US20230204974A1 - Piezoelectric mems actuator for compensating unwanted movements and manufacturing process thereof - Google Patents
Piezoelectric mems actuator for compensating unwanted movements and manufacturing process thereof Download PDFInfo
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- G02B26/0833—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD
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- H10N30/204—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators using bending displacement, e.g. unimorph, bimorph or multimorph cantilever or membrane benders
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Abstract
A method of making a MEMS actuator with a monolithic body of semiconductor material includes forming a supporting portion of semiconductor material, orientable with respect to first and second rotation axes, the first rotation axis being transverse with respect to the second rotation axis, and forming a first frame of semiconductor material. The method further includes forming first deformable elements, of semiconductor material, coupled to the first frame, and configured to control a rotation of the supporting portion about the first rotation axis. The method also includes forming a second frame of semiconductor material, and forming second deformable elements, of semiconductor material, coupled to the first frame and to the second frame, and configured to control a rotation of the supporting portion about the second rotation axis. The first and second deformable elements are formed to carry respective first and second piezoelectric actuation elements.
Description
- This is a division of United States Application for Pat. No. 16/880,141, filed on May 21, 2020, which claims the priority benefit of Italian Application for Patent No. 102019000007219, filed on May 24, 2019, the contents of both of which are hereby incorporated by reference in its entirety to the maximum extent allowable by law.
- This disclosure relates to a Micro-Electro-Mechanical System (MEMS) piezoelectric actuator for compensating unwanted movements and to a manufacturing process thereof. In particular, hereinafter reference is made to a piezoelectric MEMS actuator configured to carry out optical image stabilization (OIS) in optical devices such as, for example, digital still cameras (DSCs), in particular for autofocus applications, without this disclosure being limited thereto.
- As is known, actuators are devices that convert a physical quantity of one type into another physical quantity of a different type; in particular, the quantity deriving from conversion usually leads to some form of movement or mechanical action.
- Recently, actuators of micrometric and nanometric dimensions have been proposed, also referred to as micro-actuators or nano-actuators, which can be manufactured using a semiconductor technology (for example, MEMS technology) and therefore at contained costs. Such micro-actuators and nano-actuators may be used in a wide range of devices, in particular in mobile and portable devices.
- Examples of micro-actuators are valves, switches, pumps, linear and rotary micromotors, linear positioning devices, speakers and optical devices (for example, optical autofocus devices).
- Known micro-actuators may work according to four physical principles:
- Electrostatic: they exploit the attraction between conductors that are oppositely charged;
- Thermal: they exploit the displacement caused by thermal expansion or contraction;
- Piezoelectric: they exploit the displacement caused by stresses and strains induced by electrical fields; and
- Magnetic: they exploit the displacement caused by the interaction between different elements having magnetic characteristics, such as permanent magnets, external magnetic fields, magnetizable materials, and electric current conductors.
- Each technology has advantages and limits in terms of power consumption, movement rapidity, force exerted, movement amplitude, movement profile, simplicity of manufacture, amplitude of the applied electrical signals, robustness, and sensitivity, which render use thereof advantageous in certain applications, but not in others and therefore determine their field of use.
- Hereinafter a MEMS actuator operating according to the piezoelectric principle and in particular exploiting MEMS thin-film piezo (TFP) technology is considered.
- TFP MEMS technology currently uses a unimorphic mode of actuation, wherein a structure (for example, a membrane, a beam or a cantilever), usually formed of at least two superimposed layers, undergoes bending as a result of variations in the applied stress. In this case, a controlled alteration of the strain is obtained in one of the layers, referred to as active layer, which causes a passive strain in the other layer or layers, referred to also as inactive or passive layers, with consequent bending of the structure.
- The above technique is advantageously used for bending the membrane, the beam, or the cantilever in applications where it is desired to obtain a vertical movement, i.e., a movement in a direction perpendicular to the plane in which the structure lies, for example, in an ink printhead, autofocus systems, micro-pumps, microswitches and speakers.
- For instance,
FIGS. 1A and 1B show acantilever beam 1 constrained at afirst end 2 and free to bend at asecond end 3. Thebeam 1 is here formed by a stack of layers including: a supportinglayer 5, for example, of semiconductor material with a first conductivity type, for example, P; anactive layer 6, for example, of piezoelectric material (PZT); and atop layer 7, for example, of semiconductor material with a second conductivity type, for example, N. - In presence of a reverse biasing, as illustrated in
FIG. 1B , the applied electrical field causes strains in thebeam 1, which causes a movement of thesecond end 3 downwards. - An embodiment of a piezoelectric MEMS actuator applied to a generic optical device is illustrated in
FIGS. 2A and 2B . Here, the optical device, designated by 10, comprises a deformable part ormembrane 15, for example of glass, such as BPSG (BoroPhosphoSilicate Glass), resting, through a lens element 11 (for example of polymeric material), on asupport 12, which is also, for example, of glass; themembrane 15 further carries twopiezoelectric regions 13, arranged at a mutual distance apart. - In absence of biasing, in
FIG. 2A , themembrane 15 and thelens element 11 have planar surfaces and do not modify the path of alight beam 16 that passes them. When thepiezoelectric regions 13 are biased, inFIG. 2B , they cause a deformation of themembrane 15. The deformation of the central area of themembrane 15 is transmitted to thelens element 11, whose top surface bends, modifying the focus of thelens element 11 and therefore the path of thelight beam 16. It is thus possible to modify the characteristics of optical transmission of theoptical device 10. - It is furthermore known that known optical devices, such as digital still cameras, may be subject, in use, to unwanted movements induced from outside, such as vibrational movements induced by quivering of the user’s hand that is using the digital still camera.
