Technical Abstracts
In Case You Missed It
Components
“FlexiCores: Low Footprint, High Yield, Field-Reprogrammable Flexible Microprocessors”

Authors: Nathaniel Bleier, et al.

Abstract: Flexible electronics is a promising approach to target applications whose computational needs are not met by traditional silicon-based electronics due to their conformality, thinness, or cost requirements. A microprocessor is a critical component for many such applications; however, it is unclear whether it is feasible to build flexible processors at scale (i.e., at high yield), since very few flexible microprocessors have been reported and no yield data or data from multiple chips has been reported. Also, prior manufactured flexible systems were not field-reprogrammable and were evaluated either on a simple set of test vectors or a single program. A working flexible microprocessor chip supporting complex or multiple applications has not been demonstrated. Finally, no prior work performs a design space of flexible microprocessors to optimize area, code size, and energy of such microprocessors.

In this work, the authors fabricate and test hundreds of FlexiCores – flexible 0.8µm IGZO TFT-based field-reprogrammable 4- and 8-bit microprocessor chips optimized for low footprint and yield. They show that these gate count-optimized processors can have high yield (4-bit FlexiCores have 81% yield – sufficient to enable sub-cent cost if produced at volume). We evaluate these chips over a suite of representative kernels – the kernels take 4.28ms to 12.9ms and 21.0µJ to 61.4µJ for execution (at 360nJ per instruction). The authors also present the first characterization of process variation for a flexible processor – the authors observe significant process variation (relative standard deviation of 15.3% and 21.5% in terms of current draw of 4-bit and 8-bit FlexiCore chips respectively). Finally, the authors perform a design space exploration and identify design points much better than FlexiCores: the new cores consume 45-56% the energy of the base design, and have code size less than 30% of the base design, with an area overhead of nine to 37%. (International Symposium on Computer Architecture, June 2022, https://dl.acm.org/doi/10.1145/3470496.3527410)

Materials
“Rapid Photolithographic Fabrication of High Density Optical Interconnects Using Refractive Index Contrast Polymers”

Authors: Julie I. Frish, et al.

Abstract: New polymer optical interconnect materials that the authors term refractive index contrast (RIC) polymers are ideally suited to a wide variety of photonic interconnect applications as the refractive index can be tuned over the range of n = 1.42 to 1.56, while index contrast Δn can be precisely tuned through composition and ultraviolet exposure; the waveguides can be directly patterned in dry films with no wet or dry etching processes required. RIC polymer interconnects thus have the ability to access numerous photonic platforms, including silicon photonic chips, ion-exchange (IOX) glass optical substrates, and optical fiber arrays. The authors demonstrate for the first time efficient single-mode polymer interconnect fabrication via a maskless lithography approach that exhibits low loss adiabatic coupling (~1.5dB at 1550nm) to IOX waveguides through the formation of grayscale tapers. (Optical Materials Express, vol. 12, no. 5, 2022, https://opg.optica.org/DirectPDFAccess/F2850C64-9BF0-449E-9E03207E48AB4EC4_471361/ome-12-5-1932.pdf)

SPC
“Time to Failure Prediction on a Printed Circuit Board Surface Under Humidity Using Probabilistic Analysis”

Authors: Sajjad Bahrebar and Rajan Ambat

Abstract: This paper presents the probabilistic study of time to failure (TTF), which is caused by combinations of various important controllable factors on a printed circuit board (PCB) surface under humidity. The study investigated the impact of four changeable factors including pitch distance, temperature, contamination, and voltage, each at three levels upon the surface insulation resistance test boards. Constant 98% relative humidity with adipic acid as contamination related to flux residue was used for a 20-h parametric experiment. Two main states were considered on the whole output current measurements: the stable part before the short transition phase and the unstable part after due to electrochemical migration (ECM) on the PCB surface. Leakage current (LC) in the first state and TTF at the beginning of the second stage was measured with five replications for each condition as the predictive indicator in all models. The trend of LC and TTF was also investigated on three levels of each factor. In addition, probabilistic distribution analysis using fitted Weibull distribution, multivariate regression analysis, and the classification and regression tree (CART) analysis were used to predict the probability of TTF and failure risk prediction on the PCB surface. All the prediction models had an acceptable prediction of TTF at diverse accuracy levels, according to changing factors/levels. Nevertheless, the multivariate regression analysis had the best prediction, highest R2, and lowest error compared to the other models. (Journal of Electronic Materials, May 18, 2022, https://link.springer.com/article/10.1007/s11664-022-09668-7)

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