Patent GB-1177939-A (GB)
Title: Method of Making a Memory Device
IPC: G11C11/22
Filed: 1966-12-15
Abstract: 1,177,939. Dielectric data storage apparatus. E. W. BLISS CO. 15 Dec., 1966 [14 Feb., 1966], No. 56145/66. Heading H3B. A memory device, comprising an element 14 of piezoelectric material, an element 12 of ferroelectric material, and an element 20 of electrically conductive material mechanically coupling elements 12 and 14, is produced by providing a structure comprising first, second and third layers and then treating the layers to produce the device. Construction.-Memory element 12 has its major surfaces coated with silver 16 the lower coating being secured by a layer of conductive epoxy material to a similar coating 16 on driving element 14. The whole assembly is coated with epoxy material 30 for acoustic damping. In a modified structure the memory and drive elements are secured together in a staggered relationship using a non-conductive epoxy cement. The adjacent electrodes in both embodiments are connected to a common lead 20. The memory element may be of barium titanate, Rochelle salt, or potassium niobate, but preferably both the memory and drive elements are of lead zirconium titanium oxide. Epoxy material is dispensed with in a preferred embodiment (Fig. 13, not shown). Alternate layers of green ceramic and powdered platinum oxide are built up, with ceramic materials at the bottom and top and at two intermediate levels. The assembly is then fired to fuse the materials. The outer layers form the damping means and the intermediate layers form the memory and drive elements. Operation.-Element 14 is permanently polarized in one or other sense by connecting a bias source between leads 20 and 26, and the information to be stored in element 12 is then applied to leads 20 and 22 in the form of a voltage of one or the other polarity. For non- destructive read-out a voltage pulse is applied between heads 20 and 26, having an amplitude well below that necessary to permanently polarize element 14. This causes an abrupt change of dimensions of 14, which stresses 12 and gives rise to an output voltage on lead 22 having a polarity indicative of the stored data. Matrices (Fig. 12).-Common drive elements 14 are used for each row of a matrix, with individual memory elements at each storage location. The acoustic damping may be provided by a substrate of lead zirconium titanium oxide, or the assembly may instead, or additionally, be coated with epoxy material. Address information is applied to register 72 and is decoded at 70 to energize the appropriate write switch 64 and connect the required lead 20 to ground. Leads 26 remain open-circuited. The word to be written is applied to register 58 for application to write driver 60. Signals of appropriate polarity are thereby applied to leads 22. During read-out a pulse is applied to the appropriate lead 26, leads 20 are connected to a common ground, and the output voltage on each lead 22 is sensed. The construction is such that stresses parallel as well as normal to the surface of driving element 14 are coupled to memory element 12. The elements may be cylindrically or spherically curved and the adjacent surfaces of the elements need not be flat.