Sol Krongelb

Unidirectional anisotropy in nickel-iron films by exchange coupling with antiferromagnetic films

A new process for obtaining unidirectional anisotropy in 80:20 NiFe films is described. This process was applied to the biasing of a magnetoresistive (MR) read head and no Barkhausen noise was observed in its output.

An integrated magnetoresistive read, inductive write high density recording head

The design, fabrication and performance of an experimental thin film recording head is described which has 25 μm and 125 μm track width magnetoresistive (MR) read elements combined with a single turn thin film inductive write head. The MR read elements are shielded to provide high linear resolution with an equivalent read gap of 1/2 μm and are internally biased by means of a permanent magnet film in the gap. The best head performance with a 0.5 μm air bearing on a high performance disk was: write current of 400 mA peak, isolated pulse readback signal of 40 mV peak per mm of track width at 10 mA sense current, with a 6 db density of 440 flux changes per mm (11 kfci).

Electrochemical process for advanced package fabrication

Interconnections for high-end applications are essentially low-resistance transmission-line structures with precisely controlled cross-sectional shapes and dimensions. The relatively thick copper conductors-typically 6 µm or more-combined with the stringent control required on the 10-20-µm-wide cross sections stretches the capabilities of the subtractive etch and lift-off processes that are typically used in semiconductor fabrication to pattern evaporated and sputtered metal films. Electroplating through a photoresist mask, which has proven itself to be a highly effective, precision manufacturing process for thin-film magnetic recording heads, is, however, capable of meeting and far exceeding the requirements of package fabrication. This paper describes the fabrication of a package structure that integrates traditional dry-process technologies with electrolytic copper plating to form the conductors, polyimide backfill and planarization steps to form the dielectric, and electroless deposition to selectively clad the copper lines to prevent adverse reaction of the copper with water generated during the polyimide cure. The discussion highlights salient issues which are pertinent to the compatibility of the individual process steps and to the extension of the technology to more demanding packaging structures and to other applications.

Annealing of thin magnetoresistive permalloy films

The figure of merit of magnetoresistive Permalloy thin films, which are commonly used for bubble domain sensors, is shown to improve considerably after annealing treatments. This improvement is caused by a lowering of the electrical resistivity, due to particle size and grain growth with activation energies of 0.70 ± 0.05 eV and 1.86 ± 0.15 eV, respectively. Comparisons indicate that thin permalloy films, which are deposited at 250°C and subsequently annealed, are superior as sensor materials to those deposited at 325°C.

Integrated, variable-reluctance magnetic minimotor

The use of lithography and electroplating to fabricate variable-reluctance, nearly planar, integrated minimotors with 6-mm-diameter rotors on silicon wafers is described. The motors consist of six electroplated Permalloy® horseshoe-shaped cores that surround the rotor. Copper coils are formed around each core. The Permalloy and copper electroplating baths, electroplating seed layers, and through-mask plating techniques are similar to those used to fabricate inductive thin-film heads. High-aspect-ratio optical lithography or X-ray lithography was used to form the various resist layers. The rotors were fabricated separately, released from the substrate, and then slipped onto the shaft, which was plated as part of the stator fabrication process. The fabrication processes for stator and rotor are described in this paper, and initial minimotor operation data are presented.

Study of field‐driven wall‐configuration conversions for laminated Permalloy in the easy‐axis state

Laminated Permalloy, with edge‐curling walls replacing closure domains, has been proposed to increase permeability and reduce wall noise in recording. However, in structures meeting the criteria for Slonczewski’s ‘‘easy‐axis’’ state, normal walls often coexist with edge‐curling walls. We have used our laser magneto‐optic microscope to study inductive‐head‐yoke shaped elements of two and four Permalloy layers separated by nonmagnetic, metallic spacers. In the four‐magnetic‐layer sample a state with a single wall, terminating at the edge‐curling regions and lying along the easy‐axis direction, is often observed on the top and bottom layers. Some elements may be driven into an easy‐axis state with no observed domain walls. The two‐magnetic‐layer sample also exhibited simultaneous one‐wall structures on the top and bottom layers. The other stable configuration was a no‐wall state on the top layer and a two‐wall (three‐domain) state on the lower layer. These ‘‘coupled’’ states were exceptionally stable in both...

A permalloy current sensor

The design, fabrication and output characteristics of a thin film Permalloy magnetoresistive magnetic field sensor in a balanced bridge configuration are described. The bridge elements consist of two magnetostatically coupled Permalloy films (100 to 500 A°) separated by a thin film titanium spacer (100 to 1,000 A°). When this bridge is integrated with electrically isolated overlay conductors, the resulting device is ideally suited to sense currents in power supply applications over a 0 to 100 MHz frequency range with negligible dc offset. Devices with 35 mV peak outputs optimized to sense 50, 250 and 500 mA peak currents have been implemented and tested.

Grain growth in Ni-Fe thin films

Abstract Grain growth in vapor-deposited 81 at.% Ni+19 at.% Fe thin films 200 and 400 A thick in the temperature range 350°–450°C has been investigated by transmission electron microscopy. The results have been interpreted in terms of a previously published model of grain growth in thin films on substrates. The activation energy for grain growth in this alloy has been determined as 1.7±0.2 eV.

Fabrication and operation of indented angelfish bubble-domain shift register

A clear-view bubble-domain shift register with an angelfish pattern sputter etched into the surface of orthoferrite platelets was fabricated and its operation was demonstrated. For a typical Gd-orthoferrite platelet ∼ 70 μm thick, shift register operation was realized with triangles etched to a depth of ∼ 6 μm with an edge gradient of ∼ 1.3. Specimen preparation and device operation are described.

Application of electrodeposition processes to advanced package fabrication

Conductors for advanced packaging have thicknesses of the order of 6 microns and aspect ratios that are approaching 1: 1. These requirements are well within the capabilities of electrodeposition technology. The experience of the last decade in using electrodeposition to build thin-film recording heads which have similar and in some respects even more demanding specifications than packaging structures is directly applicable to the needs of packaging. This paper will show the application of resist-pattern plating to fabricating conductors for packaging will discuss the capabilities and limitations of resist-pattern plating plating and will indicate the parameters that need to be understood and controlled for the successful application of electrodeposition technology to microelectronic structures. A multi-level package structure can be considered as a repetition of several conductor and via levels. Each conductor/via level is made by first sputter depositing a seed layer of Cr/Cu in which the Cu is of the order of 2000 A thick. A layer of photoresist is then applied over the seed layer and openings are patterned in the resist to defme the conductor pattern. Electrical contact is now made to the seed layer and the part is immersed in an electroplating solution to deposit Cu in the openings defmed by the resist pattern. The thickness of the deposit is determined by the time and current density of plating the thickness of the photoresist must slightly exceed the desired