Nonvolatile memory

• US 6,507,509 B1
• Filed: 08/17/2001
• Issued: 01/14/2003
• Est. Priority Date: 09/30/1999
• Status: Expired due to Fees

• Current Assignee: Japan Science & Technology Trading Co. Limited
• Original Assignee: Japan Science And Technology Corpration, NEC Corporation
• Inventors: Yasui, Takanari, Sone, Junichi, Ohtsuka, Youichi, Tsai, Jaw-Shen, Nakamura, Yasunobu
• Primary Examiner(s): Nelms, David
• Assistant Examiner(s): NGUYEN, THINH T
• Application Number:
  US09/856,913
• Time in Patent Office: 515 Days
• Field of Search: 365/145, 365/65, 365/200, 357/23.5, 438/157, 395/24, 257/295
• US Class Current: 365/145
• 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 11/22 using ferroelectric elements
• CPC Class Codes: G11C 11/5657 using ferroelectric storage elements
• CPC Class Codes: H01L 29/7613 Single electron transistors; Coulomb blockade devices H01L29/7888 takes precedence
• CPC Class Codes: H01L 29/78391 the gate comprising a layer which is used for its ferroelectric properties
• CPC Class Codes: H01L 29/7888 Transistors programmable by two single electrons
• CPC Class Codes: H10B 53/00 Ferroelectric RAM [FeRAM] devices comprising ferroelectric memory capacitors

Abstract

High device reliability, a reduction in power consumption, and a high operation speed are achieved. When a predetermined bias voltage is applied between a source 1 and a drain 2 to change a gate voltage, a current discretely flows between the source 1 and the drain 2 in accordance with quantized electrostatic energy levels in an island electrode 3. The switching ON/OFF of the current between the source 1 and the drain 2 in this case is enabled by applying ½-electron charge to a gate. When the gate voltage induces polarization in a ferroelectric layer 6, its electric field is applied to the island electrode 3. The current between the source 1 and the drain 2 in this case can be measured with high sensitivity. Charge holding is carried out by the polarization in the ferroelectric layer 6, and stored data can be held even if power supply is cut off.

Claims

1. A non-volatile memory comprising:

a single electron transistor having a gate, a ferroelectric layer on said gate, and an island electrode on said ferroelectric layer opposite said gate, said island electrode being held between a source and a drain by interpolating insulating layers that are between the island electrode and each of the source and the drain, said island electrode being electrically switched by a change of polarization of said ferroelectric layer caused by application of a charge as small as ½

electron to said gate.

5. A non-volatile memory according to claim 1, further comprising a diffusion barrier layer formed on a substrate,

wherein said gate is disposed on said diffusion layer.

6. A non-volatile memory according to claim 5, wherein said diffusion barrier layer has a TiO_x film thickness substantially set equal to 20 nm, alternatively higher.

7. A non-volatile memory according to claim 1, wherein said gate is made of one selected from Pt and RhO_x.

8. A non-volatile memory according to claim 1, wherein said ferroelectric layer is made of one selected from PbTiO₃, PbZr_xTi₁₋

xO₃, (Pb,Sr)TiO₃, (Pb<sub>1−

y</sub>Sr_y)(Ti₁₋

) Zr_xO₃, SrBi₂Ta₂O₉, BaTiO₃, Bi₃Ti₄O₁₂, LiNbO₃, and SrBi₂Ta_xNb₁₋

O₉.

12. A non-volatile memory according to claim 1, wherein said island electrode, said source and said drain are made of one of Al and Ti.

13. A non-volatile memory according to claim 1, wherein said ferroelectric layer is brought into contact with said island electrode, said source and said drain and with said gate and said diffusion barrier layer around said gate.

29. The non-volatile memory of claim 1, further comprising a Low-k layer between said island electrode and said ferroelectric layer.

30. The non-volatile memory of claim 29, further comprising an upper gate directly on said ferroelectric layer adjacent to said Low-k layer.

2. A non-volatile memory comprising:

a gate;

a ferroelectric layer disposed on said gate;

a Low-k layer disposed on said ferroelectric layer; and

an island electrode disposed on said Low-k layer, held between a source and a drain by interpolating insulating layers between the island electrode and each of the source and the drain, and electrically connected to said gate.

