Patent Description:
Several applications provide for the ability to sense microparticles. For example, a device able to sense particulate matter suspended in air can be expediently employed in order to monitor the pollution level of an environment.

Among the available sensing devices capable to sense microparticles, such as particulate matter, sensing devices implemented by MEMS (Micro-Electro-Mechanical System) devices are known.

Generally, a MEMS device is a device comprising miniaturized mechanical, electrical and/or electronic components integrated in a same semiconductor material substrate, for example silicon, by means of micromachining techniques (for example, lithography, deposition, etching, deposition, growth).

Known MEMS devices for sensing microparticles (hereinafter also referred to as "MEMS microparticles sensing device" or simply "MEMS sensing device" for the sake of conciseness) have one or more cantilevered members excited in resonance by driving elements comprising mechanical piezoceramic, electrostatic, piezoelectric and electrothermal components. A sticking coating is provided on one or more sensing surfaces of the cantilevered member in order to capture microparticles. The microparticles stuck on the sticking coating cause a resonance variation depending on the amount of microparticles.

The Applicant has found that known MEMS microparticles sensing devices are not efficient due to one or more of the following drawbacks.

Known MEMS microparticles sensing devices are provided with a sticking coating for capturing microparticles, and after each use, need to be subjected to a cleaning operation directed to the removal of the sticking coating together with the microparticles stuck thereon followed by the application of a new sticking coating in order reset the MEMS sensing device to its original condition.

Therefore, the known MEMS microparticles sensing devices are not suited for those applications in which frequent sensing operations have to be performed. Moreover, since the cleaning operation may require the use of specific instrumentations and/or substances for the removal of the old sticking coating and the application of a new sticking coating, the known MEMS microparticles sensing devices are also not particularly suited for the "on the field" applications. Another example of a device for sensing microparticles is described by the document <CIT>, wherein the device comprises a particle sensor made of a ceramic structure of layers configured for receiving and sensing the particles carried by an air flow generated by a vacuum outside the device.

In view of the above, an aim of the present invention is to provide a MEMS microparticles sensing device which is not affected by the abovementioned drawbacks.

According to the invention, a MEMS sensing device for sensing microparticles in an environment external to the MEMS sensing device and a method are provided, according to the attached claims.

The features and advantages of the present invention will be better understood from following detailed description of embodiments thereof, provided merely by way of non-limitative examples, to be read in conjunction with the attached drawings. In this regard, it is explicitly intended that the drawings are not necessarily drawn to scale (with some details thereof that may be exaggerated and/or simplified) and that, unless otherwise stated, they are simply used for conceptually illustrating the described structures and processes. Particularly:.

<FIG> is a view from above and <FIG> is a section view of a portion of a sensor <NUM> of a MEMS microparticles sensing device (hereinafter, simply "MEMS sensing device").

In the following of the present description, direction terminology (such as for example, top, bottom, higher, lower, lateral, central longitudinal, transversal, vertical) will be only used for describing the sensor <NUM> as well as other elements of the MEMS sensing device which will be described in the following in relation to the very specific orientation illustrated in the figures, and not for describing possible specific orientation these elements will have during their operation.

On this regard, a reference direction system is shown including three orthogonal directions X, Y, Z.

The sensor <NUM> comprises a membrane <NUM> mechanically coupled with a piezoelectric element <NUM> configured to be actuated through electric signals for causing flexural motion thereof. When the piezoelectric element <NUM> is actuated, the membrane <NUM> oscillates about its equilibrium position at a corresponding resonance frequency fr.

The resonance frequency fr depends on several factors, such as the size, shape, material and mass of the membrane <NUM>. When microparticles are located on or above the membrane <NUM>, the resulting mass of the membrane <NUM> increases, causing a corresponding variation in the resonance frequency fr. A relationship is thus established between the mass/amount of microparticles on the membrane <NUM> and the variation in the resonance frequency fr (generally, the higher the mass/amount of microparticles, the lower the resonance frequency). This relationship is advantageously exploited by the MEMS sensing device comprising the sensor <NUM> for sensing microparticles in an environment wherein the MEMS sensing device is located. The MEMS sensing device comprising the sensor <NUM> is configured to sense (e.g., assess the mass/amount of) microparticles according to the resonance frequency fr.

According to an exemplary embodiment, the sensor <NUM> has a resonance frequency fr that is of the order of hundreds of kHz or MHz. For example, the resonance frequency fr of the sensor <NUM> in absence of microparticles on the membrane <NUM> is about <NUM>.

Here, the sensor <NUM> has an architecture based on the architecture of a Piezoelectric Micromachined Ultrasonic Transducer device ("PMUT device").

