MEMS particle sensors

Abstract

Embodiments of the present disclosure relate to a MEMS particle sensor. A MEMS sensing device for sensing particles in an external environment of the MEMS sensing device is provided. The MEMS sensing device includes a semiconductor body that integrates a sensor and a pump unit, the sensor includes a sensor cavity, a membrane suspended above the sensor cavity, and a piezoelectric element, the piezoelectric element is located above the membrane, and is configured to cause the membrane to oscillate around an equilibrium position at a corresponding resonant frequency when a sensing electrical signal is applied to the piezoelectric element during a first operation phase of the MEMS sensing device, the resonant frequency depends on the number of particles located on the membrane, the membrane has a plurality of through holes for establishing fluid communication between the sensor cavity and the environment; the pump is configured to reduce the air pressure in the sensor cavity relative to the air pressure of the environment during the first operation phase, so that the particles adhere to the membrane by suction through the plurality of through holes.

Description

Technical Field

[0001] The present disclosure relates to the field of micro-electromechanical systems (hereinafter referred to as "MEMS"). One embodiment of the present disclosure relates to a MEMS device for sensing particles. Background Art

[0002] Several applications offer the ability to sense particles. For example, a device that can sense particulate matter suspended in the air can be conveniently used to monitor pollution levels in an environment.

[0003] Among available sensing devices capable of sensing particles such as particulate matter, sensing devices implemented by MEMS (Micro Electro Mechanical Systems) devices are known.

[0004] Generally, a MEMS device is a device comprising miniaturized mechanical, electrical and / or electronic components integrated in the same semiconductor material substrate (eg, silicon) by means of microfabrication techniques (eg, lithography, deposition, etching, deposition, growth).

[0005] A known MEMS device for sensing particles (hereinafter also referred to as a "MEMS particle sensing device" or simply referred to as a "MEMS sensing device" for simplicity) has one or more cantilever members resonantly excited by a driving element including mechanical piezoelectric ceramics, electrostatic, piezoelectric, and electrothermal components. A sticky coating is provided on one or more sensing surfaces of the cantilever member to capture particles. Particles stuck to the sticky coating cause a resonance change depending on the number of particles. Summary of the invention

[0006] Applicants have discovered that known MEMS particle sensing devices are inefficient due to one or more of the following disadvantages.

[0007] Known MEMS particle sensing devices are provided with a sticky coating for capturing particles and after each use require a cleaning operation aimed at removing the sticky coating and the particles stuck thereon and then applying a new sticky coating in order to reset the MEMS sensing device to its original condition.

[0008] Therefore, known MEMS particle sensing devices are not suitable for applications where frequent sensing operations must be performed. In addition, since cleaning operations may require the use of special instruments and / or substances to remove the viscous coating and apply a new viscous coating, known MEMS particle sensing devices are also not particularly suitable for "field" applications.

[0009] In view of this, an object of the present invention is to provide a MEMS particle sensing device that is not affected by the above-mentioned defects.

[0010] According to the present disclosure and in accordance with the accompanying claims, there is provided a MEMS sensing device and method for sensing particles in an environment external to the MEMS sensing device. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The features and advantages of the present disclosure will be better understood from the following detailed description of embodiments thereof, which are provided by way of non-limiting example only, to be read in conjunction with the accompanying drawings. In this regard, it is expressly intended that the drawings are not necessarily drawn to scale (with some details thereof being exaggerated and / or simplified) and that, unless otherwise indicated, they are intended merely to illustrate the described structures and processes in a conceptual manner.

[0012] Figure 1A and Figure 1B illustrates (a portion of) a sensor of a MEMS particle sensing device according to an embodiment of the present disclosure;

[0013] Figure 2A and Figure 2B illustrates a simplified view of a MEMS particle sensing device during a sensing phase and during a cleaning phase according to an embodiment of the present disclosure;

[0014] FIG. 3A to FIG. 3C Another version of a MEMS particle sensing device according to an embodiment of the present disclosure is illustrated;

[0015] 4A to 4H illustrates steps of a process for manufacturing a MEMS particle sensing device according to an embodiment of the present disclosure;

[0016] FIG. 5A to FIG. 5D illustrates steps of a process for manufacturing a MEMS particle sensing device according to another embodiment of the present disclosure;

[0017] Figure 6 are top plan views of various embodiments of MEMS particle sensing devices.

[0018] Figure 7 yes Figure 6 Cross section of a MEMS particle sensing device;

[0019] Figure 8 is a schematic diagram of a system including another embodiment of a MEMS particle sensing device;

[0020] Fig. 9 is a cross-section of another embodiment of a MEMS particle sensing device; and

[0021] Fig.10 An electronic system including at least one MEMS particle sensing device according to an embodiment of the present disclosure is illustrated in simplified block diagram form. DETAILED DESCRIPTION

[0022] Figure 1A FIG. 1 is a top view of a sensor 100 of a MEMS particle sensing device (hereinafter referred to as “MEMS sensing device”) according to an embodiment of the present disclosure. Figure 1B is a cross-sectional view of a portion of the sensor 100 .

[0023] Throughout the remainder of this specification, directional terms (such as, for example, top, bottom, high, low, sideways, center longitudinal, lateral, vertical) will be used only to describe the sensor 100 and other elements of the MEMS sensing device described below with respect to the very specific orientations illustrated in the figures, and not to describe possible specific orientations that these elements will have during their operation.

[0024] In this regard, a reference direction system is shown as including three orthogonal directions X, Y, Z.

