Non-volatile two-transistor programmable logic cell and array layout
View Patent ↗A two-transistor non-volatile memory cell is formed in a semiconductor body. A memory-transistor well is disposed within the semiconductor body. A switch-transistor well is disposed within the semiconductor body and is electrically isolated from the memory transistor well. A memory transistor including spaced-apart source and drain regions is formed within the memory-transistor well. A switch transistor including spaced-apart source and drain regions is formed within the switch-transistor well region. A floating gate is insulated from and self aligned with the source and drain regions of the memory transistor and switch transistor. A control gate is disposed above and aligned to the floating gate and with the source and drain regions of the memory transistor and the switch transistor.
1. An array of non-volatile memory cells including:
a semiconductor body;
a plurality of memory-transistor wells disposed within the semiconductor body;
for each of the memory-transistor wells a first switch-transistor well disposed within the semiconductor body to a first side of the memory transistor well and electrically isolated from the memory transistor well and a second switch-transistor well disposed within the semiconductor body to a second side of the memory transistor well opposite the first side and electrically isolated from the memory transistor well;
a memory transistor formed within each memory-transistor well and including spaced-apart source and drain regions;
a first switch transistor formed within each first switch-transistor well region and including spaced-apart source and drain regions;
a second switch transistor formed within each second switch-transistor well region and including spaced-apart source and drain regions;
a floating gate segment insulated from and self aligned with the source and drain regions of each memory transistor and the first and second switch transistors with which it is associated; and
a control gate disposed above and self aligned with respect to the floating gate segments and with the source and drain regions of the memory transistors and the switch transistors.
2. The array of claim 1 wherein the semiconductor body is an n-type well disposed in a p-type semiconductor substrate.
3. The array of claim 1 wherein the memory-transistor wells and the switch-transistor wells are formed to different depths.
4. The array of claim 1 wherein:
the semiconductor body is n-type;
the memory-transistor wells and the switch transistor wells are both p-type wells; and
the memory transistors and the switch transistors are all n-channel transistors.
5. The array of claim 4 wherein the memory-transistor wells are electrically isolated from the switch-transistor wells by a deep-trench isolation region.
6. The array of claim 4 wherein the memory-transistor wells are optimized for memory-transistor characteristics and the switch-transistor wells are optimized for switch-transistor characteristics.
7. The array of claim 4 wherein:
the semiconductor body is an n-type well formed in a semiconductor substrate; and
the switch-transistor p-type wells are spaced apart from the memory-transistor p-type wells and are isolated from the memory transistor p-type wells by the n-type well.
8. The array of claim 7 further including:
a higher doped n-type well disposed between and further isolating the memory-transistor p-type wells and the switch-transistor p-type wells.