The sensor <NUM> may have a circular (or substantially circular) shape (along a plane parallel to directions Y and Z). In the alternative, the sensor <NUM> may have different shapes, such as a square (or substantially square) shape, a rectangular (or substantially rectangular) shape, a triangular (or substantially triangular) shape, hexagonal (or substantially hexagonal) shape, or an octagonal (or substantially octagonal) shape.

The sensor <NUM> is formed in a body <NUM> of semiconductor material, hereinafter referred to as semiconductor substrate <NUM>. Semiconductor substrate <NUM> may integrate other components useful for the sensor <NUM>. The semiconductor substrate <NUM> may be a monocrystalline silicon substrate, hereinafter simply referred to as silicon substrate <NUM>. The silicon substrate <NUM> of the PMUT device <NUM> illustrated in <FIG> has a front operative surface <NUM> extending parallel to plane YZ.

In <FIG>, the silicon substrate <NUM> comprises a sensor substrate cavity <NUM> (only a portion thereof illustrated in <FIG>) defining a hollow space delimited by lateral walls extending substantially along planes XZ and YZ, a bottom wall extending substantially along plane YZ, and a top wall extending substantially along plane YZ. However the lateral, bottom and/or top walls of the cavity <NUM> may be slanted.

The membrane <NUM> has a top surface <NUM> and a bottom surface <NUM>, extending, at rest, substantially parallel to plane YZ.

According to an embodiment, the membrane <NUM> has a circular (or substantially circular) shape (along a plane parallel to plane YZ); however, the membrane <NUM> may have different shapes, such as a square (or substantially square) shape, a rectangular (or substantially rectangular) shape, a triangular (or substantially triangular) shape, hexagonal (or substantially hexagonal) shape, or an octagonal (or substantially octagonal) shape.

The membrane <NUM> is suspended above the sensor substrate cavity <NUM>.

The bottom surface <NUM> of the membrane <NUM> corresponds to a portion of the top surface of the hollow space defined by the sensor substrate cavity <NUM>.

In <FIG>, the top surface <NUM> of the membrane <NUM> is flush with the front operative surface <NUM> of the silicon substrate <NUM>.

In <FIG>, the membrane <NUM> is made of the same material of the silicon substrate <NUM>, i.e., silicon, particularly monocrystalline silicon.

Optionally, the membrane <NUM> comprises one or more membrane cavities <NUM> for increasing the elasticity of the membrane <NUM>.

The piezoelectric element <NUM> is located above the top surface <NUM> of the membrane <NUM>. In <FIG>, an electric insulating layer <NUM> is provided between the top surface <NUM> of the membrane <NUM> and the piezoelectric element <NUM>. The electric insulating layer <NUM> may comprise an electric insulating material, such as silicon dioxide.

The piezoelectric element <NUM> is configured to:.

In fact, microparticles deposited onto the membrane <NUM> cause a change in the mass of the membrane <NUM> and, thus, of the oscillation frequency. Therefore, the electric signals generated by the sensor <NUM> also undergo a change in frequency and this frequency change may be used to detect the mass of the deposited microparticles.

In <FIG>, the piezoelectric element <NUM> has a circular (or substantially circular) shape (along a plane parallel to plane YZ); however, the piezoelectric element <NUM> may have different shapes, such as a square (or substantially square) shape, a rectangular (or substantially rectangular) shape, a triangular (or substantially triangular) shape, hexagonal (or substantially hexagonal) shape, or an octagonal (or substantially octagonal) shape.

In <FIG>, the piezoelectric element <NUM> comprises a piezoelectric material layer <NUM>, e.g., comprising aluminum nitride or PZT, between a top conductive layer <NUM> (above piezoelectric material layer <NUM>) and a bottom conductive layer <NUM> (below piezoelectric material layer <NUM>). For example, each of the top and the bottom conductive layers <NUM>, <NUM> comprises titanium-tungsten and/or platinum; and, according to an exemplary preferred embodiment of the piezoelectric material layer <NUM> comprises PZT and the top and the bottom conductive layers <NUM>, <NUM> comprises platinum.

The top conductive layer <NUM> and the bottom conductive layer <NUM> (or at least portions thereof) form electrodes of the piezoelectric element <NUM> across which it is possible to:.

The piezoelectric element <NUM> comprises a piezoelectric element opening <NUM> that uncovers a corresponding portion <NUM> of the underlying membrane <NUM>. In <FIG>, the piezoelectric element opening <NUM> is located at a central portion of the piezoelectric element <NUM> so that the corresponding portion <NUM> of the underlying membrane <NUM> not covered by the piezoelectric element <NUM> is at least substantially located at the center of the membrane <NUM>.

