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High-performance small-track-width metal-in-gap heads made by reactive-ion etching
Journal of Magnetism and Magnetic Materials 83 (1990) 34-47 North-Holland
HIGH-PERFORMANCE SMALL-TRACK-WIDTH MADE BY REACTIVE-ION ETCHING C.W.M.P. SILLEN, J.J.M. RUIGROK, and J.B. GIESBERS Philips Rex Lab., 5600 JA Eindhoven,
Very-small-track-width etching.
Electrical
45
METAL-IN-GAP
M.G.J. VEPkEK-HEIJMAN,
HEADS
A.J.G. BODE-FASSBENDER
The Netherlands
ferrite and Metal-In-Gap
(MIG) video heads were manufactured with the help of reactive-ion show very good read and write performance, as expected from theories.
measurements
1. Introduction
most
appropriate
technique
(e.g.
in comparison
with
for manufacturing small-track-width (I 10 urn) heads in a reproducible and accurate way. For profiling ferrite substrates by RIE an Al,O, mask with a thickness of 0.5-1.5 pm is used. Application of an HCl plasma (RIE) instead of an Ar plasma (physical etching) results in an increase of the ferrite etch rate by a factor of 5 and a reduction of the Al *O, etch rate by a factor of 2. Consequently, the selectivity (ratio of ferrite to mask etch rate), which is 1 for an Ar plasma, is enhanced by a factor of 10. The resulting etched profiles have smooth (70 o ) walls and show hardly any trenching [2]. In contrast with grinding no damaged ferrite surface layer is introduced by the RIE-process. The concept of a MIG head with a permalloy/ sendust gap cladding is described in ref. (31. For the manufacture of this head type with a RIE-ed track width, a RIE-ed ferrite substrate and a flat substrate are both covered by a sputtered permalloy/sendust layer and then bonded together by a SiO,-MoAu gap. In the present investigation the coil chamber is made by lasercutting the cores (i.e. no additional flux guide from the coil chamber). grinding)
The necessity of small-track-width ferrite and MetalIn-Gap (MIG) heads is elucidated in ref. [l]. Track-width definition in a MIG head (and a ferrite head) can be realized by laser-cutting the head (fig. la), by profiling the substrate, e.g. by grinding or Reactive-Ion Etching (RIE) (fig. lb), or, only for a MIG head, by profiling the gap cladding, possibly in combination with the substrate (fig. lc). For a MIG head, the option of profiling the substrate before deposition of the gap cladding (fig. lb) offers the possibility of extra flux transport through the metal covering the inclined edges of the ferrite. In addition, extra flux can be provided from the coil chamber (which is also possible for the other options).
2. Technology The etch depth of at least 5-10 urn in the ferrite substrate required for the preparation of a small-trackwidth MIG head, demands high rates and selectivities. which can be obtained with RIE. This technique - a combination of physical etching (ion bombardment) and etching with a chemical-reactive gas [2] - is the
m
high-MS
matem
[3
Fig. 1. MIG heads with track-width ting, (b) preprofiling, (c) profiling tion. 0304-8853/90/$03.50 (North-Holland)
glass
definition by: (a) laser-cutafter gap cladding deposi-
0 Elsevier Science Publishers
B.V
3. Experimental results 10 RIE-ed ferrite heads and 10 RIE-ed MIG heads with track widths of 4-7.5 pm and a gap length of 0.2-0.3 pm have been prepared (cf. e.g. figs. 2a and b) and measured. In the MIG heads a permalloy/sendust layer of approximately 3 urn has been applied, hence satisfying the demand for gap cladding thickness in relation to track width expressed by eq. (1) in ref. [l]. Fig. 2c shows a SEM picture of a RIE-ed ferrite head with a track width of 1.25 pm. thus emphasizing the enormous potential of this technique for realizing very small track widths. The relatively small etch depth results in extra (RIE-ed) gaps with a considerable length (ca. 7 urn), next to the main gap. This RIE-ed gap can be avoided by removing the ferrite close to the RIE-ed profile by laser-cutting (like in fig. la).
