The 3D stacked hybrid memory relies on a hysteretic Nano-Electro-Mechanical Field Effect Transistor (NEMFET) inverter to store data, and on adjacent CMOS based logic to allow for read/write operations, and data preservation. In this paper we assess the feasibility of a hybrid memory cell, and explore the design space of 3D stacked hybrid dual-port memory arrays which combine the appealing NEMFET properties, i.e., ultra-low leakage currents and abrupt switching, with the CMOS technology versatility. In the evaluation we performed a comparison in terms of footprint, access time, and energy, against state of the art CMOS dual-ports memories, considering small and large size memory arrays (8-Kbytes up to 128-Kbytes) implemented in various technology nodes. The 3D NEMFETCMOS hybrid dual-port memory is on the average 25% smaller and 8% and 95% larger in terms of footprint when compared to 90nm, 65nm and 45nm CMOS implementations, respectively. The write access time is approximately 2 higher, as it is dominated by the mechanical movement of the NEMFET’s suspended gate, while the read access time is about 12% lower, when compared with 45nm CMOS counterparts. For small size memories our proposal results in at least 15% and 23% energy reductions for 100% and 50% data transition probability, respectively. For large size memories an energy reduction of about 40% was obtained, as in this case the static energy is predominant.@en

In this paper we introduce a novel error resilient memory architecture potentially applicable to a large range of memory technologies. In contrast with state of the art memory error correction schemes, which rely on (extended Hamming) Error Correcting Codes (ECC), we make use of Low Density Parity Check (LDPC) codes due to their close to the Shannon performance limit error correction capabilities. To allow for a cost-effective implementation we build our approach on top of a 3D memory organization which inherently fast and customizable wide-I/O vertical access allows for a smooth transfer of the required LDPC long code-words to/from an error correction dedicated die. To make the error correction process transparent to the memory users, e.g., processing cores, we propose an online memory scrubbing policy that performs the LDPC-based error detection and correction decoupled from the normal memory operation. For evaluation purposes we consider 3D memories protected by the proposed LDPC mechanism with various data width codes implementations. Simulation results indicate that our proposal clearly outperforms state of the art ECC schemes with fault tolerance improvements by a 4710× factor being obtained when compared to extended Hamming ECC. Furthermore, we evaluate instances of the proposed memory concept equipped with different LDPC codecs implemented on a commercial 40nm low-power CMOS technology and evaluate them on actual memory traces in terms of error correction capability, area, latency, and energy. Our results indicate that the LDPC protected memories offer substantially improved error correction capabilities, when compared to state of the art extended Hamming ECC, being able to assure clean runs for memory error rates α <; 3 × 10-2, which demonstrate that our proposal can potentially successfully protect system on a chip memory systems even in very harsh environmental conditions.@en

In this paper we propose a novel error correction scheme/architecture specially tailored for polyhedral memories which: (i) allows for the formation of long codewords without interfering with the memory architecture/addressing mode/data granularity and (ii) make use of codecs located on a dedicated tier of the 3D memory stack. For a transparent error correction process we propose an online memory scrubbing policy that performs the error detection and correction decoupled from the normal memory operation. To evaluate our proposal we consider as a case study a 4-die 4-MB polyhedral memory and simulate various data width codes implementations. The simulations indicate that our proposal outperforms state of the art single error correction schemes in terms of error correction capability, being able to diminish the Word Error Rates (WER) by many orders of magnitude, e.g., WER from 10^-10 to 10^-21 are achieved for bit error probabilities between 10^-4 and 10^-6, while requiring less redundancy overhead. The scrubbing mechanism hides the codec latency and provides up to 10% and 25% write and read latency reductions, respectively. In addition, by relocating the encoders/decoders from the memory dies to a dedicated one a 13% footprint reduction is obtained and parallel energy effective scrubbing can be enabled, which results in further WER reductions.

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Through-Silicon Vias (TSV) based 3D Stacked IC (3D-SIC) technology introduces new design opportunities for wide operand width addition units. Different from state of the art direct folding proposals we introduce two cost-effective 3D Stacked Hybrid Adders with identical tier structure, which potentially makes the manufacturing of hardware wide-operand fast adders a reality. An N-bit
adder implemented on a K identical tier stacked IC performs in parallel two N=K-bit additions on each tier according to the anticipated computation principle. Inter-tier carry signals performing the appropriate sum selection are propagated by TSVs. The practical implications of direct folding and of our hybrid carry-select/prefix approaches are evaluated by a thorough case study on 65nm CMOS 3D adder implementations, for operand sizes up to 4096 bits and 16 tiers. Our simulations indicate that in almost all configurations at least one of the two proposed 3D stacked hybrid approaches is faster than the fastest 3D folding approach. When considering an appropriate metric for 3D designs, i.e., the delay-footprint-heterogeneity product, the hybrid adders substantially outperform the folding counterparts by a factor in-between 1:67 and 23:95.@en