In <FIG>, the membrane <NUM> comprises, at the central portion <NUM>, a set of through holes <NUM> crossing the entire thickness of the membrane <NUM> (along direction Z) from the top surface <NUM> to the bottom surface <NUM>. In this way, fluid communication is established between the sensor substrate cavity <NUM> and the external environment through the membrane <NUM>. For example, the through holes <NUM> are located close to each other so that the central portion <NUM> of the membrane <NUM> defines a sieve-like structure.

According to an alternative (not illustrated in the figures), no piezoelectric element opening <NUM> is provided, and the through holes <NUM> extend through a (e.g., central) portion of the piezoelectric element <NUM>. In this case, the through holes <NUM> extends across the thickness of the piezoelectric element <NUM> and the thickness of the membrane <NUM>.

In <FIG>, the piezoelectric element <NUM> and the parts of the central portion <NUM> of the membrane <NUM> between adjacent through holes <NUM> are covered with a passivation layer <NUM>, for example comprising Undoped Silicate Glass (USG) or Silicon Nitride.

As will be described in detail hereinafter, the through holes <NUM> of the membrane <NUM> of the sensor <NUM> are configured to:.

In this way, during a sensing phase, the microparticles advantageously adhere against the membrane <NUM>, allowing an improved microparticles sensing, and, during the cleaning phase, the microparticles located on the membrane <NUM> are advantageously blown away, allowing an improved cleaning of the membrane <NUM>.

The diameter of the through holes <NUM> may be properly set according to the size of the microparticles to be sensed; for example, the diameter of the through holes may be set to correspond to the average diameter of the microparticles to be sensed; in the alternative, the diameter of the through holes may be set to correspond to a value lower than the average diameter of the microparticles to be sensed. For example, if the microparticles to be sensed are Particulate Matter (PM), the diameter of the through holes <NUM> may be advantageously set to <NUM> (for sensing PM<NUM> particulate matter), <NUM> (for sensing PM<NUM> particulate matter), or <NUM> (for sensing PM<NUM> particulate matter).

As will be described in detail hereinafter, the air pressure inside the sensor substrate cavity <NUM> of the sensor <NUM> is controlled by feeding/drawing up air to/from the sensor substrate cavity <NUM> through one or more pumps configured to:.

In <FIG>, the top conductive layer <NUM> comprises a first top plate <NUM>(<NUM>) and a second top plate <NUM>(<NUM>) that are electrically insulated one to another, and can apply/receive independent electric signals, for example by means of two separated and dedicated electrode pads P(<NUM>), P(<NUM>) (visible in <FIG>).

In addition, in <FIG>, the bottom conductive layer <NUM> comprises a first bottom plate <NUM>(<NUM>) and a second bottom plate <NUM>(<NUM>) that are electrically insulated one to another, and can apply/receive independent electric signals, for example by means of two separated and dedicated electrode pads B(<NUM>), B(<NUM>) (visible in <FIG>).

The first top plate <NUM>(<NUM>) and the second top plate <NUM>(<NUM>) are concentric, with the second top plate <NUM>(<NUM>) surrounding the first top plate <NUM>(<NUM>). Similarly, the first bottom plate <NUM>(<NUM>) and the second bottom plate <NUM>(<NUM>) are concentric, with the second bottom plate <NUM>(<NUM>) surrounding the first bottom plate <NUM>(<NUM>). Since each of the top conductive layer <NUM> and bottom conductive layer <NUM> comprises two concentric plates that are electrically insulated to each other and that can be driven independently, advantageously it is possible to selectively modify the shape (and particularly the concavity) of the membrane <NUM> during the sensing and cleaning phase in order to favor the adhesion/removal of microparticles to/from the membrane <NUM>.

In the alternative, the first top plate <NUM>(<NUM>) may be employed as a sensing plate, while the second top plate <NUM>(<NUM>) may be biased to change the concavity of the membrane <NUM>.

According to another embodiment not illustrated in the figures, in order to cause a change in the concavity of the membrane <NUM>, the piezoelectric material layer <NUM> advantageously comprises two separated and independent portions of piezoelectric material.

In the alternative, the top conductive layer <NUM> may be a single plate, and the concavity of the membrane <NUM> may be not substantially modified during the sensing and cleaning phases (in this case, the adhesion/removal of microparticles to/from the membrane <NUM> is only caused by the suction/blowing force caused by the air pressure of the sensor substrate cavity <NUM>).

