Gate length upsizing for low leakage standard cells
This disclosure describes a library optimization system that creates modified standard cells with reduced leakage currents that meet predefined cell area, timing, and leakage requirements. The library optimization system selects transistors to upsize based upon the fact that transistors of a same type, such as p-channel or n-channel transistors, that are connected in series produce a small reverse bias between the gate and source, known as a stacking effect. The stacking effect results in an inherent decrease in leakage current for the series-connected transistor chain. As such, the library optimization system adjusts gate lengths of transistors that are not part of the transistor series chains having a relatively large amount of same type transistors.
1. A method comprising:
selecting one or more first series chains of transistors of a same type, wherein each of the one or more first series chains of transistors comprises a greater number of transistors than any of one or more second series chains of transistors, wherein the one or more first series chains of transistors and the one or more second series chains of transistors are included in a standard cell;
creating a modified standard cell from the standard cell by increasing a gate length of one or more of the second series chains of transistors;
adding the modified standard cell to a standard cell library in response to determining that the modified standard cell meets one or more design requirements;
creating an integrated circuit design that comprises at least one instance of the modified standard cell stored in the standard cell library; and
generating mask layer data based upon the integrated circuit design, wherein the mask layer data is configured to generate a plurality of masks for construction of an integrated circuit corresponding to the integrated circuit design; and
forming the plurality of masks for construction of the integrated circuit corresponding to the integrated circuit design.
2. The method of claim 1 further comprising:
determining a largest stack number of the standard cell, wherein the largest stack number is a largest amount of transistors of the same type that are connected in series in the standard cell; and
performing the selecting of the one or more first series chains of transistors based upon the largest stack number, wherein each of the one or more first series chains of transistors comprises an amount of transistors equal to the largest stack number.
3. The method of claim 2 wherein, in response to determining that the modified standard cell does not meet at least one of the one or more design requirements, the method further comprises:
decrementing the largest stack number, resulting in a decremented stack number;
determining one or more third series chains of transistors having the decremented stack number of transistors of the same type, wherein the one or more third series chains of transistors comprise the one or more first series chains of transistors and at least one of the one or more second series chains of transistors;
creating a different modified standard cell by increasing the gate length of one or more of fourth series chains of transistors, wherein each of the one or more fourth series chains of transistors has a lesser number of transistors than any one of the one or more third series chains of transistors; and
adding the different modified standard cell to the standard cell library in response to determining that the different modified standard cell meets the one or more design requirements.
4. The method of claim 3 wherein at least one of the one or more design requirements that the modified standard cell does not meet is selected from the group consisting of an area design requirement, a timing requirement and a leakage requirement.
5. The method of claim 1 wherein:
a leakage current of the modified standard cell is less than a leakage current of the standard cell; and
a footprint area of the modified standard cell is a same size as a footprint area of the standard cell.
6. The method of claim 1 wherein:
a leakage current of the modified standard cell is less than a leakage current of the standard cell and more than a leakage current of a low leakage standard cell, wherein the low leakage standard cell comprises a plurality of upsized transistors cells each having an increased gate length; and
a footprint area of the modified standard cell is larger than a footprint area of the standard cell and less than a footprint area of the low leakage standard cell.
7. The method of claim 1 wherein:
a leakage current of the modified standard cell is less than a leakage current of the standard cell and more than a leakage current of a low leakage standard cell, wherein the low leakage standard cell comprises a plurality of upsized transistors cells each having an increased gate length; and
a footprint area of the modified standard cell is a same size as a footprint area of the low leakage standard cell; and
one or more timing specifications of the modified standard cell are faster than one or more corresponding timing specifications of the low leakage standard cell.
8. A system comprising:
one or more processors;
a memory accessible by the one or more processors;
one or more subsystems utilizing at least one of the one or more processors and configured to:
select one or more first series chains of transistors of a same type, wherein each of the one or more first series chains of transistors comprises a greater number of transistors than any of one or more second series chains of transistors, wherein the one or more first series chains of transistors and the one or more second series chains of transistors are included in a standard cell;
create a modified standard cell from the standard cell by increasing a gate length of one or more of the second series chains of transistors;
add the modified standard cell to a standard cell library in response to determining that the modified standard cell meets one or more design requirements;
create an integrated circuit design utilizing at least one instance of the modified standard cell stored in the standard cell library; and
generate mask layer data based upon the integrated circuit design, wherein the mask layer data is configured to generate a plurality of masks for construction of an integrated circuit corresponding to the integrated circuit design; and
form a plurality of masks for construction of an integrated circuit corresponding to the integrated circuit design.
9. The system of claim 8 wherein the one or more subsystems are further configured to:
determine a largest stack number of the standard cell, wherein the largest stack number is a largest amount of transistors of the same type that are connected in series in the standard cell; and
perform the selecting of the one or more first series chains of transistors based upon the largest stack number, wherein each of the one or more first series chains of transistors comprises an amount of transistors equal to the largest stack number.
10. The system of claim 9 wherein, in response to determining that the modified standard cell does not meet at least one of the one or more design requirements, the one or more subsystems are further configured to:
decrement the largest stack number, resulting in a decremented stack number;
determine one or more third series chains of transistors having the decremented stack number of transistors of the same type, wherein the one or more third series chains of transistors comprise the one or more first series chains of transistors and at least one of the one or more second series chains of transistors;
create a different modified standard cell by increasing the gate length of one or more of fourth series chains of transistors, wherein each of the one or more fourth series chains of transistors has a lesser number of transistors than any one of the one or more third series chains of transistors; and
add the different modified standard cell to the standard cell library in response to determining that the different modified standard cell meets the one or more design requirements.