Showing papers by "IBM published in 1970"

A relational model of data for large shared data banks

Abstract: Future users of large data banks must be protected from having to know how the data is organized in the machine (the internal representation). A prompting service which supplies such information is not a satisfactory solution. Activities of users at terminals and most application programs should remain unaffected when the internal representation of data is changed and even when some aspects of the external representation are changed. Changes in data representation will often be needed as a result of changes in query, update, and report traffic and natural growth in the types of stored information.Existing noninferential, formatted data systems provide users with tree-structured files or slightly more general network models of the data. In Section 1, inadequacies of these models are discussed. A model based on n-ary relations, a normal form for data base relations, and the concept of a universal data sublanguage are introduced. In Section 2, certain operations on relations (other than logical inference) are discussed and applied to the problems of redundancy and consistency in the user's model.

Superlattice and negative differential conductivity in semiconductors

Abstract: We consider a one-dimensional periodic potential, or "superlattice," in monocrystalline semiconductors formbeyd a periodic variation of alloy composition or of impurity density introduced during epitaxial growth. If the period of a superlattice, of the order of 100A, is shorter than the electron mean free path, a series of narrow allowed and forbidden bands is expected duet o the subdivision of the Brillouin zone into a series of minizones. If the scattering time of electrons meets a threshold condition, the combined effect of the narrow energy band and the narrow wave-vector zone makes it possible for electrons to be excited with moderate electric fields to an energy and momentum beyond an inflection point in the E-k relation; this results ina negative differential conductance in the direction of the superlattice. The study of superlattices and observations of quantum mechanical effects on a new physical scale may provide a valuable area of investigation in the fieId of semiconductors.

Electrical-Resistivity Model for Polycrystalline Films: the Case of Arbitrary Reflection at External Surfaces

Abstract: In this paper, the total resistivity of a thin metal film is calculated from a model in which three types of electron scattering mechanisms are simultaneously operative: an isotropic background scattering (due to the combined effects of phonons and point defects), scattering due to a distribution of planar potentials (grain boundaries), and scattering due to the external surfaces. The intrinsic or bulk resistivity is obtained by solving a Boltzmann equation in which both grain-boundary and background scattering are accounted for. The total resistivity is obtained by imposing boundary conditions due to the external surfaces (as in the Fuchs theory) on this Boltzmann equation. Interpretation of published data on grain-boundary scattering in bulk materials in terms of the calculated intrinsic resistivity, and of thin-film data in terms of the calculated total resistivity suggests that (i) the grain-boundary reflection coefficient in Al is \ensuremath{\approx} 0.15, while it is somewhat higher in Cu; (ii) the observed thickness dependence of the resistivity in thin films is due to grain-boundary scattering as well as to the Fuchs size effect; and (iii) the common observation that single-crystal films possess lower resistivities than polycrystalline films may be accounted for by grain-boundary effects rather than by differences in the nature of surface scattering.

Control flow analysis

Abstract: Any static, global analysis of the expression and data relationships in a program requires a knowledge of the control flow of the program. Since one of the primary reasons for doing such a global analysis in a compiler is to produce optimized programs, control flow analysis has been embedded in many compilers and has been described in several papers. An early paper by Prosser [5] described the use of Boolean matrices (or, more particularly, connectivity matrices) in flow analysis. The use of “dominance” relationships in flow analysis was first introduced by Prosser and much expanded by Lowry and Medlock [6]. References [6,8,9] describe compilers which use various forms of control flow analysis for optimization. Some recent developments in the area are reported in [4] and in [7]. The underlying motivation in all the different types of control flow analysis is the need to codify the flow relationships in the program. The codification may be in connectivity matrices, in predecessor-successor tables, in dominance lists, etc. Whatever the form, the purpose is to facilitate determining what the flow relationships are; in other words to facilitate answering such questions as: is this an inner loop?, if an expression is removed from the loop where can it be correctly and profitably placed?, which variable definitions can affect this use? In this paper the basic control flow relationships are expressed in a directed graph. Various graph constructs are then found and shown to codify interesting global relationships.

