International audience

Reliable electronics plays a major role in shaping our daily lives, being a key enabler for critical applications, such as space missions, avionics, automotive, medicine, banking, automated industry, wireless communication networks, etc. However, design of highly reliable electronic systems remains a challenge with the advances in semiconductor technology and increase in integrated circuit (IC) complexity. In this work, we introduce the Horizon Europe Twinning project TWIN-RELECT, aimed at strengthening the scientific expertise in designing reliable integrated circuits. The paper presents the general project concept and objectives, and main directions of the joint research activities. The primary scientific goal is to contribute to the development of novel, more efficient, European Electronic Design Automation (EDA) tool-chain for design of reliable chips.

Studying the radiation effects on electronic devices is essential for avionics and space systems. The shrinking technology nodes and increasing density of devices enhance the sensitivity of electronic systems to ionizing radiation. Due to their crucial role, memories and processors are the highest contributors to soft errors in systems, making them the best candidates for studying these effects. This work introduces the radiation environment in space and atmosphere and the main effects that the different types of ionizing particles that are present in these environments may produce on electronic devices. Furthermore, mainly focusing on Single-Event Effects (SEEs), it presents approaches and tools for modeling SEEs and their impact on memories and microprocessors. Additionally, experimental results targeting a Commercial-Off-The-Shelf self-refresh Dynamic RAM are presented. These experiments are based on radiation test campaigns in particle accelerators with neutrons and protons. Finally, an overview of issues and mitigation techniques for microprocessors is exposed.

Solutions based on artificial intelligence and brain-inspired computations like Artificial Neural Networks (ANNs) are suited to deal with the growing computational complexity required by state-of-the-art electronic devices. Many applications that are being deployed using these computational models are considered safety-critical (e.g., self-driving cars), producing a pressing need to evaluate their reliability. Besides, state-of-theart ANNs require significant memory resources to store their parameters (e.g., weights, activation values), which goes outside the possibility of many resource-constrained embedded systems. In this light, Approximate Computing (AxC) has become a significant field of research to improve memory footprint, speed, and energy consumption in embedded and high-performance systems. The use of AxC can significantly reduce the cost of ANN implementations, but it may also reduce the inherent resiliency of this kind of application. On this scope, reliability assessments are carried out by performing fault injection test campaigns. The intent of the paper is to propose a framework that, relying on the results of radiation tests in Commercial-Off-The-Shelf (COTS) devices, is able to assess the reliability of a given application. To this end, a set of different radiation-induced errors in COTS memories is presented. Upon these, specific fault models are extracted to drive emulation-based fault injections.

Increasing the number of bits per cell and technology scaling are ways to reduce the cost per gigabyte of flash memories and solid-state drives (SSDs). Unfortunately, this trend has a negative impact on data retention capability and cycling endurance. Periodic data refresh allows dealing with a reduced retention time and, indirectly, may be used to improve cycling endurance. A worst case data refresh frequency is not optimal in the presence of important temperature variations as it may become unnecessarily pessimistic and alter the SSD response latency and energy consumption. Here, a flexible data refresh methodology is proposed based on approximations of the Arrhenius-curves employed to describe the temperature impact on the retention capability of flash memories. These approximations may be implemented with the help of a small module called A-timer. For an asymmetric temperature distribution between 30°C and 70°C, it is estimated that the refresh frequency can be reduced by more than 63× and almost 3× for respectively charge detrapping and SILC failure mechanisms.

Solid-state drives (SSDs) based on NAND flash memories provide an attractive storage solution as they are faster and less power hungry than traditional hard-disc drives (HDDs). Aggressive storage density improvements in flash memories enabled reductions of the cost per gigabit but also caused reliability degradations. A recent large-scale study revealed that the uncorrectable bit error rates (UBER) in data center SSDs may fall far below the JEDEC standard recommendations. Here, a technique is proposed to improve the tolerated raw bit error rate (RBER) based on the observation that (a) a small SSD ratio may have a much higher RBER than the rest and (b) the RBER is dominated by the retention error rate. Instead of employing stronger but costly error-correcting codes a statistical approach is used to estimate the remaining retention time, i.e., the reliable data storage time, of flash memory pages. This estimation can be performed each time a memory page is read based on the number of detected retention errors and the elapsed time since data was programmed. The fact that the estimated remaining retention time is smaller than a maximum time interval before the next read operation is an indication that data needs to be refreshed. It is estimated that the tolerated RBER can be increased by more than a decade over a storage period of 3 years if the stored data are verified on a monthly basis and refreshed only if necessary. The proposed technique has the ability to adapt the average time between refresh operations to the actual RBER. This enables performance overhead reductions with factors between 8x and 12x as compared to systematic refresh schemes.

Power-gating techniques have been adopted so far to reduce the static power consumption of an Integrated Circuit (IC). Power-gating is usually implemented by means of several power switches. Manufacturing defects affecting power switches can lead to increase the actual static power consumption and, in the worst case, they can completely isolate a functional block in the IC. Thus, efficient test and diagnosis solutions are needed. In this paper we propose a Design-for-Diagnosis architecture for Power Switches. The proposed approach has been validated through SPICE simulations on ITC'99 benchmark circuits as well as on industrial test case.

Increasing vulnerability of transistors and interconnects due to CMOS technology scaling is continuously challenging the reliability of future electronic circuits and systems. Lifetime reliability is gaining attention over performance as a design factor even for lower-end commodity applications. In this paper we propose an effective hybrid fault-tolerant architecture able to deal with permanent and transient faults in combinational parts of pipelined cores. The principle consists in triplicating the combinational logic parts but, unlike TMR, only two copies run in parallel while the third one remains in standby until an error is detected. We have implemented this approach on a MIPS microprocessor as case study. Experiments show that our approach is comparable to TMR in terms of area with a notable power saving and offers a full protection against transient and permanent faults.

