CN221239140U - Electronic device including a microelectromechanical mirror device - Google Patents

Abstract

The present disclosure relates to electronic devices including microelectromechanical mirror devices. A microelectromechanical device has a first tiltable mirror structure extending in a horizontal plane defined by a first horizontal axis and a second horizontal axis, and includes a fixed structure defining a frame that defines a cavity, a tiltable element carrying a reflective area, the tiltable element being resiliently suspended above the cavity and having a first intermediate axis of symmetry and a second intermediate axis of symmetry, the tiltable element being resiliently coupled to the frame by a first coupling structure and a second coupling structure located on opposite sides of the second horizontal axis. The first tiltable mirror structure has a drive structure coupled to the tiltable element to cause rotation about a first horizontal axis. The first tiltable mirror structure is asymmetric with respect to the second horizontal axis and has a first extension along the first horizontal axis on a first side of the second horizontal axis and a second extension greater than the first extension on a second side of the second horizontal axis opposite the first side.

Description

Electronic device including a microelectromechanical mirror device

Cross Reference to Related Applications

The present application claims the benefit of priority from italian patent application number 102022000012884 filed on month 17 of 2022, the contents of which are incorporated herein by reference in their entirety to the maximum extent allowed by law.

Technical Field

The present disclosure relates to a microelectromechanical mirror device (fabricated using microelectromechanical system MEMS technology) having optimized dimensions.

Background

Microelectromechanical mirror devices are used in portable devices, such as smartphones, tablets, notebooks, PDAs, and in optical applications, in particular to direct an optical radiation beam generated by a light source (e.g. a laser) with a desired pattern. Because of their small size, these devices allow for stringent requirements in terms of area and thickness for space usage.

For example, microelectromechanical mirror devices are used in optoelectronic devices, such as small projectors (so-called micro projectors), which are capable of projecting images from a distance and generating a desired light pattern, for example for augmented reality or virtual reality applications.

Microelectromechanical mirror devices typically include tiltable structures carrying suitable reflective (or mirror) surfaces that are resiliently supported above a cavity and made of a body of semiconductor material so as to be movable, e.g., by tilting or rotational movement, away from a corresponding main extension plane, in order to direct an incident beam of light in a desired manner.

In particular, in the case of a microelectromechanical mirror device with dual axis projection, it is desirable that the beam be deflected along two axes, which deflection may be provided by two uniaxially tiltable structures.

In this regard, fig. 1 schematically shows a micro projector 1, the micro projector 1 comprising a light source 2, e.g. a laser source, the light source 2 generating a light beam, the light beam being deflected by a micro electromechanical mirror device 3 towards a screen 4.

In the example schematically illustrated in the foregoing fig. 1, the micro-electromechanical mirror device 3 includes: a first tiltable mirror structure 3a of the single axis type, the first tiltable mirror structure 3a being controlled such that it rotates about an axis of rotation a with a resonant motion to generate a fast horizontal scan; and a second tiltable mirror structure 3b, also of the single axis type, the second tiltable mirror structure 3b being controlled such that it rotates about a respective axis of rotation a' with linear or quasi-static motion (i.e. at a frequency well below that of the resonant motion) to generate a slow vertical scan, for example a saw tooth type. The above-mentioned respective rotation axis a' is transverse, for example orthogonal or inclined at a certain non-zero angle with respect to the rotation axis a.

The first tiltable mirror structure 3a and the second tiltable mirror structure 3b cooperate to generate a scanning pattern on the screen 4, which is shown schematically in fig. 1 and indicated by 5. In particular, the first tiltable mirror structure 3a rotating about the rotation axis a "draws" a horizontal line on the second tiltable mirror structure 3 b; and the above-mentioned second tiltable mirror structure 3b, which rotates about a respective rotation axis a', directs the projection onto a desired rectangular surface on the screen 4.

The rotation of the tiltable mirror structures 3a, 3b is controlled by a respective actuation system, which may be of electrostatic, electromagnetic or piezoelectric type, for example.

Electrostatic actuation systems typically have the disadvantage of requiring high operating voltages, whereas electromagnetic actuation systems typically require high power consumption; it is therefore proposed to control the movement of the tiltable mirror structure using piezoelectric actuation.

Microelectromechanical mirror devices with piezoelectric actuation have the advantage of requiring reduced actuation voltage and power consumption compared to devices with electrostatic or electromagnetic actuation. Furthermore, a Piezoresistive (PZR) sensor element for sensing the driving condition of the mirror (in dependence of the applied stress or assumed displacement or position) and for providing a feedback signal to allow feedback control of the same driving can be easily provided.

There is a general need to reduce the size of tiltable mirror structures for the above described microelectromechanical mirror apparatus in order to achieve reduced total area occupation. This need is particularly evident, for example, when the mirror device is used in glasses or headphones for virtual reality or augmented reality applications.

In the case of microelectromechanical mirror devices with biaxial projection, the size reduction not only requires a size reduction of the individual tiltable mirror structures, but also a proper mutual arrangement of the above-described structures in order to optimize the occupied volume as a whole.

In this respect, fig. 2 schematically shows a microelectromechanical mirror device with a biaxial projection, again indicated with 3, in which possible means corresponding to the first tiltable mirror structure 3a and the second tiltable mirror structure 3b are placed in a closed position in order to reduce the occupied volume.

A problem that may occur with similar configurations of the micro-electromechanical mirror device 3 is manifested by the possibility that the output beam (OUT) reflected by the second tiltable mirror structure 3b is intercepted (even partly) by the body of the first tiltable mirror structure 3a, thus creating clipping of the light projection.

Accordingly, there is a need in the art to provide a microelectromechanical mirror device that overcomes the previously emphasized problems and has a reduced footprint, with optimized dimensions.

Disclosure of utility model

Disclosed herein is an electronic device that includes a microelectromechanical mirror device having a first tiltable mirror structure in a first semiconductor material die that extends in a horizontal plane defined by a first horizontal axis and a second horizontal axis. The first tiltable mirror structure is characterized by a fixed structure defining a frame that defines a cavity, a tiltable element that carries a reflective region that is resiliently suspended above the cavity, having a first intermediate axis of symmetry and a second intermediate axis of symmetry that are parallel to the first horizontal axis and the second horizontal axis, and a drive structure coupled to the tiltable element for rotation about the first horizontal axis in a resonant motion. The first tiltable mirror structure is asymmetric with respect to the second horizontal axis and has different extension dimensions along the first horizontal axis on opposite sides of the second horizontal axis.

