Ferroelectric FETs Based Nonvolatile Logic in Memory Circuits
Among the beyond complementary metal oxide semiconductor (CMOS) devices being explored, ferroelectric field effect transistors (FeFETs) are considered as one of the most promising. FeFETs are being studied by all major semiconductor manufacturers, and experimentally, FeFETs are making rapid progress. FeFETs also stand out with the unique hysteretic <inline formula> <tex math notation="LaTeX"$I_{\text {ds} /tex math>/inline formula> <inline formula> <tex math notation="LaTeX"$V_{\text {gs} /tex math>/inline formula> characteristic that allows a device to function as both a switch and a nonvolatile (NV) storage element. We exploit this FeFET property to build two categories of fine grained logic in memory (LiM) circuits: 1) ternary content addressable memory (TCAM) which integrates efficient and compact logic/processing elements into various levels of memory hierarchy; 2) basic logic function units for constructing larger and more complex LiM circuits. Two writing schemes (with and without negative supply voltages respectively) for FeFETs are introduced in our LiM designs. The resulting designs are compared with existing LiM approaches based on CMOS, magnetic tunnel junctions (MTJs) resistive random access memories (ReRAMs) ferrorelectric tunnel junctions (FTJs) etc. that afford the same circuit level functionality. Simulation results show that FeFET based NV TCAMs offer lower area overhead than MTJ (79% and CMOS (42% less) equivalents, as well as better search energy delay products (EDPs) than TCAM designs based on MTJ <inline formula> <tex math notation="LaTeX"$149\times /tex math>/inline formula> ReRAM <inline formula> <tex math notation="LaTeX"$1.7\times /tex math>/inline formula> and CMOS <inline formula> <tex math notation="LaTeX"$1.3\times /tex math>/inline formula> in array evaluations. NV FeFET based LiM basic circuit blocks are also more efficient than functional equivalents based on MTJs in terms of propagation delay <inline formula> <tex math notation="LaTeX"$4.2\times /tex math>/inline formula> and dynamic power <inline formula> <tex math notation="LaTeX"$2.5\times /tex math>/inline formula> A case study for an FeFET based LiM accumulator further demonstrates that by employing FeFET as both a switch and an NV storage element, the FeFET based accumulator can save area (36% and power consumption (40% when compared with a conventional CMOS accumulator with the same structure.
IEEE Transactions on Very Large Scale Integration (VLSI) Systems