In order to improve performance and reduce cost, multi-processor system on chip (MPSoC) is increasingly becoming attractive. At the same time, 3D integration emerges as a promising technology for high density integration. 3D homogeneous MPSoCs combine the benefits of both. However, high current demand and large on-chip switching activity variations introduce severe power supply noises (PSN) for 3D MPSoCs, which can increase critical path delay, and degrade chip performance and reliability. Meanwhile, thermal gradient should also be considered for 3D MPSoCs to avoid hot spots. In the paper, we investigate the PSN effects of different workloads and propose an effective PSN estimation method. Then, a heuristic workload assignment algorithm is proposed to suppress PSN under the given thermal constraint. The experimental results show that PSNs can be reduced significantly compared with thermal-balanced workload assignment scheme, and the system performance can be improved as well.

In this paper, we investigate the generation of diagnostic test vectors targeting the intra-cell defects. Experimental results carried out on an industrial circuit show that we actually increase the diagnosis resolution by adding few more diagnostic test patterns.

Physical Design (PD) issues are becoming a major challenge with technology scaling in integrated circuits. Multi-aggressor crosstalk, power supply noise and ground bounce are some of the PD issues that cause considerable path delay variations. Therefore, these PD issues need to be considered during path delay testing to ensure better delay defect coverage. In this paper, we first show that the path delay Automatic Test Pattern Generation (ATPG) test methods are incapable of generating an input pattern that can capture worst-case path delay in circuits. We, then present our Physical Design Aware Pattern Generation (PDAPG) method to generate an input test pattern that can capture worst-case path delay in the presence of PD issues. We propose a backtrace X-filling approach to identify the relevant X-bits causing worst-case path delay. Simulations performed on ITC'99 benchmark circuits show that our PDAPG method is capable of providing high quality input test patterns in comparison with conventional path delay ATPG test methods.

With the continuous scaling down of the transistor size, the so-called intra-cell defects are more and more frequent. In this paper we propose a defect grading tool able to evaluate the efficiency of the applied test set. The test set efficiency is quantified w.r.t. the intra-cell defect coverage and the intra-cell diagnosis resolution.

Through-Silicon-Vias (TSVs) are the key enablers of 3D integration technology. Therefore, the reliability of 3D-ICs rely on the quality of TSV testing. TSVs are prone to defects that may introduce small delay variations that can cause quality and reliability issues. Moreover, physical and electrical conditions, such as TSV dimensions, coupling and IR-drop, may affect path delay variations and consequently affect the detectability of small delay faults (SDF) induced by defective TSVs. In this work, we study the test quality and pattern effectiveness for SDF induced by TSVs. We quantity test quality using statistical delay quality level (SDQL) metric and test patterns are generated with commercial ATPG tools.

Power-gating techniques have been adopted so far to reduce the static power consumption of an Integrated Circuit (IC). Power gating is usually implemented by means of several power switches. Manufacturing defects affecting power switches can lead to increase the actual static power consumption and, in the worst case they can completely isolate a functional block of the IC. In this paper we present a novel Design for Test & Diagnosis to increase the test quality and diagnosis accuracy of power switches. The proposed approach has been validated through SPICE simulations on ITC'99 benchmark circuits.

CMOS technology trends at one side open up some opportunities like making small and power efficient devices available, which in turn allow to put more functionality into a single chip. However, on the other side it poses some challenges like making devices vulnerable to hard and soft errors. In this paper we propose an efficient fault-tolerant architecture able to deal with permanent and transient faults in combinational parts of pipeline structures. The principle consists in triplicating the combinational logic parts but, unlike TMR, only two copies are running in parallel while the third one remains in standby until an error is detected. We implement this approach on a MIPS microprocessor as case study to make it resilient against transient and permanent faults.

In this paper we propose a novel Power Supply Noise (PSN) sensor. It is based on timing uncertainty measure. Compared to state of the art it allows to measure the PSN events in more accurate way. The proposed sensor is actually under validation and patent reviewing process.

3D-IC test becomes a challenge with the increasing number of TSVs and demands for effective 3D aware test techniques. In this work, we propose a timing aware model to capture delay variations on a path due to resistive open TSVs. The key idea is to analytically model delay and apply our correlation-based resistive open TSV detection method to attain path delay fault coverage. We propose two methods to investigate timing variation introduced by resistive open TSVs in a critical path delay with multiple TSVs. Method I computes the correlation of multiple TSVs in a path to overall path delay to determine if TSVs are the source of the introduced delay. Method II pinpoints which TSV is faulty by computing the delay fault coverage of each TSV in a path with multiple TSVs. Our results indicate the accuracy of our proposed method and promotes early identification of resistive open defects TSVs.

Magnetic random access memory (MRAM) is an emerging technology with potential to become the universal on-chip memory. Among existing MRAM technologies, thermally assisted switching (TAS)-MRAM technology offers several advantages compared with other technologies: selectivity, single magnetic field, and high-integration density. In this paper, we analyze the impact of resistive-open defects on TAS-MRAM behavior. Electrical simulations were performed on a hypothetical 16 word TAS-MRAM architecture enabling any combination of read and write operations. Results show that read and write sequences may be affected by resistive-open defects that may induce single and double-cell faulty behaviors. As a next step, we will exploit the analyses results to guide the test phase by providing effective test algorithms targeting faults related to actual defects affecting TAS-MRAM architectures.

Design of power delivery network (PDN) is a constrained optimization problem. An ideal PDN must limit voltage drop that results from switching circuits' transients, satisfy current density constraints that arise from electromigration limits, yet use only minimal metal resources so that design density targets can be met. It should also provide an efficient thermal conduit to address heat flux. Furthermore, an ideal PDN should be a regular structure to facilitate design productivity and manufacturability, yet be resilient to address varying power demands across its distribution area. In 3-D ICs, these problems are further constrained by the need to minimize through-silicon via (TSV) area and bridge power lines of different dimensions across tiers, while addressing varying power demands in lateral and vertical directions. In this paper, we propose an unconventional power grid optimization solution that allows us to resize each tier individually by applying tier-specific constraints and yet be optimal in a multitier network, where each tier is locally resized while globally constrained. Tier-specific constraints are derived from electrical and thermal targets of 3-D PDNs. Two resizing algorithms are presented that optimize 3-D PDNs standalone or 3-D PDNs together with TSVs. We demonstrate these solutions on a three-tier setup where significant area savings can be achieved.

