Efficient method and computer program for modeling and improving static memory performance across process variations and environmental conditions

Abstract

An efficient method and computer program for modeling and improving stating memory performance across process variations and environmental conditions provides a mechanism for raising the performance of memory arrays beyond present levels/yields. Statistical (Monte-Carlo) analyses of subsets of circuit parameters are performed for each of several memory performance variables and then sensitivities of each performance variable to 15 each of the circuit parameters are determined. The memory cell design parameters and/or operating conditions of the memory cells are then adjusted in conformity with the sensitivities, resulting in improved memory yield and/or performance. Once a performance level is attained, the sensitivities can then be used to alter the probability distributions of the performance variables to achieve a higher yield. Multiple cell designs can be compared for performance, yield and sensitivity of performance variables to circuit parameters over particular environmental conditions in order to select the best cell design.

1 . A method for improving a design of a memory cell, comprising: 
 selecting particular associated subsets of memory cell circuit parameters for each of a plurality of operational performance variables;    determining statistics for each memory cell circuit parameter within said unique subsets for simulation;    statistically simulating each of said operational performance variables over systematic variations of each memory cell circuit parameter in said associated subset for each simulated operational performance variable;    computing sensitivities of each of said operational performance variables to said variations of said memory cell circuit parameters within said associated subset.    
   
   
       2 . The method of  claim 1 , wherein said selecting is performed by: 
 performing multiple statistical analyses of a full set of devices within said memory cell over variations of circuit parameters for said full set of devices;    computing sensitivities of each of said operational performance variables to said variations of said memory cell circuit parameters within said full set of devices; and    comparing said sensitivities for each of said operational performance variables to a threshold criteria to select said associated subsets of parameters as those parameters for which an associated operational performance variable has a higher sensitivity.    
   
   
       3 . The method of  claim 2 , further comprising performing said multiple statistical analyses, said computing and comparing on multiple cell designs of differing order and further comprising selecting one or more of said multiple cell designs for further analysis by determining which of said multiple cell designs have lower values of said sensitivities.  
   
   
       4 . The method of  claim 1 , further comprising performing said selecting, determining, simulating and computing on multiple cell designs of differing order and further comprising selecting one or more of said multiple cell designs for further analysis by determining which of said multiple cell designs have lower values of said sensitivities.  
   
   
       5 . The method of  claim 1 , further comprising adjusting one or values within associated subsets in conformity with a result of said computing for each of said operational performance variables, whereby design of said memory cell is improved.  
   
   
       6 . The method of  claim 1 , further comprising: 
 eliminating one or more parameters from one or more of said subsets in conformity with a result of said computing; and    repeating said determining, simulating and computing, wherein said repetition is performed on said one or more subsets having a reduced number of parameters.    
   
   
       7 . The method of  claim 1 , wherein said plurality of performance variables includes write stability and read stability, and wherein said simulating simulates said memory cell for each of write stability, write delay, read stability and read delay over said associated subset.  
   
   
       8 . A workstation computer system comprising a processor for executing program instructions and a memory coupled to said processor for storing program instructions, said program instructions including program instructions for altering design parameters of a memory cell, said program instructions comprising program instructions for: 
 selecting particular associated subsets of memory cell circuit parameters for each of a plurality of operational performance variables;    determining statistics for each memory cell circuit parameter within said unique subsets for simulation;    statistically simulating each of said operational performance variables over systematic variations of each memory cell circuit parameter in said associated subset for each simulated operational performance variable;    computing sensitivities of each of said operational performance variables to said variations of said memory cell circuit parameters within said associated subset.    
   
   
       9 . The workstation computer system of  claim 8 , wherein said program instructions for selecting further comprise program instructions for: 
 performing multiple statistical analyses of a full set of devices within said memory cell over variations of circuit parameters for said full set of devices;    computing sensitivities of each of said operational performance variables to said variations of said memory cell circuit parameters within said full set of devices; and    comparing said sensitivities for each of said operational performance variables to a threshold criteria to select said associated subsets of parameters as those parameters for which an associated operational performance variable has a higher sensitivity.    
   
   
       10 . The workstation computer system of  claim 9 , wherein said program instructions for performing said multiple statistical analyses, said computing and comparing are executed for multiple cell designs of differing order and further comprising program instructions for selecting one or more of said multiple cell designs for further analysis by determining which of said multiple cell designs have lower values of said sensitivities.  
   
   
       11 . The workstation computer system of  claim 8 , wherein said program instructions for selecting, determining, simulating and computing are executed for multiple cell designs of differing order and further comprising program instructions for selecting one or more of said multiple cell designs for further analysis by determining which of said multiple cell designs have lower values of said sensitivities.  
   
   
       12 . The workstation computer system of  claim 8 , further comprising program instructions for adjusting one or values within associated subsets in conformity with a result of said computing for each of said operational performance variables, whereby design of said memory cell is improved.  
   
   
       13 . The workstation computer system of  claim 8 , further comprising program instructions for: 
 eliminating one or more parameters from one or more of said subsets in conformity with a result of said computing; and    repeatedly executing said program instructions for determining, simulating and computing, wherein said repetition is performed on said one or more subsets having a reduced number of parameters.    
   
   
       14 . The workstation computer system of  claim 8 , wherein said plurality of performance variables includes write stability and read stability, and wherein said program instructions for simulating simulate said memory cell for each of write stability, write delay, read stability and read delay over said associated subset.  
   
   
       15 . A computer program product comprising media encoding program instructions for execution on a workstation computer, said program instructions for altering design parameters of a memory cell, said program instructions comprising program instructions for: 
 selecting particular associated subsets of memory cell circuit parameters for each of a plurality of operational performance variables;    determining statistics for each memory cell circuit parameter within said unique subsets for simulation;    statistically simulating each of said operational performance variables over systematic variations of each memory cell circuit parameter in said associated subset for each simulated operational performance variable;    computing sensitivities of each of said operational performance variables to said variations of said memory cell circuit parameters within said associated subset.    
   
   
       16 . The computer program product of  claim 15 , wherein said program instructions for selecting further comprise program instructions for: 
 performing multiple statistical analyses of a full set of devices within said memory cell over variations of circuit parameters for said full set of devices;    computing sensitivities of each of said operational performance variables to said variations of said memory cell circuit parameters within said full set of devices; and    comparing said sensitivities for each of said operational performance variables to a threshold criteria to select said associated subsets of parameters as those parameters for which an associated operational performance variable has a higher sensitivity.    
   
   
       17 . The computer program product of  claim 16 , wherein said program instructions for performing said multiple statistical analyses, said computing and comparing are executed for multiple cell designs of differing order and further comprising program instructions for selecting one or more of said multiple cell designs for further analysis by determining which of said multiple cell designs have lower values of said sensitivities.  
   
   
       18 . The computer program product of  claim 15 , wherein said program instructions for selecting, determining, simulating and computing are executed for multiple cell designs of differing order and further comprising program instructions for selecting one or more of said multiple cell designs for further analysis by determining which of said multiple cell designs have lower values of said sensitivities.  
   
   
       19 . The computer program product of  claim 15 , further comprising program instructions for adjusting one or values within associated subsets in conformity with a result of said computing for each of said operational performance variables, whereby design of said memory cell is improved.  
   
   
       20 . The computer program product of  claim 15 , further comprising program instructions for: 
 eliminating one or more parameters from one or more of said subsets in conformity with a result of said computing; and    repeatedly executing said program instructions for determining, simulating and computing, wherein said repetition is performed on said one or more subsets having a reduced number of parameters.