IAD vs. Multi-Cavity Interference Filters

Awareness Technology uses Ion Assisted Deposition (IAD) filters which are more expensive, but will give superior performance far longer than multi-cavity filters, resulting in reduced service costs and down-time for filter replacement.

Awareness Technology specializes in optical design, and has always considered filter quality to be of major importance in achieving photometric accuracy and, therefore, reliable test results. Because of this consideration, Awareness Technology chooses only Ion Assisted Deposition (IAD) filters when manufacturing Stat Fax and ChemWell instruments.  IAD filters are also referred to as “hard coat” filters.

Before IAD technology was commercially available, Awareness Technology used the best quality 3-cavity sealed interference filters on the market.  In 1993, after extensive testing of regular production lots of both types of filters, Awareness Technology confidently made the change to superior filters; ones produced using IAD technology.

What is IAD?

Prior to the 1990's, narrow-band interference filters were subject to instability and deterioration due to humidity, aging, and temperature changes, resulting in low peak transmittance and out-of-band transmittance ("leakage").

Filters manufactured using IAD technology and processes are vastly superior to sealed soft-coated interference filters especially in terms of stability and longevity.

IAD is an advanced coating process that yields significant reduction in film porosity in an effort  to solve the stability problems inherent to soft coated filters. The principal function of IAD is to bombard the coating material with accelerated ions to densify the coating.

An ion gun is directed at the substrate, and when energized, establishes a plasma stream of high energy particles flowing toward the substrate. As the accelerated ions collide with the coating material at the substrate, the coating material is compacted creating a dense film structure.

Filters produced using IAD have demonstrated spectral shift characteristics approaching and often achieving zero, comparing very favorably with the 10 to 20 nm shift typical of conventionally deposited coatings.

Testing

Both types of filters were tested in an environmental test chamber (temperature and humidity) that was designed to simulate MIL-STD-810C for the purpose of testing the environmental integrity of the filters. Each day in the test chamber corresponds to approximately 1 year of operation in extreme (high) temperature and humidity.  Filters were tested for 7 days and checked for delamination, visible deterioration and %T changes periodically, with a final inspection and assessment on day 7.

The multi-cavity filters exhibited incipient delamination sometimes as early as the third day in the test chamber, and most failed at the end of 7 days, either by delamination or >10% increase in %T.

View Multi-cavity filter - clouded after 3 day test

View Multi-cavity filter - delaminated after 7 day test

Over the course of 3 years, we continued environmental testing of filters from every production lot. A sample filter was randomly selected and placed in the test chamber. With very few exceptions, the IAD filters passed the tests of their physical integrity, %T and exhibited no significant peak shift.

View IAD filter - after 7 day test

In another test, a set of filters (340, 405, 450, 492, 545, 600 - IAD type) were placed outdoors and exposed to direct sunlight, rain and temperature extremes typical of South Florida. After 2 years, the filters had no significant change in physical integrity, %T or peak shift.

Because we use these higher quality, longer lasting, more expensive filters, we may not always compete on price alone with companies selling cheap instruments with low quality filters.  When a competitor's instruments are brand new, their filters may give adequate results, but as the filters deteriorate, results can become unsatisfactory. It is important that customers realize the long-term value and the advantages of IAD filters over the multi-cavity type. The small additional cost of IAD technology filters is negligible when compared to the advantages in added dependability and overall performance of the instrument over many years.