SRAM testing is becoming more and more challenging due to issues caused by continuous device scaling. Fabricated SRAMs are submitted to random and systematic process variability, which strongly affect the cell's behavior and also the ability of test algorithms to detect faults. Traditionally, bias conditions have been used to improve the behavior of the SRAM under process variations by applying body bias to compensate for the effect of variability. Based on the same principle, bias conditions also affect the cell's behavior when resistive-opens are present, hence affecting test's defect coverage capability. Both body- and source-bias conditions are analyzed in this paper to find the way to improve defect detect ability in the SRAM cell. Source-biasing has been proven to be the more effective of the two, leading to more than 3X improvement of the defect detected value. Also, by adapting the source-bias conditions to process parameter values, over- and under-testing of the SRAM can be avoided.

Low-power SRAMs embed mechanisms for reducing static power consumption. When the SRAM is not accessed during a long period, it switches into an intermediate low-power mode. In this mode, a voltage regulator is used to reduce the voltage supplied to the core-cells as low as possible without data loss. Thus, faulty-free behavior of the voltage regulator is crucial for ensuring data retention in core-cells when the SRAM is in low-power mode. This paper investigates the root cause of data retention faults due to voltage regulator malfunctions. This analysis is done under realistic conditions (i.e., industrial core-cells affected by process variations). Based on this analysis, we propose an efficient test flow for detecting data retention faults in low-power SRAMs.

Three-dimensional stacking technology promises to solve the interconnect bottleneck problem by using Through-Silicon-Vias (TSVs) to vertically connect circuit layers. However, manufacturing steps may lead to partly broken or incompletely filled TSVs that may degrade the performance and reduce the useful lifetime of a 3D IC. Due to combinations of physical factors such as switching activity, supply noise and crosstalk, path delays can experience speed-up or slow-down that could let the effect of resistive open TSV go undetected by conventional test methods. In this work, we present a metric based on probabilistic analysis to detect delay defects induced by resistive opens that occur on signal line TSVs. Our experimental result will show the accuracy of the proposed metric.

Functional operations of a Static Random Access Memory (SRAM) are strongly affected by random variability in core-cell transistors and by the variability-induced threshold voltage mismatch between the transistors of the Input-Output (IO) circuitry (especially Sense Amplifiers). This variability also affects the faulty behavior of the SRAM array. This paper is focused on the analysis of static and dynamic faults due to resistive-open defects in the SRAM core-cell, taking into account the effects of random process variability in core-cells and IO circuitry. Statistical analyses have been performed to evaluate the SRAM failure probabilities accounting for defects at each possible location. The results show that random process variability in the SRAM core-cell and IO circuitry have an important effect on the behavior of an SRAM array and also on the defect coverage of various commonly-used test sequences. It is shown that under variability, the minimum defect size detected with maximum probability is more than 2X larger than the minimum size detected in nominal conditions, thus leaving a large range of defects undetected. Several stress conditions during test have been evaluated to assess their capability to increase the defect coverage under random process variability.

In current technologies, the robustness of Static Random Access Memories (SRAM) has to be investigated under any possible source of disturbance. In this paper, we evaluate the reliability of an SRAM cell exposed to atmospheric neutron radiation, affected by random threshold voltage variation and under different operation conditions (supply voltage, process corner and temperature). The SRAM cell's Soft Error Rate (SER) at simulation level is estimated using accurate models of atmospheric neutron induced currents. The study shows that in extreme operation conditions and under random process variability, the SER of an SRAM can reach values up to 3X larger than the nominal value, or down to 2X smaller than the nominal value. This large SER range confirms the importance of our study and justifies the need for further evaluation of circuits under radiation at the simulation level.

Read and write assist techniques are widely adopted to allow voltage scaling in low-power SRAMs. In particular, this paper analyzes two assist techniques: word line level reduction and negative bit line boost. The analyzed assist techniques improve read stability and write margin of core-cells when the SRAM operates at a lowered supply voltage. In this work, we investigate the impact of such assist techniques on the faulty behavior of low-power SRAMs. This analysis is based on extensive injection of resistive-open and resistive-bridging defects in core-cells of a commercial low-power SRAM. Our study determines the most stressful configuration of assist circuits to detect each faulty behavior induced by injected defects. We show that, by applying most stressful configurations of assist circuits during test phase, defect coverage can be increased up to 89% w.r.t. test solutions that do not exploit assist circuits. Based on this analysis, we present an efficient test solution that exploits the configuration of assist circuits as a parameter to maximize the detection of studied defects, while reducing time complexity up to 73% w.r.t. test flows using state-of-the-art test algorithms.

Voltage regulation systems offer an efficient mechanism for reducing static power consumption of SRAMs. When the SRAM is not accessed for a long period, it switches into an intermediate low-power mode. In this mode, a voltage regulator is used to reduce the voltage supplied to the core-cell array as low as possible without data loss. Therefore, reliable operation of such device must be ensured by using adequate test techniques. In this work, we propose low area overhead built-in self-test (BIST) and built-in self-repair (BISR) schemes that can be embedded on the SRAM to automatically test and repair the voltage regulator. Simulation results prove the effectiveness of the proposed technique for detecting, diagnosing and repairing voltage regulators of low-power SRAMs.

