Improving the CoNiMnP Electrodeposition Process Using Taguchi Design of Experiments

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1 D /21/ /D642/6/$28. The Electrochemical Society Improving the CoNiMnP Electrodeposition Process Using Taguchi Design of Experiments Michael D. Grapes and Christopher J. Morris z U.S. Army Research Laboratory, Sensors and Electron Devices Directorate, Adelphi, Maryland 2783, USA Thin film magnetic materials with out-of-plane anisotropy are important for microelectromechanical systems MEMS actuation and other applications requiring forces at a distance. Electrodeposited magnetic alloys are the most easily integrated option because they do not require high temperature processing or exotic seed layers. However, electrodeposition processes can be inconsistent and optimizing such processes is difficult because of the large number of factors typically involved: seed layer, bath chemistry, physical bath parameters, and current density. Such problems are well-suited to Taguchi design of experiments, which we used to determine and optimize factors with the largest influence on residual stress and out-of-plane magnetic properties of CoNiMnP films. A new process recipe resulted which yielded a maximum energy density of 5.3 kj/m 3, a remanence of 22 mt, and a coercivity of 93 ka/m. These results provide improved properties for immediate application in magnetic MEMS and should guide future work in the optimization of CoNiMnP and other electroplated cobalt alloys. 21 The Electrochemical Society. DOI: / All rights reserved. Manuscript submitted July 13, 21; revised manuscript received September 7, 21. Published October 19, 21. Methods Experiment. For our system, we identified nine important factors and varied them across 12 different experiments Table I. The 12 experiments were each replicated twice for a total of 24 samples. Each sample was a 1 mm diameter single-side polished 1 Si wafer, cleaned for 2 min in Piranha followed by a 3 s HF dip prior to seed layer deposition. Following seed layer deposition, a 1 cm 2 piece of polyimide tape was used to mask the center of each wafer from plating. Its subsequent removal allowed for thickness measurements. Electroplating was conducted in a 7.57 l, 15 cm deep rectangular polyethylene tank at room temperature 23 C and at constant current Agilent E3631A dc power supply. A cobalt sheet Alfa Aesar, Ward Hill, MA, 99.95% pure was used as the anode, and a purpose-built fixture maintained a fixed spacing of 1 cm between the anode and work piece. All plating baths contained.4 mol/l of NaCl and.5 mol/l of NaH 2 PO 2 H 2 O, and were mixed for at least 24 h before use. Three Design of Experiments DoE factors concerned different plating bath compositions, the first being metal salt type. Baths with sulfate salts used CoSO 4 5H 2 O and NiSO 4 6H 2 O. Baths with chloride salts used CoCl 2 6H 2 O and NiCl 2 6H 2 O. The second DoE facz christopher.morris17@us.army.mil Permanent magnet materials are attractive for microelectromechanical systems MEMS because they can provide forces at a distance, with energy densities which can exceed those for electrostatic sensors or actuators. 1 While a variety of permanent magnet materials can be made as thin films, not all of them fit the requirements of MEMS. 2 First, large values for remanence and coercivity are needed to maximize the energy a magnet can provide, BH max. In addition, it must be possible to deposit MEMS magnetic thin films at or near room temperature with low residual stress. Finally, in most MEMS applications, out-of-plane sensing and actuation are desired. 3-5 For such devices, large out-of-plane anisotropy is needed. The principal methods currently used to deposit magnetic thin films are electrodeposition, sputtering, and pulsed-laser deposition PLD. 2 Because both sputtering and PLD typically produce amorphous deposits, substrate heating during deposition and/or a high temperature postdeposition anneal is required to drive crystallization of the magnetic material. These heating steps are often incompatible with other materials used in MEMS fabrication, making sputtering and PLD of limited value for MEMS. Electrodeposition, on the other hand, does not require high temperature postprocessing and can be applied to a wide variety of MEMS devices. As such, it has become the technique of choice for integrating magnetic materials in MEMS. Most electrodeposited magnetic thin films are alloys of cobalt, including CoPt, 6 CoPtP, 7 CoNiP, 6 and CoNiMnP. These materials are typically patterned by electroplating through a photoresist mask. The nonmagnetic elements in these alloys segregate at grain boundaries and frustrate grain growth, promoting small grains 8 which enhance coercivity by increasing the number of pinning sites for domain walls. 