According to another (not illustrated) embodiment, only one between the top conductive layer <NUM> and the bottom conductive layer <NUM> comprises two concentric bottom plates that are electrically insulated one to another, and that can be driven independently, while the other one is made of a single plate (in this case, the conductive layer made of a single plate is configured to operate as a sensing plate for applying/collecting electric signals to/from the piezoelectric material layer <NUM>).

In <FIG>, in order to reduce the possibility that microparticles remain stuck on the membrane <NUM> during the cleaning phase, a non-stick coating layer <NUM> is provided on the passivation layer <NUM>. For instance, the non-stick coating layer <NUM> comprises a hydrophobic material, such as for example FAS-<NUM>.

<FIG> illustrate a simplified (i.e., without depicting some elements thereof, such as the piezoelectric element, for the sake of simplicity) section view of a MEMS microparticles sensing device <NUM> during the sensing phase (<FIG>) and during the cleaning phase (<FIG>).

MEMS sensing device <NUM> of <FIG> comprises the sensor <NUM> already described with reference to <FIG> and a pump <NUM> configured to control the air pressure inside the sensor substrate cavity <NUM> of the sensor <NUM>.

The pump <NUM> is a MEMS pump device. For example, the pump <NUM> is a valveless micropump. In <FIG>, the pump <NUM> is a piezoelectric valveless micropump comprising a pump membrane <NUM> mechanically coupled with a piezoelectric element (not illustrated in the figure) configured to be actuated through electric signals for causing flexural motion of the pump membrane <NUM>. The pump membrane <NUM> forms a top wall of a pump substrate cavity <NUM>.

In <FIG>, the pump substrate cavity <NUM> is in fluid communication with the sensor substrate cavity <NUM> of the sensor <NUM> through a first duct <NUM>(<NUM>) and is in fluid communication with the external environment through a second duct <NUM>(<NUM>).

During the sensing phase (see <FIG>), the pump <NUM> is controlled in order to draw air from the sensor substrate cavity <NUM> through the first duct <NUM>(<NUM>) and expel said air into the external environment through the second duct <NUM>(<NUM>). In this way, the air pressure inside the sensor substrate cavity <NUM> is reduced with respect to the environmental air pressure outside the sensor substrate cavity <NUM>. This reduced pressure causes in turn microparticles (identified in <FIG> with reference <NUM>) suspended in the external environment to be attracted against the membrane <NUM> by a suction force through the through holes <NUM> of the membrane <NUM>. In this way, the mass increment caused by the attracted microparticles <NUM> can be efficiently assessed in a stable way by the sensor <NUM> without requiring a dedicated sticking coating.

During the cleaning phase (see <FIG>), the pump <NUM> is controlled in order to feed air coming from the external environment through the second duct <NUM>(<NUM>) into the sensor substrate cavity <NUM> through the first duct <NUM>(<NUM>). In this way, the air pressure inside the sensor substrate cavity <NUM> is increased with respect to the environmental air pressure outside the sensor substrate cavity <NUM>. This increased pressure causes in turn microparticles <NUM> attached against the membrane <NUM> to be removed from the membrane <NUM> by a blowing force through the through holes <NUM> of the membrane <NUM>. In this way, the microparticles <NUM> can be efficiently removed from the membrane and the sensor <NUM> can be reset to its original condition to allow subsequent sensing phases being efficiently carried out without being forced to perform long, complicated and cumbersome operations for removing sticking coatings followed by the application of new sticking coatings.

In particular, the pump <NUM> is controlled to draw air from the sensor substrate cavity <NUM> through the first duct <NUM>(<NUM>) and expel air into the external environment through the second duct <NUM>(<NUM>) during the sensing phase by causing the pump membrane <NUM> to have a concave shape directed downwardly.

In this case, the pump <NUM> is controlled to feed air coming from the external environment through the second duct <NUM>(<NUM>) into the sensor substrate cavity <NUM> through the first duct <NUM>(<NUM>) during the cleaning phase by causing the pump membrane <NUM> to have a concave shape directed upwardly.

Selective direction of air in the sensing and cleaning phases may be obtained by variable section ducts <NUM>(<NUM>) and <NUM>(<NUM>), as discussed hereinbelow. In the alternative, other solution may be devised for generating the desired flow direction of air.

<FIG> is a top view of a MEMS sensing device <NUM> with variable section ducts <NUM>(<NUM>) and <NUM>(<NUM>). Here, the geometry is such as to favor passage of flow from the from the sensor substrate cavity <NUM> to the external environment.

