Method of improving on-chip power inductor performance in DC-DC regulators

• US 7,351,593 B1
• Filed: 05/25/2005
• Issued: 04/01/2008
• Est. Priority Date: 01/24/2005
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Johnson, Peter, Hopper, Peter J., Hwang, Kyuwoon, Drury, Robert
• Primary Examiner(s): Picardat; Kevin M
• Application Number:
  US11/137,767
• Time in Patent Office: 1,042 Days
• Field of Search: 438/3, 257/295
• US Class Current: 438/3
• CPC Class Codes: H02M 7/003 Constructional details, e.g. physical layout, assembly, wiring or busbar connections

Abstract

A method is provided for forming the ferromagnetic core of an on-chip inductor structure. In accordance with the method, a static, permanent magnet is placed in proximity to a semiconductor wafer upon which the ferromagnetic core is being electroplated. The permanent magnet is place such that the magnetic field is orthogonal to the wafer. The “easy” axis material is that plated parallel parallel to the magnet'"'"'s field and saturates at a lower applied field. The “hard” axis is that plated perpendicular to the applied magnetic filed and saturates later, at a higher current level. This plating approach results in optimum magnetic alignment of the ferromagnetic core so as to maximize both the field strength/magnetic flux slope and magnitude before magnetic material saturation occurs.

Claims

1. A method of forming magnetic material on a substrate layer, the method comprising:

providing a permanent magnet in proximity to the substrate layer such that the magnetic field created by the permanent magnet is orthogonal to a substantially planar surface of the substrate layer;

forming a layer of magnetic material on the substantially planar surface.

2. A method as in claim 1, and wherein the magnetic material is a ferromagnetic material.

3. A method as in claim 2, and wherein the magnetic material is electroplated Permalloy.

4. A method as in claim 1, and wherein the magnetic material is selected from the group consisting of Permalloy, FeCrB, ZrCrTa, CoCr and CoFeNi.

5. A method of fabricating a switching regulator circuit on a semiconductor substrate, the method comprising;

forming a switching transistor structure on a substantially planar surface of the semiconductor substrate;

forming an inductor structure on the semiconductor substrate, the inductor structure being connected to the switching transistor structure, the inductor structure including upper and lower magnetic plates and a conductor core formed between the upper and lower magnetic plates, and

wherein the upper and lower magnetic plates are electroplated in the presence of a magnetic field that is orthogonal to the substantially planar surface of the semiconductor substrate.