Elastocapillary folding using stop-programmable hinges fabricated by 3D micro-machining

TL;DR

This paper demonstrates precise elastocapillary folding of silicon nitride structures using stop-programmable hinges fabricated by advanced 3D micro-machining techniques, enabling accurate micro-assembly with potential for complex device fabrication.

Contribution

It introduces a novel nano-patterning method for fabricating stop-programmable hinges with precise folding angles, advancing micro-assembly capabilities.

Findings

Achieved accurate folding angles of 70.6±0.1° and 90° in silicon nitride structures.

Developed a batch fabrication process using corner lithography and silicon etching.

Proved the feasibility of micro-assembly with programmable folding angles.

Abstract

We show elasto-capillary folding of silicon nitride objects with accurate folding angles between flaps of 70.6$\pm$0.1{\deg} and demonstrate the feasibility of such accurate micro-assembly with a final folding angle of 90{\deg}. The folding angle is defined by stop-programmable hinges that are fabricated starting from silicon molds employing accurate three-dimensional corner lithography. This nano-patterning method exploits the conformal deposition and the subsequent timed isotropic etching of a thin film in a 3D shaped silicon template. The technique leaves a residue of the thin film in sharp concave corners which can be used as an inversion mask in subsequent steps. Hinges designed to stop the folding at 70.6{\deg} were fabricated batchwise by machining the V-grooves obtained by KOH etching in (110) silicon wafers; 90{\deg} stop-programmable hinges were obtained starting from silicon molds obtained by dry etching on (100) wafers. The presented technique is applicable to any folding angle and opens a new route towards creating structures with increased complexity, which will ultimately lead to a novel method for device fabrication.