- In particular, in use, one or more lenses of the optical device receive a light beam and focus it towards an image sensor, housed in the optical device; next, the image sensor receives and processes the focused light beam to generate an image.
- However, when the optical device is subjected to unwanted movements, the optical path of the light beam through the lenses towards the image sensor is deflected; consequently, the image sensor receives the light beam in a shifted position with respect to the case with no movements induced from outside. Consequently, the image sensor may generate a low quality image, for example, an out-of-focus image.
- To address this issue, in the last few years optical devices integrating actuators and corresponding sensing systems configured to quantify and compensate the unwanted movements have been developed.
- For instance, United States Pat. No. 9,625,736, incorporated by reference, describes an actuator of the type schematically represented in
FIGS. 3A-3B . In particular,FIG. 3A shows an example of a portion of an optical device 30 (e.g., a digital still camera) including anactuator 40 for compensating unwanted movements induced from outside and generating displacements along an X axis and an Y axis of a Cartesian reference system XYZ. In the example illustrated, theactuator 40 is a voice coil motor (VCM), i.e. an electromagnetic actuator. - The
optical device 30 comprises a supportingstructure 32, comprising a casing 52 (not shown inFIG. 3B for clarity reasons), and asubstrate 42 defining a first and asecond surface structure 32 houses afirst cavity 34, in communication with the external environment through anopening 36 formed in thecasing 52 at thefirst surface 32A. In particular, thecavity 34 houses theactuator 40. - The
substrate 42, of semiconductor material (e.g. polysilicon), has arecess 44 facing the outside of the supportingstructure 32 and housing a first printed circuit board (PCB) 46. - The first printed
circuit board 46 carries amovement sensor 48 and an integrateddriving circuit 49, electrically coupled together through conductive paths (not illustrated). - A first, a second, a third, and a fourth permanent
magnetic element 51A-51D are arranged within the supportingstructure 32 and have, for example, a parallelepipedal shape with a reduced thickness in top view (FIG. 3B ). In particular, the first and the second permanentmagnetic elements structure 32 and have longer sides (in the top view ofFIG. 3B ) parallel to the X axis of the Cartesian reference system XYZ; likewise, the third and the fourth permanentmagnetic elements structure 32, and have longer sides (in the top view ofFIG. 3B ) parallel to the Y axis of the Cartesian reference system XYZ. - The permanent
magnetic elements 51A-51D are arranged along the side walls of thecasing 52, inside it, and surround theactuator 40 at a distance. - The
casing 52 extends alongside and over the permanentmagnetic elements 51A-51D, as well as at least in part extends laterally with respect to the substrate 42 (FIG. 3A ). - The
optical device 30 further comprises animage acquisition module 38, including a first and a secondoptical module - In detail, the
first module 60 comprises afirst lens 70, configured to receive alight beam 72 from the external environment. Thesecond module 61 comprises second lenses 71 (three schematically shown inFIG. 3 ), optically coupled to thefirst lens 70. - The
image acquisition module 38 is accommodated in abarrel 80, in acavity 81 thereof. - Moreover, the
optical device 30 comprises a second printedcircuit board 82, coupled to thebarrel 80 at atop surface 82A thereof to delimit thecavity 81 of thebarrel 80 at the bottom. Animage sensor 84 extends on thetop surface 82A of the second printedcircuit board 82; for example, theimage sensor 84 is formed by an array of diodes and is electrically coupled to the second printedcircuit board 82. Moreover, theimage sensor 84 is operatively coupled to theimage acquisition module 38; in particular, the first and the secondoptical modules light beam 72 on theimage sensor 84. - The
actuator 40 of theoptical device 30 comprises a magnetic body 90 (e.g. of ferromagnetic material), surrounding thebarrel 80, and acoil 92, extending around themagnetic body 90 and electrically coupled to theintegrated driving circuit 49 by conductive paths (not shown). - In use, when the
optical device 30 is subject to unwanted movements induced from outside, themovement sensor 48 detects these movements and generates an electrical signal, which is transmitted to theintegrated driving circuit 49; theintegrated driving circuit 49 processes the electrical signal and determines, for example, the magnitude and direction of the force generated by the movements on theoptical device 30. - On the basis of the processed information, the
integrated driving circuit 49 generates a current that is fed to thecoil 92 to move theimage detection structure 38 along the X and Y axes. - In detail, as a result of passage of the current in the
coil 92, a Lorentz force acts between the actuator 40 and the permanentmagnetic elements 51A-51D and causes movement of theimage acquisition module 38, together with thebarrel 80 and the second printedcircuit board 82, toward the first or the second permanentmagnetic element magnetic element - Consequently, the
light beam 72 is deflected by an angle correlated to the magnitude of the Lorentz force, compensating the unwanted movements. - The
actuator 40 of theoptical device 30 enables a correction of the optical path of thelight beam 72 by an angle that, for medium-level digital still cameras is, for example, ±0.75° and, for professional digital still cameras, is, for example, ±1.50°. - However, optical devices of the type illustrated in
FIG. 3 have some disadvantages. - In particular, the
actuator 40 moves theimage acquisition module 38 at a limited speed, since the electromagnetic actuation is slow. - Moreover, the current used by the
coil 92 of theactuator 40 to generate a Lorentz force sufficient to compensate the unwanted movements induced from outside is high (e.g. comprised between 50 mA and 80 mA). - There is a need in the art to provide a MEMS actuator and a manufacturing process therefore that overcome the drawbacks of the prior art.
