Means and method for operating a resistive array
View Patent ↗The present invention is a means and method for constructing and operating a 3-D array and, more particularly, a 3-D memory array. This array can be manufactured as a monolithic integrated circuit at low cost by virtue of the limited number of steps per layer of memory elements. The low number of steps results by having the storage elements separated by a resistive component as opposed to an active component. The 3-D array is in essence, an array of 2-D resistive arrays (row-planes) having a long dimension (typically along the rows) and a short dimension (typically in the direction of the stacked layers). Any one row-plane can be isolated from the rest and be accessed independently from all of the other row-planes in the 3-D array. This makes it possible to operate and analyze a single row-plane as a mostly stand-alone circuit. The present invention lends itself to single bit accesses as well as simultaneous multiple bit accesses.
1. A method for accessing a two-dimensional memory array within a three-dimensional or multi-dimensional memory array comprising a plurality of conductive posts, a conductive selection line having a determinate resistivity per unit length, and a plurality of memory elements, the memory elements having a first contact connected to said conductive selection line and a second contact connected to a respective conductive post, comprising the steps of:
i. identifying a memory element to be accessed,
ii. determining the voltage on said conductive selection line at the first contact of the memory element to be accessed,
iii. biasing the conductive post corresponding to the memory element to thereby cause a current to flow in the memory element,
iv. estimating a plurality of different voltages generated on said conductive selection line at other memory elements between said memory element to be accessed and the end of the conductive selection line where a voltage is applied,
v. biasing the conductive posts corresponding to other memory elements between said memory element to be accessed and said end of the conductive selection line where a plurality of different voltages are applied to approximately the plurality of different voltages estimated to be generated on said conductive selection line at said other memory elements to thereby cause no current to flow in said other memory elements.
2. The method of claim 1 further comprising estimating a resistance or equivalent value for a memory element when calculating a voltage.
3. The method of claim 2 whereby the estimated resistance or equivalent value is approximately the greatest value typically encountered for a memory element.
4. The method of claim 2 whereby the estimated resistance or equivalent value is approximately the least value typically encountered for a memory element.
5. The method of claim 2 whereby the estimated resistance or equivalent value is approximately midway between the greatest and the least value typically encountered for a memory element.
6. The method of claim 2 further comprising measuring a current to determine a bit state.
7. A three dimensional information storage device comprising a plurality of two-dimensional arrays whereby at least one two-dimensional array comprises:
i. a first plurality of conductive lines that are connected to current controlling devices in the substrate and generally perpendicular to the substrate surface,
ii. a second plurality of conductive lines that have a determinate resistivity per unit length and that are orthogonal to the first set of conductive lines and that are generally parallel to the substrate surface, and
iii. a plurality of information storage elements, each being proximate to a point of intersection of the first and second sets of conductive lines, the information storage elements having a first contact connected to one line of said second plurality of conductive lines and a second contact connected to one line of said first plurality of conductive lines,
whereby accessing an information storage element comprises the steps of:
a. identifying an information storage element to be accessed,
b. determining the voltage on one line of said second plurality of conductive lines at the point of the first contact of the information storage element to be accessed,
c. biasing the one line of said second plurality of conductive lines corresponding to the point of the first contact to thereby cause a current to flow in the information storage element,
d. estimating a plurality of different voltages generated on said one line of said second plurality of conductive lines at other information storage elements between said information storage element to be accessed and the end of one line of said second plurality of conductive lines where a voltage is applied,
e. biasing to approximately said plurality of different estimated voltages those lines of the first plurality of conductive lines that are connected to the second contact of the other information storage elements between said information storage element to be accessed and said end of one line of said second plurality of conductive lines where a voltage is applied to thereby cause no current to flow in said other information storage elements.
8. The three dimensional information storage device of claim 7 whereby the two-dimensional arrays are generally parallel to each other.
9. The three dimensional information storage device of claim 7 whereby the first plurality of conductive lines comprises a selected line and a plurality of unselected lines whereby, when an information storage element is being accessed, the lines of the plurality of unselected lines are biased such that there is little or no voltage difference between a given unselected line and the voltage on a line of the second set of conductive lines at the point where said line of the second set of conductive lines passes said unselected line.
10. The three dimensional information storage device of claim 9 whereby, when an information storage element is being accessed, a voltage is applied to the selected line such that current will flow through the information storage element being accessed.
11. The three dimensional information storage device of claim 7 whereby the information storage element comprises a phase-change material.
12. The three dimensional information storage device of claim 11 whereby the phase-change material comprises a Chalcogenide alloy.
13. The three dimensional information storage device of claim 12 whereby the Chalcogenide alloy comprises GST.