In particular, here, the first duct <NUM>(<NUM>) and the second duct <NUM>(<NUM>) have a tapered shape, in such a way that, during the operation of the pump <NUM>, the air flow from the pump <NUM> to the sensor <NUM> is lower than the air flow from the sensor <NUM> to the pump <NUM>, i.e., when the pump <NUM> is activated, the net air flow is directed from the sensor substrate cavity <NUM> to the external environment. Particularly, in <FIG>, the first duct <NUM>(<NUM>) has a section area (parallel to plane XZ) that increases by moving from the sensor substrate cavity <NUM> to the pump cavity <NUM>, and the second duct <NUM>(<NUM>) has a section area (parallel to plane XZ) that increases by moving from the pump cavity <NUM> to the outside of the pump <NUM>.

<FIG> is a top view of a MEMS sensing device - identified with reference <NUM>"-according to a further embodiment. The elements of the MEMS sensing device <NUM>" corresponding to the elements of the MEMS sensing device <NUM> will be identified using the same references used in the previous figures, and their description will be omitted for the sake of brevity. In <FIG>, two pumps are provided, identified with references <NUM>(<NUM>) and <NUM>(<NUM>). Pump <NUM>(<NUM>) is in fluid communication with the sensor substrate cavity <NUM> of the sensor <NUM> through a duct <NUM>(<NUM>,<NUM>) and with the external environment through a duct <NUM>(<NUM>,<NUM>). Pump <NUM>(<NUM>) is in fluid communication with the sensor substrate cavity <NUM> of the sensor <NUM> through a duct <NUM>(<NUM>,<NUM>) and with the external environment through a duct <NUM>(<NUM>,<NUM>).

Here, the duct <NUM>(<NUM>,<NUM>) and the duct <NUM>(<NUM>,<NUM>) have a tapered shape, in such a way that, during the operation of the pump <NUM>(<NUM>), the air flow from the pump <NUM>(<NUM>) to the sensor <NUM> is lower than the air flow from the sensor <NUM> to the pump <NUM>(<NUM>), i.e., when the pump <NUM>(<NUM>) is activated, the net air flow is directed from the sensor <NUM> to the external environment.

Furthermore, the duct <NUM>(<NUM>,<NUM>) and the duct <NUM>(<NUM>,<NUM>) have a tapered shape in such a way that, during the operation of the pump <NUM>(<NUM>), the air flow from the pump <NUM>(<NUM>) to the sensor <NUM> is higher than the air flow from the sensor <NUM> to the pump <NUM>(<NUM>), i.e., when the pump <NUM>(<NUM>) is activated, the net air flow is directed from to the external environment to the sensor <NUM>. Particularly, here, the duct <NUM>(<NUM>,<NUM>) has a section area (parallel to plane XZ) that increases by moving from the sensor <NUM> to the pump <NUM>(<NUM>), and the duct <NUM>(<NUM>,<NUM>) has a section area (parallel to plane XZ) that increases by moving from the pump <NUM>(<NUM>) to the outside of the pump <NUM>, while the duct <NUM>(<NUM>,<NUM>) has a section area (parallel to plane XZ) that decreases by moving from the sensor <NUM> to the pump <NUM>(<NUM>), and the duct <NUM>(<NUM>,<NUM>) has a section area (parallel to plane X Z) that decreases by moving from the pump <NUM>(<NUM>) to the outside of the pump <NUM>(<NUM>).

Accordingly, during the sensing phase, the pump <NUM>(<NUM>) is activated and the pump <NUM>(<NUM>) is deactivated, and during the cleaning phase, the pump <NUM>(<NUM>) is deactivated and the pump <NUM>(<NUM>) is activated.

<FIG> is a top view of a MEMS sensing device <NUM>‴that is a modified version of the MEMS sensing device <NUM>" illustrated in <FIG>.

In <FIG>, the pump <NUM>(<NUM>) is replaced by a pair of pumps <NUM>(<NUM>)(a), <NUM>(<NUM>)(b) fluidly connected in parallel to each other and configured to be operated in antiphase and the pump <NUM>(<NUM>) is replaced by a pair of pumps <NUM>(<NUM>)(a), <NUM>(<NUM>)(b) fluidly connected in parallel to each other and configured to be operated in antiphase. In this way, by activating the pumps <NUM>(<NUM>)(a), <NUM>(<NUM>)(b) during the sensing phase with a mutual phase shift of <NUM>° and by activating the pumps <NUM>(<NUM>)(a), <NUM>(<NUM>)(b) during the cleaning phase with a mutual phase shift of <NUM>°, undesired pulsating air flows are advantageously reduced.