Power supply noise and ground bounce can cause considerable path delay variations. Capturing the worst case power supply noise at a gate level is not a sufficient indicator for measuring the worst case path delay. Furthermore, path delay variations depend on multiple parameters such as input stimuli, cell placement, switching frequency, and available decoupling capacitors. All these variables obscure the rapport between supply noise and path delay and make the selection of stimuli for worst case path delay a difficult task during test pattern generation. In this paper, we utilize power supply noise and ground bounce distribution along with physical design data to generate test patterns for capturing worst case path delay. We propose accurate close-form mathematical models for capturing the effect of power supply noise and ground bounce on path delay. These models are based on modified nodal analysis formulation of power and ground networks, where current waveforms are obtained from levelized simulation and cell library characterization. The proposed test pattern generation flow is a simulated-annealing-based iterative process, which utilizes mathematical models for capturing the impact of supply noise on path delay for a given input pattern. We perform experiments on ITC'99 benchmarks and show that path delay variation can be considerable if test patterns are not properly selected.

3-D integration presents a path to higher performance, greater density, increased functionality and heterogeneous technology implementation. However, 3-D integration introduces many challenges for power and thermal integrity due to large switching currents, longer power delivery paths, and increased parasitics compared to 2-D integration. In this work, we provide an in-depth study of power and thermal issues while incorporating the physical design characteristics unique to 3-D integration. We provide a qualitative perspective of the power and thermal dissipation issues in 3-D and study the impact of Through Silicon Vias (TSVs) size for their mitigation. We investigate and discuss the design implications of power and thermal issues in the presence of decoupling capacitors, TSV/on-die/package parasitics, various resonance effects and power gating. Our study is based on a ten-tier system utilizing existing 3-D technology specifications. Based on detailed power distribution and heat dissipation models, we present a comprehensive analysis of TSV tapering for alleviating power and thermal integrity issues in 3-D ICs.

Magnetic Random Access Memory (MRAM) is an emerging memory technology. Among existing MRAM technologies, the Thermally Assisted Switching (TAS) MRAM technology offers several advantages such as selectivity, single magnetic field and high integration density. In this paper, we analyze resistive-bridge defects that may affect the TAS-MRAM architecture. Electrical simulations were performed on a hypothetical 16-words TAS-MRAM architecture enabling any sequences of read/write operations. Results show that both read and write operations may be affected by these defects. Especially, we demonstrate that resistive-bridge defects may have a local (single cell) or global (multiple cells) impact on the TAS-MRAM functioning. As these analysis results will be further used to develop effective test algorithms targeting faults related to actual resistive bridge-defects that may affect TAS-MRAM architecture.

High peak power consumption during test may lead to yield loss. On the other hand, reducing too much test power may lead to test escape. In order to overcome this problem, test power has to mimic the power consumed during functional mode, being as high as possible but not crossing the frontier of over-consumption. Measuring power consumption is a very time consuming activity, therefore many works in the literature focused on the indirect ways to provide power consumption estimation in a fast manner. In this paper we concentrate on a similar issue, concentrating our effort on devising a fast method for the identification and estimation of the peak power produced by test patterns. In particular we provide a detailed discussion on case studies related to peak power estimation of CPU cores when executing functional patterns, the proposed method uses the gate-level description of the CPU to identify a subset of time points over the entire test pattern that are showing the most significant peak power values. The proposed methodology has been validated on two case studies synthesized in a 65nm industrial technology.

Managing the power consumption of circuits and systems is challenging not only during functional operations but also during manufacturing test. In this paper, we first explain why it is important to control power consumption during test application. We will introduce the basic concepts and discuss issues arising from excessive power dissipation during test. Then, we explain how it is possible to control power consumption during test. We will provide an overview of existing structural and algorithmic solutions for power-aware testing, and we will show how low power circuits can be tested safely without affecting yield and reliability.

In this work, we present a new power supply noise sensor based on timing uncertainty measurements. The proposed sensor can detect power supply noise events in a more accurate way compared to the state of the art solutions. Experimental results validated the efficiency of the proposed approach.

Magnetic Random Access Memory (MRAM) is an emerging technology with the potential to become the universal on-chip memory. Among the existing MRAM technologies, the Thermally Assisted Switching (TAS) MRAM technology offers several advantages compared to the others technologies: selectivity, single magnetic field and integration density. As any other types of memory, TAS-MRAMs are prone to defects, so TAS-MRAM testing needs definitely to be investigated since only few papers can be found in the literature. In this paper we analyze the impact resistive-open defects on the heat current of a TAS-MRAM architecture. Electrical simulations were performed on a hypothetical 4×4 TAS-MRAM architecture enabling any read/write operations. Results show that W0 and/or W1 operations may be affected by the resistive-open defects. This study provides insights into the various types of TAS-MRAM defects and their behavior. As future work, we plan to utilize these analyses results to guide the test phase by providing effective test algorithm targeting fault related to actual defects that may affect TAS-MRAM architecture.

Thermally Assisted Switching Magnetic Random Access Memory (TAS-MRAM) is an emerging technology that offers several advantages compared to existing non-volatile memory technologies. In this paper we show how coupling faults induced by resistive-open defects impact the TAS-MRAM architecture. Results shows that read and write operations may be affected these defects and may induce single and double cell faulty behaviors.

Three-dimensional (3D) integration is a fast emerging technology that offers integration of high density, fast performance and heterogeneous circuits in a small footprint. Through-Silicon-Vias (TSVs) enable 3D integration by providing fast performance and short interconnects among tiers. However, they are also susceptible to defects that occur during manufacturing steps and cause crucial reliability issues. In this paper, we perform an analysis of resistive-open defects (ROD) on TSVs considering coupling effects (i.e. inductive and capacitive) and a wide frequency spectrum. Our experiments show that both substrate coupling and switching frequency can have a significant impact on weak open TSV behavior.

