Electroforming of Electronic Devices

Electroforming of Electronic Devices [1997]
 

by 
Lubomyr T. Romankiw
IBM Thomas J. Watson Research Center
Yorktown Heights, NY, USA

Editor’s Note: Dr. Lubomyr Romankiw, who was the AESF Scientific Achievement Award recipient in 1991, was judged by the attendees at the March 1996 AESF Electroforming Symposium as being the "excellence in presentation" winner among the individuals who presented papers at that event (The introductory chapter was republished in this space in August).  This is an edited version of his informative discussion of plating-through-mask technology.  In traditional electroforming, the object is an entity by itself and is expected to part readily from the substrate after plating.  In plating through-mask-technology in electronics, the electroformed metal has to adhere very strongly to the substrate, and it usually represents only one layer of a multilayer structure.  Dr. Romankiw's paper covers a history of the development of plating-through-mask technology in electronics, patterning and pattern transfer, plating through lithographic masks as used in thin film heads, thin film chip carrier manufacture and in fabrication of a prototype of an integrated magnetic mini-motor.  The predictions for the next fifteen years (from 1996) at the end of the paper are particularly interesting.  In the end, his work was revolutionary, and advanced commercial disk storage technology used in computers, digital cameras and other devices.  He and Dr. David Thompson developed a technique that produced the first practical and manufacturable thin film magnetic head, which increased the density of data stored on magnetic disks and dramatically reduced the cost of data storage.  A printable pdf of this paper can be accessed and printed HERE.

Introduction

Electroforming is an old art that has been practiced by electroplaters for many years.  In this process, the metal is deposited onto a cathode mandrel or into a mold.  Upon completion of the plating, the mandrel/mold and the plated metal are separated.  The plated metal represents an entity by itself - a finished part.

To electroform parts, plating is usually done onto a suitably pretreated cathode for easy parting, such as a dielectric coated with a thin film of Ag that has limited adhesion, onto an austenitic stainless steel mandrel or onto copper overcoated with a thin flash of chromium.  Because of the thin native oxide on both stainless steel and chromium, an electroformed part is easily removed from them.  The adhesion has to be sufficient for the electroformed metal not to separate before the electroforming process is completed.  In some cases, the plating is done onto a substrate that has features formed in it (LP records or CD disks, for example).  The objective is to replicate the features present in the polymer substrate into the metal that will subsequently be used as a stamping die.  In other cases, plating is done through a resist mask onto a metal mandrel (in the fabrication of screens, masks, etc.).  Many examples of traditional electroforming are included in the proceedings of the 1996 symposium.¹

How electroforming for electronics contrasts with traditional approaches

By contrast, when electroforming metal patterns for electronic applications, the electrodeposit that is made through a resist mask usually does not represent a finished product by itself.  It also is rarely removed off the substrate.  Instead, it remains on it and becomes an integral part of the electronic or magnetic device being built.  Indeed, the device may contain several such through-mask electroformed layers, each having a different pattern and each being separated from the previous one by a dielectric.  Because good adhesion of the plated pattern is of critical importance most of the time, a special adhesion layer is deposited on the dielectric to ensure excellent adhesion of the plated features to the substrate.  The adhesion layer consists of an evaporated or sputtered refractory metal (such as Cr, Ti, Ta, etc.).  In the same vacuum step, it is overcoated by a conducting metal, such as Cu, Ag, Au or Ni to form a cathode.  Refractory metals usually provide very good adhesion to oxides and other dielectrics.  Metals such as Cu, Au, Ag, Ni and others adhere well to the top side of the refractory metal.  The refractory metal, therefore, serves as a bridge between the dielectric and the metal.

Electroforming in electronics is known by many names

The application of electroforming in electronics is known under several different names: Plating through lithographic masks;² plating through masks; pattern plating; plate-up; and additive plating.  Recently, the acronym LIGA has been appearing in the field of micro-electro-mechanical systems (MEMS).  LIGA is an abbreviation of the German Lithographie, Galvanoformung and Abformung (lithography, electroforming and replication),³ and was coined by Kernforschungszeutrum Karlsruhe (KfK) in Germany.³

Through-mask technology

In electronics, the plating through lithographic polymeric mask technology or electroforming had its beginning in the late 1960s.  Inventions and breakthroughs (Fig. 1) led to the current extensive use and popularity of the electroforming process in electronics.²  The electroforming through mask was first tried in connection with fabrication of magnetic storage devices.  In order to build thin film inductive read-write heads, it was necessary to produce μm-size copper conductor coils nearly square in cross section, with as many conductor turns crowded around the magnetic yoke as possible.^4,5,6  The yoke was only 100 μm high, with a separation between the yoke legs of only 15-20 μm (Fig. 2).

