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Iridium Ir Notes


Iridium (Ir) General Information

Iridium is a rare metal which belongs to the platinum group of elements on the Periodic Table. It has a melting point of 2,410°C, a density of 22.42 g/cc, and a vapor pressure of 10-4 Torr at 2,380°C. It is silvery white in appearance and considered to be very corrosion resistant. Its main application is as a hardening agent for platinum alloys, but it can also be found in devices used in high temperature environments. It is evaporated under vacuum to make particle and surface modification coatings, data storage devices, and fuel cells.

Iridium Ir Specifications

Material TypeIridium
SymbolIr
Atomic Weight192.217
Atomic Number77
Color/AppearanceSilvery White, Metallic
Thermal Conductivity150 W/m.K
Melting Point (°C)2,410
Coefficient of Thermal Expansion6.4 x 10-6/K
Theoretical Density (g/cc)22.42
SputterDC
Max Power Density
(Watts/Square Inch)
100*
Type of BondIndium, Elastomer
Z Ratio0.129
E-BeamFair
Temp. (°C) for Given Vap. Press. (Torr) 10-8:  1,850
10-6:  2,080
10-4:  2,380

* This is a recommendation based on our experience running these materials in KJLC guns. The ratings are based on unbonded targets and are material specific. Bonded targets should be run at lower powers to prevent bonding failures. Bonded targets should be run at 20 Watts/Square Inch or lower, depending on the material.

Z-Factors

Empirical Determination of Z-Factor

Unfortunately, Z Factor and Shear Modulus are not readily available for many materials. In this case, the Z-Factor can also be determined empirically using the following method:

  • Deposit material until Crystal Life is near 50%, or near the end of life, whichever is sooner.
  • Place a new substrate adjacent to the used quartz sensor.
  • Set QCM Density to the calibrated value; Tooling to 100%
  • Zero thickness
  • Deposit approximately 1000 to 5000 A of material on the substrate.
  • Use a profilometer or interferometer to measure the actual substrate film thickness.
  • Adjust the Z Factor of the instrument until the correct thickness reading is shown.

Another alternative is to change crystals frequently and ignore the error. The graph below shows the % Error in Rate/Thickness from using the wrong Z Factor. For a crystal with 90% life, the error is negligible for even large errors in the programmed versus actual Z Factor.

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