Accurate and unobtrusive monitoring of surface biopotentials is of paramount importance for physiological studies and wearable healthcare applications. Thin, light-weight, and conformal bioelectrodes are highly desirable for biopotential monitoring. This report demonstrates the fabrication of sub-300 nm thin, dry electrodes that are self-adhesive and conformable to complex 3D biological surfaces and thus capable of excellent quality of biopotential (surface electromyogram and surface electrocardiogram) recordings. Measurements reveal single-day stability of up to 10 h. In addition, the bending stiffness of the sensor is calculated to be ≈0.33 pN m 2 , which is comparable to stratum corneum, the uppermost layer of human skin, and this stiffness is over two orders of magnitude lower than the bending stiffness of a 3.0 µm thin sensor. Laminated on a prestretched elastomer, when relaxed, the sensor forms wrinkles with a period and amplitude equal to 17 and 4 µm, respectively, which these values agree with theoretical calculations. Finally, with skin vibrations of up to ≈15 µm, the sensor exhibits motion artifact-less monitoring of surface biopotentials, in contrast to a wet adhesive electrode that shows much greater influence.

between a human touch, a touch of a metallic object, and no touch, while being immune to noise. Finally, ultralight, at 0.7 g m −2 , it allows for a multitude of applications where the weight of the electronics is of uttermost importance.A fully functioning e-skin, laminated on human subject's hands, is shown in Figure 1 a, with the e-skin device layout depicted in Figure 1 b. It incorporates simple resistive tactile sensors and organic fi eld effect transistors (OFET) used to actively control the sensor information. OFET devices were electrically characterized with recorded average mobility of 0.34 cm 2 Vs −1 , and the ON/OFF ratio of ≈10 5 . Also, the threshold voltage V T , was measured to be approximately −1.72 V. The yield, calculated on 44 devices, was recorded as ≈98%, with only a single faulty device. Following the fabrication process on a rigid glass slide, the devices were manually delaminated and subjected to physical/ mechanical fl exibility tests. The H 2 O-delaminated fi lm was deposited onto a 60% prestretched elastomer that was subsequently relaxed. This resulted in a highly irregular surface, with multiple wrinkles for the fi lm to adhere to. The elastomer was subsequently stretched 100 times to demonstrate good adhesion and physical durability of the devices. The devices were electrically characterized following the physical fl exibility test, with a typical pre-and post-stretched transconductance curves shown in Figure 2 a. It can be seen that the device ON current underwent a marginal increase, with the poststretched average mobility increasing to 0.39 cm 2 Vs −1 , while the OFF and leakage ( I G ) currents, as well as the ON/OFF ratios, remained largely unchanged. The V T also experienced a shift to −1.03 V. Figure 2 b depicts SEM image of an OFET fi lm, placed directly atop of a relaxed elastomer, after the device was electrically characterized. Because the fragile nature of the fi lm did not allow for a direct cross-sectional analysis, angled top view was analyzed instead. The shown image reveals extremely folded and compliant nature of the fi lm. Detailed analysis of the inset reveals a folded edge of the fi lm (top right corner), allowing for extrapolation of a bending radius to being less than 2 µm. This, we believe, is the primary reason why our fi lm can undergo such extreme bending, folding and elastomer stretching, while preserving its good electrical performance.The CVD-deposited biocompatible Parylene serves as the top and bottom (substrate) encapsulation layers, making it an ideal candidate for external and internal medical applications. [27][28][29][30] For our initial investigations of the biocompatibility of our e-skin, we have chosen a relatively simple and safe test, namely The ability to accurately monitor 3D structures, for instance changes of temperature or shape of printed circuit boards, packaged food, or biological organs, without affecting the structure being monitored, presents a unique set of challenges and has been termed imperceptible electronics. [1][2][3][4][5] ...

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