Variable capacitor compromising MEMS devices for radio frequency applications

摘要

A variable capacitor (300) comprises cells (200, 400) that have an RF electrode (202, 402) coupled to a bond pad (30). Each cell comprises a plurality of MEMS devices (100) the capacitance of which can be changed by means of a movable electrode. The MEMS devices are placed in a sealed cavity of the cell and are arranged next to each other along the length of the RF electrode of the cell. The RF electrode of each cell can be trimmed so as to obtain an RF line (402) and a further ground electrode (404) and so as to scale the RF capacitance of the cell without impacting the mechanical performance of the MEMS cells. Each cell has the same control capacitance irrespective of the RF capacitance. This allows each cell to use the same isolation resistor required for RF operation and thus each cell has the same parasitic capacitance. This allows the CMOS control circuit to be optimized and the dynamic performance of the cells to be matched.

主权项

1. A variable capacitor, comprising: a substrate;
one or more bond pads disposed over the substrate; a first cell disposed over the substrate and coupled to the one or more bond pads, the first cell having a first end and a second end and comprising: an RF electrode coupled to the one or more bond pads and the first end of the first cell; a plurality of MEMS devices disposed over the RF electrode, each MEMS device having a first end and a second end and each MEMS device disposed over the RF electrode; and one or more ground electrodes coupled to the first end and the second end of each MEMS device and to the second end of the first cell; and a second cell disposed over the substrate and coupled to the one or more bond pads, the second cell having a first end and a second end and comprising: an RF electrode coupled to the one or more bond pads; a plurality of MEMS devices disposed over the RF electrode, each MEMS device having a first end and a second end and less than all of the total MEMS devices in the second cell are disposed over the RF electrode; and one or more ground electrodes coupled to the first end and the second end of each MEMS device and to the second end of the first cell.