The electronic device includes a first coupling structure on a first side of a second horizontal axis, the first coupling structure having a single torsion spring connected to the tiltable element and the frame, the single torsion spring extending linearly along the first horizontal axis. The second coupling structure is characterized by a first torsion spring and a second torsion spring with a binding element therebetween, the springs being connected to the tiltable element, the binding element and the frame along a first horizontal axis.

The single torsion spring of the first coupling structure has a first width along the second horizontal axis that is less than a corresponding second width of the first torsion spring of the second coupling structure.

The single torsion spring of the first coupling structure has a first torsional stiffness and the first torsion spring of the second coupling structure has a second torsional stiffness, a ratio between the first torsional stiffness and the second torsional stiffness being between 0.55 and 0.65.

The drive structure is positioned entirely on a second side of the second horizontal axis on the same side as the second coupling structure.

The drive structure comprises a single pair of drive arms coupled to the tiltable element formed by a first drive arm and a second drive arm symmetrically arranged with respect to the first horizontal axis and the second coupling structure. The first and second drive arms are integrally coupled to a frame of the fixed structure, suspended above the cavity, and carrying respective piezoelectric structures on a top surface thereof opposite the cavity.

The drive structure is further characterized by a first displacement transmission structure and a second displacement transmission structure, which are symmetrically arranged with respect to the first horizontal axis and are interposed between the second ends of the first and second drive arms and the respective ends of the constraining elements of the second coupling structure. Each displacement transfer structure is configured to transfer drive of the first drive arm or the second drive arm to a respective end of the constraint element.

Each of the first and second displacement transfer structures includes a first arm extending linearly along the first horizontal axis and coupled between the second end of the corresponding drive arm and the rigid connection element proximate the tiltable element, and a second arm extending linearly along the first horizontal axis parallel to the first arm and coupled between the rigid connection element proximate the tiltable element and a respective end of the constraint element of the second coupling structure.

The second end of the single torsion spring of the first coupling structure is connected to the frame by a first coupling elastic element and a second coupling elastic element extending from the second end towards the respective long side of the frame transversely to the single torsion spring parallel to the second horizontal axis.

The second end of the single torsion spring of the first coupling structure is connected to the frame by a first coupling elastic element and a second coupling elastic element, which are folded and have an overall extension along the first horizontal axis connecting the second end of the single torsion spring to the first short side of the frame.

The electronic device has a first coupling elastic element and a second coupling elastic element, and a portion of a single torsion spring extending within a recess provided in the frame at the first short side.

The reinforcing structure is coupled below the tiltable elements of the first tiltable mirror structure as a mechanical reinforcement for the tiltable elements.

The apparatus also includes a second tiltable mirror structure having a tiltable element that rotates in linear or quasi-static motion about an axis of rotation. The second tiltable mirror structure cooperates with the tiltable elements of the first tiltable mirror structure to direct an incident light beam. The second tiltable mirror structure is disposed in a second semiconductor material die having a fixed structure that defines a frame that defines a cavity that houses the tiltable element. The frame defines an outer side surface of the second die having a concave pattern shape to form a recess that accommodates at least a portion of the first die of the first tiltable mirror structure.

The second tiltable mirror structure is arranged such that its horizontal plane is at a specific angle of less than 90 ° relative to the horizontal plane of the first tiltable mirror structure.

The recess has a basin shape and is delimited by a base portion extending parallel to the first horizontal axis and a wall portion inclined or orthogonal with respect to the base portion.

The second tiltable mirror structure further includes an actuation structure coupled to the tiltable element and configured to rotate it about an axis of rotation. The actuating structure is characterized by a first pair of drive arms and a second pair of drive arms, each pair of drive arms being formed by a first drive arm and a second drive arm arranged symmetrically with respect to the axis of rotation. Each drive arm has a first end integrally coupled to the frame and a second end resiliently coupled to the tiltable element by a respective decoupling elastic element. The outer side surface is arranged in a closed position with reduced separation gap with respect to the drive arm and the tiltable element during the whole extension along the first horizontal axis.

The electronic device is an optoelectronic device comprising a light source for generating a light beam. The microelectromechanical mirror device acts as a mirror module with biaxial projection for receiving the light beam and directing it to an external screen or display surface at a distance from the optoelectronic device.

An aspect of the present disclosure provides an electronic device including a microelectromechanical mirror device including a first tiltable mirror structure disposed in a first semiconductor material die, the first tiltable mirror structure having a main extension in a horizontal plane defined by a first horizontal axis and a second horizontal axis, wherein the first tiltable mirror structure includes: a securing structure defining a frame defining a cavity; a tiltable element carrying a reflective area, resiliently suspended over the cavity, and having first and second intermediate axes of symmetry parallel to the first and second horizontal axes, respectively, the tiltable element being resiliently coupled to the frame by first and second coupling structures located on opposite sides of the second horizontal axis; and a drive structure coupled to the tiltable element and configured to rotate the tiltable element about the first horizontal axis in a resonant motion; wherein the first tiltable mirror structure is asymmetric with respect to the second horizontal axis and has along the first horizontal axis: a first extension dimension on a first side of the second horizontal axis; and a second extension dimension, the second extension dimension being greater than the first extension dimension, the second extension dimension being on a second side of the second horizontal axis and opposite the first side.

