Isolation-less, contact-less array of nonvolatile memory cells each having a floating gate for storage of charges, and methods of manufacturing, and operating therefor
View Patent ↗An isolation-less, contact-less nonvolatile memory array has a plurality of memory cells each with a floating gate for the storage of charges thereon, arranged in a plurality of rows and columns. Each memory cell can be of a number of different types. All the bit lines and source lines of the various embodiments are buried and are contact-less. In a first embodiment, each cell can be represented by a stacked gate floating gate transistor coupled to a separate assist transistor. The entire array can be planar; or in a preferred embodiment each of the floating gate transistors is in a trench; or each of the assist transistors is in a trench. In a second embodiment, each cell can be represented by a stacked gate floating gate transistor with the transistor in a trench. In a third embodiment, each cell can be represented by two stacked gate floating gate transistors coupled to a separate assist transistor, positioned between the two stacked gate floating gate transistors. The entire array can be planar; or in a preferred embodiment each of the floating gate transistors is in a trench; or each of the assist transistors is in a trench. Novel methods to manufacture the arrays and methods to program, erase, and read each of these embodiments of the memory cells is disclosed.
1. An array of non-volatile memory cells comprising:
a semiconductor substrate;
a plurality of non-volatile memory cells formed in said substrate, arranged in a plurality of rows and columns;
each memory cell comprising;
a first terminal and a second terminal with a channel therebetween in said substrate, said channel having a first portion and a second portion;
a transistor gate insulated from said substrate and positioned to control the conduction of current in said first portion of said channel;
a floating gate insulated from said substrate and positioned to control the conduction of current in said second portion of said channel;
a control gate capacitively coupled to the floating gate;
a plurality of buried bit lines in said substrate arranged substantially parallel to one another;
each buried bit line electrically connected to the first terminal of memory cells arranged in the same column; wherein adjacent memory cells in the same row share a common buried bit line;
a plurality of buried source lines in said substrate arranged substantially parallel to one another; each buried source line electrically connected to the second terminal of memory cells arranged in the same column; wherein adjacent memory cells in the same row share a common buried source line;
a plurality of gate lines arranged substantially parallel to one another, each gate line electrically connected to the transistor gate of memory cells arranged in the same column; and
a plurality of word lines ranged substantively parallel to one another, each word line electrically connected to the control gate of memory cells arranged in the same row.
2. The array of claim 1 wherein said first portion of said channel is adjacent to said first terminal, and said second portion of said channel is adjacent to and between said first portion of said channel and said second terminal and wherein said buried bit line is between adjacent transistor gates of cells adjacent to one another in the same row; and wherein said buried source line is between adjacent floating gates of cells adjacent to one another in the same row.
3. The array of claim 2 further comprising;
a plurality of trenches in said substrate substantially parallel to one another each trench having a first sidewall, a second sidewall and a bottom wall;
each buried source line being along said bottom wall of a trench;
wherein floating gates of first memory cells in the same column are positioned in the same trench insulated from said first sidewall, and floating gates of second memory cells in the same column, adjacent to said first memory cells are positioned in said same trench insulated from said second sidewall.
4. The array of claim 3 wherein adjacent memory cells in the same row share a common control gate and wherein said common control gate is positioned in said trench insulated from said floating gates.
5. The array of claim 4 wherein said plurality of trenches are spaced apart from one another, with a substantially planar surface on said substrate between each pair of adjacent trenches; wherein transistor gates of memory cells, are insulated and spaced apart from the planar surface, and each transistor gate is adjacent to a trench.
6. The array of claim 5 wherein each of said buried bit lines is in said substrate along said planar surface and between a pair of transistor gates.
7. The array of claim 2 further comprising;
a plurality of trenches in said substrate substantially parallel to one another; each trench having a first sidewall, a second sidewall and a bottom wall;
each buried bit line being along said bottom wall of a trench;
wherein transistor gates of first memory cells in the same column are positioned in the same trench insulated from said first sidewall, and transistor gates of second memory cells in the same column, adjacent to said first memory cells are positioned in said same trench insulated from said second sidewall.
8. The array of claim 7 wherein adjacent memory cells in the same row share a common transistor gate anti wherein said common transistor gate is positioned in said trench insulated from said first and second side walls.
9. The array of claim 8 wherein said plurality of trenches are spaced apart from one another, wit a substantially planar surface on said substrate between each pair of adjacent trenches; wherein floating gates of memory cells, are insulated and spaced apart from the planar surface, and cach floating gate is adjacent to a trench.
10. The array of claim 9 wherein each of said buried source lines is in said substrate along said planar surface and between a pair of floating gates.