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Direct Laser and Ultraviolet Lithography of Porous Silicon Photonic Crystal Devices
Vanderbilt University inventors have developed a simple method to locally change the optical properties of porous silicon multilayers and photonic crystal architectures. Spatial localization and lithography of photonic crystals are necessary for the employment of Porous silicon photonic crystal structures in integrated applications, such as photonic circuits and biosensor arrays. This game changing technique allows for direct manipulation of the optical properties of these substrates. The various types of structures and devices that this process enables are very cost effective and high quality.
Porous silicon is recognized for its light emission properties and its potential in optical switches, biosensors, solar cells and omnidirectional mirrors
The refractive index of porous silicon can be easily varied by tuning its porosity, making it a building block for thin film optical devices
By alternating layers of low and high porosity, porous silicon photonic band-gap structures can be formed
Current techniques for achieving varying porosities include laser heating and hydrofluoric acid dips, which lead to loss of resolution and cumbersome processing
Lithography and ion beam irradiation can spatially define porous silicon photonic crystals, but these methods require expensive, specialized fabrication instruments.
In this technology a two-step process is utilized to (a) produce porous silicon multilayers and photonic crystal architectures and (b) inhibit the subsequent transformation of optical properties of the structures formed. The direct photolithography method used promotes and controls local oxidation via UV radiation or high intensity (λ=532.8 nm) laser beam exposure of unmasked regions of the sample. Then a subsequent alcohol bath treatment creates spectral degradation selectively in non-irradiated regions only. The power of this technology lies in the fact that conventional silicon processing technologies are used to produce optical and opto-electronic devices for laser, optical computation, telecommunications and other applications. Potential devices include patterned porous silicon waveguides, optical filters, optical switches, and photonic band-gap structures.
Unique Features and Competitive Advantages
First photolithography method to directly manipulate the optical properties of porous silicon multilayers, heterostructures, and photonic crystal architectures
Conventional silicon processing techniques are utilized
Improved quality of devices and reduced costs compared to devices made by currently used processes
Can be used to form waveguides with both vertical and lateral confinement
Intellectual Property and Development Status
Pending US patent application US2009/0111046A1
Spatially localized one-dimensional porous silicon photonic crystals, H. Park, J. H. Dickerson, and S. M. Weiss, Applied Physics Letters, 92, 011113 (2008)