Force sensor with strain relief

A force sensor for detecting a force applied to a display surface of a device, the force sensor comprising:

• a cover forming a portion of an exterior surface of the device;
• a first transparent force-sensitive film and a second transparent force-sensitive film with anisotropic strain properties disposed in a stack below the cover and each transparent force-sensitive film having:
• a primary direction oriented in a plane of the respective transparent force-sensitive film for which a strain in the primary direction results in a substantially reduced net charge;
• an array of strain-relief features formed into the respective transparent force-sensitive film and oriented in a first direction that is transverse to the primary direction thereby allowing the respective transparent force-sensitive film to deflect in a direction approximately perpendicular to the first direction;
• and
• a display element disposed below the stack of transparent force-sensitive films;
• wherein:
• the primary direction of the first transparent force-sensitive film is different from the primary direction of the second transparent force-sensitive film.

A force sensor for detecting a force of a touch on a display of a device, the force sensor comprising:

• a first transparent force-sensitive film having:
• polymer chains oriented in a first primary direction in a plane of the first transparent force-sensitive film, such that a strain in the first primary direction results in a substantially reduced net charge;
• an array of strain-relief features formed into the first transparent force-sensitive film and oriented in a first direction that is transverse to the first primary direction;
• and
• a second transparent force-sensitive film, separated from the first transparent force-sensitive film by an adhesive layer and having:
• polymer chains oriented in a second primary direction in a plane of the second transparent force-sensitive film, such that a strain in the second primary direction results in a substantially reduced net charge;
• and
• an array of strain-relief features formed into the second transparent force-sensitive film oriented in a second direction that is transverse to the second primary direction;
• wherein
• each of the first and the second transparent force-sensitive films are formed from a material that exhibits a strain-direction dependent charge polarity;
• the first direction is substantially perpendicular to the second direction;
• and
• the first primary direction is different from the second primary direction.