Compact testing of RAM: Schemes, tools and results

Pseudo-ring or pi-testing is a technique of compact testing random access memory (RAM) as well as embedded memory. Pi-testing consists in performing one or more iterations where a linear automaton is emulated by the memory itself. The result of pi-iteration, i.e. the virtual automaton state, is compared with expected one. Synthesis of pi-test algorithm is reduced to select the testing scheme - ring or scan, and setup its parameters such as structure, trajectory, seed and others. This paper presents the pi-tests for all single-cell static and dynamic faults, also for all static two-cell faults. The pi-test of static single-cell faults contains 5 iterations each of them with length equal to 3N, where N is the RAM array size. Two-cell static pi-test contains 15 iterations that also can detect a part of dynamic single-cell faults. The pi-test for dynamic single-cell faults contains 10 iterations. Repartition laws for probabilistic (random) faults were established. Knowing of laws allows to estimate apriori the number of pi-test experiments required to ensure the needed risk level of manufacturing RAM devices.