Fabrication of micro- and nano-structured materials using mask-less processes

Abstract

Micro- and nano-scale devices are used in electronics, micro-electro- mechanical, bio-analytical and medical components. An essential step for the fabrication of such small scale devices is photolithography. Photolithography requires a master mask to transfer micrometre or sub-micrometre scale patterns onto a substrate. The requirement of a physical, rigid mask can impede progress in applications which require rapid prototyping, flexible substrates, multiple alignment and 3D fabrication. Alternative technologies, which do not require the use of a physical mask, are suitable for these applications. In this paper mask-less methods of micro- and nano-scale fabrication have been discussed. The most common technique, which is the laser direct imaging (LDI), technique has been applied to fabricate micrometre scale structures on printed circuit boards, glass and epoxy. LDI can be combined with chemical methods to deposit metals, inorganic materials as well as some organic entities at the micrometre scale. Inkjet technology can be used to fabricate micrometre patterns of etch resists, organic transistors as well as arrays for bioanalysis. Electrohydrodynamic atomisation is used to fabricate micrometre scale ceramic features. Electrochemical methodologies offer a variety of technical solutions for micro- and nano-fabrication owing to the fact that electron charge transfer can be constrained to a solid–liquid interface. Electrochemical printing is an adaptation of inkjet printing which can be used for rapid prototyping of metallic circuits. Micro-machining using nano-second voltage pulses have been used to fabricate high precision features on metals and semiconductors. Optimisation of reactor, electrochemistry and fluid flow (EnFACE) has also been employed to transfer micrometre scale patterns on a copper substrate. Nano-scale features have been fabricated by using specialised tools such as scanning tunnelling microscopy, atomic force microscopy and focused ion beam. The methodologies adopted for nano-fabrication have analogies with the micrometre scale patterning methods. Currently, the resolution of mask-less techniques is lower than that of lithographic methods using a physical mask. However, in future, hybridisation or combination of the mask-less methods could lead to high resolution and higher precision micro- and nano-scale patterning methods.

Rigorous Coupled‐Wave Analysis of Surface Plasmon Enhancement from Patterned Immobilization on Nanogratings

“…A number of methods have been reported for the fabrication of nanometric metallic gratings or periodic structures, generally based on a metallic lift-off process of an electron-beam patterned polymeric resist or fastreplication techniques [23]. Features smaller than 100 nm have been demonstrated [24].…”

Sono-electrodeposition transfer of micro-scale copper patterns on to A7 substrates using a mask-less method

“…The development of alternative microfabrication technologies which allow batch processing but avoid or minimise repeated and direct patterning of the substrate is therefore of considerable interest [7,8,17]. The Electrochemical nano Fabrication using Chemistry and Engineering (EnFACE) technology is one such method, which has explored the possibility of performing selective deposition or etching on 4 a substrate [18][19][20][21].…”

“…The proposed technique does, however, require careful control of the reactor design, and a narrow inter-electrode gap of less than 500 µm [17][18][19][20]. The thin gap between the electrodes can limit mass transport and anodic or cathodic gas evolution resulting in bubble formation and retention has also been recognised as issue [20][21] which could limit its potential use.…”

“…acid-free) electrolyte [17][18][19][20]. Therefore, in order to fully exploit the potential of the technique, a method to provide adequate mass transfer between the two closely spaced electrodes is essential.…”

Electrochemical Formation of Free-Standing 3D Structures Using Injection of Additives

“…Tip based electrochemical machining has been widely used in the past to subtractively machine metallic or non-metallic structures for microdevices. 10,11 However, electrochemical deposition processes have not been used until more recently for additive formation of 3D metal [12][13][14][15] and conductive polymer [16][17][18] micro-structures. Metal electrodeposition typically involves the reduction of metal ions into metal atoms on a conductive substrate.…”