2.1.3 Current Density

The antifuse substrate metallization has a nominal cross-section area of 30 um² (15 um x 2 um). At the antifuse contact, the metal cross section narrows to 4 um2 (2 um x 2 um). Table 2 provides the maximum current density experienced by the metallization.

Table 2: Current Density

Iantifuse	Metal Line A/cm2	Antifuse-Metal Interface A/cm2
90	3.00E+05	2.25E+06
240	8.00E+05	6.00E+06
300	1.00E+06	7.50E+06
100	3.33E+05	2.50E+06
120	4.00E+05	3.00E+06
290	9.67E+05	7.25E+06
80	2.67E+05	2.00E+06
70	2.33E+05	1.75E+06
75	2.50E+05	1.88E+06

Figure 5 below details the current waveforms applied. The active low output enables of the ACT540 are toggled at the shown pulse widths. The 540 have active low outputs and the inputs are tied to Vcc.

Figure 5: Current Stress Waveforms

In addition to the circuits driven by the ACT540s. Each substrate has two metallization lines running across the length and width of the substrates. The North/South line had zero programmed antifuses; the East/West line had 1 programmed antifuse. The original purpose was to use the known temperature coefficient of resistance of the aluminum metallization to monitor substrate temperature. This did not prove useful, however, each of the strings was biased with 1 mA constant current source and the voltage across the line was monitored and recorded over 1400 hours at 25 C, 85 C and 125 C.

Figures 6a and b are the original current traces taken at the time the devices were setup for the 25 C devices. One interesting observation was the initial difference between the units. S/N 4 appears to be out-of-family from the other 5 units. The reason for this is not known.

Figure 6a: Baseline s/n 1 +25 C Current Waveforms, 10/6/95




Figure 6b: Baseline s/n 4 +25 C Current Waveforms, 10/6/95