Non-Volatile Memory Array With Resistive Sense Element Block Erase and Uni-Directional Write

• US 20110026305A1
• Filed: 10/12/2010
• Published: 02/03/2011
• Est. Priority Date: 10/10/2008
• Status: Active Grant

• Current Assignee: Everspin Technologies Incorporated
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Lu, Yong, Li, Hai, Carter, Andrew John, Reed, Daniel S.
• Granted Patent: US 8,213,259 B2
• Time in Patent Office: Days
• US Class Current: 365/148
• CPC Class Codes: G11C 11/1659 Cell access
• CPC Class Codes: G11C 11/1675 Writing or programming circuits or methods
• CPC Class Codes: G11C 13/0004 comprising amorphous/crystalline phase transition cells
• CPC Class Codes: G11C 13/0011 comprising conductive bridging RAM [CBRAM] or programming metallization cells [PMCs]
• CPC Class Codes: G11C 13/003 Cell access
• CPC Class Codes: G11C 13/0069 Writing or programming circuits or methods
• CPC Class Codes: G11C 13/0097 Erasing, e.g. resetting, circuits or methods
• CPC Class Codes: G11C 2013/009 Write using potential difference applied between cell electrodes
• CPC Class Codes: G11C 2213/76 Array using an access device for each cell which being not a transistor and not a diode

Abstract

A non-volatile memory cell and associated method of use are disclosed. In accordance with various embodiments, the memory cell includes a switching device and a resistive sense element (RSE) connected in series between first and second control lines. The first control line is supplied with a variable voltage and the second control line is maintained at a fixed reference voltage. A first resistive state of the RSE is programmed by lowering the variable voltage of the first control line below the fixed reference voltage of the second control line to flow a body-drain current through the switching device. A different, second resistive state of the RSE is programmed by raising the variable voltage of the first control line above the fixed reference voltage to flow a drain-source current through the switching device.

Claims

1. A non-volatile memory cell, comprising:

a transistor comprising source and drain regions spanned by a gate region; and

a resistive sense element (RSE) connected to the drain region of the transistor, the RSE programmed to a first resistance by flowing a first write current through the RSE and then through the drain and source regions of the transistor, the RSE programmed to a second resistance by flowing a second write current through the drain region and then through the RSE, the second write current bypassing the source region.

2. The non-volatile memory cell of claim 1, in which the source region is maintained at a fixed reference voltage during application of the respective first and second write currents.

3. The non-volatile memory cell of claim 2, in which a bit line terminal connected to the RSE opposite the transistor is provided with a voltage greater than the fixed reference voltage during the flow of the first write current, and with a voltage less than the fixed reference voltage during the flow of the second write current.

4. The non-volatile memory cell of claim 1, in which the transistor is formed from a substrate of semiconductor material in which the source and drain regions are provided as spaced-apart localized doped regions with a channel therebetween, the gate region formed adjacent to the channel so that application of a voltage to the gate alters a conductivity of the channel between the respective doped regions.

5. The non-volatile memory cell of claim 1, wherein the source and drain regions are respectively characterized as first and second n+ doped regions in a semiconductor substrate, the substrate further comprising an adjacent p+ doped contact area, wherein the first write current comprises a transistor source-drain current that sequentially flows through the RSE, the second n+ doped region and the first n+ doped region, and wherein the second write current comprises a transistor body-drain current that sequentially flows from the p+ doped contact area across the substrate to the second n+ doped region, and then through the RSE, the transistor body-drain current not passing through the first n+ doped region.

6. The non-volatile memory cell of claim 1, further comprising a voltage source terminal that connects the source region to a reference voltage source to apply a fixed reference voltage thereto, and a bit line terminal connected to the RSE opposite the transistor and adapted to receive a first voltage above the fixed reference voltage to initiate said flow of the first write current, and adapted to receive a second voltage below the fixed reference voltage to initiate said flow of the second write current.

7. The non-volatile memory cell of claim 1, in which the second write current has a magnitude that is greater than a magnitude of the first write current.

