Passivation Coatings for RF Power Devices

This project aims to increase the reliability of radio frequency (RF) devices used in accelerator facilities by reducing/eliminating corrosion and erosion produced from the high purity de-ionized water cooling systems. Although metal interconnects are required for electrical and thermal performance, they susceptible to two major failure mechanisms, corrosion and erosion. Currently RF loads are purchased with anticorrosion coating, which must be re-applied as routine preventative maintenance. In addition to costs of coatings, accelerator down time is a significant expense. By reducing maintenance costs of current accelerator components, more resources can be focused on conducting research. The proposed approach will use atomic layer deposition (ALD) to deposit highly uniform ceramic thin films onto the metalized surfaces susceptible to the corrosion and erosion. Since ceramics are inert and hard, the ALD coating will provide corrosion resistance and erosion protection, thereby increasing reliability. The RF load surface will be treated with an organic self assembled monolayer (SAM) prior to ALD. The SAM will provide an ideal surface for ALD bonding, improve uniformity by masking surface defects in the metal, and provide compliance for coefficient of thermal expansion (CTE) mismatch. This innovative metal-organic-ceramic combination will extend the useable life of water cooled RF devices. During the Phase I program, a ceramic coating formulation and ALD parameters (temperature, pressure) were identified that showed superior performance to the baseline. The nanometer thickness coating performance was analyzed by comparing the ALD coated sample with bare copper, nickel-gold plated copper (Cu/Ni/Au) and stainless steel sample. The samples were subjected to the following four tests: corrosion, erosion, thermal oxidation and thermal cycling. In all the four tests, the ALD coating showed improved performance (by an order of magnitude in terms of corrosion resistance). Advanced Cooling Technologies Inc. (ACT) has partnered with Calabazas Creek Research Inc. to develop the RF load used in DOE accelerator facility with ALD coating for corrosion and erosion resistance. In addition, ACT has partnered with Communications and Power Industries Inc. to solve a similar corrosion-erosion problem in the copper cooling channels of RF traveling wave tubes (TWT). ACT plans to reach a technology readiness level (TRL) of 5 for RF loads and 6 for TWT. A follow-on Phase III commercialization plan is presented in the proposal. Commercial Applications and Other Benefits: Currently, corrosion and erosion are leading causes of failure in water cooled RF devices. The coating process developed is this Phase I SBIR will reduce maintenance costs and downtime of DOE accelerator facilities. This process is not only applicable to cooling loops in accelerator facilities, but all copper-water cooling systems that suffer from corrosion and erosion.