- According to this disclosure, a MEMS actuator and a manufacturing process thereof are provided.
- Disclosed herein is a method of making a MEMS actuator comprising a monolithic body of semiconductor material. The method includes: forming a supporting portion of semiconductor material; forming a first frame of semiconductor material; forming first deformable elements, of semiconductor material, coupled to the first frame; forming a second frame of semiconductor material; and forming second deformable elements, of semiconductor material, coupled to the first frame and to the second frame. The first and second deformable elements are formed to carry respective first and second piezoelectric actuation elements.
- The method may further include: forming, on a first surface of a first wafer of semiconductor material, a first insulating layer; forming, on the first insulating layer, a membrane layer of semiconductor material; forming, on the membrane layer, a second insulating layer; forming, on the second insulating layer, a first electrode; forming, on the first electrode, a piezoelectric region; forming, on the piezoelectric region, a second electrode; forming an opening in the second insulating layer, thereby exposing a first portion of the membrane layer; removing selective portions of the first wafer, thereby forming the supporting portion, the first and second frames, and the first and second deformable elements; forming an adhesive layer coating the first electrode, the piezoelectric region, the second electrode, and the second insulating layer; coupling a second wafer to the adhesive layer, thereby forming a third wafer; removing portions of the first wafer and of the first insulating layer from a second surface of the first wafer, thereby forming substrate portions laterally delimiting a cavity, delimiting membrane portions of the first and second deformable elements; and detaching the second wafer by removing the adhesive layer.
- The method may further include: forming a first insulating layer fon a first surface of a first wafer of semiconductor material via thermal growth; epitaxially growing a membrane layer on the first insulating layer; forming a second insulating layer on the membrane layer; and forming a first stack of layers extending over the first surface of the first wafer.
- The first stack of layers may be formed by a layer from which a first electrode is formed, a layer from which a piezoelectric region is formed, and a layer from which a second electrode is formed.
- The first stack of may be is etched to form a first electrode on the second insulating layer, a piezoelectric region on the first electrode, and a second electrode on the piezoelectric region.
- The second insulating layer may be etched to form an opening, thereby exposing a portion of the membrane layer.
- The method may further include forming, over the first stack of layers, a second stack of layers via deposition and definition to include a first passivation layer and a second passivation layer on the first passivation layer.
- First and second contact openings may be defined in the first and second passivation layers to expose respective portions of the first and second electrodes.
- The second stack of layers may be further formed to include a first metallization layer on the second passivation layer and extending through the first contact opening to contact the second electrode, and to include a second metallization layer on the second passivation layer and extending through the second contact opening to contact the first electrode.
- The second stack of layers may be further formed to include a third passivation layer on the second passivation layer and first and second metallization layers, with a third contact opening being formed in the third passivation layer to expose at least in part the first metallization layer.
- The method may further include depositing and defining a contact layer over the second stack of layers, and etching the membrane layer to define the first and second deformable elements and to define trenches in the membrane layer.
- The method may also include depositing an adhesive layer on the third passivation layer and the contact layer, and coupling a carrier wafer to the adhesive layer to obtain a second wafer and delimited by a top surface and a bottom surface.
- The method may additionally include flipping the second wafer and etching the second wafer from its bottom surface to form first, second, and third substrate portions, a cavity being delimited between the first and second substrate portions, wherein the etching exposes a back side of the membrane layer.
- The method may include etching the first insulating layer to define first and second connections arms and the first and second frames, then removing the adhesive layer via thermal release to thereby detach the carrier wafer from the first wafer.
- The first wafer may be diced
- Also disclosed herein is a method of making a MEMS actuator comprising a monolithic body of semiconductor material. The method includes: forming a supporting portion of semiconductor material, orientable with respect to first and second rotation axes, the first rotation axis being transverse with respect to the second rotation axis; forming a first frame of semiconductor material; forming first deformable elements, of semiconductor material, coupled to the first frame, and configured to control a rotation of the supporting portion about the first rotation axis; forming a second frame of semiconductor material; and forming second deformable elements, of semiconductor material, coupled to the first frame and to the second frame, and configured to control a rotation of the supporting portion about the second rotation axis, wherein the first and second deformable elements are formed to carry respective first and second piezoelectric actuation elements.
- The first frame may be formed to have an elongated hexagonal shape, with two first sides parallel to a first symmetry axis and four end sides extending transverse to the first symmetry axis and a second symmetry axis, wherein the first symmetry axis and the second symmetry axis are parallel to the first and second rotation axis, wherein the first deformable elements extend perpendicularly to the first symmetry axis.
- The second frame may be formed to have a regular quadrangular shape with sides parallel to the end sides of the first frame, and wherein the second deformable elements extend parallel to the first symmetry axis.
- Forming the first deformable elements may be accomplished by forming first and second elastic elements of the first deformable elements on opposite sides of the supporting portion and extending transversely to the first symmetry axis. Forming the second deformable elements may be accomplished by forming first and second elastic elements of the second deformable element on opposite sides of the first frame and extending transversely to the second symmetry axis.