[0025] The sensor 100 comprises a membrane 110 mechanically coupled to a piezoelectric element 120 configured to be actuated by an electrical signal for causing a flexural motion thereof. When the piezoelectric element 120 is actuated, the membrane 110 oscillates about its equilibrium position at a corresponding resonant frequency fr.

[0026] The resonant frequency fr depends on several factors, such as the size, shape, material, and mass of the membrane 110. When particles are located on or above the membrane 110, the resulting mass of the membrane 110 increases, resulting in a corresponding change in the resonant frequency fr. Therefore, a relationship is established between the mass / number of particles on the membrane 110 and the change in the resonant frequency fr (generally, the higher the mass / number of particles, the lower the resonant frequency). A MEMS sensing device including the sensor 100 advantageously utilizes this relationship to sense particles in the environment in which the MEMS sensing device is located. A MEMS sensing device including the sensor 100 is configured to sense particles (e.g., assess their mass / number) based on the resonant frequency fr.

[0027] According to an exemplary embodiment, the sensor 100 has a resonance frequency fr of the order of hundreds of kHz or MHz. For example, in the absence of particles on the membrane 110, the resonance frequency fr of the sensor 100 is about 500 kHz.

[0028] Here, the sensor 100 has an architecture based on the architecture of a piezoelectric micromachined ultrasonic transducer device (“PMUT device”).

[0029] The sensor 100 may have a circular (or substantially circular) shape (along a plane parallel to directions Y and Z). In alternative embodiments, the sensor 100 may have a different shape, such as a square (or substantially square) shape, a rectangular (or substantially rectangular) shape, a triangular (or substantially triangular) shape, a hexagonal (or substantially hexagonal) shape, or an octagonal (or substantially octagonal) shape.

[0030] The sensor 100 is formed in a body 125 of semiconductor material, hereinafter referred to as semiconductor substrate 125. The semiconductor substrate 125 may integrate other components useful for the sensor 100. The semiconductor substrate 125 may be a single crystal silicon substrate, hereinafter referred to as silicon substrate 125. Figure 1A and Figure 1B The silicon substrate 110 of the illustrated PMUT device 100 has a front operating surface 127 extending parallel to the plane YZ.

[0031] exist Figure 1B In the embodiment, the silicon substrate 125 includes a sensor substrate cavity 130 ( Figure 1B 1 ), the sensor substrate cavity 130 defines a hollow space defined 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 side walls, bottom wall, and / or top wall of the cavity 130 may be inclined.

[0032] The membrane 110 has a top surface 132 and a bottom surface 134 which, when at rest, extend substantially parallel to the plane YZ.

[0033] According to an embodiment, the membrane 110 has a circular (or substantially circular) shape (along a plane parallel to plane YZ); however, the membrane 110 may have a different shape, such as a square (or substantially square) shape, a rectangular (or substantially rectangular) shape, a triangular (or substantially triangular) shape, a hexagonal (or substantially hexagonal) shape, or an octagonal (or substantially octagonal) shape.

[0034] The membrane 110 is suspended above the sensor substrate cavity 130 .

[0035] The bottom surface 134 of the membrane 110 corresponds to a portion of the top surface of the hollow space defined by the sensor substrate cavity 130 .

[0036] exist Figure 1B In FIG. 1 , the top surface 132 of the membrane 110 is flush with the front operating surface 127 of the silicon substrate 125 .

[0037] exist Figure 1A and Figure 1B In the embodiment, the membrane 110 is made of the same material as the silicon substrate 125 (ie, silicon, specifically, single crystal silicon).

[0038] Optionally, the membrane 110 includes one or more membrane cavities 135 for increasing the elasticity of the membrane 110 .

[0039] The piezoelectric element 120 is located above the top surface 132 of the membrane 110. Figure 1A and Figure 1B In FIG. 1 , an electrically insulating layer 136 is provided between the top surface 132 of the membrane 110 and the piezoelectric element 120. The electrically insulating layer 136 may include an electrically insulating material, such as silicon dioxide.

[0040] The piezoelectric element 120 is configured as:

[0041] When an electrical signal is applied across the piezoelectric element 120, the membrane 110 is caused to oscillate, and

[0042] In response to the oscillation of the membrane 110 , an electrical signal is generated.

[0043] In fact, the particles deposited on the membrane 110 cause a change in the mass of the membrane 110, thus causing a change in the oscillation frequency. Therefore, the electrical signal generated by the sensor 100 also undergoes a frequency change, and this frequency change can be used to detect the mass of the deposited particles.

[0044] exist Figure 1A and Figure 1B , the piezoelectric element 120 (along a plane parallel to plane YZ) has a circular (or substantially circular) shape; however, the piezoelectric element 120 may have different shapes, such as a square (or substantially square) shape, a rectangular (or substantially rectangular) shape, a triangular (or substantially triangular) shape, a hexagonal (or substantially hexagonal) shape, or an octagonal (or substantially octagonal) shape.

[0045] exist Figure 1A and Figure 1B In the embodiment, the piezoelectric element 120 includes a piezoelectric material layer 140, for example, including aluminum nitride or PZT, which is located between a top conductive layer 160 (above the piezoelectric material layer 140) and a bottom conductive layer 162 (below the piezoelectric material layer 140). For example, each of the top conductive layer 160 and the bottom conductive layer 162 is titanium tungsten and / or platinum; and according to an exemplary preferred embodiment, the piezoelectric material layer 140 includes PZT and the top conductive layer 160 and the bottom conductive layer 162 include platinum.

