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MATÉRIAUX MAGNÉTIQUES POUR
HYPERFRÉQUENCESTHICK FERRITE FILMS BY CHEMICAL TRANSPORT
A. Braginski, D. Buck, J. Degenford, T. Oeffinger
To cite this version:
A. Braginski, D. Buck, J. Degenford, T. Oeffinger. MATÉRIAUX MAGNÉTIQUES POUR HY-
PERFRÉQUENCESTHICK FERRITE FILMS BY CHEMICAL TRANSPORT. Journal de Physique
Colloques, 1971, 32 (C1), pp.C1-142-C1-144. �10.1051/jphyscol:1971146�. �jpa-00214473�
M A ERIAUX MA GNETIQUES POUR H YPERFREQUENCES
THICK FERRITE FILMS BY CHEMICAL TRANSPORT
A. I. BRAGINSKI, D. C . BUCK, J. E. DEGENFORD and T. R. OEFFINGER Westinghouse Electric Corp., Pittsburgh, Pa. and Baltimore, Md., U. S . A.
R&um6. - Dkposition homogkne des couches polycristallines de ferrites contenant Mg, Mn, Ni, Cr, Co est accompli par transport chimique en utilisant Clz gazeux. La structure granulaire et les proprietks des couches ne dkpendent pas de leur kpaisseur. Les caractkristiques des matkriaux et leur performance dans les appareils hyperfrkquences sont similaires aux propriktks des matkriaux ckramiques.
Abstract. - Thick polycrystalline ferrite layers containing Mg, Mn, Ni, Cr, Co are uniformly deposited by chemical transport using Cl2 as a reaction gas. The deposit morphology and propertres are thickness independent. Material charac- teristics and microwave device performance are comparable to those of sintered ceramic materials.
I. Introduction.
-
We previously reported the pre- paration of thick, polycrystalline Mg-Mn ferrite and ferrochrornite films by Chemical Transport Deposi- tion (CTD) [I, 21. This method is interesting because of its simplicity. Some films, however, were of insuf- ficient chemical uniformity. The films had columnar morphology and grain size increased with thickness.Film properties were thus thickness-dependent. Since layers up to 1 mm thick are of interest for micro- wave device application, we attempted to optimize the CTD process.
This paper reviews the progress in deposition and the material properties obtained. CTD now appears to be a valuable tool in laboratory preparation of thick ferrite layers.
11. Film uniformity. - To achieve chemical trans- port of ferrite A through vapor phase C, we use rever- sible transfer reactions of the type [3] :
TI (chlorination)
> T,
(oxidation) (1) In case of chlorination/oxidation reaction B is C1, or HCI, and C is a mixture of chlorides and 0, or H 2 0 vapor formed. TI>
T, is obtained in a close- spaced source-substrate configuration [I]. The trans- port mechanism dominant in the flow system at total gas pressure C p,
= 1 atm is diffusion. At not too high concentrations of gas B, cB, the transport rate, RAY is proportional to c, and inversely proportional to the source-deposit spacing, A . High RA is achieved at the desired temperature when the standard Gibbs free energy change of reaction (1) is AGOz
0, and the standard entropy change has a highly positive value : AS0>>
0 [4].Typical ferrite free energies of formation are high : AG = 0 to
-
10 kcal/mole. Thus under the attack of gas B the compound A breaks down into more stable constituent oxydes A,, A,,...
having AG of the order of-
100 kcal/mole. The oxide mixture A = A x+
A,. f is transported uniformly if AG: = AG; =..-
and ASx 0 = AS: =-.-
For typical ferrite oxide components this is usually not the case.Computed AGO and AS0 indicate, however, that better uniformity and higher RA should be obtained for B = C12 than for HCl previously used [I].
For ferrites formed from MgO, MnO, NiO, COO, Fe203, Cr203, high densification (- 100
%)
of the multi-oxide source inhibits selective chlorination, resulting in fairly uniform transport if B = Cl,.Deposit uniformity tests included chemical analysis and saturation magnetization, 4 nM,. Mg-Mn ferrite growth rates were typically 0.5 mm/h at TI = 1 250 OC, T, = 1 150 OC, c,,, = 10 Vol.