The electroforming (or plating through mask technology) for electronic thin film head fabrication was first introduced at the T.J. Watson Research Center.  We have decided to exploit, for this purpose, the combination of lithography and plating processes, similar to those used in electroforming, with the key differences being as outlined earlier. Each electroformed layer was only part of a completed multilayer structure. After introducing the electroforming-through-resist mask in thin film heads, we have introduced this technology also in the fabrication of bubble memory.

Because bubble memory required sub-micron dimensions in addition to the optical lithography, we have also explored and extended the plating-through-mask technology to e-beam and X-ray lithographically formed patterns.^7,8  Having demonstrated in 1974 an unparalleled fidelity of pattern replication of the plating-through-mask technology, gold electroforming was adopted as the only successful process for fabrication of X-ray lithography masks (which requires pattern replication nearly on atomic level).  In 1976, we made public the fact that X-ray masks produced by plating can be inverted several times with almost no loss of fidelity.⁸  Several mother-daughter replicas were produced using electroplated gold.  In each replication, the height-to-width aspect ratio of the plated pattern was increased without loss of fidelity in the subsequent replicas.  Figure 3 shows a structure with 60:1 aspect ratio, with six μm thick, 1 μm wide patterns separated by 1000 Å  spaces produced by X-ray lithography followed by gold plating.

As the understanding of the plating-through-resist masks grew, precision tools, processes and process controls were developed, and through-mask plating technology became a critical technology in magnetic thin film head manufacturing.  Today, several hundred millions of heads per year are manufactured by electronic companies around the world, using the plating-through-mask technology, representing a $2-3 billion market.  There is currently no deposition method that can compete cost-wise with electroforming for thin film head manufacturing.  Plating through-masks has also become the exclusive fabrication process for very high fidelity X-ray masks and has been adopted in manufacturing as low-cost, high-precision thin film chip carriers.  High aspect ratio structures with up to 12:1 were produced, not only using X-ray lithography, but also using optical lithography and through-mask plating (Fig. 4).²

Electronic parts require very tight thickness tolerances, exceptionally uniform current distribution and mass transport, very rapid real-time on-line process control and good understanding of the relation between solution chemistry, nucleation, film growth and other parameters that define the material, magnetic, electrical and other properties.  Most of these requirements are affected by uniformity of agitation, pattern distribution and current distribution.  A unique paddle plating cell design has been developed that provides extremely reproducible agitation and permits plating - very reproducibly - films with excellent current and thickness distribution on a wafer.^9,10  It is known that agitation in a plating tank is hard to reproduce, and that scaling up of the plating environment is very difficult.  In the paddle cell, because of the method of agitation used, agitation is easy to reproduce and the paddle plating tanks are easy to scale up from a small laboratory size tank to a full-scale manufacturing tank.  The agitation is accomplished by a windshield wiper-like device (arm) moving only a millimeter away from the cathode.  We have investigated these relationships and have come up with a model that permits us to approach the electrochemical process with a considerable amount of under¬standing.^11-14

Patterning & pattern transfer

For a long time, the most popular technique for pattern transfer in electronics was wet chemical etching.  This process runs into limitations because as device density increases, it becomes necessary to place conductors closer and closer together, and at the same time to maintain the largest possible cross-sectional area of the conductors.

A considerable amount of work has been and is still being done on dry processes of pattern transfer, such as sputter etching, reactive ion etching and lift-off.  The advantages and limitations of various pattern transfer techniques have been studied and compared with the electroplating through-mask technology.¹⁵  A comparison of the various techniques is shown in Fig. 5.  It is easy to conclude that the plating through-masks is the only technique that permits the highest packing density, the highest cross-sectional area and the tallest structures.  This technology has been clearly demonstrated in electronics to be the only one that is capable of producing truly three-dimensional, micron-size structures with nearly atomic resolution and vertical walls, as it is known to do in electroforming of much larger articles for automotive, aerospace, jewelry and other applications.

