CN117123456A - Piezoelectric micromachined pressure transducer with high sensitivity and related fabrication process - Google Patents

Abstract

The present disclosure relates to piezoelectric micromachined pressure transducers with high sensitivity and related manufacturing processes. A micromechanical pressure transducer comprising: a fixed body of semiconductor material transversely defining a main cavity; a conductive structure suspended on said main cavity and including at least one pair of deformable structures and movable regions, The movable region is formed from a semiconductor material and is mechanically coupled to the stationary body through the deformable structure. Each deformable structure includes: a support structure of semiconductor material including a first beam and a second beam, each of the first beam and the second beam having a structure secured to the fixed body and the movable region respectively. end, the first beam is stacked on the second beam at a distance; and at least one piezoelectric transducing structure is mechanically coupled to the first beam. The piezoelectric transducing structures are electrically controllable such that they cause corresponding deformations of the corresponding support structures and corresponding translations of the movable regions in the translation direction.

Description

Highly sensitive piezoelectric micromachined pressure transducers and related manufacturing processes

Technical field

The present disclosure relates to a piezoelectric micromachined pressure transducer with high sensitivity and a corresponding manufacturing process.

Background technique

As is known, there are currently many pressure transducers available, such as so-called piezoelectric micromachined ultrasonic transducers (PMUTs), which are microelectromechanical systems (MEMS) type devices that allow the conversion of pressure signals (e.g. acoustic signals) into electrical signals and vice versa. Furthermore, it is known that PMUT transducers usually comprise an actuated piezoelectric structure, which in turn comprises a region of piezoelectric material; typically, this piezoelectric material is so-called PZT.

Regarding PZT, it is known that, assuming that the PZT region has the shape of a parallelepiped and an orthogonal reference frame XYZ, the value of the so-called parameter d ₃₁ relates the degree of shortening of the PZT region along X to the extent of the electric field along Z. The value of parameter d ₃₁ of PZT is approximately ten times higher than that of other possible piezoelectric materials, such as aluminum nitride AlN. For this reason, PZT is particularly suitable for situations where the PMUT transducer is mainly used as a transducer from electrical signals to acoustic signals, i.e. it is used as a sound source. However, PZT is also characterized by a particularly high value of element ε ₃₃ of the dielectric constant tensor; this means that each actuated structure formed from PZT has a high capacitance. Therefore, when the PMUT transducer is used for reception, i.e. for converting _acoustic signals into electrical signals, the voltage generated by With the same mechanical stress induced by the acoustic signal, the actuating structure produces a lower voltage.

In fact, PMUT transducers including an actuating structure formed from PZT are not very sensitive when used as, for example, a pressure sensor. More generally, regardless of the type of piezoelectric material, there is a need to have a pressure transducer with good sensitivity in reception without compromising effectiveness during the transmission step.

Contents of the invention

The present disclosure therefore provides a solution that allows this need to be at least partially met.

In accordance with the present disclosure, there is provided a pressure transducer and method of manufacturing as defined in the appended claims.

In at least one embodiment of a pressure transducer or device of the present disclosure, the pressure transducer or device includes a body of semiconductor material; a cavity extending into the body; and overlying the cavity. the movable structure of semiconductor material; a support structure of semiconductor material extending from the body to the movable structure, and the support structure suspends the transducing structure above the cavity; in the An auxiliary cavity in the support structure; a first piezoelectric transducer structure, the first piezoelectric transducer structure is located on the support structure and overlaps with the auxiliary cavity; and on the support structure a second piezoelectric transducing structure, the second piezoelectric transducing structure being spaced apart from the first piezoelectric transducing structure, and the second piezoelectric transducing structure being stacked with the second piezoelectric transducing structure.

Description of the drawings

For a better understanding of the present disclosure, embodiments thereof will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Figure 1 schematically shows a perspective view of an array of transducer devices;

Figure 2 schematically shows a perspective view of the transducer device;

Figure 3 schematically shows a perspective view of a section of the transducer device shown in Figure 2 taken along section line III-III;

Figure 4 schematically shows an enlarged perspective view of a part of the transducer device shown in Figure 3;

Figures 5A-5B schematically illustrate simplified perspective views of the transducer device shown in Figure 2 under different operating conditions;

Figure 6 shows equivalent mechanical diagrams of the transducer device shown in Figure 2 in a stationary state (top) and a non-stationary state (bottom);

Figure 7 shows the trend of electrical signals over time;

Figure 8 schematically shows a top view of a variant of the transducer arrangement;

Figures 9-11 and 14-15 schematically show cross-sections of the transducer device during corresponding steps of the manufacturing process, with reference to the same section lines W-W indicated in Figure 2;

Figure 12 schematically shows a part of a cross-section of the transducer device during corresponding steps of the manufacturing process, see the section line KK indicated in Figure 2; and

Figure 13 schematically shows a perspective view of a section of a part of the transducer device during a corresponding step of the manufacturing process, see section line K-K.

