Editor’s note: This is part one of an ongoing series on testing
memory. Engineers have traditionally characterized floating-gate
NAND flash memory using DC instruments such as source-
measurement units (SMUs) after pulse generators had programmed
and/or erased the memory cell. This approach requires some type
of switch to apply the DC or pulse signal alternately to the
device under test (DUT). Occasionally, oscilloscopes were used
to verify pulse fidelity (pulse width, overshoot, pulse voltage
level, rise time, fall time) at the DUT. Measuring the pulse is
important because the flash memory state is quite sensitive to
the pulse voltage level. The use of oscilloscopes was relatively
rare, even in research, however, because the required setup for
oscilloscope measurements differed from that for the pulse-
source/DC-measure approach. Even when scopes were used for flash
characterization, the complexity of measuring the transient
current meant that voltage was the only measurement taken while
pulsing. The transitio