Summary form only given. Low-power SRAMs embed power gating mechanisms for reducing static power consumption. Power gating is applied in SRAMs using power switches for controlling the supply voltage applied to the various memory blocks (array, decoders, I/O logic, etc.). This paper provides a detailed analysis based on electrical simulations to describe the impacts of resistive-open defects on the power mode control logic, which generates control signals of power switches.

Electronic system reliability over soft errors is very critical as the transistor size shrinks. Many recent works have defined the device error rate under radiation for SRAMs in hold mode (static) and during operation (dynamic). This paper evaluates the impact of running test algorithms on SRAMs exposed to neutron radiation in order to define their stressing factor. The results that we show are based on experiments performed at the TSL facility in Uppsala, Sweden using a Quasi-Monoenergetic neutron beam. The evaluation of the test algorithms is based on the calculated device SEU cross section.

Low-power SRAMs embed power gating mechanisms for reducing static power consumption. Power gating is implemented through power switches for controlling the supply voltage applied to the various memory blocks (array, decoders, I/O logic, etc.). This way, one or more memory blocks can be disconnected from the power supply during a long period of inactivity, thus reducing static power consumption. This paper focuses on low-power SRAMs, and in particular, the power gating mechanisms of core-cells and peripheral circuitry. We provide a detailed analysis based on electrical simulations to characterize the impact of resistive-open defects on the power mode control logic. Based on this analysis, we introduce appropriate fault models that represent the observed faulty behaviors. Finally, we propose an efficient test solution targeting the set of identified fault models.

Memory design and test represent very important issues. Memories are designed to exploit the technology limits to reach the highest storage density and high-speed access. The main consequence is that memory devices are statistically more likely to be affected by manufacturing defects. The challenge of testing SRAM memories consists in providing realistic fault models and test solutions with minimal application time. Due to the complexity of the memory device, fault modeling is not trivial. Classical memory test solutions cover the so-called `static faults' (such as stuck-at, transition, and coupling faults) but are not sufficient to cover faults that have emerged in latest VDSM technologies and which are referred to as `dynamic faults'. This tutorial aims at introduce and guide to new test approaches developed so far for dealing with dynamic faults in the latest generation of SRAM memories.

Although CMOS technology scaling offers many advantages, it suffers from robustness problem caused by hard, soft and timing errors. The robustness of future CMOS technology nodes must be improved and the use of fault tolerant architectures is probably the most viable solution. In this context, Duplication/Comparison scheme is widely used for error detection. Traditionally, this scheme uses a static comparator structure that detects hard error. However, it is not effective for soft and timing errors detection due to the possible masking of glitches by the comparator itself. To solve this problem, we propose a pseudo-dynamic comparator architecture that combines a dynamic CMOS transition detector and a static comparator. Experimental results show that the proposed comparator detects not only hard errors but also small glitches related to soft and timing errors. Moreover, its dynamic characteristics allow reducing the power consumption while keeping an equivalent silicon area compared to a static comparator. This study is the first step towards a full fault tolerant approach targeting robustness improvement of CMOS logic circuits.

Launch-off-Capture (LOC) and Launch-off-Shift (LOS) are the two main test schemes for at-speed scan delay testing. In the literature, it has been shown that LOS has higher performance than LOC in terms of fault coverage and test length, but higher peak power consumption during the launch-to-capture cycle. Power reduction seems to be the key to really exploit LOS test scheme. However, it has been proven that reducing too much test power can lead to test escape due to under-test. In this context, this study proposes a smart X-filling framework able to adapt peak power consumption during the launch-to-capture cycle according to the functional power, i.e. the power consumption of the circuit in functional mode. Here, the main goal is to obtain a final test set with peak power consumption as close as possible to the functional power. Experimental results, carried out on the well-known ITC'99 benchmarks, prove the feasibility of the proposed approach.

It has become necessary to reduce power during LSI testing. Particularly, during at-speed testing, excessive power consumed during the Launch-To-Capture (LTC) cycle causes serious issues that may lead to the overkill of defect-free logic ICs. Many successful test generation approaches to reduce IR-drop and/or power supply noise during LTC for the launch-off capture (LOC) scheme have previously been proposed, and several of X-filling techniques have proven especially effective. With X-filling in the launch-off shift (LOS) scheme, however, adjacent-fill (which was originally proposed for shift-in power reduction) is used frequently. In this work, we propose a novel X-filling technique for the LOS scheme, called Adjacent-Probability-based X-Filling (AP-fill), which can reduce more LTC power than adjacent-fill. We incorporate AP-fill into a post-ATPG test modification flow consisting of test relaxation and X-filling in order to avoid the fault coverage loss and the test vector count inflation. Experimental results for larger ITC'99 circuits show that the proposed AP-fill technique can achieve a higher power reduction ratio than 0-fill, 1-fill, and adjacent-fill.

In this paper, a novel hybrid fault tolerant architecture for digital circuits is proposed in order to enable the use of future CMOS technology nodes. This architecture targets robustness, power consumption and yield at the same time, at area costs comparable to standard fault tolerance schemes. The architecture increases circuit robustness by tolerating both transient and permanent online faults. It consumes less power than the classical Triple Modular Redundancy (TMR) approach while utilizing comparable silicon area. It overcomes many permanent faults occurring throughout manufacturing while still tolerating soft errors introduced by particle strikes. These can be done by using scalable redundancy resources, while keeping the hardened combinational logic circuits intact. The technique combines different types of redundancy: information redundancy for error detection, temporal redundancy for soft error correction and hardware redundancy for hard error tolerance. Results on largest ISCAS and ITC benchmark circuits show that our approach has an area cost negligible of about 2% to 3% with a power consumption saving of about 30% compared to TMR. Finally, it deals with aging phenomenon and thus, increases the expected lifetime of logic circuits.

Low-power SRAMs embed power gating facilities for reducing power consumption. Power gating is applied using power switches for controlling the supply voltage applied to the memory cells i.e. one or more memory blocks can be disconnected from the power supply during a long time of inactivity, thus reducing the power consumption. In this paper, we provide a detailed analysis on the impact that defective power switches impose on the behavior of SRAM core-cells. Furthermore, we propose efficient test solutions to detect such faulty behaviors.

