Patented Precision Patterning of Multiple Dichroic Coatings

Dichroic Filter Array Patented Patterned Coatings Technology
Innovative techniques pioneered by Ocean Thin Films are ushering in a new generation of optical filter technologies. Traditional patterning processes such as metal masking or dicing & re-assembly, have significant drawbacks that are overcome by the use of microlithographic technologies.

Optical Coatings with Microlithographic Precision
Ocean Thin Films has pioneered an optical coatings production methodology that combines modern optical thin film deposition techniques with microlithographic procedures. This patented process enables micron-scale precision patterning of multiple optical thin film dichroic coatings on a single substrate.

With its new process, Ocean Thin Films can create multi-patterned arrays of different optical filters for use in multispectral sensors, dense wavelength division multiplexers, micro-electro-mechanical devices (commonly referred to as MEMS) and optical waveguide-based devices. The process also can be applied to multi-part bonded filter applications common to the manufacture of digital data projectors and CCD camera detectors. In fact, a wide variety of optical coatings can be patterned, including dielectric multi-layer reflectors, bandpass filters, dichroic edge filters and broadband anti-reflection coatings. In addition, the Ocean Thin Films technique can be used to deposit enhanced metal reflectors, low-reflectivity opaque metals and electrically conductive transparent patterns.

The Ocean Thin Films Process
The production of a patterned optical multi-layer coated element begins with the application of photoresist to the surface. To generate a pattern, we align the mask and then expose and develop the photoresist. This creates a resist pattern on the coating surface. Next, the prepared substrates are placed into a vacuum chamber for controlled deposition of the multi-layer coating.

After deposition of the filter, the patterned coating is rinsed in solvent, which removes any unwanted multi-layer and resist leaving the desired patterned filter coating. This sequence can be repeated as needed, allowing multiple filters to be deposited.



Advantages of the Precision Patterning Process
Because the Ocean Thin Films process relies on precision microlithography instead of cut metal masks to pattern the deposited coatings, features as small as 2 µm can be produced, with spatial registration to within 1 µm. There are other advantages as well:

Undesired "shadowing" or thickness drop-off of the coating at pattern edges -- unavoidable with cut masks -- is eliminated due to the pattern edge break produced in the lift-off process. Intricate coating patterns of any shape or size can be manufactured without the machining limits inherent to metal masks. The cost of microlithographic tooling does not increase significantly with pattern complexity. Cut metal masks are less durable than microlithographic tooling. Metal masks must be cleaned often to remove coating deposits, and can be easily damaged in handling.

Patterned dichroic filter coatings have optical and physical properties comparable to traditional non-patterned coatings, and have very high resistance to humidity and temperature. And because the coatings are applied directly to substrates and devices, their mechanical resistance to shock and vibration is an improvement over commonly used bonded discrete filter windows.

Implications for Design Engineers
Photonics technologies are becoming smaller and more commonly integrated into microelectronic and micromechanical systems. With our dichroic filter-making process, engineers can integrate wavelength-selective filtering structures much earlier into the design process. What's more, because the deposition process delivers multi-layer optical structures directly onto a component, it is no longer necessary to make a physical transition from micron-sized, on-chip structures to macroscopic diced and bonded optical filter elements -- and back again -- for wavelength-selective integrated optoelectronic and optomechanical devices.

For example, optical bandpass filters can be deposited directly onto waveguide structures or active photodetector regions, to create microscopic wavelength-selective detectors.

Multi-layer RGB color filters can be produced as a single filter array for devices such as CCD camera detectors and LCD display panels, or as a rotating filter wheel for projection display applications. Selected bandpass filters can be combined in arrays for use with multi-spectral detector systems, or patterned in a ring structure in industrial and medical fiber optic instruments. Also, patterned bandpass filters can be used in dense wavelength division multiplexer and photonics-based microprocessor applications. Optical filter coatings can be deposited onto MEMS structures to form "tunable" filter elements, waveguide relays, and switches (from deposited reflector and beamsplitter coatings) on micromechanical mounts.

Ocean Thin Films has pioneered an optical coating technology that provides a precise, cost-effective means to integrate a variety of optical thin film coatings into the design and manufacture of an entire new generation of opto-mechanical and opto-electronic devices.