Plating through lithographic masks

The typical process steps used in fabrication of patterns using the plating through mask technology are demonstrated in Fig. 6.  The substrate is usually a dielectric that is typically metallized first with an adhesion layer of 50 to 500 Å of refractory metal (such as Cr, Ti, Ta, etc.) followed immediately in the same vacuum pump down, by a 400 to 5000 Å of Ni, Au, Co or NiFe as a cathode plating surface.  In the case of Ni or NiFe, occasionally the adhesion layer is omitted, but then the Ni or NiFe is deposited at 200 to 300°C to form the Ni-oxide and Fe-oxide bond between the oxygen in the dielectric and the metal.

The seed layer is coated with an organic polymer, an optical, e-beam, or X-ray resist that, when exposed through a mask, will leave certain areas depolymerized and ready to be dissolved by the developing solution.  After development and upon water rinsing and drying, any remaining organic residue of the resist is removed by plasma ashing with oxygen-containing plasma.  The open areas are then electroplated through.

If a Novolac-type positive working resist is used, the plating solution usually readily wets and fills even a very high-resolution pattern.  Upon completion of the plating, the remaining resist is removed by second exposure and development.  The seed layer and adhesion layer are then removed by chemical etching or by sputter etching or RIE.  This leaves the plated features isolated on top of the dielectric substrate.  These features are then overcoated with a new dielectric.  If necessary, the structure is planarized and the process is repeated as many more times as is required to complete the device.¹⁶

The fidelity of electroformed pattern is extremely high, and if a high resolution resist is used, the pattern can be extremely densely packed.  When optical lithography is replaced by e-beam and by the X-ray lithography, pattern dimensions as small as 0.1 μm have been achieved.⁸  Additionally, an important feature of X-ray lithography is that, because of the extremely short wavelength, it is capable of producing nearly vertical walls in very thick PMMA resist (Fig. 3).  Because of this, three-dimensional structures with completely vertical walls can be fabricated.

Thin film heads

Shown in Fig. 7 are a top view and a cross-sectional view of a magnetic thin head typical of the heads that have been in use since 1979 in most of the magnetic storage devices using hard disks.  This is an inductive read-write head with 31 electroplated copper conductor turns and an electroplated horseshoe magnet.  (A typical fabrication process of such a head is described in Ref. 10.)  The substrate is Al₂O₃•TiC ceramic overcoated with sputtered Al₂O₃.  The structure contains four separately electroplated through-mask permalloy layers (81% Ni; 19% Fe alloy) and two copper conductor layers that are also electroplated through lithographic masks.

Several hundred - or even thousands - heads are fabricated on each substrate.  The heads are arranged in rows and columns, with each head lithographically defined by several lithographic masks used sequentially in the process.  For each metal and dielectric layer, a different mask is used.  When the sequential process is completed, the wafer is cut into sliders, with one head per slider.  The overall sequence is:

• Sputtering of thin seed layer of NiFe alloy, which will serve as a cathode for plating of the first leg of the horseshoe magnet through a photoresist mask, and then plating of permalloy and etching away of the seed layer. 

• Sputtering and defining into shape, by etching, 0.3 to 0.5 μm of Al₂O₃, which will define the magnetic gap in the finished horseshoe magnet (the head).

• Sputtering a seed layer that consists of Cr and Cu, applying resist, exposing and developing the outline of the first pancake-shaped copper conductor coil and then plating the first copper conductor coil through the mask.  After plating approximately three μm of the Cu, removing the resist mask and sputter etching the thin Cu seed and Cr adhesion layers.

• Forming the dielectric that will separate the first level of Cu conductors from the second by applying a Novolac photosensitive resin, defining it by the photo processing, and then hard-baking it to serve as insulation between the coils.

• Sputtering a new Cr and Cu seed layer and electroforming through resist mask the seed layer of the Cu conductors in the same way as the first layer was formed.

• Forming a second hard-baked Novolac dielectric layer on top of the second level Cu coil in the same way as the first hard-baked dielectric layer was formed.

• Forming the second leg of the horseshoe magnet by sputtering the thin permalloy seed layer and then electroforming the thicker permalloy by electroplating through resist mask and then etching the excess permalloy and the seed layer.

