Formation of Thick Dense Yttrium Iron Garnet Films Using Aerosol Deposition

Summary

This report describes the use of a custom-built system to perform aerosol deposition of thick films of yttrium iron garnet onto sapphire substrates at RT. The deposited films are characterized using scanning electron microscopy, profilometry, and ferromagnetic resonance to give a representative overview of the capabilities of the technique.

Abstract

Aerosol deposition (AD) is a thick-film deposition process that can produce layers up to several hundred micrometers thick with densities greater than 95% of the bulk. The primary advantage of AD is that the deposition takes place entirely at ambient temperature; thereby enabling film growth in material systems with disparate melting temperatures. This report describes in detail the processing steps for preparing the powder and for performing AD using the custom-built system. Representative characterization results are presented from scanning electron microscopy, profilometry, and ferromagnetic resonance for films grown in this system. As a representative overview of the capabilities of the system, focus is given to a sample produced following the described protocol and system setup. Results indicate that this system can successfully deposit 11 µm thick yttrium iron garnet films that are  > 90% of the bulk density during a single 5 min deposition run. A discussion of methods to afford better control of the aerosol and particle selection for improved thickness and roughness variations in the film is provided.

Introduction

Aerosol deposition (AD) is a thick-film deposition process that can produce layers up to several hundred micrometers thick with densities greater than 95% of the bulk¹. The deposition process is believed to occur through a continual process of impact, fracture or deformation, adhesion, and densification of particles. Figure 1 depicts this process as a series of steps showing particle impact and densification over several steps. As shown, the particles move toward the substrate with a typical velocity of 100–500 m/sec. As the initial particles impact with the substrate they fracture and adhere to the substrate. This anchoring layer provides ....

Protocol

1. Powder Preparation

1. Sieve as-received yttrium iron garnet (YIG) powder to obtain 100–150 g of agglomerates sized less than 53 µm.
2. Place the sieved powder into a furnace to dry for at least 24 hr at a temperature greater than 300 °C.

2. Substrate Preparation

1. Clean a substrate of desired size, e.g., 3 mm x 3 mm using acetone then isopropanol. Dry using nitrogen gas.

3. Performing Aerosol Deposition

1. Mount the sample to the translation mounting stage.
   1. Place double-sided copper tape to the mounting stage. Place the clean....

Results

After the deposition is complete, the coated substrates are removed from the deposition chamber and inspected using an optical stereo microscope. Samples are typically brushed and washed with isopropanol to remove excess powder that remained during re-pressurization to atmosphere. Film characterization was performed on the representative results presented here using scanning electron microscopy to assess the morphology of the film, profilometry to assess the film thickness, uniformity, and roughness, and ferromagnetic re.......

Discussion

The SEM image in Figure 4 indicates that significant fracture and densification is occurring during the deposition process. The image is taken of the top surface of the film, which shows a small number of voids and grains. The observable region is the last of the material to be deposited and therefore does not benefit from the further impact and densification process of subsequent particles as illustrated by impact from particle 2 and 3 in Figure 1. The film density within the volume of .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Ferromagnetic Resonance Spectrometer	www.bruker.com/	9.5 GHz Spectrometer
Scanning Electron Microscope	www.zeiss.com	LEO Supra 55
Profilometer	www.kla-tencor.com/	D-120
Stereo Microscope	www.microscopes.com	Omano Stereo Microscope	Used for inspection directly after removal from deposition chamber
Double-sided Copper Tape	www.2spi.com	05085A-AB	hold-down clips or other adhesives may be used
Nitrile Exam Gloves	www.fishersci.com	19-130-1597D
2-propanol	www.fishersci.com	A451SK-4
Acetone	www.fishersci.com	A11-1
Yttrium Iron Garnet Powder	www.trans-techinc.com/	Call for Product Information	Powder is custom made to order and ground to specifications
Stainless Steel Spoon	www.fishersci.com	14-429E	Used for scooping and transferring powder
Alumina Boats	www.coorstek.com/	65580
Drying Furnace	www.paragonweb.com	KM14 ceramic furnace	Furnace is connected to air during drying
Powder Sieves	www.advantechmfg.com/	270SS8F	A selection of mesh openings are needed to sieve from large down to target size
Ultra High Purity Nitrogen Gas	www.praxairdirect.com	NI 5.0UH-3K	Used as medium for aerosol.
Air Breathing Quality	www.praxairdirect.com	AI BR-4KN	Used inside furnace during drying
Lab Balance	www.balances.com/	Sartorius ED224S Lab Balance	Used for weighing powder
Sapphire Wafers	www.pmoptics.com/	PWSP-313211