Detection of Transistor Stuck-Open Faults in Asynchronous Inputs of Scan Cells

In many designs asynchronous inputs are used to set and/or reset flip-flops. Considering a scan cell implementation used in an industrial design we show that stuck-open faults in some transistors driven by asynchronous inputs require two new flush tests. Such faults, if left undetected, cause functional failures. The two new tests increase the overall stuck-open fault coverage of each scan cell by approximately 5%. This will significantly improve the overall test quality due to the large number of scan cells contained in large industrial designs.