The completed head (Fig. 7) has about a 100-μm-wide yoke (approximately the width of a human hair); the pole tip is only about 5 μm wide.  The Cu conductors are 3.8 μ m tall, 3 μm wide, and the spaces between them are 2 μ m wide. All the metal layers were plated through optically exposed Novolac-type-positive working resist.  Each layer was produced as described in Fig. 3.  Because of the need to have very precise permalloy composition and very uniform thickness distribution, the wafers are plated in a paddle cell.⁹  The paddle cell design and the mode of agitation make this tool particularly useful in plating parts-through-resist masks that require very precise alloy composition, and very reproducible thickness uniformity.

Thin film chip carriers

The thin film chip carriers are used in nearly all computers.  They are the substrates to which semiconductor chips are attached.  They provide connection and electrical communication paths between the chips and the other parts of the computer.  The chip carrier shown in Fig. 8 consists of a ceramic module with several layers of paste metallurgy on which 11 layers of Cu conductors were formed by plating of Cu through Novolac-type-positive working resist.  Each layer is produced using the process described in Fig. 6.  The conductors are 15 μm wide and 5 μm thick.  Each time after the seed layer was removed, polyimide was applied.  The polyimide is the dielectric separating and insulating the conductors from each other.  For the purpose of illustration, the figure shows a section of the thin film chip carrier from which the polyimide was removed by oxygen plasma treatment.  The 11 layers of Cu metallurgy, formed by plating through photoresist masks, can be clearly observed.  The edges of each conductor and of each via are clearly defined.  Such high conductor density, small spaces between the conductors, excellent electrical conductivity and sharp edge definition would be very difficult to achieve by other patterning techniques.

Integrated magnetic minimotor

The minimotor discussed in this article belongs to a class of devices known as MEMS (micro-electro-mechanical systems).  This very rapidly developing field is making very effective use of the electroforming or plating through mask technology.  In micromechanics, linear actuators, rotary motors and a variety of sensors and instruments are shrunken by orders of magnitude from the well-known, smaller mechanically machined and assembled dimensions.  The plating-through-mask technology, particularly when the patterns are defined by X-ray lithography, provide entirely new capabilities to this field because it is capable of extremely large depth of focus.  The plating-through patterned-resist made possible a variety of magnetic devices, some of which require very tall, extremely closely spaced structures with very tight dimensional tolerances.  The plating approach opened up many new possibilities in the field of micromechanics and in micromechanical systems (MEMS).  As discussed, in this particular field, electroforming or plating through lithographic masks is known under the acronym "LIGA."  There are only a few MEMS devices in manufacturing today that utilize electroforming.  It is predicted that many MEMS devices based on plating processes will be in use by the year 2000 and that plating will be widely used in MEMS device fabrication thereafter.

There are a variety of experimental devices that have been built and dem-onstrated, including accelerators, gyro-scopes, motors, linear calculators and more (see Figs. 9-13).

Electroforming technology has huge impact on several areas

The introduction of plating through mask technology as a process has had an unprecedented impact on magnetic storage density capability.  Storage density per square inch has increased from two million in 1976 to 1000 million bits/in.² in 1996, and the density storage race still continues.  The information that once required several 14-in.-diameter disks when using ferrite heads, with the invention of thin film heads and thin film disks, can now be stored on two or three of 3¼- or even 2½-in.-diameter disks.  It is anticipated that electroplating through lithographic masks processes will carry us through year 2010, all the way to the theoretical limit of the magnetic recording.

Another important impact of the capability of high density magnetic storage - with its electroformed through resist mask heads - was the development of the Internet, with the servers capable of storing very large amounts of data and being capable of readily transmitting, in fractions of seconds, extremely large volumes of data from servers to the personal computers connected to the Internet.

In the electronics industry, since the first introduction of plating-through-masks to electroform thin film heads in 1979, this technology has been introduced in fabrication of conductors in thin film silicon chip carriers, in high resolution printed circuit boards, and was explored as a potentially important technique for circuitization of the silicon chips.

The application of the electroforming approach through-resist-mask is making possible what was once the impossible: Micromotors, accelerators, micro-valves, electro-optical devices and many other three-dimensional structures.  Micromechanics is on the verge of nearly explosive growth.  Its application is being considered in a variety of areas: Automotive, magnetic storage, medical instruments, aerospace, and military and civilian applications in which it is expected to replace very mechanically fabricated and assembled complex mechanically fabricated and assembled instruments.

