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98 DESIGN007 MAGAZINE I APRIL 2022 From those humble and practical begin- nings, the spectrum of wearable electronic products has expanded immeasurably with improvements in materials, manufacturing, and processing technologies in concert with engineering and scientific creativity. Enabling most of the advances has been flexible circuit technology with integrated electronic devices of every imaginable type, including everything from simple LEDs to sensors of every stripe, processors, and even flexible batteries. What has also proven highly enabling to flexible elec- tronic assemblies has been advances in silicon wafer thinning which makes normally brittle silicon integrated circuits truly flexible and bendable (Figure 4). While thinning was developed for die stack- ing, it has proven an important benefit for mak- ing thin flexible electronic assemblies and thus opening doors to new applications. A collabo- ration between the Air Force Research Labo- ratory and American Semiconductor in 2017 produced a flexible silicon-on-polymer chip with more than 7,000 times the memory capa- bility of any current flexible integrated circuit on the market at the time. e manufacturing took advantage of flexible hybrid electron- ics, integrating traditional manufacturing techniques with 3D electronic print- ing to create thin, flexible semiconductors that can augment efforts in wearable technology, asset monitor- ing, logistics and more. 3 In recent years, some of the original terminology used exclusively for flexible has been altered and recast by technology marketers. What was once referred to as polymer thick film flex- ible circuit technology is being rebranded as "flex hybrid electronics" (FHE) and, with the newly intro- duced term fueled by significant funding from the U.S. government (especially the military) and in-kind contributions from players in industry, FHE is making new electronic design industry inroads and bringing new-found attention to time-honored flexible circuit tech- nology, with wearable electronics oen serv- ing as a marquee application under the newly applied terms. For decades, flexible circuits/printed elec- tronics have been employed to solve many challenges and create new solutions to prob- lems; of high interest has been areas related to health, especially remote monitoring of indi- vidual health. Flexible circuits have long been used in medical products such as for the inter- connection of piezo ceramic transducer heads for ultrasonic imaging systems, but they have also been successfully used in catheter diag- nostics, such as for electrophysiology studies to pinpoint and correct heart nerve pathways to mitigate or eliminate life threatening heart arrhythmias. e recent boost in awareness of flexible circuit technology, brought on by the strong marketing of FHE, is causing a rising tide in interest, which is "liing all boats" as increasing numbers of product designers turn Figure 4: Silicon chips are brittle in their as-manufactured state, however, when thinned they can be bent and flexed as shown. (Source: U.S. Air Force)