Nonvolatile memory and method of programming the same memory
View Patent ↗There is provided a method of programming a non-volatile memory which can solve the problem of the data write system of the existing flash memory that a load capacitance of bit lines becomes large, the time required by the bit lines to reach the predetermined potential becomes longer, thereby the time required for data write operation becomes longer and power consumption also becomes large because the more the memory capacitance of memory array increases, the longer the length of bit lines becomes and the more the number of bit lines increases. In the non-volatile memory of the invention comprising the AND type memory array in which a plurality of memory cells are connected in parallel between the local bit lines and local drain lines, the local drain lines are precharged by supplying thereto a comparatively higher voltage from the common drain line side (opposite side of the main bit lines), the main bit lines are selectively precharged by applying thereto the voltage of 0V or a comparatively small voltage depending on the write data and thereafter a drain current is applied only to the selected memory cells to which data is written by applying the write voltage to the word lines in order to implant the hot electrons to the floating gate.
1. A nonvolatile memory apparatus comprising:
a nonvolatile memory cell having a threshold voltage within one of a plurality of threshold voltage ranges in accordance with data stored therein;
a first signal line coupled to a first terminal of the nonvolatile memory cell;
a second signal line coupled to a second terminal of the nonvolatile memory cell;
a word line coupled to a control terminal of the nonvolatile memory cell; and
a control circuit,
wherein the control circuit is adapted to control program operations,
wherein in a program operation in which the threshold voltage of the nonvolatile memory cell is to be changed from one of said plurality of threshold voltage ranges to another, the control circuit performs control to discharge a voltage charged in the first signal line to a first voltage level, to charge a second voltage having a level higher than the first voltage level to the second signal line, and then to supply a program voltage to the word line, and
wherein current flows from the second terminal of the nonvolatile memory cell to the first terminal of the nonvolatile memory cell during a first period for charging a parasitic capacitance of the first signal line after supplying the program voltage in the program operation.
2. A nonvolatile memory apparatus according to claim 1 ,
wherein in a program operation in which the threshold voltage of the nonvolatile memory cell is not to be changed to another threshold voltage range, the control circuit performs control to discharge a voltage charged in the first signal line to a third voltage level which is higher than the first voltage level, to charge the second voltage to the second signal line, and then to supply the program voltage to the word line, and
wherein current flow from the second terminal of the nonvolatile memory cell to the first terminal of the nonvolatile memory cell is inhibited by the third voltage charged in the first signal line.
3. A nonvolatile memory apparatus according to claim 2 ,
wherein the control circuit performs control to discharge the voltage charged in the first signal line to the first voltage level, and then to charge voltage to the first signal line limited to the third voltage level.
4. A nonvolatile memory apparatus according to claim 3 ,
wherein the first signal line is coupled to a bit line via a first switch, and
wherein the first switch is turned on during discharging of the voltage charged in the first signal line.
5. A nonvolatile memory apparatus according to claim 4 ,
wherein the parasitic capacitance of the first signal line is smaller than a parasitic capacitance of the bit line.
6. A nonvolatile memory apparatus according to claim 5 ,
wherein the nonvolatile memory cell has an electron charge region for changing the threshold voltage thereof by injecting electrons into the electron charge region, and
wherein a hot electron generated by the current flowing from the second terminal to the first terminal is injected to the electron charge region.
7. A nonvolatile memory apparatus according to claim 6 ,
wherein the control circuit is adapted to control an erase operation,
wherein in the erase operation, the control circuit performs control to supply an erase voltage to the word line for ejecting an electron injected into the electron charge region by FN tunneling.