- The first and second elastic elements of the first deformable elements may be formed as respective first and second deformable arms carrying the first piezoelectric actuation elements and respective first and second connection arms, connecting opposite ends of respective successive ones of the first and second deformable arms, thereby forming a serpentine shape.
- The first and second elastic elements of the second deformable elements may be formed as respective third and fourth deformable arms carrying the second piezoelectric actuation elements and respective third and fourth connection arms, connecting opposite ends of respective successive third and fourth deformable arms, thereby forming the serpentine shape.
- For a better understanding, embodiments thereof are now described, purely by way of non-limiting example, with reference to the attached drawings, wherein:
-
FIGS. 1A and 1B show simplified side views of a known piezoelectric MEMS actuator in a resting condition and in a deformation condition, respectively; -
FIGS. 2A and 2B show simplified side views of another known piezoelectric MEMS actuator, used in an optical device in a resting position and in a deformation condition, respectively; -
FIG. 3A is a schematic cross-section of a known optical device; -
FIG. 3B is a schematic top view with removed parts of the optical device ofFIG. 3A ; -
FIG. 4 shows a top view of the present MEMS actuator according to a first embodiment; -
FIG. 5 is a perspective bottom view of the MEMS actuator ofFIG. 4 ; -
FIG. 6 is a longitudinal section of a part of the MEMS actuator ofFIG. 4 , taken along section line VI-VI ofFIG. 4 ; -
FIGS. 7 and 8 are perspective views of the MEMS actuator ofFIG. 4 , in different operating positions; -
FIG. 9 is a top view of the present MEMS actuator according to another embodiment; -
FIG. 10 is a top view of the present MEMS actuator according to a further embodiment; and -
FIGS. 11-15 are cross-sections through a portion of the MEMS actuator ofFIGS. 3, 9, and 10 , in subsequent manufacturing steps. -
FIGS. 4-6 show schematically aMEMS actuator 100 of a piezoelectric type. In particular, theMEMS actuator 100 is configured to integrate optical devices, for example for autofocus, and allows compensation of unwanted movements. - The MEMS actuator 100 is formed by a
monolithic body 101 of semiconductor material (e.g., polysilicon) having a generally parallelepipedal shape with a first and a secondlarger surface FIGS. 4-6 , theMEMS actuator 100 has (in top view) a square shape, with a side of, for example, 7 mm x 7 mm and a depth (in the Z direction) of, for example, 710 µm. - The
body 101 of theMEMS actuator 100 comprises a supportingportion 102 having, in top view (FIG. 4 ), a quadrangular shape (for example, square); and afirst frame 104 surrounding the supportingportion 102, having a polygonal shape in top view (for example, of an elongated hexagon), and coupled to the supportingportion 102 by firstdeformable elements 115; and asecond frame 108 surrounding thefirst frame 104, having, in top view, a quadrangular shape (for example, square), and coupled to thefirst frame 104 by seconddeformable elements 116. Thesecond frame 108 is here rotated through 45° with respect to thefirst frame 104. - In particular, in the embodiment shown in
FIGS. 4-6 , the two diagonals of thesecond frame 108 form a first and a second symmetry axis A, B of the supportingportion 102, transverse (in particular, perpendicular) with respect to each other and further forming symmetry axes for thefirst frame 104, which is elongated in the direction of the first symmetry axis A. In particular, thefirst frame 104 has twolonger sides 104A, parallel to each other and to the first symmetry axis A, and fourshorter sides 104B (parallel two by two), transverse with respect to the symmetry axes A and B (here set at 45°). The longer sides 104A of thefirst frame 104 are therefore transverse (at 45°) with respect to the sides of thesecond frame 108, and theshorter sides 104B of thefirst frame 104 are parallel (two by two) to the sides of thesecond frame 108. - In particular, the symmetry axes A, B intersect each other at a center O and lie in an XY plane of the Cartesian reference system XYZ, similar to the
larger surfaces MEMS actuator 100, due to the negligible depth of the MEMS actuator 100 (along the axis Z). - The supporting
portion 102 has anopening 120 having, for example, a circular shape, with center O at the center of thesecond frame 108 and of theMEMS actuator 100. - The MEMS actuator 100 carries a
lens 125 of transparent material (e.g., glass, such as BPSG, silicon oxide, or PSG) bonded, for example glued, to the supportingportion 102 on thesecond surface 100B of the actuator and here having a parallelepipedal shape. In greater detail, theopening 120 is configured to enable, in use, the passage of a light beam through thelens 125. - The first
deformable elements 115 comprise a first and asecond spring element deformable elements 116 comprise third andfourth spring elements - The first and the
second spring elements portion 102 by respective first ends 106A, 107A, and fixed to thefirst frame 104 by respective second ends 106B, 107B. In the embodiment illustrated inFIGS. 4 and 5 , the first and thesecond spring elements - In particular, the first and the
second spring elements deformable arms second connection arms second connection arms deformable arms connection arm deformable arms - Likewise, the third and the
fourth spring elements first frame 104 at respective first ends 110A, 111A and to thesecond frame 108 at respective second ends 110B, 111B. In the embodiment illustrated inFIGS. 4 and 5 , the third and thefourth spring elements - Similarly to the first and the
second spring elements fourth spring elements deformable arms fourth connection arms fourth connection arms deformable arms 140, 142 (in a direction parallel to the second symmetry axis B) to form the serpentine structure. - The first ends 106A, 107A of the first and the
second spring elements portion 102 in a symmetrical position with respect to the second symmetry axis B, spaced at a distance from, and on the same side of, the first symmetry axis A, for example, in proximity to thethird spring element 110. Moreover, the second ends 106B, 107BA of the first and thesecond spring elements first frame 104 at two respectiveshorter sides 104B, in a symmetrical position with respect to the second symmetry axis B, and are spaced at a distance from, and on the same side of, the first symmetry axis A, here in proximity to thefourth spring element 111. - Likewise, the first ends 110AB, 111A of the third and the