While plating through mask technology has found many uses in electronics, made possible thin film magnetic heads and a variety of other devices, and represents several billion dollars in business per year in electronics, there are still many reluctant engineers and skeptics among the physicists and electrical engineers.  They look on the field of electroplating as an art rather than a controllable and reproducible science.  For suggestions on how to change these views, the reader is referred to a paper written in 1984.²⁰

Electroplating-through-mask technology has found its way into fabrication of almost all components of a modern computer, and has enabled manufacture of personal computers and laptops.  Because of its very high precision, faithful replication of masks and ability to form very high aspect ratio structures, it now commands a multi-billion-dollar market per year in electronics alone.  It has still yet an exciting future with its latest application in MEMS.  Who can foresee its next application?

Acknowledgment

Dr. Romankiw extends his sincere thanks to his co-workers who have worked with him for more than 25 years to change the perception of plating from an art to a science by demonstrating its usefulness in many areas of electronics and in MEMS.  He acknowledges that part of the motor project was done under ARPA sponsorship.

References

1.   G. DiBari & R. Parkinson, Proc. AESF Electroforming Course & Symposium, 33 (1996).

2.   L.T.Romankiw, "Evolution of Plating Through Lithographic Mask Technology," Proc. ECS Symp. of Mag. Materials, Processes & Devices IV, Applications to Storage & Microelectromechanical Systems (MEMS), Ed. by L.T. Romankiw & D.A. Herman Jr., PV 95-18, 253 (1995).

3.   E.W. Becker, W. Ehrfeld, P. Hagman, A. Mauer, & D. Muchmayer, "Fabrication of Microstructure with High Aspect Ratios & Great Structural Heights by Synchrotron Radiation Lithography, Galvanoforming & Plastic Molding," Microelectronic Engineering, 4, 34 (1986).

4.   R.E. Jones Jr., "IBM 3370 Film Head Design & Fabrication," IBM Publication: Disk Storage Development, 6 (1975).

5.   L.T. Romankiw, S. Krongelb, D.A. Thompson, R. Anderson, E.E. Castellani, P.M. McCaffrey, A.T. Pfeiffer & B.J. Stoeber, ECS Extended Abstracts, Vol. 79-2, 1170 (1979).

6.   L.T. Romankiw, "Thin Film Inductive Heads: From One to Thirty-one Turns," Proc. ECS Symp. on Magnetic Materials, Processes & Devices, PV 90-8, 39 (1990).

7.   L.T. Romankiw, E.E. Castellani & M. Hatzakis, "Additive Electroplating Limits for Gold Conductors Using PMMA Electron Beam Resist," J. ECS Long Abstracts, No. 208 (1974).

8.   E. Spiller, R. Fader, J. Topalian, E.E. Castellani, L.T. Romankiw & M. Heritage, "X-ray Lithography for Bubble Devices," Solid State Technology, 62-68 (April 1976).

9.   J.V. Powers, L. T. Romankiw, "Electroplating Cell Including Means to Agitate the Electrolyte in Laminar Flow," U.S. Patent 4,652,442 (1972).

10. P. Andricacos & L.T. Romankiw, "Magnetically Soft Materials in Data Storage: Their Properties & Electrochemistry," Advances in Electrochemical Science & Engineering, Vol. 3, VCH Publishers Inc., NY, NY, 1994; p. 303.

11. S.Mehdizadeh, J. Dukovic, P.C. Andricacos, L.T. Romankiw & H.Y. Cheh, "Optimization of Electrodeposit Uniformity by the Use of Auxiliary Electrodes," Journal ECS, 137, 110 (1990).

12. S. Mehdizadeh, J. Dukovic, P.C. Andricacos, L.T. Romankiw & H.Y. Cheh, "The Influence of Lithographic Patterning on Current Distribution: A Model for Microfabrication by Electrodeposition," Journal ECS, 139, 78 (1990).

13. S. Mehdizadeh, J. Dukovic, P.C. Andricacos, L.T.Romankiw & H.Y. Cheh, "The Influence of Lithographic Patterning on Current Distribution in Electrochemical Microfabrication II: Experimental Study & Mass-transfer Effect," Journal ECS, 140, 3497 (1993).