The Flash technology is the most popular non-volatile memory technology. In this paper, we present the ability of a SPICE-like model of the ATMEL TSTAC™ eFlash technology to guide the design and test phases. This model is composed of two layers: a functional layer representing the Floating Gate (FG) and a programming layer able to determine the channel voltage level controlling the Fowler-Nordheim tunneling effect. It is able to guide the test phase since it allows analyzing and modeling defects that may affect the eFlash array. This analysis highlights the interest of the proposed model to identify a realistic set of fault models that has to be tested, thus enhancing existing solutions for TSTAC™ eFlash testing. The proposed model is also helpful to guide the design phase. Data presented in the paper demonstrate its accuracy compared to silicon measurements, usefulness to predict the technology shrinking and usefulness to guide the pulse programming method.

As technology scales down, the effects of power supply noise and ground bounce are becoming significantly important. In the existing literature, it has been shown that excessive power supply noise can affect the path delay, while ground bounce is either neglected or assumed similar to power supply noise. In this work, we present a detailed study of combined and uncorrelated power supply noise and ground bounce and their impact on the path delay. Our analyses show that different combination of power supply noise and ground bounce can lead to either delay speed-up or slow-down. Furthermore, our study shows the degrading influence of supply noise resonance on the path delay. We perform HSPICE simulations for path delay analysis on various technology nodes i.e. 130nm, 90nm, 65nm and 45nm.

A comprehensive SRAM test must guarantee the correct functioning of each cell of the memory (ability to store and to maintain data), and the corresponding addressing, write and read operations. SRAM testing is mainly based on the concept of fault model used to mimic faulty behaviors. Traditionally, the effects of bit line coupling capacitances have not been considered during the fault analysis. However, recent works show the increasing impact of bit line coupling capacitances on the SRAM behavior. This paper reviews and discusses preview works addressing the issues coming from bit line parasitic capacitances and data contents on SRAM testing, pointing out the impacts of these effects on the existing test solutions. Then, we introduce two optimizations of the state-of-the-art test solution able to take into account the influence of bit line coupling capacitances while reducing the test length of about 60% and 80%, respectively.

High power consumption during test may lead to yield loss and premature aging. In particular, excessive peak power during at-speed delay fault testing represents an important issue. In the literature, several techniques have been proposed to reduce peak power consumption during at-speed LOC or LOS delay testing. On the other hand, some experiments have proved that too much test power reduction might lead to test escape and reliability problems. So, in order to avoid any yield loss and test escape due to power issues during test, test power has to map the power consumed during functional mode. In literature, some techniques have been proposed to apply test vectors that mimic functional operation from the switching activity point of view. The process consists of shifting-in a test vector (at low speed) and then applying several successive at-speed clock cycles before capturing the test response. In this paper, we propose a novel flow to determine the functional power to be used as test power (upper and lower) limits during at-speed delay testing. This flow is also used for comparison purpose between the above-mentioned test scheme and power consumption during the functional operation mode of a given circuit. The proposed methodology has been validated on an Intel MC8051 micro controller synthesized in a 65 nm industrial technology.

This paper proposes an innovative approach to cope with defects in SRAM bit-cell array. Traditional approaches use spare parts (rows, columns or blocks) to replace defective bit-cells. Instead of replacing defective bit-cells, we propose to operate the SRAM with reduced storage capacity whenever defective bit-cells are present. We implement this feature through a programmable combinational logic, called Scrambling Module (SM), which scrambles the memory addresses. The scrambling changes the addresses of the defective bit-cells, grouping them in an idle address zone located at the end of the memory address plan. The SM is described by using a mathematical formulation based on linear algebra. The proposed technique can be used in combination with traditional redundancy approaches using spare rows and/or columns. The effectiveness of three different SM is demonstrated, considering a 1MBit SRAM. For a given level of defect tolerance, it is shown that our technique can reduce the amount of spare area by several orders of magnitude. Moreover, as the SM is implemented as an external block, it does not affect the maximum operation frequency of the SRAM. Instead, it affects the memory access delay.

This paper addresses the problem of logic diagnosis of System-on-Chip (SoC). We propose a diagnosis approach based on a matching algorithm between a set of predicted failures and the set of failures observed during the test phase. The result of the diagnosis is a ranked list of suspected nets able to explain the observed failures. Experimental results show the diagnosis accuracy of the proposed approach in terms of absolute number of suspects. Moreover, a comparison with an industrial reference tool highlights the reliability of our approach.

This paper introduces a simulator that allows analyzing the radiation induced errors on memory devices. The simulator takes all the radiation effects on SRAM into account and can be easily tuned on the base of data gained during radiation experiments and/or presented in literature. We also present a case study application in which the proposed simulator is used to validate a low-cost hardware platform for soft error detection in avionic environment by the mean of atmospheric balloons in the context of HAMLET project.

Reliability analysis of SRAM core-cells requires statistical methods with very high accuracy to cope with very low failure probabilities. Although new statistical methods have been recently proposed, to the best of our knowledge, there is no method able to evaluate the joint failure probability (the probability that at least one failure mechanism occurs) of an SRAM core-cell with enough accuracy in a reasonable time. We propose a statistical simulation method based on the analytical integration of the multivariate Gaussian distribution function.

At-speed scan testing has become mandatory due to the extreme CMOS technology scaling. The two main at-speed scan testing schemes are namely Launch-Off-Shift (LOS) and Launch-Off-Capture (LOC). As it can be easily implemented, LOC has been widely investigated in the literature in the last few years, especially regarding test power consumption. Conversely, LOS has received much less attention. In this paper, we propose a comparison between the two testing schemes in terms of transition fault coverage and power consumption, in order to quantify the pros and cons of LOS with respect to LOC. This study shows that LOS not only exhibits higher performance in coverage but also does not require as much extra power as predicted, especially in terms of peak power. These facts may represent convincing arguments for its wider use and development.