Another aspect of the present disclosure provides an electronic device comprising a microelectromechanical mirror device having a first tiltable mirror structure in a first semiconductor material die, the first tiltable mirror structure extending in a horizontal plane defined by a first horizontal axis and a second horizontal axis, wherein the first tiltable mirror structure comprises: a fixed frame closing the cavity; a tiltable reflective element having first and second intermediate axes of symmetry parallel to the first and second horizontal axes, the tiltable reflective element being resiliently connected to the frame by first and second coupling mechanisms located on opposite sides of the second horizontal axis; and a drive mechanism linked to the tiltable reflective element to cause rotation about the first horizontal axis using resonant motion; wherein the first tiltable mirror structure is asymmetric about the second horizontal axis and has a varying extension along the first horizontal axis; wherein the first coupling mechanism positioned on a first side of the second horizontal axis comprises a single torsion spring connected to the tiltable reflective element and the frame, the single torsion spring extending linearly along the first horizontal axis; wherein the second coupling mechanism includes first and second torsion springs extending along the first horizontal axis, and a restraint assembly between the first and second torsion springs, wherein the first and second torsion springs are connected to the tiltable reflective element, the restraint assembly, and the frame.

Drawings

For a better understanding, the preferred embodiments are now described, purely by way of non-limiting example, with reference to the accompanying drawings, in which:

FIG. 1 schematically illustrates a prior art micro-projector provided by a pair of tiltable mirror structures;

FIG. 2 schematically illustrates a prior art microelectromechanical mirror device having a biaxial projection and a possible arrangement of corresponding tiltable mirror structures;

FIG. 3 illustrates a schematic plan view of a tiltable mirror structure for a microelectromechanical mirror apparatus having resonant motion in accordance with one aspect of the present disclosure;

FIG. 4 illustrates the tiltable mirror structure of FIG. 3 during corresponding rotational movements;

FIGS. 5A and 5B schematically illustrate tiltable mirror structures in plan view and cross-sectional view, respectively, according to another aspect of the present disclosure;

6A-6C illustrate schematic plan views of further variations of tiltable mirror structures in accordance with one aspect of the present disclosure;

FIGS. 7A and 7B illustrate schematic plan views of respective variations of another tiltable mirror structure for a microelectromechanical mirror apparatus having linear or quasi-static motion in accordance with one aspect of the present disclosure;

8A-8B schematically illustrate possible combined arrangements of tiltable mirror structures for a microelectromechanical mirror apparatus according to one aspect of the present disclosure;

FIGS. 9 and 10 illustrate schematic diagrams of layouts of semiconductor material wafers in which tiltable mirror structures are provided, according to one aspect of the present disclosure; and

Fig. 11 is a schematic block diagram of an optoelectronic device (e.g., a micro projector) using the microelectronic mirror devices disclosed herein.

Detailed Description

FIG. 3 illustrates a tiltable mirror structure, indicated generally at 10, that is based on MEMS technology; the tiltable mirror structure 10 is designed to provide resonant fast scanning motion (thus, for example, the first tiltable mirror structure 3a of the above-described micro electromechanical mirror apparatus 3 corresponding to the micro projector 1 of fig. 1).

As will be described in detail below, according to one aspect of the present disclosure, tiltable mirror structure 10 has an asymmetric configuration along its main extension axis in order to achieve a reduction in size along the main extension axis.

Tiltable mirror structure 10 is formed in a die 11 of semiconductor material, in particular silicon, and has a tiltable element 12, which tiltable element 12 has a main extension in a horizontal plane xy (when stationary) and is arranged such that it rotates in resonance with a fast movement about a first axis a, which is parallel to a first horizontal axis x of the above-mentioned horizontal plane xy (which first horizontal axis x in this case represents the above-mentioned main extension axis of tiltable mirror structure 10).

The first axis a represents the intermediate axis of symmetry of the tiltable element 12 and generally represents the intermediate axis of symmetry of the tiltable mirror structure 10.

A second axis B orthogonal to the above-mentioned first axis a and intersecting the above-mentioned first axis a at the geometric center O of the tiltable element 12 in the horizontal plane xy represents another intermediate symmetry axis in the above-mentioned tiltable element 12. The second axis B is parallel to the second horizontal axis y, orthogonal to the first horizontal axis x and defines, together with the above-mentioned first horizontal axis x, a horizontal plane xy.

As previously described, and as will be described in detail below, according to one aspect of the present disclosure, tiltable mirror structure 10 is generally asymmetric with respect to the second axis B (and with respect to the second horizontal axis y) and has along the first horizontal axis x: a first extension d1 on a first side of the second axis B; and a second extension d2 greater than the first extension d1 on a second side of the shaft B opposite the first side (the total extension of the tiltable mirror structure 10 along the first horizontal axis x is denoted by d, where d=d1+d2).

Purely by way of example, the first extension d1 may be equal to 3.5mm and the second extension d2 may be equal to 4.5mm (total extension d equal to 8 mm); typically, the first extension d1 may be between 3mm and 4.5mm in this example (the lower limit being related to the mechanical stress limit that the elastic element can withstand).

The tiltable element 12 is suspended above a cavity 13, the cavity 13 being provided in the die 11 and defining a support element carrying a reflective area 12' (e.g. made of aluminum or gold, depending on whether the projection is in the visible or infrared region) to define a mirror element.

The tiltable element 12 is elastically coupled to a fixed structure 14, the fixed structure 14 being formed in the die 11 described above and defining a frame 14' on a horizontal plane xy; the frame 14' has a substantially rectangular shape in the horizontal plane xy and delimits and encloses the cavity 13.

In particular, the tiltable element 12 is elastically coupled to the frame 14 'by a first coupling structure 15a and a second coupling structure 15B, the first coupling structure 15a and the second coupling structure 15B extending longitudinally along the first horizontal axis x, suspended above the cavity 13, between the frame 14' and the tiltable element 12, on opposite sides of the tiltable element 12 about the second axis B.

In detail, the first coupling structure 15a arranged on the above-mentioned first side of the second shaft B is in this case formed by a single torsion spring 16a, which torsion spring 16B has a first end coupled to the tiltable element 12 and a second end coupled to the frame 14' (in particular corresponding to the first short side). In the illustrated embodiment, the torsion spring 16a has a linear beam shape extending along a first horizontal axis x.

In contrast, the second coupling structure 15b comprises a first torsion spring 16b ' and a second torsion spring 16a ", and a restraining element 18 interposed between the above-mentioned first torsion spring 16b ' and second torsion spring 16b", the first torsion spring 16b ' and the second torsion spring 16a "having a linear beam shape extending along the first horizontal axis x.

