US Patent 7176889 Force sensing pointing device with click function

An input device for an electronic system includes a force sensor having conductive interdigitated traces on a bottom substrate and a flexible substrate spaced apart from the bottom substrate. The flexible substrate has a resistive layer deposited on a bottom side facing the interdigitated traces. A snap dome is positioned over a portion of the force sensor flexible substrate. A flexible keymat membrane is positioned over the force sensor and the snap dome. The keymat membrane bottom surface faces the force sensor flexible substrate. The keymat membrane bottom surface has a protruding region surrounding the snap dome and spaced above the force sensor flexible substrate. A center keycap on the keymat membrane top surface is positioned over the snap dome. A surrounding keycap on the keymat membrane encloses the center keycap and is positioned over the keymat membrane protruding region.