Disturb testing
The purpose of the Disturb test is to pulse stress a device in an array test structure, then make a
measurement, such as V
T
, on a device adjacent to the pulsed device.
The goal is to measure the amount of V
T
shift in adjacent cells, either in the programmed or erased
states, when a nearby device is pulsed with either a program, erase, or program and erase waveform.
The typical measurement is a V
T
extraction based on a Vg-Id sweep, but you can configure any type
of dc test. This test is similar to the endurance test, except that the pulsing and measuring are
performed on adjacent devices.
The solid-line blue circle indicates the cell to be pulse stressed, and the dotted-line red circles are the
adjacent memory cells that will be disturbed by the stressing. This is the stress / measure process:
• Initial test conditions: SMU4 outputs a dc voltage to turn on the control devices for the array.
This connects instrumentation at the top of array to the flash memory cells. SMU2 and SMU3 are
set to output 0 V. This ensures that only the Cell 2 is turned on during pulse stressing.
• Pulse stressing: The output relay for SMU1 is opened, and the gate and drain of Cell 2 are
pulse stressed by Pulse Card 1 (ch 1) and Pulse Card 2 (ch 1).
• Disturbed cell testing: The outputs for the pulse cards are turned off and their output relays are
opened. SMU1 and SMU2 are then used to perform a dc Vg-Vd sweep on Cell 1 to determine V
T
.
Connections for disturb testing
The following figure shows the connections used for disturb testing. A switch matrix is recommended
for testing array test structures for both endurance or disturb. However, you can do a limited test of an
array structure without using a switch matrix.
The following figure also shows connection to an array test structure, where one of the four
SMU+pulse card channels was split. This provides a total of five test signals to provide the minimum
necessary channels for the select pins (Bit Line Select, Bit Lines 1 and 2), to the pulse DUT (circled in
blue), and the measure DUTs (circled in dashed purple). This configuration allows for pulsing one
DUT while performing disturb measurements on the three DUTs labeled Measure.
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