Conductor Stripes Research Articles

A Powered Floor System with Integrated Robot Localization

One of the most pressing issues in the field of mobile robotics is power delivery. In the past, we have proposed a powered floor based solution. In this article, we propose a system which combines a powered floor with a robot pose estimation system. The floor on which the mobile robots stand is composed of an array of interdigitated conductors that provide DC power supply; the stripes of conductors are interwoven similarly to what happens in a carpet, thus creating a sort of checkerboard of positive and negative pads. The robots are powered through sliding contacts. The power supply voltage is modulated with a binary encoding that uniquely identifies each conductor stripe power line; in this way, each robot is able to self-localize, by exploiting the information coming from the contacting pins. We describe the theoretical framework that allows concurrent power delivery and localization (with error boundaries). Then, we present the experimental evaluation that we performed using a prototype realization of the proposed powered floor system.

Π Unileg Thermoelectric Structure for Cycling Robustness at High Temperature and Low Manufacturing Cost

Unileg-type thermoelectric generators have proven to be a good choice for high-temperature applications, because their composition from a single thermoelectric material avoids different thermal expansion coefficients, giving the structure good mechanical strength and increased lifespan during thermal cycling. These structures are usually composed of a thermoelectric pellet with metallic electrical conductors joining the hot and cold ends of consecutive pellets. The novel unileg structure described herein is designed to deal with one of the main issues with traditional devices, viz. the physical and chemical stability of the solder between the pellet and the conductor at the hot side. The material for which this structure is proposed is a p-type Ca3Co4O9 semiconductor oxide, due to its chemical stability at high temperature and good machinability. This final requirement is related to the main innovation of the structure, viz. a partial cut that divides the pellet longitudinally, leaving two legs joined by an uncut section, forming a section similar to the letter Π. The metallic conductor stripe usually employed in unileg thermoelectric generator manufacturing is replaced by a coating of conductive material, in this case silver, on one of the legs resulting from the cut. Due to these operations, one of the legs is practically short-circuited and acts as an electrical conductor for the unileg structure, eliminating the need for soldering at the hot end of the pellet.

Fabrication of a transversal multilayer thermoelectric generator with substituted calcium manganite

AbstractThe sintering behavior and thermoelectric performance of Ca0.99Gd0.01Mn0.99W0.01O3was studied, and a multilayer thermoelectric generator was fabricated. The addition of CuO as sintering additive was found to be effective for the reduction in the sintering temperature from 1300°C to about 1000°C‐1050°C. Dense samples were obtained after firing at 1050°C, whereas some porosity remained after firing at 1000°C. Samples sintered at reduced temperature exhibit lower electrical conductivity, whereas the Seebeck coefficientS = −150 μV/K at 100°C is not affected by lowering the sintering temperature. The figure of merit is ZT = 0.12 at 700°C for samples sintered at 1300°C; ZT = 0.08 and 0.03 were obtained for multilayer laminates sintered at 1050°C and 1000°C, respectively. A transversal multilayer thermoelectric generator (TMLTEG) was built by stacking layers of substituted CaMnO3green tapes, and printing AgPd conductor stripes onto the thermoelectric layers at an angle of 30° relative to the direction of the heat flow. The multilayer stack was co‐fired at 1000°C. The TMLTEG has a power output of 2.5 mW at ∆T= 200 K in the temperature interval of 25°C‐300°C. A meander‐like generator with larger power output comprising six TMTEGs is also presented.

Design of high frequency inductors based on magnetic films

Magnetically coated stripe inductors with conductor insulated from the magnetic film and with conductor in direct electrical contact with the magnetic film are analyzed. A simple equivalent circuit model shows that for the structure without insulation, regardless of the fact that the dc resistivity of the magnetic film is much higher than that of the conductor, most of the driving current flows in the magnetic film at frequencies where the impedance of the device is dominated by inductance, i.e., where the quality factor Q>1. This effect of current re-distribution significantly lowers the performance of the device. A design is proposed having insulation layers to avoid current flow in the magnetic film, which is broken up in sections along the conductor stripe to avoid displacement currents in the system.

Electromigration Lifetime and Step Coverage in Al/Cu/Si Thin Film Conductors

ABSTRACTElectromigration-induced failure was investigated in Al/Cu/Si conductor stripes deposited over trenches cut into an oxide layer and compared with those deposited onto flat areas. The results indicate a reduction in lifetime which is proportional to the size of the step to be covered and this reduction is in excess of what is expected from simple current density scaling. In addition, the electromigration performance of conductors deposited over topology did not correlate well with the performance on flat structures.

Electromigration and mechanical stress in aluminium conductor tracks passivated by anodisation

The electromigration lifetime of integrated circuit metallisation is commonly found to increase if the metallisation is covered with a passivation layer such as glass. We have investigated the electromigration behaviour of aluminium conductor stripes under different thicknesses of oxide passivation formed by anodisation. The ionic drift velocity of anodised stripes was measured using the Blech-Kinsbron edge displacement technique (Thin Solid Films25 327 (1975)) and it was found that the drift velocity decreased with increasing anodisation thickness. Stripes tested with a reversed current drifted backwards with an initial velocity which exceeded the original forward velocity. These results are related to a change in the self-diffusivity of aluminium as a result of high compressive stresses imposed by the anodised layer, and the distribution of stress in a drifting stripe is discussed. A general conclusion is that passivation layers can support compressive stresses sufficient to retard mechanical failure processes in metallisation in two distinct ways, either by raising the threshold stress for the nucleation of damage such as hillocks or whiskers, or by reducing the diffusivity in the metallisation.