[0046] The top conductive layer 160 and the bottom conductive layer 162 (or at least a portion thereof) form electrodes of the piezoelectric element 120, across which electrodes it is possible to:

[0047] applying an electrical signal to the piezoelectric material layer 140 to cause the membrane 110 to oscillate, and

[0048] The electrical signal generated by the piezoelectric material layer 140 in response to the oscillation of the membrane 110 is collected.

[0049] The piezoelectric element 120 includes a piezoelectric element opening 165 that exposes a corresponding portion 166 of the underlying film 110. Figure 1A and Figure 1B In the embodiment, the piezoelectric element opening 165 is located at a central portion of the piezoelectric element 120 so that a corresponding portion 166 of the underlying film 110 not covered by the piezoelectric element 120 is at least substantially located at the center of the film 110 .

[0050] exist Figure 1A and Figure 1B 1 , the membrane 110 includes a set of through holes 168 at the central portion 166, which span the entire thickness of the membrane 110 (along the direction Z) from the top surface 132 to the bottom surface 134. In this way, fluid communication is established between the sensor substrate cavity 130 and the external environment through the membrane 110. For example, the through holes 168 are located close to each other so that the central portion 166 of the membrane 110 defines a sieve-like structure.

[0051] According to an alternative (not shown in the figures), no piezoelectric element opening 165 is provided and the through hole 168 extends through a (eg central) portion of the piezoelectric element 120. In this case, the through hole 168 extends across the thickness of the piezoelectric element 120 and the thickness of the membrane 110.

[0052] exist Figure 1B 1 , portions of the central portion 166 of the membrane 110 between the piezoelectric element 120 and adjacent through-holes 168 are covered with a passivation layer 170, for example, comprising undoped silicate glass (USG) or silicon nitride.

[0053] As described in detail below, the through-holes 168 of the membrane 110 of the sensor 100 are configured as:

[0054] When the air pressure inside the sensor substrate cavity 130 decreases relative to the ambient air pressure outside the sensor substrate cavity 130, the particles are caused to adhere to the membrane 110 by suction (sensing phase);

[0055] When the air pressure inside the sensor substrate cavity 130 increases relative to the ambient air pressure outside the sensor substrate cavity 130 , the particles are blown off the membrane 110 by the blowing force (cleaning phase).

[0056] In this way, during the sensing phase, the particles advantageously adhere to the membrane 110 , thereby allowing improved particle sensing, and during the cleaning phase, the particles located on the membrane 110 are advantageously blown away, thereby allowing improved cleaning of the membrane 110 .

[0057] The diameter of the through hole 168 can be appropriately set according to the size of the particles to be sensed; for example, the diameter of the through hole can be set to correspond to the average diameter of the particles to be sensed. In an alternative, the diameter of the through hole can be set to correspond to a value lower than the average diameter of the particles to be sensed. For example, if the particles to be sensed are particulate matter (PM), the diameter of the through hole 168 can be advantageously set to 1 μm (for sensing PM2.5 particles), 2 μm (for sensing PM5 particles), or 4 μm (for sensing PM10 particles).

[0058] As described in detail below, the air pressure within the sensor substrate cavity 130 of the sensor 100 is controlled by feeding / extracting air to / from the sensor substrate cavity 130 via one or more pumps configured to:

[0059] During the first sensing phase, air is drawn from the sensor cavity 130 and exhausted to the external environment through a pump port different from the through-hole 168;

[0060] During the cleaning phase, air from the external environment is fed into the sensor cavity 130 through the pump port.

[0061] exist Figure 1B In the embodiment, the top conductive layer 160 includes a first top plate 160(1) and a second top plate 160(2) which are electrically insulated from each other and can be connected to each other by means of two separate dedicated electrode pads P(1), P(2) ( Figure 1A (as seen in Figure 2) applies / receives independent electrical signals.

[0062] In addition, Figure 1B In the embodiment, the bottom conductive layer 162 includes a first bottom plate 162(1) and a second bottom plate 162(2) which are electrically insulated from each other and can be connected to the bottom conductive layer 162 by means of two separate dedicated electrode pads B(1), B(2) ( Figure 1A (as seen in Figure 2) applies / receives independent electrical signals.

[0063] The first top plate 160(1) is concentric with the second top plate 160(2), wherein the second top plate 160(2) surrounds the first top plate 160(1). Similarly, the first bottom plate 162(1) is concentric with the second bottom plate 162(2), wherein the second bottom plate 162(2) surrounds the first bottom plate 162(1). Because each of the top conductive layer 160 and the bottom conductive layer 162 includes two concentric plates that are electrically insulated from each other and can be driven independently, advantageously, the shape (specifically, the concavity) of the membrane 110 can be selectively modified during the sensing and cleaning stages to facilitate the adhesion of particles to / removal of particles from the membrane 110.

[0064] Specifically:

[0065] During the sensing phase, the second top plate 160(2) and the second bottom plate 162(2) are used as sensing plates for applying / collecting electrical signals to / from the piezoelectric material layer 140, while the first top plate 160(1) and the first bottom plate 162(1) are biased to have a mutual voltage difference ΔV, the mutual voltage difference ΔV having a value such that the membrane 110 has an upwardly directed concave shape, thereby facilitating the adhesion of particles to the membrane 110;

[0066] During the cleaning phase, the second top plate 160 ( 2 ) and the second bottom plate 162 ( 2 ) are biased to have a mutual voltage difference ΔV of such a value that the membrane 110 has an upwardly directed concave shape, thereby discouraging particles from adhering to the membrane 110 .

[0067] In an alternative, the first top plate 160 ( 1 ) may be used as the sensing plate, while the second top plate 160 ( 2 ) may be biased to change the concavity of the membrane 110 .