2,9,1 CoNiMnP, the alloy studied here, was first described as a candidate for perpendicular recording 11,12 because of its significant out-of-plane anisotropy. According to the initial studies, perpendicular anisotropy in CoNiMnP films is due to the epitaxial growth of CoNiMnP in the vicinity of the seed layer interface. 11,12 This process produces a preferred crystallite orientation leading to columnar grains of magnetic material with the easy axis aligned perpendicularly to the substrate. Subsequent reports of electrodeposited CoNiMnP cover a range of methods and results. In Ref. 13, Liakopoulos et al. combined elements from Ref. 11 and 12 to fabricate CoNiMnP magnet arrays for MEMS actuation, yielding intrinsic coercivities of ka/m and remanences of.2.3 T. Later in Ref. 14, the same group reports on the effects of electroplating CoNiMnP under an applied external magnetic field, likely motivated by evidence that applying a magnetic field during plating can influence the preferred orientation of ferromagnetic deposits. 15,16 Guan and Nelson proposed a different bath composition using sulfate salts and small concentrations of the rare earth salts Nd 2 SO 4 3 and Ce 2 SO 4 3 to produce CoNiMnP films with lower stress. 17 They report coercivities of ka/m, remanences of.8.1 T, and energy densities of kj/m 3. Su et al. reported the results of plating with eight different combinations of electrolyte composition and plating parameters, 18 reporting an intrinsic coercivity of 29 ka/m, a remanence of.2 T, and a maximum energy product of 1.2 kj/m 3. While together these studies do discuss all of the important parameters, each focuses only on a subset of these parameters. As such, results are easy to interpret, but it is unclear how results will change when other variables are modified. Our goal was to improve the standard process for electrodepositing CoNiMnP by looking at all important parameters rather than just a subset. We used the Taguchi method of design of experiments because it allowed us to test a large number of parameters with a relatively small number of experiments. A trade-off was that we only tested two values of each parameter. Such a trade-off may have reduced our chances of obtaining a fully optimized product but would nevertheless result in both a better understanding of which parameters are significant, and which values would lead to improved magnetic and mechanical properties.

2 D643 Table I. Summary of parameter settings for each test run. See text for details of each parameter. Plating bath Electroplating parameters Plating surface Run no. Salt type Concentration Additives ph Current density ma/cm 2 Plating time min Magnetic field Agitation Seed layer Surface treatment 1 Sulfate Low No No No Gold Yes 2 Sulfate Low No No Yes Gold No 3 Sulfate Low Yes Yes No Copper Yes 4 Sulfate High No Yes No Copper No 5 Sulfate High Yes Yes Yes Gold Yes 6 Sulfate High Yes No Yes Copper No 7 Chloride Low Yes No No Copper No 8 Chloride Low Yes Yes Yes Gold No 9 Chloride Low No Yes Yes Copper Yes 1 Chloride High Yes No No Gold Yes 11 Chloride High No No Yes Copper Yes 12 Chloride High No Yes No Gold No tor was bath concentration, with low concentration baths containing.1 mol/l of Co and Ni salts,.5 mol/l of MnSO 4 H 2 O, and.4 mol/l ofh 3 BO 3. High concentration baths contained.5 mol/l of Co and Ni salts,.15 mol/l of MnSO 4 H 2 O, and.65 mol/l ofh 3 BO 3. A third factor was the inclusion or absence of four additives based on those used by Guan and Nelson: 17.5 mol/l saccharin,.7 mol/l sodium lauryl sulfate,.2 mol/l Ce 2 SO 4 3, and.2 mol/l Nd 2 SO 4 3. The ph of all baths was allowed to vary and is given in Table I for each bath. We selected four factors to test the effects of other electroplating process parameters. Current density was either 5 or 1 ma/cm 2. The actual current used for plating was calculated by multiplying the desired current density by the estimated exposed area. We also used both a short 5 min and long 2 min plating time to test the effect of film thickness. In doing so, we recognized that maintaining fixed times would not necessarily result in fixed thicknesses because different baths would exhibit different plating rates. However, given that historical plating rates were unavailable, and lacking an in situ thickness measurement system, we used fixed plating times in an attempt