Split-channel antifuse array architecture
Generally, the present invention provides a variable thickness gate oxide anti-fuse transistor device that can be employed in a non-volatile, one-time-programmable (OTP) memory array application. The anti-fuse transistor can be fabricated with standard CMOS technology, and is configured as a standard transistor element having a source diffusion, gate oxide, polysilicon gate and optional drain diffusion. The variable gate oxide underneath the polysilicon gate consists of a thick gate oxide region and a thin gate oxide region, where the thin gate oxide region acts as a localized breakdown voltage zone. A conductive channel between the polysilicon gate and the channel region can be formed in the localized breakdown voltage zone during a programming operation. In a memory array application, a wordline read current applied to the polysilicon gate can be sensed through a bitline connected to the source diffusion, via the channel of the anti-fuse transistor. More specifically, the present invention provides an effective method for utilizing split channel MOS structures as an anti-fuse cell suitable for OTP memories.
1. An anti-fuse transistor formed on a semiconductor material-comprising:
a diffusion region coupled to a first conductor;
a first gate dielectric proximate to the diffusion region and over a first portion of a channel region surface;
a second gate dielectric over the first gate dielectric and a second portion of the channel region surface adjacent the first channel region surface, a combined thickness of the second gate dielectric and the first gate dielectric defining a thick gate oxide, and the second gate dielectric over the second portion of the channel region surface defining a thin gate oxide; and,
a polysilicon gate over the thin gate oxide and the thick gate oxide, the polysilicon gate being coupled to a second conductor.
2. The anti-fuse transistor of claim 1 , wherein the thin gate oxide has a thickness corresponding to a gate oxide of a low voltage transistor formed on the semiconductor material.
3. The anti-fuse transistor of claim 2 , wherein the thick gate oxide has a thickness corresponding to another gate oxide of a high voltage transistor formed on the semiconductor material.
4. The anti-fuse transistor of claim 3 , wherein the thick gate oxide includes a combination of an intermediate gate oxide and the thin gate oxide.
5. The anti-fuse transistor of claim 3 , wherein the diffusion region has an LDD implant substantially the same as another LDD implant of one of the low voltage transistor, the high voltage transistor, and a combination of both the low and the high voltage transistors.
6. The anti-fuse transistor of claim 1 , wherein the thick gate oxide and the polysilicon gate have a first common edge adjacent to the diffusion region, and the thin gate oxide and the polysilicon gate have a second common edge defined by at least two line segments being at an angle to each other.
7. The anti-fuse transistor of claim 6 , wherein the angle is one of 135 degrees and 90 degrees.
8. The anti-fuse transistor of claim 1 , wherein an edge of the diffusion region and a portion of the polysilicon gate is free of salicidation.
9. The antifuse transistor of claim 1 , where the first conductor is a bitline and the second conductor is a wordline.
10. An anti-fuse transistor formed on a semiconductor material comprising:
a diffusion region coupled to a first conductor;
a thin gate oxide over a first portion of a channel region surface, the thin gate oxide consisting of a first gate dielectric having a first thickness;
a thick gate oxide between the diffusion region and the thin gate oxide, and over a second portion of the channel region surface, the thick gate oxide having a second thickness substantially corresponding to a combined thickness of the first gate dielectric and a second gate dielectric;
a polysilicon gate over the thin gate oxide and the thick gate oxide, the polysilicon gate being coupled to a second conductor.
11. The anti-fuse transistor of claim 10 , wherein the thin gate oxide corresponds to a gate oxide of a low voltage transistor formed on the semiconductor material.
12. The anti-fuse transistor of claim 11 , wherein the thick gate oxide corresponds to another gate oxide of a high voltage transistor formed on the semiconductor material.