Patent Description:
Microelectromechanical (so-called MEMS - Micro Electro Mechanical System) pressure sensors (or barometers) are known of impermeable or hermetic type or in any case resistant to water (so-called "waterproof").

These pressure sensors may be used in portable or wearable electronic apparatuses, such as smartphones, smartbands or smartwatches, which may be used for underwater applications or in general inside the water.

These pressure sensors typically comprise a detection structure having a membrane suspended above a cavity and in which detection elements (for example piezoresistors) are provided to detect the deformation caused by impinging pressure waves.

The detection structure is integrated within a package, usually together with a corresponding signal reading and processing electronics, provided as an ASIC (Application Specific Integrated Circuit), which provides a pressure signal indicative of the detected pressure.

The aforementioned package has an inlet opening, to allow the detection of the external pressure, and internally defines a cavity wherein the aforementioned detection structure and the associated ASIC are accommodated.

Typically, this cavity is filled with a protective material, such as a coating gel (so-called "potting gel"), which coats and protects the detection structure and the ASIC for example from contaminants, dust, chemicals, fluids (in particular water), coming from the external environment. Only this protective material is in contact with the external environment, effectively making the cavity (filled with the same protective material) impermeable or hermetic.

In addition to detecting the pressure value (and possibly an associated altitude value), the pressure sensor may be used, by a processing module (possibly integrated in the aforementioned ASIC and provided, for example, with an artificial intelligence processing core), for the recognition of activities performed by the user of the portable or wearable electronic apparatus. By way of example, some activities that may be detected, by recognizing corresponding patterns in the pressure signal, include: user's steps; weight lifting; use of an elevator; use of a bicycle; swimming (or snorkeling).

While using the pressure sensor, water or other liquids (such as sweat, rain, etc.) may enter the cavity from the aforementioned access opening, coming into contact with the protective material. In general, any material that is foreign to the pressure sensor may enter the package, for example including contaminating particles or the like.

The pressure signal provided by the pressure sensor may be affected by the presence of this foreign material; for example in case of water (more generally of liquid), the detected signal cannot be correctly used, for example for the recognition of activities, up to the evaporation of the same water; the presence of water may in fact modify the pressure detection due to different environmental factors, the evaporation rate, the surface tension, etc..

For example, the pressure signal may vary more slowly, thus delaying the time after which the pattern recognition may be used to detect the user activity.

It is also known that some pressure sensors may have a double full scale, a first full scale for detecting the environmental pressure (or barometric pressure, for example for monitoring altitude or elevation) and a second (higher) full scale for detecting the pressures occurring inside the water (e.g. for depth monitoring).

In these pressure sensors, an automatic detection of the insertion inside the water (i.e. of the operating environment variation, from the external environment, air, to the in-water or underwater environment) may be implemented, in order to automatically activate/deactivate some specific functions and, in particular, to automatically vary the full scale value used for pressure detection. In this regard, the full scale change may be implemented by a suitable adjustment of the gain factors of the reading electronics associated with the pressure detection.

The automatic detection of the operating environment variation is generally implemented exclusively, or mainly, as a function of the detected pressure value. For example, the pressure sensor full-scale automatic variation may be implemented in case the detected pressure value exceeds a certain threshold that is higher than air or barometric pressure (in this case activating an higher full scale), or is below a certain threshold that is lower than the same barometric pressure (in this case activating a lower full scale), for a set time interval.

In general, however, it has been observed that currently used solutions do not allow to cover all the possible cases of use in the aforementioned automatic recognition of operating environment variation. For example, a slow introduction into the water of the electronic apparatus (e.g. a smartwatch) in which the pressure sensor is integrated might not be correctly detected.

In general, the possibility exists for errors (so-called "false positives") to occur in detecting the operating environment variation, as different events may in principle cause a pressure variation that may be incorrectly interpreted as an operating environment change.

For example, in the case of wearable electronic apparatuses, a false positive in detecting the introduction into the water may cause a variation, in this case undesired, in the pressure sensor full scale, when the electronic apparatus is actually still operative in air and/or may cause some functions of the apparatuses to be erroneously disabled. Prior art documents relevant to the invention are patent documents <CIT>, <CIT>, and <CIT>.

The aim of the present solution is in general to overcome the drawbacks of the known solutions previously highlighted.

According to the present disclosure, therefore, a pressure sensor device and a corresponding method for detecting the presence of foreign material are provided, as defined in the attached claims.

For a better understanding of the invention, embodiments thereof are now described, purely by way of nonlimiting example and with reference to the attached drawings, wherein:.

<FIG> shows a pressure sensor device <NUM>, comprising a pressure detection structure <NUM> provided in a first die <NUM> of semiconductor material, in particular silicon.