[0068] According to another embodiment not shown in the figures, in order to allow the concavity of the membrane 110 to vary, the layer of piezoelectric material 140 advantageously comprises two separate independent portions of piezoelectric material.

[0069] In an alternative, the top conductive layer 160 may be a single sheet and the concavity of the membrane 110 may remain substantially unchanged during the sensing and cleaning phases (in which case particle adhesion to / removal from the membrane 110 is caused solely by suction / blowing forces caused by the air pressure of the sensor substrate cavity 130).

[0070] According to another (not shown) embodiment, only two electrically insulated and independently drivable concentric bottom plates are included between the top conductive layer 160 and the bottom conductive layer 162, while the other is made of a single plate (in this case, the conductive layer made of a single plate is configured to be used as a sensing plate for applying / collecting electrical signals to / from the piezoelectric material layer 140).

[0071] exist Figure 1A and Figure 1B In order to reduce the possibility of particles remaining stuck to the membrane 110 during the cleaning stage, a non-stick coating 190 is provided on the passivation layer 170. For example, the non-stick coating 190 includes a hydrophobic material, such as, for example, FAS-17.

[0072] Figure 2A and Figure 2B The MEMS particle sensing device 200 is shown in the sensing stage ( Figure 2A ) and cleaning phase ( Figure 2B ) during a simplified (i.e., some of its elements, such as piezoelectric elements, are not depicted for simplicity) cross-sectional view.

[0073] Figure 2A and Figure 2B The MEMS sensing device 200 includes the reference Figure 1A and Figure 1B The sensor 100 and the pump 205 configured to control the air pressure inside the sensor substrate cavity 130 of the sensor 100 are described.

[0074] The pump 205 is a MEMS pump device. For example, the pump 205 is a valveless micro pump. Figure 2A and Figure 2B In the embodiment, the pump 205 is a piezoelectric valveless micro pump including a pump membrane 210, which is mechanically coupled to a piezoelectric element (not shown) configured to be actuated by an electrical signal to cause a flexural motion of the pump membrane 210. The pump membrane 210 forms a top wall of a pump substrate cavity 230.

[0075] exist Figure 2A and Figure 2B , the pump substrate cavity 230 is in fluid communication with the sensor substrate cavity 130 of the sensor 100 via a first conduit 240(1) and is in fluid communication with the external environment via a second conduit 240(2).

[0076] In the sensing phase (see Figure 2A ), the pump 205 is controlled to draw air from the sensor substrate cavity 130 through the first conduit 240(1) and exhaust the air into the external environment through the second conduit 240(2). In this way, the air pressure inside the sensor substrate cavity 130 is reduced relative to the ambient air pressure outside the sensor substrate cavity 130. This reduced pressure in turn causes the particles suspended in the external environment (in Figure 2A and Figure 2B The particles 245 are attracted to the membrane 110 by suction through the through-holes 168 of the membrane 110. In this way, the mass increment caused by the attracted particles 245 can be efficiently evaluated by the sensor 100 in a stable manner without the need for a dedicated adhesive coating.

[0077] During the cleaning phase (see Figure 2B ), the pump 205 is controlled so as to feed air from the external environment through the second conduit 240(2) into the sensor substrate cavity 130 through the first conduit 240(1). In this way, the air pressure inside the sensor substrate cavity 130 increases relative to the ambient air pressure outside the sensor substrate cavity 130. This increased pressure in turn causes the particles 245 attached to the membrane 110 to be removed from the membrane 110 by the blowing force through the through holes 168 of the membrane 110. In this way, the particles 245 can be effectively removed from the membrane and the sensor 110 can be reset to its original condition to allow the subsequent sensing phase to be effectively carried out without being forced to perform a long, complicated and cumbersome operation for applying a viscous coating and then a new viscous coating.

[0078] Specifically, by making the pump membrane 210 have a downwardly pointing concave shape, during the sensing phase, the pump 205 is controlled to draw air from the sensor substrate cavity 130 through the first conduit 240 ( 1 ) and to exhaust the air to the external environment through the second conduit 240 ( 2 ).

[0079] In this case, by giving the pump membrane 210 an upwardly directed concave shape, during the cleaning phase the pump 205 is controlled to feed air from the external environment through the second conduit 240 ( 2 ) into the sensor substrate cavity 130 through the first conduit 240 ( 1 ).

[0080] As discussed below, selective direction of the air during the sensing and cleaning phases may be achieved through the variable section ducts 240(1) and 240(2). In the alternative, other solutions may be devised to generate the desired flow direction of the air.

[0081] Figure 3A is a top view of a MEMS sensing device 200 having variable cross-section conduits 240(1) and 240(2). Here, the geometry facilitates a flow path from the sensor substrate cavity 130 to the external environment.

[0082] Specifically, here, the first duct 240(1) and the second duct 240(2) have a conical shape in such a way that during operation of the pump 205, the air flow from the pump 205 to the sensor 100 is lower than the air flow from the sensor 100 to the pump 205, i.e., when the pump 205 is activated, a net air flow is directed from the sensor substrate cavity 130 to the external environment. Figure 3A , the first conduit 240(1) has a cross-sectional area (parallel to plane XZ) that increases by moving from the sensor substrate cavity 130 to the pump cavity 230, and the second conduit 240(2) has a cross-sectional area (parallel to plane XZ) that increases by moving from the pump cavity 230 to the outside of the pump 205.

