Nonvolatile semiconductor memory device and method of manufacturing the same

• US 6,198,657 B1
• Filed: 03/13/2000
• Issued: 03/06/2001
• Est. Priority Date: 03/15/1999
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Miike, Shogo, Uekubo, Masaki
• Primary Examiner(s): NGUYEN, TAN
• Application Number:
  US09/524,560
• Time in Patent Office: 358 Days
• Field of Search: 365/185.04, 365/185.29, 365/195
• US Class Current: 365/185.04
• CPC Class Codes: G11C 16/22 Safety or protection circuits preventing unauthorised or accidental access to memory cells

Abstract

A nonvolatile memory device is provided capable of shipping after setting it as a flash memory or as a one-time memory, and which cannot be altered to a flash memory once it has been used as a one-time memory. The nonvolatile memory device of the present invention has a circuit structure such that when a nonvolatile memory receives an instruction of prohibiting erasure of internal data, the instruction is stored by setting a prescribed flag provided in the nonvolatile memory at a predetermined value, and the content of the present nonvolatile memory cannot be erased after packaging, so that it is impossible for a user to alter the values of the flag which indicates whether erasure of data is prohibited or permitted.

Claims

1. A nonvolatile memory device provided with an erasure prohibiting circuit for prohibiting erasure of the content of data in said nonvolatile memory device, wherein said erasure prohibiting circuit permanently prohibits erasure of the data when an instruction to prohibit erasure is directed from the outside of said nonvolatile memory device.

2. A nonvolatile memory device according to claim 1, wherein said erasure prohibiting circuit comprises an erasure prohibiting memory portion for storing either one of first information for prohibiting erasure or second information for permitting erasure.

3. A nonvolatile memory device according to claim 2, wherein said erasure prohibiting circuit comprises in the erasure prohibiting memory portion, an setting erasure circuit for writing said first information, and a setting writing circuit for writing said second information.

4. A nonvolatile memory device according to claim 3 comprising,

an erasure instructing resistor for storing a decoded erasure instruction for instructing erasure of the data content;

and

an erasure circuit for erasing the data content in the memory cell array based on the output of said erasure instructing resistor;

wherein, said erasure prohibiting circuit comprises an erasure prohibition control circuit for controlling whether or not the output of said erasure instructing resistor is transmitted to said erasure circuit, and an erasure setting circuit is allowed to be energized, only when an output of said erasure prohibition control circuit outputs an erasure permission.

5. A nonvolatile memory device according to claim 4, wherein said erasure prohibiting circuit is provided with an erasure prohibition release means for forcibly converting the output of said erasure prohibition control circuit to the erasure permission state.

6. A nonvolatile memory device according to claim 5, wherein said erasure prohibition release means is made operable only when the nonvolatile memory device is in the form of a wafer.

7. A nonvolatile memory device according to claim 4, wherein said erasure prohibiting circuit is provided with an erasure prohibition initializing means for forcibly writing first information into said erasure prohibition memory portion.

8. A nonvolatile memory device according to claim 7, wherein said erasure prohibiting initializing means is made operable only when the nonvolatile memory device is in the form of a wafer.

9. A nonvolatile memory device according to claim 3 comprising,

an erasure instructing resistor for storing a decoded erasure instruction;

and

an erasure circuit for erasing a data content in a memory cell array based on the output of said erasure instructing resistor;

wherein said erasure prohibiting circuit comprises an erasure prohibition control circuit for controlling whether or not said erasure instructing resistor is reset, and the setting erasure circuit is allowed to be energized only when the erasure prohibition control circuit outputs an erasure permission.

10. A nonvolatile memory device according to claim 1 comprising:

an erasure instructing resistor for storing a decoded erasure instruction for instructing erasure of the data content; and

an erasure circuit for erasing the data content in a memory cell array based on an output of said erasure instructing resistor;

wherein said erasure prohibiting circuit comprises an erasure prohibition control circuit for controlling whether or not an output of said erasure instructing resistor is transmitted to said erasure circuit.

11. A nonvolatile memory device according to claim 1, wherein the nonvolatile memory device comprises:

an erasure instructing resistor for storing a decoded erasure instruction; and

an erasure circuit for erasing the data content in the memory cell array based on an output of said erasure instructing resistor;

wherein, said erasure prohibiting circuit comprises an erasure prohibition control circuit for controlling whether or not said erasure instructing resistor is reset based on a setting state of said erasure prohibition memory portion.

12. A nonvolatile memory device, wherein the electrically writable and erasable nonvolatile semiconductor memory device comprises a memory means that stores the erasure permitted state or the erasure prohibited state, and wherein said memory means is set at the erasure permitted state only when an erasure prohibiting setting means capable of setting either one of the erasure permitted state or the erasure prohibited state, and an erasure prohibition release means for forcibly releasing the erasure prohibited state, and said erasure prohibition release means are in the released state.

13. A nonvolatile semiconductor memory device, wherein in the electrically writable and erasable nonvolatile memory device comprises a memory means that stores the erasure permitted state or the erasure prohibited state, and wherein said electrically erasable memory device comprises:

an erasure prohibition setting means capable of setting the electrically writable and erasable nonvolatile memory devices to either one of the erasure permitted state or the erasure prohibited state based on information stored in said memory means; and

an erasure restricting means for setting the memory means at the erasure permitted state when the erasure prohibition setting means is in the erasure prohibited state.

14. A method for manufacturing a nonvolatile memory device comprising the steps of:

forming a plurality of nonvolatile memory chips on a substrate;

inspecting a threshold value of a memory cell in each nonvolatile memory chip;

initializing an erasure prohibition memory portion that is provided in a erasure prohibiting circuit for prohibiting erasure of a data content for storing either one of first information that prohibits erasure or second information that permits erasure;

encapsulating the wafer after separated it into a plurality of nonvolatile memory chips in packages;

writing a predetermined program into said nonvolatile memory chip; and

writing erasure prohibition information in said erasure prohibiting memory portion.