Yttrium Iron Garnet Thick Films Formed by the Aerosol Deposition Method for Microwave Inductors

We have employed the aerosol deposition method (ADM) to direct-write 40 $\mu$m-thick polycrystalline films of yttrium iron garnet (YIG, Y$_3$Fe$_5$O$_{12}$) at room temperature onto patterned gold inductors on sapphire substrates at a deposition rate of 1--3 $\mu$m/min as a first step toward integration into microwave magnetic circuits. A challenge to integrating magnetic films into current semiconductor technology is the high-temperature regime (900--1400$^\circ$C) at which conventional ferrite preparation takes place. The ability of the ADM to form dense, thick films at room temperature makes this a promising approach for integrated magnetics where low-temperature deposition and thick films are required. The ADM YIG film has an rms roughness of 3--4 $\mu$m, is comprised of nano-crystalline grains with a density 50\% of the theoretical value. XRD patterns of the as-deposited film and starting powder indicate a polycrystalline single-phase film. In-plane VSM and FMR measurements reveal a saturation of 22 emu/g, coercivity of 27 Oe, and linewidth of 360 Oe. Early measurements of air-filled and YIG-filled gold inductors between 0.01--10 GHz indicate an improved inductance of nearly a factor of 2 at low frequency. At higher frequency, resonance effects diminish this improvement.