Semiconductor memory column decoder device and method
Semiconductor memory devices and methods include a flash memory cell array fabricated in a well, with memory cells in the same column connected to each other in series and connected to a respective bit line. The memory devices also include a column decoder, a data register buffer unit, a row decoder, an erase control unit, and an input/output buffer unit. In one or more embodiments, the erase control unit applies voltages to the well to erase the memory cells in a manner that avoids breaking down p-n junctions formed by transistors fabricated in the well. In another embodiment, high voltage transistors are used to selectively isolate the bit lines from and couple the bit lines to a peripheral circuit in pairs so that each high voltage transistor is shared by two bit lines.
1. A memory, comprising:
a bit line coupled to a memory cell fabricated in a well;
a transistor fabricated in the well, the transistor coupled to the bit line; and
an erase control circuit configured to provide a first voltage to the well and further configured to bias the bit line to a non-zero second voltage, wherein a difference between the non-zero second voltage and the first voltage is less than a breakdown voltage of the transistor.
2. The memory of claim 1 , wherein the transistor is configured to couple the memory cell to a data register buffer, the data register buffer configured to store data being written to or read from the memory cell.
3. The memory of claim 1 , wherein the transistor is an n-type transistor.
4. The memory of claim 1 , wherein the transistor comprises a first transistor and the memory cell comprises a second transistor that has the same operating characteristics as the first transistor.
5. The memory of claim 4 , wherein the second transistor is an n-type transistor and the well is a p-type well.
6. The memory of claim 1 , wherein the transistor is a column decoder transistor.
7. A memory, comprising:
a plurality of serially-coupled memory cells fabricated in a well;
a bit line coupled to the plurality of serially-coupled memory cells;
a transistor fabricated in the well, the transistor coupled between the bit line and the plurality of serially-coupled memory cells; and
an erase control circuit configured to provide an erase voltage to the well, the erase control circuit further configured to bias the bit line to a non-zero bit line voltage to provide a difference between the non-zero bit line voltage and the erase voltage that is less than a breakdown voltage of the transistor.
8. The memory of claim 7 , wherein the transistor comprises a first transistor and a memory cell of the plurality of serially-coupled memory cells comprises a second transistor, wherein the first and second transistors are of a same form and size.
9. The memory of claim 7 , wherein the transistor comprises a select transistor directly coupled to the plurality of serially-coupled memory cells.
10. The memory of claim 7 , wherein the transistor comprises a decoder transistor coupled to the plurality of serially-coupled memory cells through a select transistor.
11. The memory of claim 10 , further comprising a decoder unit transistor coupled to the decoder transistor, wherein the decoder unit transistor is electrically isolated from the well and is of a larger size than the decoder transistor.
12. The memory of claim 7 , wherein the erase control circuit is configured to couple the erase voltage to the well to provide the erase voltage to the well, and the erase control circuit is further configured to decouple the erase voltage from the well.
13. The memory of claim 7 , wherein the transistor is a decoder transistor, the memory further comprising a select transistor fabricated in the well, wherein the select transistor is coupled between the decoder transistor and the plurality of serially-coupled memory cells.
14. A method, comprising:
discharging a voltage of a well that includes a memory cell and a transistor fabricated therein, wherein the transistor is coupled between a bit line and the memory cell; and
clamping the bit line coupled to the memory cell at a non-zero clamp voltage, wherein a difference between the non-zero clamp voltage and the voltage of the well is less than a breakdown voltage of the transistor coupled to the bit line and the memory cell.
15. The method of claim 14 , further comprising charging the well to an erase voltage.
16. The method of claim 14 , wherein discharging the voltage of the well comprises providing a discharge voltage to the bit line.
17. The method of claim 14 , wherein the transistor is a column decode transistor.
18. The method of claim 14 , wherein clamping the bit line at the non-zero clamp voltage is after discharging the voltage of the well begins.
19. The method of claim 14 , wherein the well further comprises a plurality of serially coupled memory cells.