Test and Measurement
Figure 5 Figure 6
rise/fall times than the PG mode, but it can measure both the cables between the WGFMU module and the RSU in a
current and voltage. bundle and by creating a current return path near the DUT by
connecting the MOSFET substrate and source pads to the
Practical measurement considerations shield of the signal lines going to the gate and drain.
To perform accurate RTS measurements, a variety of factors
including measurement equipment performance, Sampling Rate
characteristics of the DUT and environmental noise have to be The measurement current noise can be reduced by
taken into account. In the following sections, we will explain measurement averaging. Figure 7 shows an example of how
how to mitigate these factors. averaging can reduce this noise.Increasing the averaging time
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further reduces the noise of the measured current. However, if
Measurement Equipment and the sampling rate is longer than the time constant of electron
www
Environmental Noise capture or emission, then the RTS noise will not be observed
.eur If the RTS noise being measured is below the current on the measured current. Using a lower current measurement
oasiasemiconductor
measurement noise floor, then the RTS noise cannot be range also reduces the measurement current noise floor. In
observed. Figure 6 shows the noise floor for the current this case, the bandwidth of the current measurement circuit
measurement ranges of the B1500A’s WGFMU module. Note: determines the upper limit of the frequency components of
This is supplemental data and it is not a guaranteed the RTS noise.
specification of the module. In addition, other environmental
factors such as vibration and electromagnetic interference can Current Measurement Bandwidth
.com
impact RTS noise measurement. To eliminate vibration related Table 1 is supplemental information showing the bandwidth
noise, a semiautomatic wafer prober with proper vibration (defined by the -3 dB point) of the B1500A’s WGFMU
isolation should be used. To eliminate electromagnetic module’s current measurement circuit (with a 25 pF load).
square4
Issue III 2009
interference, the current measurement loop should be kept as (Note: Actual bandwidth may be further degraded due to
small as possible. The current loop can be minimized by tying additional capacitive load from cabling and the device)
Since the bandwidth of the lower current ranges is lower
than that of the higher current ranges, when choosing a
current measurement range make sure that you have sufficient
bandwidth to detect the RTS noise that you are trying to
measure. In addition to the measurement equipment, the
characteristics of the DUT also need to be considered.
Measurement Conditions
Since the boundary traps that are capturing electrons and
generating the RTS noise have spatial and energy
distributions, the time constants and (in-turn) the level of RTS
noise strongly depend on the bias voltages applied to the
MOSFET gate and drain. Figure 8 shows examples of the RTS
noise with different applied gate voltages.
The above example is an NMOS FET with dimensions of
Figure 7 0.44 µm (W) by 0.24 µm (L) and an oxide thickness of 4nm.
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