The first die <NUM> has a top surface 4a and a bottom surface 4b, with extension parallel to a horizontal plane xy and opposite to each other along a vertical axis z, orthogonal to the aforementioned horizontal plane xy.

The pressure detection structure <NUM> comprises a first membrane <NUM>, provided at the top surface 4a, arranged above a first cavity <NUM>, buried within the die <NUM>; in other words, the first membrane <NUM> is interposed between the underlying first cavity <NUM> and the aforementioned top surface 4a of the first die <NUM>.

Detection elements <NUM>, in particular piezoresistors, are arranged within the first membrane <NUM>, configured to allow detection of deformations of the first membrane <NUM> due to impinging pressure waves.

The pressure sensor device <NUM> further comprises a processing circuit <NUM>, implemented as an ASIC, integrated in a second die <NUM> of semiconductor material, in particular silicon, having a respective top surface 12a and a respective bottom surface 12b.

In the illustrated embodiment, the aforementioned first and second dies <NUM>, <NUM> are arranged stacked, with the top surface 12a of the second die <NUM> coupled, by a first bonding region <NUM>, to the bottom surface 4b of the first die <NUM>.

First bonding wires <NUM> electrically connect first pads <NUM> carried by the top surface 4a of the first die <NUM>, to respective second pads <NUM> carried by the top surface 12a of the second die <NUM>, to allow the electrical connection between the pressure detection structure <NUM> (and the corresponding detection elements <NUM>) and the processing circuit <NUM>.

In particular, the processing circuit <NUM> is configured to generate, as a function of electrical signals provided by the detection elements <NUM>, a pressure signal, indicative of the pressure value impinging on the first membrane <NUM>.

The pressure sensor device <NUM> further comprises a package <NUM>, configured to internally accommodate the aforementioned stack formed by the pressure detection structure <NUM> and the associated processing circuit <NUM>, in an impermeable or hermetic manner.

The package <NUM> comprises a base structure <NUM> and a body structure <NUM>, arranged on the base structure <NUM> and having a cup shape and internally defining an housing cavity <NUM>, in which the pressure detection structure <NUM> and the processing circuit <NUM> are arranged.

In particular, the bottom surface 12b of the second die <NUM> is coupled, by a second bonding region <NUM>, to an internal surface 21a of the base structure <NUM>, facing the aforementioned housing cavity <NUM>.

Second bonding wires <NUM> electrically connect third pads <NUM> carried by the top surface 12a of the second die <NUM> to respective fourth pads <NUM> carried by the internal surface 21a of the base structure <NUM>, to allow the electrical connection between the processing circuit <NUM> and the external environment outside of the package <NUM>.

To this end, through vias <NUM>, electrically conductive, traverse the entire thickness of the base structure <NUM> and connect the aforementioned fourth pads <NUM> to connection elements <NUM>, for example provided in the form of respective pads (as in the illustrated example) or of conductive bumps, carried by an external surface 21b of the same base structure <NUM>, arranged in contact with the external environment.

In a manner not illustrated, these connection elements <NUM> may be contacted from outside of the package <NUM>, for example for transmitting the pressure signal to a control and management unit of an electronic apparatus, in which the pressure sensor device <NUM> is incorporated.

The aforementioned body structure <NUM> has upwardly (at an end opposite to the base structure <NUM>) an access opening <NUM>, in fluidic communication with the housing cavity <NUM>, for allowing introduction within the package <NUM> of pressure waves to be detected.

A coating material <NUM> fills almost entirely the aforementioned housing cavity <NUM> and entirely covers and coats the aforementioned stack formed by the pressure detection structure <NUM> and the associated processing circuit <NUM>, to ensure impermeability thereof; this coating material (potting gel) <NUM> is in particular a coating gel, for example a silicone gel.

Conversely, a top portion <NUM>' of the housing cavity <NUM> remains free from the aforementioned coating material <NUM> and therefore contains air in fluidic communication with the external environment through the access opening <NUM>.

According to a particular aspect of the present solution, the pressure sensor device <NUM> further comprises a piezoelectric transduction structure <NUM>, of ultrasonic type, so-called PMUT (Piezoelectric Micromachined Ultrasonic Transducer).

This piezoelectric transduction structure <NUM> is integrated in the same first die <NUM> wherein the pressure detection structure <NUM> is made; in particular, the first die <NUM> therefore comprises a first portion <NUM>', wherein the pressure detection structure <NUM> is integrated, and a second portion <NUM>", separate and distinct from the first portion <NUM>', wherein the piezoelectric transduction structure <NUM> is integrated.