14. J.O. Dukovic, "Current Distribution & Shape Change in Electrodeposition of Thin Films for Microelectronic Fabrication," Advances in Electrochemical Science & Engineering, Vol. 3, 119, VCH Publishers, NY, NY (1994).

15. L.T. Romankiw, "Pattern Generation in Metal Films Using Wet Chemical Techniques: A Review," ECS Monograms, "Etching for Pattern Definition," 161 (1976).

16. S. Krongelb, J.O. Dukovic, M.L. Komsa, S. Mehdizadeh, L.T. Romankiw, P.C. Andricacos, A.T. Pfeiffer & K. Wong, "The Application of Electrodeposition Process to Advanced Fabrication," Proc. SPIE, Microelectronic Interconnects & Packages: Optical & Electrical Technologies, Vol. 1389, 249 (1990).

17. R. Feder, E. Spiller & J. Topelian, "Replication of 0.1 μm Geometries with X-ray Lithography," J. Vac. Sci, Techn., Vol. 12, 1332 (Nov/Dec 1975).

18. B. Loechel, A. Maciossek, H.J. Quenzer & B. Wagner, "Electrochemical Microfabrication II," Proc. ECS, PV 94-32, 100 (1994).

19. R.E. Acosta, et al., "Integrated Variable Reluctance Magnetic Minimotor," Proc. ECS Magnetic Materials, Processes & De¬vices IV: Application to Storage & Microelectromechanical Systems (MEMS), PV 95-18, 508 (1995).

20. L.T. Romankiw, "Electrochemical Technology in Electronics Today & Its Future: A Review," Oberfläche-Surface, 25, No. 8, 243 (1984).

About the author (at the time of publication and updated)

Dr. Lubomyr T. Romankiw is an IBM Fellow in IBM's T.J. Watson Research Center, Yorktown Heights, NY(10598), where he has been affiliated since 1962.  He holds a B.Sc. in chemical engineering from the University of Alberta and M.Sc. and Ph.D. degrees in metallurgy from MIT.  The holder of 65 patents and more than 120 published inventions, Dr. Romankiw has also published more than 150 scientific papers and reports.  His research has dealt with nearly all aspects of plating and etching technology as used in the electronics industry.  He is a co-inventor of laser-enhanced plating and etching.  His work - particularly in electrochemistry and electrochemical technology in the electronics and electrochemical fabrication of thin film heads for high-performance magnetic storage - has had immense impact on the industry.

Dr. Romankiw's perspective in research has always been to find and give a scientifically sound explanation to observed phenomena and to relate plating conditions, solution chemistry, electrode kinetics and processing parameters to structure and properties of the deposits and device performance.  As a result, with his co-workers, he has made a substantial contribution toward making plating technology a science.  He organized eight major electroplating symposia in connection with the Electrochemical Society (ECS) and the International Society of Electrochemists on plating for magnetic and electronic applications and was co-editor of seven volumes of symposia proceedings.  His work on the development of thin film inductive and MR re-cording head processes, X-ray mask lithography, laser-enhanced plating, electroetching and other aspects of application of electrochemical technology in electronic device fabrication has earned him 12 IBM Outstanding Invention and Outstanding Contribution Awards, along with 24 IBM Invention Achievement Awards.

In 1991, Dr. Romankiw was named as the AESF Scientific Achievement Award recipient.  He has also received other prestigious awards and recognition: in 1990, elected a Fellow of ECS, Inc.: a charter member of IBM's Academy of Technology in 1987; and a member of the Academy of Engineering Sciences of Ukraines in 1992.  He was awarded the Vittoria de Nore Medal of ECS in 1994; the IEEE Morris A. Lieberman Award in 1994; and was awarded the Perkin Medal in 1993 by the Society of Chemical Industries of the U.S., the highest honor of the chemical industry, for his inventions and development of thin film head technologies.  He also received the Inventor of the Year Award from the Eastern New York Intellectual Property Law Association (2000) and the Inventor of the Year Award from the New York Intellectual Property Law Association (2001). 

In a ceremony on May 2, 2012, he was one of two IBM scientists inducted into the National Inventor’s Hall of Fame for their invention that paved the way for the advancement of commercial disk storage technology used in computers, digital cameras and other devices.  He and Dr. David Thompson were honored for their invention of a technique that produced the first practical and manufacturable thin film magnetic head, which increased the density of data stored on magnetic disks and dramatically reduced the cost of data storage.