial layer and the modified sheet resistance under the contact Epitaxial layers with Al doping between 55×1015 and 2×1019 cm−3 yielded specific contact resistances between 29×10−2 and 15×10−5 Ω cm2 A good theoretical fit to the contact resistance data was obtained by assuming the metal‐6H‐SiC barrier height to equal 037 eV

Molded case circuit breaker contact

Abstract: A movable contact bridge of a molded case limiting circuit breaker is supported by a bar by a system of springs enabling opening with electrodynamic repulsion. The contact bridge cooperates with stationary contacts rigidly secured to current input conductors in the shape of half-loops. An anvil is adjoined to the rear of the stationary contacts to increase the closing impact effect of the contact bridge and prevent contact resistance dispersions. The anvil is made of ferromagnetic material increase the magnetic field for blowout of the arc to the extinguishing chambers.

High performance capacitors using nano-structure multilayer materials fabrication

Abstract: A high performance capacitor fabricated from nano-structure multilayer materials, such as by controlled, reactive sputtering, and having very high energy-density, high specific energy and high voltage breakdown. The multilayer capacitors, for example, may be fabricated in a "notepad" configuration composed of 200-300 alternating layers of conductive and dielectric materials so as to have a thickness of 1 mm, width of 200 mm, and length of 300 mm, with terminals at each end of the layers suitable for brazing, thereby guaranteeing low contact resistance and high durability. The "notepad" capacitors may be stacked in single or multiple rows (series-parallel banks) to increase the voltage and energy density.

Using compound electrodes in electrical impedance tomography

Abstract: A compound electrode composed of a large outer electrode to inject current and a small inner electrode to sense voltage was developed and used to measure voltages from a physical phantom. The measured voltages were smaller in amplitude than those from conventional electrodes, demonstrating that the compound electrode can minimize contact impedance voltage drop from the measured data. A finite-element model was used for the compound electrode and incorporated into the regularized Newton-Raphson reconstruction algorithm. A sensitivity study showed that the reconstructed resistivity distributions are less dependent on the unknown contact resistance values for a compound electrode than a conventional electrode and that the use of a compound electrode results in improved images for the reconstruction algorithm. >

Electrical contact resistance under high loads and elevated temperatures

Abstract: This research is focused on characterizing electrical contact resistance involved in resistance spot welding of thin sheet steels. It is part of a larger study in which a mathematical simulation of the welding process is being developed. A special test fixture has been fabricated that allows contact resistance at the electrode-to-sheet interface and the sheet-to-sheet interface to be measured under typical welding pressures (e.g., 14 ksi) and from room temperature to elevated temperatures. Bare and galvanized mild and HSLA steels have been considered. The nature of the contact resistance is discussed, and experimental findings are presented

A controllable mechanism of forming extremely low‐resistance nonalloyed ohmic contacts to group III‐V compound semiconductors

Abstract: This work refers basically to the detailed understanding of the natural phenomena in real tunneling metal‐semiconductor contacts. A mechanism of forming extremely low‐resistance nonalloyed Ti/Pt/Au ohmic contacts to a variety of III‐V compound semiconductors, e.g., InGaAs, InAs, and GaAs, is presented. Epitaxial layers of either type with different doping levels ranging from 1×1019 to 2×1020 cm−3 were employed in order to determine electrical parameters that guarantee pure tunneling behavior of the contacts. Ti/Pt/Au contacts formed on p‐InGaAs Zn doped to 1×1020 cm−3 and on n‐InGaAs Si doped to 5×1019 cm−3 yielded a specific contact resistance of 4.8×10−8 and 4.3×10−8 Ω cm2, respectively. The same metallization scheme applied to 4×1019 cm−3 Si‐doped n‐InAs gave a specific contact resistance of 1.7×10−8 Ω cm2 for the as‐deposited and annealed samples. An extremely low value of 2.8×10−8 Ω cm2 was evaluated for contacts on p‐GaAs doped with Be to 2×1020 cm−3. The contact properties are discussed in relation...

