Handbook of Modern Coating Technologies
Nanoimprinting
| FIGURE 5-10 Image of a separately standing line of a protrusion with a high-aspect ratio and a characteristic width of 22 nm—obtained by exposure to focused 2-MeV proton beam [127]. |
| Au |
| Cr |
| FIGURE 5-11 Schematic of nanostamp fabrication by PBW technology [129]. PBW, Proton beam writing. |
Projection optical, X-ray, and electron- and ion-beam lithographies are most frequently used for batch production of small-sized structures arranged with high density over a large area. However, the technical complexities and the anticipated increase in the manufacturing costs of producing sub-100-nm structures necessitate the search for alternative solutions. The combination of lithographic technologies using focused charged particle beams with nanoimprinting may be a method of choice for some specific purposes [129,130]. By way of example, Fig. 5—11 shows a process flowchart for manufacturing 3D stamps relying on PBW technologies and Ni electrodepositron. The Si(100) substrate is first covered with Cr (20 mm) and Au (200 mm) layers to enhance adhesion and electric conduction, then a layer of polymethyl methacrylate (PMMA) resist is centrifugally deposited and irradiated by a focused proton beam with an energy of 2 MeV (Fig. 5—11A). Thereafter, another metallic layer is laid on the upper surface to form the stamp base and ensure the conductivity needed for
electrodeposition (Fig. 5—11B). Treatment with a developer results in a three-dimensional structure (Fig. 5—11C), then a nickel electrodeposition is executed (Fig. 5—11D). The process is completed by separating the stamp from the template (Fig. 5—11E) and nanoimprinting (Fig. 5—11F). Such stamps can be reused up to 15 times in succession without an appreciable deterioration of reproducibility.
- Biophysics and medicine
The narrow channels produced by PBW technology are tens of nanometers wide and their height is a few dozen times greater than the width. They can be used to study biomolecules. Fig. 5—12A depicts a prototype biosensor structure (interdigital electrodes with a gap of ~85 nm). Information about biomolecules is derived from the measurement of total electric resistance between the electrodes. Inasmuch as each specific type of biomolecules has a definite electrical conductivity, such a sensor can be applied to study various biomolecules, including simple toxins (e.g., formaldehyde), large DNA sequences, hormones, and more specialized biomolecules, such as anti-HIV antibodies.
| FIGURE 5-12 An image of a nanobiosensor structure. (A) Optical components produced by proton beam writing. (B) Images of a ring resonator created in a layer of SU-8 resistive material on an Si substrate; the inset shows a well-defined space with specific features of 200 nm in size. (C) Optical image of a microlens array fabricated from a 15-mm thick PMMA resistive material [131]. |
