Non-Volatile Memory with Improved Programming and Method Therefor

Abstract

Non-volatile memory that has non-volatile charge storing capability such as EEPROM and flash EEPROM is programmed by a programming system that applies to a plurality of memory cells in parallel. Enhanced performance is achieved by programming each cell to its target state with a minimum of programming pulses using a data-dependent programming voltage. Further improvement is accomplished by performing the programming operation in multiphase where each successive phase is executed with a finer programming resolution such as employing a programming voltage with a gentler staircase waveform. These features allow rapid and accurate convergence to the target states for the group of memory cells being programmed in parallel, thereby allowing each cell to store several bits of information without sacrificing performance.

1 . A method of programming a multi-state memory cell to threshold voltage corresponding to a target state in a memory device, the method comprising: 
 determining a target state for the memory cell;    programming a first portion of the threshold voltage corresponding to the selected target state of the memory cell using a first selected programming strength dependent on the target state;    determining whether the first portion of the threshold voltage verifies as successfully programmed in response to said programming a first portion of the threshold voltage;    in response to the first portion of the threshold voltage verifying as successfully programmed, adjusting the programming strength to a second selected programming strength;    programming a second portion of the threshold voltage corresponding to the selected target state of the memory cell using the second selected programming strength, wherein the second portion of the threshold voltage is greater than the first portion of the threshold voltage and less than or equal to the threshold voltage corresponding to the selected target state of the memory cell; and    determining whether the second portion of the threshold voltage verifies as successfully programmed in response to said programming a second portion of the threshold voltage.    
   
   
       2 . The method of  claim 1 , wherein the second portion of the threshold voltage is less than the threshold voltage corresponding to the selected target state of the memory cell.  
   
   
       3 . The method of  claim 1 , wherein the second portion of the threshold voltage is equal to the threshold voltage corresponding to the selected target state of the memory cell.  
   
   
       4 . The method of  claim 1 , further comprising, after the step of determining whether the first portion of the threshold voltage verifies as successfully programmed, a step of returning to the step of programming a first portion of the threshold voltage corresponding to the selected target state of the memory cell using a first selected programming strength dependent on the target state if it is determined that the first portion of the threshold voltage does not verify as successfully programmed in response to said programming a first portion of the threshold voltage.  
   
   
       5 . The method of  claim 1 , wherein the second selected programming strength is weaker than the first selected programming strength.