Read-only memory and read-only memory devices

• US 6,236,587 B1
• Filed: 09/13/1999
• Issued: 05/22/2001
• Est. Priority Date: 09/01/1997
• Status: Expired due to Fees

• Current Assignee: Thin Film Electronics ASA
• Original Assignee: Thin Film Electronics ASA
• Inventors: Nordal, Per-Erik, Leistad, Geirr I., Gudesen, Hans Gude
• Primary Examiner(s): Dinh, Son T.
• Assistant Examiner(s): PHUNG, ANH K
• Application Number:
  US09/297,467
• Time in Patent Office: 617 Days
• Field of Search: 365/105, 365/100, 365/175, 365/115, 365/94
• US Class Current: 365/105
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: G11C 11/5664 using organic memory material storage elements
• CPC Class Codes: G11C 11/5692 read-only digital stores using storage elements with more than two stable states
• CPC Class Codes: G11C 13/0014 comprising cells based on organic memory material
• CPC Class Codes: G11C 13/0016 comprising polymers
• CPC Class Codes: H10B 20/00 Read-only memory [ROM] devices

Abstract

A read-only memory is made electrically addressable over a passive conductor matrix, wherein at least a portion of the volume between intersection of two conductors (2;4) in the matrix defines a memory cell (5) in the read-only memory. Data are stored as impedance values in the memory cells. The memory cells (5) comprise either an isolating material (6) which provides high impedance or one or more inorganic or organic semiconductors (9), preferably with an anisotropic conducting property. The semiconductor material (9) forms a diode junction at the interface to a metallic conductor (2;4) in the matrix. By suitable arrangement of respectively the isolating material (6) and semiconductor material (9) in the memory cells these may be given a determined impedance value which may be read electrically and corresponds to logical values in a binary or multi-valued code. The read-only memory device may be realized either as planar or also volumetrically by stacking several read-only memories (ROM) above each other and connecting them with the substrate (1) via addressing buses (14). Such read-only memory devices may be implemented on memory cards with standard card interfaces and used for storage of source information.

Claims

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 and provided such that the electrodes form a substantially orthogonal x,y matrix;

wherein the electrodes (2) 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 are provided at least one semiconductor material (9) with rectifying properties in relation to a selected electrical conducting electrode material and a first 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 logic state in each case is given by the impedance value of the memory cell (5), said impedance value substantially being given by either the impedance characteristics of the semiconductor material or the impedance characteristics of the isolating material, and the impedance characteristic of the diode junction;

characterized in that the y electrodes (4) are provided on a second electrical isolating material (12) which is realized as strip-like structures of substantially same form and extension as the y electrodes (4) and provided adjacent to the x electrodes (2) as part of the matrix, that the semiconductor material is provided over the electrode structures,

a contact area (11) in the memory cell (5) thus being defined by the portions which respectively extend along each side edge of the y electrode (4) where it overlaps the x electrode (2) in the memory cell (5),

that a first logic state of a memory cell (5) in the read-only memory is generated by an active portion of the semiconductor material (9) covering the whole contact area (11) in the memory cell, the diode junction thus comprising the whole contact area of the memory cell, that a second logic state in a selected memory cell (5) in the read-only memory is generated by both electrode structures in the memory cell being covered by the first isolating material (6),

that one or more additional logic states in a memory cell (5) in the read-only memory is generated by an active portion of the semiconductor material (9) covering only 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 binary or multi-valued code,

and that said one or more additionally logic states are given by impedance values determined by the extension of the active portion of the semiconductor material, and the extension of the part of the contact area which forms the diode junction; and

that 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, the extension of the active portion of the semiconductor material, the extension of the part of the contact area which forms the diode junction, and the impedance characteristic of the diode junction.

2. A read-only memory according to claim 1, wherein the read-only memory constitutes a binary logic memory characterized in that the first logic state which either represents a logical 0 or a logical 1, is given by the effective forward bias resistance of a diode formed in a memory cell (5) wherein the semiconductor material (9) contacts both the x electrode (2) and the y electrode (4), and that the second or the additional logic state which correspondingly shall represent either a logical 1 or a logical 0, is given by a selected resistance value for the first isolating material (6) provided in a memory cell (5) wherein the semiconductor material (9) does not contact either the x electrode (2) or the y electrode (4).

3. A read-only memory according to claim 2, characterised in that the isolating material (6) in a memory cell (5) has an infinite resistance value.

4. A read-only memory according to claim 1, wherein the read-only memory is realized as a multilevel logic memory with two or more additional logic states, characterized in that the first logic state is given by the effective forward bias resistance of a diode formed in a memory cell (5) wherein the semiconductor material (9) contacts both the x and the y electrodes (2,4), and that the additional logic states are given by determined resistance values for the isolating material (6) provided in a memory cell (5) wherein the semiconductor material (9) at most contacts either the x electrode (2) or the y electrode (4) and the determined resistance value in each case lies between the effective forward bias resistance of a memory cell (5) formed with a diode, and infinite.