to gain some control over the thicknesses produced. Past results suggest that the presence of a magnetic field during deposition is a significant effect, 14,18 so for some of the samples we placed the fixture holding them between two rectangular ferrite magnets item 3C18, Adams Magnetic Products Co., Elizabethtown, KY. The magnets provided a perpendicular magnetic flux density of.1 T during electroplating. Finally, agitation can enhance or otherwise affect film uniformity, so we tested samples with and without nitrogen bubbling. The final two factors concerned the plating seed layer. Two common seed layers for CoNiMnP are gold and copper, so we tested both in our experiment. We used dc magnetron sputtering CVC 61 to deposit gold seed layers 2 Å with chromium adhesion 3 Å, and dc sputtering Metron 329 to deposit copper seed layers 2 Å with titanium adhesion 3 Å. We also assessed the effect of surface cleaning prior to electroplating because such cleaning is necessary prior to patterning in high aspect ratio photoresist features. 5 The cleaning procedure involved subjecting the seed layer to oxygen plasma SPI Plasma, West Chester, PA, Prep II for 5 min immediately before electroplating. Both low residual stress and strong magnetism are important for MEMS magnetic material. We calculated residual stress from measurements of wafer curvature before and after electroplating Tencor FLX 298 coupled with film thickness measured by surface profilometry Ambios XP-2. We used small 1cm 2 portions of each sample to measure magnetic hysteresis loops using a vibrating sample magnetometer VSM, Lakeshore 74 with a maximum field of 15 ka/m. To calculate the volume of magnetic material in each sample, we measured the dimensions of each sample using digital calipers, computed the surface area, and multiplied that area by the film thickness. We measured both in-plane and out-of-plane coercivities to confirm perpendicular anisotropy. Finally, the elemental composition of each sample was assessed using a scanning electron microscope Hitachi S-45 equipped with energy dispersive X-ray spectroscopy PGT Prism 6. Magnetics. We looked at four figures of merit to characterize our magnetic material: coercivity H c, intrinsic coercivity H ci, remanence B r, and maximum energy product BH max. For all but intrinsic coercivity, sample geometry affects the calculation of these values because B = H i + M 1 involves the internal field H i and not the applied field H a.ina closed-circuit measurement, H i = H a, but in an open-circuit measurement technique such as VSM, a demagnetizing field H d reduces the internal field H i = H a H d 2 The demagnetizing field is related to magnetization M by H d = N M 3 where N is the demagnetization factor for the axis being measured. Combining Eq. 2 and 3, the internal field is H i = H a N M 4 This correction must be used in Eq. 1 when calculating the remanence, coercivity, and BH max from VSM data in order to obtain accurate results. The demagnetization factor varies between and 1 depending on sample geometry. Calculating it is seldom straightforward, but in this case, we approximated unpatterned thin films as infinite planes for which N in-plane = and N out-of-plane = 1. Comparison with analytical expressions for the demagnetization coefficient of rectangular prisms 19 confirms that these approximations incur errors of less than.2%. Statistics. Our analysis considered the per-factor mean, which characterizes the effect of each factor level by the average result obtained from all samples created using that factor level. It is calculated as X n = L x n,i 5 N i where X is the factor, n is the factor level, L is the number of levels, N is the total number of samples, and x n,i are the values for each N/L

3 D644 sample. Plots of per-factor mean show trends within each factor which help specify an optimal recipe. To measure the significance of each factor, we used analysis of variance ANOVA. ANOVA allowed us to sort factors according to their influence and quantify the confidence we have that observed effects were due to those factors and not due to random error. ANOVA begins with the per-factor sum of squares L SS X = X i X 2 6 i where X i is the per-factor mean for level i, L is the number of levels, and X is the mean of all the X i. The total sum of squares SS T is the sum of all per-factor sums of squares. The contribution of each factor is then p X = SS X 1% 7 SS T Although Eq. 7 gives an initial estimate of which factors are important, it does not test their significance. To test significance, an estimation of experimental