In this paper, we present a comparative study on the effects of resistive-bridging defects in the SRAM core-cells, considering different technology nodes. In particular, we analyze industrial designs of SRAM core-cell at the following technology nodes: 90nm, 65nm and 40nm. We have performed an extensive number of simulations, varying the resistive value of defects, the power supply voltage, the memory size and the temperature. Experimental results show malfunctions not only within the defective core-cell, but also in other core-cells (defect-free) of the memory array.

In the context of SRAM testing, we propose a methodology to define proper conditions under which SRAMs should be tested to improve their reliability. This methodology is especially suitable to deal with the impact of threshold voltage variability affecting SRAM core-cell transistors. By establishing an objective manner of comparing different test conditions, the proposed study shows how it is possible to detect SRAM core-cells with poor quality by applying a reduced set of test runs. The proposed methodology also allows determining the most appropriate DfT (Design-for-Test) technique for each peculiar SRAM design and technology.

Flash memories are based on the floating gate technology allowing the write and erase data electronically. Such a technology can be prone to complex defects leading to faulty behaviors. In this paper, we introduce an electrical model of the ATMEL TSTACTM eFlash memory technology. The model is composed of two layers: a functional layer representing the floating gate and a programming layer able to determine the channel voltage level controlling the Fowler-Nordheim tunneling effect. The proposed model has been validated by means of simulations and comparisons with ATMEL silicon data. We apply this model for the analysis of defect-induced failures. As a case study, a resistive defect injection is considered.

This paper reports and analyzes the results of alpha radiation testing campaigns on an embedded microprocessor manufactured with different standard cell libraries, each one enforcing Design for Manufacturing rules at a specific level. A set of analog simulations has been performed on flip-flops built with different physical layouts to reproduce and evaluate the effects of ionizing particles. The results of simulation experiments are presented and discussed, highlighting the configurations which are more likely to improve the system reliability, and then compared with radiation experiments data. Finally, we give a physical interpretation of the observed variations on radiation sensitivity.

In this paper, we propose a memory based test bench able to record soft errors that may occur to modern circuits in a certain environment. This system allows a good flexibility from different points of view. It is conceived to be modular, programmable, low power consuming and portable. Consequently, it can operate in various experimental conditions such as under artificial sources of particles as well as in natural ambience, from the earth surface to spatial environment.

In this paper we investigate the possibility of using commercial synthesis tools to build parity predictors for nano-electronic gates designs. They will be used as redundant resources for robustness improvement for future CMOS technology nodes.

This study investigates the reasons why test power reduction through X-filling techniques works well for cycle-average power reduction but is not so efficient concerning instantaneous peak power reduction.

Negative Bias Temperature Instability (NBTI) is a degradation phenomenon that occurs in PMOS transistors during circuit lifetime. Recent works have proposed transistor level and circuit level models that allow designers to deal with such phenomenon. Based on these models and taking into account Random Dopant Fluctuation (RDF), we study the possibility of detecting SRAM core-cells that are prone to NBTI failures during post-production test. For this purpose, we introduce a statistical simulation method that allows estimating the amount of NBTI affected core-cells that pass or fail under given test conditions. Supply voltage, temperature, word line pulse width, word line pulse voltage and bit line voltage are the parameters considered as test conditions. An industrial core-cell design with a 65 nm technology is used as case study.

The importance of delay faults proportionally increases when entering in the nano-technology era, and logic diagnosis must localize delay faults as precisely as possible to speed-up yield ramp-up. This paper presents a logic diagnosis approach targeting delay faults. The proposed approach is based on the single-location-at-a-time (SLAT) paradigm used to determine a set of suspects. It addresses the case of sequential circuits tested at-speed. The main advantages of this approach are that it can manage a comprehensive set of delay faults, and that it is independent on the size of the delay (induced by the fault). Experimental results show the effectiveness of the proposed approach in terms of absolute number of suspects.

Core-cell stability represents the ability of the core-cell to keep the stored data. With the rapid development of semiconductor memories, their test is becoming a major concern in VDSM technologies. It provides information about the SRAM design reliability, and its effectiveness is therefore mandatory for safety applications. Existing core-cell stability design-for-test (DfT) techniques consist in controlling the voltage levels of bit lines to apply a weak write stress on the core-cell under test. If the core-cell is weak, the weak write stress induces the faulty swap of the core-cell. However, these solutions are costly in terms of area and test application time, and generally require modifications of critical parts of the SRAM (core-cell array and/or the structure generating the internal auto-timing). In this paper, we present a new DfT technique for stability fault detection. It consists in modulating the word line activation in order to perform an adjustable weak write stress on the targeted core-cell for stability fault detection. Compared to existing DfT solutions, the proposed technique offers many advantages: programmability, low area overhead, low test application time. Moreover, it does not require any modification of critical parts of the SRAM.

This paper presents a logic diagnosis approach targeting bridging faults. The proposed approach is performed in two phases, (i) a fault localization phase based on the single-location-at-a-time (SLAT) paradigm determining a set of suspects, and (ii) a fault model allocation phase associating a set of fault models to each suspect identified during the first phase. The main advantages of this approach are that the fault localization phase is fault model independent, and that the fault model allocation phase is able to deal at the same time with several bridging fault models leading to either static or dynamic faulty behaviors. Experimental results on full scan circuits show the diagnosis accuracy of the proposed approach in terms of absolute number of suspects. Moreover, a comparison with an industrial reference tool highlights the reliability of our approach.

Embedded flash memories are dominated by the NOR architecture but NAND is becoming more and more adopted due to its high storage capacity. This paper presents a preliminary study on actual defects in NAND array.

