Focused Ion Beam Micromachining of Microgratings on Arbitrary Angled Facets on Optical Materials

We have invented a technique for micromachining of fine structures on tiny angled facets using a focused ion beam technique. FIB micromachining for the fabrication of optical/photonic devices is an area of expertise at the UC Nanoelectronics Laboratory (NanoLab). The ability to fabricate a diffraction grating of micrometer dimensions on facets of arbitrary angles on an optic chip is very useful for implementing wavelength-division multiplexing (WDM) technology and integrated optics. However, this task is not compatible with conventional fabrication technologies. In the environment of an optical chip, a large number of tiny, precise optical elements are crowded together. Even slight contamination or minor scratching can ruin the entire optical system. However, it is very common to place an optical surface at a certain angle, or to locate an optical element at a specific position. This factor dramatically increases the difficulty of integrated optical system fabrication.

Advantages

1. Using the new technique, a diffractive optical element can be easily integrated into an optoelectronic device such as a WDM demultiplexer, or a tunable semiconductor laser on the same substrate.

2. Gratings created using this technique have pitch sizes from a couple of hundred nanometers to several micrometers, covering the light band from ultraviolet to infrared.

3. The technique eliminates the need for complicated equipment and programming required by traditional diamond ruling and holographic patterning methods.

4. The micrograting fabrication method can be applied to a variety of materials, including any reasonable conductive material (such as semiconductors and metals), and insulators, with the aid of charge neutralizing devices. As a result, the micromachined grating can be integrated naturally into a conventional semiconductor optoelectronic chip.

Areas of Application

Optoelectronics; fiber optic communications devices; “system-on-a-chip” designs.

*For more information, contact the Intellectual Property Office of University of   Cincinnati, refer Item Number 102004

http://www.ipo.uc.edu/tech/results.cfm?item_number=102004

Focused Ion Beam (FIB) Fabrication

Focused ion beam fabrication and analysis includes milling of GaN bragg gratings for use in solid state lasers.  Most optical devices of GaN-based materials are grown on sapphire because of good crystal quality. However, conventional processing procedures are difficult in forming high reflective laser mirror facets.  This difficulty is mainly due to the large misalignment between sapphire and epitaxial GaN layer. Currently, laser facets are formed by either the cleaving method or by dry plasma etching (which generates a large degree of ion-induced damage). Therefore, the current goal of  this project is to look for a simple and efficient processing technique to fabricate bragg gratings with low mirror loss and proper mode selection for use in laser diodes.  Pictured to the right is milling experimentation done on NanoLab GaN.  Using the same FIB system but with different goals in mind, rare earth dopants have been implanted into a variety of hosts.  As an example, praseodymium has been implanted into GaN and bright red fluorescence obtained that is visible to the naked eye (see top right).  To aid in this leading edge research a liquid metal ion source fabrication station has been constructed and serves the sole purpose of allowing creation of a variety of previously researched and novel implantations sources within the Nanolab.

Applications of FIB implanted materials.

Upconversion luminescence has been obtained from Er-implanted GaN films by focused-ion-beam implantation. FIB implantation was performed on GaN films grown by molecular-beam epitaxy in the Nanolab, hydride vapor-phase epitaxy, and metalorganic chemical-vapor deposition. After implantation, the GaN samples were annealed at 1100° C for 1h in various ambients (Ar, N₂, and O₂). Strong green upconversion was observed at 523nm and 546nm under red (840nm) and infrared (1.0m m) excitation. Upconversion intensity was measured for Er doses ranging from 4.3´ 10¹² to 2.4´ 10¹⁶ atoms/cm². Maximum upconversion intensity at 546nm was observed at a dose of 1~2´ 10¹⁵ atoms/cm², which corresponds to an atomic percentage of 0.3~0.6%.  Upconversion is pictured to the left, with the laser spot size defining the region of emission within the rectangular implant reg