error is obtained by creating an error pool from the least significant factors. The error sums of squares SS E and degrees of freedom df E are the sums of the per-factor sum of squares SS X and degrees of freedom df X for all factors in the error pool. The df X for factor X is always one less than the number of levels tested e.g., a two-level factor has one degree of freedom. The variance of each factor is its sum of squares scaled by the number of degrees of freedom V X = SS X df X Similarly, the variance of the error is V E = SS E 9 df E The F-ratio is a comparison of the source variance to the error variance and is calculated only for those factors not included in the error pool F = V X 1 V E This F-ratio, along with the degrees of freedom of the numerator and denominator, is used in an F-test to return p, the probability that any apparent effect may be just due to random error. For a desired confidence level 1 p, a threshold F-ratio F th is obtained from an F-table and used to calculate a confidence interval CI 8 Table II. Percent contribution to the total variation for each factor, as calculated from Eq. 7. Factor Stress % Out-of-plane BH max % Salt type 2.9. Concentration Additives Current density Plating time Magnetic field Agitation Seed layer Surface treatment Residual stress. The residual stress ranged from 2.7 MPa compressive to 7 MPa tensile. The average stress across all runs was 38.1 MPa tensile. The per-factor mean plot for residual stress is given in Fig. 1, with error bars representing 9% confidence intervals calculated from Eq. 11. All but the one 2.7 MPa sample exhibited tensile stresses, so all mean stresses plotted in Fig. 1 are tensile. As seen in the graph, the three factors with nonoverlapping error bars met requirements for 9% confidence. The most significant factor was seed layer 98.7% confidence. On average, samples plated on copper seed layers exhibited residual stresses of about 4% lower than those plated on gold. Assuming that both the seed layers and CoNiMnP grew with their close-packed planes parallel to the substrate and that the crystal structure of CoNiMnP can be approximated by that of cobalt, we expected lattice mismatches of 1.6% on copper and 13.% on gold. While CoNiMnP has not been observed to exhibit long-range epitaxy, a substantial portion of the stress in thin films can still be attributed to short-range epitaxy in the vicinity of the seed layer. 17 This effect explains the higher stress observed with gold seed layers. An almost equally significant factor was bath concentration 98.4% confidence, with higher concentration baths producing more tensile films. As shown in Fig. 2, higher concentration baths generally produced deposits with higher cobalt content, and deposits with higher cobalt content generally exhibited higher residual stress. It is interesting to note that while the mole ratio of the two major components, Co and Ni, was constant for each bath, the resulting Co fraction ranged between 55% and 9%. Also, the majority of the remaining elemental composition was Ni, with total elemental percentages of Co + Ni falling between 92% and 99% in each case. Therefore, the alloy was similar to the binary system of Co Ni, which exhibits higher stress with increasing Co content. 2 CI = F th V E df X L 11 For our analysis, we constructed the error pool from the three smallest contributions df E =3 and used a 9% confidence level p.1 for which F th = Results and Discussion Table II gives percent contributions of each factor to residual stress and out-of-plane BH max. The fact that some percentages were notably larger than others indicated that those factors were likely significant. In the subsequent sections, we discuss trends for these significant factors and how they affected residual stress and BH max. Figure 1. Color online Per-factor mean plot for residual stress showing the trends for each factor. The dashed line is the mean stress for all samples, 38.1 MPa. Error bars represent the 9% confidence interval, as calculated from Eq. 11. Downloaded 28 Oct 21 to Redistribution subject to ECS license or copyright; see

