Memory cell capable of storing more than two logic states by using programmable resistances
First Claim
1. A programmable resistor of a memory circuit comprising a mixture of titanium and oxygen coupled to conduct a heating current, wherein at least a portion of said mixture is configured to reach a temperature near 450°
- C. while said heating current is present, and wherein said mixture is configured to at least partially transform to TiO2.
7 Assignments
0 Petitions
Accused Products
Abstract
A system and process which enables storage of more than two logic states in a memory cell. In one embodiment, a programmable resistor is coupled in series with a transistor between a supply voltage and a data read line. When an access signal is asserted, the transistor provides a conductive path, and a voltage drop is sustained by the programmable resistor. The programmable resistor has a resistance which is set during a programming step to one of a plurality of values by passing a heating current through the programmable resistor for one of a corresponding plurality of predetermined lengths of time. When the access signal is asserted, the voltage drop sustained across the programmable resistor is indicative of the stored logic state. An analog-to-digital (A/D) converter is coupled to the data read line so as to sense the voltage drop and determine the state represented. Since the additional logic states may be used to represent additional information bits, this memory circuit increases the number of bits that may be stored per memory cell, thereby increasing the storage density and reducing the cost per bit.
54 Citations
20 Claims
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1. A programmable resistor of a memory circuit comprising a mixture of titanium and oxygen coupled to conduct a heating current, wherein at least a portion of said mixture is configured to reach a temperature near 450°
- C. while said heating current is present, and wherein said mixture is configured to at least partially transform to TiO2.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A memory circuit comprising:
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an access transistor having a gate, wherein said gate is coupled to receive an access signal, and wherein said access transistor is configured to provide a conductive path between a supply voltage and a data read line when said access signal is asserted; a programmable resistor coupled between said supply voltage and said data read line in series with said access transistor, wherein said programmable resistor is configured to sustain a voltage drop when said access signal is asserted; and an analog-to-digital converter coupled said data read line to detect a value indicative of said voltage drop, wherein said analog to digital converter is configured to convert said value to one of at least three distinct digital values. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17)
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18. A method for storing more than two logic states in a memory cell, comprising the steps of:
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fabricating an array of access transistors each having a gate, wherein said gate is coupled to receive an access signal, and wherein each of said access transistors is configured to provide a conductive path between a supply voltage and a data read line when said access signal is asserted; fabricating an array of programmable resistors, wherein each of said programmable resistors is coupled between said supply voltage and said data read line in series with a corresponding one of said access transistors, wherein each of said programmable resistor is configured to sustain a voltage drop when said access signal is asserted; and applying a heating current to a first set of programmable resistors for a first predetermined length of time to cause said first set of programmable resistors to have a first resistance; applying a heating current to a second set of programmable resistors for a second predetermined length of time to cause said second set of programmable resistors to have a second resistance; and applying a heating current to a third set of programmable resistors for a third predetermined length of time to cause said third set of programmable resistors to have a third resistance. - View Dependent Claims (19, 20)
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Specification