In detail, the first torsion spring 16b' has a first end coupled to the tiltable element 12 and a second end coupled to the constraint element 18. The second torsion spring 16b "has a first end coupled to the constraining element 18 (on the opposite side with respect to the first torsion spring 16b 'along the first horizontal axis x) and a second end coupled to the frame 14' (in particular to a corresponding second short side opposite to the above-mentioned first short side); the length of the second torsion spring 16b "along the first horizontal axis x is smaller, in particular much smaller, than the corresponding length of the first torsion spring 16 b'.

In general, the torsion springs 16a, 16b', 16b″ described above have a high stiffness to bend along the first and second horizontal axes x, y of the horizontal plane xy and yield to torsion about the axis a, allowing the tiltable element 12 to rotate.

The above-mentioned restraining element 18 is rigid and has in this example a substantially rectangular shape in the horizontal plane xy, the width of which (in a direction parallel to the second horizontal axis y) is much greater with respect to the torsion springs 16b', 16b ", and the length of which (in a direction parallel to the first horizontal axis x) is in this example comparable to the length of the second torsion spring 16 b". The aforementioned constraint element 18 crosses the first axis a, having a first end and a second end arranged on opposite sides of the aforementioned first axis a along the second horizontal axis y.

Tiltable mirror structure 10 further includes a drive structure 20, the drive structure 20 being coupled to the tiltable element 12 and configured to rotate it about a first axis A; the driving structure 20 is integrally arranged on the above-mentioned second side of the second shaft B, i.e. on the same side as the second coupling structure 15B.

According to one aspect of the present disclosure, tiltable mirror structure 10 does not include a drive structure disposed on the first side of the second axis B that is on the same side as the first coupling structure 15 a.

In detail, the above-described driving structure 20 includes a single pair of driving arms formed of a first driving arm 22a and a second driving arm 22b, the first driving arm 22a and the second driving arm 22b being disposed at opposite sides of the first axis a and the second coupling structure 15b and being symmetrical with respect to the first axis a and the second coupling structure 15b and having a longitudinal extension parallel to the first horizontal axis x.

In the embodiment shown in fig. 1, the driving arms 22a, 22b have a substantially rectangular shape, the first end of which is integrally coupled to the frame 14' of the fixed structure 14, the driving arms 22a, 22b being suspended above the cavity 13 and carrying respective piezoelectric structures 23 (in particular comprising lead zirconate-lead titanate PZT) at respective top surfaces (opposite to the cavity 13 described above), for example having substantially the same extension in the horizontal plane xy with respect to the respective driving arms 22a, 22 b.

The piezoelectric structure 23 is formed (in a manner not shown in detail) by superimposing a bottom electrode region made of a suitable conductive material, arranged above the corresponding driving arm 22a, 22 b; a piezoelectric material region (e.g., formed of a PZT thin film) disposed on the bottom electrode region; and a top electrode region disposed on the piezoelectric material region.

The above-mentioned driving structure 20 further comprises a first displacement transmission structure 25a and a second displacement transmission structure 25b, the first displacement transmission structure 25a and the second displacement transmission structure 25b being arranged symmetrically to each other with respect to the first axis a and interposed between the second ends of the first driving arm 22a and the second driving arm 22b and the respective ends of the constraint element 18 of the second coupling structure 15b, respectively.

Each of the first and second displacement transmission structures 25a, 25b comprises a first arm 26 having a linear extension along the first horizontal axis x and coupled between the second end of the corresponding drive arm 22a, 22b and a rigid connection element 27, the rigid connection element 27 being arranged in the vicinity of the tiltable element 12; and a second arm 28, the second arm 28 also having a linear extension along the first horizontal axis x, the second arm 28 being parallel to the first arm 26 and coupled between the above-mentioned rigid connection element 27 close to the tiltable element 12 and the first end or the second end of the constraint element 18 of the coupling structure 15 b. Thus, the second arm 28 is interposed between the first torsion spring 16b' of the second coupling structure 15b and the first arm 26.

The tiltable mirror structure 10 further includes a Piezoresistive (PZR) sensor 30, the PZR sensor 30 being suitably arranged such that it provides a sensing signal associated with rotation of the tiltable element 12 about a first axis A; the sensing signal may be provided external to the micro-electromechanical mirror device 1 to enable feedback control for driving the tiltable element 12 described above.

In the embodiment shown in fig. 3, the piezoresistive sensor 30 is arranged in the frame 14 '(e.g. by surface diffusion of doping atoms) at the coupling area of the frame 14' and the second torsion spring 16b″ of the second coupling structure 15 b. The piezoresistive sensor 30 is arranged such that it senses the stress associated with the torsion of the second torsion spring 16b "described above and thus provides an indication related to the rotational movement of the tiltable element 12.

The tiltable mirror structure 10 further comprises a plurality of electrical contact pads 32, which electrical contact pads 32 are carried by the fixed structure 14 at the frame 14', electrically connected (not shown in detail in fig. 3 above) to the piezoelectric structures 23 of the drive arms 22a, 22b through respective electrical connection tracks to allow electrical biasing thereof by electrical signals from outside the micro electromechanical mirror apparatus 1 (e.g., provided by biasing means of an electronic device in which the tiltable mirror structure 10 is integrated). The electrical contact pads 32 are also connected to the piezoresistive sensor 30 to output the sensing signals.

During operation of tiltable mirror structure 10, as schematically shown in FIG. 4, application of a bias voltage to the piezoelectric structure 23 of the first drive arm 22a (the bias of the piezoelectric structure 23 relative to the second drive arm 22b has a positive value, e.g., it can be connected to a ground reference potential) can cause a positive angular rotation about the first axis A.

Accordingly, applying a bias voltage to the piezoelectric structure 23 of the second drive arm 22b (the bias of the piezoelectric structure 23 with respect to the first drive arm 22a has a positive value, which may be connected to a ground reference potential in this case, for example) may cause a corresponding negative angular rotation about the above-mentioned first axis a.