Detailed ways

FIG. 1 shows an array 1 of transducer devices 2 identical to one another, formed in an integrated manner in the same semiconductor body 4 (for example formed of silicon) of a die 11 and according to a matrix scheme layout. Figure 1 also shows the orthogonal reference frame XYZ.

In particular, the semiconductor body 4 forms a fixed body 5 which consists at the top and bottom respectively of a top surface S _t which may be called a surface and a bottom surface S _b which may be called an opposite surface opposite the surface S _t (in FIG. 2 visible in) defined. The top surface S _t and the bottom surface S _b are parallel to the XY plane and are shared between the transducer devices 2 . The top surface _St and the bottom surface _Sb are referred to as the top surface and the bottom surface based on the orientations shown in FIGS. 1-3 of the present disclosure.

Furthermore, for each transducer device 2 , the fixed body 5 laterally delimits a corresponding cavity 7 , which is referred to below as main cavity 7 . The main cavity 7 visible in Figure 3 is open downwards (for example, the main cavity extends from the top surface _St to the bottom surface _Sb through the fixed body) and faces the bottom surface _Sb ; furthermore, without loss of generality, Lower, the main cavity 7 is bounded by side walls 35 formed by the fixed body 5 and having, for example, a cylindrical shape. Furthermore, each transducer arrangement 2 includes a respective transducing structure 6 suspended above a respective main cavity 7 as described in more detail below. In this regard, since the transducer devices 2 are equal to each other, only one of them is described below, as shown for example in FIGS. 2 and 3 .

In detail, the transducing structure 6 includes a movable region 8 formed of a semiconductor material (eg, silicon), and three deformable structures indicated by 10 .

The deformable structures 10 are equal to each other and are arranged symmetrically with respect to an axis of symmetry H parallel to the Z-axis. Furthermore, the deformable structure 10 has elongated shapes along respective directions of elongation, these elongated shapes being arranged such that pairs of adjacent directions of elongation are angularly spaced 120° apart. In other words, without loss of generality, the direction of elongation is radial.

Each deformable structure 10 includes a corresponding outer piezoelectric structure 12 and a corresponding inner piezoelectric structure 14 and a corresponding support structure 15. The outer piezoelectric structure 12 and the inner piezoelectric structure 14 are piezoelectric transducing structures. In the resting state, the support structure 15 lies in the same plane parallel to the XY plane. In the following, for the sake of brevity, only one deformable structure 10 is described.

In detail, the support structure 15 includes a top beam 20 and a bottom beam 22 which, without loss of generality, are equal to each other in a resting state and have the shape of a parallelepiped with its longitudinal axis parallel to the can The elongation direction of the deformation structure 10 .

The top beam 20 is stacked at a distance on the bottom beam 22 vertically (ie, parallel to the Z-axis). Furthermore, both the top beam 20 and the bottom beam 22 have a corresponding first end integrated with the fixed body 5 and in particular with the side wall 35 , and a corresponding second end integrated with the movable area 8 . In the resting state, the top beam 20 lies in a corresponding plane parallel to the XY plane; the bottom beam 22 lies in a corresponding plane parallel to the XY plane.

Furthermore, the top beam 20 and the bottom beam 22 define a cavity 23 at the top and bottom respectively, which is hereafter referred to as a secondary cavity 23. In the resting state, the secondary cavity 23 has a substantially parallelepiped shape and, as explained below, is laterally open.

Concerning the movable area 8, it has a planar shape and is delimited at the top by a first surface _S1 , which in the resting state is coplanar with the top surface _St of the fixed body 5. Furthermore, the movable area 8 is bounded at the bottom by a second surface S ₂ , _which is parallel to the XY plane and faces the main cavity 7 below.