Analogously, the present MEMS sensing device may include the combination of one or more sensors with one or more (single or pairs of) pump properly connected and operated during the sensing and cleaning phases.

<FIG> illustrate main steps of a process for manufacturing a MEMS sensing device. The manufacturing process illustrated in the <FIG> can be used for manufacturing the MEMS sensing device comprising a single sensor <NUM> and a single pump <NUM> as the MEMS sensing device <NUM> of <FIG> or the MEMS sensing device <NUM>' of <FIG>. The same manufacturing process can be directly employed also to manufacture other MEMS sensing devices, such as the ones illustrated in <FIG>.

By making reference to <FIG>, the sensor <NUM> and the pump <NUM> are manufactured starting from a same semiconductor substrate <NUM>, e.g., of silicon.

Then the sensor substrate cavity <NUM> for the sensor <NUM>, the pump cavity <NUM> for the pump <NUM> and the duct <NUM>(<NUM>) between the two cavities (see <FIG>) are formed in semiconductor substrate <NUM>.

The substrate cavity <NUM>, the pump cavity <NUM> and the duct <NUM>(<NUM>) may be manufactured based on the method disclosed in the patent <CIT> and in the patent application <CIT> (filed by the same Applicant). Briefly, lithographic masks are used having a honeycomb lattice. Then, using said masks, trench etching of the silicon substrate is performed to form corresponding silicon columns. After the removal of the lithographic masks, epitaxial growth is performed in a deoxidizing environment (e.g., in an atmosphere with a high concentration of hydrogen, preferably using SiHCl<NUM>), so that an epitaxial layer grows on top of the silicon columns, trapping gas (H<NUM>) present therein. An annealing step is then carried out, causing a migration of the silicon atoms, which tend to arrange themselves in lower energy positions. Consequently, the silicon atoms of the silicon columns migrate completely, forming the sensor substrate cavity <NUM>, the pump cavity <NUM> and the duct <NUM>(<NUM>).

The portion of the semiconductor substrate <NUM> directly over the sensor substrate cavity <NUM> forms the membrane <NUM>, and the portion of the semiconductor substrate <NUM> directly over the pump cavity <NUM> forms the pump membrane <NUM>.

In <FIG>, membrane cavities <NUM> are formed in the membrane <NUM> and in the pump membrane <NUM> for increasing the elasticity thereof. The membrane cavities <NUM> may be formed using the abovementioned method disclosed in the patent <CIT> and in the patent application <CIT>. However, the membrane cavities <NUM> are optional.

In <FIG>, an electric insulating layer <NUM> , e.g., of oxide is deposited on the front operative surface <NUM> of the semiconductor substrate <NUM>, for example by means of a Low pressure Chemical Vapor Deposition (LPCVD using tetraethyl orthosilicate as precursor), and a stack <NUM> is deposited on the electric insulating layer <NUM>. The stack <NUM> comprises a layer of piezoelectric material, e.g., comprising aluminum nitride or PZT, between two conductive layers, for example a TiW layer and/or a platinum layer.

In <FIG>, the stack <NUM> is patterned so as to form:.

The piezoelectric element <NUM> is also patterned to obtain the first top plate <NUM>(<NUM>) and the second top plate <NUM>(<NUM>) from the top conductive layer <NUM>. In the alternative, the piezoelectric element <NUM> may be patterned so that the top conductive layer <NUM> is made of a single plate (i.e., the first top plate <NUM>(<NUM>) and the second top plate <NUM>(<NUM>) are not formed). In addition, also the piezoelectric element <NUM> is patterned to separate the bottom conductive layer <NUM> in two plates.

In <FIG>, the passivation layer <NUM> (for example USG or Silicon Nitride) is deposited.

In <FIG>, the through holes <NUM> are formed at the piezoelectric opening <NUM> by performing a selective etching operation.

Then, the non-stick coating layer <NUM> (e.g., a hydrophobic material, such as for example FAS-<NUM>) is deposited on the passivation layer <NUM>.

<FIG> illustrate steps of another process for manufacturing a MEMS sensing device.

In <FIG>, the sensor <NUM> and the pump <NUM> are manufactured starting from a same semiconductor substrate <NUM>, e.g., of silicon.

Then, <FIG>, a recess <NUM> is formed in the semiconductor substrate <NUM> by means of an etching process. The recess <NUM> is patterned so as to correspond to the sensor substrate cavity <NUM> for the sensor <NUM>, the pump cavity <NUM> for the pump <NUM> and the duct <NUM>(<NUM>) between the two cavities (see <FIG>).

