The advent of peptide microarray technology now offers a unique platform for studying the full spectrum of peptide attributes in a massively parallel, miniaturized, and automated fashion (23, 31). Using peptide microarrays to explore peptide binding to soluble, recombinant MHC class II molecules represents a departure from traditional one-peptide-at-a-time assays. It allows the simultaneous evaluation of the binding behavior of thousands of peptides for soluble MHC class II molecules, which would require considerable investments of time and patient material if more traditional approaches were implemented. We report here, as a paradigm, the use of a peptide microarray chip to determine the binding of soluble MHC class II molecules to immobilized candidate peptides from human immunodeficiency virus type 1B (HIV-1B). The MHC class II binding groove, unlike that of MHC class I molecules, is open at both ends and thus allows spatial interaction with test peptides linked to a scaffold (32, 33, 38).
If cases and controls are not genotyped together on the same chip, extra effort must be made during quality control and subsequent analyses to minimize artefacts (for example, by adding the genotyping batch as a covariate in the analyses). It should be noted that although samples are assumed to be a random draw from the population, this assumption is not the case in the presence of participation bias and unmatched socio-demographic factors17,47.
Die Fugger 2 Download Chip
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An on-chip solution for health monitoring of semiconductor power switches subjected to thermo-mechanical metal fatigue degradation is proposed. The fatigue detection relies on the correlation between the progress of the main failure mechanism, which is critical to the functionality of the device, and a parallel degradation of a non-critical sensing structure using a different mechanism. Both mechanisms are driven by the same cyclic thermo-mechanical load. This study specifically develops a sensing structure for detecting power metallization aging through electrically detectable ratcheting behavior in the routing metal layer underneath. Experiments have been carried out on a dedicated test structure with electrical sensing of the health monitoring structure. Meanwhile, the main degradation progress was observed via scanning electron microscopy in regular intervals. Results show that the proposed approach will reliably work only for detecting degradation driven by repeated high overload events.
The aforementioned studies belong to the well-established field of system-level or in-lab health condition monitoring. Our work is focused on on-chip level implementation, which is considered a pioneering field that has been less explored in the literature. Ritter and Pfost [10,11,12] made a relevant contribution in the field of DMOS power technologies.
Ritter and Pfost investigated the use of non-vital, inner layer metal meanders to detect aging of vital metal structures in the same layers as the meanders. This study was performed on a lateral DMOS technology with promising results. The monitoring solution proposed here is also based on the implementation of an on-chip non-vital structure that degrades due to thermo-mechanical stress. Unlike the proposal showed in [10], a non-vital structure in an inner aluminum layer is meant to be used for detecting aging of the top copper metallization. This notion is due to the solution proposed in [10,11,12] that is not directly applicable to the sheet power metallization of a vertical technology. Degradation of the inner non-vital structure is driven by thermo-mechanical stress as is the degradation of power metallization. Nonetheless, the degradation mechanism is different. Such a structure has an electrical signature that varies with its degradation status, and a dedicated on-chip circuit can read it. The very goal of this research is to investigate the relation between a change in the electrical signature and the degradation status of the power metallization. Given that power metallization fatigue is a common reliability concern [13], the testing method proposed in this study can be relevant to several different power technologies.
We investigate a dedicated test-chip, which reproduces the same thermo-mechanical behavior of a DMOS power switch. The test-chip contains the fatigue-monitoring structures under investigation. An on-chip polysilicon resistor generates heat. This condition allows us to perform thermal cycling and has the samples experience thermo-mechanical fatigue. The test-chips designed for this technique are called poly-heaters [18]. A more detailed description of the test-chip is provided in Sect. 4.
Section 5 describes the equipment used for thermal cycling and microscopy analysis. Thermal cycling is performed in an airtight chamber, with forming gas flowing to prevent chip oxidation. The SEM is used for taking a picture of the power metallization of each sample before and after cycling (Figs. 4, 5, 6, 7, 8,9). The variation of the thermal cycling parameters, such as peak and base temperatures and pulse duration and period, affect degradation processes. A way to validate the proposed monitoring principle is to compare the effect of cycling parameter variations on ratcheting-induced short-circuit occurrence and power metal degradation. If the variation of a parameter has a modest effect on one of the two degradation processes and a dramatic effect on the other, then the proposed health monitoring principle is unreliable.
The test-chip used for this experiment is a simplified structure that emulates the thermo-mechanical behavior of a DMOS power switch without including any DMOS active area. As anticipated in Sect. 3, a resistive polysilicon layer heats the chip. Figure 1 shows the basic structure of the test-chip. The large black rectangle connected to the relative pad represents the perimeter of the power metallization. The blue rectangles represent the aluminum lines. The light-brown area represents the polysilicon resistor. The relative contacts can be found at the top and bottom. The yellow squares represent the vias connecting the aluminum lines to the power metallization. Proportions are not respected in this pictures: the real aluminum lines have a different aspect ratio, with a bigger length compared to the width, and they are present in a larger number. In the technology considered here, aluminum lines may or may not have vias connecting them to the power metallization. The latter acts as a source terminal.
Setup schematic. The dashed line encloses the components that constitute the test-chip. The power metallization and the metal line only have a connection terminal that simultaneously acts as a force and a sense terminal
The voltage source V1 provides a constant voltage that keeps the test-chip at a base temperature of 80 C. The switch driver opens the switch S1 and closes switch S2 to apply a pulse. Then, switch S2 is opened, and switch S1 is closed to end the pulse. 2ff7e9595c
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