Patent Description:
Water-resistant or impermeable (so-called "waterproof") microelectromechanical (MEMS - Micro Electro Mechanical System) pressure sensor devices are known.

These pressure sensor devices may for example be used in portable or wearable electronic apparatuses, such as smartphones, smartbands or smart watches, which may be used for underwater applications or in general in-water.

The aforementioned pressure sensor devices typically comprise a detection structure provided with a membrane suspended above a cavity and wherein detection elements (for example piezoresistors) are provided, to detect the deformation caused by impinging pressure waves.

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

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

Typically, this housing cavity is filled with a protective coating, such as a coating gel (so-called "potting gel"), for example of polymeric or silicone type, which coats and protects the detection structure and the ASIC from humidity and in general from contaminants coming from outside of the package. Only this protective material is in contact with the external environment, effectively making the housing cavity (filled with the same protective material) impermeable or hermetic.

In a known manner, electrical test procedures of a pressure sensor device, in particular at the end of a corresponding manufacturing process, include carrying out a plurality of pressure measurements at different temperature values, to calibrate the response of the same pressure sensor device as the temperature varies (for example in order to adapt, as a function of the temperature, the pressure signal provided at the output during subsequent normal operation).

These test procedures typically envisage use of an external test equipment, provided with measurement probes and configured to adjust the temperature of a test chamber wherein the pressure sensor device is arranged, to vary the temperature thereof and acquire corresponding calibration pressure signals. For example, the pressure signal at the output of the pressure sensor device may be acquired at the following different calibration temperature values (or set points): <NUM>, <NUM>,<NUM> and <NUM>.

A suitable temperature sensor may be integrated in the pressure sensor device, in order to implement a feedback control of the temperature reached by the same pressure sensor device during the calibration phase.

A problem affecting this test procedure is related to the fact that the aforementioned protective coating within the package of the pressure sensor device is thermally insulating, due to the reduced thermal conductivity of the material of which it is made.

Consequently, during the aforementioned test procedure, long waiting times are generally needed to reach the desired calibration temperature values; in particular, these waiting times may even be in the order of tens of seconds.

By way of example, <FIG> shows the test temperature trend during a calibration procedure, considering a plurality of different pressure sensor devices subject to electrical testing.

This <FIG> shows the ramps required for the temperature to stabilize around the calibration values; in the example, these ramps (indicated with "Ramp1", "Ramp2" and "Ramp3") have the following average durations, considering the pressure sensor devices tested: about <NUM> for the ramp from <NUM> to <NUM> (Ramp1); about <NUM> for the ramp from <NUM> to <NUM> (Ramp2); and about <NUM> for the ramp from <NUM> to <NUM> (Ramp3).

In particular, time delays mainly occur in proximity of the calibration values, when the reduction of the thermal gradient between the measurement chamber and the inside of the pressure sensor device determines a reduction in the heat transfer rate and consequent waiting times for reaching the calibration values.

These waiting times generally entail a considerable overall duration of the electrical procedures for testing of the pressure sensor devices.

Moreover, the circuitry required in the external test equipment for controlling and adjusting the calibration temperature for the pressure sensor device is rather complex.

<CIT> discloses a portable electronic device including a pressure sensor having an integrated heater. The heater may be operated to heat some or all of the pressure sensor for pressure sensor testing, calibration, or temperature-controlled pressure sensing operations.

<CIT> discloses a CMOS-based sensing device comprising a substrate having an etched portion, a membrane region formed over an area of the etched portion of the substrate, a flow sensor formed within the membrane region and a pressure sensor formed within the membrane region.

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

According to the present invention, a system for electrical testing of a pressure sensor device and a corresponding method are therefore provided, as defined in the attached claims.

For a better understanding of the present solution, embodiments thereof are now described, purely by way of non-limiting example and with reference to the attached drawings, wherein:.

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

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

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

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

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

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

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

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

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

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

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

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

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

In a manner not illustrated, these external connection elements <NUM> may be contacted, from the outside of the package <NUM>, for example by a control unit of an electronic apparatus wherein the pressure sensor device <NUM> is incorporated, or, as will be discussed in detail hereinbelow, by an electrical testing equipment.