fourth spring elements first frame 104 at two respectivelonger sides 104A, in a position symmetrical with respect to the first symmetry axis A, and are spaced at a distance from, and on the same side of, the second symmetry axis B, for example, adjacent to thefirst spring element 106. Moreover, the second ends 110B, 111B of the third and thefourth spring elements second frame 108 in a position symmetrical with respect to the first symmetry axis A, and are spaced at a distance from, and on the same side of, the second symmetry axis B, here in a position adjacent to thesecond spring element 107. - Due to the arrangement of the
deformable arms connection arms second frame 108, in proximity to the corners of the latter, they have variable lengths, as may be seen inFIGS. 4 and 5 . - As may be seen in particular in
FIG. 5 , thedeformable arms body 101, except at their own ends, so as to have a high flexibility, as described in detail hereinafter with reference toFIG. 6 . For instance, they may have a thickness comprised between 4 µm and 100 µm, in particular here 80 µm. - Each of the
deformable arms respective strip 150 of piezoelectric material, for example of a ceramic with a base of lead-titanate-zirconate (PZT) or of aluminum nitride (AlN). -
FIG. 6 shows the structure of the firstdeformable arm 130; this structure is identical also for thedeformable arms FIG. 6 also shows a portion of the first frame 104 (in particular, of one of the longer sides 104A). - In detail, the
deformable arm 130 comprises a first and asecond substrate portion cavity 810. Thelonger side 104A comprises athird substrate portion 702C, laterally delimiting, together with thesecond substrate portion 702B, atrench 755. - A first insulating
layer 704, for example, of silicon oxide, extends on thesubstrate portions 702A-702C. - A
membrane layer 706, of semiconductor material (e.g., polysilicon), extends on the first insulatinglayer 704; in particular, it is partially suspended over thecavity 810 to form here a membrane 812 (portion of reduced thickness, also visible inFIG. 5 ). - A second insulating
layer 180, for example of silicon oxide, extends at least in part over themembrane layer 706. - The
strip 150 extends on the second insulatinglayer 180; in particular, thefirst strip 150 comprises a stack formed by afirst electrode 171, apiezoelectric region 172 and asecond electrode 173. Thestrip 150 forms a capacitor. In use, thefirst electrode 171 is connected to a reference potential (for example, ground) and thesecond electrode 173 is connected to avoltage source 200 through first conductive paths 210 (schematically illustrated inFIG. 4 ). - A
first passivation layer 730, for example of aluminum oxide, extends on the first insulatinglayer 180 and on the first and thesecond electrodes piezoelectric region 172; moreover, asecond passivation layer 732, for example, of USG (Undoped Silicon Glass), extends over thefirst passivation layer 730. In particular, a first and a second contact opening 740, 741 extend through the first and the second passivation layers 730, 732 and expose portions of the first and thesecond electrodes strip 150. - A first and a
second metallization layer second passivation layer 732 and in thecontact openings second electrodes - A
third passivation layer 736, for example, of nitride, extends on thesecond passivation layer 732 and on the first and the second metallization layers 734A, 734B. A third contact opening 750 extends through thethird passivation layer 736 and exposes a portion of thefirst metallization layer 734A. - A
contact layer 752, of conductive material (for example, gold, Au), extends on thethird passivation layer 736 and fills the third contact opening 750 to electrically contact thefirst metallization layer 734A. - With reference once again to
FIG. 4 , thestrips 150 of the first and the seconddeformable arms first voltage source 200 through the firstconductive paths 210, and thestrips 150 of the third and the fourthdeformable arms second voltage generator 202 through second conductive paths 212 (schematically illustrated inFIG. 4 ). - Application of a static actuation voltage (for example of 40 V) to the
strips 150 of the third and the fourthdeformable arms fourth connection arms deformable arms fourth spring elements first frame 104, thefirst spring element 106, thesecond spring element 107 and the supportingportion 102 rotate approximately about the second symmetry axis B, as illustrated inFIG. 7 (where theMEMS actuator 100 is shown rotated by 90° counterclockwise with respect to the top view ofFIG. 5 ). - Likewise, by applying a static actuation voltage (for example of 40 V) to the
strips 150 of the first and the seconddeformable arms second connection arms deformable arms portion 102 approximately about the first symmetry axis A, as illustrated inFIG. 8 (where theMEMS actuator 100 is shown rotated through 90° counterclockwise with respect to the top view ofFIG. 5 ). - By simultaneously biasing all the
strips 150 and modulating the actuation voltage applied to them, it is possible to rotate the supportingportion 102 about both the rotation axes A, B by a selectable angle (up to a maximum value of, for example, 1.2°). -
FIG. 9 shows another embodiment of the present MEMS actuator. In detail,FIG. 9 shows aMEMS actuator 300 having a general structure similar to theMEMS actuator 100 illustrated inFIGS. 4-6 , so that parts similar to the ones illustrated and described with reference toFIGS. 4-6 are designated inFIG. 9 by reference numbers increased by 200 and will not be described any further. - In the embodiment of
FIG. 9 , the first and thesecond spring elements second spring element 307 may be obtained by rotating thefirst spring element 306 through 180° with respect to the center O. Likewise, the third and thefourth spring elements fourth spring element 311 may be obtained by rotating thethird spring element 310 through 180° with respect to the center O. - In the present embodiment, each of the
strips 350 is electrically connected to a respective voltage source 400-403; in this way, in use, eachstrip 350 may be actuated independently from the other strips 350. - In use, the MEMS actuator 300 of