A class of optimal minimum odd-weight-column SEC-DED codes

Abstract: The class of codes described in this paper is used for single-error correction and double-error detection (SEC-DED). It is equivalent to the Hamming SEC-DED code in the sense that for a specified number k of data bits, the same number of check bits r is used. The minimum odd-weight-column code is suitable for applications to computer memories or parallel systems. A computation indicates that this code is better in performance, cost and reliability than are conventional Hamming SEC-DED codes.

Photoelectric work functions of transition, rare-earth, and noble metals.

Abstract: Photoelectric work functions of polycrystalline films of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Pd, Ag, La, Ce, Nd, Sm, Eu, Gd, Hf, Pt, and Au are reported.

A model for the formation of amorphous Si by ion bombardment

Abstract: The effective annealing of ion implantations in Si is aided by the formation of continuous amorphous layer. The amorphous layer regrows epitaxially at 500–600°C and incorporates the dopant in an electrically active, uncompensated form. A phenomenological model is proposed which, with adjustable parameters, accounts for the variation of the critical dose required to produce a continuous amorphous layer by ion bombardment with ion, target, temperature, and, with minor additional assumptions, dose rate.

Probability of error, equivocation, and the Chernoff bound

Abstract: Relationships between the probability of error, the equivocation, and the Chernoff bound are examined for the two-hypothesis decision problem. The effect of rejections on these bounds is derived. Finally, the results are extended to the case of any finite number of hypotheses.

Reduction of electromigration in aluminum films by copper doping

Abstract: We have found that the lifetime of aluminum films subjected to high current densities at elevated temperatures can be increased by the addition of copper. Previous studies have indicated that the failure mechanism is a combination of electromigration-induced phenomena, including nucleation and growth of voids, which are gated primarily by material transport along grain boundaries. On the basis of the present study, it appears that the presence of copper causes an appreciable retardation in the rate at which this overall combination of processes takes place, thereby producing a considerable increase in lifetime.

Calculation of Coefficients of Capacitance of Multiconductor Transmission Lines in the Presence of a Dielectric Interface

Abstract: A method is given for the numerical determination of the coefficients of capacitance for a class of multiconductor transmission-line systems. This class includes systems without ground planes, or with one or two ground planes, with the lines embedded in one or two layers of dielectrics. The conductors can be of any cross section that can be approximated adequately by polygons. The method is a refinement of the subareas method in which the assumption of a "staircase function" surface charge density, that is, constant charge density over each subarea, is replaced by the assumption of a piecewise linear charge density over the conductor surfaces, and the charge density parameters are determined by making a least-squares fit to the potential to the boundary conditions of the problem.

Interaction of Elastic Strain with the Structural Transition of Strontium Titanate

Abstract: Second-order displacive transitions of a type often observed in crystals of perovskite structure are analyzed by means of a phenomenological model employing optical soft-mode and elastic-strain coordinates. Relations connecting spontaneous distortion, soft-mode vibrational frequencies, and elastic constants of a tetragonal low-temperature phase are derived. These relations are found to be consistent with existing x-ray, neutron, EPR, Raman, Brillouin, and ultrasonic data for SrTi${\mathrm{O}}_{3}$. From these data, it is inferred that properties of SrTi${\mathrm{O}}_{3}$ are isotropic to a considerable degree and that, of the small anisotropy which determines the symmetry of the low-temperature phase, interaction with strain contributes a large portion. Under certain assumptions, the soft-mode force constant inferred from the data appears to vary fairly smoothly through the transition temperature. Discontinuities in the specific heat and the temperature-derivative of the restoring-force coefficient amounting to 1.3% in SrTi${\mathrm{O}}_{3}$ and about 8% in LaAl${\mathrm{O}}_{3}$ are predicted.