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

A protective coating <NUM> fills almost entirely the aforementioned housing cavity <NUM> and entirely covers and coats the aforementioned stack formed by the pressure detection structure <NUM> and the associated processing circuit <NUM>, to ensure its protection from water (or in general from contaminants coming from the external environment); this protective coating <NUM> is in particular a coating gel (potting gel), for example a polymeric or silicone gel.

According to an aspect of the present solution, the pressure sensor device <NUM> further comprises, integrated in the same first die <NUM>, a heating structure <NUM> (shown schematically in <FIG>), configured to allow heating of the pressure detection structure <NUM>, internally to the package <NUM> of the same pressure sensor device <NUM>.

In detail and with reference also to <FIG> (which shows, by way of example, the aforementioned membrane <NUM> with a cross-shaped arrangement of four detection elements <NUM>), this heating structure <NUM> comprises a plurality of resistive elements <NUM>, arranged in proximity of the membrane <NUM>, at the top surface 4a of the first die <NUM>.

Such resistive elements <NUM> are for example made by respective regions of polysilicon (or other suitable material) formed on the top surface 4a of the first die <NUM>, laterally and externally with respect to the membrane <NUM>.

In the example shown, the membrane <NUM> is substantially square-shaped in the horizontal plane xy and the aforementioned resistive elements <NUM> are arranged in two groups, aligned respectively to a first and a second side, opposite to each other, of the same membrane <NUM>.

These resistive elements <NUM> are electrically parallel-connected to each other by a first and a second conductive track 43a, 43b, also provided on the same top surface 4a of the first die <NUM>. In particular, the first conductive track 43a connects first ends of the aforementioned resistive elements <NUM> to each other and to a first pad 44a formed on the aforementioned top surface 4a; and the second conductive track 43b connects second ends of the aforementioned resistive elements <NUM> to each other and to a second pad 44b.

During operation, the first pad 44a is for example set to a supply potential (Val) and the second pad 44b is set to a reference potential (ground, GND), such that a heating current flows through the aforementioned resistive elements <NUM>, causing heating thereof and, consequently, causing a variation in the temperature of the adjacent pressure detection structure <NUM>.

Advantageously, the parallel connection of the resistive elements <NUM> allows a low resistance to the flow of the aforementioned heating current to be obtained, so to reduce the electrical consumption associated with the aforementioned heating.

For example, in the illustrated embodiment, the aforementioned heating structure <NUM> comprises twenty-four resistive elements <NUM> parallel-connected to each other, each provided with a polysilicon region having a width equal to <NUM> and a length equal to <NUM>, to form an overall resistance having the value of <NUM>Ω (considering a resistivity for the polysilicon equal to <NUM>Ω/sq).

The pressure sensor device <NUM> moreover comprises further pads <NUM>, which are electrically connected (in a manner not illustrated) to the detection elements <NUM> arranged in the membrane <NUM>, to allow detection of deformations of the same membrane <NUM>.

Furthermore, the pressure sensor device <NUM> comprises at least one temperature sensor <NUM> (schematically shown in the same <FIG>), also integrated in the first die <NUM>, in the example in proximity to the membrane <NUM>, for allowing detection of the temperature of the pressure detection structure <NUM>. To this end, the aforementioned temperature sensor <NUM> is electrically connected (in a manner not illustrated) to respective pads <NUM>, also formed on the top surface 4a of the first die <NUM>.

In a manner not illustrated in detail, respective first +bonding wires <NUM> may electrically connect the first and the second pads 44a, 44b and the further pads <NUM> and <NUM> to the processing circuit <NUM> integrated in the second die <NUM>.

In a possible embodiment, as schematically shown in the aforementioned <FIG>, this processing circuit <NUM> may comprise a temperature adjustment module <NUM>, integrated in the second die <NUM> and configured to control the supply of the aforementioned heating current to the heating structure <NUM>, on the basis of a feedback control of the temperature reached by the pressure detection structure <NUM>, detected through the aforementioned temperature sensor <NUM>, in particular during a test and temperature calibration procedure of the pressure sensor device <NUM>.

