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Tantalum Oxide Tablets for High Quality Coatings

Posted 4 years ago and updated 1 week ago
Category: Product News

Lorad can now offer high quality, US manufactured, Tantalum oxide tablets for thin – film optical coating applications. Bulk manufacturing of Tantalum oxide Tablets by Lorad allows us to maintain a very competitive market position, and this is passed on to our customers.

One layer of a batch of tantalum oxide tablets in a high temperature furnace

(The above figure shows one layer of a batch of tantalum oxide tablets in a high temperature furnace)

Tantalum oxide ( pentoxide) is widely used in optical coatings. It has a useful transmission range from the near UV (350nm), extending out to the IR (approximately 8 microns, 8000nm). 

Tantalum oxide is a high refractive index material. It forms durable, hard, scratch resistant coatings which, in addition, have a high threshold resistance to laser radiation damage. Tantalum oxide thin-films are most frequently paired with a low index material such as silicon dioxide (see Lorad high quality Silicon Dioxide granules) in thick, low stress, multi-stack coatings. Tantalum oxide is particularly well-known for its applications in the telecommunications industry, where it is well suited to operate with Nd-doped YAG lasers.  Its low absorption in the near IR region is particularly important. 

In addition, Tantalum oxide ( pentoxide), finds applications in the electronics industry as a thin –film gate dielectric, where its low leakage current is a well-known advantageous feature. 

Tantalum oxide is, typically, manufactured as 8-10mm D x 5mm H fully oxidized white tablets. These tablets are the most popular for industrial coating applications.  As with many oxides, the material requires some pre-conditioning to stabilize the dynamic Ta:O ratio during e-beam evaporation. This simply entails slowly sweeping the e-beam over the tablets to obtain a uniform surface melt. As the system is powered up to obtain a full melt, pressure or an RGA monitor is used to determine when a stable melt is obtained. At this point, coating can commence. 

 

Typical Evaporation Conditions: E-Beam
Temperature: approx. 2000oC
Rate: 2-5 angstroms/second
Partial Pressure of Oxygen Gas: 1x10-4torr , to maintain stoichiometry of the coating.
Substrate Temperature: 150oC - 300oC

The evaporation source is frequently held in a graphite or tantalum liner.

 

Standard Properties
Formula: Ta2O5 ……..Tantalum oxide, tantalum pentoxide, tantalum (V) oxide.
Formula weight: 441.89 (one mol)
Color: White
Melting Temperature: 1872oC
Crystal Density: 8.2 -8.3g.cm-3

If the appropriate oxygen partial pressure is maintained during evaporation, good stoichiometry thin-films are obtained with low absorption over it full transmission range. As with most thin films, some post deposition baking ( approx. 400oC ) can improve absorption characteristics although, IBAD techniques usually obviate this requirement. As with all oxide, the refractive index is critically dependent upon film stoichiometry in this case, the Ta: O ratio. Typically, n = 2.30 to 1.98. It should be noted tha IBAD will, usually yield a slightly higher n = 2.08, but precise values will depend upon the evaporation conditions.