RF power transistor device with high performance shunt capacitor and method thereof
An integrated shunt capacitor comprises a bottom plate ( 86,88 ), a capacitor dielectric ( 92 ) overlying a portion of the bottom plate, a top plate ( 62 ) overlying the capacitor dielectric, a shield ( 74 ) overlying a portion of the top plate ( 62 ); and a metallization feature ( 70 ) disposed about and isolated from at least two sides of the top plate ( 62 ), the metallization feature ( 70 ) for coupling the bottom plate ( 86,88 ) to the shield ( 74 ). In one embodiment, an RF power transistor has an impedance matching network including an integrated shunt capacitor as described herein.
1. An integrated shunt capacitor comprising:
a conductive bottom plate;
a capacitor dielectric overlying a portion of the bottom plate;
a conductive top plate overlying the capacitor dielectric;
a shield overlying a portion of the top plate, wherein the shield is isolated from the top plate; and
a metallization feature disposed (i) along at least two sides of the top plate and (ii) isolated from the at least two sides of the top plate, wherein the metallization feature electrically couples the bottom plate to the overlying shield, further wherein (iii)(a) the metallization feature that extends along and is isolated from the sides of the top plate, (iii)(b) the bottom plate, and (iii)(c) the overlying shield together form a grounded chamber for isolating a corresponding portion of the integrated shunt capacitor from parasitic interference external to the integrated shunt capacitor.
2. The shunt capacitor of claim 1 , further comprising:
a bond pad disposed adjacent to the top plate, wherein a top metal metallization couples the bond pad to the top plate, in a region of the top plate not covered by the shield overlying a portion of the top plate.
3. The shunt capacitor of claim 1 , wherein the metallization feature comprises a U-shaped feature, as viewed from a top down perspective.
4. The shunt capacitor of claim 3 , further wherein the U-shaped feature extends along a first dimension on two sides and along a second dimension on a third side of the shunt capacitor.
5. The shunt capacitor of claim 1 wherein the metallization feature includes both a first layer metallization metal and a second layer metallization metal.
6. The shunt capacitor of claim 1 , wherein the shield comprises a grounding shield, the grounding shield including a metallization coupled to a ground potential.
7. The shunt capacitor of claim 6 , further wherein coupling together of the bottom plate, metallization feature, and grounding shield reduces a series resistance of the bottom plate to ground potential.
8. The shunt capacitor of claim 6 , wherein the shunt capacitor comprises a unit cell implementation.
9. The shunt capacitor of claim 8 , wherein the bottom plate, metallization feature, and grounding shield provide a grounded chamber for isolating a corresponding portion of the unit cell from external interference.
10. The shunt capacitor of claim 8 , further comprising:
a plurality of unit cell implementations disposed adjacent to one another, wherein bottom plates of adjacent unit cell implementations are merged together.
11. The shunt capacitor of claim 1 , wherein the shunt capacitor is implemented in an impedance matching network of a radio frequency (RF) power transistor.
12. The shunt capacitor of claim 1 , further comprising:
a semiconductor substrate; and
an isolation layer overlying the substrate, wherein the bottom plate overlies the isolation layer.
13. The shunt capacitor of claim 1 , wherein the bottom plate comprises tungsten silicide and wherein the capacitor dielectric comprises nitride.
14. The shunt capacitor of claim 1 , wherein the portion of the top plate shielded by the shield comprises a percentage of the top plate tailored according to requirements of a given radio frequency (RF) power transistor application.
15. A radio frequency (RF) power transistor having an impedance matching network including an integrated shunt capacitor as claimed in claim 1 .
16. An integrated shunt capacitor comprising:
a conductive bottom plate;
a capacitor dielectric overlying a portion of the bottom plate;
a conductive top plate overlying the capacitor dielectric;
a shield overlying a portion of the top plate. wherein the shield comprises a grounding shield, the grounding shield including a metallization coupled to a ground potential; and
a metallization feature disposed about and isolated from at least two sides of the top plate, the metallization feature for coupling the bottom plate to the shield,
wherein the shunt capacitor comprises a unit cell implementation,
wherein the bottom plate, metallization feature, and grounding shield provide a grounded chamber for isolating a portion of the unit cell from external interference, and
wherein the grounded metallization feature extending along three sides of the unit cell forms a grounded wall for reducing a parasitic interference external to the unit cell.
17. An integrated shunt capacitor comprising:
a conductive bottom plate;
a capacitor dielectric overlying a portion of the bottom plate;
a conductive top plate overlying the capacitor dielectric;
a shield overlying a portion of the top plate; and
a metallization feature disposed about and isolated from at least two sides of the top plate, the metallization feature for coupling the bottom plate to the shield, wherein the shunt capacitor comprises a unit cell implementation, further comprising:
a bonding pad; and
an arrangement of shunt capacitor unit cells disposed around at least two side edges of the bonding pad.
18. The shunt capacitor of claim 17 , wherein the shield further includes overlying a portion of the top plate of each unit cell of the arrangement of shunt capacitor unit cells disposed around the bonding pad.
19. The shunt capacitor of claim 18 , wherein the arrangement includes first, second, and third pluralities of unit cells disposed around three side edges of the bonding pad, respectively.
20. The shunt capacitor of claim 19 , further wherein each plurality of unit cells is coupled to a corresponding side of the bonding pad through a metallization extension coupled to a corresponding top plate contact via of each unit cell of each plurality of unit cells.