78 IEEE TRANSACTIONS ON MAGNETICS, VOL. 38, NO. 1, JANUARY 2002 Spin Tunneling Heads Above 20 Gb/in Sining Mao, Janusz Nowak, Dian Song, Paul Kolbo, Lei Wang, Member, IEEE, Eric Linville, Doug Saunders, Ed Murdock, and Pat Ryan, Member, IEEE Abstract—Spin tunneling recording heads above 20 Gb/in have been fabricated using a bottom tunneling junction stack. The spin tunneling stack is made of Ta/PtMn/CoFe/Ru/CoFe/AlO/NiFe/Ta and stabilized by a permanent magnet abutted junction. The effec- tive junction width is about 0.4 m wide and lapped to the junc- tion with an optimum stripe height. The barrier has resistance area product of 15–20 m , leading to a typical head resistance of around 50 . Isolated pulses during the spin-stand test shows large signal up to 10 mV. On track error rate floor is better than 10 and the head signal-to-noise ratio is also better than that of a con- ventional spin valve GMR head. The areal density estimated (using BER of 10 ) is above 20 Gb/in . Index Terms—Areal density, micromagnetic modeling, spin- stand test, spin tunneling heads, TGMR. I. INTRODUCTION I N ORDER to meet the challenge in sensitivity and ampli- tude requirement for recording heads in the magnetic data storage industry, spin tunneling heads (or tunneling valve or tunneling GMR) have been considered as one of the promising candidates after spin valve/GMR heads [1]–[4]. In this work, a tunneling head design is proposed and fabricated. The electrical testing data indicate that the head is capable of areal density of 20 Gb/in . In addition, the performance is compared with stan- dard spin valve heads. On-track error rate floor is better than 10 and the head signal-to-noise ratio (SNR) is also better than that of a conventional spin valve GMR head. The structure of a spin tunneling junction is similar to the spin valve except that the nonmagnetic Cu spacer is replaced by an insulating tunnel barrier (typically Al O ) [4]–[7]. The tunnel barrier has a thickness much less than a typical Cu spacer layer in order to achieve the low product which is critical for a recording head application. Another major difference between these two apparatus is that the current in a tunneling giant mag- netoresistance (TGMR) head junction is applied perpendicular to the plane of the film (so called CPP mode—current perpen- dicular-to-plane). In addition, the CPP head design is simpler than a spin valve because the MR ratio is not directly related to lead resistance, head geometry, and film thickness. The tunneling heads discussed in this paper utilize improved design and testing methods based on our previous 10 G proto- types of TGMR heads. Changes were made to accommodate the top and bottom lead electrodes and eliminate the shield as elec- trodes. This reduces the magnetic interaction between the mag- netic shield and heads. The objective of this work is to demon- Manuscript received June 25, 2001. The authors are with Seagate Technology, Bloomington, MN 55435 USA (e-mail: Sining.Mao@seagate.com). Publisher Item Identifier S 0018-9464(02)01283-9. Fig. 1. Wafer layout of a TGMR head. Not to scale. strate the technology feasibility of a recording head using a spin tunneling junction, as compared with a standard spin valve head. Fabrication processes have been advanced recently for low re- sistance-area product junctions [8]–[11]. This low junction process enables the TGMR head to be more extendible for ultrahigh areal density head application, but it is not the focus of this paper. While much effort is focused on further lowering the product and many additional questions remain on the shot noise and reliability of thin tunnel barriers, we explore the possibility of implementing a spin tunneling head to the current spin valve head scheme without adding system level complexity. It was found in this work that at a certain areal density the spin tunneling head may be used in place of the spin valve head to give better performance. II. HEAD DESIGN AND FABRICATION The TGMR head construction is based on a Seagate 10 G-Gb/in spin tunneling head design with changes to ac- commodate the top and bottom lead electrodes and eliminate the shields as electrodes to reduce the magnetic interaction between the magnetic shield and heads. The spin tunneling stack is made of Ta/PtMn/CoFe/Ru/CoFe/AlO/NiFe/Ta and stabilized by a permanent magnet abutted junction. The reader processing begins with ion milling of the TGMR stack trilayer, namely the free layer, the barrier, and the pinned layer to form the bottom electrode. Then a junction is defined by timed ion mill stopping in the pinning layer. Then we use a self-aligning process to lift off an insulating layer to isolate the top electrode from the bottom (Fig. 1). In the end, a top electrode is deposited and connected to the recessed lead (left contact pad in Fig. 1). 0018–9464/02$17.00 © 2002 IEEE