In particular, the drive of the first drive arm 22a in a first direction (e.g., downward, as previously shown in fig. 4) along the orthogonal axis z is transmitted to the first end of the constraining element 18 by the first displacement transmitting structure 25 a; similarly, drive of the second drive arm 22a in a second direction (e.g., downward) of the aforementioned orthogonal axis z is transmitted to the second end of the restraining element 18 via the second displacement transmission structure 25b, thereby causing torsion of the first torsion spring 16b' and subsequent rotation of the tiltable element 12.

In more detail, according to one aspect of the present disclosure, the torsion spring 16a of the first coupling structure 15a has a first width t1 along the second horizontal axis y, which first width t1 is smaller than a corresponding second width t2 of the first torsion spring 16b' of the second coupling structure 15 b.

In particular, the torsional stiffness k1 of the torsion spring 16a is even 40% lower than the corresponding torsional stiffness k2 of the first torsion spring 16 b'; in the embodiment shown in fig. 3, this different torsional stiffness is due primarily to the different widths, since the lengths of the torsion springs are substantially the same (to maintain a similar stress distribution).

In general, the ratio (k 1/k 2) between the above torsional rigidities is preferably between 0.55 and 0.65; in other words, the torsional stiffness k1 of the single torsion spring 16a is between 55% and 65% of the torsional stiffness k2 of the first torsion spring 16 b'.

Fig. 5A and 5B schematically show different embodiments of the tiltable mirror structure 10, which envisages the presence of a reinforcing structure 33 coupled under the tiltable element 12, which reinforcing structure 33 acts as a mechanical reinforcement for the tiltable element 12 described above (and also serves to ensure its flatness in the horizontal plane xy in the rest state); the reinforcing structure 33 may have, for example, a ring shape, and be arranged at the periphery of the tiltable element 12 (the reinforcing structure 33 is formed substantially on the back surface of the die 11).

In particular, in the embodiment shown in fig. 5B, the die 11 is SOI (silicon on insulator) in which the tiltable element 12, the first coupling structure 15a and the second coupling structure 15B are arranged in an active layer 34a of the die 11, and the reinforcement structure 33 is arranged in a support layer 34B of the die 11. In this case, the frame 14' is provided in the active layer 34a and the support layer 34b of the die 11, and is also provided in the corresponding insulating layer 34c, the insulating layer 34c being interposed between the active layer 34a and the support layer 34 b.

A support wafer 37, coupled for example by bonding, is also present under the die 11.

In this embodiment, due to the presence of the reinforcement structure 33 described above, the size of the tiltable mirror structure 10 can be further reduced, particularly the length of the first coupling structure 15a and the corresponding torsion spring 16a (i.e., the first extension dimension d 1) while maintaining the same operating frequency.

In the example shown, the above-mentioned first extension d1 of the tiltable mirror structure 10 is for example equal to 2.5mm, the above-mentioned second extension d2 is equal to 4mm (total extension d is equal to 6.5 mm), with the same optical properties (in particular the same opening angle) as the structure described with reference to fig. 3.

In this embodiment, the frame 14' may also be arranged in another asymmetrical manner, with the aforesaid first and second short sides having different widths along the first horizontal axis x (i.e. the portions on opposite sides of the aforesaid second axis B that are guided along the second horizontal axis y). In particular, the width w1 of the side coupled to the first coupling structure 15a (the aforementioned first short side) in this case is smaller than the width w2 of the side coupled to the second coupling structure 15b (the aforementioned second short side).

Referring to fig. 6A-6C, further variant embodiments of tiltable mirror structure 10 are now shown that aim to reduce the size and corresponding area occupation of the tiltable mirror structure described above.

In particular, in the embodiment shown in fig. 6A, the second end of the single torsion spring 16A of the first coupling structure 15a is not directly coupled to the frame 14'. Conversely, the second end is coupled to the frame 14' by a first coupling elastic element 40a and a second coupling elastic element 40b, which are linear, which extend transversely to the torsion spring 16a parallel to the second horizontal axis y, from the second end towards the respective long side of the frame 14' (it should be noted that in this case the torsion spring 16a is therefore not coupled to the first short side of the frame 14 ').

Advantageously, this variant embodiment allows to reduce the length of the torsion spring 16a of the first coupling structure 15a.

In the variant embodiment shown in fig. 6B, the above-mentioned first coupling elastic element 40a and second coupling elastic element 40B are folded and have a general extension along the first horizontal axis x, re-coupling the above-mentioned second end of the torsion spring 16a of the first coupling structure 15a to the first short side of the frame 14'.

Due to the folded configuration of the first coupling elastic element 40a and the second coupling elastic element 40B described above, an even greater reduction of the first extension dimension d1 of the tiltable mirror structure 10 can be obtained on the first side of the second axis B; typically, the space occupation of the die is optimized.

In the variant embodiment of fig. 6C, the first coupling elastic element 40a and the second coupling elastic element 40b described above likewise have a folded configuration, and furthermore, a majority of the torsion springs 16a of the first coupling structure 15a extend within the grooves 45 provided in the frame 14' at the corresponding first short sides. In this way, an even greater reduction in the first extension dimension d1 of the tiltable mirror structure 10 can be achieved on the first side of the second axis B.

As previously described, tiltable mirror structure 10 can be used as a first tiltable mirror structure 3a (see fig. 1 and 2 described above) in a microelectromechanical mirror apparatus 3 (e.g., a mirror module defining a biaxial projection with a micro projector), the first tiltable mirror structure 3a being driven in resonance to generate a fast scan, the microelectromechanical mirror apparatus 3 further comprising a second tiltable mirror structure 3b, the second tiltable mirror structure 3b being controlled to rotate in linear or quasi-static motion about a respective axis of rotation to generate a slow scan.

As discussed in detail, the resulting size reduction for the first tiltable mirror structure 3a helps to reduce the overall volume footprint of the micro electromechanical mirror apparatus 3.

However, it has been realized that for the purpose of such volume reduction, it is suggested to optimize the dimensions of the second tiltable mirror structure 3b as well, and also to provide the optimized engagement arrangement of the first tiltable mirror structure 3a and the second tiltable mirror structure 3b described above.

Thus, another aspect of the present disclosure provides a microelectromechanical mirror device 3 with dual-axis projection, the microelectromechanical mirror device 3 comprising the tiltable mirror structure 10 (serving as a first tiltable mirror structure 3 a) as described previously to optimize the size and arrangement of the associated second tiltable mirror structure 3 b.