9. A non-volatile memory according to claim 2, wherein said Low-k layer is made of one selected from SiO₂ and Si₃N₄.

10. A non-volatile memory according to claim 2, wherein said ferroelectric layer is made of one selected from PbZr_xT₁₋

x, and (Pb<sub>1−

y</sub>Sr_y)(Ti<sub>1−

x</sub>)ZrxO₃, and has a thickness set substantially equal to about 100 nm, and said Low-k layer is made of one selected from SiO₂ and Si₃N₄, and has a thickness set substantially equal to 10 nm, alternatively lower.

11. A non-volatile memory according to claim 2, wherein said ferroelectric layer is made of SrBi₂Ta₂O₉, and has a thickness set substantially equal to about 200 nm, and said Low-k layer is made of one selected from SiO₂ and Si₃N₄, and has a thickness set substantially equal to 20 nm, alternatively lower.

14. A non-volatile memory according to claim 2, further comprising a diffusion barrier layer formed on a substrate,

wherein said gate is disposed on said diffusion layer.

15. A non-volatile memory according to claim 14, wherein said diffusion barrier layer has a TiO_x film thickness substantially set equal to 20 nm, alternatively higher.

16. A non-volatile memory according to claim 2, wherein said gate is made of one selected from Pt and Rho_x.

17. A non-volatile memory according to claim 2, wherein said ferroelectric layer is made of one selected from PbTiO₃, PbZr_xTi₁₋

xO₃, (Pb,Sr)TiO₃, (Pb<sub>1−

y</sub>Sr_y)(Ti<sub>1−

x</sub>) Zr_xO₃, SrBi₂Ta₂O₉, BaTiO₃, Bi₃Ti₄O₁₂, LiNbO₃, and SrBi₂Ta_xNb<sub>1−

x</sub>O₉.

18. A non-volatile memory according to claim 2, wherein said island electrode, said source and said drain are made of one of Al and Ti.

19. A non-volatile memory according to claim 2, wherein said ferroelectric layer is brought into contact with said island electrode, said source and said drain and with said gate and said diffusion barrier layer around said gate.

3. Anon-volatile memory comprising:

a gate;

a ferroelectric layer disposed on said gate;

an upper gate disposed on said ferroelectric layer;

a Low-k layer disposed on said ferroelectric layer; and

an island electrode disposed on said Low-k layer, held between a source and a drain by interpolating insulating layers between the island electrode and each of the source and the drain, and electrically connected to said gate.

4. A non-volatile memory according to claim 3, wherein said ferroelectric layer includes a perovskite phase portion formed on said gate, and a pyrochlore phase portion formed on a portion other than said gate.

20. A non-volatile memory according to claim 3, further comprising a diffusion barrier layer formed on a substrate,

wherein said gate is disposed on said diffusion layer.

21. A non-volatile memory according to claim 20, wherein said diffusion barrier layer has a TiO_x film thickness substantially set equal to 20 nm, alternatively higher.

22. A non-volatile memory according to claim 3, wherein said gate is made of one selected from Pt and Rho_x.

23. A non-volatile memory according to claim 3, wherein said ferroelectric layer is made of one selected from PbTiO₃, PbZr_xTi₁₋

xO₃, (Pb,Sr)TiO₃, (Pb<sub>1−

y</sub>Sr_y) (Ti<sub>1−

x</sub>) Zr_xO₃, SrBi₂Ta₂O₉, BaTiO₃, Bi₃Ti₄O₁₂, LiNbO₃, and SrBi₂Ta_xNb<sub>1−

x</sub>O₉.

24. A non-volatile memory according to claim 3, wherein said Low-k layer is made of one selected from SiO₂ and Si₃N₄.

25. A non-volatile memory according to claim 3, wherein said ferroelectric layer is made of one selected from PbZr_xT₁₋

x, and (Pb<sub>1−

y</sub>Sr_y)(Ti<sub>1−

x</sub>) ZrxO₃, and has a thickness set substantially equal to about 100 nm, and said Low-k layer is made of one selected from SiO₂ and Si₃N₄, and has a thickness set substantially equal to 10 nm, alternatively lower.

26. A non-volatile memory according to claim 3, wherein said ferroelectric layer is made of SrBi₂Ta₂O₉, and has a thickness set substantially equal to about 200 nm, and said Low-k layer is made of one selected from SiO₂ and Si₃N₄, and has a thickness set substantially equal to 20 nm, alternatively lower.

27. A non-volatile memory according to claim 3, wherein said island electrode, said source and said drain are made of Al, alternatively Ti.

28. A non-volatile memory according to claim 3, wherein said ferroelectric layer is brought into contact with said island electrode, said source and said drain and with said gate and said diffusion barrier layer around said gate.