In the resting state, the movable region 8 and the fixed body 5 laterally delimit three groove cavities 29 which, without loss of generality, are equal to each other and extend vertically through the entire thickness of the movable region 8 , so that they face the first surface S ₁ and the second surface S ₂ . The trench cavity 29 is thus open downwardly and upwardly (for example, extending completely through the thickness of the movable area so that the trench cavity 29 is in fluid communication with the main cavity 7 ); in particular, in the resting state, the trench cavity The body 29 faces downwards towards the corresponding part of the main cavity 7 . In other words, as shown in Figure 3, the trench cavity 29 extends from the first surface _S1 to the second surface _S2 . For example, the trench cavity 29 is in fluid communication with the main cavity 7 .

In more detail, any trench cavity 29 is considered to include a respective peripheral portion 30A and first and second linear portions 30B, 30C in communication with each other. The peripheral portion 30A has an approximately circumferential portion shape, while the first and second linear portions 30B, 30C have a segmented shape, parallel to the respective radial directions and extending from corresponding ends of the peripheral portion 30A; by way of example only, the first linear portion Portion 30B is arranged counterclockwise relative to second linear portion 30C. In fact, the peripheral portion 30A and the first and second linear portions 30B, 30C laterally delimit a portion of the movable area 8 which in top view has the shape of a substantially corresponding circular sector. Furthermore, considering any pair formed by the first and second trenches and the second trench cavity 29 , the second trench cavity 29 is, for example, arranged counterclockwise with respect to the first trench cavity 29 , the first trench cavity 29 The first linear portion 30B of the trench cavity 29 extends between the movable area 8 and the first side of the corresponding support structure 15 , while the second linear portion 30C of the second trench cavity 29 extends between the movable area 8 and the first side of the corresponding support structure 15 . extending between the second sides of the corresponding support structures 15; in addition, the aforementioned first and second linear portions 30B, 30C are parallel to the elongation direction of the deformable structure 10 to which the aforementioned support structure 15 belongs. Furthermore, the top beam 20 and the bottom beam 22 of the support structure 15 laterally define the aforementioned first and second linear portions 30B, 30C extending on opposite sides of the support structure 15 and connected with the support structure 15. The corresponding structural cavities 23 are laterally connected and, as mentioned before, are laterally open on both sides.

The first and second linear portions 30B, 30C may be referred to as linear slits, slots or trenches. Peripheral portion 30A may be referred to as a peripheral slit, slot or trench.

Referring again to any deformable structure 10 , a corresponding outer piezoelectric structure 12 extends partially over and is partially integral with the first end of the top beam 20 of the underlying support structure 15 extends above the part of the fixed body 5. The corresponding inner piezoelectric structure 14 is laterally offset relative to the outer piezoelectric structure 12 along the elongation direction of the deformable structure 10; furthermore, the inner piezoelectric structure 14 is partially located on the second side of the roof beam 20 of the underlying support structure 15. extends over the second end of the roof beam 20 and extends partially over the portion of the movable area 8 that is integral with the second end of the roof beam 20 .

Without loss of generality, the inner piezoelectric structure 14 and the outer piezoelectric structure 12 may be equal to each other. Furthermore, as shown in FIG. 4 , with reference to inner piezoelectric structure 14 (but the same considerations apply to outer piezoelectric structure 12 ), inner piezoelectric structure 14 may comprise a stack of regions including: a planar dielectric region 31 , for example, formed of silicon oxide and disposed on the first surface S ₁ ; a planar bottom electrode region 32, for example, formed of platinum and disposed in direct contact with the dielectric region 31; a planar piezoelectric region 34, for example, made of PZT Formed and arranged on the bottom electrode region 32 in direct contact with the bottom electrode region 32; a planar top electrode region 36 formed, for example, of platinum (or for example, TiW or IrO2) and arranged on the piezoelectric region 34, with direct contact; and a planar-shaped passivation region 38 formed, for example, of silicon nitride (SiN) and arranged on the top electrode region 36 in direct contact with the top electrode region 36 .

In a manner known per se, the bottom electrode region 32 and the top electrode region 36 can be in electrical contact with an external circuit (not shown and eg formed by a semiconductor die other than the semiconductor die 11 ) (eg via corresponding pads) ) for applying a voltage between the bottom electrode region 32 and the top electrode region 36 in order to control the transducer device 2 during transmission in the presence of deformation of the deformable structure 10 caused by the acoustic signal, and/or In the case of controlling the transducer device 2 in reception, the voltage established between the bottom electrode area 32 and the top electrode area 36 is received and processed as described below.

