Texas Instruments Corporation

Other

Carl Z Zhou

John Anthony Rodriguez

Richard Allen Bailey

Keith A Remack

Fazela M Vohra

Disclosed embodiments include a testing system that electrically connects to an integrated circuit (IC) having ferroelectric memory (FRAM) cells. The testing system programs the FRAM cells to a first data state and then iteratively reads the programmed cells at a plurality of reference voltages to identify a reference voltage limit that indicates a first occurrence at which at least one of the cells fails to return the first data state when read. Iteratively reading the cells includes reading each cell at an initial reference voltage at which all the cells return the first data state, and then reading each of the programmed cells at each of the remaining reference voltages by incrementally changing the initial reference voltage in one direction until the reference voltage limit is identified. The testing system sets the reference in the IC at an operating level based on the reference voltage limit.

Setting of reference voltage for data sensing in ferroelectric memories

A data retention reliability screen of integrated circuits including ferroelectric random access memory (FRAM) arrays. Sampled groups of cells in the FRAM array are tested at various reference voltage levels, after programming to a high polarization capacitance data state and a relaxation time at an elevated temperature. Fail bit counts of the sample groups at the various reference voltage levels are used to derive a test reference voltage, against which all of the FRAM cells in the integrated circuit are then tested after preconditioning (i.e., programming) and another relaxation interval at the elevated temperature, to determine those cells in the integrated circuit that are vulnerable to long-term data retention failure.

Screening for data retention loss in ferroelectric memories

A method of setting the reference voltage for sensing data states in integrated circuits including ferroelectric random access memory (FRAM) cells of the one-transistor-one capacitor (1T-1C) type. In an electrical test operation, some or all of the FRAM cells are programmed to a particular polarization state. A 'shmoo' of the reference voltage for sensing the data state is performed, at one or more worst case electrical or environmental conditions for that data state, to determine a reference voltage limit at which the weakest cell fails to return the correct data when read. A configuration register is then written with a reference voltage based on this reference voltage limit, for example at the limit plus/minus a tolerance.

A reliability screen of integrated circuits including ferroelectric random access memory (FRAM) arrays for stuck bits. The FRAM devices are subjected to a high temperature bake in wafer form. A 'shmoo' of the reference voltage is performed, at an elevated temperature, for each device to identify a first reference voltage at which a first cell in the device fails a read of its low polarization capacitance data state, and a second reference voltage at which a selected number of cells in the device fail the read. The slope of the line between the first and second reference voltages, in the cumulative fail bit count versus reference voltage plane, is compared with a slope limit to determine whether any stuck bits are present in the device.

Screening for later life stuck bits in ferroelectric memories

A method for testing VLSI circuits comprises a two-pass diagnostic method for testing a circuit wherein a first pass comprises a conventional test flow wherein an ATPG tool generates a set of test patterns and identifies possible faulty nets within the circuit. A second pass focuses on a designated critical subset of the circuit extracted using a method for extracting a subset for failure diagnosis of the tested circuit. A second pass utilizes an extraction algorithm which extracts one or more critical subsets of the circuit in order to obtain more accurate failure diagnosis.

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Carl Z Zhou