Hans Helmut Zappe

Josephson quantum interference computer devices

Josephson devices are potential elements for ultra-fast computers. Rather complex logic and memory circuits have been realized. Here quantum interference devices with improved speed and power performance are discussed. Latching and non-latching logic operation is possible and experiments with non-latching circuits are reviewed. Memory applications of quantum interference devices are also considered.

A single flux quantum Josephson junction memory cell

Operation of a DRO single flux quantum Josephson junction memory cell is described. Writing and sensing is performed with coincident currents. The device acts as its own sense detector, switching to the gap voltage if a flux quantum was stored. Dense arrays not requiring standby power are potentially feasible.

Angular dependence of magnetic annealing effects in permalloy base films

Attempts have been made to interpret magnetic annealing effects by assuming that the uniaxial anisotropy is caused by a directional order of local atomic configurations. By studying both evaporated and electroplated films, it is found that during an anneal the number of such elementary anisotropy sources is conserved. The angular dependence of magnetic annealing effects can be described by assuming a reorder of elementary anisotropy sources parallel to the magnetization at a rate independent of the magnetization direction. In the absence of a physical model describing the kinetics of reorder, it is shown how experimental values of the anisotropy field measured during hard-axis anneals can be used to predict for any annealing direction, the changes in anisotropy field, skew, and coercivity. Changes in angular dispersion were also studied but could not be explained satisfactorily. The variations of all main film parameters are found to be reversible during subsequent easy-axis anneals, and the recovery of the anisotropy field during such an anneal can be used to predict the recovery of all other parameters.

Josephson Computer Technology

Spurred by an insatiable thirst for machines with ever growing computing power, increasing attention is being given to today’s fastest systems, collectively known as supercomputers [1]. Here we shall concentrate on high performance machines of a different class, powerful future computers expected to exceed present day capabilities by over one order of magnitude. The discussion will center on one possible approach that promises to achieve the required technological breakthroughs. It is a superconductive technology based on the Josephson effect.

A dynamic determination of the anisotropy field and the damping constant of thick magnetic films

A new dynamic method for the measurement of H k and the damping constant T of thick magnetic films is presented from both the theoretical and practical standpoint. The method is based on a property of the differential equation (1), which has been found to be adequate if applied to the read cycle. It is found that, if the easy-axis sense signals obtained with linearly rising hard-axis fields of different rise times are plotted vs. the respective hard-axis fields, the maxima of the sense signals lie almost precisely on a straight line. This straight line cuts the field axis at H k . From the slope of this line it is possible to deduce T , which is primarily the eddy-current time constant for thick films. The resistivity of the magnetic material can, in this case, be evaluated directly if the physical dimensions of the film are known. The influence of dispersion and skew is discussed and found to be reasonably small. The further advantages are that no instrumental integration is needed and that the reading is quite precise. Small variations of H k can, therefore, be easily recorded. Practical results obtained with thick magnetic films illustrate this method.

Nondestructive readout in thick magnetic film devices

To study the nondestructive readout properties of thick magnetic film devices, sense voltages are computed for triangular interrogate word pulses. Eddy currents are assumed to be the exclusive damping mechanism. For a given pulse rise time one can obtain a maximum signal peak value with a given optimum film thickness, and the read signal of an optimized film can be approximated by simple analytical functions. In an attempt to describe the nondestructive readout stability, a relation is developed between pulse widths, angle of rotation of the magnetization, and reversibility threshold.