Dissolution of Monocrystalline Silicon Nanomembranes and Their Use as Encapsulation Layers and Electrical Interfaces in Water-Soluble Electronics

Abstract

The chemistry that governs the dissolution of device-grade, monocrystalline silicon nanomembranes into benign end products by hydrolysis serves as the foundation for fully eco/biodegradable classes of high-performance electronics. This paper examines these processes in aqueous solutions with chemical compositions relevant to groundwater and biofluids. The results show that the presence of Si(OH) and proteins in these solutions can slow the rates of dissolution and that ion-specific effects associated with Ca can significantly increase these rates. This information allows for effective use of silicon nanomembranes not only as active layers in eco/biodegradable electronics but also as water barriers capable of providing perfect encapsulation until their disappearance by dissolution. The time scales for this encapsulation can be controlled by introduction of dopants into the Si and by addition of oxide layers on the exposed surfaces.The former possibility also allows the doped silicon to serve as an electrical interface for measuring biopotentials, as demonstrated in fully bioresorbable platforms for in vivo neural recordings. This collection of findings is important for further engineering development of water-soluble classes of silicon electronics.

Materials, Mechanics Designs, and Bioresorbable Multisensor Platforms for Pressure Monitoring in the Intracranial Space

“…These timescales are consistent with those separately reported for each of the constituent materials: Mg, W, lightly doped Si, and highly doped Si dissolve at rates of 50–100 µm d −1 (largely affected by the initial oxidation on the surface), 100–250 nm d −1 , 50–100 nm d −1 , and 5–10 nm d −1 , respectively. [ 14,28,29,32 ] Increasing the thicknesses of the Si MM and PLGA interlayers, the doping concentration of the Si MM and/or the ratio of lactic acid in the PLGA will increase the respective times.…”

“…Previous studies demonstrate that monocrystalline Si membranes are perfect water barriers for timescales shorter than those required for hydrolysis to consume the silicon. [ 28,29,37,38 ] As a result, changes in the resistances of the Mg traces in these experiments result from passage of water through the wax composite material, and then through the PLGA and the interfaces with the silicon.…”

“…Reducing the thicknesses to tens of nanometers can reduce these timescales, but at the expense of increased mechanical fragility. By contrast, lightly doped monocrystalline silicon, which is also impermeable to water, [ 28,29 ] dissolves at a comparatively high rate (50–100 nm d −1 ), to yield dissolution times that are in the range of weeks or months for layers with thicknesses in the micron range. Here, the problem is that the dissolution itself can lead to drifts in sensor performance, at levels that can be significant over timeframes of interest.…”

Bioresorbable Materials on the Rise: From Electronic Components and Physical Sensors to In Vivo Monitoring Systems

“…Two years later, the same research group deepened the understanding on dissolution kinetics of Si NMs in ground‐water and biofluid media . The authors investigated the dissolution rate of Si NMs (B‐doped, 10 15 cm −3 , 200 nm thick) in PBS (1×) spiked with different concentrations of albumin (0.01–35 g L −1 ), Si(OH) 4 (0–300 mg L −1 ) and cations (Na + , Mg 2+ and Ca 2+ , 1 × 10 −3 m ) at 37 °C.…”

“…Similar passive electrodes were fabricated by and Lee et al using Mo traces for electrical connection, instead of a single long Si nanomembrane; SiO 2 was used as encapsulation layer, leaving openings for Si recording regions.…”