Three-dimensional one-time-programmable memory comprising dummy bit lines
A multi-bit-per-cell three-dimensional read-only memory (3D-OTP MB ) comprises a plurality of dummy bit lines. It comprises a plurality of OTP cells stacked above a semiconductor substrate. Each OTP array comprises at least four dummy bit lines.
1. A multi-bit-per-cell three-dimensional read-only memory (3D-OTP MB ) with at least three states including first, second and third states, comprising:
a semiconductor substrate with transistors thereon;
an OTP array stacked above said semiconductor substrate, comprising:
a plurality of data OTP cells including a first data OTP cell in said first state, a second data OTP cell in said second state, and a third data OTP cell in said third state;
a first dummy OTP cell in said first state and a first dummy bit line associated therewith;
a second dummy OTP cell in said second state and a second dummy bit line associated therewith;
a third dummy OTP cell in said second state and a third dummy bit line associated therewith;
a fourth dummy OTP cell in said third state and a fourth dummy bit line associated therewith;
a plurality of contact vias coupling said OTP array to said semiconductor substrate;
a first differential amplifier on said semiconductor substrate, said first differential amplifier having a first input coupled with said first and second dummy bit lines, having a second input coupled with a first selected one of said data OTP cells;
a second differential amplifier on said semiconductor substrate, said second differential amplifier having a third input coupled with said third and fourth dummy bit lines, having a fourth input coupled with a second selected one of said data OTP cells;
wherein said first data OTP cell and said first dummy OTP cell are unprogrammed; said second data OTP cell, said second dummy OTP Cell and said third dummy OTP cell are programmed by a first programming current; and, said third data OTP cell and said fourth dummy OTP cell are programmed by a second programming current different from said first programming current.
2. The 3D-OTP MB according to claim 1 , wherein said second data OTP cell has a larger resistance than said third data OTP cell.
3. The 3D-OTP MB according to claim 1 , wherein said first programming current is smaller than said second programming current.