4 D high concentration 6. tress (M MPa) res sidual st low concentration Co content (wt%) Figure 2. Color online Residual stress as a function of cobalt content in the CoNiMnP alloy for low and high concentration baths. Cobalt content is relative to the remaining three elements. Shaded regions highlight results obtained from both low and high concentration bath groups. Agitation was the third largest contributor 92.6% confidence, with agitated samples showing more tensile stress than those which were not agitated. Agitation likely prevented hydrogen gas from accumulating on the sample surface during electroplating. Without agitation, hydrogen trapped in the film would form voids and make the film stress appear more compressive. 1 Films produced with agitation did not have this compressive stress contribution, resulting in higher tensile stress values. It is worth noting that two factors, additives and plating time, were not found to be significant in determining the residual stress. Although these additives were specifically tested to reduce stress, 17 the reason that we found no significant correlation was likely that it was masked by more significant effects. Although plating time did affect magnetic properties as expected with increased film thicknesses 6 and as discussed in the following section, there was no significant effect of film thickness as determined by plating time on residual stress. The stress of thin films generally does depend on thickness, but this dependence is largest when the thickness is less than 1 m. The fact that we found no correlation is not surprising given that all films in this study were in the 1 6 m range. Out-of-plane maximum energy product. We based the optimization of out-of-plane magnetic properties on the maximum energy product, which reflects the effects of both remanence and coercivity. The per-factor mean plot for out-of-plane BH max is given in Fig. 3. The maximum energy product ranged from.5 kj/m 3 run 8 to kj/m 3 run 11, with an average across all runs of.676 kj/m 3. Although we observed a large variation in intrinsic coercivity ka/m, nearly all samples exhibited out-ofplane anisotropy, as indicated in Fig. 4. Four factors were significant at the 9% confidence level. The largest variation was observed for stress relief additives, which reduced BH max by about 7% when included. The reason may have been the effects of additives on bath ph level, as Fig. 5 shows that additives tended to reduce ph significantly. Figure 5 also indicates that better remanence was generally observed at higher ph levels. It is generally known that the ph level affects the degree to which phosphorus segregates at grain boundaries, which in turn influences grain size and resulting magnetic properties. It is also known that this segregation can both increase and decrease over various ph ranges. 21 The fact that magnetic properties improved over the ph range of 2 5 may be attributed to phosphorous segregation, although further electron microscopy and analysis methods would be needed to verify this hypothesis. The second most influential factor was agitation 97.7% confidence. On average, samples plated with agitation exhibited BH max Figure 3. Color online Per-factor mean plot for out-of-plane BH max showing the trends for each factor. The dashed line is the mean out-of-plane BH max for all samples,.676 kj/m 3. Error bars represent the 9% confidence interval, as calculated from Eq. 11. values twice as large as those plated without agitation. It appears that agitation enhanced sample uniformity by preventing hydrogen accumulation and refreshing the plating solution around the sample. This effect is illustrated in Fig. 6, where one of the two significant factors differing between the samples was that the sample in Fig. 6a was agitated, while that in Fig. 6b was not. The other significant factor was that the sample in Fig. 6a was plated at high concentration and the sample in Fig. 6b was plated at low concentration. The nonagitated sample showed more surface roughness and lacked the perpendicularly oriented grains observed in the agitated sample, characteristic of higher out-of plane coercivity. The third most influential factor was plating time 95.8% confidence, with longer times yielding larger BH max values. While the very large distribution of plating rates resulted in an almost continuous distribution of thicknesses, Fig. 7 shows that as expected, samples which were plated longer were generally thicker. Figure 7 also indicates that thicker films had higher remanence. The link between plating time and BH max for CoNiMnP thus appeared to be thickness, in agreement with results that have been obtained for other electroplated cobalt alloys. 6,7 Although thickness may be dic- ) rinsic co oercivity (ka/m mean intr out-of-plane in-plane run number Figure 4. Color online Average intrinsic coercivity across the 12 different factor combinations runs. For most runs, the out-of-plane intrinsic coercivity was substantially higher than the in-plane intrinsic coercivity.