Evaluation of ohmic contacts formed by B+ implantation and Ti‐Au metallization on diamond

Abstract: Low‐resistance ohmic contacts have been fabricated on a naturally occurring B‐doped diamond crystal and on polycrystalline diamond films by B ion implantation and subsequent Ti/Au bilayer metallization. A high B concentration was obtained at the surface by ion implantation, a post‐implant anneal, and a subsequent chemical removal of the graphite layer. A bilayer metallization of Ti followed by Au, annealed at 850 °C, yielded specific contact resistance (ρc) values of the order of 10−5 Ω cm2 for chemical vapor deposition grown polycrystalline films and the natural IIb crystal. The ρc values from transmission line model measurements on three different contact configurations, namely, standard rectangular pads, rectangular pads on diamond mesas, and three‐ring circular structures have been compared. These contacts were stable to a measurement temperature of ∼400 °C and no degradation due to temperature cycling was observed. Chemical analysis by x‐ray photoelectron spectroscopy (XPS) in conjunction with Ar+ sputter depth profiling of the annealed samples indicated that the Au overlayer was not effective in preventing oxidation of the underlying Ti. The XPS study also indicated the formation of TiC at the Ti/diamond interface.

Formation of extremely low resistance Ti/Pt/Au ohmic contacts to p‐GaAs

Abstract: Nonalloyed Ti/Pt/Au contacts to heavily doped p‐GaAs have been fabricated using effective cleaning of the semiconductor surface by bombardment with low energy Ar+ ions (60 eV) prior to the metal deposition. Short‐time annealing cycles for 1 and 20 s were employed in order to restore the primary properties of the subsurface layer disordered during ion bombardment. Annealing at temperatures ranging from 420 to 530 °C provides formation of contacts with an extremely low resistivity of 2.8×10−8 Ω cm2. A definite correlation between electrical properties and structural modifications of the contact interface was found. Measurements of the contact resistivity at different ambient temperatures yielded a good quantitative agreement with the theoretically predicted values using the field‐emission model. The results indicate that the metal‐semiconductor junctions formed under optimal conditions are intimate and that tunneling is the dominant mechanism of the current flow.

Review of the thermal contact conductance of junctions with metallic coatings and films

Abstract: The reliability of standard electronic modules may be improved by decreasing overall module temperature. This may be accomplished by enhancing the thermal contact conductance at the interface between the module frame guide rib and the card rail to which the module is clamped. The surface irregularities resulting from the machining or extruding of the components cause the true contact area to be much less than the apparent contact area, increasing the contact resistance. Some metallic coatings deform easily under load and increase the contact area and associated conductance. This investigation evaluates possible coatings and determines those most suitable for enhancing contact conductance based upon predictions using existing theories for thermal contact conductance of coated junctions.

Au(Pt)Pd ohmic contacts to p-ZnTe

Abstract: Au(Pt)Pd ohmic contacts to p-ZnTe are reported, with a determination of the optimum annealing temperature and the optimum Pd layer thickness The specific contact resistance, measured by the transmission line method, was as low as 5*10/sup -6/ Omega cm/sup -2/ This value of the specific contact resistance is two orders of magnitude lower than that of Au or Au/Pt contact to p-ZnTe >

Shallow ohmic contact to both n‐ and p‐GaAs

Abstract: A shallow Pd/Ge/Ti/Pt/ohmic contact for both n‐ and p‐GaAs has been investigated. The contacts were rapid thermally annealed in N2 for 15 s at temperatures from 350 to 550 °C. The lowest average specific contact resistances were 4.7×10−7 and 6.4×10−7 Ω cm2 for the n‐ and p‐GaAs, respectively, when the n‐GaAs was doped with Si to 2×1018 cm−3 and the p‐GaAs was doped with carbon to 5×1019 cm−3. Electrical measurements and Auger depth profiles showed that the contacts were stable as they remained ohmic after an anneal at 300 °C for 20 h for both n‐ and p‐GaAs. The p contact is more stable than the n contact at the higher temperatures where there is more As outdiffusion as determined by Auger depth profiles. Transmission electron microscopy showed that the interfaces between the p‐GaAs and the contacts were smooth for both as‐grown and annealed samples, and no oxides were detected.

