Auto-focusing actuator and camera module including flexible diaphragm for mobile phone camera and wireless capsule endoscope

Abstract

Recent cellular phones have high-resolution, compact digital camera modules that have several millions of pixels. Although being small, such several mega-pixel camera modules definitely need to be able to execute auto-focusing and/or optical zooming in order to obtain precise images. Hence, image photographing devices having driving mechanisms that can move a lens group in the direction parallel to an optical axis have appeared such as piezoelectric type, linier motor type, and voice coil motor type. Although these technologies are already popular in existing digital cameras, driving mechanism for camera modules in cellular phones needs to be extremely improved because their requirements are totally different from usual digital cameras. Compact image photographing devices, which are installed in mobile apparatuses, should improve portability by reducing their sizes and weights and increase use-time of a battery by reducing power consumption. Weakened suspension (e.g. thickness is 0.02 mm or less) in order to minimize an elastic coefficient for drastic decrease of driving current frequently occurs permanent step-out of a lens group by plastic deformation of the metal suspensions when it comes to getting shocks from accidental drops of a handset. The proposed auto-focusing actuator using conductive polyimide as a flexible diaphragm satisfies these requirements of ultra slim cell phones. This polyimide suspension shows ultimate toughness when it comes to drop-test of cell phones. This actuator also shows high performance quite enough for several mega-pixel camera modules for ultra slim cellular phones; the moving range is up to 0.35 mm, the DC sensitivity is 0.2 mm/140 mA, and the resistance at the terminal is 22 Ohm, whereas the aperture is 6.8 mm, and the overall size is 10 x 10 x 3.95 mm. Most of all, the robustness against drop and shock has been dramatically increased, with no change of reliability under high temperature and high humidity condition, because of the flexibility of the conductive polyimide suspension.