5 D rem manence e (mt) with additives without additives reman nence ( mt) minutes 2 minutes ph Figure 5. Color online Out-of-plane remanence vs bath ph. Shaded regions enclose results obtained with and without rare earth salt and other additives, with the exception of one outlying data point close to ph = sample thickness (nm) Figure 7. Color online Out-of-plane remanence vs sample thickness. Shaded regions enclose results obtained at short and long plating times, with the exception of one outlying data point close to a sample thickness of 3 nm. tated by other device requirements for a particular application, these results indicate that thicker films will generally lead to better magnetic properties and performance. Finally, concentration was a fourth significant contributor 94.5% confidence, with higher concentration baths producing films with higher BH max. In the previous section, higher concentration baths were linked with increased cobalt content, and again in Fig. 8, we see that higher concentration baths generally produced films with higher cobalt content and correspondingly higher intrinsic coercivity. Assuming that out-of-plane anisotropy in CoNiMnP is derived a) CoNiMnP from the anisotropy of cobalt s hcp crystal structure, 12 higher cobalt concentrations should result in higher anisotropy and therefore higher out-of-plane coercivities. Confirmation Run Based on the previous discussion, in Table III we specify optimal recipes for both minimum stress and maximum BH max based on the range of factors tested in Table I. As shown in Table III, five of the nine optimal factors for high BH max were in contrast to the optimal factors for low stress, including the concentration level and use of agitation which we found to be significant for both targets. Rather than confirming both baths, we placed a higher importance on magnetic properties and chose to confirm only the optimal BH max recipe. For the confirmation run we retained the experimental current density of 5 ma/cm 2 and plating time of 2 min. Two samples were prepared using the same procedures outlined in the experimental methods section. Results. At 5 ma/cm 2, we observed a plating rate of about 1 nm/min. The elemental composition of the final alloy was predominantly cobalt 86.7% with nickel making up most of the remainder 9.8%, followed by phosphorus 3.2% and manganese.3%. The residual tensile stress measured in films plated with the Seed layer Si substrate 1 m 2 b) ivity (ka A/m) 15 high concentration CoNiMnP intrinsi c coerc 1 5 low concentration Seed layer Si substrate 1 m Figure 6. Cross-sectional scanning electron microscope images of a a sample from run 11, which had the highest out-of-plane intrinsic coercivity, and b a sample from run 3, which had the lowest out-of-plane intrinsic coercivity Co content (wt%) Figure 8. Color online Intrinsic coercivity vs cobalt content for low and high concentration baths. Cobalt content is relative to the remaining three elements. Shaded regions highlight results obtained from both low and high concentration bath groups.

