Integrated circuit chip with improved array stability
View Patent ↗A multi-threshold integrated circuit (IC) that may be supplied by multiple supplies, with an array of latches such as an array static random access memory (SRAM) cells and a CMOS SRAM with improved stability and reduced subthreshold leakage. Selected devices (NFETs and/or PFETs) in array cells and support logic, e.g., in the data path and in non-critical logic, are tailored for lower gate and subthreshold leakage. Normal base FETs have a base threshold and tailored FETs have a threshold above. In a multi-supply chip, circuits with tailored FETs are powered by an increased supply voltage.
1. A multi-supply CMOS static random access memory (SRAM) supplied by a base supply, portions of said multi-supply SRAM being supplied by an increased supply, said increased supply supplying a voltage above said base supply, said multi-supply SRAM comprising:
an array of SRAM cells, each of said SRAM cells comprising:
a pair of tailored NFET pass gates, each connected between a storage node and one of a pair of complementary bit lines, and
a pair of cross-coupled inverters connected between an increased supply line (V dd+ ) line and a supply return line, each of said cross coupled inverters comprising:
a first tailored n-type field effect transistor (NFET) exhibiting less leakage at the base supply voltage than base NFETs having a stated base design characteristic, said first tailored NFET connected drain to source between a storage node and a return voltage, and
a PFET connected drain to source between said storage node and said V dd+ line, said storage node of the other of said pair of cross-coupled inverters connected to a control terminal of both said first tailored FET and said FET of said second conduction type;
a word line decoder selecting a row of said cells in said array;
a plurality of word line drivers connected to V dd+ and each driving a word line in a selected said row, said word line connected to a control terminal in both of said pair of tailored NFET pass gates, said word line driver selectively driving said word line substantially to V dd+ ;
a bit decoder selecting a column of said cells in said array;
at least one sense amplifier sensing data stored in a selected one of said cells;
at least one input/output (I/O) driver powered by V dd , each said I/O driver passing written data to a selected said colunm and redriving sensed said data;
local clock logic powered by Vdd and providing local timing for each cell access; and
glue logic powered by V dd and controlling accesses to said SRAM.
2. A multi-supply CMOS SRAM as in claim 1 , wherein said tailored NFETs exhibit less leakage at said V dd+ than NFETs having said stated base design characteristic at V dd .
3. A multi-supply CMOS SRAM as in claim 2 , wherein said stated base characteristic is a stated design gate dielectric thickness and said tailored NFETs have a thicker gate oxide than said stated design gate dielectric thickness.
4. A multi-supply CMOS SRAM as in claim 2 , wherein said stated base characteristic is a channel dopant characteristic and said tailored NFETs have a subthreshold leakage reduction channel implant.
5. A multi-supply CMOS SRAM as in claim 2 , wherein said stated base characteristic is gate oxide and said tailored NFETs have a high k gate dielectric material.
6. A multi-supply CMOS SRAM as in claim 2 , wherein said stated base characteristic is a stated design gate dielectric thickness and a channel dopant characteristic and said tailored NFETs have a subthreshold leakage reduction channel implant and a thicker gate oxide than a stated design gate oxide thickness.
7. A multi-supply CMOS SRAM as in claim 6 , wherein said stated base characteristic is a base threshold voltage (V T ) and said tailored NFETs have an increased threshold voltage (V T+ ) that is greater than said base V T .
8. A multi-supply CMOS SRAM as in claim 7 , wherein said V dd+ exceeds said V dd at least by the difference between the base V T and said increased V T+ , i.e., V dd+ −V dd >V T+ −V T .
9. A multi-supply CMOS SRAM as in claim 8 , wherein said CMOS SRAM is on a partially depleted (PD) silicon on insulator (SOI) chip.
10. A multi-supply CMOS SRAM as in claim 9 , wherein selected FETs in said word line decoder, said bit decoder and each said at least one sense amplifier are tailored said FETs.
11. A multi-supply CMOS SRAM as in claim 10 , wherein selected said tailored FETs are in identified non-critical paths in said local clock driver, each said at least one I/O driver and said glue logic and connected to V dd+ .
12. A multi-supply CMOS SRAM as in claim 11 , wherein logic in identified critical paths essentially consist of base devices.