Precision laser adjustable thin film capacitors
Disclosed are apparatus and 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 adjusting the resulting capacitance value of a thin film capacitor while such capacitor is in operation in a circuit, comprising:
providing a capacitor having respective first and second terminals; and
providing a capacitor array, situated electrically between such respective first and second terminals, such capacitor array comprising a plurality of respectively valued sub-component capacitors, arranged so that respective of such sub-component capacitors may be removed from the resulting capacitance value of such adjustable thin film capacitor; and
adjusting the resulting capacitance value of such thin film capacitor by respectively removing therefrom selected of such respectively valued sub-component capacitors;
wherein such sub-component capacitors comprise a base value capacitor and plural parallel coupled capacitors configured such that one or more of the parallel coupled capacitors may be effectively removed from such parallel connection;
such plural parallel coupled capacitors are coupled by way of fusible links, configured in a capacitive laddering effect; and
such adjusting step includes adjusting the resulting capacitance value of such thin film capacitor by selectively removing one or more of such parallel coupled capacitors from such parallel connection thereof by disrupting their corresponding fusible links, so as to correspondingly adjust the resulting capacitance value of such thin film capacitor.
2. The method as in claim 1 , wherein:
such fusible links coupling the plurality of capacitors in parallel may be respectively ablated by laser irradiation; and
such method further includes covering at least such fusible links with a laser radiation transparent passivation layer, whereby such resulting capacitance value of such thin film capacitor may be adjusted via laser trimming of such laser-ablative fusible links while such thin film capacitor is in an intended use environment.
3. The method as in claim 2 , further including situating such fusible links such that no electrode of a respective subcomponent 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.
4. The method as in claim 1 , 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.
5. 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.