Materials Processing and Fabrication

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A great amount of research effort is devoted to developing new ways to apply materials to substrates in extremely thin organized layers so as to improve performance and to make the large scale manufacturing of devices economical. Some techniques that are practical for developing a single device with record breaking efficiency would not work for making millions of devices in a production line. Also engineers must be concerned with the durability of devices under real world conditions of heat, moisture and oxygen. At the same time new nanotechniques and self assembly make it possible to build novel structures virtually one molecule at a time.

See Wikipedia Microelectromechanical systems


Microfabrication Overview

Much microfabrication is done in cleanroom facilities such as that at the Washington Technology Center

Crystallization and Deposition Techniques

Spin coater

Physical

Bulk Crystal growth

Evaporation

Sputtering

doping

Micro-printing

Chemical- epitaxial growth techniques

Liquid phase epitaxy Molecular Beam Epitaxy MBE

Chemical vapor depostion MOCVD

CBE

Self Assembly

Current research into Self Assembled Materials is pointing to ways that thin layers can be built up in a highly organized manner. This provides more control of the dipole moment of applied surfaces.

Molecular Workbench simulation for electrostatic self assembly

Self assembly nanotechnology

Patterning - Lithography

Photolithography

negative process

positive process

soft lithography

Lift - off process

Resist processing

Exposure Nanoimprinting


E-beam Lithography

X-ray lithography

Soft Lithography

Thermomechanical nanolithography

Metallization

Ohmic contact

An intimate metal contact with a semiconductor such that the current voltage curve is linear and symmetric. This is typically created with a vacuum deposited metal coating.

Schottky contacts

Annealing

Etching

wet etching

dry etching

plasma etching

Rapid thermal processing

and annealing

Holography

Passivation and packaging

Poling

Optically assisted poling

Electric Field poling

Optoelectronics Fabrication

Polymer waveguide fab: RIE

Reactive Ion Etching of a polymer with applied mask

Reactive Ion Etching (RIE) is used to convert a slab waveguide into a channel waveguide.

  1. First a slab is prepared with a core layer (higher index of refraction) is placed on a polymer undercladding on a silicon substrate.
  2. A metallic photo mask is applied to protect the core material.
  3. A plasma of oxygen is used to eat away the unmasked portion of the polymer.
  4. The metalic mask is removed and the ribbon of core material is fully encased with overcladding.

Sol-gel waveguide fabrication

Sol-gel waveguide fabrication (including gray scale masking)

This technique builds a complex sol-gel waveguide using completely wet techniques (no vacuum required). Direct illumination by UV through a mask is able to fix portions of the core in place, while unfixed portions are washed away. A series of steps like this can be used to build a complex device.

Polymer waveguide fab: Results

Etched polymer waveguide

The company Photon X has commercialized the polymer waveguide process. The SEM (5micron line shown) shows very smooth sidewalls from a high quality etching process. Walls can only have roughness of 40-50 nm before there is significant optical loss. The polymer waveguide shows excellent light transmission through a 4 mum x 4 mum waveguide core that has been designed to couple very well with an optical fiber.

See Yeniay [1]

Polymer waveguide fab UV curing

Two waveguides produced by UV photo curing process

This waveguide is created using the same UV curing process that is used with sol-gels. This shows two waveguides very close to each other. The channel is very difficult to control using photo etching process. The SEM shows a little cross striation but overall very good quality results.

See Viens 1999 [2]

Polymer athermal Array Waveguide Gradiant AWG filter

Measured fiber-to-fiber transmission spectra

An array waveguide gradiant is used to separate out wavelengths into separate ports. To characterize the device you shine a variety of wavelengths through the device simulating various information carriers and then measure the output from each port. The fluorinated polymer device was able to achieve these results:

  • Insertion loss: 3 dB
  • Adjacent crosstalk: -30dB
  • Non-adjacent crosstalk: -28 dB

This passive polymer technology is being used to connect servers (interconnects) in server forms over very short distances with tremendous data rates.


Temperature dependence.png

An athermal device performs equally well at different temperatures without temperature control.

Wavelength Temperature Dependence dλ/dt :

  • without superstrate: 12pm/ °C
  • with superstrate: - 0.5pm/ °C

See Gao 2002 [3]





References

  1. Yeniay, et. al. J. Lightwave Tech. 22, 154
  2. Viens, et. al. Proc. SPIE (1999)
  3. Gao, et. al. European Conference on Optical Comm.2002
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