Highly integrated ternary semiconductor memory device
A TCAM (ternary content addressable memory) cell array is provided with a search input node into which one bit of search data is inputted, a plurality of data input nodes into which a bit corresponding to one bit of search data is inputted, and a plurality of memory cells arranged in rows and columns. Each of the plurality of memory cells further includes a first cell storing one bit of said storage data, and a logical operation cell determining whether or not said search data and storage data match. A gate of a transistor forming each of a plurality of memory cells extends along the direction of said rows. Each of a plurality of wells in the region where the memory array is formed is formed so as to continue to a corresponding well of an adjacent memory cell in the direction of said columns.
1. A semiconductor memory device, comprising a plurality of memory cells arranged in rows and columns, each memory cell being configured to hold information of two bits and including:
a first cell capable of holding information of one bit;
a second cell capable of holding information of one bit and placed adjacent to said first cell in a direction of said columns;
a bit line pair extending along the direction of said columns and connected to both of said first and second cells;
first and second word lines extending along a direction of said rows and connected to said first and second cells, respectively; and
a logical operation cell placed adjacent, in the direction of said rows, to both of said first and second cells extending along the direction of the columns, and outputting results based on search data and information held in said first and second cells, wherein
a gate of a transistor forming each of said plurality of memory cells extends along the direction of said rows, and
a region where each of said plurality of memory cells is formed includes first to third wells aligned in this order along the direction of said rows, and said first and third wells are of a first conductivity type and said second well sandwiched between said first and third wells is of a second conductivity type.
2. The semiconductor memory device according to claim 1 , wherein
each of said plurality of memory cells further includes
a search line pair for transferring said search data extending along the direction of said columns and connected to said logical operation cell, and
a match line extending along the direction of said rows and connected to said logical operation cell.
3. The semiconductor memory device according to claim 2 , wherein
said first and second word lines are formed of a first metal interconnection layer,
said search line pair is formed of a second metal interconnection layer,
said match line is formed of a third metal interconnection layer,
said first metal interconnection layer is located beneath said third metal interconnection layer, and
said third metal interconnection layer is located above said second metal interconnection layer.
4. The semiconductor memory device according to claim 2 , wherein
said search line pair is formed of a first metal interconnection layer,
said first and second word lines and said match line are formed of a second metal interconnection layer, and
said first metal interconnection layer is located beneath said second metal interconnection layer.
5. The semiconductor memory device according to claim 1 , wherein
first and second memory cells among said plurality of memory cells that are adjacent to each other in the direction of said rows further include
a search line pair for transferring said search data extending in a border portion between said first and second memory cells along the direction of said columns, and shared by and connected to logical operation cells of said first and second memory cells.
6. The semiconductor memory device according to claim 5 , wherein
said logical operation cell of said first memory cell is connected to a first match line crossing said first and second memory cells that are adjacent to each other along the direction of the rows, and
said logical operation cell of said second memory cell is connected to a second match line crossing said first and second memory cells that are adjacent to each other in the direction of the rows.
7. A semiconductor memory device, comprising:
first and second memory cells placed adjacent to each other in a direction of rows, each of said first and second memory cells including
a first cell being configured to hold information of one bit,
a second cell being configured to hold information of one bit and placed adjacent to said first cell in a direction of columns, and
a logical operation cell placed adjacent, in the direction of said rows, to both of said first and second cells extending along the direction of said columns, and outputting results based on search data and information held in said first and second cells;
first and second word lines extending along the direction of said rows and connected to said first and second cells, respectively, in each of said first and second memory cells;
a first bit line pair extending along the direction of said columns and connected to said first and second cells in said first memory cell;
a second bit line pair extending along the direction of said columns and connected to said first and second cells in said second memory cell; and
a search line pair extending along the direction of said columns, connected to said logical operation cell in each of said first and second memory cells, and transferring said search data.
8. The semiconductor memory device according to claim 7 , wherein
write of data is collectively carried out on said first and second memory cells in one write cycle.
9. The semiconductor memory device according to claim 7 , wherein
said first and second memory cells are formed in SOI substrate.