As will be discussed in detail below, this aspect of the present disclosure contemplates a suitable die patterning in which the second tiltable mirror structure 3b is formed for purposes of not only reducing size but also facilitating mutual positioning with the first tiltable mirror structure 3 a.

Referring now to FIG. 7A, an embodiment of a tiltable mirror structure 50 is described that can be used as the above-described second tiltable mirror structure 3b in a micro electromechanical mirror apparatus 3.

Generally, the tiltable mirror structure 50 is provided, for example, as described in detail in U.S. patent publication 2020/0192199 (corresponding to European patent application EP366672A 1), which is incorporated herein by reference.

Tiltable mirror structure 50 has a shape that is perfectly symmetrical with respect to a first horizontal axis x 'and a second horizontal axis y' of a respective horizontal plane x 'y' and is fabricated in a respective semiconductor material, particularly a silicon die 51.

Tiltable mirror structure 50 is provided with respective tiltable elements 52, which tiltable elements 52 are arranged such that they rotate (in quasi-static motion) about respective rotation axes a ' (parallel to a first horizontal axis x ') and carry reflective surfaces 52'. In the example shown, the tiltable element 52 has a rectangular shape in the horizontal plane x ' y ', which rectangular shape is elongated along the respective rotation axis a '.

In particular, the die 51 comprises a fixed structure 54 defining a frame 54', the frame 54' delimiting and surrounding the cavity 53, the tiltable element 52 being housed in the cavity 53; a first supporting (or anchoring) element 55a and a second supporting (or anchoring) element 55b integral with the frame 54' extend from the frame 54' along the respective rotation axes a ' described above, inside the cavity 53, on opposite sides with respect to the tiltable element 52.

The tiltable elements 52 are elastically coupled to the first and second support elements 55a, 55b by first and second suspension elastic elements 56a, 56b, the first and second suspension elastic elements 56a, 56b having a high stiffness for out-of-plane movements and yielding for torsion about the respective rotation axes a'. These first and second suspension elastic elements 56a and 56b also extend along the respective rotation axes a', as extensions of the first and second support elements 55a and 55 b.

Tiltable mirror structure 50 also includes an actuation structure 60, the actuation structure 60 being coupled to the tiltable element 52 and configured to rotate it about a respective axis of rotation A'; the actuating structure 60 is interposed between the tiltable element 52 and the fixed structure 54 and helps support the tiltable element 50 above the cavity 53.

The actuating structure 60 comprises a first and a second pair of driving arms, each pair being formed by a first driving arm 62a and a second driving arm 62b, the first and second driving arms 62a, 62b being arranged on opposite sides of and symmetrical with respect to a respective rotation axis a' and a respective one of the first and second supporting elements 55a, 55 b.

Each drive arm 62a, 62b is suspended above the cavity 53 and carries a respective piezoelectric structure 63 (comprising in particular PZT); in the example of the linear type, each driving arm 62a, 62b has a first end integrally coupled to the frame 54' and a second end elastically coupled to the tiltable element 52 by a respective decoupling elastic element 64a, 64b (having a high stiffness with respect to out-of-plane motion and yielding with respect to torsion).

According to a particular aspect of the present disclosure, the frame 54' of the die 51 defining the outer side surface 51' of the die 51 described above has a suitable patterned shape at its longitudinal extension parallel to the respective rotation axis a '. In other words, the above-mentioned frame 54' does not have a rectangular or square profile in the horizontal plane x ' y '.

In particular, this outer lateral surface 51 'is patterned in a concave manner, such that it defines respective recesses 66 on both sides of the tiltable element 52 with respect to the first horizontal axis x'.

In the previously described embodiment shown in fig. 7A, each recess 66 has a basin shape and is defined by: a base 66a extending along a first horizontal axis x', external to the tiltable element 52; and a wall portion 66b inclined (in a "V" shape) with respect to the base portion 66 a.

In a different embodiment shown in fig. 7B, the recess 66 has a "U" shape in a horizontal plane x 'y', the base 66a extending along a first horizontal axis x ', in which case the wall 66B extends orthogonally along a second horizontal axis y'.

In both embodiments, the outer side surface 51 'is disposed in close proximity with a small or minimal separation gap relative to the drive arms 62a, 62b and the tiltable elements 52 by extending along the entire extent of the first horizontal axis x' in order to optimize the area occupation in the horizontal plane x 'y'.

In other words, tiltable mirror structure 50 thereby minimizes the extension of inactive areas (i.e., empty spaces that do not have specific functions in the above described structure).

It should be noted that in the embodiment shown in FIG. 7B, the drive arms 62a, 62B described above extend along the second horizontal axis y '(rather than along the first horizontal axis x') so that the tiltable mirror structure 50 has an overall "H" shape in the horizontal plane x 'y'.

As schematically shown in fig. 8A (relative to the embodiment of fig. 7A) and 8B (relative to the embodiment of fig. 7B), according to certain aspects of the present disclosure, the assembly of the microelectromechanical mirror device 3 provides that the first tiltable mirror structure 3a (i.e., tiltable mirror structure 10 described above) is at least partially housed in the recess 66 of the tiltable mirror structure 50 (which, as previously described, provides the second tiltable mirror structure 3B) so as to optimize the total volume occupation and also obtain a very tight arrangement between the same first tiltable mirror structure 3a and second tiltable mirror structure 3B.

In particular, the second tiltable mirror structure 3b is arranged such that the respective horizontal plane x 'y' is at a certain angle (less than 90 °) with respect to the horizontal plane xy of the first tiltable mirror structure 3 a.

In this way, a very compact final assembly can be obtained and also the dimensions of the first tiltable mirror structure 3a and the second tiltable mirror structure 3b having the same optical requirements (e.g. in terms of opening angle) for the same first tiltable mirror structure 3a and second tiltable mirror structure 3b can be reduced.

From a manufacturing perspective, the fabrication of the die 51 of the tiltable mirror structure 50 requires defining non-parallel scribe lines on a wafer of semiconductor material in the case of patterning the corresponding outside surface 51'. To this end, stealth dicing techniques may be used and/or "dummy" structures (non-functional) may be provided between the die 51 prior to dicing.