In more detail, the piezoelectric region 34 has a thickness of, for example, less than 5 μm, that is, it forms a so-called PZT thin film. Furthermore, in a manner known per se, when subjected to a voltage (more precisely to an electric field), the piezoelectric region 34 is aligned in the direction of elongation of the corresponding deformable structure 10 relative to the case where the piezoelectric region 34 is not subjected to a voltage. shortening; this shortening induces mechanical tension and corresponding deformation of the inner piezoelectric structure 14 and therefore also of the corresponding deformable structure 10 , as described below; the same considerations apply for piezoelectric regions belonging to the outer Case of piezoelectric structure 12.

In detail, when voltage is applied to the inner piezoelectric structure 14, that is, when voltage is applied between the bottom electrode region 32 and the top electrode region 36 of the inner piezoelectric structure 14, and assuming that no voltage is applied to the external piezoelectric structure When structure 12 is formed, deformation of each internal piezoelectric structure 14 causes the top beam 20 and bottom beam 22 of the underlying support structure 15 to bend downward based on the orientation shown in FIGS. 5A and 5B such that the top beam 20 and bottom beam 22 The second end is lowered parallel to the Z-axis relative to what would occur under stationary conditions.

Lowering of the second ends of the top beam 20 and the bottom beam 22 of the support structure 15 of the deformable structure 10 causes a downward translation of the movable region 8 along the axis of symmetry H, as shown in Figure 5A, where for the sake of simplicity, the secondary beams are not shown. Cavity 23.

Similarly, when voltage is applied to the outer piezoelectric structures 12 , and assuming no voltage is applied to the inner piezoelectric structures 14 , deformation of each outer piezoelectric structure 12 causes the top beam 20 and the bottom beam 22 of the underlying support structure 15 to be based on The orientation shown in Figures 5A and 5B is curved upward so that the second ends of the top beam 20 and the bottom beam 22 rise parallel to the Z-axis relative to what would occur at rest.

The elevation of the second ends of the top beam 20 and the bottom beam 22 of the support structure 15 of the deformable structure 10 causes a corresponding upward translation of the movable region 8 along the axis of symmetry H, as shown in Figure 5B.

In the case of upward translation and in the case of downward translation, as a first approximation, the movable area 8 does not undergo any rotation. An upward translation or direction based on the direction shown in Figures 5A and 5B may be referred to as a first translation or direction, and a downward translation or direction based on this direction may be referred to as a second translation opposite to the first translation or direction. or direction.

In more detail, in the case shown in Figure 5A and in the case shown in Figure 5B, the movable area 8 is subjected to a translation parallel to the Z-axis relative to the resting state. In other words, the movable area 8 moves like a piston, as shown in Figure 6, where the top diagram refers to the resting state and the bottom diagram refers to the case where the movable area 8 is translated upward (for simplicity, the diagram of Figure 6 only Two support structures 15) are shown. This is due to the fact that each support structure 15 includes a pair of beams; in this way, the movable area 8 is constrained to translate parallel to the Z-axis without being subjected to rotation or deformation.

Thus, operationally, the outer piezoelectric structure 12 and the inner piezoelectric structure 14 can be controlled to cause the movable region 8 to oscillate about the rest position such that the oscillation generates an acoustic signal. For example, first and second series of unipolar voltage pulses may be applied to the outer piezoelectric structure 12 and the inner piezoelectric structure 14 respectively, each pulse having, for example, a sinusoidal shape, the first and second series of pulses having a period T and in The time offset is T/2, as shown in Figure 7.

The piston movement of the movable region 8 also occurs when the transducer device 2 is used for reception, ie when the transducer device 2 is used to convert a pressure signal (eg an acoustic signal) impinging on the transducer device 2 into A corresponding electrical signal is generated by the outer piezoelectric structure 12 and the inner piezoelectric structure 14 which follow the corresponding support structure 15 caused by the translation of the movable area 8 ( In particular, this translation is caused precisely by the acoustic signal, corresponding to the deformation of the top beam 20).

Rather, due to the described constraining mechanism, the acoustic signal causes an oscillation of the movable area 8 along the axis of symmetry H around the position assumed in stationary conditions, regardless of the direction of the origin. The piston translation mechanism of the movable area 8 allows the size of the piezoelectric area 34 and therefore the capacitance value of the corresponding piezoelectric structure to be included, since it optimizes the energy exchange between the acoustic signal and the movable area 8 and thus maximizes Deformation of the piezoelectric region increases sensitivity. In fact, unlike what occurs for example in the (known) case of coupling of a piezoelectric structure to a suspended membrane, in the presence of an acoustic signal there is no retention of the movable region 8 in the position assumed in stationary conditions. part. If, conversely, a piezoelectric structure is coupled to a suspended membrane and has the same area as the piezoelectric region, the sensitivity is limited by the fact that in the presence of an acoustic signal only the central part of the membrane undergoes deformation, and not the peripheral parts. undergoes no deformation since it is fixed to a fixed body; in other words, the piezoelectric region is not effectively mechanically excited.