The usual techniques for memory diagnosis are mainly based on signature analysis. They consist in creating a fault dictionary that is used to determine the correspondence between the signature and the fault models affecting the memory. The effectiveness of such diagnosis methods is therefore strictly related to the fault dictionary accuracy. To the best of our knowledge, most of existing signature-based diagnosis approaches targets static faults only. In this paper, we present a new diagnosis approach that represents an alternative to signature-based approaches. This new diagnosis technique, named history-based diagnosis, makes use of the effect-cause paradigm already developed for logic design diagnosis. It consists in creating a database containing the history of operations (read and write) performed on a faulty memory core-cell. This information is crucial to track the root cause of the observed faulty behavior and it can be used to generate the set of possible fault primitives representing the set of suspected fault models. This new diagnosis method is able to identify static as well as dynamic faults. Although applied to SRAMs in this paper, it can be effective also for other memory types such as DRAMs. Experimental results are provided to prove the efficiency of the proposed methodology in generating a list of suspected faults as well as the location of the faulty components in the memory.

In this paper we analyze the test power of SRAM memories and demonstrate that the full functional pre-charge activity is not necessary during test mode because of the predictable addressing sequence. We exploit this observation in order to minimize power dissipation during test by eliminating the unnecessary power consumption associated with the pre-charge activity. This is achieved through a modified pre-charge control circuitry, exploiting the first degree of freedom of March tests, which allows choosing a specific addressing sequence. The efficiency of the proposed solution is validated through extensive Spice simulations

Resistive-open defects appear more and more frequently in VDSM technologies. In this paper we present a study concerning resistive-open defects in the core-cell of SRAM memories. The first target of this work is a comparison of the effect produced by resistive-open defects in the 0.13 μm and 90 nm core-cell. We show that the 90 nm core-cell is more robust than the 0.13 μm core-cell in presence of resistive-open defects. On the other hand we show that dynamic faults are most likely to occur in the 90 nm than in 0.13 μm core-cell. Finally we propose a unique March test solution that ensures the complete coverage of all the extracted fault models for both technologies.

In this paper, we present an exhaustive study on the effects of resistive-open defects in the pre-charge circuits of SRAM memories. In particular, we have analyzed the influence of resistive-opens placed in different locations of these circuits. In SRAM memories, the pre-charge circuits operate the pre-charge and equalization at a certain voltage level, in general Vdd, of all the couples of bit lines of the memory array. This action is essential in order to ensure correct read operations. Each defect studied in this paper disturbs the pre-charge circuit in a different way and for different resistive ranges, but the produced effect on the normal memory action is always the perturbation of the read operations. This faulty behavior can be modeled with un-restored write faults (URWFs) and un-restored read faults (URRFs), because there is an incorrect pre-charge/equalization of the bit lines after a write or read operation that disturbs the following read operation. In the last part of the paper, we demonstrate that the test of URWFs is more rentable in terms of resistive defect detection than that of URRFs.

In this paper, we present a novel study on data retention faults (DRFs) in SRAM memories. We analyze in detail the electrical origins of these faults, starting from the most common till those that lead to what we have called hard to detect DRFs. In general, DRFs are supposed to be produced by very high resistive-open defects that affect the refreshment loop of the core-cell. We demonstrate that lower values of resistance may produce hard to detect DRFs. Moreover, each resistive-open defect produces a particular faulty behavior of the core-cell that changes for different ranges of the resistive value. We analyze different cases and we propose for each one an efficient test procedure based on March tests. In particular, we propose to stimulate the defective cells in some cases by indirect accesses and in some other cases by emphasizing natural noise phenomenon of SRAM memories (such as the ground bounce).

In this paper we present an exhaustive analysis of resistive-open defect in core-cell of SRAM memories. These defects that appear more frequently in VDSM technologies induce a modification of the timing within the memory (delay faults). Among the faults induce by such resistive-open defects there are static and dynamic read destructive fault (RDF), deceptive read destructive fault (DRDF), incorrect read fault (IRF) and transition fault (TF). Each of them requires specific test conditions and different kind of March tests are needed to cover all these faults (TF, RDF, DRDF and IRF). In this paper, we show that a unique March test solution can ensure the complete coverage of all the faults induced by the resistive-open defects in the SRAM core-cells. This solution simplifies considerably the problem of delay fault testing in this part of SRAM memories.

This paper presents an analysis of dynamic faults in core-cell of SRAM memories. These faults are the consequence of resistive-open defects that appear more frequently in VDSM technologies. In particular, the study concentrates on those defects that generate dynamic Read Destructive Faults, dRDFs. In this paper, we demonstrate that read or write operations on a cell involve a stress on the other cells of the same word line. This stress, called Read Equivalent Stress (RES), has the same effect than a read operation. On this basis, we propose to modify the well known March C-, which does not detect dRDFs, into a new version able to detect them. This is obtained by changing its addressing order with the purpose of producing the maximal number of RES. This modification does not change the complexity of the algorithm and its capability to detect the former target faults.

This paper presents a new March test solution for detection of ADOFs (Address Decoder Open Faults), and resistive-ADOFs that are the consequence of resistive-open defects in address decoders of SRAM memories. In this study, we briefly analyze the test conditions and the March test requirements for these particular faults and we introduce some modifications to the well known March C- making it able to detect ADOFs and resistive-ADOFs, without increasing its complexity and its ability to detect the former target faults. The reformulation of March C-, called March iC-, is essentially based on introducing a particular address sequence and a particular read/write data sequence. The proposed March iC- extends the ability of March-based test solutions in detecting dynamic faults in SRAM memories.

This paper presents a comparative analysis of open (ADOF: Address Decoder Open Fault) and resistive open defects in address decoders of embedded-SRAMs. Such defects are the primary target of this study because they are notoriously hard-to-detect faults. In particular, we consider dynamic defects which may appear in the transistor parallel plane of address decoders. From this study, we show that test conditions required for ADOFs testing (sensitization and observation) can be partially used also for resistive open defect testing.