Metal-insulator-metal capacitors
An interdigitated Metal-Insulator-Metal (MIM) capacitor provides self-shielding and accurate capacitance ratios with small capacitance values. The MIM capacitor includes two terminals that extend to a plurality of interdigitated fingers separated by an insulator. Metal plates occupy layers above and below the fingers and connect to fingers of one terminal. As a result, the MIM capacitor provides self-shielding to one terminal. Additional shielding may be employed by a series of additional shielding layers that are isolated from the capacitor. The self-shielding and additional shielding may also be implemented at an array of MIM capacitors.
1. An interdigitated Metal-Insulator-Metal capacitor, comprising:
a first terminal extending to a plurality of metal fingers formed in a first layer, two of the metal fingers being outermost of the fingers;
a second terminal extending to one or more metal fingers formed in the first layer and interspaced between the first terminal fingers; and
a plurality of metal plates occupying layers above and below the first layer, the metal plates extending to the first layer at least to the outermost metal fingers and connected to the outermost metal fingers.
2. The capacitor of claim 1 , wherein the outermost metal fingers are coupled to secondary metal fingers, the outermost metal fingers and secondary metal fingers substantially surrounding the other of the metal fingers.
3. The capacitor of claim 1 , further comprising shielding layers occupying layers above and below the plurality of metal plates and separated from the metal plates by at least one dielectric layer each above and below the plurality of metal plates, the shielding layers electrically isolated from the metal fingers.
4. The capacitor of claim 3 , further comprising a series of stacked metal strips and vias connecting the shielding layers, the series and shielding layers forming a shield substantially encompassing the plurality of metal plates.
5. The capacitor of claim 3 , wherein the shielding layers are separated from the plurality of metal plates by at least one dielectric layer each above and below the plurality of metal plates.
6. The capacitor of claim 3 , wherein the shielding layers include metal plates.
7. The capacitor of claim 3 , wherein one of the shielding layers includes a diffused region.
8. The capacitor of claim 1 , wherein the second terminal extends beyond the plurality of metal fingers by a length exceeding a respective fringing-field extent, fingers of the second terminal being coupled together with the second terminal at a region exceeding the fringing-field extent.
9. The capacitor of claim 1 , wherein the second terminal extends beyond the plurality of metal fingers by a length exceeding a fringing-field generated by the plurality of metal fingers, fingers of the second terminal being coupled together at a region between the plurality of metal plates.
10. An array of capacitors, comprising:
at least two capacitors, each capacitor comprising:
(i) a plurality of metal fingers formed in a first metal layer and coupled to a respective first terminal; and
(ii) a plurality of metal plates occupying layers above and below the first layer, the metal plates interspaced between and extending to the first layer at least to the outermost metal fingers and connected to the outermost metal fingers; and
a second terminal formed in the first metal layer and extending to at least one common metal finger between the plurality of metal fingers of each capacitor.
11. The array of claim 10 , wherein the second terminal extends beyond the plurality of metal fingers of each of the capacitors by a length exceeding a fringing-field extent from the metal fingers, fingers of the second terminal being coupled together at a region exceeding the fringing-field extent.
12. The array of claim 10 , wherein the second terminal includes a plurality of common metal fingers, the plurality of common metal fingers coupled together at a region between the plurality of metal plates of at least one of the plurality of capacitors.
13. The array of claim 12 , wherein the at least one of the capacitors includes secondary metal fingers coupled to the outermost metal fingers, the outermost metal fingers and secondary metal fingers substantially surrounding the common metal fingers at three sides.
14. An interdigitated Metal-Insulator-Metal capacitor comprising:
a plurality of parallel metal fingers formed in a first layer and separated by a dielectric;
a first terminal coupled to a first subset of the plurality of parallel metal fingers, two of the first subset of the plurality of parallel metal fingers being outermost of the fingers;
a second terminal coupled to a second subset of the plurality of metal fingers, the second subset being interspaced between the first subset and electrically insulated from the first terminal by the dielectric; and
a plurality of metal plates occupying layers above and below the first layer, the metal plates extending to the first layer at least to the outermost metal fingers and connected to the outermost metal fingers.