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The development of Spin-transfer torque magnetic RAM (STT-MRAM) mass production requires high-quality dedicated test solutions, for which understanding and modeling of manufacturing defects of the magnetic tunnel junction (MTJ) is crucial. This paper introduces and characterizes a new defect called Back-Hopping (BH); it also provides its fault models and test solutions. The BH defect causes MTJ state to oscillate during write operations, leading to write failures. The characterization of the defect is carried out based on manufactured MTJ devices. Due to the observed non-linear characteristics, the BH defect cannot be modelled with a linear resistance. Hence, device-aware defect modeling is applied by considering the intrinsic physical mechanisms; the model is then calibrated based on measurement data. Thereafter, the fault modeling and analysis is performed based on circuit-level simulations; new fault primitives/models are derived. These accurately describe the way the STT-MRAM behaves in the presence of BH defect. Finally, dedicated march test and a Design-for-Test solutions are proposed., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Computer Engineering, Quantum & Computer Engineering

The power consumption of modern highly complex chips during scan test is significantly higher than the power consumed during functional mode. This leads to substantial heat dissipation, excessive IR drop, and unrealistic timing failures of the integrated circuits (ICs) under test. In this brief, a ByPassable Scan Data Retention Flip-Flop (BPS-DRFF) is proposed for low-power IC test. The proposed flip-flop contains two secondary latches. The output of the "function" secondary latch goes to the following combinational circuits, while the other "shadow" secondary latch is used to shift test vectors during scan test. By gating the output of the function secondary latch, the redundant switching activity in the combinational circuits is eliminated during scan shift, thereby reducing the test power consumption significantly. The suppressed switching activity also leads to lower IR drop across the chip, increasing the chip manufacturing yield. Furthermore, the shadow latch is reused for data retention in the sleep mode while performing power gating, thereby alleviating the area cost of the shadow latch. The proposed BPS-DRFF also eases the hold time sign-off in the test mode due to the elongated clock-to-Q contamination delay that is brought in by the shadow latch. The proposed design is applied to an AES-128 crypto core in a UMC 55-nm low power CMOS technology. Experiment results show that 68.5% power is saved during scan test with the proposed BPS-DRFF, compared to the standard scan retention flip-flop.

The popularity of perpendicular magnetic tunnel junction (pMTJ)-based spin-transfer torque magnetic random access memories (STT-MRAMs) is growing very fast. The performance of such memories is very sensitive to magnetic fields, including both internal and external ones. This article presents a magnetic-field-aware compact model of pMTJ, named the MFA-magnetic tunnel junction (MTJ) model, for magnetic/electrical co-simulation of MTJ/CMOS circuits. Magnetic measurement data of MTJ devices, with diameters ranging from 35 to 175 nm, are used to calibrate an in-house magnetic coupling model. This model is subsequently integrated into our developed compact pMTJ model, which is implemented in Verilog-A. The superiority of the proposed MFA-MTJ model for device/circuit co-design of STT-MRAM is demonstrated by simulating a single pMTJ as well as STT-MRAM full circuits. The design space is explored under PVT variations and various configurations of magnetic fields., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Computer Engineering, Quantum & Computer Engineering

Editor's notes: The authors present an IR-drop-based power-domain-scenario-based test methodology along with an in-field diagnosis technique. This utilizes on-chip monitor (OCM) circuits, and the toggle patterns can be designed with test pattern generation algorithms.

The manufacturing process of STT-MRAM requires unique steps to fabricate and integrate magnetic tunnel junction (MTJ) devices which are data-storing elements. Thus, understanding the defects in MTJs and their faulty behaviors are paramount for developing high-quality test solutions. This article applies the advanced device-aware test to intermediate (IM) state defects in MTJ devices based on silicon measurements and circuit simulations. An IM state manifests itself as an abnormal third resistive state, which differs from the two bi-stable states of MTJ. We performed silicon measurements on MTJ devices with diameter ranging from 60nm to 120nm; the results show that the occurrence probability of IM state strongly depends on the switching direction, device size, and bias voltage. We demonstrate that the conventional resistor-based fault modeling and test approach fails to appropriately model and test such a defect. Therefore, device-aware test is applied. We first physically model the defect and incorporate it into a Verilog-A MTJ compact model and calibrate it with silicon data. Thereafter, this model is used for a systematic fault analysis based on circuit simulations to obtain accurate and realistic faults in a pre-defined fault space. Our simulation results show that an IM state defect leads to intermittent write transition faults. Finally, we propose and implement a device-aware test solution to detect the IM state defect., Computer Engineering, Quantum & Computer Engineering

Understanding the defects in magnetic tunnel junctions (MTJs) and their faulty behaviors are paramount for developing high-quality tests for STT-MRAM. This paper characterizes and models intermediate (IM) state defects in MTJs; IM state manifests itself as an abnormal third resistive state, apart from the two bi-stable states of MTJ. We performed silicon measurements on MTJ devices with diameter ranging from 60 nm to 120 nm; the results reveal that the occurrence probability of IM state strongly depends on the switching direction, device size, and applied bias voltage. To test such defect, appropriate fault models are needed. Therefore, we use the advanced device-aware modeling approach, where we first physically model the defect and incorporate it into a Verilog-A MTJ compact model and calibrate it with silicon data. Thereafter, we use a systematic fault analysis to accurately validate a theoretically predefined fault space and derive realistic fault models. Our simulation results show that the IM state defect causes intermittent write transition faults. This paper also demonstrates that the conventional resistor-based fault modeling and test approach fails in appropriately modeling IM defects, and hence incapable of detecting such defects., Computer Engineering, Quantum & Computer Engineering

Understanding the manufacturing defects in magnetic tunnel junctions (MTJs), which are the data-storing elements in STT-MRAMs, and their resultant faulty behaviors are crucial for developing high-quality test solutions. This paper introduces a new type of MTJ defect: synthetic anti-ferromagnet flip (SAFF) defect, wherein the magnetization in both the hard layer and reference layer of MTJ devices undergoes an unintended flip to the opposite direction. Both magnetic and electrical measurement data of SAFF defect in fabricated MTJ devices is presented; it shows that such a defect reverses the polarity of stray field at the free layer of MTJ, while it has no electrical impact on the single isolated device. The paper also demonstrates that using the conventional fault modeling and test approach fails to appropriately model and test such a defect. Therefore device-Aware fault modeling and test approach is used. It first physically models the defect and incorporate it into a Verilog-A MTJ compact model, which is afterwards calibrated with silicon data. The model is thereafter used for fault analysis and modeling within an STT-MRAM array; simulation results show that a SAFF defect may lead to an intermittent Passive Neighborhood Pattern Sensitive Fault (PNPSF1i) when all neighboring cells are in logic '1' state. Finally, test solutions for such fault are discussed., Computer Engineering, Quantum & Computer Engineering

This article describes a software tool for automated probe-mark analysis that minimizes the chance of human subjectivity and error. Researchers have developed a Python-based software tool for automated probe-mark analysis for micro-bumps to characterize the quality of probing of large-array fine-pitch micro-bumps in the context of prebond testing of 3D-SICs. In this article, researchers compare manual and automatic measurements. The results show that the automatic approach yields comparable results with the measured offsets we have gathered by manual measurements, but at a much faster speed. The algorithms in the software tool are deterministic, such that different runs on the same data will give identical results, while the results of the manual approach were often influenced by human subjectivity. The researchers also show their automated approach to be robust in the sense that the tool handles top-view as well as tilted-view images, images with varying SEM contrast settings, and multiple probe marks.