Nonvolatile memory device comprising one-time-programmable lock bit register
A nonvolatile memory device comprises a one-time-programmable (OTP) lock bit register. The nonvolatile memory device comprises a variable-resistance memory cell array comprising an OTP block that store data and a register that stores OTP lock state information indicating whether the data is changeable. The register comprises a variable memory cell. An initial value of the OTP lock state information is set to a program protection state.
1. A nonvolatile memory device, comprising:
a variable-resistance memory cell array comprising a memory block that stores protected data;
a register that stores lock state information indicating whether the protected data is changeable, wherein the register comprises a variable-resistance memory cell and an initial value of the lock state information is set to a program protection state; and
a mode controller that changes the protected data stored in the memory block in response to the lock state information,
wherein the mode controller causes the register to store program unprotection information in response to a hidden code received from an external source.
2. The nonvolatile memory device of claim 1 , further comprising:
an address decoder that selects the memory block,
wherein the mode controller causes the address decoder to select the memory block where the register stores program unprotection information.
3. The nonvolatile memory device of claim 1 , further comprising:
a write driver that programs the memory block,
wherein the mode controller causes the write driver to program the memory block where the register stores program unprotection information.
4. The nonvolatile memory device of claim 1 , wherein the lock state information comprises program protection information or program unprotection information.
5. The nonvolatile memory device of claim 1 , wherein the variable-resistance memory cell array comprises phase-change memory cells.
6. The nonvolatile memory device of claim 1 , wherein the variable-resistance memory cell comprises a phase-change memory cell and the program protection state corresponds to an amorphous state of a phase-change material in the phase-change memory cell.
7. A method of operating a nonvolatile memory device comprising a variable-resistance memory cell array comprising a memory block that stores protected data, and a variable-resistance memory cell that stores lock state information indicating whether the protected data is changeable, the method comprising:
initializing the variable-resistance memory cell to a program protection state;
receiving a security code;
in response to the security code, changing the variable-resistance memory cell to a program unprotection state;
while the variable-resistance memory cell is in the program unprotection state, programming the memory block;
receiving a data protection command; and
in response to the protection command, changing the variable-resistance memory cell to the program protection state.
8. The method of claim 7 , wherein the memory block is a one-time-programmable memory block.
9. The method of claim 7 , wherein the nonvolatile memory device is a phase-chance random access memory device.
10. The method of claim 7 , further comprising:
receiving a request to access the memory block; and
rejecting the request upon determining that the variable-resistance memory cell is in the program protection state.
11. The method of claim 7 , wherein the variable-resistance memory cell is a phase-change memory cell and the program protection state corresponds to an amorphous state of a phase-change material in the phase-change memory cell.