Strong, thorough, and efficient memory protection against existing and emerging DRAM errors

Memory protection is necessary to ensure the correctness of data in the presence of unavoidable faults. As such, large-scale systems typically employ Error Correcting Codes (ECC) to trade off redundant storage and bandwidth for increased reliability. Single Device Data Correction (SDDC) ECC mechanisms are required to meet the reliability demands of servers and large-scale systems by tolerating even severe faults that disable an entire memory chip. In the future, however, stronger memory protection will be required due to increasing levels of system integration, shrinking process technology, and growing transfer rates. The energy-efficiency of memory protection is also important as DRAM already consumes a significant fraction of system energy budget. This dissertation develops a novel set of ECC schemes to provide strong, safe, flexible, and thorough protection against existing and emerging types of DRAM errors. This research also reduces energy consumption of such protection while only marginally impacting performance. First, this dissertation develops Bamboo ECC, a technique with strongerthan-SDDC correction and very safe detection capabilities (≥ 99.999994% of data errors with any severity are detected). Bamboo ECC changes ECC layout based on frequent DRAM error patterns, and can correct concurrent errors from multiple devices and all but eliminates the risk of silent data corruption. Also, Bamboo ECC provides flexible configurations to enable more adaptive graceful downgrade schemes in which the system continues to operate correctly after even severe chip faults, albeit at a reduced capacity to protect against future faults. These strength, safety, and flexibility advantages translate to a significantly more reliable memory sub-system for future exascale computing. Then, this dissertation focuses on emerging error types from scaling process technology and increasing data bandwidth. As DRAM process technology scales down to below 10nm, DRAM cells are becoming more vulnerable to errors from an imperfect manufacturing process. At the same time, DRAM signal transfers are getting more susceptible to timing and electrical noises as DRAM interfaces keep increasing signal transfer rates and decreasing I/O voltage levels. With individual DRAM chips getting more vulnerable to errors, industry and academia have proposed mechanisms to tolerate these emerging types of errors; yet they are inefficient because they rely on multiple levels of redundancy in the case of cell errors and ad-hoc schemes with suboptimal protection coverage for transmission errors. Active Guardband ECC and All-Inclusive ECC make systematic use of ECC and existing mechanisms to provide thorough end-to-end protection without requiring redundancy beyond what is common today. Finally, this dissertation targets the energy efficiency of memory protection. Frugal ECC combines ECC with fine-grained compression to provide versatile and energy-efficient protection. Frugal ECC compresses main memory at cache-block granularity, using any left over space to store ECC information. Frugal ECC allows more energy-efficient memory configurations while maintaining SDDC protection. Its tailored compression scheme minimizes insufficiently compressed blocks and results in acceptable performance overhead. The strong, thorough, and efficient protection described by this dissertation may allow for more aggressive design of future computing systems with larger integration, finer process technology, higher transfer rates, and better energy efficiencyElectrical and Computer Engineerin

Effects of pentacene-doped PEDOT:PSS as a hole-conducting layer on the performance characteristics of polymer photovoltaic cells

We have investigated the effect of pentacene-doped poly(3,4-ethylenedioxythiophene:poly(4-styrenesulfonate) [PEDOT:PSS] films as a hole-conducting layer on the performance of polymer photovoltaic cells. By increasing the amount of pentacene and the annealing temperature of pentacene-doped PEDOT:PSS layer, the changes of performance characteristics were evaluated. Pentacene-doped PEDOT:PSS thin films were prepared by dissolving pentacene in 1-methyl-2-pyrrolidinone solvent and mixing with PEDOT:PSS. As the amount of pentacene in the PEDOT:PSS solution was increased, UV-visible transmittance also increased dramatically. By increasing the amount of pentacene in PEDOT:PSS films, dramatic decreases in both the work function and surface resistance were observed. However, the work function and surface resistance began to sharply increase above the doping amount of pentacene at 7.7 and 9.9 mg, respectively. As the annealing temperature was increased, the surface roughness of pentacene-doped PEDOT:PSS films also increased, leading to the formation of PEDOT:PSS aggregates. The films of pentacene-doped PEDOT:PSS were characterized by AFM, SEM, UV-visible transmittance, surface analyzer, surface resistance, and photovoltaic response analysis

Bamboo ECC: Strong, safe, and flexible codes for reliable computer memory

Growing computer system sizes and levels of integration have made memory reliability a primary concern, necessitating strong memory error protection. As such, large-scale systems typically employ error checking and correcting codes to trade redundant storage and band-width for increased reliability. While stronger memory protection will be needed to meet reliability targets in the future, it is undesirable to further increase the amount of storage and bandwidth spent on redundancy. We propose a novel family of single-tier ECC mecha-nisms called Bamboo ECC to simultaneously address the conflicting requirements of increasing reliability while maintaining or decreasing error protection overheads. Relative to the state-of-the-art single-tier error protection, Bamboo ECC codes have superior correction capabilities, all but elim-inate the risk of silent data corruption, and can also increase redun-dancy at a fine granularity, enabling more adaptive graceful down-grade schemes. These strength, safety, and flexibility advantages translate to a significantly more reliable memory system. To demon-strate this, we evaluate a family of Bamboo ECC organizations in the context of conventional 72b and 144b DRAM channels and show the significant error coverage and memory lifespan improvements of Bamboo ECC relative to existing SEC-DED, chipkill-correct and double-chipkill-correct schemes. 1

