Due to ever increasingly need for high-performance and low-cost non-volatile memory devices, new types of non-volatile memory devices have emerged such as, magnetic random-access memory (MRAM) devices, resistive random-access memory (RRAM) devices, phase change memory (PCM) devices, and write-once memory (WOM) devices. Among those emerging non-volatile memory devices, the WOM devices (e.g., eFuse devices, anti-Fuse devices, one-time programmable devices, etc.) have gained particular interests since the WOM devices offer various advantages, for example, low manufacturing cost, etc. In addition, as the WOM device typically allows data to be written only once (i.e., the WOM device is non-reversible once written), the WOM device can be used for security purposes, e.g., to permanently store key chip information such as chip/manufacture ID, access codes and error maps.
In conventional memory devices, for example, static random-access memory (SRAM) devices or dynamic random-access memory (DRAM) devices, memory cells of the memory device are typically tested through writing a data pattern (i.e., a pattern of data bits) to the memory cells and then reading a respective written data bit from each of the memory cells. Because of such a non-reversible characteristic, the WOM device cannot be tested like conventional memory devices. Typically, the WOM device includes a plurality of dummy memory cells for test purposes. In particular, each memory cell of the WOM device uses one or more dummy memory cells as respective spares, each of which is configured to store a same data bit. As such, even though an original memory cell is malfunctioning under a test mode, the original memory cell's spare(s) can be used (e.g., to replace the original one) as so to allow a reliable operation of the WOM device, as a whole.
To assure that each memory cell of the WOM device receives a fair test (i.e., a correct test) under the above-mentioned test mode, typically, peripheral circuits (e.g., a column decoder, a row decoder, etc.) of the WOM devices are also tested. In conventional WOM devices, at least a whole row of the memory cells are written to test the column decoder, and at least a whole column of the memory cells are written to test the row decoder. Since the memory cells of the WOM device are allowed to be written only once, after being written, the memory cells become “unusable,” also known as “burned.” Burning the whole row and column of memory cells wastes “usable” memory cells in the conventional WOM device. Thus, conventional ways of testing the WOM devices are not entirely satisfactory.
USPTO Backgrounds
USPTO Backgrounds