FIG. 9 operates in a way similar to what described with reference toFIGS. 7-8 , except for the first and thesecond spring elements portion 302 in the opposite direction approximately about the first symmetry axis A, and the third and thefourth spring elements first frame 304 and of the supportingportion 302 in the opposite direction approximately about the second symmetry axis B. Thevoltage sources voltage sources - By providing the
deformable arms portion 302, and, therefore, the lens (not illustrated), by an angle, for example, of +1.57° and -1.57° with respect to the rotation axes A, B. -
FIG. 10 shows a further embodiment of the present MEMS actuator. In detail,FIG. 10 shows aMEMS actuator 500 having a general structure similar to theMEMS actuator 300 illustrated inFIG. 9 ; therefore parts similar to the ones illustrated and described with reference toFIG. 9 are designated inFIG. 10 by reference numbers increased by 200 and will not be described any further. - In particular, the
MEMS actuator 500 comprises, in addition to the geometry described above with reference toFIG. 9 , a first, a second, a third and a fourthtorsional arm spring element second frames torsional arms torsional arms - In detail, the first and the second
torsional arms deformable arm second spring elements first frame 504, crossed by the first symmetry axis A). - Likewise, the third and the fourth
torsional arms deformable arm fourth spring elements second frame 508, crossed by the second symmetry axis B). - In use, the MEMS actuator 500 of
FIG. 10 operates in a way similar to what described for the MEMS actuator 300 ofFIG. 9 . - From simulations, it has been verified that, with respect to the
MEMS actuator 300 illustrated inFIGS. 9-13 , theMEMS actuator 500 has a higher resistance to external loads, as well as a higher resonance frequency due to the presence of thetorsional arms torsional arms -
FIGS. 11-15 show subsequent steps of a manufacturing process of theMEMS actuator deformable arms second frames MEMS actuator 100, in particular to one of thedeformable arms 130 and to a portion of the first frame 104 (in particular, one of the longer sides 104A). - In detail,
FIG. 11 shows afirst wafer 700, having atop surface 700A and abottom surface 700B; in particular, thefirst wafer 700 is processed according to manufacturing steps that are similar to what described in United States Pat. Application Publication No. 2014/0313264 A1, incorporated by reference. Consequently, the steps for manufacturing thefirst wafer 700 common to the above mentioned patent are briefly outlined hereinafter. - The
first wafer 700 comprises asubstrate 702, of semiconductor material (for example, silicon); the first insulatinglayer 704, extending on thesubstrate 702; themembrane layer 706, extending on theintermediate layer 704; the second insulatinglayer 180 ofFIG. 6 ; and a first stack oflayers 710, extending over thetop surface 700A. - In detail, the first and the second insulating
layers membrane layer 706 is epitaxially grown and has a thickness comprised, for example, between 25 and 100 µm, e.g. 60 µm. - The stack of
layers 710 comprises layers that are designed to form thefirst electrode 171, thepiezoelectric region 172, and thesecond electrode 173 ofFIG. 6 and, therefore, are designated inFIG. 11 by the same reference numbers. - Next,
FIG. 12 , the stack oflayers 710 is defined according to etching techniques so as to form the first and thesecond electrodes piezoelectric region 172. Moreover, the second insulatinglayer 180 is defined according to etching techniques to form anopening 720, which exposes aportion 722 of themembrane layer 706. - Next,
FIG. 13 , a second stack oflayers 725 is deposited and defined according to deposition and definition techniques. - In particular, the second stack of
layers 725 comprises thefirst passivation layer 730; and thesecond passivation layer 732, extending on thefirst passivation layer 730. The first and the second passivation layers 730, 732 are deposited and defined to form the first and the second contact opening 740, 741 and expose, respectively, portions of the first and thesecond electrodes - The second stack of
layers 725 further comprises the first and the second metallization layers 734A, 734B, deposited and defined according to deposition and definition techniques, to form electrical connection lines. - The second stack of
layers 725 further comprises thethird passivation layer 736, which is defined to form thethird contact opening 750 and, therefore, to expose at least in part thefirst metallization layer 734A. - Next,
FIG. 14 , thecontact layer 752 is deposited and defined. - Moreover, in a way not shown, the
membrane layer 706 is etched using known etching techniques. In this step, the geometry of the thinner portions of the body 101 (in particular, membranes forming thedeformable arms FIG. 6 ) are formed in themembrane layer 706. - In detail, an adhesive layer 765 (for example, a coupling adhesive such as BrewerBOND® 305, https://www.brewerscience.com/products/brewerbond-materials/, having a thickness so as to planarize the structure) is deposited on the
third passivation layer 736 and on thecontact layer 752 using deposition techniques. - Next, once again
FIG. 14 , acarrier wafer 770 is coupled to theadhesive layer 765; for example, thecarrier wafer 770 may be a DSP (Double Side Polished) wafer having a thickness, for example, of 400 µm. In this way, asecond wafer 800 is obtained, delimited at the top by atop surface 800A and at the bottom by thebottom surface 700B. - Then,
FIG. 15 , thesecond wafer 800 is flipped over and etched from thebottom surface 700B using masking and etching techniques. In particular, thesubstrate 702 is etched and selectively removed throughout its thickness (for example, using DRIE) so as to form thesubstrate portions 702A-702C, thecavity 810 and a first part of thetrench 755; then, the first insulatinglayer 704 is etched and selectively removed. In this step, definition of the geometry of thebody 101, in particular of theinternal portion 102, theconnection arms frames cavity 810 is thus formed and exposes at least in part themembrane layer 706 and theadhesive layer 765. - The
adhesive layer 765 is then removed via thermal release techniques (e.g. WaferBOND®, https://www.brewerscience.com/products/waferbond-ht-10-10/) so as to detach thecarrier wafer 770 from thefirst wafer 700. Before or after detachment of thecarrier wafer 700, thefirst wafer 700 is diced, to form a plurality ofadjacent bodies 101. - Next, in a way not shown, the
wafer 700 is diced to form the MEMS actuator 100 ofFIGS. 4-6 . - The present MEMS actuator and the manufacturing process thereof have many advantages.
