Proton Beam Writing:Protons being ~2000 times heavier than electrons have minimum proximity effect & have straight trajectories while penetrating resist materials. It can also be scanned and deflected on demand by electromagnetically or electrostatically. Moreover, protons can be focused though not as fine as electrons.

This results in straight walls, high aspect ratio, possibility of multilevel structures. In principle, any geometric shape can be fabricated.

Physical processesDue to interaction of Radiation with PMMA:SIMULATED

Electron beam lithography:

• Finely focused electron beam• Beam forming system• Scanning facility• On-demand beam deflection system

Structure fabricated by electron beam lithography

Electron beam interacts with resistand undergo elastic and in-elastic collisions.elastic collisions lead to deflection of beam while, in-elastic collisions lead to energy loss. Scattering process leads to broadeningof structure. Broadening is minimizedby using higher energy electron beam.Rest of the process is similar to photolithography

Electron source: electron (source) – electron (matter) collision: • large scattering (low mass & high kinetic energy)• 50 keV electrons can penetrate 40 µm deep PMMA• lateral spread of about 20 µm

100 µm

SOFT LITHOGRAPHY – non photolithographic technique

a) Micro contact printingb) Moldingc) Nanoimprintd) Dip Pen Lithography

Micro contact printing: elastomeric stamp with relief on its surface to generate patterned SAMs on the surface of both planar and curved substrates

Nanoimprinting:A metallic or a robust stamp is fabricated withdesirable features.

The metallic stamp is pressed against a suitable polymer substrate for prototyping – called replication.

Nanoimprinting is a technique where stamp is pressed at hot condition (~ glass transition temperature of the polymer where the pattern is replicated) and released at low temperature.

Briefly the process is referred to as hot embossing and cold release.

Features – high through put

Ni- stamp

Polycarbonate

Nanoimprint – hot embossing

Replica by cold release

Polycarbonate

Overview of schematic representation for the fabrication process

a) patterning positive tone photoresist

b) Sample developed, leaving behind cylinders of resist

c) Heat the sample above Tg, the resist melts andReflow to form spherical microlens

e) Ni – sulphamide (over) electroplating

d) Thin metal coating for electical contacts

f) Ni- Stamp delamination

g) Nanoimprint Lithography

h) Prototyping Replication

Silicon wafer

20nm Cr

200nm Au

10µm PMGI resist spin coated

PMGI: polymethylglutarimide

Polymer microlens replication by Nanoimprint Lithography using proton beam fabricated Ni stamp

Microlenses and microlens array are finding applications mainly in the domain of optical microsystems, e.g. optical trapping, optical interconnects, biomedicalinstruments, optical data storage and optical communications. Such a wide range of potential applications of these microphotonic devices have attracted a lot of different types of fabrication techniques. The fabrication of 3D lenses and array of microlenses are attempted using different types of micromachining techniques, for example: reflow of photoresist, LIGA, e-beam writing, polymer surface controlled microlens, eximer laser, focused ion beam – milling and deposition of SiO2, MeV proton deep lithography. Each of these fabrication techniques has its own advantages and disadvantages, mainly with respect to physical type, quality of the microlenses and fabrication time.

Polymer microlens replication by Nanoimprint Lithography using proton beam fabricated Ni stamp

In this regard, proton beam writing (PBW) technique, which is a direct write method, has been shown to be an effective one in constructing such microlens array. Inspite of several positive features about fabrication by of PBW, it is comparatively a slow process. In order to have a large scale production of such microstructures, the following criteria needs to be fulfilled – (a) high through-put, (b) cost effective and (c) ability to fabricate a high quality metallic stamp for fast replication/prototyping.

A schematic flow chart of the above procedure is shown in Fig. 1. A 2 MeV proton beam focused to a spot size of 1 lm · 1 lm, was scanned magnetically over an area of 400 lm · 400 lm. The scanning was done in such a manner that array of desired circular features were unexposed. Such a patterned resist was developed in a mixture of 1-methoxy- 2-propanol-acetate :ethanolamine : de-ionised water at a volume ratio of 60:20:5:15.

This gave rise to pillar like cylindrical resist, which was heated above glass transitiontemperature, at 290 C for 30 min. The resist melted and due to surface tension these array of cylindrical resist took a shape of spherical microlens array. A thin layer of second metallization, i.e. Ti, was coated on top surface which acted as a cathode base for metallic electroplating. The metallic stamp was delaminated from polymer layer by immersing in toluene. This metallic stamp with a base of 500 lm thickness was used for Nanoimprint Lithography(NIL). The surface of the stamp featuring structures for replicating microlens array required cleaning by diluted hydrochloric acid and rinsed with isopropyl alcohol.For NIL prototyping, the metallic stamp was hot embossed against 500 lm polycarbonate (PC) sheet (refractive index of 1.587) for 30 s at 150 C and 30 bar pressure in a Nanoimprinter. In this method, array of spherical microlenses and different dimensions of cylindrical lenses were replicated on PC sheet.

The optically measured focal lengths (f) were found to be in good agreement(Fig. 5) with those calculated using the following equation: f = R/(n -1), where R (the radius of curvature) = (r2 + h2)/2h; where r = half the aperture, i.e. width of the lens and h is the height of the fabricated lens and n = refractive index of the material.

Sol-gel

Generation of a dispersion of colloidal particles suspended in Brownian motion within a fluid matrix.

Colloids are suspension of particles of linear dimensions between 1nm and 1 m. The colloidal suspensions can subsequently convert to viscous gels and then to solid materials

Sol-gel preparation leads to the greatest possible homogeneous distribution of the dopant ion in the host matrix.

Products have high purity and homogeneity, ease of processing and composition control

Sol-gel synthesis involving following steps Ageing Gelation Drying Densification

Needs for bioceramics: dental, knee, hip and temporomandibular joint replacements

Coating of Lenses for

• Head lamps• Fog lamps• Rear lamps

Focus: Automobile

Increasing demand for lighter designs, more safety and comfort create possibilities for novel coatings

Increasing demand for lighter designs, more safety and comfort create possibilities for novel coatings

Exterior• AntiScratch Coatings for polycarbonate glazing• Easy-to-Clean for sensors, windscreens, headlamps

Interior• Instrument covers• Lighting covers• Control elements• Light guides

Uncoated Coated

Sol-gel technology

R

OH

OHHO

Si

Silane/ Siloxane

Sol-gel process

Sol

Application/hardening

Dilution

Coating withnano-scaled structures

Spray coating flood coating

Thermal

RT, T, IR, Laser

Radiation

UV, VIS, Laser

Application and hardening

E-Beam

e-

Summary

Coatings help to

add functionality to interior lighting parts

keep them bright under difficult operating conditions

improve cleanliness of control elements

Coatings: One way to upgrade interior lighting partsCoatings: One way to upgrade interior lighting parts

Questions?