Stability in thyristor-based memory device

• US 6,462,359 B1
• Filed: 03/22/2001
• Issued: 10/08/2002
• Est. Priority Date: 03/22/2001
• Status: Expired due to Fees

• Current Assignee: T-Ram, LLC
• Original Assignee: T-Ram, Inc.
• Inventors: Nemati, Farid, Cho, Hyun-jin, Robins, Scott
• Primary Examiner(s): Nelms, David
• Assistant Examiner(s): Tran, Mai-Huong
• Application Number:
  US09/814,980
• Time in Patent Office: 565 Days
• Field of Search: 257/137, 257/109, 257/335, 257/750, 365/96
• US Class Current: 257/107
• CPC Class Codes: G11C 11/39 using thyristors or the avalanche or negative resistance type, e.g. PNPN, SCR, SCS, UJT
• CPC Class Codes: H01L 29/7436 Lateral thyristors
• CPC Class Codes: H01L 29/749 with turn-on by field effect

Abstract

A semiconductor device having a thyristor-based memory device exhibits improved stability under adverse operating conditions related to temperature, noise, electrical disturbances and light. In one particular example embodiment of the present invention, a semiconductor device includes a thyristor-based memory device that uses a shunt between a base and emitter region in a thyristor that effects a leakage current in the thyristor. The thyristor includes a capacitively coupled control port and anode and cathode end portions. Each of the end portions has an emitter region and an adjacent base region, and the current shunt is located between the emitter and base region of one of the end portions of the thyristor. The current shunt is configured and arranged to shunt low-level current between the emitter region and the adjacent base region, and in doing so improves the ability of the device to operate under adverse conditions that would, absent the shunt, result in inadvertent turn on, while keeping the standby current of the memory device to an acceptably low level.

Claims

1. A semiconductor device, comprising:

a memory having a data-storage circuit;

a thyristor device having anode and cathode end portions, each end portion including an emitter region and an adjacent base region, the thyristor device further having a capacitively-coupled port that is controlled to switch the thyristor device between on and off states for write access; and

a current-shunt region adapted to shunt low-level current at a base region of at least one of the end portions and inhibit the thyristor device from switching inadvertently from an off state to an on state.

2. The semiconductor device of claim 1, wherein the current shunt region resistively couples an emitter and base region of the anode portion.

3. The semiconductor device of claim 1, wherein the current shunt region resistively couples an emitter and base region of the cathode portion.

4. The semiconductor device of claim 1, further comprising an array of thyristors, each thyristor having anode and cathode end portions, each of the end portions having an emitter region and an adjacent base region, and a current shunt region resistively coupling the emitter region and the adjacent base region at either one or both of the end portions, the array being adapted to store data for use in conjunction with the semiconductor device.

5. The semiconductor device of claim 1, wherein the current shunt region is coupled to the emitter region through a low resistance contact and, to the adjacent base region, through a comparatively higher resistive contact.

6. The semiconductor device of claim 5, wherein the current shunt region includes a depletion region that resistively couples the emitter region to the adjacent base region.

7. The semiconductor device of claim 5, further comprising a semiconductor substrate, the thyristor being located in the semiconductor substrate, and wherein the current shunt region includes material adjacent the emitter and extending into the substrate below the emitter.

8. The semiconductor device of claim 1, wherein the current shunt region includes a tunnel junction formed between the emitter region and the adjacent base region of at least one of the end portions.

9. The semiconductor device of claim 8, wherein the tunnel junction is a heavily doped region, and the heavily doped region and adjacent base region have a common polarity.

10. The semiconductor device of claim 8, wherein the tunnel junction extends between the emitter region and the adjacent base region, and below the emitter region.

11. The semiconductor device of claim 1, wherein the current shunt region includes a tunnel dielectric over the adjacent base region and a tunnel node over the tunnel dielectric.

12. The semiconductor device of claim 1, wherein the end portions are arranged at opposite ends of the thyristor device and along a horizontal plane, and wherein the emitter region and adjacent base region of each end portion are arranged along the horizontal plane.

13. The semiconductor device of claim 1, wherein the memory includes a plurality of memory cells arranged in an array and further including a plurality of the thyristor devices, each of the plurality of the thyristor devices being configured and arranged to provide data storage capability for a corresponding one of the plurality of memory cells.

14. The semiconductor device of claim 1, wherein the current shunt region is configured and arranged to shunt an amount of current that sufficiently inhibits turn-on of the thyristor-based device.

15. A semiconductor device having a thyristor-based device comprising:

a memory cell;

a thyristor storing data in the memory cell and having a capacitively-coupled control port and anode and cathode end portions, each of the end portions having an emitter region and a base region; and

means for coupling to the base region of one of the end portions and for shunting low-level current at the base region of said one of the end portions.

16. A semiconductor device, comprising:

a memory having a data-storage circuit;

a thyristor device having anode and cathode end portions each of which includes an emitter region and an n-type base region or p-type base region, and further having a capacitively-coupled port that is controlled to switch the thyristor device for passing current or blocking current through the end portions; and

a current-shunt region coupled to at least one of the base regions and adapted to shunt low-level current at said one of the base regions and inhibit the thyristor device from switching inadvertently from an off state to an on state.

17. The semiconductor device of claim 16, wherein the capacitively-coupled port of the thyristor device is facing at least one of the emitter region and an adjacent base region.

18. The semiconductor device of claim 16, wherein the current-shunt region is configured and arranged to shunt low-level current between said one of the base regions and a node that is part of the thyristor device.

19. The semiconductor device of claim 16, wherein the current-shunt region is configured and arranged to shunt low-level current between said one of the base regions and a node that is external to the thyristor device.

20. The semiconductor device of claim 19, further including a plurality of similarly adapted data-storage circuits and wherein the node that is external to the thyristor device is a voltage reference line common to each of the plurality of similarly adapted data-storage circuits.

21. The semiconductor device of claim 16, wherein said at least one of the base regions is doped n-type and wherein the current shunt region is adapted to shunt low-level current between said n-type base region and another node biased at a voltage at least equal to a voltage at which the adjacent emitter region of said end portion is biased.

22. The semiconductor device of claim 16, wherein said at least one of the base regions is doped p-type and wherein the current shunt region is adapted to shunt low-level current between said p-type base region and another node biased at a voltage not greater than a voltage at which the adjacent emitter region of said end portion is biased.

23. The semiconductor device of claim 16, wherein the current shunt region is adapted to shunt low-level current between said base region and another node biased at a voltage that is one of:

at least equal to a voltage at which the adjacent emitter region of said end portion is biased if said at least one of the base regions is doped n-type; and

not greater than a voltage at which the adjacent emitter region of said end portion is biased if said at least one of the base regions is doped p-type.

24. A semiconductor device, comprising:

means for storing data;

a thyristor device including a capacitively-coupled port and anode and cathode end portions each of which includes an emitter region and an n-type base region or p-type base region, the capacitively-coupled port being adapted to switch the thyristor device between a current passing mode and a current blocking mode; and

at the base region of at least one of the end portions, means for shunting low-level current that could otherwise cause the thyristor device to switch on inadvertently.