Spiral inductors, transformers and baluns formed from flexible dielectric sheets
New types of circuit elements for integrated circuits include structures wherein a thickness dimension is much greater than a width dimension and is more closely spaced than the width dimension in order to attain a tight coupling condition. The structure is suitable to form inductors, capacitors, transmission lines and low impedance power distribution networks in integrated circuits. The width dimension is on the same order of magnitude as skin depth. Embodiments include a spiral winding disposed in a silicon substrate formed of a deep, narrow, conductor-covered spiral ridge separated by a narrow spiral trench. Other embodiments include a wide, thin conductor formed in or on a flexible insulative ribbon and wound with turns adjacent one another, or a conductor in or on a flexible insulative sheet folded into layers with windings adjacent one another Further, a method of manufacture includes directional etching of the deep, narrow spiral trench to form a winding in silicon.
1 . An inductor comprising:
a conductive element on a flexible dielectric sheet, with a thickness of the conductive element being substantially greater than a width of the conductive element;
a winding of the flexible dielectric sheet formed in a continuous symmetric pattern and wound into a roll so that segments of the conductive element are adjacent one another and separated by the flexible dielectric sheet to attain a tight coupling condition defined as a high coupling coefficient across multiple turns; and
terminals coupled to each end of the conductive element for external electrical connection, wherein the conductive element and the flexible dielectric sheet are folded such that the thickness of portions of the conductive element adjacent to the terminals extends perpendicular to the thickness of at least a portion the conductive element in the roll.
2 . The inductor of claim 1 wherein the width is selected to be on a same order of magnitude as skin depth.
3 . The inductor of claim 1 wherein the winding has a straight innermost segment with a Q that is greater than one at a design frequency of the inductor.
4 . An inductor comprising:
a conductive element on a flexible dielectric ribbon, with a thickness of the conductive element being substantially greater than a width of the conductive element;
a winding disposed in a coil of the flexible dielectric ribbon around a central axis such that the conductive element defines turns adjacent one another and separated by the flexible dielectric ribbon to attain a tight coupling condition defined as a high coupling coefficient across multiple turns; and
terminals coupled to each end of the conductive element for external electrical connection; wherein the conductive element and the flexible dielectric ribbon are folded such that the thickness of portions of the conductive element adjacent to the terminals extends perpendicular to the thickness of at least a portion of the conductive element in the coil.
5 . The inductor of claim 4 wherein the width is selected to be on a same order of magnitude as skin depth.
6 . The inductor of claim 4 wherein the winding has a straight innermost segment with a Q that is greater than one at a design frequency of the inductor.
7 . An electrical component comprising:
a flexible dielectric sheet having first conductive traces disposed thereon, wherein a thickness of the first conductive traces is substantially greater than a width of the first conductive traces, the first conductive traces each having segments forming a continuous symmetric pattern, wherein the flexible dielectric sheet is wound into a roll and arranged so that the segments of the first conductive traces are adjacent one another and separated by the flexible dielectric sheet to attain a tight coupling condition defined as a high coupling coefficient across multiple turns of the roll; and
terminals coupled to each end of the first conductive traces for external electrical connection, wherein the first conductive traces and the flexible dielectric sheet are folded such that the thickness of portions of the first conductive traces adjacent to the terminals extend perpendicular to the thickness of at least a portion of the first conductive traces in the roll.
8 . The electrical component of claim 7 wherein the first conductive traces comprise at least three first conductive traces each having first portions that are substantially a same thickness and second portions that are a different thickness, and wherein each of the first conductive traces are electrically coupled to different pins of the terminals.
9 . The electrical component of claim 7 wherein the flexible dielectric sheet is folded in overlay so that the segments of the first conductive traces are adjacent one another to provide an inductor.
10 . The electrical component of claim 7 wherein the flexible dielectric sheet has one or more second conductive traces disposed thereon, the one or more second conductive traces having a shorter length than the first conductive traces, the first conductive traces forming a primary winding of a transformer and the one or more second conductive traces forming a secondary winding of a transformer.
11 . The electrical component of claim 7 wherein the flexible dielectric sheet has one or more second conductive traces disposed thereon, the one or more second conductive traces having a shorter length than the first conductive traces, the first conductive traces forming a primary winding of a balun and the one or more second conductive traces forming a secondary winding of a balun.
12 . The electrical component of claim 7 wherein the flexible dielectric sheet is a flexible printed circuit board (PCB).
13 . The electrical component of claim 7 wherein a length of the first conductive traces on the flexible dielectric sheet is at least five times longer than a length of one of the terminals.
14 . The electrical component of claim 7 wherein an inner dimension of the multiple turns of the first conductive traces is equal to or greater than a thickness of the first conductive traces.
15 . The electrical component of claim 7 wherein the multiple turns of the first conductive traces include at least five turns.
16 . A printed circuit board (PCB) having the electrical component of claim 7 coupled thereto, wherein the multiple turns of the first conductive traces are disposed on a front side of the PCB, and portions of the flexible dielectric sheet extend through the PCB so that the terminals are electrically coupled to a back side of the PCB.