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Read-only memory and read-only memory device

  • US 6,380,597 B1
  • Filed: 09/13/1999
  • Issued: 04/30/2002
  • Est. Priority Date: 09/01/1997
  • Status: Expired due to Fees
First Claim
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1. An electrically addressable non-volatile read-only memory, comprising a plurality of memory cells (5) which in a write operation comprising a part of the manufacturing process of the read-only memory, permanently each are assigned one or two or more logic states according to a determined protocol which in the memory defines permanently written or stored data, and a passive matrix of electrical conductors (2, 4) for the addressing wherein the passive electrical conductor matrix comprises a first and a second electrode structure in respective mutually spaced apart and parallel planes and with parallel electrodes (2, 4) in each plane provided such that the electrodes form a substantially orthogonal x,y matrix wherein the electrodes in the first electrode structure comprise the columns of the matrix or x electrodes and the electrodes (4) in the second electrode structure comprise the rows of the matrix or y electrodes, wherein at least a portion of the volume between the intersection of an x electrode (2) and a y electrode (4) defines a memory cell (5) in the read-only memory, wherein the mutually overlapping portions of the x electrode (2) and the y electrode (4) in the memory cell (5) each defines a contact area (11) in the memory cell (5), wherein at least one semiconductor material (9) is provided between the electrode structures and with rectifying properties in relation to a selected electrical conducting electrode material, and an electrical isolating material (6), wherein the semiconductor material (9) in electrical contact with an electrode (2, 4) in the memory cell forms a diode junction in the interface between semiconductor material and electrode material, wherein a first logic state of a memory cell (5) in the read-only memory is formed by an active portion of the semiconductor material (9) covering the whole contact area (11) in the memory cell, said active portion of the semiconductor material (9) including an extension, the diode junction comprising the whole contact area of the memory cell, wherein a second logic state in a selected memory cell (5) in the read-only memory is formed by at least one electrode structure in the memory cell being covered by the isolating material (6), and wherein a logic state in each case is given by the impedance value of the memory cell (5), said impedance value substantially being given by one or more of the following factors:

  • the impedance characteristics of the semiconductor material, the impedance characteristics of the isolating material, and the impedance characteristic of the diode junction, characterized in that one or more additional logic states in a memory cell (5) in the read-only memory is formed by an active portion of the semiconductor material (9) covering a part of the contact area (11) such that the data which are stored in the memory may be represented by the logic states in a multi-valued code, and that said one or more additional logic states are given by impedance values determined by the extension of the active portion of the semiconductor material.

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