Masahiko Hatatani

Single-pole/TMR heads for 140-gb/in/sup 2/ perpendicular recording

Single-pole writers and tunneling magnetoresistive (TMR) readers for 140-Gb/in/sup 2/ perpendicular recording were fabricated and their recording performance was tested. Data erasure, which is observed as write instability in a repeated read-write operation, can be suppressed by combining a laminated pole and low throat height. Fe-Co/Ni-Cr laminated film was used to reduce the remanent magnetization of the main pole after patterning. Narrow track writers with a 120-nm-wide trapezoidal pole showed a good write ability of 30 dB or more in overwrite for media with high coercivity of up to 7 kOe. Also, negligibly small skew writing was confirmed. TMR heads with a sensor width of 85 nm and a head resistance of 250 /spl Omega/ showed approximately 30 dB of head signal-to-noise ratio (SNR). A potentially higher SNR with a higher operating voltage was suggested from a measured output versus sensing current curve. Calculations showed that the side reading was suppressed in a side-shielded design. A 10% amplitude width of the microtrack profile of a 100-nm-wide reader was reduced from 198 to 162 nm by applying the side shields.

CPP–GMR Heads With a Current Screen Layer for 300

Current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) heads with a current screen layer were fabricated, and the recording performance was measured. An output voltage of 1.9 mV and head-amp signal-to-noise ratio (SNR) of about 30 dB were obtained from a 50-nm-wide head with an operating voltage of 120 mV. The MR ratio was 4%-5%, shield gap was 36 nm and resistance was 72 Omega. With using the thermal fly-height control (TFC), the fabricated head showed a potential to yield a 382 Gb/in2 recording (1252 kBPI times 305 kTPI). The current screen structure reduced the spin torque noise since just a low sensing current of 1-2 mA was required for obtaining a high output. Newly developed CPP-GMR films with a current screen layer showed the MR ratio of 18%-19% with the RA product of 0.2-0.3 Omega ldr mum2. Calculation showed that this film allows us to achieve 30 dB or more in the head-amp SNR when the sensor width was 40 nm or larger. The current screen CPP-GMR head is thus an attractive candidate that has a high potential suitable for an areal density of 500 Gb/in2 or more. Below 40 nm, an all metal CPP-GMR head with the MR ratio of 10% or more would be the best candidate.

{\hbox{Gb/in}}^{2}

To reduce the side-reading effect and obtain a narrower effective read track width, the side-shield effect was studied by computer simulations and experiments. Computer simulations show that the side shield, which consists of a soft magnet, can reduce the effective read track width. To examine the effect, a side-shielded tunneling magnetoresistive head was fabricated. In the head, to place a soft magnet by the sensor side, a closed-flux structure was applied for longitudinal bias instead of a conventional abutted junction. Microtrack profile measurements agreed with simulated results, and the side-shield effect was clearly demonstrated.

Recording

Shielded GMR heads with an in-stack bias layer were designed, fabricated, and their read performance was measured. Since the bias layer and the free layer antiferromagnetically couple at the edge of the sensor, a closed magnetic flux structure (CFS) is formed. The results of micromagnetic simulation revealed that when an MnIr antiferromagnetic layer is used to pin the magnetization of the bias layer, the Ms⋅t of the bias layer normalized by that of the free layer should be between 1.2 and 1.5. Here Ms and t are the saturation magnetization and the thickness of the layer. The read waveform of the fabricated head was noise free and well biased. The obtained read sensitivity of the CFS head was four times higher than that of a conventional abutted junction head. Calculation revealed that the read sensitivity of the CFS head was almost five times higher than that of conventional heads when the magnetic track width was reduced to 100 nm. Thus, CFS heads show potential for high track density recording.Shielded GMR heads with an in-stack bias layer were designed, fabricated, and their read performance was measured. Since the bias layer and the free layer antiferromagnetically couple at the edge of the sensor, a closed magnetic flux structure (CFS) is formed. The results of micromagnetic simulation revealed that when an MnIr antiferromagnetic layer is used to pin the magnetization of the bias layer, the Ms⋅t of the bias layer normalized by that of the free layer should be between 1.2 and 1.5. Here Ms and t are the saturation magnetization and the thickness of the layer. The read waveform of the fabricated head was noise free and well biased. The obtained read sensitivity of the CFS head was four times higher than that of a conventional abutted junction head. Calculation revealed that the read sensitivity of the CFS head was almost five times higher than that of conventional heads when the magnetic track width was reduced to 100 nm. Thus, CFS heads show potential for high track density recording.

Side-shielded tunneling magnetoresistive read head for high-density recording

In this paper, the effect of the lower shield materials on the breakdown voltage of the lower insulating gap layer has been investigated. A hybrid shield CoNbZr layer on NiFe shield was applied ton the read , and the resulting narrow gap heads performance in reading was observed.

Read performance of GMR heads with in-stack longitudinal bias layer

Current perpendicular to plane (CPP)-type heads having various magnetic shield shapes were fabricated, and their medium signal-to-noise ratios (SNRs) and micro-track profiles (MTPs) were measured. To find out how to improve the sharpness of an MTP, we calculated the relationship between a magnetic read width (MRW) and a magnetic shield shape and a shield-to-shield gap spacing (Gs). In our calculation based on the reciprocity principle, a nonuniform magnetic potential reflecting the sensitivity in the free layer was introduced to give a precise MTP. The calculation indicates that a narrow Gs and a parallel shield are effective in obtaining a sharper MTP. The calculation results were also confirmed by experimental data. Measurement using a perpendicular medium shows that the medium SNR gets higher as the MTP becomes sharper. Thus, CPP-type heads with a sharp MTP have an advantage in getting good SNR performance

Applying amorphous CoNbZr shield to improve the dielectric-breakdown voltages of the gap layers of narrow-gap read heads

Perpendicular recording with sufficient thermal stability has great potential for next-generation recording with areal densities over 100 Gb/in/sup 2/. One of the biggest problems for single-pole writers is head-induced erasure, such as erase-after-write This erasure is due to the high remanent magnetization of the main pole. We fabricated single-pole writers with a domain stabilization technique to reduce the remanence, and highly sensitive tunneling magnetoresistive (TMR) readers for 100 Gb/in/sup 2/ perpendicular recording.