A varactor comprising a first layer separated from a second layer by an insulating layer, wherein the first layer is a first type of semiconductor material and the second layer is a second type of semiconductor material and the insulation layer is arranged to allow an accumulation region to be formed in the first layer and second layer when a positive bias is applied to the first layer and the second layer and a depletion region to be formed in the first layer and second layer when a negative bias is applied to the first layer and the second layer.
1. A varactor comprising
a first layer separated from a second layer by an insulating layer, wherein the first layer is a p type of semiconductor material and the second layer is a n type of semiconductor material;
wherein the insulation layer is arranged to allow an accumulation region to be formed in the first layer and second layer when a positive bias is applied to the first layer and the second layer; and
a depletion region to be formed in the first layer and second layer when a negative bias is applied to the first layer and the second layer, the varactor characterized in that the first layer has a first doping p type region formed at the boundary to the insulating layer and a second p+ doping region formed on top of the first doping p type region.
2. A varactor according to claim 1 , wherein the doping impurities of the first layer and the second layer are arranged to be reduced at the boundary to the insulation layer to aid the formation of a depletion region within the first layer and second layer.
3. A varactor according to claim 1 , wherein the first doping region has a reduced number of doping impurities compared to the second doping region to aid the formation of a depletion region within the first layer.
4. A varactor according to claim 3 , wherein the second layer comprises a first n doping region and a second n+ doping region.
5. A varactor according to claim 1 , wherein:
the second layer has a first doping region formed at the boundary to the insulation layer and a second doping region;
the first doping region has a reduced number of doping impurities compared to the second doping region to aid the formation of a depletion region within the second layer.
6. A varactor according to claim 1 , wherein the insulation layer is an oxide layer.
7. A varactor according to claim 2 , wherein the first doping region has a reduced number of doping impurities compared to the second doping region to aid the formation of a depletion region within the first layer.
8. A varactor according to claim 2 , wherein:
the second layer has a first doping region formed at the boundary to the insulation layer and a second doping region;
the first doping region has a reduced number of doping impurities compared to the second doping region to aid the formation of a depletion region within the second layer.
9. A varactor according to claim 3 , wherein:
the second layer has a first doping region formed at the boundary to the insulation layer and a second doping region;
the first doping region has a reduced number of doping impurities compared to the second doping region to aid the formation of a depletion region within the second layer.
10. A varactor according to claim 4 , wherein:
the second layer has a first doping region formed at the boundary to the insulation layer and a second doping region;
the first doping region has a reduced number of doping impurities compared to the second doping region to aid the formation of a depletion region within the second layer.
11. A varactor according to claim 2 , wherein the insulation layer is an oxide layer.
12. A varactor according to claim 3 , wherein the insulation layer is an oxide layer.
13. A varactor according to claim 4 , wherein the insulation layer is an oxide layer.
14. A varactor according to claim 5 , wherein the insulation layer is an oxide layer.