Non-volatile semiconductor memory device
View Patent ↗The present invention provides a non-volatile memory capable of realizing erase/write operations in sufficiently small division units while suppressing an increase in chip area to the minimum, and shortening an erase time. Two of a physical erase state and a logical erase state are provided as threshold voltage distribution states of each memory cell. In the logical erase state, a threshold voltage criterion of the memory cell is shifted to a state higher than the physical erase state. When data rewriting of the memory cell placed in the physical erase state is performed, a logical erase is performed and the threshold voltage criterion is shifted to a high voltage level. The logical erase simply shifts the voltage level of the threshold voltage criterion. Since an electrical charge accumulated in the memory cell is not moved, erasing can be done at high speed and in a short period of time.
1. A non-volatile semiconductor memory device comprising:
a memory cell array having a plurality of non-volatile memory cells, the memory cell array being divided into a plurality of first erase units respectively including a plurality of second erase units; and
a control circuit which executes erase and write operations of each selected memory cell in the memory cell array in accordance with erase or write instructions,
wherein the control circuit includes a first erase control unit which performs an erase in the first erase unit and a second erase control unit which performs an erase in the second erase unit,
wherein the second erase control unit sets a voltage applied to the target memory cell at erasing smaller in absolute value than at erasing by the first erase control unit and makes short the time necessary for erasure, and
wherein when the second erase unit including each selected memory cell is in a state in which erasing and writing are being done by the first erase control unit, the second erase control unit erases the second erase unit including the selected memory cell.
2. The non-volatile semiconductor memory device according to claim 1 ,
wherein the memory cells of the memory cell array are arranged over a well region in matrix form,
wherein the first erase units are of well units, and
wherein the second erase units are of word lines arranged corresponding to memory cell rows.
3. The non-volatile semiconductor memory device according to claim 1 ,
wherein the memory cell array is divided into a plurality of blocks each having sectors including a plurality of memory cell rows respectively,
wherein the first erase units are of the blocks, and
wherein the second erase units are of the sectors.
4. A non-volatile semiconductor memory device, comprising:
a memory cell array having a plurality of non-volatile memory cells, the memory cell array being divided into a plurality of first erase units respectively including a plurality of second erase units; and
a control circuit which executes erase and write operations of each selected memory cell in the memory cell array in accordance with erase or write instructions,
wherein the control circuit includes a first erase control unit which performs an erase in the first erase unit and a second erase control unit which performs an erase in the second erase unit,
wherein the second erase control unit sets a voltage applied to the target memory cell at erasing smaller in absolute value than at erasing by the first erase control unit and makes short the time necessary for erasure,
wherein the control circuit further includes a write control unit which executes writing on the second erase units each placed in a non-written state, of the memory cell array upon a state in which the addressed second erase unit is erased by the first erase control unit and data writing has been conducted thereby, and sets the addressed second erase unit to an invalid state,
wherein the second erase control unit executes erasing by the second erase control unit on the first erase units when second rewrite units lying within the first erase units are all set to an invalid state, and sets the rewrite units in the first erase units to a valid state, and
wherein the first erase control unit executes erasing of the first erase units under the first erase control unit when the second rewrite units lying in the first erase units are all invalidated after erasing thereof by the second erase control unit.