In detail, the piezoelectric transduction structure <NUM> comprises a second membrane <NUM>, provided at the top surface 4a of the die <NUM>, arranged above a second cavity <NUM>, buried within the die <NUM>; in other words, the second membrane <NUM> is interposed between the underlying second cavity <NUM> and the aforementioned top surface 4a of the first die <NUM>.

The second membrane <NUM> has for example a thickness along the vertical axis z equal to <NUM> and a substantially circular extension in the horizontal plane xy with a diameter equal to <NUM>, while the second cavity <NUM> has a thickness equal to <NUM> along the same vertical axis z.

Above the second membrane <NUM> a piezoelectric stack <NUM> is provided, formed by a bottom electrode 38a, a piezoelectric material region 38b and a top electrode 38c (the piezoelectric material region 38b being interposed between the bottom electrode 38a and the top electrode 38b and the same bottom electrode 38a being arranged on the top surface 4a of the first die <NUM>, with extension substantially corresponding to the underlying second membrane <NUM>).

In a manner not shown in detail, suitable electrical connection tracks connect the aforementioned bottom electrode 38a and top electrode 38b to respective of the first pads <NUM> carried by the top surface 4a of the first die <NUM>, for the connection, through respective of the second pads <NUM> carried by the top surface 12a of the second die <NUM>, to the processing circuit <NUM>.

In particular, the processing circuit <NUM> comprises (as schematically illustrated in the aforementioned <FIG>) a driving module 39a for the piezoelectric transduction structure <NUM>, for providing suitable biasing signals to the aforementioned bottom electrode 38a and top electrode 38b to cause the deformation of the second membrane <NUM> and generate detection acoustic waves (in particular ultrasound waves, for example with a resonance frequency around <NUM>); and also a detection module 39b, to read the electrical signals transduced by the same bottom electrode 38a and top electrode 38b when the second membrane <NUM> is deformed by impinging acoustic waves, due to the echo of the aforementioned detection acoustic waves.

During operation, the aforementioned piezoelectric transduction structure <NUM> allows detecting the presence of foreign material within the package <NUM>, in particular interposed between the coating material <NUM> and the access opening <NUM>, in the aforementioned top portion <NUM>' of the housing cavity <NUM>, by detecting the acoustic impedance change associated with the presence of the same coating material <NUM>.

The echo produced by the detection acoustic waves generated by the piezoelectric transduction structure <NUM> is detected by the same piezoelectric transduction structure <NUM> (and for example processed by the aforementioned detection module 39b of the processing circuit <NUM>).

In particular, the detected signal has characteristics (for example in terms of amplitude and of a corresponding time trend) which are affected by the presence of the aforementioned foreign material, which in fact causes an acoustic impedance change and a different reflection pattern of the detection acoustic waves. For example, the detection module 39b is configured to determine the amplitude of peaks in the detected signal and/or the time position of the same peaks with respect to an instant of generation of the aforementioned detection acoustic waves.

<FIG> schematically shows the presence of a foreign material region <NUM>, in the example having a localized arrangement (with variable dimensions) above the same coating material <NUM>; this foreign material region <NUM> is in the example a drop (or a certain amount) of residual water which is present in the top portion <NUM>' of the housing cavity <NUM> and has not yet evaporated.

However, it is highlighted that this foreign material region <NUM> may alternatively be of a different liquid or include one or more solid particles of contaminating material.

<FIG> show, schematically, the simulated trend of the detection acoustic waves due to deformation of the second membrane <NUM> of the piezoelectric transduction structure <NUM>, in the absence of the aforementioned foreign material region <NUM>, in three different time instants from the generation of the same detection acoustic waves by the piezoelectric transduction structure <NUM>.

In particular, <FIG> highlights the reflection due to the acoustic impedance change at the interface between the coating material <NUM> and the air in the top portion <NUM>' of the housing cavity <NUM>, at the access opening <NUM> of the package <NUM>.

<FIG> shows the actual trend of the vertical displacement (along the vertical axis z), indicated by Sd, of the surface of the second membrane <NUM>, where it is possible to identify an amplitude peak due to the actuation of the piezoelectric stack <NUM> and subsequently the echo due to reflection at the interface between the coating material <NUM> and air.

<FIG> shows the corresponding trend of the detection signal, indicated by Sr, as a function of the response of the piezoelectric detection structure <NUM> upon receiving the aforementioned echo, in the example having a maximum amplitude peak after a time interval of <NUM> subsequently to actuation of the piezoelectric stack <NUM>.

<FIG> show a similar simulation relating to the trend of the detection acoustic waves due to the deformation of the second membrane <NUM> of the piezoelectric transduction structure <NUM>, this time in the presence of the aforementioned foreign material region <NUM>, in the three different time instants from generation of the detection acoustic waves by the same piezoelectric transduction structure <NUM>.