Application of partial-response channel coding to magnetic recording systems

Abstract: A magnetic recording channel can be regarded as a "partial-response" channel because of its inherent differentiation in the readback process. The conventional NRZI method of recording is shown to be equivalent to the "precoding" of this particular partial-response channel, the purpose of which is to limit the propagation of error in the channel output. Using this new viewpoint, one can readily adopt an error detection scheme (developed for general partial-response channels) that takes full advantage of the inherent redundancy in the three-level channel output. The detection scheme is optimum in the sense that it detects all detectable errors with minimum delay. The paper also describes a new high-density recording method, named the "Interleaved NRZI," which is obtained by molding an ordinary recording channel into a different type of partial-response channel, resulting in a potential increase in information density. Implementation of the corresponding optimum error detection scheme is also presented. Finally, performance of these error detection schemes is evaluated in terms of probabilities of detecting single and double errors within a certain finite delay.

Application of RF discharges to sputtering

Abstract: The operation of rf discharges is described and the internal distribution of voltages is considered. The significance of this with respect to sputtering, particularly of insulators, is then discussed. An equivalent circuit for the discharge is presented and the influence of such parameters as pressure and magnetic field on the components of this circuit is described. Finally, energy distributions for positive ions, electrons, and negative ions incident at the substrate during deposition are given.

Aluminum films deposited by rf sputtering

Abstract: The feasibility of depositing aluminum thin films by means of rf sputtering has been investigated. Film characteristics compatible with the requirements of conductive stripes in integrated circuits have been obtained. The rate of film deposition has been related to rf power dissipation, argon pressure, geometry, and magnetic field. Film characteristics such as electrical resistivity, stress, grain size, and orientation have been studied and compared to the characteristics of films deposited by means of evaporation. The effects of annealing on some of these characteristics have been determined.

Transient Analysis of Lossless Coupled Transmission Lines in a Non-Homogeneous Dielectric Medium

Abstract: This paper presents an effective method for computing the transient response of an n-conductor, coupled transmission-line system, which is characterized by multiple propagation modes of unequal phase velocities. To derive the computational algorithm, an equivalent circuit consisting of n decoupled transmission lines in conjunction with two congruence transformers was constructed and converted into two disjointed resistive n-ports. It is shown that the electrical behavior of the coupled transmission lines can be completely described by the static capacitance matrices of the conductor system. The experimental result obtained on a three-conductor, microstrip printed circuit was found to be in excellent agreement with the computed result.

Minimal energy dissipation in logic

Abstract: Minimal energy dissipations for the logic process based on thermodynamics and general phase space considerations are known. The actual availability of these minimal dissipations has not, however, been demonstrated. These minimal dissipation sources in a computing system also act as noise sources and thereby lead to questions about the ultimate available reliability of the computing process. A new and hypothetical device is presented in this paper and used to construct a physically analyzable computing system. It is demonstrated that this system has dissipations larger than, but of the same order of magnitude as, the original minimal quantities. It is also shown that any required reliability can be obtained with this device, without increased energy expenditure, but at the expense of an increasing time per computational step.

Raman Spectra of Polycrystalline Solids; Application to the Pb Ti 1 − x Zr x O 3 System

Abstract: It is shown that Raman scattering from polycrystalline piezoelectric solids contains all of the essential features of Raman single-crystal spectra even when the crystal spectrum is quite anisotropic As an illustration of the Raman powder technique, the ceramic ferroelectric-antiferroelectric system PbTi${\mathrm{O}}_{3}$-PbZr${\mathrm{O}}_{3}$ has been investigated and the "soft" $E(\mathrm{TO})$ optical phonon modes measured in the tetragonal ferroelectric region

Raman Studies of Underdamped Soft Modes in PbTi O 3

Abstract: Unlike other ferroelectric perovskites, PbTi${\mathrm{O}}_{3}$ displays temperature-dependent Raman spectra consisting of underdamped modes, including the "soft" transverse-optical (TO) modes. Moreover, the softest TO mode shows linewidth divergence at the ferroelectric-to-paraelectric transition. Also in contrast to previously studied perovskites, Raman selection rules are rigorously obeyed in both the ferroelectric and paraelectric states.