C. W.M.P.
46
Fig. 2. RIE-ed track-width
definition
Sillen et al. / Small-track-width
metal-in-gap
heads
in ferrite (a), (c) and MIG heads (10 )*m/div). (a) w = 5.7 pin, (b) w = 7.2 pm, (c) w = 1.25 ~“m.
Electrical measurements were performed with a rotating tape set-up, so track-following problems did not occur, in spite of the very small track widths. Results for head efficiency and output are presented in ref. [l] and fig. 3. To determine the separate recording (writing) and playback (reading) behaviour of the RIEed heads cross measurements [4] with a tilted sputtered sendust (TSS) head [5] have been performed (cf. fig. 4). The recording performance on Metal Powder (MP) tape of the ferrite head is less than 0.5 times that of the TSS head. The recording performance of the MIG head is as good as that of the TSS head (with its much thicker metal layers). Due to the good long-wavelength recording performance of the MIG head, a high low-frequency output (fig. 3) and a very good colour carrier-to-noise ratio (> 60 dB) were measured. The playback behaviour of the ferrite and MIG heads is slightly better than that of the large-track-width TSS head, due to the high efficiency [l]. The small opposite undulations in the recording and playback performance figures, R and P, in fig. 4 are caused by destructive and constructive interferences. Part of the signals recorded by the large-track-width
TSS head are read by the large RIE-ed gap and interfere with signals read by the main gap. (The head-to-tape distance is very small with respect to the length of the RIE-ed gaps ( = l/100). Hence, the field singularities at the edges of this gap, cf. fig. 7.6 in ref. [6], are very important. Consequently the undulations are not restricted to long wavelengths.) The effects vanish, when the RIE-ed gaps are absent. Of course, since R X P is free of undulations, recording and playback with the same head does not show the undulations, cf. fig. 3. 4. Conclusions For definition of very small track widths in ferrite and MIG heads Reactive Ion Etching (RIE) offers the possibility of obtaining sufficiently deep etched profiles in a reproducible and accurate way. It introduces hardly any residual stress in the ferrite, hence avoiding deterioration of the ferrite properties. In a small-trackwidth MIG head, a thin gap cladding (i.e. short sputtering time) suffices for an optical (long-wavelength) recording performance (like e.g. the TSS head). The playback performance is slightly better than that of large-track-width high-density recording heads.
+
10
r
MIGITSS
2
0
t
'0
5
10
I [MHz]
15
f [MHz!
-
Fig. 3. Output vs. frequency of a RIE-ed ferrite head (w = 5.7 pm) and a RIE-ed MIG head (w = 7.2 pm) (MP tape with H, = 120 kA/m, o = 6.28 m/s).
10
5
L
Fig. 4. Cross-measurement of a RIE-ed ferrite pm) and a RIE-ed MIG head (w = 7.2 pm): and Playback (P) performance relative to that (MP tape with H, = 120 kA/m, u = 5
4
head (w = 5.7 Recording (R) of a TSS head m/s).
C. W.M.P. Sillen et al. / Small-track-width metal-in-gap heads References [l] J.J.M. Ruigrok, C.W.M.P. Sillen and L.R.M. van Rijn, J. Magn. Magn. Mat. 83 (1990) 41. [2] M.J.G. Heijman, Plasma Chem. Plasma Process 8 (1988) 383. [3] C.W.M.P. Sillen, J.J.M. Ruigrok, A. Broese van Groenou and U. Em, IEEE Trans. Magn. MAG-24 (1988) 1802.
47
[4] J.J.M. Ruigrok, IEEE Trans. Magn. MAG-20 (1984) 875. [5] T. Kobayashi, M. Kubota, H. Satoh, T. Kumara, K. Yamauchi and S. Takahashi, IEEE Trans. Magn. MAG-21 (1985) 1536. [6] J.J.M. Ruigrok, (Elsevier Science Publishers, Amsterdam, 1990) Short Wavelength Magnetic Recording, to be published.