For example, fig. 9 shows a portion of a semiconductor material, particularly a silicon wafer 70, in which a plurality of dies 51 are provided, each of which integrates a corresponding tiltable mirror structure 50 (in accordance with the embodiments discussed above with reference to fig. 7A). The dummy die is highlighted, indicated by 72, except that the scribe lines indicated by LT are non-parallel, in which case the dummy die is interposed between the dies 51 along the second horizontal axis y'.

To optimize manufacturing costs, an alternative arrangement of die 51 in wafer 70 may be provided that does not require the presence of dummy die 72 as described above.

For example, fig. 10 shows a corresponding semiconductor material, in particular a silicon wafer 70, in which a plurality of dies 51 are provided, each of which integrates a corresponding tiltable mirror structure 50 (this time in accordance with the embodiments discussed above with reference to fig. 7B). In addition to the non-parallel scribe lines indicated by LT, in this case, the absence of the dummy die 72 described above is highlighted given the continuous and adjacent arrangement of the die 51.

As shown in fig. 11, the micro-electromechanical mirror device 3 may advantageously be used in an optoelectronic device, such as a micro-projector 80, for example, functionally coupled to a portable electronic apparatus 81 (such as a smartphone or augmented reality or virtual reality glasses or headphones).

In particular, optoelectronic device 80 includes a light source 82, such as a laser-type light source, for generating a light beam 83; a microelectromechanical mirror device 3, which acts as a mirror module with biaxial projection and serves to receive the light beam 83 and to direct the light beam 83 towards a screen or display surface 85 (externally and placed at a distance from the above-mentioned optoelectronic device 80); a first drive circuit 86 for providing appropriate control signals to the light source 82 to generate the light beam 83 from the image to be projected; a second drive circuit 88 for providing suitable control signals to the actuation structure of the micro-electronic mirror device 3; and an interface 89 for receiving from the control unit 90 a first control signal for controlling the first drive circuit 86 and a second control signal for controlling the second drive circuit 88, in which case the control unit 90 is external, for example comprised in the portable electronic device 81.

The control unit 90 also receives feedback signals provided by the micro-electromechanical mirror device 3 via the interface 89 for feedback control of the driving of the tiltable structure 2 as described above.

These advantages are apparent from the foregoing description.

In any event, it is emphasized again that the described asymmetric embodiment of tiltable mirror structure 10 (3 a) allows for a reduced area occupation of the same tiltable mirror structure 10, in particular the above-described reduction of the first extension d1 of the first side of the second axis B.

Thus, as described with reference to the prior art, this embodiment allows to avoid clipping of the light projection due to the close arrangement between the tiltable mirror structures 3a, 3b of the microelectromechanical mirror apparatus 3 with biaxial projection.

Furthermore, the shaping of the die 51 of the tiltable mirror structure 50 (3 b) and the resulting assembly with optimized volume occupation of the resulting micro electromechanical mirror apparatus 3 (due to the compact arrangement of the tiltable mirror structures 3a, 3 b) is also advantageous.

In general, the present disclosure allows for the advantages of piezoelectric actuation (i.e., using a reduced bias voltage with reduced energy consumption to obtain high displacement) and mirror actuated piezoresistive sensing to be utilized, while having improved mechanical and electrical performance relative to known solutions.

Finally, it is clear that modifications and variations may be made to what has been described and illustrated without departing from the scope of the present utility model as defined in the appended claims. For example, it is emphasized that the described asymmetric embodiments of tiltable mirror structure 10 can also find advantageous application for different configurations of the same tiltable mirror structure 10, e.g., in the case of structures with quasi-static motion, and thus are intended to provide slow scanning, e.g., zig-zag scanning, on a corresponding projection screen. This may be advantageous, for example, where the required opening angle is not high and it is important to reduce the overall space occupation of the microelectromechanical mirror device.

Claims (21)

1. An electronic device comprising a microelectromechanical mirror device, the microelectromechanical mirror device comprising a first tiltable mirror structure disposed in a first semiconductor material die, the first tiltable mirror structure having a main extension in a horizontal plane defined by a first horizontal axis and a second horizontal axis, wherein the first tiltable mirror structure comprises:

A securing structure defining a frame defining a cavity;

A tiltable element carrying a reflective area, resiliently suspended over the cavity, and having first and second intermediate axes of symmetry parallel to the first and second horizontal axes, respectively, the tiltable element being resiliently coupled to the frame by first and second coupling structures located on opposite sides of the second horizontal axis; and

A drive structure coupled to the tiltable element and configured to rotate the tiltable element about the first horizontal axis in a resonant motion;

Wherein the first tiltable mirror structure is asymmetric with respect to the second horizontal axis and has along the first horizontal axis:

a first extension dimension on a first side of the second horizontal axis; and

A second extension dimension, the second extension dimension being greater than the first extension dimension, the second extension dimension being on a second side of the second horizontal axis and opposite the first side.

2. The electronic device of claim 1, wherein the first coupling structure is disposed on the first side of the second horizontal axis and comprises a single torsion spring having a first end coupled to the tiltable element and a second end coupled to the frame and having a linear extension along the first horizontal axis; and wherein the second coupling structure comprises: first and second torsion springs having an extension along the first horizontal axis; and a constraining element interposed between the first torsion spring and the second torsion spring; the first torsion spring has a first end coupled to the tiltable element and a second end coupled to the constraint element, and the second torsion spring has: coupled to a first end of the restraining element along the first horizontal axis on an opposite side relative to the first torsion spring, and coupled to a second end of the frame.

3. The electronic device of claim 2, wherein the single torsion spring of the first coupling structure has a first width along the second horizontal axis that is less than a corresponding second width of the first torsion spring of the second coupling structure.

4. The electronic device of claim 2, wherein the single torsion spring of the first coupling structure has a first torsional stiffness and the first torsion spring of the second coupling structure has a second torsional stiffness; and wherein the ratio between the first torsional stiffness and the second torsional stiffness is between 0.55 and 0.65.

5. The electronic device of claim 2, wherein the drive structure is disposed entirely on the second side of the second horizontal axis on the same side as the second coupling structure.

