Integrated Progressive Built-In Self-Repair (IPBISR) Techniques for NAND Flash Memory

Built-in self-repair (BISR) techniques and error correction codes (ECC) are widely used for repairing permanent faults and transient faults of flash memory, respectively. The main drawbacks of these techniques include the large granularity of spare usage and the uniform ECC protection capabilities. To cure these dilemmas, a novel Integrated Progressive BISR (IPBISR) technique which integrates fine-grained BISR (FGBISR) and progressive ECC (PECC) technique is proposed in this paper. Repairable fault types (RFTs) are first presented such that spare replacement can be conducted at the word-, page-, column-, and NAND block levels. We also propose the Complete March-FT (March-CFT) test algorithm which can also detect the read disturb faults not covered by the conventional March-FT algorithm. Besides the conventional fault models, the passability of each flash memory cell can also be tested. Therefore, the generated syndrome of March-CFT can be used to determine the RFTs of the detected faults. Instead of merely using redundancies for repairing different RTFs, we also incorporate PECC technique in IPBISR for repairing faulty cells occurred during manufacturing and field usage. PECC can progressively enhance the protection levels when the current protection capability is exhausted. A simulator is implemented for evaluating the novelties of the proposed IPBISR technique. Experimental results show that repair rate, yield, and reliability can be enhanced greatly with negligible hardware overhead.