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EP-4243432-B1 - FIVE DEGREES OF FREEDOM MEMS ACTUATOR FOR AUTOFOCUS, OPTICAL IMAGE STABILIZATION, AND SUPER RESOLUTION IMAGING IN MINIATURE CAMERAS

EP4243432B1EP 4243432 B1EP4243432 B1EP 4243432B1EP-4243432-B1

Inventors

  • GALAOM, AHMED
  • BANSS, ALI
  • BA-TIS, Faez
  • Ben-Mrad, Ridha

Dates

Publication Date
20260506
Application Date
20190125

Claims (3)

  1. A camera module comprising: a) a five degrees of freedom (5-DOF) MEMS electrostatic microactuator (100), comprising: i) an inner MEMS structure (200), comprising an inner stator (230) and an inner rotor (220), said inner rotor (220) defining an x-y plane having an x-axis and a y-axis, and a z-axis being normal to the x-y plane, wherein said inner rotor (220) comprises of a load stage (224) to hold a load and a plurality of moving inner capacitive electrodes (222) that are attached to the inner stator (230) via a plurality of inner mechanical springs (221), said inner stator comprises of a plurality of fixed inner capacitive electrodes (223), wherein said plurality of moving and fixed inner capacitive electrodes in the inner MEMS structure engage in the presence of a voltage potential resulting in a translation of the inner rotor that holds the load along the x-axis (250) or the y-axis; ii) a middle MEMS structure (300), comprising a middle stator (330) and a middle rotor (320), wherein said inner MEMS structure (200) is rigidly attached to said middle rotor (320) of the middle MEMS structure (300), said middle rotor comprises of a plurality of moving middle capacitive electrodes (322) that are attached to the middle stator (330) via a plurality of middle mechanical springs (321), said middle stator (330) comprises of a plurality of fixed middle capacitive electrodes (323), wherein said plurality of moving and fixed middle capacitive electrodes in the middle MEMS structure engage in the presence of a voltage potential resulting in a translation of the middle rotor (320) that holds said inner MEMS structure (200) along the y-axis (350) or the x-axis, and iii) an outer MEMS structure (400), comprising an outer stator (430) and an outer rotor (420), wherein said middle MEMS structure (300) is rigidly attached to said outer rotor (420), said outer rotor (420) comprises of a plurality of moving outer capacitive electrodes (422) that are attached to the outer stator (430) via a plurality of outer mechanical springs (421), said outer stator (430) comprises of a plurality of fixed outer capacitive electrodes (432), wherein said plurality of moving and fixed outer capacitive electrodes in the outer MEMS structure (400) engage in the presence of a voltage potential resulting in a translation of the outer rotor (420) that holds said inner (200) and middle (300) MEMS structures along the axis z (450), and/or a bi-axial tilt of the outer rotor (420) about the x-axis (451) or the y-axis (452); iv) said plurality of moving inner capacitive electrodes (222) and said plurality of moving middle capacitive electrodes (322) are an array of through openings (225 and 325) or tubes having a plurality of walls, wherein a plurality of moving comb drive fingers (222 and 322) extend from the plurality of walls of each said array of through openings along the x-y plane, and v) said plurality of fixed inner capacitive electrodes (223) and said plurality of fixed middle capacitive electrodes (323) are an array of pistons, wherein a plurality of fixed comb drive fingers (223 and 323) extend from a lateral side of each piston along the x-y plane and interdigitate with said plurality of moving comb drive fingers in the inner (220) and middle (320) rotors; b) a circuit board (703) attached to a top or a bottom side of said microactuator; c) an image sensor (600) attached to the load stage (224) of said microactuator, wherein the said image sensor is wire-bonded directly to the circuit board; d) a housing (701) enclosing the said microactuator and said image sensor (600), and e) a set of optical lenses (702) attached directly to said housing or attached to a 3-degrees of freedom MEMS piston-tube electrostatic microactuator (800) which is attached to said housing.
  2. The camera module of claim 1, wherein said microactuator (100) tilts the image sensor (600) about an in-plane axes to correct for a static and dynamic optical tilt and/or achieving super resolution imaging.
  3. The camera module of claim 1, wherein the wire-bonding signals of the image sensor are channeled through the microactuator structure.

