Electronic Device Having Force Sensor Air Flow Promotion Structures

Abstract

An electronic device such as a device with a display may have a force sensor. The force sensor may include capacitive electrodes separated by a deformable layer such as a layer of an elastomeric polymer. The display or other layers in the electronic device may deform inwardly under applied force from a finger of a user or other external object. As the deformed layers contact the deformable layer, the deformable layer is compressed and the spacing between the capacitive electrodes of the force sensor decreases. This causes a measurable rise in the capacitance signal and therefore the force signal output of the force sensor. To prevent the deformable layer from sticking to the inner surface of the display layers, air flow promotion structures may be interposed between the deformable layer and the inner surface of the display. The air flow promotion structures may include spacer pads with anti-stick surfaces.

What is claimed is: 
     
         1 . An electronic device, comprising:
 first and second capacitive sensor electrodes separated by a deformable layer;   a layer that is separated from the first capacitive sensor by an air gap and that deforms towards the first electrode when a force is applied by an external object; and   air flow promotion structures interposed between the layer and the first capacitive sensor electrode to enhance air flow in the air gap when the force has been removed from the layer and the layer is moving away from the first electrode.   
     
     
         2 . The electronic device defined in  claim 1  wherein the air flow promotion structures include at least one spacer pad. 
     
     
         3 . The electronic device defined in  claim 2  wherein the spacer pad has a textured anti-stick surface. 
     
     
         4 . The electronic device defined in  claim 2  wherein the spacer pad has a hydrophobic coating. 
     
     
         5 . The electronic device defined in  claim 2  wherein the spacer pad has an elastic modulus of at least 1 GPa and a height of 10-100 microns. 
     
     
         6 . The electronic device defined in  claim 2  wherein the spacer pad comprises a layer of polymer. 
     
     
         7 . The electronic device defined in  claim 6  further comprising a layer of adhesive that attaches the layer of polymer to the deformable layer. 
     
     
         8 . The electronic device defined in  claim 2  wherein the air flow promotion structures include a plurality of spacer pads including the at least one spacer pad. 
     
     
         9 . The electronic device defined in  claim 8  wherein the plurality of spacer pads include first spacer pads having a first height and second spacer pads having a second height that is different than the first height. 
     
     
         10 . The electronic device defined in  claim 1  wherein the deformable layer comprises an elastomeric polymer layer. 
     
     
         11 . The electronic device defined in  claim 10  wherein the first electrode comprises one of a plurality of electrodes on the elastomeric polymer layer. 
     
     
         12 . The electronic device defined in  claim 1  further comprising a display, wherein the layer that is separated from the first capacitive sensor by the air gap comprises part of the display. 
     
     
         13 . The electronic device defined in  claim 12  wherein the display includes a backlight unit and wherein the layer that is separated from the first capacitive sensor by the air gap comprises part of the backlight unit. 
     
     
         14 . An electronic device operable by a user with an external object, comprising:
 a housing;   a display mounted in the housing, wherein the display has display layers that deform inwardly in response to pressure from the external object;   a capacitive force sensor that measures force levels applied by the external object to the display cover layer by making capacitance measurements using electrodes separated by an elastomeric layer; and   an array of spacer pads covering the elastomeric layer, wherein the display layers press against the array of spacer pads and compress the elastomeric layer when the display layers are bent inwardly.   
     
     
         15 . The electronic device defined in  claim 14  wherein the spacer pads include first spacer pads having a first height and second spacer pads having a second height that is different than the first height. 
     
     
         16 . The electronic device defined in  claim 15  wherein the first and second spacer pads are arranged in a checkerboard pattern on the elastomeric layer. 
     
     
         17 . The electronic device defined in  claim 14  further comprising touch sensor circuitry that makes position measurements on the external object. 
     
     
         18 . An electronic device, comprising:
 a display that deforms inwardly when pressed with a force by an external object;   an array of first capacitive electrodes on a first surface of an elastomeric layer;   a second capacitive electrode on an opposing second surface of the elastomeric layer;   force sensing circuitry that measures the force by measuring capacitances between the first capacitive electrodes and the second capacitive electrode; and   an array of spacer pads on the first surface of the elastomeric layer that are contacted by an inner surface of the display when the display deforms inwardly and thereby deforms the elastomeric layer and increases the measured capacitances.   
     
     
         19 . The electronic device defined in  claim 18  wherein the spacer pads include polymer layers. 
     
     
         20 . The electronic device defined in  claim 19  wherein the spacer pads have anti-stick surfaces. 
     
     
         21 . An electronic device having an outer surface, comprising:
 first and second capacitive sensor electrodes separated by a deformable layer that is overlapped by the outer surface;   a layer that is separated from the deformable layer by an air gap, wherein the deformable layer and the layer that is separated from the deformable layer contact each other across the air gap when a force is applied to the outer surface by an external object; and   air flow promotion structures that enhance air flow in the air gap when the force has been removed from the layer and the layer is moving away from the first electrode.   
     
     
         22 . The electronic device defined in  claim 21  wherein the air flow promotion structures comprise openings in the deformable layer. 
     
     
         23 . The electronic device defined in  claim 21  wherein the air flow promotion structures comprise recesses in the deformable layer. 
     
     
         24 . The electronic device defined in  claim 21  wherein the recesses comprise deformations in the deformable layer. 
     
     
         25 . The electronic device defined in  claim 21  wherein the air flow promotion structures comprise deformations in the layer that is separated from the deformable layer by the air gap. 
     
     
         26 . The electronic device defined in  claim 21  further comprising a display, wherein the deformable layer is attached to the display. 
     
     
         27 . The electronic device defined in  claim 26  wherein the air flow promotion structures comprise an array of spacer pads on the deformable layer. 
     
     
         28 . The electronic device defined in  claim 21  further comprising a display, wherein the layer that is separated from the deformable layer is attached to the display. 
     
     
         29 . The electronic device defined in  claim 21  wherein the air flow promotion structures include at least one hole that passes through the first capacitor sensor electrode.