[0083] Figure 3B 2 is a top view of a MEMS sensing device identified with reference numeral 200″ according to another embodiment of the present disclosure. Elements of the MEMS sensing device 200″ corresponding to elements of the MEMS sensing device 200 are identified using the same reference numerals as used in the previous figures, and their descriptions are omitted for the sake of brevity. Figure 3BIn the embodiment, two pumps are provided, which are identified by reference numerals 205(1) and 205(2). Pump 205(1) is in fluid communication with the sensor substrate cavity 130 of sensor 100 via conduit 240(1,1) and in fluid communication with the external environment via conduit 240(1,2). Pump 205(2) is in fluid communication with the sensor substrate cavity 130 of sensor 100 via conduit 240(2,1) and in fluid communication with the external environment via conduit 240(2,2).

[0084] Here, duct 240(1,1) and duct 240(1,2) have a conical shape in such a way that during operation of pump 205(1), the air flow from pump 205(1) to sensor 100 is lower than the air flow from sensor 100 to pump 205(1), i.e., when pump 205(1) is started, the net air flow is directed from sensor 100 to the external environment.

[0085] Furthermore, conduit 240(2,1) and conduit 240(2,2) have a conical shape in such a way that during operation of pump 205(2), the air flow from pump 205(2) to sensor 100 is higher than the air flow from sensor 100 to pump 205(2), i.e., when pump 205(2) is started, a net air flow is directed from the external environment to sensor 100. Specifically, here, pipe 240(1,1) has a cross-sectional area (parallel to plane XZ) that increases by moving from sensor 100 to pump 205(1), and pipe 240(1,2) has a cross-sectional area (parallel to plane XZ) that increases by moving from pump 205(1) to the outside of pump 205, while pipe 240(2,1) has a cross-sectional area (parallel to plane XZ) that decreases by moving from sensor 100 to pump 205(2), and pipe 240(2,2) has a cross-sectional area (parallel to plane XZ) that decreases by moving from pump 205(2) to the outside of pump 205(2).

[0086] Thus, during the sensing phase, pump 205(1) is activated and pump 205(2) is deactivated, and during the cleaning phase, pump 205(1) is deactivated and pump 205(2) is activated.

[0087] Figure 3C is a top view of a MEMS sensing device 200'', which is Figure 3B A modified version of the illustrated MEMS sensing device 200 ”.

[0088] exist Figure 3CIn the embodiment of the present invention, pump 205(1) is replaced by a pair of pumps 205(1)(a), 205(1)(b) which are fluidly connected in parallel with each other and configured to operate in anti-phase, and pump 205(2) is replaced by a pair of pumps 205(2)(a), 205(2)(b) which are fluidly connected in parallel with each other and configured to operate in anti-phase. In this way, by activating pumps 205(1)(a), 205(1)(b) with a mutual phase shift of 180° during the sensing phase and by activating pumps 205(2)(a), 205(2)(b) with a mutual phase shift of 180° during the cleaning phase, undesirable pulsating air flow is advantageously reduced.

[0089] Similarly, the present MEMS sensing device may include a combination of one or more sensors and one or more (single or paired) pumps connected and operated in an appropriate manner during the sensing and cleaning phases.

[0090] 4A to 4H The main steps of the process of manufacturing a MEMS sensing device are illustrated. 4A to 4H The illustrated manufacturing process can be used to manufacture a MEMS sensing device including a single sensor 100 and a single pump 205, as FIG. 2A to FIG. 2B The MEMS sensing device 200 or Figure 3A The same manufacturing process can also be used to manufacture other MEMS sensing devices, such as Figure 3B and Figure 3C The illustrated MEMS sensing device.

[0091] By reference Figure 4A , the sensor 100 and the pump 205 are fabricated starting from the same semiconductor substrate 125 (eg, silicon).

[0092] Then, a sensor substrate cavity 130 for the sensor 100, a pump cavity 230 for the pump 205, and a conduit 240 (1) between the two cavities are formed in the semiconductor substrate 125 (see FIG. 2A to FIG. 2B ).

[0093] The substrate cavity 130, the pump cavity 230 and the pipeline 240 (1) can be manufactured based on the method disclosed in the patent US 7,294,536 (submitted by the same applicant) and the patent application US 2008 / 261345. In short, a photolithography mask having a honeycomb grid is used. Then, the silicon substrate is grooved using the mask to form corresponding silicon pillars. After removing the photolithography mask, epitaxial growth is performed in a deoxidized environment (for example, in an atmosphere of high concentration of hydrogen, preferably using SiHCl3) so that the epitaxial layer grows on top of the silicon pillar, thereby capturing the gas (H2) present therein. Then, an annealing step is performed to migrate the silicon atoms, which tend to arrange themselves in positions with lower energy. Therefore, the silicon atoms of the silicon pillar are completely migrated, thereby forming the sensor substrate cavity 130, the pump cavity 230 and the pipeline 240 (1).

[0094] The portion of the semiconductor substrate 125 directly above the sensor substrate cavity 130 forms the membrane 110 , and the portion of the semiconductor substrate 125 directly above the pump cavity 230 forms the pump membrane 210 .

[0095] exist Figure 4C In the present invention, a membrane cavity 135 is formed in the membrane 110 and the pump membrane 210 for increasing the elasticity thereof. The membrane cavity 135 can be formed using the above-mentioned method disclosed in patent US7,294,536 and patent application US 2008 / 261345. However, the membrane cavity 135 is optional.