6. The electronic device of claim 5, wherein the drive structure comprises a single pair of drive arms coupled to the tiltable element formed by a first drive arm and a second drive arm, the first drive arm and the second drive arm being disposed on opposite sides of and symmetrically with respect to the first horizontal axis and the second coupling structure; wherein each of the first and second drive arms has a first end integrally coupled to the frame of the fixed structure, the first and second drive arms being suspended above the cavity and carrying respective piezoelectric structures at respective top surfaces opposite the cavity.

7. The electronic device of claim 6, wherein the drive structure further comprises a first displacement transfer structure and a second displacement transfer structure arranged symmetrically to each other with respect to the first horizontal axis and interposed between the second ends of the first and second drive arms and the respective ends of the constraining element of the second coupling structure; each displacement transfer structure is configured to transfer drive of the first drive arm or the second drive arm to a respective end of the constraint element.

8. The electronic device of claim 7, wherein each of the first and second displacement transfer structures comprises:

A first arm having a linear extension along the first horizontal axis and coupled between the second end of a corresponding drive arm and a rigid connection element disposed adjacent to the tiltable element; and

A second arm having a linear extension along the first horizontal axis, the linear extension being parallel to the first arm and coupled between the rigid connection element and a respective end of the constraining element of the second coupling structure, the rigid connection element being in proximity to the tiltable element.

9. The electronic device of claim 2, wherein the second end of the single torsion spring of the first coupling structure is coupled to the frame by first and second coupling elastic elements of a linear type having an extension from the second end toward a respective long side of the frame transverse to the single torsion spring parallel to the second horizontal axis.

10. The electronic device of claim 2, wherein the electronic device comprises a memory device,

The second end of the single torsion spring of the first coupling structure is coupled to the frame by a first coupling elastic element and a second coupling elastic element; and

The first and second coupling elastic elements are folded and have an overall extension along the first horizontal axis coupling the second end of the single torsion spring to a first short side of the frame.

11. The electronic device of claim 10, wherein the first and second coupling elastic elements, and a portion of the single torsion spring extend within a recess provided in the frame at the first short side.

12. The electronic device of claim 1, wherein the first tiltable mirror structure further comprises a stiffening structure coupled below the tiltable element as a mechanical stiffener for the tiltable element.

13. The electronic device of claim 1, further comprising a second tiltable mirror structure provided with a tiltable element configured to rotate in linear or quasi-static motion about an axis of rotation and arranged to cooperate with the tiltable element of the first tiltable mirror structure to direct an incident light beam;

Wherein the second tiltable mirror structure is disposed in a second semiconductor material die, the second tiltable mirror structure having a main extension in a horizontal plane defined by a first horizontal axis and a second horizontal axis and having a fixed structure defining a frame, the frame defining a cavity in which the tiltable element is disposed; the frame defines an outside surface of the second semiconductor material die having a concave pattern shape to define a recess at least partially accommodating the first semiconductor material die of the first tiltable mirror structure.

14. The electronic device of claim 13, wherein the second tiltable mirror structure is arranged such that the horizontal plane is arranged at an angle of less than 90 ° relative to the horizontal plane of the first tiltable mirror structure.

15. The electronic device of claim 13, wherein the recess has a basin shape and is defined by a base extending parallel to the first horizontal axis and a wall portion that is inclined or orthogonal relative to the base.

16. The electronic device of claim 13, wherein the second tiltable mirror structure further comprises an actuation structure coupled to the tiltable element and configured to rotate the tiltable element about the axis of rotation; the actuation structure comprises a first and a second pair of driving arms, each pair being formed by a first driving arm and a second driving arm, the first and second pairs of driving arms being arranged on opposite sides of the rotation axis and symmetrically with respect to the rotation axis, each driving arm having a first end integrally coupled to the frame and a second end elastically coupled to the tiltable element by a respective decoupling elastic element; wherein the outer side surface is arranged in a closed position with a reduced separation gap relative to the drive arm and the tiltable element throughout extension along the first horizontal axis.

17. The electronic device of claim 1, wherein the electronic device is an optoelectronic device comprising a light source for generating a light beam, wherein the microelectromechanical mirror device acts as a mirror module with biaxial projection for receiving the light beam and directing the light beam to an external screen or display surface at a distance from the optoelectronic device.

18. An electronic device comprising a microelectromechanical mirror device having a first tiltable mirror structure in a first semiconductor material die, the first tiltable mirror structure extending in a horizontal plane defined by a first horizontal axis and a second horizontal axis, wherein the first tiltable mirror structure comprises:

A fixed frame closing the cavity;

A tiltable reflective element having first and second intermediate axes of symmetry parallel to the first and second horizontal axes, the tiltable reflective element being resiliently connected to the frame by first and second coupling mechanisms located on opposite sides of the second horizontal axis; and

A drive mechanism linked to the tiltable reflective element to cause rotation about the first horizontal axis using resonant motion;

Wherein the first tiltable mirror structure is asymmetric about the second horizontal axis and has a varying extension along the first horizontal axis;

Wherein the first coupling mechanism positioned on a first side of the second horizontal axis comprises a single torsion spring connected to the tiltable reflective element and the frame, the single torsion spring extending linearly along the first horizontal axis;

Wherein the second coupling mechanism includes first and second torsion springs extending along the first horizontal axis, and a restraint assembly between the first and second torsion springs, wherein the first and second torsion springs are connected to the tiltable reflective element, the restraint assembly, and the frame.

19. The electronic device of claim 18, wherein the single torsion spring of the first coupling mechanism has a first width along the second horizontal axis that is less than a corresponding second width of the first torsion spring of the second coupling mechanism.

20. The electronic device of claim 18, wherein the electronic device comprises a memory device,

The single torsion spring of the first coupling mechanism has a first torsional stiffness and the first torsion spring of the second coupling mechanism has a second torsional stiffness;

the ratio between the first torsional stiffness and the second torsional stiffness is between 0.55 and 0.65.

21. The electronic device of claim 18, wherein the drive mechanism is positioned entirely on a second side of the second horizontal axis on the same side as the second coupling mechanism.