5. A read-only memory according to claim 1, characterized in that the first isolating material (6) in selected memory cells (5) is provided over the electrode structures in the form of a separate layer-like isolator patch (7) which wholly or partly covers the electrodes (2,4) in the memory cell (5), a selected memory cell dependent on the active portion of the semiconductor material and/or the diode junction area in the latter case acquiring a logic state which corresponds to a level in a multi-valued code.

6. A read-only memory according to claim 5, characterized in that the semiconductor material (9) is provided over the electrode structures in a global layer and besides over the isolator patches (7) in the selected memory cells (5).

7. A read-only memory according to claim 5, characterized in that the semiconductor material (9) is provided over the electrode structures and adjacent to the isolator patch (7) in the selected memory cells (5), such that the semiconductor material (9) and the isolator patches (7) mutually flush in a common continuous layer.

8. A read-only memory according to claim 1, characterized in that the first isolating material (6) is provided over the electrode structures in the form of a substantially global layer, and with removed portions (8) in selected memory cells (5), such that the removed portion wholly or partly exposes the electrodes (2, 4) in a selected memory cell (5), said memory cell dependent on the active portion of the semiconductor material (9) and/or the diode junction area in the latter case acquiring a logic state which corresponds to a level in a multi-valued code.

9. A read-only memory according to claim 8, characterized in that the semiconductor material (9) is provided over the electrode structures and over the isolating layer (6) in a global layer and besides contacts the electrode structures in the removed portions of the isolating layer (6).

10. A read-only memory according to claim 8, characterized in that the semiconductor material (9) is provided over the electrode structures and adjacent to the isolating layer (6) in the selected memory cells (5), such that the semiconductor material (9) and the isolating layer (6) mutually flush in a common continuous layer.

11. A read-only memory according to claim 1, characterized in that the semiconductor material (9) in selected memory cells (5) is provided over the electrode structures in the form of a separate layer-like semiconductor patch (10) which wholly or partly covers the electrodes (2,4) in the memory cell (5), a selected memory cell dependent on the active portion of the semiconductor material (9) and/or the diode junction area in the latter case requiring a logic state which corresponds to a level in the multivalued code.

12. A read-only memory according to claim 11, characterized in that the first isolating material (6) being provided over the electrode structures in a global layer and besides over the semiconductor patches (10) in the selected memory cells (5).

13. A read-only memory according to claim 11, characterized in that the first isolating material (6) is provided over the electrode structures and adjacent to the semiconductor patches (10) in the selected memory cells (11) such that the first isolating material (6) and the semiconductor patches (10) mutually flush in a common continuous layer.

14. A read-only memory according to claim 1, characterized in that the semiconductor material (9) is provided over the electrode structures in the form of a substantially global layer (9) and with removed portions (17) in selected memory cells (5), such that a removed portion (17) wholly or partly exposes the electrodes (2,4) in a selected memory cell (5), said memory cell dependent on the active portion of the semiconductor material and/or the diode junction area in the latter case acquiring a logic state which corresponds to a level in a multivalued code.

15. A read-only memory according to claim 14, characterized in that the first isolating material (6) is provided over the electrode structures and the semiconductor material (9) in a global layer and besides isolates the electrode structures in the removed portions (17) of the semiconductor layer (9).

16. A read-only memory according to claim 14, characterized in that first isolating material (6) is provided over the electrode structures and adjacent to the semiconductor layer (9) in the selected memory cells (5), such that the first isolating material (6) and the semiconductor layer (9) mutually flush in a common continuous layer.

17. A read-only memory according to claim 1, characterized in that the semiconductor material (9) is amorphous silicon.

18. A read-only memory according to claim 1, characterized in that the semiconductor material (9) is polycrystalline silicon.

19. A read-only memory according to claim 1, characterized in that the semiconductor material (9) is an organic semiconductor.

20. A read-only memory according to claim 19, characterized in that the organic semiconductor (9) is a conjugated polymer.

21. A read-only memory according to claim 1, characterized in that the semiconductor material (9) is an anisotropic conductor.

22. A read-only memory according to claim 1, characterized in that the semiconductor material (9) comprises more than one semiconductor.

23. A read-only memory according to claim 1, characterized in that the semiconductor material (9) has been added or combined with an electrical conducting material.

24. A read-only memory according to claim 1, characterized in that the semiconductor material (9), the isolating material (6) and the electrode structures are realized as thin films.

25. A read-only memory comprising one or more read-only memories (ROM) according to claim 1, characterized in that the read-only memory (ROM) is provided on a substrate (1) of semiconductor material or between substrates (1;

3) of semiconductor material and via the substrates connected with driver and control circuits (13) for driving and addressing, said driving and control circuits (13) being integrated in the substrate (1) or the substrates (1;

3) and realized in a semiconductor technology compatible with the substrate material.

26. A read-only memory comprising two or more read-only memories according to claim 1, characterized in that the read-only memory is stacked in layers in order to provide a volumetric memory device, that the volumetric memory device is provided on a substrate (1) of semiconductor material or between substrates (1;

3) of semiconductor material and via the substrate or the substrates connected with driver and control circuits (13) for driving and addressing, said driving and control circuits (13) being integrated with the substrate (1) or the substrates (1;

3) and realized in a semiconductor technology compatible with the substrate material.