Analytical representation of the Percus-Yevick hard-sphere radial distribution function

Abstract: Explicit analytical expressions, written in terms of complex variables and suitable for rapid computer evaluation, are presented for the Percus-Yevick hard-sphere radial distribution function, g(R), for R ˇ- 5σ. Some effects of truncating g(R) to unity past R = 5 σ are discussed.

Global common subexpression elimination

Abstract: When considering compiler optimization, there are two questions that immediately come to mind; one, why and to what extent is optimization necessary and two, to what extent is it possible. When considering the second question, one might immediately become discouraged since it is well known that the program equivalency problem is recursively unsolvable. It is, of course, clear from this that there will never be techniques for generating a completely optimum program. These unsolvability results, however, do not preclude the possibility of ad hoc techniques for program improvement or even a partial theory which produces a class of equivalent programs optimized in varying degrees. The reasons why optimization is required seem to me to fall in two major categories. The first I will call “local” and the second “global”.

Cooperative Phenomena in Resonant Electromagnetic Propagation

Abstract: Phenomena of coherent resonant propagation can be considered as resulting from the cooperative interaction of a certain number of excited two-level systems. It is shown that these phenomena can be characterized by a specific "maximum cooperation number" and by the associated "cooperation time." These are defined for the superradiant state, but their meaning and usefulness can be extended to other situations. The alternative description of of superradiance as a spontaneous or as a stimulated effect is also discussed and it is shown that with the help of the new concepts, the Dicke quantum perturbative treatment can be reconciled with the semiclassical theories.

Block codes for a class of constrained noiseless channels

Abstract: A class of discrete noiseless channels having upper and lower bounds on the separation between adjacent nonzero input symbols is considered. Recursion relations are derived for determining the number of input sequences which satisfy the constraints for all block lengths, and the asymptotic information rate is calculated. Applications to compaction and synchronization are discussed. An optimal algebraic block coding scheme for such channels is developed.

Thermal properties of very fast transistors

Abstract: Recent predictions that thermal effects will limit future transistor speed improvement motivated an interest in predicting and measuring these effects. A mathematical model of the three-dimensional transient heat flow problem is presented which takes into account the physical structure of the device and the actual region of power dissipation. At any point within the device, the model predicts the time-dependent temperature response to a change in power dissipation. A new method of measuring the local time-dependent thermal behavior of small bipolar transistors is described and used to verify the model. It was found that the thermal spreading resistance becomes important in silicon transistors when the emitter stripe dimensions approach 1 µ. Furthermore, the thermal response is much slower than the electrical response. Also, it was confirmed that adjacent devices in integrated circuits are essentially thermally isolated as far as thermal spreading resistance is concerned.

Exchange mechanisms in europium chalcogenides

Abstract: Superexchange mechanisms, which are mostly responsible for the nnn exchange constanIt I2 in Eu chalcogenides, are investigated in detail. In contrast with the usual 3d transition metal compounds, the Kramers-Anderson mechanism is estimated to be one order of magnitude too small to explain the experimental results due to a small 4f → 2p transfer energy. The mechanism by which a p electron is transferred to a 5d state through the d-f exchange interaction gives the correct order of magnitude for I2, with a negative sign, even though it is a sixth-order perturbation. The cross term between the above two mechanisms is shown to be nearly as important as the second mechanism and may have a positive sign. The indirect exchange mechanisms, in which the anion p level has no important role, are responsible for the nn exchange constant I1. The phonon-assisted mechanism proposed by Smit is estimated to be more than one order of magnitude smaller than the experimental value. The d-f mixing term is proved to be responsible for I1, in good agreement with experiment.