Method for laser adjustable thin film capacitors
Disclosed are methodology for providing a precision laser adjustable (e.g., trimmable) thin film capacitor array. A plurality of individual capacitors are formed on a common substrate and connected together in parallel by way of fusible links. The individual capacitors are provided as laddered capacitance value capacitors such that a plurality of lower valued capacitors corresponding to the lower steps of the ladder, and lesser numbers of capacitors, including a single capacitor, for successive steps of the ladder, are provided. Precision capacitance values can be achieved by either of fusing or ablating selected of the fusible links so as to remove the selected subcomponents from the parallel connection. In-situ live-trimming of selected fusible links may be performed after placement of the capacitor array on a hosting printed circuit board.
1. A method of making a capacitor array configured for post production in-situ laser trimmable use, for adjustment of the resulting capacitance value thereof while such capacitor array is in operation in a circuit, such method comprising:
providing a substrate;
forming a first metallization layer on the substrate and having a first portion thereof providing a respective connection portion for a first terminal and providing a plurality of common electrode areas, and having a second portion thereof providing a respective connection portion for a second terminal;
forming a dielectric layer on the first metallization layer and having respective first and second windows formed therein and aligned for respective association with such first and second terminal connection portions of the such first metallization layer;
forming a second metallization layer on such dielectric layer and having respective first and second terminal connection portions thereof aligned with corresponding such portions of the first metallization layer, and having a plurality of second electrode layers for correspondence with selected portions of such common electrode areas of the first metallization layer, and having a respective plurality of fusible links which are respectively ablatable by laser irradiation and associated respectively with such second electrode layers for fusibly connecting such second electrode layers with a selected one of such first and second terminal connections portions of the second metallization layer;
forming a laser radiation transparent passivation layer over the second metallization layer and having respective first and second windows formed therein and aligned for respective association with such first and second terminal connection portions of the second metallization layer; and
providing termination plating received in such first and second windows of such passivation layer and interconnected with the first metallization layer via such respective windows of such dielectric layer and of such passivation layer, and via such respective first and second terminal connection portions of the second metallization layer; and
adjusting the resulting capacitance value of such capacitor array with laser ablation through such passivation layer of selected fusible links while such capacitor array is operative in a circuit, for precise trimming of such capacitor array capacitance value.
2. The method as in claim 1 , wherein such termination plating comprises copper.
3. The method as in claim 1 , wherein such plurality of second electrode layers of the second metallization layer, such corresponding selected portions of such common electrode areas of the first metallization layer, and such dielectric layer situated therebetween, form respectively valued sub-component capacitors, arranged so that respective of such sub-component capacitors may be removed from the resulting capacitance value of such capacitor array upon ablation of its respective fusible link.
4. The method as in claim 3 , wherein such sub-component capacitors comprise a base value capacitor and plural parallel coupled capacitors configured in a capacitive laddering effect, such that one or more of the parallel coupled capacitors may be effectively removed from such parallel connection.
5. The method as in claim 4 , wherein such capacitive laddering configuration includes at least one respective single capacitor of relatively larger capacitive value and a plurality of substantially duplicative capacitors of at least two relatively lower capacitive values.
6. The method as in claim 4 , wherein:
such capacitive laddering configuration includes at least two respective single capacitors having capacitive values respectively of at least 1.0 pF; and
such plurality of substantially duplicative capacitors includes at least ten of such capacitors having capacitive values of respectively no more than 0.5 pF.
7. The method as in claim 3 , wherein such fusible links are situated such that no electrode of a respective sub-component capacitor lies either above or below a respective fusible link, so that subsequent ablation of any fusible link does not create potential shorts or leakages.