P/N junction device having porous emitter

Abstract: In a semiconductor P/N junction device, a porous emitter is provided which has high saturation current to limit injected charge when the device is conducting The porous emitter includes a lightly doped region abutting a contact on the surface of the device to regulate minority carrier injection under forward bias and shield the contact from stand-off field when the device is not conducting One or more heavily doped regions are provided in the first region to provide low contact resistance for the flow of majority carriers into the emitter

Metallization process for a semiconductor device

Abstract: A contact for a semiconductor device has a via extending through a dielectric and collimated titanium in the via. Depositing titanium by collimation places sufficient metal into high aspect ratio contacts to make good electrical connection. The collimated titanium may be reacted in a nitrogen containing ambient to form a titanium silicide layer at the bottom of the contact and a titanium nitride layer over the titanium silicide layer. The titanium silicide layer provides good electrical contact to a device in a silicon semiconductor substrate and lowers contact resistance. Tungsten may be deposited over the colliminated titanium to form a conductor layer. The titanium nitride layer provides a sticking layer for the tungsten. The contact structure and the method are useful in high aspect ratio contacts present in VLSI multilevel interconnected devices such as dynamic random access memories.

Silver based alloy electric contact material

Abstract: The present invention relates to a kind of silver based alloy as electric contact material. Its composition comprises at least one of the rare earth elements (Sm, Yb, Eu, Tm, Ho, Dy and Er),at least one of the elements (Fe, Co, Ni, W, V, Cr, Zr, B, C and Si) and at least one of the elements (Sn, Al, Cu, Zn, Ga, Ge, In, Mn, Bi and Mg). Besides, in the alloy at least one of the elements (La, Ca, Y, Gd, Pr, Nd and Lu) can be added. Said alloy material has the advantages of good arc-suppression property, welding resistance, burn-out resistance and adhesion resistance. Its contact resistance is low and stable, production process is simple, cost is low, workability is good, and its service life can be up to hundred thousand times for miniature relay so it can be substituted for AgCdO to a certain extent.

Series resistance of self-aligned silicided source/drain structure

Abstract: The external resistance of the self-aligned silicided source/drain structure is examined by two-dimensional simulation considering recession of the contact interface due to the consumption of silicon during the silicidation process. It is observed that the recessed contact interface forces a significant amount of current to flow into the high-resistivity part of the junction, resulting in an increase of resistance as large as several hundred ohms-micrometers in comparison with the surface contact structure. The increase scales up with the scaledown of the minimum feature size, and the expected benefits of the salicide structure diminish for the sub-half-micrometer devices. A simple analytical explanation is proposed. By considering the recession of the contact interface, the reported high external resistance of short-channel MOSFETs is explained. Different source/drain contact types are compared, and it is concluded that the conventional salicide process should be modified for sub-half-micrometer devices. >

Effect of back contact impedance on frequency dependence of capacitance‐voltage measurements on metal/diamond diodes

Abstract: Differential capacitance‐voltage (C‐V) measurements were performed on Al and Pt rectifying contacts fabricated on natural (type IIb) diamonds. The C‐V data showed frequency dependence, which decreased significantly after reducing the back contact impedance. The frequency dependence seems primarily to be an effect of the contact capacitance, contact resistance, and bulk resistance of diamond. A model which includes these variables has been proposed to explain this frequency dependence using both large and small back contact impedances.

Method of forming low resistance contacts at the junction between regions having different conductivity types

Abstract: A thin film transistor structure having a first and a second polycrystalline silicon layer of different conductivity types (P and N) has a high resistance contact at the resultant P-N junction. This contact resistance is reduced by forming TiSi2 (titanium disilicide) or other refractory metal silicides such as cobalt or molybdenum in specific regions, namely the P-N junction contact. Titanium disilicide consumes the portion of the second polycrystalline silicon layer in the P-N contact junction and at the same time consumes a small portion of the underlying first polycrystalline silicon layer, such that the high resistance P-N junction now no longer exists.

Method for measuring contact resistance

Abstract: An improved method for measuring contact resistance during device testing is disclosed. After a device under text has been properly positioned to make a contact with a test fixture, a first test current is forced between two pins of the device under test through an isolating diode and the voltage drop associated therewith is measured. Then, a second test current is forced to take the same path and the voltage drop associated therewith is also measured. The values of the forced currents and the measured voltage drops are then used to determine the dynamic resistance of the path, which includes the resistance of two contacts. The determined dynamic resistance or a derivative thereof is then used as an indication of the contact resistance between the test fixture and the device under test.

Method for fabricating low resistance contacts of semiconductor device

Abstract: A method for fabricating contacts of a semiconductor device capable of achieving a reduced contact resistance by using a material, such as TiSi 2 , exhibiting a low potential barrier to a N + diffusion layer for a contact for the N + diffusion layer and a material, such as PtSi, exhibiting a low potential barrier to a P + diffusion layer for a contact for the P + diffusion layer and performing two independent masking works respectively for the N + diffusion layer and the P + diffusion layer.