%,
A = 1mm.
Uni- form transport could not be obtained for the Fe203- Y203 system. We deposited, however, single phase YIG and YFeO, by transporting Fe203 in atmospheres containing YCI, vapor and some oxygen excess. The deposit growth rate was 5 to 10 microns/hour atT I = 1250 OC, c,,, = 0.1 Vol.
%,
A = 3 mm.111. Morphology and properties.
-
The hetero- geneous nucleation rate and resulting deposit morpho- logy can be strongly influenced by the partial pressure of the reactants and thus by the deposition rate [5].High deposition rate per mole of C1, results in thick- ness-independent grain size of 10 to 100 microns and in rather laminar morphology for even very thick (h = 1.5 mm) Mg-Mn ferrite deposits. The surface roughness is 5 to 10
%
as opposed to 30%
for B = HCl. The deposit density is equal to theoretical value to within experimental error (_t 2%).
The deposition rate is optimized by proper choice of the oxygen concentration, cO,, in carrier gas (He
+
0,) supplied to the reaction space. The oxygen controls the ferrite oxygen stoichiometry and thus the dielectric loss tangent. Figure 1 shows an exampleCurve 59"iDl-A
I I I 3 1
FIG. 1.
-
Example of CTD-rates, Ds and DA, efficiency, VA,and the deposit tg 6, dependence on the oxygen concentration in carrier gas. Deposition at T I = 1250 O C , A Z 3 mm, total
gas flow
-
2.8 limn.Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971146
THICK FERRITE FILMS BY CHEMICAL TRANSPORT C 1 - 143
of the effect of co2 on the source reaction rate, D,, deposition rate, DAY and the transport efficiency, q,. The X-band dielectric loss, tg
a,,
is also plotted.Increasing c,, results in the shift of the reaction (1) equilibrium to the left. As D, decreases the transport efficiency increases. The DAY however, shows peak at co2 = co2 optimum. The subsequent decrease of DA is due to both the drop in D, and local eel,
increase at the deposit ; free C1, is produced by the reverse reaction. Deviation from the average cCl2 can be substantial. For co, increasing above cO, optimum, the atmosphere at the deposit becomes less oxidizing which should result in higher dielectric losses. In fact, minimum tg 6, coincides with D,,,, at co, optimum. The co2 optimum depends on the ferrite system and increases with cCl2.
Table I shows that the saturation magnetization, 4 nM,, resonance linewidth, AH, and tg 6, of CTD samples are comparable to those of sintered speci- mens. Data of Table I hold for deposition on ceramics and platinum [I]. Deposition on gold needs further optimization because of lower deposition temperature (T, 2 900 OC) and resulting low DA at
C
p i = 1 atm.IV. Device test. -We evaluated thick films at X-band as microstrip circulator pucks and 100
%
ferrite-filled microstrip sections.
Circulators 12.5 mm in diameter, including impe- dance transformers, are fabricated of 0.25 mm thick deposits on Pt ground plane with Au conductors plated on p = 0.15 pm-finished ferrite top surface.
For test samples made of material I (Table I), isola- tion was greater than 20 dB over an 11
O/,
band. Inser- tion loss was IL = 0.8 dB, while the calculated mini- mum was IL = 0.56 dB.Since phase shift results were previously reported [1], ferrite-filled microstrip tests were limited to insertion loss evaluation. CTD ferrite layers 25 mm long and
h = 1.0 mm thick were used t o form 2, = 50 ohm line with Cu strip conductor w = 0.7 mm wide (w/h = 0.7) and t = 2 to 2.5 pm thick. Cu ground plane was also plated after removing the film subs- trate. Both ferrite surfaces had 0.15 pm finish. Trans- mission data were corrected for reflection losses.