6 D647 Table III. Recipes for lowest stress and largest out-of-plane BH max. Lowest stress Largest out-of-plane BH max Salt type Sulfate Sulfate Bath concentration Low a High a Additives Yes No a Current density 1 ma/cm 2 5mA/cm 2 or lower Thickness Thicker is better Thicker is better a Magnetic field No No Agitation No a Yes a Seed layer Copper a Copper Surface treatment No Yes a Most influential factors exceed 9% confidence. confirmation recipe was 27.8 MPa, which was slightly lower than the average residual stress in the 24 original samples 38.1 MPa, despite not being an optimal bath for low stress. A typical M H curve for the material deposited using the confirmation recipe is given in Fig. 9. Perpendicular demagnetization effects reduced the effective field experienced by the sample, and despite applying the maximum field allowed by the instrument, we were not able to fully saturate the sample. Therefore, our reported magnetic properties may be slightly less than the actual values. Despite the underestimation, the sample in Fig. 9 had an out-of-plane remanence of 22 mt, a coercivity of 93 ka/m, an intrinsic coercivity of 18 ka/m, and a maximum energy product of 5.3 kj/m 3. This result was significantly higher than the average BH max for the 24 original samples.676 kj/m 3, somewhat higher than the original sample with the best BH max kj/m 3, and exceeded many values previously reported. 14,17 Su et al. reported a value of 11.2 kj/m 3 for films approaching 15 m in thickness, produced at a current density of 2 ma/cm The bath recipe specified here may produce films of equal or greater BH max if the thickness is increased because thicker films did generally lead to higher remanence values as shown in Fig. 7. Furthermore, although we did not find a current density variation between 5 and 1 ma/cm 2 to play a significant role in determining magnetic properties, a larger range may have revealed different results. In other words, it is possible that even lower current densities would lead to better magnetic properties, which would be an interesting path to pursue in future studies. (T) 4 M internal field (ka/m) Figure 9. Color online Out-of-plane M-H hysteresis loop for the optimized material, showing remanence of.22 T and intrinsic coercivity of 18 ka/m. Conclusions In this study we successfully used a Taguchi designed experiment to generate a new CoNiMnP electroplating process yielding improved out-of-plane magnetic properties and reduced stress. We found that air bubble agitation and bath concentration were significant factors for both residual stress and magnetic properties. A lack of agitation produced films with lower residual stress and low perpendicular intrinsic coercivity, while the use of agitation noticeably improved the intrinsic coercivity at the expense of increased stress. Similarly, low concentration baths produced films with less residual stress but lower intrinsic coercivity than high concentration baths. We also found that seed layer played the most important role in determining the residual stress, with copper seed layers giving lower stress than gold. Finally, the importance of deposition thickness in out-of-plane magnetic properties was confirmed, with thicker deposits leading to larger out-of-plane BH max. These results contribute in several significant ways to the topic of electroplated CoNiMnP. Electroplating under a magnetic field resulted in no significant improvement, in contrast to previous reports asserting that an applied magnetic field enhances magnetic properties. 4,5,14,18 We found that air bubble agitation substantially improved magnetic properties. This result may have been obtained in Ref. 18, although the improvement was not explicitly attributed to agitation in that study. High concentration baths produced deposits with the best magnetic properties when simultaneously considering all other parameters in this study, while previous work indicates that low concentration baths are preferable. Finally, we found substantial evidence to support the conclusion that copper is a superior seed layer to gold, while previous studies have generally used copper and gold interchangeably without a clear motivation for the choice. Based on these results, we specified recipes to optimize both residual stress and out-of-plane magnetization, experimentally confirming the latter recipe. We obtained an out-of-plane BH max value of 5.3 kj/m 3, 7.8 times higher than the average of all the original samples and 2% higher than the best of the original samples. This result confirmed that the Taguchi designed experiment yielded improved properties and will guide future optimization of Co-based electrodeposited alloys. U.S. Army Research Laboratory assisted in meeting the publication costs of this article. References 1. D. Niarchos, Sens. Actuators, A, 19, D. Arnold and N. Wang, J. Microelectromech. Syst., 18, J. S. Bintoro, P. J. Hesketh, and Y. H. Berthelot, Microelectron. J., 36, H. J. Cho and C. H. Ahn, J. Microelectromech. Syst., 11, Y. Su, H. Wang, and W. Chen, Proc. Inst. Mech. Eng., Part C: J. Mech. Eng. Sci., 222, G. Pattanaik, D. M. Kirkwood, X. Xu, and G. Zangari, Electrochim. Acta, 52, I. Zana, G. 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