[0096] exist Figure 4D In the embodiment, an electrically insulating layer 136, for example made of oxide, is deposited on the front operative surface 127 of the semiconductor substrate 125, for example by means of low pressure chemical vapor deposition (LPCVD using tetraethyl orthosilicate as a precursor), and a stack 402 is deposited on the electrically insulating layer 136. The stack 402 comprises a piezoelectric material layer between two conductive layers (for example, a TiW layer and / or a platinum layer), the piezoelectric material layer comprising, for example, aluminum nitride or PZT.

[0097] exist Figure 4E In the embodiment, the stack 402 is patterned to form:

[0098] The piezoelectric element 120 is aligned with the sensor substrate cavity 130 to obtain the layers 160, 162, 140 (see Figure 1A );

[0099] Piezoelectric element opening 165 (see Figure 1A ),as well as

[0100] Another piezoelectric element 410 , aligned with the pump chamber 230 , is used to actuate the pump membrane 210 .

[0101] The piezoelectric element 120 is also patterned to obtain a first top plate 160(1) and a second top plate 160(2) from the top conductive layer 160. In an alternative embodiment, the piezoelectric element 120 can be patterned so that the top conductive layer 160 is made of a single plate (i.e., the first top plate 160(1) and the second top plate 160(2) are not formed). In addition, the piezoelectric element 120 is also patterned to separate the bottom conductive layer 162 into two plates.

[0102] exist Figure 4F In the process, a passivation layer 170 (eg, USG or silicon nitride) is deposited.

[0103] exist Figure 4G In the embodiment, a through hole 168 is formed at the piezoelectric opening 165 by performing a selective etching operation.

[0104] Then, a non-stick coating 190 (eg, a hydrophobic material such as, for example, FAS-17) is deposited on the passivation layer 170 .

[0105] FIG. 5A to FIG. 5D Illustrated are steps of another process for fabricating a MEMS sensing device.

[0106] exist Figure 5A In FIG. 1 , the sensor 100 and the pump 205 are fabricated starting from the same semiconductor substrate 125 (eg, made of silicon).

[0107] Then, if Figure 5B As shown, a recess 505 is formed in the semiconductor substrate 125 by means of an etching process. The recess 505 is patterned so as to correspond to the sensor substrate cavity 130 for the sensor 100, the pump cavity 230 for the pump 205, and the conduit 240 (1) between the two cavities (see FIG. 2A to FIG. 2B ).

[0108] exist Figure 5C In the embodiment, a silicon-on-insulator (SOI) substrate 506 including an active layer (also referred to as a device layer 512), a buried oxide layer (also referred to as a box layer 514) and a support layer (also referred to as a handling layer 516) is inverted upside down (i.e., the handling layer 516 is located on the top) and bonded to the semiconductor substrate 125 to close the recess 505 upward. In this way, a sensor substrate cavity 130 for the sensor 100, a pump cavity 230 for the pump 205 and a conduit 240 (1) are thus formed (see FIG. 2A to FIG. 2B ).

[0109] exist Figure 5D In the process, the handling layer 516 is removed, for example, by means of a mechanical polishing process, until the box layer 514 is exposed, so as to define the membrane 110 and the pump membrane 210 from the device layer 512 and the electrically insulating layer 136 from the box layer 514 .

[0110] Then, the manufacturing process is similar to that already referenced FIG. 4D to FIG. 4H It should be noted that according to this embodiment, the film cavity 135 is not formed.

[0111] Figure 6 and Figure 7 A portion of a MEMS sensing device 300 is shown having an impedance measurement structure 301 in addition to the piezoelectric element 120. Specifically, the impedance measurement structure 301 includes interdigitated sensing electrodes.

[0112] Generally, MEMS sensing device 300 has a similar overall structure as sensing devices 200 , 200 ′, 200 ″, 200 ′″; therefore, like components are denoted by the same reference numerals and will not be described again.

[0113] The piezoelectric element 120 and the impedance measurement structure 301 extend on the semiconductor substrate 125; the piezoelectric element 120 here has a ring shape and surrounds the impedance measurement structure 301. Specifically, the top conductive layer 160, the bottom conductive layer 162 and the piezoelectric material layer 140 are all ring-shaped.

[0114] The impedance measurement structure 301 includes a first impedance measurement electrode 302 and a second impedance measurement electrode 303. In the MEMS sensing device 300, the impedance measurement electrodes 302 and 303 cross each other and are in a ring shape.

[0115] The impedance measurement electrodes 302 and 303 are made of a conductive material. For example, the impedance measurement electrodes 302 and 303 are made of gold.

[0116] Specifically, Figure 6 The first impedance measurement electrode 302 includes a plurality of first electrode portions 304, and the second impedance measurement electrode 303 includes a plurality of second top electrode portions 305. The first electrode portions 304 and the second electrode portions 305 intersect each other and are electrically isolated from each other.

[0117] The first electrode portions 304 are semi-ring-shaped and are electrically coupled to each other and to the first connection portion 310 .

[0118] The second electrode portions 305 are also semi-annular in shape, and are electrically coupled to each other and to the second connection portion 311 .

[0119] The piezoelectric element 120 is here annular and is formed of two parts 120-1 and 120-2, which can be electrically coupled to form an electrically single top electrode 160 and an electrically single bottom electrode 162 ( Figure 7 ). The first connection portion 310 and the second connection portion 311 extend between the portions 120 - 1 , 120 - 2 of the piezoelectric element 120 and are insulated therefrom.

[0120] The electric wire 307 is connected to the first connection portion 310 and the second connection portion 311 of the impedance measurement structure 301 and is connected to the piezoelectric element 120 .

[0121] The through hole 168 here also extends across the entire thickness of the membrane 110 between the first electrode portion 304 and the second electrode portion 305. Figure 6 , (for simplicity, only one is shown).