Table I1 compares calculated and experimental loss for CTD material I (Table I), similar sintered Mg-Mn ferrite, and sapphire. The resistive and dielectric attenuation factors, a, and a,, were computed 163 with correction for effective surface resistivity due to surface roughness [7]. Magnetic attenuation was neglected ; thus the total attenuation a = a,
+
a,.Satisfactory agreement between theory (a) and expe- riment (a,,) is found for sapphire which unlike the ferrite samples was measured as a resonator. For both sintered and CTD-ferrite a,,
>
a. We attribute the discrepancy to connector radiation and TM, surface mode generation. (TM, was observed in bulk samples with h = 1.2 mm). Attenuation by CTD and sintered ferrite appears equivalent. The microstrip phase shifter figure of merit deduced from our data is38 deg/cm
F = = 380 deg/dB at 9 GHz for 1 mm 0.10 dB/cm
thick CTD-ferrite with Cu ground plane. For Pt ground plane we expect Fm,, = 220 deg/dB.
In order to obtain highest possible Finlatching rema- nence phase shifters without threading latching wires through holes in ferrite film, we consider the use of a multilayer film structure. The metal ground plane is plated on a ferrite layer and the microstrip ferrite is deposited on top of it to form a partly-closed-magnetic path with the bottom layer. Hysteresis loops measured on such a structure are very close to those obtained for a toroidal film sample under comparable excitation.
V. Conclusion. - Polycrystalline ferrite layers deposited by chemical transport have material pro- TABLE I
Material properties (Average Data), T = 25 OC
Ferrite Material CTD-I Ceramic-Sintered CTD-I1 Ceramic-Sintered
-
- - --
Approximate composi- Mg1.13Mno.osFe1.8204 Mgt.lMno.lFel.sO4 M ~ I . I M ~ O . ~ ~ F ~ I . Z ~ C ~ O . S ~ O ~ Mg1.0Mno.zFe1.zCr0.604 tion (analyzed)
Frequency band of appli- X S
cation
4 TEMs (gauss) 2 000-2 200 1 800-2 000 700-900 700-800
AH, X-band (oersted) 300 100 450 i: 50 180-200 140-180
tg a,, X-band, x 104 4-8 10 10-20 10
TABLE I1
Microstrig losses. Microstrip data : 2, = 50 R, w/h = 0.7, t = 2 pm, p r 0.15 pm Microstrip
Thickness
h Conduc- tg S,
Sample mm tor x 104
-
-- -
CTD Mg-Mn 1 .O Cu 6
ferrite I
Sintered Mg-Mn ferrite 0.63 Cu 3 (similar composition TT1-390)
Sapphire 0.63 Au 1
Calculated loss [6, 71 w. E
ac as a,
+
azdB/cm dB/cm dB/cm
Measured loss Normalized (*)
f Xex an
GHz dB/cm dB/cm
- - -
9
.o
0.10 0.1012.5 0.13 0.11
9.2 0.12 0.075
11.0 0.18 0.10
9.0 0.08 0.045
to 0.13 to 0.075 (*) Referred to f = 9 GHz, h = 1 mm, Cu conductor.
C 1 - 144 A. I. BRAGINSKI, D. C. BUCK, J. E. DEGENFORD AND T. R. OEFFINGER
perties and microwave device performance comparable We acknowledge the cooperation of F. Harris to those of sintered bulk ferrites. Thus, CTD is a and J. H. Rudolph. J. A. Kerestes and M. T. Miller valuable preparation tool suitable for technical use. provided technical assistance.
References BRAGINSKI (A. I.) and BUCK (D. C.), IEEE Trans.,
1969, MAG-5, 924.
BRAGINSKI (A. I.) and OEFFINGER (T. R.). , , J. ADDI. - A
Phys., '1970; 41, 1350.
SCHLFER (H.), Chemical Transport Reactions, Acad.
Press, N. Y., 1964.
ALCOCK (C. B.) and JEFFES (J. H.), Trans. Inst. Mining Met., 1967, 76, C246.
151 FEIST (W. M.), STEEL (S. R.) and READEY (D. W.), Physics of Thin Films, Acad. Press. N. Y., 1969, vol. 5.
[6] PUCEL (R. A.), MASS^ (D. J.) and HARTWIG (C. P.), IEEE Trans., 1968, MTT-16, 342.
171 LENDING (R. D.), Proc. of NEC, 1955, 11, 395.