For example, outer piezoelectric structure 12 and inner piezoelectric structure 14 may be sized such that each piezoelectric structure has a capacitance equal to approximately 2 pF (picofarads). Furthermore, the transducer arrangement 2 can achieve sensitivity values of the order of mV per Pascal, which are much higher than currently obtainable in the case of transducers applying piezoelectric structures to membranes.

Different embodiments are also possible, in which the number of deformable structures 10 is different from three and/or the deformable structures have a different arrangement; for example, Figure 8 shows an embodiment still comprising three deformable structures 10, which The deformable structures extend in respective directions of elongation that are parallel to each other. The shape of the trench cavity (here designated 129) changes accordingly.

Referring again to the number of deformable structures 10, in a typical embodiment (not shown) only two deformable structures 10 may be included. Furthermore, embodiments (not shown) are possible in which each support structure 15 includes more than two beams.

The array 1 of transducer devices 2 may be manufactured by a manufacturing process described below which, for simplicity, involves operations related to the manufacturing of a single transducer device 2 of the type shown in Figures 2-4. Furthermore, the following FIGS. 9 to 11 and 14 to 15 relate to the section line WW shown as an example in FIG. 2 .

First, as shown in FIG. 9 , the semiconductor body 4 is formed such that it is defined at the top by the temporary surface S _temp and includes a main buried cavity 107 for forming the main cavity 7 . The semiconductor body 4 is bounded at the bottom by a base surface S _b .

The buried cavity 107 extends at a distance below the temporary surface S _temp , ie it is covered by a corresponding part of the semiconductor body 4 . For example, the formation of the main buried cavity 107 can occur in a manner known per se and therefore not shown in detail, as explained in EP 1,577,656, namely by first forming a plurality of laterally offset trenches in the semiconductor substrate , followed by performing epitaxial growth to close the trench on top, and finally by performing a thermal treatment leading to the migration of the semiconductor material and the formation of the main buried cavity 107 .

Subsequently, as shown in FIG. 10 , a secondary buried cavity 123 is formed, which is used to form the corresponding secondary cavity 23 and cover the main buried cavity 107 . To this end, the same method for forming the main buried cavity 107 can be performed from the above-mentioned portion of the semiconductor body 4 covering the main buried cavity 107 . This step of the manufacturing process may require an increase in the thickness of the semiconductor body 4 which is defined at the top by the top surface _St once the formation of the secondary buried cavity 123 is completed.

In fact, the secondary buried cavities 123 are substantially equal to each other, extending at the same height (measured along the Z-axis) relative to the underlying main buried cavity 107, ie they are coplanar and laterally offset. Each secondary buried cavity 123 is thus covered by a corresponding top 120 of the semiconductor body 4 , which top 120 extends between the top surface _St and the underlying secondary buried cavity 123 ; furthermore, referred to as the bottom 122 of the semiconductor body 4 A corresponding portion of the semiconductor body 4 extends between each secondary buried cavity 123 and the underlying main buried cavity 107 .

Then, as shown in FIG. 11 , in a manner known per se, a respective outer piezoelectric structure 12 and a respective inner piezoelectric structure 14 (shown schematically) are formed over each top 120 of the semiconductor body part 4 .

Subsequently, etching (eg dry etching) is performed from the top surface _St such that it selectively removes portions of the semiconductor body 4 and forms the trench cavity 29 and thus the support structure 15 and the movable region 8 .

In particular, the effect of this etching is visible, for example, in FIGS. 12 and 13 , which refer to the section line KK shown through the example in FIG. 2 and show, respectively, before and after the aforementioned etching. The latter part of the semiconductor body 4 .

