19.4 embedded 1Mb ReRAM in 28nm CMOS with 0.27-to-1V read using swing-sample-and-couple sense amplifier and self-boost-write-termination scheme

Abstract

Resistive RAM (ReRAM) is a promising nonvolatile memory with low write energy, logic-process compatibility, and compact cell area. The 1T1R ReRAM [1-3] fits embedded applications requiring fast read (RD) access time (T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AC</inf> ) and low RD-V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DDMIN</inf> , particularly for devices powered by batteries or energy harvesters. The cross-point ReRAM [4-6] is meant for high capacities with high RD-V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DDMIN</inf> and slow T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AC</inf> . As devices shrink, ReRAMs have higher cell resistance (R) and greater variations in write time and R, which reduces the R-ratio (R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</inf> /R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> ) between the high-R state (HRS, R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</inf> ) and low-R state (LRS, R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> ). ReRAM also have a high R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> , which enables a larger voltage drop across ReRAM to reduce write voltage and cell-switch (CS) size. Thus, ReRAM macro designs suffer: (1) small sensing margin (SM), limited RD-V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DDMIN</inf> , and slow T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AC</inf> due to high-R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> and small R-ratio; (2) increase in energy due to large set DC-current (I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC-SET</inf> ) resulting from wide set-time (T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SET</inf> ) distribution. This study develops a swing-sample-and-couple (SSC) voltage-mode sense amplifier (VSA) to overcome (1), enabling 1.8× greater SM for lower RD-V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DDMIN</inf> and 1.7× faster T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AC</inf> across various V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DD</inf> , compared to conventional differential-input (CD) VSAs. To reduce >99% set energy, we use a 4T self-boost-write-termination (SBWT) scheme to cut off I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC-SET</inf> of faster-T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SET</inf> devices, with an area penalty below 0.5%. A fabricated 28nm 1Mb ReRAM macro achieves T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AC</inf> = 404ns at V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DD</inf> = 0.27V and confirms the I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC-SET</inf> cut-off by SBWT.