[0122] Figure 7 Also shown are a top electrode contact portion 320 in direct electrical contact with the top conductive layer 160 and a bottom contact portion 321 in direct electrical contact with the bottom conductive layer 162 through an opening in the passivation layer 170; and another passivation layer 322 covering the entire structure.

[0123] Figure 6 and Figure 7 The MEMS sensing device 300 operates in a similar manner to the MEMS sensing devices 200 , 200 ′, 200 ″, but is also capable of performing some measurements regarding properties of the particles.

[0124] Specifically, during the sensing phase, particles adhered to the membrane 110 change the impedance of the MEMS sensing device 300 so that a processor coupled to the first connection portion 310 and the second connection portion 311 and receiving the electrical signal generated by the impedance measurement structure 301 can detect the properties of the particles (metal / dielectric properties).

[0125] During the cleaning phase, the MEMS sensing device 300 operates as discussed above.

[0126] Figure 8 A different MEMS sensing device, identified by reference numeral 350 , is shown.

[0127] The MEMS sensing device 350 also has an impedance measurement structure 301 including interdigitated electrodes, but here the interdigitated electrodes (also referred to herein as impedance measurement electrodes 302 and 303 ) are in a comb shape.

[0128] Figure 8 Also shown is an electronic processor 360 for impedance measurement.

[0129] The MEMS sensing device 350 operates as indicated above with respect to the MEMS sensing device 300 .

[0130] Fig. 9 A portion of a MEMS sensing device 400 is shown having a piezoelectric element 120 and an impedance measurement structure 301. The impedance measurement structure 301 comprises interdigitated sensing electrodes.

[0131] Here, the piezoelectric element 120 is circular or disc-shaped and extends below the impedance measurement structure 301. Specifically, the piezoelectric element 120 has a larger diameter than the diameter of the impedance measurement structure 301.

[0132] Figures 6 to 9 The MEMS sensing devices 300, 350 and 400 may use different masks to match the reference 4A to 4H or FIG. 5A to FIG. 5D The impedance measurement structure 301 is fabricated in a similar manner as described above. Specifically, the first electrode portion 304 and the second electrode portion 305 are formed from the same layer used to form the top contact portion 320 and the bottom contact portion 321 of the piezoelectric element 120.

[0133] Fig.10 A block diagram of an electronic system 600 including at least one of the MEMS sensing devices 200 , 200 ′, 200 ″, 200 ′″, 300 , or 400 is illustrated.

[0134] The electronic system 600 is suitable for use in electronic devices such as, for example, personal digital assistants, computers, tablets, and smart phones.

[0135] In addition to the MEMS sensing devices 200, 200', 200", 200'", the electronic system 600 may include a controller 605, such as, for example, one or more microprocessors and / or one or more microcontrollers; an input / output device 610, 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 analog signals; a wireless interface 615, for exchanging messages with a wireless communication network (not shown), for example via radio frequency signals. Examples of the wireless interface 615 may include an antenna and a wireless transceiver; a storage device 620, such as, for example, a volatile storage device and / or a non-volatile storage device; a supply device 625, such as a battery, for supplying power to the electronic system 600; and one or more communication channels (buses) for allowing data to be exchanged between the MEMS sensing device 200, 200', 200", 200'", 300, 400 and the controller 605 and / or the input / output device 610 and / or the wireless interface 615 and / or the storage device 620 and / or the battery 625 when the MEMS sensing device 200, 200', 200", 200'", 300, 400, the controller 605 and / or the input / output device 610 and / or the wireless interface 615 and / or the storage device 620 and / or the battery 625 are present.

[0136] Finally, it will be apparent that numerous variations and modifications may be made to what has been described and illustrated herein, all falling within the scope of the present disclosure as defined by the appended claims.

[0137] For example, the various embodiments described above can be combined to provide other embodiments.

[0138] The various embodiments described above can be combined to provide other embodiments. In view of the above specific implementation, these and other changes can be made to the embodiments. 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 and their equivalents to the full range of rights enjoyed by these claims. Therefore, the claims are not limited by the present disclosure.

Claims

1. A MEMS sensing device for sensing particles in an external environment of the MEMS sensing device, the MEMS sensing device comprising: Semiconductor body, integrated sensors and pumps; wherein the sensor comprises a sensor cavity, a membrane suspended above the sensor cavity, and a piezoelectric element, the piezoelectric element being located above the membrane and configured to cause the membrane to oscillate about an equilibrium position and at a resonant frequency that depends on the number of particles located on the membrane when a sense electrical signal is applied to the piezoelectric element during a first operating phase of the MEMS sensing device; wherein the membrane comprises a plurality of through holes configured to establish fluid communication between the sensor cavity and the environment; wherein the pump is adjacent to the sensor, connected to the sensor via a conduit extending in the semiconductor body, and configured to cause the air pressure in the sensor cavity to be reduced relative to the air pressure of the environment during the first operating phase so that particles adhere to the membrane by suction through the plurality of through-holes; and The pump is configured to increase the air pressure in the sensor cavity relative to the air pressure of the environment during the second operating phase so that particles are blown away from the membrane by a blowing force through the plurality of through holes, thereby cleaning the membrane.

