*3.5.1. Micro-contact printing (soft lithography)*

This is known as soft lithography that usually uses the relief patterns on a PDMS (polydimethylsiloxane) stamp in order to form patterns of self-assembled monolayers (SAMs) of ink on the surface of a substrate through conformal contact. This technique has wide range of application in cell biology, microelectronics, surface chemistry, micromachining, Patterning cells, patterning DNA and Patterning protein.

Figure 9 represents the process of Micro-contact printing. This process involves the application of ink to stamp, application of stamp to surface, removal of stamp and residues rinsed off

**Figure 9.** Schematic of the Micro-contact printing process (Courtesy: IBM Zurich)

Advantages of Micro-contact printing:


Limitation in Micro-contact Printing:


### *3.5.2. Nano-imprint lithography*

Nanoimprint lithography (NIL) is an emerging process that can produce sub-10nm features. It is a simple process that uses a mould to emboss the resist with the required pattern. After embossing the resist, compressed resist material is removed using anisotropic etching and the substrate exposed. It can produce features at extremely small resolutions that cover a large area with a high throughput and relatively low cost, which is main advantage of this technique. It can be adapted to transfer all components needed to create a thin film transistor on a plastic substrate. It involves pressing and heating a thin film between a patterned template and a substrate. Upon heating, the patterned film adheres only to the substrate [ref Fig. 10]. This has high throughput and is relatively inexpensive compared to developing extreme deep UV lithography for commercial viability. It is also flexible enough to be used at chip level with several layers or at the wafer level when single layer is required. It can give resolutions lower than 10nm with high throughput at low cost. One of the current barriers to production at these resolutions is the development of mould. It can be used for fabricating nanoscale photodetectors, silicon quantum-dot, quantum wire and ring transistors (Chou, S.Y. 1996)

**Figure 10.** Schematic diagram of the steps involved in the nanoimprint lithographic process [Courtesy: Source: AZo‐ Nano]