In more detail, referring to the intermediate surface S ₁₀₇ to indicate the top surface of the main buried cavity 107 , the portion of the semiconductor body 4 extending vertically between the top surface _St and the intermediate surface S ₁₀₇ of the semiconductor body 4 is removed to form a trench. peripheral portion 30A of cavity 29 ; furthermore, for each secondary buried cavity 123 , remove the portion of the corresponding top 120 of the semiconductor body 4 that is laterally offset with respect to the corresponding outer piezoelectric structure 12 and the corresponding inner piezoelectric structure 14 , and The lower portion of the corresponding bottom portion 122 of the semiconductor body 4; the remaining portions of the top portion 120 and the bottom portion 122 of the semiconductor body 4 form corresponding top beams 20 and corresponding bottom beams 22 respectively. This results in the first linear portion 30B and the second linear portion 30C of the trench cavity 29 and thus the support structure 15 and the movable area 8 . This allows each part of the secondary buried cavity 123 interposed between the corresponding top beam 20 and the corresponding bottom beam 20 to form a corresponding secondary cavity 23, as shown in Figure 14, and as shown in Figure 15, which again Reference section line W-W.

Then, as shown in FIG. 15 , etching (for example, dry etching) is performed from the back side (ie, from the bottom surface S _b ), thereby removing the portion of the semiconductor body 4 arranged between the main buried cavity 107 and the bottom surface S _b . In this way, the main buried cavity 107 is opened downward (for example, by forming an opening extending from the bottom surface S _b to the buried cavity 107 ) and the main cavity 7 is formed. The transducer device 2 is thus formed.

From the previous description, the advantages offered by this solution are clear.

In particular, this solution allows the use of piezoelectric regions with reduced area and therefore reduced capacitance, thus optimizing sensitivity. This solution, although particularly useful in the case where the piezoelectric area is formed from PZT, due to the high value of the element ε ₃₃ , is also useful in cases where the piezoelectric materials are different, even when it is desired to optimize the sensitivity and contain The size of the transducer is also useful.

Finally, it will be apparent that modifications and variations may be made in the transducer arrangements and manufacturing processes described and illustrated herein without departing from the scope of the present disclosure as defined by the appended claims.

For example, rather than a single piezoelectric region, each piezoelectric structure may include a stack formed of two or more piezoelectric regions with an intermediate conductive region between the two or more piezoelectric regions to increase transmission The force applied to the movable area during the step.

A variant (not shown) is also possible in which each deformable structure 10 includes only one piezoelectric structure; in this case the movable area 8 can only move below or above the position assumed in the resting state.

A micromechanical pressure transducer can be summarized as comprising a fixed body (5) of semiconductor material, which laterally delimits a main cavity (7); and a conductive structure (6), which is suspended in said main cavity (7) and includes at least a pair of deformable structures (10) and a movable region (8), the movable region (8) being formed of a semiconductor material and mechanically coupled to the fixed body (8) through the deformable structure (10) 5); and wherein each deformable structure (10) includes a support structure (15) of semiconductor material, the support structure includes first and second beams (20, 22), each beam having a structure respectively fixed to the fixed body (5 ) and the end of the movable area (8), the first beam (20) is superimposed on the second beam (22) at a certain distance; and at least one piezoelectric transducing structure (12, 14) mechanically coupled to a first beam (20); and wherein the piezoelectric transducing structures (12, 14) are electrically controllable so as to cause corresponding deformation of the corresponding support structure (15) and movement of the movable area (8) along the translation direction (H) Translate accordingly.

Under stationary conditions, the first and second beams (20) may extend parallel to the reference plane (XY); and the translation direction (H) may be perpendicular to the reference plane (XY).

The movable area (8) may have a planar shape, which may be parallel to the reference plane (XY).

The first and second beams (20, 22) of each support structure (15) may define respective secondary cavities (23) at the top and bottom respectively, which may be laterally open.

The number of the deformable structures (10) may be equal to three; the first and second beams (20, 22) of each support structure (15) may be elongated parallel to the corresponding elongation direction; the deformable structure (10) The directions of elongation of the first and second beams (20, 22) may be angularly spaced 120° apart.

Each deformable structure (10) may comprise at least one of a respective external piezoelectric transducing structure (12) partially covering the fixed body (5); and a corresponding internal piezoelectric transducing structure. Energy structure (14) partially covering the movable area (8).

Each piezoelectric transducing structure (12, 14) may include a corresponding piezoelectric region (34) of PZT.

The piezoelectric transducing structure (12, 14) may also be configured to convert deformations of the corresponding support structure (15) caused by translation of the movable area (8) caused by the acoustic signal striking the transducer (2) into electrical energy. Signal.

The array of transducers (2) may be summarized as comprising a semiconductor die (11) and a plurality of transducers (2) integrated in the semiconductor die (11).