Description

FIELD OF THE INVENTION The invention relates, generally, to the field of MEMS electrostatic actuators that provide large forces and are able to translate and rotate large masses, and particularly, to the field of miniature cameras to achieve autofocus (AF) and/or optical image stabilization (OIS) to counteract hand-shaking motion, and super resolution imaging to achieve zooming. BACKGROUND OF THE INVENTION Different types of MEMS electrostatic micro-actuators have been used to achieve Autofocus (AF) and Optical Image Stabilization (OIS) in miniature cameras. US Patent No. US9264591B2 discloses a MEMS electrostatic actuator to achieve OIS and AF by providing a multiple of degrees of freedom (DOF) motion to move the image sensor. The actuator also utilizes mechanical flexures/springs between the driving comb electrodes and the load stage for the purpose of amplifying the rotational strokes and to reduce the coupling effect between motion along different axes. Such structure, elastic flexures between the load and driving electrodes, significantly reduces the electrostatic forces acting on the load. It also introduces mechanical coupling between different motions as one set of springs (i.e. four mechanical springs) are connected to a single load stage and are responsible to move the load stage along multiple axes. When the driving electrodes move the load along one axis of motion by exerting a force transmitted to the load through two springs, the other two springs connected to the load transmit the motion to other not-moving electrodes and vice versa. Such mechanical coupling is undesired in MEMS actuation. Another MEMS electrostatic actuator is used to achieve OIS in miniature cameras and presented in US patent No. US 9578217B2. The actuator is able to move the image sensor along 3-DOF in-plane motion, i.e., translation along the x and y axes and rotation about the z-axis to achieve OIS. This actuator is unable to provide translational motion along the optical axis z to achieve autofocus, which makes its use in compact cameras. Therefore, it has limited benefits as it provides only a partial functionality for a camera (achieves OIS only and not AF). Furthermore, US2016/187614A1 discloses an example of an autofocus system known in the art. There is an increasing need for a single actuator that is able to provide large force and totally decoupled motion along the 3 axes (x, y, and z) such that autofocus, optical image stabilization and super resolution imaging are all enabled using the single MEMS actuator. SUMMARY OF THE INVENTION The invention is set out in independent claim 1. Preferred embodiments of the invention are outlined in dependent claims 2 and 3. The present invention discloses a 5 degrees-of-freedom (5-DOF) electrostatic microactuator that is able to provide the translation motions along the x, y, and z axes and two bi-axial tilt motion about the x and y axes. The actuator utilizes nested MEMS structures such that the translation motion along each axis is totally decoupled from the motion along the other axes. The novel 5 degrees-of-freedom (5-DOF) electrostatic microactuator consists of 3 MEMS structures that are nested with respect to each other. These structures are referred to as inner, middle, and outer MEMS structures. The inner MEMS structure provides in-plane translation motion along the x-axis and it holds the load stage. The inner MEMS structure is rigidly attached to the rotor of the middle MEMS structure and is mechanically separated from the stator of the middle MEMS structure through trenches. Therefore, the inner MEMS structure holding the target load is considered as a load that has to be displaced by the rotor of the middle MEMS structure which provides a translation motion along the y-axis. Similarly, the middle MEMS structure is rigidly attached to the rotor of the outer MEMS structure and is mechanically separated from the stator of the outer MEMS structure. Therefore, the inner and outer MEMS structures are considered as a load that needs to be displaced by the rotor of the outer MEMS structure in a 3-DOF motion, i.e. translation along the z-axis, and bi-axial tilt about the x and y axes. The actuator is fabricated using two silicon wafers: upper and lower. The lower one is a Silicon on Insulator (SOI) that has an insulating layer to be utilized for the electrical insulation between various MEMS structures. The upper structure is a standard Si wafer. Different parts of the 3 MEMS structures are formed within the thicknesses of those wafers. The inner MEMS structure consists of an inner stator and an inner rotor. The inner stator comprises a base, an electrical insulating layer, an electrical connection layer, fixed comb electrodes, fixed combs' supporting pillars, and a bonding frame that mechanically connects the inner MEMS structure with the rotor of the middle MEMS structure. The inner rotor comprises a load stage, moving comb electrodes that are rigidly connected to each o