Bell Telephone Laboratories

John M Geary

Hans George Mattes

Domain wall motion in a slab of ferroelectric material gives rise to an electrical signal which may correspond, e.g., to electrode width fluctuations or to a radiation pattern incident on a sensitive layer. A device may have numerous ferroelectric readout tracks, in which case the number of electrical leads can be minimized by a layout in which unidirectional movement of a planar ferroelectric domain wall not only serves to scan a track but also select a track from a large number of tracks. Such device operation is a feature of a device in which a ferroelectric slab is cut, e.g., in the manner of a comb or ladder. Resulting devices may be operated by judicious cycling of voltages at as few as two control electrodes, one defining an access track, and the other being common to the readout tracks.

Multi-track ferroelectric device

Digital devices such as, e.g., shift registers and logical gates are disclosed which are predicated on domain wall motion in a film of a ferroelectric material, such as, e.g., gadolinium molybdate or lead germanate. Disclosed devices comprise electrodes on both sides of the film of ferroelectric material and may further comprise a resistive layer whose presence facilitates domain wall motion past inter-electrode gaps. Electrodes or facing portions of electrodes define regions in the film and, in particular, an input region and an output region. To facilitate series connection of devices, electrodes are designed so as to cause energy gain during device operation. According to such design, surface area of an output region is larger than surface area of an input region. A current sensor is electrically connected to an electrode defining such output region.

Ferroelectric digital device

Analog readout devices are disclosed which utilize domain wall motion in a film of ferroelectric material to produce an electrical signal having a desired waveform. Disclosed devices comprise electrodes disposed on facing sides of the film, at least one electrode being patterned in correspondence with the desired waveform. Readout from devices may be direct or as the difference between two signals produced by domain wall motion. In the latter case, constant-width pairs of electrodes may be used in combination with a feedback circuit to ensure constant-velocity ferroelectric wall motion.

Ferroelectric analog device

A reader for optically encoded information such as a credit card having an embossed data track includes an array of radiant energy transmitting elements and a single detector element formed on a planar chip. The chip is seated in a recessed area formed in a unitary lens assembly which includes a first integral lens array for focusing energy from each of the transmitting elements at particular points on the credit card, and a second integral lens array for focusing energy reflected from each of the points on the card onto the detector. Circuitry is provided to sequentially energize the transmitting elements, so that the focusing points, which preferably form a line transverse to the data track, are scanned. Signals from the detector element are processed by establishing a continuously variable threshold level derived as a function of the peak amount of reflected energy and by comparing the detector element output with the thresold value at several time intervals within the scanning period. The entire data track is read by repeating the scanning cycle as the credit card or other record medium is moved relative to the lens assembly.

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Summit, NJ, United States of America

John M Geary