HIGH-PERFORMANCE SMALL-TRACK-WIDTH MADE BY REACTIVE-ION ETCHING C.W.M.P. SILLEN, J.J.M. RUIGROK, and J.B. GIESBERS Philips Rex Lab., 5600 JA Eindhoven,
Very-small-track-width etching.
Electrical
45
METAL-IN-GAP
M.G.J. VEPkEK-HEIJMAN,
HEADS
A.J.G. BODE-FASSBENDER
The Netherlands
ferrite and Metal-In-Gap
(MIG) video heads were manufactured with the help of reactive-ion show very good read and write performance, as expected from theories.
measurements
1. Introduction
most
appropriate
technique
(e.g.
in comparison
with
for manufacturing small-track-width (I 10 urn) heads in a reproducible and accurate way. For profiling ferrite substrates by RIE an Al,O, mask with a thickness of 0.5-1.5 pm is used. Application of an HCl plasma (RIE) instead of an Ar plasma (physical etching) results in an increase of the ferrite etch rate by a factor of 5 and a reduction of the Al *O, etch rate by a factor of 2. Consequently, the selectivity (ratio of ferrite to mask etch rate), which is 1 for an Ar plasma, is enhanced by a factor of 10. The resulting etched profiles have smooth (70 o ) walls and show hardly any trenching [2]. In contrast with grinding no damaged ferrite surface layer is introduced by the RIE-process. The concept of a MIG head with a permalloy/ sendust gap cladding is described in ref. (31. For the manufacture of this head type with a RIE-ed track width, a RIE-ed ferrite substrate and a flat substrate are both covered by a sputtered permalloy/sendust layer and then bonded together by a SiO,-MoAu gap. In the present investigation the coil chamber is made by lasercutting the cores (i.e. no additional flux guide from the coil chamber). grinding)
The necessity of small-track-width ferrite and MetalIn-Gap (MIG) heads is elucidated in ref. [l]. Track-width definition in a MIG head (and a ferrite head) can be realized by laser-cutting the head (fig. la), by profiling the substrate, e.g. by grinding or Reactive-Ion Etching (RIE) (fig. lb), or, only for a MIG head, by profiling the gap cladding, possibly in combination with the substrate (fig. lc). For a MIG head, the option of profiling the substrate before deposition of the gap cladding (fig. lb) offers the possibility of extra flux transport through the metal covering the inclined edges of the ferrite. In addition, extra flux can be provided from the coil chamber (which is also possible for the other options).
2. Technology The etch depth of at least 5-10 urn in the ferrite substrate required for the preparation of a small-trackwidth MIG head, demands high rates and selectivities. which can be obtained with RIE. This technique - a combination of physical etching (ion bombardment) and etching with a chemical-reactive gas [2] - is the
m
high-MS
matem
[3
Fig. 1. MIG heads with track-width ting, (b) preprofiling, (c) profiling tion. 0304-8853/90/$03.50 (North-Holland)
glass
definition by: (a) laser-cutafter gap cladding deposi-
0 Elsevier Science Publishers
B.V
3. Experimental results 10 RIE-ed ferrite heads and 10 RIE-ed MIG heads with track widths of 4-7.5 pm and a gap length of 0.2-0.3 pm have been prepared (cf. e.g. figs. 2a and b) and measured. In the MIG heads a permalloy/sendust layer of approximately 3 urn has been applied, hence satisfying the demand for gap cladding thickness in relation to track width expressed by eq. (1) in ref. [l]. Fig. 2c shows a SEM picture of a RIE-ed ferrite head with a track width of 1.25 pm. thus emphasizing the enormous potential of this technique for realizing very small track widths. The relatively small etch depth results in extra (RIE-ed) gaps with a considerable length (ca. 7 urn), next to the main gap. This RIE-ed gap can be avoided by removing the ferrite close to the RIE-ed profile by laser-cutting (like in fig. la).