A process for manufacturing a micromachined pressure transducer which may be summarized as comprising forming from a semiconductor body (4) a main cavity (7) laterally surrounded by a fixed body (5) of semiconductor material; forming a conductive structure (6) , the conductive structure (6) is suspended on the main cavity (7) and includes at least a pair of deformable structures (10) and a movable area (8), the movable area (8) is made of semiconductor material Forming and mechanically coupling the deformable structure (10) to the stationary body (5); and wherein forming a transducing structure (6) includes, for each deformable structure (10): forming a support for a semiconductor material Structure (15) comprising first and second beams (20, 22), each beam having an end fixed to a fixed body (5) and a movable area (8) respectively, the first beam (20) having a certain overlying the second beam (22); and forming at least one piezoelectric transducing structure (12, 14) mechanically coupled to the first beam (20); and wherein the piezoelectric transducing structure (12, 14) is electrically controllable in order to cause corresponding deformations of the corresponding support structure (15) and corresponding translation of the movable area (8) in the translation direction (H).

The semiconductor body (4) may be defined by a front surface (S _t ), and the process may further include forming a main buried cavity (123) in the semiconductor body (4); and for each deformable structure (10), forming an arrangement A corresponding secondary buried cavity (123) between the front surface (S _t ) of the semiconductor body (4) and the main buried cavity (123) such that the corresponding first portion (120) of the semiconductor body (4) is interposed between the front surface (S _t ) and the secondary buried cavity (123), and the corresponding second portion (122) of the semiconductor body (4) is interposed between the secondary buried cavity (123) and the main buried cavity (107 ); for each deformable structure (10), forming said at least one piezoelectric transducing structure (12, 14) on a corresponding first portion (120) of the semiconductor body (4); and for each deformable Structure (10) to selectively remove portions of respective first and second portions (120, 22) of a semiconductor body (4) such that said first and second portions (120, 122) of the semiconductor body (4) ) respectively form corresponding first beams (20) and corresponding second beams (22).

The fabrication process may also include selectively removing portions of the semiconductor body (4) interposed between the front surface (S _t ) and the main buried cavity (107) to form trenches laterally defining the movable region (8) (30A).

The semiconductor body (4) may be further defined by a back surface ( _Sb ), and the process may further include selectively removing the semiconductor body (4) interposed between the back surface ( _Sb ) and the main buried cavity (107) ) part to form the main cavity (7).

The various embodiments described above may be combined to provide additional embodiments. If desired, aspects of the embodiments may be modified to employ concepts from various patents, applications, and publications to provide additional embodiments.

These and other changes may be made to the embodiments in light of the above detailed description. In general, in the following claims, the terms used should not be interpreted as limiting the claims to the specific embodiments disclosed in the specification and claims, but should be interpreted as including all possible embodiments as well as these rights The full scope of authorized equivalents is claimed. Accordingly, the claims are not limited by this disclosure.

Claims (20)

1. A micromechanical pressure transducer, comprising:

a fixed body of semiconductor material laterally defining a main cavity;

a transduction structure suspended on the main cavity and comprising at least one pair of deformable structures and a movable region formed of semiconductor material and mechanically coupled to the fixed body by the deformable structures;

and wherein each deformable structure comprises:

a support structure of semiconductor material comprising a first beam and a second beam, each having an end fixed to the fixed body and the movable region, respectively, the first beam being superimposed on the second beam at a distance; and

at least one piezoelectric transduction structure mechanically coupled to the first beam;

and wherein the piezoelectric transduction structure is electrically controllable so as to cause a deformation of the respective support structure and a respective translation of the movable region in a translation direction.

2. The transducer of claim 1, wherein, in a resting condition, the first beam and the second beam extend parallel to a reference plane; and wherein the translation direction is perpendicular to the reference plane.

3. The transducer of claim 2, wherein the movable region has a planar shape parallel to the reference plane.

4. The transducer of claim 1, wherein the first and second beams of each support structure define respective secondary cavities at the top and bottom, respectively, the secondary cavities being laterally open.

5. The transducer of claim 1, wherein the number of deformable structures is equal to three; and wherein the first and second beams of each support structure are elongated parallel to the corresponding direction of elongation; and wherein the directions of elongation of the first and second beams of the deformable structure are angularly spaced apart by 120 °.