The structural and electrical properties of low‐resistance Ni contacts to InP

Abstract: We have investigated the electrical and metallurgical behavior of the Ni-InP contact system. Specific contact resistivity (Rc) values in the low 10 exp -7 Omega-sq cm range are achieved with Ni-only contacts on n-InP by sintering at 400 C for several minutes. The postsinter contact metallization consists of three layers, arranged in the sequence: InP/Ni3P/Ni2P/In. Extended sintering (40 min) at 400 C brings about a rise in Rc to the 10 exp -4 Omega-sq cm range. After extended sintering, the contact metallization is found to consist of only two layers, arranged in the sequence: InP/Ni2P/In. Based on the correlation between low Rc and the presence of Ni3P at the metal-InP interface, it is suggested that the presence of Ni3P is the cause of the low Rc values. We show that the sintering schedule used to achieve low values of Rc is accompanied by substantial metal-InP interdiffusion that results in severe device degradation.

Low contact resistivity ohmic contacts to 6H-silicon carbide

Abstract: The resistivity of ohmic contacts to N/sup +/ 6H-silicon carbide substrates, with Ti as the contact material, was studied using the circular TLM structure Two dimensional numerical simulation of the circular TLM structures were performed to analyze the current distribution and its influence on the extraction procedure A contact resistivity of 2/spl times/10/sup -5/ ohm-cm/sup 2/ was obtained without any high temperature anneal by using an N/sup +/ surface implant layer This contact resistivity is an order of magnitude lower than any of the previously reported values for n-type 6H-silicon carbide >

Formation of SiO/sub 2/ on contact surface and its effect on contact reliability

Abstract: Electrical contact failure due to thermal decomposition of low-molecular-weight silicone vapor evaporated from such silicone products as oils and rubbers was investigated in a simulated environment. A glassy film deposit was found on the contact surface after exposure to elevated temperature in an atmosphere containing an extremely small quantity of the silicone. The film was clearly identified as amorphous SiO/sub 2/ by ellipsometry, X-ray photoelectron spectrometry (XPS), and X-ray diffractometry (XRD). The growth of the film was directly related to the concentration of silicone vapor and temperature. The growth law was an exponential function of the exposure time. The film increases static contact resistance when it is thicker than 800 AA and the load is less than 5 g. The relationship between the concentration of the vapor, temperature, film thickness, and contact resistance is represented schematically. >

Contact resistance measurements recorded at conductive polymer/high-temperature superconductor interfaces

Abstract: Methods of making electrical contact to high-T[sub c] superconductors with conductive polymers are described. In addition, three- and four-point resistance measurements are acquired on samples of YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]], GdBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]], and Pb[sub 0.3]Bi[sub 1.7]Sr[sub 1.6]Ca[sub 2.4]Cu[sub 3]O[sub 10] using poly(3-hexylthiophene) contacts in order to determine the temperature dependence of the conductive polymer/superconductor contact resistance. Although the polymer/superconductor contact resistance displays activated behavior above T[sub c] and increases as the temperature is lowered, below T[sub c] there is a precipitous decrease in the resistance at that interface. Similar measurements completed on systems where the superconducting components are substituted by normal metals do not show any signs of such contact resistance decreases. Possible reasons for the decrease in the polymer/superconductor interface resistance at T[sub c] are discussed. 18 refs., 3 figs., 1 tab.

Distributed parameter analysis of dark I-V characteristics of the solar cell: estimation of equivalent lumped series resistance and diode quality factor

Abstract: The present investigation deals with the distributed parameter analysis of the p–n junction solar cell in the current-induced case at low level injection. The theory, for the first time, takes into account the metal–semiconductor contact resistance, along with the base bulk resistance and the diffused layer shear resistance. The transcendentally nonlinear differential equations for the emitter layer current and voltage have been solved analytically. Additionally, expressions for the I–V characteristic and equivalent ‘lumped’ series resistance have been established. Such physical parameters are very useful in the optimisation of the contact finger width and separation. Inclusion of the contact resistance, even for very small values, corresponds to the nonuniform carrier generation within the metallic grid. Therefore, the results are affected both qualitatively and quantitatively. The most important effect has been calculated in the I–V characteristics resulting from an additional contribution to the series resistance. Analysis reveals that the series resistance and the diode quality factor vary with applied current.