System and method for programming cells in non-volatile integrated memory devices
A system and method for quickly and efficiently programming hard-to-program storage elements in non-volatile integrated memory devices is presented. A number of storage elements are simultaneously subjected to a programming process with the current flowing through the storage elements limited to a first level. As a portion of these storage elements reach a prescribed state, they are removed from the set of cells being programmed and the current limit on the elements that continue to be programmed is raised. The current level in these hard-to-program cells can be raised to a second, higher limit or unregulated. According to another aspect, during a program operation the current limit allowed for a cell depends upon the target state to which it is to be programmed.
1. In a non-volatile memory including an array of multi-state storage elements connected in a plurality of columns along bit lines and along one or more rows each connected to a corresponding word line, a method of concurrently programming a plurality of the storage elements connected along a common word line from an initial condition to one of a plurality of data states, comprising:
providing for each of said plurality of the storage elements connected along the common word line a corresponding target state from said plurality of data states; and
biasing said plurality of the storage elements, wherein the biasing includes:
independently limiting the current on each of the respective bit lines to which said plurality of the storage elements are connected to not exceed a value selected from a plurality of values dependent upon the corresponding target state of the respective storage element; and
subsequently applying a programming waveform to the common word line while the respective bit lines are concurrently so limited to two or more different ones of said values.
2. The method of claim 1 , wherein said current on each of the respective bit lines is the source-drain current of the corresponding storage elements and the common word line supplies the programming waveform to the control gates of each of said plurality of the storage elements.
3. The method of claim 2 , wherein said programming waveform is a series of pulses.
4. The method of claim 1 , wherein the storage elements are charge-storing devices.
5. The method of claim 4 , wherein the storage elements are floating gate transistors.
6. A non-volatile memory comprising:
an array of multi-state storage elements connected in one or more columns along bit lines and along one or more rows each connected to a corresponding word line;
programming circuitry connectable to the bit lines and the word lines to apply a set of voltages to perform a program operation to concurrently program a plurality of the storage elements connected along a common word line from an initial condition to a corresponding target state from one of a plurality of data states, set of voltage including a programming waveform applied to the common word line; and
current limiting circuitry connectable to said bit lines to individually limit the current through said plurality of the storage elements to not exceed a value selected from a plurality of values dependent upon the corresponding target state of the respective storage elements and that are determined prior to applying the programming waveform to the common word line while the respective bit lines are concurrently so limited to two or more different ones of said value.
7. The non-volatile memory of claim 6 , wherein said set of voltages includes applying a programming waveform to common word line.
8. The non-volatile memory of claim 7 , wherein said programming waveform is a series of pulses.
9. The non-volatile memory of claim 6 , wherein the storage elements are charge-storing devices.
10. The non-volatile memory of claim 9 , wherein the storage elements are floating gate transistors.