8. The non-volatile memory cell of claim 1, in which the memory cell forms a portion of an array of nominally identical memory cells arranged into rows and columns, each memory cell in said array including a separate RSE and transistor having a source region, drain region and a gate region, and wherein each of the source regions of the memory cells in said array are coupled to a source plane connected to a reference voltage source that continuously maintains the source plane at a fixed reference voltage.

9. A semiconductor stack, comprising:

a p doped substrate in which spaced-apart first and second n+ doped regions and a p+ doped contact area are formed, the first n+ doped region and the p+ doped contact area respectively maintained at a fixed reference voltage;

a gate structure which spans a channel between the first and second n+ doped regions to form a transistor; and

a resistive sense element (RSE) connected to the second n+ doped region, the RSE programmed to a first resistance by flowing a transistor body-drain current from the p+ doped contact area to the second n+ doped region and then to the RSE, the RSE programmed to a different second resistance by flowing a transistor source-drain current through the RSE to the second n+ doped region, and across the transistor channel to the first n+ doped region.

10. The semiconductor stack of claim 9, further comprising voltage source terminals that respectively connect the first n+ doped region and the p+ doped contact area to at least one reference voltage source to maintain the first n+ doped region and the p+ doped contact area at said fixed reference voltage.

11. The semiconductor stack of claim 9, further comprising a bit line terminal connected to the RSE and adapted to receive a first voltage below the fixed reference voltage to initiate said flow of the transistor body-drain current, and adapted to receive a second voltage above the fixed reference voltage to initiate said flow of the transistor source-drain current.

12. The semiconductor stack of claim 9, in which the RSE is connected in series with the transistor between first and second control lines, the first control line connected to the RSE to provide a variable voltage thereto, the second control line connected to the first n+ doped region to provide the fixed reference voltage thereto.

13. The semiconductor stack of claim 9, further comprising a word line terminal connected to said gate which applies a first gate voltage equal to the fixed reference voltage during said flow of the transistor body-drain current and which applies a second gate voltage greater than the fixed reference voltage during said flow of the transistor source-drain current.

14. The semiconductor stack of claim 9, in which the first n+ doped region forms a source for the transistor, the second n+ doped region forms a drain for the transistor, and a portion of the p doped substrate between said first and second n+ doped regions forms said channel.

15. The semiconductor stack of claim 9, in which the source-drain current passes through the first n+ doped region and the transistor body-drain current does not pass through the first n+ doped region.

16. The semiconductor stack of claim 9, in which the body-drain current has a magnitude that is greater than a magnitude of the source-drain current.

17. A method comprising:

providing a memory cell comprising a transistor connected in series with a resistive sense element (RSE), the transistor comprising source and drain regions spanned by a gate region, the RSE connected to the drain region, and the source region maintained at a fixed reference voltage;

programming the RSE to a first electrical resistance by flowing a first write current through the memory cell that sequentially passes through the RSE and then through the drain and source regions of the transistor; and

programming the RSE to a different, second resistance by flowing a second write current through the memory cell that sequentially passes through the drain region and then through the RSE, the second write current bypassing the source region of the transistor.

18. The method of claim 17, in which the transistor is formed from a substrate of semiconductor material in which the source and drain regions are respectively provided as spaced-apart first and second n+ doped regions with a channel therebetween, the gate region formed adjacent to the channel so that application of a voltage to the gate alters a conductivity of the channel between the respective first and second n+ doped regions.

19. The method of claim 18, in which the RSE is programmed to the second resistance by flowing the second write current as a body-drain current that passes from a p+ doped contact area of the substrate and across a pn junction to the second n+ doped region while bypassing the first n+ doped region.

20. The method of claim 17, in which the second write current has a magnitude that is greater than a magnitude of the first write current and the transistor is of sufficient size to safely accommodate the first write current as a source-drain current, but is not of sufficient size to safely accommodate the second write current as a source-drain current.