In <FIG>, a Silicon-On-Insulator (SOI) substrate <NUM> comprising an active layer (also called device layer <NUM>), a buried oxide layer (also called box layer <NUM>), and a support layer (also called handle layer <NUM>) is turned upside-down (i.e., with the handle layer <NUM> on the top) and bonded to the semiconductor substrate <NUM> to upwardly close the recess <NUM>. In this way, the sensor substrate cavity <NUM> for the sensor <NUM>, the pump cavity <NUM> for the pump <NUM> and the duct <NUM>(<NUM>) are thus formed (see <FIG>).

In <FIG>, the handle layer <NUM> is removed, for example by means of a mechanical polishing process, until exposing the box layer <NUM>, so as to define the membrane <NUM> and the pump membrane <NUM> from the device layer <NUM>, and the electric insulating layer <NUM> from the box layer <NUM>.

Then, the manufacturing process proceeds in the same way as already described with reference to <FIG>. It is pointed out that, according to this embodiment, the membrane cavities <NUM> are not formed.

<FIG> and <FIG> show a portion of a MEMS sensing device <NUM> having, in addition to the piezoelectric element <NUM>, an impedance measuring structure <NUM>. In particular, the impedance measuring structure <NUM> includes interdigitated sensing electrodes.

Generally, MEMS sensing device <NUM> has an overall structure similar to sensing devices <NUM>, <NUM>', <NUM>", <NUM>‴; thus, similar parts are indicated by the same reference numbers and are not described.

The piezoelectric element <NUM> and the impedance measuring structure <NUM> extend on the semiconductor substrate <NUM>; the piezoelectric element <NUM> has here an annular shape and surrounds the impedance measuring structure <NUM>. In particular, top conductive layer <NUM>, bottom conductive layer <NUM> and piezoelectric material layer <NUM> are all annular shaped.

Impedance measuring structure <NUM> comprises a first impedance measuring electrode <NUM> and a second measuring electrode <NUM>. In MEMS sensing device <NUM>, impedance measuring electrodes <NUM> and <NUM> are interdigitated and ring-shaped.

Impedance measuring electrodes <NUM> and <NUM> are of conductive material. For example, impedance measuring electrodes <NUM> and <NUM> are of gold.

In particular, the first impedance measuring electrode <NUM> of <FIG> include a plurality of first electrode portions <NUM> and the second impedance measuring electrode <NUM> includes a plurality of second top electrode portions <NUM>. First and second electrode portions <NUM> and <NUM> are interdigitated and electrically isolated from each other.

First electrode portions <NUM> are half-ring shaped and are electrically coupled to each other and to a first connecting portion <NUM>.

Second electrode portions <NUM> are also half-ring shaped and are electrically coupled to each other and to a second connecting portion <NUM>.

Piezoelectric element <NUM> here is ring-shaped and formed by two portions <NUM>-<NUM> and <NUM>-<NUM> that may be electrically coupled to form an electrically single top electrode <NUM> and an electrically single bottom electrode <NUM> (<FIG>). First and second connecting portions <NUM> and <NUM> extend between the portions <NUM>-<NUM>, <NUM>-<NUM> of the piezoelectric element <NUM> and are insulated therefrom.

Electrical lines <NUM> are connected to the first and second connecting portions <NUM>, <NUM> of the impedance measuring structure <NUM> and to the piezoelectric element <NUM>.

Through holes <NUM> extend also here across the entire thickness of the membrane <NUM>, between the first and the second electrode portions <NUM>, <NUM>, as shown in the enlarged detail of <FIG> (only one shown for sake of simplicity).

<FIG> also shows top electrode contact portions <NUM> in direct electrical contact with the top conductive layer <NUM> through openings in the passivation layer <NUM> and bottom contact portions <NUM> in direct electrical contact with the bottom conductive layer <NUM>; and a further passivation layer <NUM> covering the entire structure.

MEMS sensing device <NUM> of <FIG> and <FIG> operate in a way that is similar to the MEMS sensing devices <NUM>, <NUM>', <NUM>", but are also able to perform some measures about the nature of the particles.

In particular, in the sensing phase, microparticles adhering against the membrane <NUM> change the impendence of the MEMS sensing device <NUM>, so that a processor coupled to first and second connecting portions <NUM>, <NUM> and receiving an electrical signal generated by the impedance measuring structure <NUM> may detect the nature (metal/dielectric) nature of the microparticles.

In a cleaning phase, the MEMS sensing device <NUM> operates as discussed above.

<FIG> shows a different MEMS sensing device, identified by reference number <NUM>.

MEMS sensing device <NUM> has also an impedance measuring structure <NUM> including interdigitated electrodes, but here the interdigitated electrodes (also called here impedance measuring electrodes <NUM> and <NUM>) are comb-like shaped.