6. The transducer of claim 1, wherein each deformable structure comprises at least one of:

a corresponding external piezoelectric transduction structure partially covering the fixed body; and

a corresponding internal piezoelectric transduction structure partially covering the movable region.

7. The transducer of claim 1, wherein each piezoelectric transduction structure comprises a respective PZT piezoelectric region.

8. The transducer of claim 1, wherein the piezoelectric transduction structure is further configured to transduce the deformation of the respective support structure caused by translation of the movable region caused by an acoustic signal impinging on the transducer into an electrical signal.

9. A transducer array comprising a semiconductor die and a plurality of transducers according to claim 1 integrated in the semiconductor die.

10. A method of manufacturing a micromechanical pressure transducer, comprising:

forming a main cavity laterally surrounded by a fixed body of semiconductor material from the semiconductor body;

forming a transduction structure suspended on the main cavity and comprising at least one pair of deformable structures and a movable region formed of semiconductor material and mechanically coupled to the fixed body by the deformable structures;

and wherein forming the transduction structure comprises performing, for each deformable structure:

forming a support structure of semiconductor material comprising a first beam and a second beam, each having ends fixed to the fixed body and the movable region, respectively, the first beam being superimposed on the second beam at a distance; and

forming at least one piezoelectric transduction structure mechanically coupled to the first beam;

and wherein the piezoelectric transduction structures are electrically controllable so as to cause a corresponding deformation of the respective support structure and a corresponding translation of the movable region in a translation direction.

11. The method of manufacturing of claim 10, wherein the semiconductor body is defined by a front surface, the method further comprising:

forming a main buried cavity in the semiconductor body; and

for each deformable structure, forming a respective secondary buried cavity disposed between the front surface of the semiconductor body and the primary buried cavity such that a respective first portion of the semiconductor body is interposed between the front surface and the secondary buried cavity and a respective second portion of the semiconductor body is interposed between the secondary buried cavity and the primary buried cavity;

forming, for each deformable structure, the at least one piezoelectric transduction structure on the respective first portion of the semiconductor body; and

portions of the respective first and second portions of the semiconductor body are selectively removed for each deformable structure such that remaining portions of the first and second portions of the semiconductor body form respective first and second beams, respectively.

12. The method of manufacturing of claim 11, further comprising selectively removing portions of the semiconductor body interposed between the front surface and the main buried cavity so as to form trenches laterally bounding the movable region.

13. The method of claim 11, wherein the semiconductor body is further defined by a rear surface, the method further comprising selectively removing portions of the semiconductor body interposed between the rear surface and the main buried cavity so as to form the main cavity.

14. An apparatus, comprising:

a body of semiconductor material;

a cavity extending into the body;

a movable structure of the semiconductor material overlying the cavity;

a support structure of the semiconductor material extending from the body to the movable structure and suspending the transduction structure above the cavity;

a secondary cavity within the support structure;

a first piezoelectric transduction structure on the support structure and overlapping the secondary cavity; and

a second piezoelectric transduction structure on the support structure, the second piezoelectric transduction structure being spaced apart from the first piezoelectric transduction structure, and the second piezoelectric transduction structure overlapping the sub-cavity.

15. The apparatus of claim 14, further comprising:

a first linear slit extending through the movable structure and on a first side of the support structure; and

a second linear slit extends through the movable structure and is located on a second side of the support.

16. The apparatus of claim 15, further comprising:

a first peripheral slit extending from the movable structure to the body, and the first peripheral slit extending from the first linear slit; and

a second peripheral slit extends from the movable structure to the body, and the second peripheral slit extends from the second linear slit.

17. The apparatus of claim 15, wherein:

the support structure includes:

a first sidewall adjacent to the first linear slit; and

a second sidewall opposite the first sidewall and adjacent the second linear slit; the secondary cavity extends from the first sidewall through the support structure to the second sidewall, the secondary cavity being exposed at the first sidewall and the secondary cavity being exposed at the second sidewall.

18. The apparatus of claim 14, wherein:

the first piezoelectric transduction structure extends onto the body; and

the second piezoelectric transduction structure extends onto the movable structure.

19. The apparatus of claim 14, wherein:

the movable structure is configured to move between a first position and a second position in operation; and

the support structure is configured to deform in operation to provide one or more degrees of freedom for the movable structure to move between the first portion and the second portion.

20. The apparatus of claim 14, wherein the support structure comprises:

a first beam portion at a first side of the secondary cavity; and

a second beam portion at a second side of the secondary cavity opposite the first side of the secondary cavity.