Transformer

1. A transformer comprising:

a semiconductor substrate comprising a first conductivity type semiconductor layer;

a semiconductor layer coil comprising a semiconductor layer coil wiring composed of a second conductivity type semiconductor layer laminated on a surface side of the first conductivity type semiconductor layer;

a trench coil electrically connected with the semiconductor layer coil in parallel;

a coil insulating layer laminated on the surface side of the first conductivity type semiconductor layer, covering over both of the semiconductor layer coil and the trench coil; and

a metal layer coil arranged on a surface of the coil insulating layer,

wherein a trench is formed in the first conductivity type semiconductor layer,

each of the semiconductor layer coil wiring and the trench has a spiral shape,

the trench and the semiconductor layer coil wiring are alternately disposed in the radial direction thereof,

the trench coil comprises (a) a trench insulating film arranged on an inner surface of the trench, and (b) a trench coil wiring composed of a conductive layer disposed within the trench and covered by the trench insulating film, and

the metal layer coil opposes both of the semiconductor layer coil and the trench coil.

2. The transformer according to claim 1 , further comprising:

a metallic compound layer arranged between the semiconductor layer coil and the coil insulating layer, the metallic compound layer making contact with the semiconductor layer coil.

3. The transformer according to claim 2 , wherein

the metallic compound layer is composed of a silicide layer.

4. An apparatus comprising:

a first coil;

a second coil magnetically connected to the first coil;

a transmitter circuit electrically connected to one of the first and second coils; and

a receiver circuit electrically connected to another of the first and second coils, wherein

the first coil comprises a semiconductor layer coil and a trench coil electrically connected with the semiconductor layer coil in parallel,

the semiconductor layer coil comprises a semiconductor layer coil wiring composed of a semiconductor layer,

the trench coil comprises a trench coil wiring composed of a conductive layer and a trench insulating film covering the trench coil wiring,

each of the semiconductor layer coil wiring and the trench coil wiring has a spiral shape,

the trench coil wiring and the semiconductor layer coil wiring are alternately disposed in a radial direction thereof, and

the second coil comprises a metal layer coil opposing both of the semiconductor layer coil and the trench coil.

5. The apparatus according to claim 4 , wherein the semiconductor layer coil further comprises a metallic compound layer arranged on the semiconductor layer coil wiring, and the metallic compound layer makes contact with the semiconductor layer coil wiring.

6. The apparatus according to claim 5 , wherein the metallic compound layer is composed of a silicide layer.

7. The apparatus according to claim 4 , further comprising a coil insulating layer disposed between the first coil and the second coil, wherein the first coil is insulated from the second coil by the coil insulating layer.

8. The apparatus according to claim 4 , wherein the transmitter circuit is electrically connected to the first coil, and the receiver circuit is electrically connected to the second coil.

9. The apparatus according to claim 4 , wherein the transmitter circuit is electrically connected to the second coil, and the receiver circuit is electrically connected to the first coil.