3.5 transistor non-volatile memory cell using gate breakdown phenomena
View Patent ↗A programmable memory cell formed useful in a memory array having column bitlines and row wordlines. The memory cell including a breakdown transistor having its gate connected to a program wordline and a write transistor connected in series at a sense node to said breakdown transistor. The gate of the write transistor is connected to a write wordline. Further, a first sense transistor has its gate connected to the sense node. A second sense transistor is connected in series to the first sense transistor and has its gate connected to a read wordline. The second sense transistor has its source connected to a column bitline.
1. A programmable memory cell formed useful in a memory array having column bitlines and row wordlines, the memory cell comprising:
a breakdown transistor having its gate connected to a program wordline;
a write transistor connected in series at a sense node to said breakdown transistor, said write transistor having its gate connected to a write wordline;
a first sense transistor having its gate connected to said sense node; and
a second sense transistor connected in series to said first sense transistor and having its gate connected to a read wordline, said second sense transistor having its source connected to a column bitline.
2. The memory cell of claim 1 wherein said write transistor has its source connected to a column sourceline.
3. The memory cell of claim 2 wherein said first sense transistor has its source connected to a column sourceline.
4. The memory cell of claim 1 wherein the drain of said first sense transistor is connected to the source of said second sense transistor.
5. The memory cell of claim 1 wherein said breakdown transistor is replaced with a MOS capacitor or polysilicon-oxide-semiconductor capacitor and said program wordline is connected to a polysilicon or metal layer of said capacitor.
6. The memory cell of claim 1 wherein said memory cell is programmed by applying a program voltage VPP to said program wordline and turning on said write transistor to allow programming current to flow through said breakdown transistor and onto a column sourceline.
7. The memory cell of claim 1 wherein said memory cell is read by turning off said write transistor, applying a read voltage VRD onto said program wordline and VDD to the gate of the second sense transistor, wherein said column bitline will have a decreasing voltage if said memory cell is programmed and a stable voltage if said memory cell is not programmed.