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. An apparatus, comprising:
a first memory string of first transistors;
a second memory string of second transistors;
a first bit line coupled to the first string;
a second bit line coupled to the second string;
a first decoder transistor fabricated in a well and coupled to the first bit line, a gate of the first decoder transistor configured to establish a potential that is raised by capacitive coupling between the gate of the first decoder transistor and the well to which an erase voltage is applied;
a second decoder transistor fabricated in the well and coupled to the second bit line, a gate of the second decoder transistor configured to establish a potential that is raised by capacitive coupling between the gate of the second decoder transistor and the well to which the erase voltage is applied; and
an additional transistor coupled in common to the first and second decoder transistors, the additional transistor configured to be a high voltage transistor, wherein the additional transistor is configured to be turned off responsive to an increase of a potential of the well when an erase voltage is applied to the well.
2. The apparatus of claim 1 , further comprising:
a data register buffer, the additional transistor being coupled between the data register buffer and a node coupled in common to the first and second decoder transistors.
3. The apparatus of claim 2 , wherein the additional transistor is configured to isolate the data register from the first and second bit lines.
4. The apparatus of claim 1 , wherein the first and second decoder transistors are configured not to be a high voltage transistor.
5. The apparatus of claim 1 , wherein the additional transistor is larger in film thickness than the first decoder transistor.
6. The apparatus of claim 1 , wherein the additional transistor is larger in film thickness than a transistor of the data register buffer.
7. The apparatus of claim 1 , wherein the additional transistor is larger in gate length than the first decoder transistor.
8. The apparatus of claim 1 , wherein the additional transistor is larger in size than the first decoder transistor.
9. The apparatus of claim 1 , comprising:
a NAND memory array comprising the first and second memory strings.
10. An apparatus, comprising:
a memory string comprising:
a drain select transistor fabricated in a well;
a source select transistor fabricated in the well; and
memory cell transistors fabricated in the well and coupled between the drain select transistor and the source select transistor;
a bit line coupled to the memory string;
a first decoder transistor fabricated in the well and coupled to the bit line, the first decoder transistor including a first gate configured to have a potential that is raised by capacitive coupling between the first gate and the well responsive to an erase voltage applied to the well;
a data register buffer comprising a sense amplifier configured to sense voltage of the bit line; and
a circuit comprising a high voltage transistor coupled between the first decoder transistor and the data register buffer, wherein a gate of the high voltage transistor is configured to receive, when an erase voltage applied to the well, a voltage different than a zero voltage such that the high voltage transistor is turned off in response to the erase voltage applied to the well.
11. The apparatus of claim 10 , wherein the circuit is configured to isolate the data register from the bit line when an erase voltage is applied to the well.
12. The apparatus of claim 10 , wherein the first decoder transistor is not a high voltage transistor.
13. The apparatus of claim 10 , wherein the high voltage transistor of the circuit is not fabricated in the well.
14. The apparatus of claim 10 , wherein the high voltage transistor of the circuit comprises a drain-source path coupled between the first decoder transistor and the data register buffer and comprises a gate to which an erase bias voltage is applied.
15. An apparatus, comprising:
a first memory string of first transistors fabricated in a well;
a second memory string of second transistors fabricated in the well;
a first bit line coupled to the first string;
a second bit line coupled to the second string;
a first decoder transistor fabricated in the well and coupled to the first bit line, the first decoder transistor including a first gate capacitively coupled to the well, wherein the first gate is configured to have a potential that is raised by the capacitive coupling between the first gate and the well responsive to an erase voltage applied to the well; a second decoder transistor fabricated in the well and coupled to the second bit line, the second decoder transistor including a second gate capacitively coupled to the well, wherein the second gate is configured to have a potential that is raised by the capacitive coupling between the second gate and the well responsive to the erase voltage applied to the well; and
an additional transistor coupled in common to the first and second decoder transistors, the additional transistor having a film thickness different than the first and second decoder transistors, wherein a gate of the additional transistor is configured to receive a voltage different than a zero voltage when an erase voltage applied to the well.
16. The apparatus of claim 15 wherein the additional transistor has a greater film thickness than the first and second decoder transistors.
17. The apparatus of claim 15 , wherein the first decoder transistor is an n-type transistor that is fabricated in the well that is formed from a p-type semiconductor zone.
18. The apparatus of claim 15 , wherein the additional transistor is not fabricated in the well.
19. The apparatus of claim 15 wherein a gate of the additional transistor is configured to receive a first voltage before an erase voltage is applied to the well and keep receiving the first voltage when the erase voltage is applied to the well.