C. W.M.P.
46
Fig. 2. RIE-ed track-width
definition
Sillen et al. / Small-track-width
metal-in-gap
heads
in ferrite (a), (c) and MIG heads (10 )*m/div). (a) w = 5.7 pin, (b) w = 7.2 pm, (c) w = 1.25 ~“m.
Electrical measurements were performed with a rotating tape set-up, so track-following problems did not occur, in spite of the very small track widths. Results for head efficiency and output are presented in ref. [l] and fig. 3. To determine the separate recording (writing) and playback (reading) behaviour of the RIEed heads cross measurements [4] with a tilted sputtered sendust (TSS) head [5] have been performed (cf. fig. 4). The recording performance on Metal Powder (MP) tape of the ferrite head is less than 0.5 times that of the TSS head. The recording performance of the MIG head is as good as that of the TSS head (with its much thicker metal layers). Due to the good long-wavelength recording performance of the MIG head, a high low-frequency output (fig. 3) and a very good colour carrier-to-noise ratio (> 60 dB) were measured. The playback behaviour of the ferrite and MIG heads is slightly better than that of the large-track-width TSS head, due to the high efficiency [l]. The small opposite undulations in the recording and playback performance figures, R and P, in fig. 4 are caused by destructive and constructive interferences. Part of the signals recorded by the large-track-width
TSS head are read by the large RIE-ed gap and interfere with signals read by the main gap. (The head-to-tape distance is very small with respect to the length of the RIE-ed gaps ( = l/100). Hence, the field singularities at the edges of this gap, cf. fig. 7.6 in ref. [6], are very important. Consequently the undulations are not restricted to long wavelengths.) The effects vanish, when the RIE-ed gaps are absent. Of course, since R X P is free of undulations, recording and playback with the same head does not show the undulations, cf. fig. 3. 4. Conclusions For definition of very small track widths in ferrite and MIG heads Reactive Ion Etching (RIE) offers the possibility of obtaining sufficiently deep etched profiles in a reproducible and accurate way. It introduces hardly any residual stress in the ferrite, hence avoiding deterioration of the ferrite properties. In a small-trackwidth MIG head, a thin gap cladding (i.e. short sputtering time) suffices for an optical (long-wavelength) recording performance (like e.g. the TSS head). The playback performance is slightly better than that of large-track-width high-density recording heads.
+
10
r
MIGITSS
2
0
t
'0
5
10
I [MHz]
15
f [MHz!
-
Fig. 3. Output vs. frequency of a RIE-ed ferrite head (w = 5.7 pm) and a RIE-ed MIG head (w = 7.2 pm) (MP tape with H, = 120 kA/m, o = 6.28 m/s).
10
5
L
Fig. 4. Cross-measurement of a RIE-ed ferrite pm) and a RIE-ed MIG head (w = 7.2 pm): and Playback (P) performance relative to that (MP tape with H, = 120 kA/m, u = 5
4
head (w = 5.7 Recording (R) of a TSS head m/s).
C. W.M.P. Sillen et al. / Small-track-width metal-in-gap heads References [l] J.J.M. Ruigrok, C.W.M.P. Sillen and L.R.M. van Rijn, J. Magn. Magn. Mat. 83 (1990) 41. [2] M.J.G. Heijman, Plasma Chem. Plasma Process 8 (1988) 383. [3] C.W.M.P. Sillen, J.J.M. Ruigrok, A. Broese van Groenou and U. Em, IEEE Trans. Magn. MAG-24 (1988) 1802.
47
[4] J.J.M. Ruigrok, IEEE Trans. Magn. MAG-20 (1984) 875. [5] T. Kobayashi, M. Kubota, H. Satoh, T. Kumara, K. Yamauchi and S. Takahashi, IEEE Trans. Magn. MAG-21 (1985) 1536. [6] J.J.M. Ruigrok, (Elsevier Science Publishers, Amsterdam, 1990) Short Wavelength Magnetic Recording, to be published.