IDDQ testing of CMOS opens: an experimental study

IDDQ testing is known to be very effective in detecting shorts in CMOS circuits. It has also been reported that open defects that lead to “floating” transistor gates can also be detected if the gate acquires a sufficient voltage to leak measurable current. Recent experiments evaluating a new on-chip IDDQ sensor indicated the possibility of additional detection mechanisms for other types of open failures, including open source and drain connections. To investigate this in more detail, we designed and fabricated two test chips in CMOS technology containing the 74181 ALU circuit. Our test chips include the capability of replacing, one at a time, individual cells in the 74181 circuits with back up cells that each contain a single open defect. In this way in addition to the fault free circuits, a total of 59 faulty circuits can be configured, each containing a different open defect. It was found that IDDQ testing with random vectors detected 48 of the 59 open defects. Analysis of the experimental data reveals new mechanisms that explain the detection of floating gate and open source and drain failures