Non-volatile programmable memory cell and array for programmable logic array
View Patent ↗A non-volatile programmable memory cell suitable for use in a programmable logic array includes a non-volatile MOS transistor of a first conductivity type in series with a volatile MOS transistor of a second conductivity type. The non-volatile MOS transistor may be a floating gate transistor, such as a flash transistor, or may be another type of non-volatile transistor such as a floating charge-trapping SONOS, MONOS transistor, or a nano-crystal transistor. A volatile MOS transistor, an inverter, or a buffer may be driven by coupling its gate or input to the common connection between the non-volatile MOS transistor and the volatile MOS transistor.
1. A plurality of non-volatile programmable memory cells formed in a semiconductor substrate of a first conductivity type and comprising:
a plurality of non-volatile MOS transistors of a second conductivity type formed in a first semiconductor region of the first conductivity type and coupled between a common first power supply potential and an individual output node;
a plurality of volatile MOS transistors of the first conductivity type formed in a semiconductor region of the second conductivity type, each volatile MOS transistor of the first conductivity type coupled between a different one of the individual output nodes and a common second power supply potential; and
a plurality of volatile MOS switch transistors of the second conductivity type formed in a second semiconductor region of the first conductivity type, each of the plurality of MOS switch transistors coupled to a different one of the individual output nodes;
wherein the first and second semiconductor regions of the first conductivity type are electrically isolated from one another.
2. The non-volatile programmable memory cell of claim 1 wherein said first semiconductor region of the first conductivity type is a well region of the first conductivity type formed within a first well region of the second conductivity type and the second semiconductor region of the first conductivity type is the semiconductor substrate.
3. The non-volatile programmable memory cell of claim 1 wherein all of the volatile MOS transistors of the first conductivity type are formed in the first well region of the second conductivity type.
4. The non-volatile programmable memory cell of claim 1 wherein said first semiconductor region of the first conductivity type is a first well region of the first conductivity type formed within a well region of the second conductivity type and the second semiconductor region of the first conductivity type is a second well region of the first conductivity type isolated from the first well region of the first conductivity type.
5. The non-volatile programmable memory cell of claim 4 wherein all of the volatile MOS transistors of the first conductivity type are formed in the first well region of the second conductivity type.
6. The non-volatile programmable memory cell of claim 1 wherein all of the non-volatile MOS transistors are floating gate transistors.
7. The non-volatile programmable memory cell of claim 1 wherein all of the non-volatile MOS transistors are flash transistors.
8. The non-volatile programmable memory cell of claim 1 wherein all of the non-volatile MOS transistors are floating charge-trapping transistors.
9. The non-volatile programmable memory cell of claim 1 wherein all of the non-volatile MOS transistors are nano-crystal transistors.
10. The non-volatile programmable memory cell of claim 1 wherein said first conductivity type is N, and said second conductivity type is P.
11. The non-volatile programmable memory cell of claim 1 further including at least one additional volatile MOS switch transistor of the second conductivity type formed in the second semiconductor region of the first conductivity type and coupled to the output node.
12. An array of non-volatile programmable memory cells formed in a semiconductor substrate of a first conductivity type and comprising:
a plurality of non-volatile MOS transistors of a second conductivity type formed in a first semiconductor region of the first conductivity type and coupled between a common first power supply potential and an individual output node;
a plurality of volatile MOS transistors of the first conductivity type formed in a semiconductor region of the second conductivity type, each volatile MOS transistor of the first conductivity type coupled between a different one of the individual output nodes and a common second power supply potential; and
a plurality of volatile MOS switch transistors of the second conductivity type formed in a second semiconductor region of the first conductivity type, each of the plurality of MOS switch transistors coupled to a different one of the individual output nodes;
a plurality of input and output buffers coupled to the plurality of volatile MOS switch transistors;
wherein:
the semiconductor region of the second conductivity type provides electrical isolation of the first semiconductor region of the first conductivity type from the second semiconductor region of the first conductivity type; and
the input and output buffers are protected from negative erase potentials used in programming the non-volatile MOS transistors by the electrical isolation provided by the semiconductor region of the second conductivity type.
13. The array of non-volatile programmable memory cells of claim 12 , wherein the second conductivity type is N, further comprising:
a deep N-well region providing further isolation of the second semiconductor region of the first conductivity type from the first semiconductor region of the first conductivity type.
14. The array of non-volatile programmable memory cells of claim 12 , wherein:
the plurality of non-volatile MOS transistors comprises a first column and a second column;
each non-volatile MOS transistor in the first column has a gate connected to the other non-volatile MOS transistors in the first column; and
each non-volatile MOS transistor in the second column has a gate connected to the other non-volatile MOS transistors in the second column.
15. The array of non-volatile programmable memory cells of claim 13 , wherein a first edge of the deep N-well region is vertically aligned with a first edge of the semiconductor region of the second conductivity type.
16. The array of non-volatile programmable memory cells of claim 13 , wherein a first edge of the deep N-well region is recessed with respect to a first edge of the semiconductor region of the second conductivity type.
17. The non-volatile programmable memory cell of claim 15 wherein said first conductivity type is N and said second conductivity type is P.