<FIG> also shows an electronic processor <NUM> for impedance measurement.

MEMS sensing device <NUM> operates as above indicated for MEMS sensing device <NUM>.

<FIG> shows a portion of a MEMS sensing device <NUM> having the piezoelectric element <NUM> and the impedance measuring structure <NUM>. The impedance measuring structure <NUM> includes interdigitated sensing electrodes.

Here, piezoelectric element <NUM> is circle or disk shaped and extends below the impedance measuring structure <NUM>. Specifically, the piezoelectric element <NUM> has a larger diameter than the impedance measuring structure <NUM>.

The MEMS sensing devices <NUM>, <NUM> and <NUM> of <FIG> may be manufactured in a similar way as described with reference to <FIG> or <FIG> with different mask to form the impedance measuring structure <NUM>. In particular, first and second electrode portions <NUM> and <NUM> are formed from a same layer used to form top and bottom contact portions <NUM>, <NUM> of the piezoelectric element <NUM>.

<FIG> illustrates a block diagram of an electronic system <NUM> comprising at least one of the MEMS sensing devices <NUM>, <NUM>', <NUM>", <NUM>‴, <NUM> or <NUM>.

The electronic system <NUM> is adapted to be used in electronic devices such as for example personal digital assistants, computers, tablets, and smartphones.

The electronic system <NUM> may comprise, in addition to the MEMS sensing device <NUM>, <NUM>', <NUM>", <NUM>‴, a controller <NUM>, such as for example one or more microprocessors and/or one or more microcontrollers, an input/output device <NUM> (such as for example a keyboard, and/or a touch screen and/or a visual display) for generating/receiving messages/commands/data, and/or for receiving/sending digital and/or analogic signals; a wireless interface <NUM> for exchanging messages with a wireless communication network (not shown), for example through radiofrequency signals. Examples of wireless interface <NUM> may comprise antennas and wireless transceivers; a storage device <NUM>, such as for example a volatile and/or a non-volatile memory device; a supply device <NUM>, for example a battery, for supplying electric power to the electronic system <NUM>; and one or more communication channels (buses) for allowing data exchange between the MEMS sensing device <NUM>, <NUM>', <NUM>", <NUM>‴, <NUM>, <NUM> and the controller <NUM>, and/or the input/output device <NUM>, and/or the wireless interface <NUM>, and/or the storage device <NUM>, and/or the battery <NUM>, when they are present.

Claim 1:
A MEMS sensing device (<NUM>, <NUM>', <NUM>", <NUM>‴; <NUM>; <NUM>; <NUM>) for sensing microparticles in an environment external to the MEMS sensing device, the MEMS sensing device comprising:
a semiconductor body (<NUM>) integrating a sensor (<NUM>) and a pump (<NUM>; <NUM>(<NUM>), <NUM>(<NUM>); <NUM>(<NUM>)(a), <NUM>(<NUM>)(b), <NUM>(<NUM>)(a), <NUM>(<NUM>)(b));
wherein the sensor (<NUM>) includes a sensor cavity (<NUM>), a membrane (<NUM>) suspended over the sensor cavity (<NUM>), and a piezoelectric element (<NUM>) located over the membrane (<NUM>) and configured to cause the membrane to oscillate about an equilibrium position and at a resonance frequency when sensing electric signals are applied to the piezoelectric element during a first operative phase of the MEMS sensing device, the resonance frequency depending on an amount of microparticles located on the membrane;
wherein the membrane (<NUM>) includes a plurality of through holes (<NUM>) configured to establish a fluid communication between the sensor cavity (<NUM>) and the environment; and
wherein the pump (<NUM>; <NUM>(<NUM>), <NUM>(<NUM>); <NUM>(<NUM>)(a), <NUM>(<NUM>)(b), <NUM>(<NUM>)(a), <NUM>(<NUM>)(b)) is adjacent to the sensor (<NUM>), is connected to the sensor through a duct (<NUM>) extending in the semiconductor body and is configured to cause air pressure in the sensor cavity (<NUM>) to be reduced with respect to the air pressure of the environment during the first operative phase, such that microparticles are caused to adhere onto the membrane (<NUM>) by a suction force through the plurality of through holes (<NUM>), and to cause air pressure in the sensor cavity (<NUM>) to be increased with respect to the air pressure of the environment during a second operative phase, such that microparticles are caused to be blown away from the membrane (<NUM>) by a blowing force through the plurality of through holes (<NUM>), thereby cleaning the membrane (<NUM>).