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To: Carl R. who wrote (3798)	7/27/1998 9:13:00 AM
From: Stitch	Read Replies (1) \| Respond to of 5058

Carl, Thread; Here is some reference on the differences between MR and GMR from IBM's excellent Almaden Research Lab site at: storage.ibm.com In the following excerpt I have emboldened a key phrase for you. I recommend a read of the entire article however. I would also recommend a browse of their whole site when you have some time. Best, Stitch Excerpted and Reprinted for personal use only: Manufacturing considerations- MR head experience pays off The GMR heads used in IBM's 11.6 Gbit/iný demonstration closely resemble heads currently being manufactured by IBM in high volumes, both MR and GMR, except certain dimensions are smaller. Since this demonstration head was produced using some actual manufacturing processes, it is likely that advanced GMR heads can be manufactured with higher areal densities than currently available in the marketplace. As future areal densities and internal data rates increase, it will be necessary to evolve production from MR to the more sensitive GMR heads. Fortunately, a majority of the manufacturing processing and testing tools are common to both MR and GMR heads. With this commonality, the years of experience gained manufacturing MR heads is being directly applied to manufacturing GMR heads. MR and GMR head processing requires photolithography to define the head structure; e.g. the features that determine the track width seen by the read head ("read track width"). The nominal MR read track width were 2/3 of the track pitch to accommodate tolerances for head width. track-to-track spacing, and track following, a 2.6 Gbits/iný (12,500 tracks/in.) HDD would require a 1.33 micron read track width. Using this estimate, the required read track widths for 10 Gbits/iný and 40 Gbits/iný is 0.68 and 0.34 microns, respectively. In addition to satisfying these read track width requirements, the photolithography must have sufficient depth of field to accurately define any non-planar head features in a merged read and write head. Fortunately, with the semiconductor industry's emphasis on higher density integrated circuits, we expect the capability of projection photolithography, with possibly a few enhancements, will be adequate to support the projected areal density growth in HDDs. MR and GMR head manufacturing also requires precision deposition tools to control film thickness. The films used in the GMR sensor are very thin and the tolerances are tight; e.g. a copper conducting spacer is less than 15 atomic layers thick. GMR heads also contain thin film materials which require precise process control to achieve compositional uniformity. These manufacturing challenges are being addressed now, so the transition from MR to GMR will be well underway by the year 2000. The basic GMR structure used will continue to follow the IBM-developed spin valve concept for this future progress. Summary GMR heads are starting to be used in HDD products, because more sensitive heads are needed to maintain high quality read-back signals, as areal densities and data rates increase. GMR technology is an evolutionary step from today's MR heads and this technology will utilize much of the design, production, and test experience associated with MR heads. GMR heads are expected to support areal densities well beyond 10 Gbits/iný; however, as areal densities continue to grow, more advanced structures beyond GMR may be required. Manufacturing challenges will continue to involve tight control of critical dimensions, film thickness and film compositions. Continued advancements in head technology are essential to maintain rapid areal density growth during the next decade, and GMR spin valve heads have been shown to have the ability to meet future areal density requirements. Truly, the era of GMR heads for magnetic storage has begun.