Non-volatile memory with induced bit lines
View Patent ↗An electrically programmable non-volatile memory cell is provided. A semiconductor substrate is prepared. A pair of spaced apart source/drain (S/D) regions is defined on the semiconductor substrate. The spaced apart S/D regions define a channel region in between. A first dielectric layer such as silicon dioxide is disposed on the S/D regions. An assistant gate is stacked on the first dielectric layer. The assistant gate has a top surface and sidewalls. A second dielectric layer comprising a charge-trapping layer is uniformly disposed on the top surface and sidewalls of the assistant gate and is also disposed on the channel region. The second dielectric layer provides a recessed trough between the S/D regions. A conductive gate material fills the recessed trough for controlling said channel region.
1. An electrically programmable nonvolatile memory array, comprising:
a semiconductor substrate of first conductivity type;
columns of spaced apart source/drain (S/D) regions defined on said semiconductor substrate;
a channel region between said source/drain (S/D) regions;
a first dielectric layer disposed on said source/drain (S/D) regions;
columns of assistant gates stacked on said first dielectric layer, wherein each of said assistant gates has a top surface and sidewalls, wherein at least one end of each said columns of assistant gates partially overlaps with a doped pickup well formed in said semiconductor substrate, and wherein a bit line voltage is provided to said doped pickup well;
a second dielectric layer comprising a charge-trapping layer uniformly disposed on said top surface and sidewalls of said assistant gate and disposed on said channel region, wherein said second dielectric layer produces a recessed trough between said source/drain (S/D) regions; and
rows of word lines laid on said second dielectric layer, said rows of word lines intersecting said columns of assistant gates;
wherein, when programming a memory cell defined by a specific row of said word lines of said electrically programmable non-volatile memory array, only two columns of said assistants gates next to said memory cell are biased to a voltage V i that is sufficient to correspondingly induced two columns of inversion regions of second conductivity type in said semiconductor substrate; and wherein said inversion regions of second conductivity type function as a source/drain of said memory cell.
2. The electrically programmable non-volatile memory array according to claim 1 wherein said first dielectric layer is made of silicon dioxide.
3. The electrically programmable non-volatile memory array according to claim 2 wherein said silicon dioxide is thermally grown.
4. The electrically programmable non-volatile memory array according to claim 1 wherein said second dielectric layer is a tri-layer dielectric.
5. The electrically programmable non-volatile memory array according to claim 1 wherein said second dielectric layer is an ONO tri-layer, and said charge-trapping layer is a silicon nitride layer sandwiched between a bottom oxide layer and a top oxide layer.
6. The electrically programmable non-volatile memory array according to claim 1 wherein said second dielectric layer is a bi-layer dielectric.
7. The electrically programmable non-volatile memory array according to claim 1 wherein said assistant gate is made of polysilicon.
8. The electrically programmable non-volatile memory array according to claim 1 wherein said word line comprises polysilicon.
9. The electrically programmable non-volatile memory array according to claim 1 wherein said word line is metal word line.