Contactless bidirectional nonvolatile memory
View Patent ↗A contactless memory architecture has a column of bidirectional multi-bit memory cells between each adjacent pair of diffused lines in a bank. The architecture includes about half as many metal lines as diffused lines, and bank select cells at both ends of the bank. Most bank select cells connect respective metal lines to respective pairs of diffused lines. For a memory access, metal lines on one side of a selected bidirectional memory cell are biased to a first voltage, and metal lines on the other side of the selected bidirectional memory cell are biased to a second voltage. The first voltage is made higher than the second voltage to select one of the storage locations in the selected cell, and the second voltage is made higher than the first voltage to select the other of the storage locations in the selected cell.
1. A method for accessing a selected storage location in a selected bidirectional memory cell within a memory containing a plurality of diffused lines, each diffused line forming source/drain regions for a column of bidirectional memory cells, the method comprising:
decoding a column address to identify a selected overlying line from a plurality of overlying lines and identify a direction for a current though the selected bidirectional memory cell;
selecting a first level for a first voltage and second level for a second voltage based on the direction for the current;
biasing all of the overlying lines that are on a first side of the selected overlying line at the first voltage and all of the overlying lines that are on a second side of the selected overlying line at the second voltage; and
activating first bank select cells that are at a first end of the bank or second bank select cells that are at a second end of the bank depending on whether the column address indicates a selected bidirectional memory cell is in an even or odd column of a selected bank, wherein each first bank select cell when activated connects a corresponding one of the overlying lines to a pair of the diffused lines, and each second bank select cell when activated connects a corresponding one of the overlying lines to a pair of the diffused lines.
2. The method of claim 1 , further comprising:
decoding a row address to identify a selected word line from a plurality of of word lines; and
activating the selected word line.
3. The method of claim 2 , further comprising decoding the row address to identify the selected bank from a plurality of banks, wherein each of the banks includes two sets of bank select cells, and activating one of the first and second sets of bank select cells comprising activating one of the two sets of bank select cells in the selected bank.