CLEAN-ECC: High Reliability ECC for Adaptive Granularity Memory System

Adaptive-granularity memory architectures have been considered mainly because of main memory bottleneck and power efficiency. Meanwhile, highly reliable protection schemes are getting popular especially in large computing systems. Unfortunately, conventional ECC mechanisms including Chipkill require a large number of symbols to guarantee strong protection with acceptable overhead. We propose a novel memory protection scheme called CLEAN (Chipkill-LEvel reliable and Access granularity Negotiable), which enables us to balance the contradicting demands of fine-grained (FG) access and strong & efficient ECC. To close a potentially significant detection coverage gap due to CLEAN's detection mechanism coupled with permanent faults, we design a simple mechanism access granularity enforcement. By enforcing coarse-grained (CG) access, we can get only the advantage of higher protection comparable to Chipkill instead of achieving the adaptive access granularity together. CLEAN showed Chipkill level reliability as well as improvement in performance, system and memory power efficiency by up to 11.8%, 10.8% and 64.9% with mixes of SPEC2006 benchmarks.1

Ground Bridge Effect on Reduction of Conducted Emission from Three-Phase Motor Drive System

In electric vehicles, the pulse width modulation scheme is widely used in three-phase motor drive systems for its high performance. However, the fast switching of semiconductor devices may induce excessively high dv/dt and di/dt, which can cause electromagnetic interference (EMI) issues, making it difficult to satisfy electromagnetic compatibility standards. In this paper, the current conducted emission test for a three-phase motor drive system is performed based on CISPR 25 component-level testing setup for AM radio frequency band, which is from 530 kHz to 1.8 MHz. Under these conditions, common-mode (CM) noise generation mechanisms of the motor drive system are identified through measurements. It is found that the dominant mechanism is the mode conversion from differential mode (DM) switching current of the three-phase PWM inverter to CM current through the cable harness due to the imbalances in the PCB structure and EMI filter network which are at the dc input side of the three-phase inverter. Based on this finding, ground (GND) bridges are added between the digital signal and power GND nets to reduce the CM noise. The GND bridge effect on the reduction of CM noise in AM band is experimentally verified and further studied using circuit simulations

Tooth caries classification with quantitative light-induced fluorescence (QLF) images using convolutional neural network for permanent teeth in vivo

Abstract Background Owing to the remarkable advancements of artificial intelligence (AI) applications, AI-based detection of dental caries is continuously improving. We evaluated the efficacy of the detection of dental caries with quantitative light-induced fluorescence (QLF) images using a convolutional neural network (CNN) model. Methods Overall, 2814 QLF intraoral images were obtained from 606 participants at a dental clinic using Qraypen C® (QC, AIOBIO, Seoul, Republic of Korea) from October 2020 to October 2022. These images included all the types of permanent teeth of which surfaces were smooth or occlusal. Dataset were randomly assigned to the training (56.0%), validation (14.0%), and test (30.0%) subsets of the dataset for caries classification. Moreover, masked images for teeth area were manually prepared to evaluate the segmentation efficacy. To compare diagnostic performance for caries classification according to the types of teeth, the dataset was further classified into the premolar (1,143 images) and molar (1,441 images) groups. As the CNN model, Xception was applied. Results Using the original QLF images, the performance of the classification algorithm was relatively good showing 83.2% of accuracy, 85.6% of precision, and 86.9% of sensitivity. After applying the segmentation process for the tooth area, all the performance indics including 85.6% of accuracy, 88.9% of precision, and 86.9% of sensitivity were improved. However, the performance indices of each type of teeth (both premolar and molar) were similar to those for all teeth. Conclusion The application of AI to QLF images for caries classification demonstrated a good performance regardless of teeth type among posterior teeth. Additionally, tooth area segmentation through background elimination from QLF images exhibited a better performance

Reduction of Mode Conversion of Differential-Mode Noise to Common-Mode Noise by Printed Circuit Board Modification for Unbalanced EMI Filter Network

This paper presents a method for the reduction of mode conversion from differential-mode (DM) noise to common-mode (CM) noise in an unbalanced EMI filter. The unbalanced nature in the EMI filter is a result of not incorporating all the required filter components due to space and cost constraints or due to the parasitic impedances of a printed circuit board (PCB). It is demonstrated that the reduction of mode conversion from DM noise to CM noise can be achieved by modifying the current path on the ground (GND) layer of the PCB of the unbalanced EMI filter. The currents on the GND layer are guided to take a longer route by introducing a cutout to the ground plane in the PCB, which increases the impedance of the current path on the GND layer. This approach does not require additional components to the EMI filter for the reduction of CM noise due to the mode conversion. Simulations show that the cutout decreases the CM noise converted from the DM noise by at least 4 dB in the AM radio frequency band (530 kHz - 1.8 MHz)