Conductively coupled flexible silicon electronic systems for chronic neural electrophysiology

Abstract

Materials and structures that enable long-term, intimate coupling of flexible electronic devices to biological systems are critically important to the development of advanced biomedical implants for biological research and for clinical medicine. By comparison with simple interfaces based on arrays of passive electrodes, the active electronics in such systems provide powerful and sometimes essential levels of functionality; they also demand long-lived, perfect biofluid barriers to prevent corrosive degradation of the active materials and electrical damage to the adjacent tissues. Recent reports describe strategies that enable relevant capabilities in flexible electronic systems, but only for capacitively coupled interfaces. Here, we introduce schemes that exploit patterns of highly doped silicon nanomembranes chemically bonded to thin, thermally grown layers of SiO as leakage-free, chronically stable, conductively coupled interfaces. The results can naturally support high-performance, flexible silicon electronic systems capable of amplified sensing and active matrix multiplexing in biopotential recording and in stimulation via Faradaic charge injection. Systematic in vitro studies highlight key considerations in the materials science and the electrical designs for high-fidelity, chronic operation. The results provide a versatile route to biointegrated forms of flexible electronics that can incorporate the most advanced silicon device technologies with broad applications in electrical interfaces to the brain and to other organ systems.

Flexible Sensors—From Materials to Applications

“…Si has been implemented in flexible sensors in the form of amorphous-Silicon (a-Si) [26,[204][205][206], polycrystalline silicon [27,28,[207][208][209][210][211][212][213], Si nanowires (SiNWs) [214][215][216], and crystalline silicon nanomembranes (SiNMs) [30,31,72,[217][218][219][220][221][222][223]. Amorphous silicon was largely employed as the active material on LCD matrices, and later transitioned for flexible sensors as a strain sensitive layer [206], semiconductor on on-site signal processing circuits [205], or as part of X-ray photodetectors [26,204].…”

“…While LTPS has been used for flexible sensors, the fabrication of this material through ELA is costly and complex. In comparison, although SiNMs are also complex to fabricate, they show superior properties compared to both a-Si and LTPS, such as mobility up to 800 cm 2 V -1 s -1 , I on /I off ratio of 10 7 and lower subthreshold swing of 210 mV/dec [217,222]. SiNMs are monocrystalline nanometer thick structures that are typically patterned and obtained from standard silicon on insulator (SOI) wafers.…”

“…Dielectric materials are typically employed in flexible sensors as part of field-effect transistors used to detect or process the desired signals, as well as part of capacitive sensors. Dielectrics compatible with flexible substrates are either inorganic, such as Al 2 O 3 [23,33,34,217,237], SiO 2 [14,15,28,30,31,34,217,218,222], HfO 2 [289,290], TiO 2 [13], or organic materials e.g., polyvinylphenol (PVP) [29,239], polyvinylpyrrolidone [170], poly(perfluorobutenylvinylether) CYTOP [10,291], PDMS [25], polylactide (PLA) [292,293], poly(vinylidene fluoride) PVDF [294][295][296], PVDF-Trifluoroethylene (PVDF-TrFE) [11,[297][298][299][300][301][302], or GO [303]. Al 2 O 3 is widely used in flexible sensors due to the possibility to deposit this material using atomic layer deposition (ALD) at room temperature (33 • C) and obtain dense (2.5 g/cm 3 ) films with a dielectric constant of 7.5, a breakdown voltage of 3.7 MV/cm and leakage currents below 10 -7 A/cm 2 (5 V bias) [304].…”

Physical sensors for skin‐inspired electronics

“…Furthermore, electrophysiological sensors can record important information about health by visualizing human body electrical signals into diagrams, such as the electrocardiogram (ECG), electromyogram (EMG), and electroencephalogram (EEG) . Various flexible and conformable electrophysiological sensors have been developed for long‐term monitoring electrophysiological signals.…”

Investigation of Low‐Current Direct Stimulation for Rehabilitation Treatment Related to Muscle Function Loss Using Self‐Powered TENG System

“…Various implantable devices are developed for healthcare monitoring purpose, such as chemical sensors to detect glucose and lactate, [1,2] flexible electronics to record electrophysiological signals, [3] optoelectronic photometers to monitor neuronal dynamics, [4] and pressure sensors for blood flow monitoring [5] and orthopedic applications. Various implantable devices are developed for healthcare monitoring purpose, such as chemical sensors to detect glucose and lactate, [1,2] flexible electronics to record electrophysiological signals, [3] optoelectronic photometers to monitor neuronal dynamics, [4] and pressure sensors for blood flow monitoring [5] and orthopedic applications.…”