Study of electromigration-induced resistance and resistance decay in Al thin-film conductors

Using an ac Bridge technique, the resistance of thin-film (500 nm thick) Al and AlCu(5%) conductor stripes was monitored during high direct current density (1×106 A cm−2) stressing. The resistance was found to increase approximately linearly with time during stressing with a rate that was thermally activated. Surprisingly the activation energy varied considerably between nominally identical samples. After 3 h of stressing, the current was turned off and an exponential decay in the resistance was observed with a time constant of several hours. The decay was also thermally activated with an energy that varied from film to film. Both results suggest that the activation energy for resistance change during electrical stress can be significantly different in nominally identical films.

Activation energy for electromigration failure in Al–Cu conductor stripes covered with polyimide

The activation energy for electromigration failure was determined for Al-4% Cu conductor stripes covered with polyimide. The activation energy was measured to be 0.88 eV, which is substantially higher than that measured previously for similar systems under glass. The difference in the activation energies is attributed to the possible presence of hydrogen in the Al–Cu grain boundaries.

A bidirectional loop-to-loop transfer gate for ion-implanted bubble devices with on chip cache organization

A new bidirectional loop-to-loop transfer gate has been designed with an N-shape conductor stripe. It is characterized for use with ion-implanted bubble devices with on chip cache organization (OCCO). The gate is operated in 4 modes for He+ ion implanted devices with 1 μm diameter bubbles. Only one of the 4 transfer modes is found to be usable for bidirectional transfer operation, according to bubble data recurrence considerations between cache and storage loops, and according to operation margin stability. Composite operation margins are obtained as 25 Oe for greater than 55 Oe in-plane drive field, even for consecutive data transfer. The bidirectional transfer gate makes possible ion-implanted bubble devices for high access performance, even in high bit density large capacity memories.

Electromigration in Al-Cu thin films with polyimide passivation

The relative electromigration performances of Al-Cu conductor stripes with various combinations of sputtered quartz and polyimide passivation above and below the conductor were compared. A vertical structure with polyimide above and sputtered quartz below the conductor proved to be the best. A model is constructed where it is shown that passivation defects are important in the reliability of thin film conductor stripes.

Observation of electromigration in heavily doped polycrystalline silicon thin films

Heavily doped P- and N-type polycrystalline silicon conductor stripes were subjected to a high direct current density stress of ∼1×106 A/cm2. It was found that all of the N-type stripes failed near the cathode, whereas all of the P–type stripes failed near the anode, thus pointing out the importance of the sign of the effective mass of the charge carriers in the momentum exchange that leads to electromigration. A model where migration of the dopant is responsible for the observed failures is suggested.

Pulse nonlinearity measurements on thin conducting films

A new pulsed nonlinearity measurement is described and applied to the characterization of thin-film conductor stripes. The method is based on the phenomenon of ’’baseline shift’’, and is substantially simpler than the already familiar third-harmonic method yet, at least potentially, just as sensitive. A model is proposed in which the observed nonlinearity is attributed to the temperature rise accompanying current in conductors and the associated resistance change. Good quantitative agreement has been obtained with predictions based on the model. A specific application of this method to reliability testing has been found in magnetic bubble memories, the lifetime of which correlated closely with pulse nonlinearity measurements.

Electromigration in conductor stripes under pulsed dc powering

Thin Ti–Au films on sapphire were powered using pulsed dc. The incidence of electromigration damage is a complex function of pulse duration and repetition rate. For a given total ``exposure'' (fixed current density for a fixed total on-time) the damage may be reduced or eliminated by using duty cycles less than 100%.

The analysis of chemical and metallurgical changes in microcircuit metalization systems

Chemical and metallurgical changes in IC metalization systems have been studied during a program of device reliability testing and evaluation. This paper discusses the four reactions responsible for the majority of the observed metalization failures: 1) migration of aluminum under silicon dioxide layers, 2) movement of silicon through both gold and aluminum wires resulting in loss of mechanical strength, 3) structural changes in the molybdenum-gold system occurring during temperature storage testing, and 4) the electrochemical attack of the molybdenum barrier layer resulting from humidity storage testing with applied bias. Using standard optical techniques and a commercially available electron beam microanalyzer/scanning electron microscope, the following results were obtained. 1) At temperatures near the silicon-aluminum eutectic point, aluminum migrated under the thermally grown oxide in the form of triangles oriented with respect to the underlying silicon. Aluminum migration was observed at lower temperatures when bias was applied to the device. This occurred at the interface of the thermal silicon dioxide and a vapor deposited glass. 2) Silicon precipitation at wire grain boundaries was observed in both aluminum and gold lead wires. The mechanisms of solid-state diffusion and high-current density electromigration of silicon resulted in wire fracture or slip at grain boundaries in the wires. 3) Silicon penetration into gold conductor stripes through defects in the molybdenum barrier layer resulted in severe reordering of the gold at temperatures in excess of 300°C. The silicon-gold eutectic was formed at temperatures greater than 370°C causing complete dewetting of the molybdenum layer. At lower temperatures, grain boundary flaking due to loss of gold cohension and adhesion was observed. 4) Whiskers which formed on molybdenum barrier layers during 85-85 humidity storage testing with applied bias contained high concentrations of sodium. Several known compounds of sodium and molybdenum are discussed in light of the X-ray data taken on the electron beam microprobe.