Efficient march test for 3-coupling faults in random access memories P. Cas ¸caval a, * , S. Bennett b,1 a Department of Computer Science, “Gh. Asachi” Technical University of Iasi, Bd. D. Mangeron, nr.53A, 6600 Iasi, Romania b Department of Automatic Control and Systems Engineering, The University of Sheffield, Mappin Street, Sheffield S13JD, UK Received 11 January 2000; revised 1 November 2000; accepted 13 November 2000 Abstract A new efficient march test algorithm for detecting the 3-coupling faults in Random Access Memories (RAM) is given in this paper. To reduce the length of the test algorithm only the 3-coupling faults between physically adjacent memory cells have been considered. The proposed test algorithm needs 38N operations. We have proved, using an Eulerian graph model, that the algorithm detects all non-interacting coupling faults. This paper also comprises a study about the ability of the algorithm to cover the interacting coupling faults. Simulation results with regard to the coupling fault coverage of the march tests, obtained based on a fault injection mechanism, are also presented in this paper.  2001 Elsevier Science B.V. All rights reserved. Keywords: Memory testing; Functional faults; Coupling faults; March test; Fault injection 1. Introduction Rapid developments in semiconductor technology have resulted in continuing growth of larger and denser random access memories (RAM) on a single chip. More time is required to test memories because of their increasing size. On the other hand, because of the increased cell density the nature of the failure mode becomes more complex and subtle. Therefore it is necessary to identify more efficient tests with the ability to detect more complex and subtle faults into the O(N) class of complexity [4]. Test procedures are constrained by two conflicting requirements: (a) to detect a wide variety of complex faults; (b) to reduce the number of memory operations in order to allow the testing of large memory size to be carried out in an acceptable period of time. Very efficient test algorithms for detecting stuck-at faults and 2-coupling faults have been proposed, see for example Refs. [1–4]. All of these are march algorithms with a reduced number of operations. For 3-coupling faults, a memory test that requires N + 36Nlog 2 N operations is given by Nair, Thatte and Abraham [1] (NTA(B) in this article). Papachristou and Sahgal [2] proposed a new algorithm with the same ability to detect 3-coupling faults but with only 37N + 24Nlog 2 N operations (PS(B) in this article). Unfortunately, for the memory chips currently available, these tests take a long time to perform. For example, assuming a cycle time of 100 ns, PS(B) takes about 4 min to test a 4 Mb memory chip and 1 h 14 min to test a 64-Mb memory chip. Of course, this time is not accep- table in many cases, such as the on-line testing. Both memory tests, NTA(B) and PS(B), are lengthy because the authors have assumed that the three coupled cells can be anywhere in the memory. In this paper we propose a new march test for 3-coupling faults with an acceptable compromise between the fault detection ability and the length of the test. We have limited ourselves to the 3-coupling faults that affect only the physi- cally adjacent memory cells. In this hypothesis, and for the cases in which the structure of memory is known (the number of columns), we have devised a test algorithm with 38N operations, which detects all restricted 3-coupling faults. 2. Memory fault model This paper focuses only on the functional faults in RAM and because the address decoders, sense amplifiers and write drivers are easier to test, we consider that these modules are fault free. Consequently, we have concentrated only on the Microprocessors and Microsystems 24 (2001) 501–509 0141-9331/00/$ - see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0141-9331(00)00103-4 www.elsevier.nl/locate/micpro * Corresponding author. Tel.: +40-32-232430; fax: +40-32-214290. E-mail addresses: cascaval@cs.tuiasi.ro (P. Cas ¸caval), s.bennett@sheffield.ac.uk (S. Bennett). 1 Tel.: +44-0-114-222-5230; fax: +44-0-114-273-1729.