In this case two reflections occur, due to the first acoustic impedance change at the interface between the coating material <NUM> and the foreign material region <NUM> and to the second acoustic impedance change between the same foreign material region <NUM> and the air, at the access opening <NUM> of the package <NUM>.

<FIG> shows the corresponding trend of the vertical displacement Sd of the surface of the second membrane <NUM>, wherein it is possible to identify the peak due to actuation of the piezoelectric stack <NUM> and subsequently a first deformation linked to the first echo due to the first reflection at the interface between the coating material <NUM> and the foreign material region <NUM> and subsequently a second deformation linked to the second echo due to the second reflection between the coating material <NUM> and the air.

<FIG> shows the corresponding trend of the detection signal Sr, upon receiving the aforementioned echoes. The maximum peak of the detection signal occurs in the example after a time interval equal to <NUM> following the actuation of the piezoelectric stack <NUM>, due to the aforementioned first echo, therefore with a greater time delay with respect to the situation of absence of the foreign material region <NUM> (see the corresponding <FIG>).

In general, it is apparent that the characteristics and the trend of the detection signal Sr are indicative of the presence of the aforementioned foreign material region <NUM> within the package <NUM>.

As illustrated in <FIG>, the aforementioned foreign material region <NUM> may also be a continuous region of material (for example of water or different liquid) which is interposed between the coating material <NUM> and the access opening <NUM>, throughout the extension of the same access opening <NUM> in the horizontal plane xy. The thickness of this foreign material region <NUM> may vary; moreover, the same foreign material region <NUM> may possibly also be present outside the access opening <NUM>, in case, for example, of immersion in water (or in another fluid) of the electronic apparatus incorporating the pressure sensor device <NUM>.

<FIG> schematically illustrates an electronic apparatus <NUM>, in particular of a wearable type (for example a smartband or smartwatch) which includes the pressure sensor device <NUM> previously described.

The electronic apparatus <NUM> comprises a main controller <NUM> (a microcontroller, a microprocessor or a similar digital processing unit), coupled to the processing circuit <NUM> of the pressure sensor device <NUM>, in order to receive information relating to the pressure detection and also relating to the presence of any foreign material detected within the package <NUM>.

The main controller <NUM>, as a function of the detection of the aforementioned foreign material, may carry out specific actions, for example (in case of water) waiting for a time interval suitable for the evaporation before carrying out a pattern recognition of the pressure signal provided by the same pressure sensor device <NUM>, or generating an alarm signal associated with the presence of the same foreign material.

The advantages provided by the present solution are clear from the previous description.

In any case, it is highlighted that integration of the piezoelectric detection structure <NUM> within the package <NUM> of the pressure sensor device <NUM> allows the detection of foreign material within the same package <NUM>, with a high accuracy and with limited energy consumption and additional area occupation.

Moreover, the detection signal provided by the aforementioned piezoelectric detection structure <NUM> may be used to assist in the determination of entry into the water of the electronic apparatus <NUM> wherein the pressure sensor device <NUM> is used, allowing the number of false detections (false positives) to be eliminated or in any case strongly reduced.

Finally, variations and modifications may be applied to the present solution, without thereby departing from the scope defined by the claims.

In particular, in a manner not illustrated, a plurality of piezoelectric detection structures <NUM> might be integrated in the first die <NUM>, arranged in a matrix or array at the top surface 4a of the same first die <NUM>.

For example, a suitable arrangement of piezoelectric detection structures <NUM> might allow scanning of the entire access cavity <NUM>, or in any case directing the generated detection acoustic waves in any desired manner.

Moreover, it is highlighted that processing of the signal associated with the detection of the echo by the piezoelectric detection structure <NUM> might be performed externally to the pressure sensor device <NUM>, instead of by the processing circuit <NUM>, for example by the aforementioned main controller <NUM> of the electronic apparatus <NUM>.

Claim 1:
A pressure sensor device (<NUM>), comprising:
a pressure detection structure (<NUM>) provided in a first die (<NUM>) of semiconductor material;
a package (<NUM>), configured to internally accommodate said pressure detection structure (<NUM>) in an impermeable manner, the package (<NUM>) comprising a base structure (<NUM>) and a body structure (<NUM>), arranged on the base structure (<NUM>), having an access opening (<NUM>) in contact with an external environment and internally defining a housing cavity (<NUM>), in which said first die (<NUM>) is arranged covered by a coating material (<NUM>),
characterized by further comprising, accommodated in said housing cavity (<NUM>), a piezoelectric transduction structure (<NUM>), of a ultrasonic type, configured to allow detection of foreign material (<NUM>) on said coating material (<NUM>) within said package (<NUM>).