2. The MEMS sensing device of claim 1 , wherein the piezoelectric element comprises a piezoelectric material layer located between a top conductive layer and a bottom conductive layer, wherein at least a portion of the top conductive layer and the bottom conductive layer form an electrode for receiving the sensing electrical signal. 3 . The MEMS sensing device of claim 2 , wherein the plurality of through holes are located at a central portion of the piezoelectric material layer. 4 . The MEMS sensing device of claim 2 , wherein the piezoelectric element comprises a piezoelectric element opening at a central portion of the membrane, wherein the plurality of through holes are located at the central portion of the membrane. 5 . The MEMS sensing device of claim 4 , further comprising a non-stick coating covering the piezoelectric element and the central portion of the membrane. The MEMS sensing device of claim 5 , wherein the non-stick coating comprises a hydrophobic material.

7. The MEMS sensing device of claim 4, wherein the top conductive layer comprises a first top plate and a second top plate, the first top plate surrounding the central portion of the membrane, the second top plate surrounding the first top plate, the first top plate and the second top plate being electrically insulated from each other, and the bottom conductive layer comprises a first bottom plate and a second bottom plate, the first bottom plate surrounding the central portion of the membrane, the second bottom plate surrounding the first bottom plate, the first bottom plate and the second bottom plate being electrically insulated from each other, wherein the second top plate and the second bottom plate are configured to receive the sensing electrical signal during the first operation phase, wherein the first top plate and the first bottom plate are configured to be biased during the first operating phase such that a voltage difference is generated across the first top plate and the first bottom plate, the voltage difference having a value causing the membrane to have an upwardly concave shape, and Wherein the second top plate and the second bottom plate are configured to be biased during the second operating phase such that a voltage difference is generated across the second top plate and the second bottom plate, the voltage difference having a value causing the membrane to have a downwardly concave shape.

8. The MEMS sensing device of claim 1 further comprising an impedance measurement structure on the membrane and over the sensor cavity. 9 . The MEMS sensing device of claim 8 , wherein the impedance measurement structure comprises a plurality of first electrode portions and a plurality of second electrode portions, the plurality of first electrode portions being electrically isolated from the plurality of second electrode portions and interdigitated with each other. 10 . The MEMS sensing device of claim 8 , wherein the impedance measurement structure is surrounded by the piezoelectric element or is arranged on a central portion of the piezoelectric element.

11. An electronic system comprising a plurality of MEMS sensing devices, each MEMS sensing device comprising: Semiconductor substrates, integrated sensors and pumps; The sensor includes a sensor cavity, a membrane suspended above the sensor cavity, and a piezoelectric element located above the membrane and configured to cause the membrane to oscillate about an equilibrium position at a resonant frequency that depends on the number of particles located on the membrane when a sense electrical signal is applied to the piezoelectric element during a first operating phase of the MEMS sensing device; The membrane includes a plurality of through holes, the plurality of through holes placing the sensor cavity in fluid communication with an ambient environment; wherein the pump is configured to cause the air pressure in the sensor cavity to be reduced relative to the air pressure of the environment during the first operating phase so that particles adhere to the membrane by suction through the plurality of through-holes; and The pump is configured to increase the air pressure in the sensor cavity relative to the air pressure of the environment during the second operating phase so that particles are blown away from the membrane by a blowing force through the plurality of through holes, thereby cleaning the membrane. 12 . The electronic system of claim 11 , wherein the respective plurality of through holes are located at a central portion of the respective membrane.

13. The electronic system of claim 11, further comprising a non-stick coating covering the piezoelectric element and the central portion of the membrane.

14. The electronic system of claim 11, wherein at least one of the plurality of MEMS sensing devices comprises a semiconductor substrate integrating a plurality of pumps, each of the plurality of pumps being in fluid communication with the sensor cavity.

15. The electronic system of claim 14, wherein the plurality of pumps is two or four pumps.

16. A method comprising: Manufacturing a MEMS sensing device for sensing particles in an environment external to the MEMS sensing device, the manufacturing comprising: At least one sensor and at least one pump are integrated into a semiconductor body, the integration comprising: forming a sensor cavity in the semiconductor body; forming a membrane over the sensor cavity, the membrane comprising a plurality of through holes; and forming a piezoelectric element over the membrane; wherein the pump is configured to cause the air pressure in the sensor cavity to be reduced relative to the air pressure of the environment during a first operating phase so that particles adhere to the membrane by suction through the set of through holes; and The pump is configured to increase the air pressure in the sensor cavity relative to the air pressure of the environment during the second operating phase so that particles are blown away from the membrane by a blowing force through the plurality of through holes, thereby cleaning the membrane.

17. The method of claim 16, wherein the plurality of through holes establish fluid communication between the sensor cavity and the environment.

18. A method for sensing particles in an external environment of a MEMS sensing device, the method comprising: During a first operating phase, applying an electrical signal to a piezoelectric element of a sensor to cause a membrane of the sensor to oscillate about an equilibrium position and at a resonance frequency, the resonance frequency being dependent on the number of particles located on the membrane, wherein the sensor is integrated in a semiconductor body and comprises a sensor cavity, wherein the membrane is suspended above the sensor cavity, and the piezoelectric element is located above the membrane, wherein the membrane comprises a plurality of through holes, the plurality of through holes being configured to establish fluid communication between the sensor cavity and the environment, During a first operating phase, the air pressure in the sensor cavity is reduced relative to the air pressure of the environment using a pump integrated in the semiconductor body, wherein the pump is adjacent to the sensor and connected to the sensor via a conduit in the semiconductor body, so that particles adhere to the membrane by suction through the plurality of through holes, and During a second operating phase, the air pressure in the sensor cavity is increased relative to the air pressure of the environment using the pump integrated in the semiconductor body so that particles are blown off the membrane by the blowing force through the plurality of through holes, thereby cleaning the membrane.

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