Non-Lithographic Silicon Micromachining Using Inkjet and Chemical Etching

Abstract

We introduce a non-lithographical and vacuum-free method to pattern silicon. The method combines inkjet printing and metal assisted chemical etching (MaCE); we call this method “INKMAC”. A commercial silver ink is printed on top of a silicon surface to create the catalytic patterns for MaCE. The MaCE process leaves behind a set of silicon nanowires in the shape of the inkjet printed micrometer scale pattern. We further show how a potassium hydroxide (KOH) wet etching process can be used to rapidly etch away the nanowires, producing fully opened cavities and channels in the shape of the original printed pattern. We show how the printed lines (width 50–100 µm) can be etched into functional silicon microfluidic channels with different depths (10–40 µm) with aspect ratios close to one. We also used individual droplets (minimum diameter 30 µm) to produce cavities with a depth of 60 µm and an aspect ratio of two. Further, we discuss using the structured silicon substrate as a template for polymer replication to produce superhydrophobic surfaces.

Silicon chambers for enhanced incubation and imaging of microfluidic droplets

“…The surface of Si is flat, and easy to micro pattern and modify, for instance to tune wettability. 48,49 Those benefits have led Si to be used as substrate for industrial DNA synthesis. 50 Digital PCR in arrays of Si microchambers (where the PCR reaction is directly done in a micrometric Si chamber rather than in droplets) has been demonstratedhighlighting the good thermal performance of Si.…”

Silicon as a microfluidic material for imaging and incubation of droplets

“…We reasoned that Si - a crystalline material - would make better droplet chambers than PDMS - an elastomer - because it is more mechanically rigid, more thermally conductive, more reflective and less permeable to water vapor (Table S1). The surface of silicon is flat, and easy to micro pattern and modify, for instance to tune wettability 46,47 . Those benefits have led Si to be used as substrate for industrial DNA synthesis 48 .…”

Fabrication of Ultra-High Aspect Ratio (>420:1) Al2O3 Nanotube Arraysby Sidewall TransferMetal Assistant Chemical Etching

“…With the continuous request for high performance nanotube-based devices, the aspect ratio of the fabricated nanotube arrays as obtained by tailoring electrochemical conditions is far from satisfactory. Metal assisted chemical etching (MacEtch), first reported by Li and Bohn in 2001 [18], offers a promising wet etching solution for generating silicon nanostructures [19][20][21][22]. In addition, the MacEtch of germanium (Ge) [23] and III−V compound semiconductors, such as GaN [24,25], GaAs [26][27][28], GaP [29], InP [30], AlGaAs [31], InGaAs [32], and InGaP [27], have also been demonstrated.…”

“…This method has the benefits of inherent simplicity, a low cost, high versatility, and high reproducibility, making it attractive for preparing silicon nanowire arrays. The conventional method for generating micrometer, submicrometer, and nanosized silicon structures with high aspect ratios [19][20][21][22] is by submerging a metal-coated Si sample into an etchant solution composed of hydrofluoric acid, hydrogen peroxide solution, and a diluting agent. Furthermore, large-area uniform micro-gratings with well controlled morphological features and depths as large as 80 µm have also been successfully produced by optimizing the MacEtch method [33].…”