- In particular, the
body 101 is monolithic and formed in the same structural, semiconductor material region carrying the piezoelectric actuation elements enabling biaxial rotation of the supporting portion 102 (strips 150) and of the optical structures (lens 125). Consequently, thebody 101 may be obtained using semiconductor manufacturing techniques, in a simple, inexpensive and reliable way. - The
spring elements portion strips 350 is obtained with low actuation voltages (for example, 40 V); consequently, the power consumption of theMEMS actuator - Finally, it is clear that modifications and variations may be made to the MEMS actuator and to the manufacturing process thereof described and illustrated herein, without departing from the scope of the present invention, as defined in the attached claims.
- For instance, the
torsional arms FIG. 14 may be also implemented in the embodiment ofFIG. 4 .
Claims (21)
1. A method of making a MEMS actuator comprising a monolithic body of semiconductor material, the method comprising:
forming a supporting portion of semiconductor material;
forming a first frame of semiconductor material;
forming first deformable elements, of semiconductor material, coupled to the first frame;
forming a second frame of semiconductor material; and
forming second deformable elements, of semiconductor material, coupled to the first frame and to the second frame;
wherein the first and second deformable elements are formed to carry respective first and second piezoelectric actuation elements.
2. The method according to claim 13 , further comprising:
forming, on a first surface of a first wafer of semiconductor material, a first insulating layer;
forming, on the first insulating layer, a membrane layer of semiconductor material;
forming, on the membrane layer, a second insulating layer;
forming, on the second insulating layer, a first electrode;
forming, on the first electrode, a piezoelectric region;
forming, on the piezoelectric region, a second electrode;
forming an opening in the second insulating layer, thereby exposing a first portion of the membrane layer;
removing selective portions of the first wafer, thereby forming the supporting portion, the first and second frames, and the first and second deformable elements;
forming an adhesive layer coating the first electrode, the piezoelectric region, the second electrode, and the second insulating layer;
coupling a second wafer to the adhesive layer, thereby forming a third wafer;
removing portions of the first wafer and of the first insulating layer from a second surface of the first wafer, thereby forming substrate portions laterally delimiting a cavity, delimiting membrane portions of the first and second deformable elements; and
detaching the second wafer by removing the adhesive layer.
3. The method according to claim 1 , further comprising:
forming a first insulating layer fon a first surface of a first wafer of semiconductor material via thermal growth;
epitaxially growing a membrane layer on the first insulating layer;
forming a second insulating layer on the membrane layer; and
forming a first stack of layers extending over the first surface of the first wafer.
4. The method according to claim 3 , wherein forming the first stack of layers is formed by forming a layer from which a first electrode is formed, a layer from which a piezoelectric region is formed, and a layer from which a second electrode is formed.
5. The method according to claim 4 , wherein the first stack of layers is etched to form a first electrode on the second insulating layer, a piezoelectric region on the first electrode, and a second electrode on the piezoelectric region.
6. The method according to claim 5 , further comprising etching the second insulating layer to form an opening, thereby exposing a portion of the membrane layer.
7. The method according to claim 6 , further comprising forming, over the first stack of layers, a second stack of layers via deposition and definition to include a first passivation layer and a second passivation layer on the first passivation layer.
8. The method according to claim 7 , further comprising defining first and second contact openings in the first and second passivation layers to expose respective portions of the first and second electrodes.
9. The method according to claim 8 , wherein the second stack of layers is further formed to include a first metallization layer on the second passivation layer and extending through the first contact opening to contact the second electrode, and to include a second metallization layer on the second passivation layer and extending through the second contact opening to contact the first electrode.
10. The method according to claim 9 , wherein the second stack of layers is further formed to include a third passivation layer on the second passivation layer and first and second metallization layers, with a third contact opening being formed in the third passivation layer to expose at least in part the first metallization layer.
11. The method according to claim 10 , further comprising depositing and defining a contact layer over the second stack of layers, and etching the membrane layer to define the first and second deformable elements and to define trenches in the membrane layer.
12. The method according to claim 11 , further comprising depositing an adhesive layer on the third passivation layer and the contact layer, and coupling a carrier wafer to the adhesive layer to obtain a second wafer and delimited by a top surface and a bottom surface.
