characterization, modeling, and design of esd protection circuits

18 Chapter 2. ESD Circuit Characterization and Design Issues
into a device. In this case, however, the 200pF capacitor is tied directly to the device under
test, which means the 1500Ω resistor is replaced by a parasitic resistance of a few ohms
and a series inductance of about 1µH. The resulting current waveform is oscillatory in
nature (Fig. 2.3), with a rise time on the order of a few nanoseconds. This model simulates
the discharge from a tool or machine such as a handler or marker. Unlike the HBM, there
is no established standard for the MM. This is most likely because the very low series
resistance implies that the dynamic impedance of the device under test and the values of
the parasitic capacitance and inductance have a large effect on the MM waveform, making
test reproducibility difficult [18]. Fig. 2.3 illustrates the drastic change in rise time and
peak current of the waveform when the series inductance is changed from 0.5µH to
2.5µH.
In the integrated-circuit industry, the human-body model test is often the sole means of
qualifying EOS/ESD reliability because it is simple to conduct and has been accepted
current / A
8.0
0.0
-8.0
L s =0.5µH L s =2.5µH
0 100 200
time / ns
Fig. 2.3 SPICE-generated short-circuit MM output current waveforms
for V c =400V, C c =200pF, R c =5Ω, C s =1pF, and C t =10pF.