13. The method according to claim 12 , further comprising flipping the second wafer and etching the second wafer from its bottom surface to form first, second, and third substrate portions, a cavity being delimited between the first and second substrate portions, wherein the etching exposes a back side of the membrane layer.
14. The method according to claim 13 , further comprising etching the first insulating layer to define first and second connections arms and the first and second frames, then removing the adhesive layer via thermal release to thereby detach the carrier wafer from the first wafer.
15. The method according to claim 13 , further comprising dicing the first wafer.
16. A method of making a MEMS actuator comprising a monolithic body of semiconductor material, the method comprising:
forming a supporting portion of semiconductor material, orientable with respect to first and second rotation axes, the first rotation axis being transverse with respect to the second rotation axis;
forming a first frame of semiconductor material;
forming first deformable elements, of semiconductor material, coupled to the first frame, and configured to control a rotation of the supporting portion about the first rotation axis;
forming a second frame of semiconductor material; and
forming second deformable elements, of semiconductor material, coupled to the first frame and to the second frame, and configured to control a rotation of the supporting portion about the second rotation axis,
wherein the first and second deformable elements are formed to carry respective first and second piezoelectric actuation elements.
17. The method according to claim 16 , wherein the first frame is formed to have an elongated hexagonal shape, with two first sides parallel to a first symmetry axis and four end sides extending transverse to the first symmetry axis and a second symmetry axis, wherein the first symmetry axis and the second symmetry axis are parallel to the first and second rotation axis, wherein the first deformable elements extend perpendicularly to the first symmetry axis.
18. The method according to claim 17 , wherein the second frame is formed to have a regular quadrangular shape with sides parallel to the end sides of the first frame, and wherein the second deformable elements extend parallel to the first symmetry axis.
19. The method according to claim 18 ,
wherein forming the first deformable elements is accomplished by forming first and second elastic elements of the first deformable elements on opposite sides of the supporting portion and extending transversely to the first symmetry axis; and
wherein forming the second deformable elements is accomplished by forming first and second elastic elements of the second deformable element on opposite sides of the first frame and extending transversely to the second symmetry axis.
20. The method according to claim 19 , wherein the first and second elastic elements of the first deformable elements are formed as respective first and second deformable arms carrying the first piezoelectric actuation elements and respective first and second connection arms, connecting opposite ends of respective successive ones of the first and second deformable arms, thereby forming a serpentine shape.
21. The method according to claim 20 , wherein the first and second elastic elements of the second deformable elements are formed as respective third and fourth deformable arms carrying the second piezoelectric actuation elements and respective third and fourth connection arms, connecting opposite ends of respective successive third and fourth deformable arms, thereby forming the serpentine shape.
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US7605966B2 (en) * | 2008-01-21 | 2009-10-20 | Stanley Electric Co., Ltd. | Optical deflector |
JP5446122B2 (en) * | 2008-04-25 | 2014-03-19 | パナソニック株式会社 | Meander type vibrator and optical reflection element using the same |
US8681407B2 (en) * | 2010-03-30 | 2014-03-25 | Panasonic Corporation | Optical reflection element |
CN103180239B (en) * | 2010-07-05 | 2016-01-06 | 艾伦·迈克 | Based on the micro electronmechanical lens actuation system of piezoelectricity |
ITTO20130312A1 (en) | 2013-04-18 | 2014-10-19 | St Microelectronics Srl | METHOD OF MANUFACTURE OF A FLUID EJECTION DEVICE AND FLUID EJECTION DEVICE |
US9306475B1 (en) * | 2014-08-01 | 2016-04-05 | Faez Ba-Tis | Piston-tube electrostatic microactuator |
JP6560897B2 (en) * | 2015-05-20 | 2019-08-14 | スタンレー電気株式会社 | Piezoelectric film laminate, method of manufacturing the same, and optical scanner |
TW201642557A (en) | 2015-05-27 | 2016-12-01 | 鴻海精密工業股份有限公司 | Voice coil motor actuator |
IT201900007219A1 (en) * | 2019-05-24 | 2020-11-24 | St Microelectronics Srl | PIEZOELECTRIC MEMS ACTUATOR FOR THE COMPENSATION OF UNWANTED MOVEMENTS AND RELATED MANUFACTURING PROCESS |
IT202000010261A1 (en) * | 2020-05-07 | 2021-11-07 | St Microelectronics Srl | PIEZOELECTRIC ACTUATOR EQUIPPED WITH A DEFORMABLE STRUCTURE HAVING IMPROVED MECHANICAL PROPERTIES AND RELATED MANUFACTURING PROCEDURE |
-
2019
- 2019-05-24 IT IT102019000007219A patent/IT201900007219A1/en unknown
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2020
- 2020-05-21 US US16/880,141 patent/US11614634B2/en active Active
- 2020-05-22 CN CN202010444104.7A patent/CN111983801B/en active Active
- 2020-05-22 EP EP20176144.2A patent/EP3745482B1/en active Active
- 2020-05-22 CN CN202020878433.8U patent/CN212723526U/en not_active Withdrawn - After Issue
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2023
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US11614634B2 (en) | 2023-03-28 |
US20200371376A1 (en) | 2020-11-26 |
CN111983801B (en) | 2023-06-23 |
EP3745482A1 (en) | 2020-12-02 |
CN111983801A (en) | 2020-11-24 |
EP3745482B1 (en) | 2022-03-16 |
CN212723526U (en) | 2021-03-16 |
IT201900007219A1 (en) | 2020-11-24 |
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