In an alternative embodiment (here not illustrated), bonding wires may connect the aforementioned first and second pads 44a, 44b directly to respective fourth pads <NUM> carried by the internal surface 21a of the base structure <NUM>, to allow the electrical connection towards the outside of the package <NUM>. In this case, the adjustment of the temperature of the pressure detection structure <NUM> through the aforementioned heating structure <NUM> may be entrusted to an electronic equipment external to the pressure sensor device <NUM>.

Tests carried out by the present Applicant have shown a high response speed by the heating structure <NUM>, for example with the possibility of raising the temperature of the pressure detection structure <NUM> from <NUM> to <NUM> in just <NUM>, for a resulting heating rate of <NUM>/s (instead of a heating rate of <NUM>/s obtainable by heating the pressure sensor device <NUM> from the outside by the external testing equipment).

The aforementioned heating structure <NUM> may therefore be operated to cause heating of the pressure detection structure <NUM> from the inside of the package <NUM> of the pressure sensor device <NUM>, during an electrical test and temperature calibration procedure of the pressure sensor device <NUM>.

In particular, the aforementioned heating structure <NUM> may cause such heating in cooperation with this external testing equipment.

In this regard, <FIG> schematically shows an electrical test system <NUM>, comprising a test chamber 49a and a testing equipment 49b, arranged in the test chamber 49a and configured to perform test and calibration procedures of the pressure sensor device <NUM>, in particular to acquire pressure signals at different calibration temperature values.

With reference to <FIG>, a first test and temperature calibration procedure is now described (which is not part of the claimed invention), wherein the adjustment of the temperature of the pressure sensor device <NUM> is entrusted in an exclusive manner to the sole heating structure <NUM> (i.e., without the intervention of the aforementioned testing equipment 49b being required).

In detail, in an initial step <NUM>, the temperature of the aforementioned test chamber 49a wherein the pressure sensor device <NUM> is accommodated during the test procedure is set to a temperature lower than a first calibration temperature value, for example a temperature equal to <NUM>.

Subsequently, at step <NUM>, a new temperature set point is iteratively established for the calibration of the pressure sensor device <NUM> (in particular, the first temperature set point, in the case of a first iteration of the procedure, is for example equal to <NUM>).

Then, at step <NUM>, the internal heating of the same pressure sensor device <NUM> is implemented, by enabling the corresponding heating structure <NUM> with the supply of the heating current.

Then, at step <NUM>, it is verified whether the established temperature set point has been reached within a first temperature range, for example ±<NUM> around the aforementioned set point (note that this verification may be implemented on the basis of the information provided by the temperature sensor <NUM> internal to the same pressure sensor device <NUM>).

In case the verification is positive, at step <NUM>, a feedback control of the heating current supplied to the heating structure <NUM> is implemented, for example by the aforementioned temperature adjustment module <NUM> internal to the processing circuit <NUM>, in order to reach a stable temperature of the same heating structure <NUM>.

In particular, at step <NUM>, it is verified that the established temperature set point is stable within a second temperature range, lower with respect to the aforementioned first temperature range, for example of ±<NUM> around the established set point.

In case the verification is positive, at step <NUM>, it is determined that the set point has been reached and, for example, the acquisition and storage of a corresponding calibration value for the pressure signal provided at the output of the pressure sensor device <NUM> is implemented.

Then, the procedure may proceed iteratively (returning to the aforementioned step <NUM>) with the setting of a new temperature set point, for example having a value higher than the previous one, until the calibration of the pressure sensor device <NUM> ends.

According to the claimed invention, heating of the pressure detection structure <NUM> may be implemented in conjunction and in cooperation by the aforementioned heating structure <NUM> internal to the pressure sensor device <NUM> and by the testing equipment 49b external to the same pressure sensor device <NUM>.

With reference to <FIG>, in this case, in an initial step <NUM> the new temperature set point is established iteratively for the calibration of the pressure sensor device <NUM> (in particular, the first temperature set point, in the case of a first iteration of the procedure).

Then, at step <NUM>, the testing equipment 49b is operated to heat from the outside, by heat conduction, the pressure detection structure <NUM> of the pressure sensor device <NUM> (the testing equipment 49b is in this case operated to generate heat within the testing chamber in which the pressure sensor device <NUM> is contained, and thereby to heat externally, by heat conduction from the outside of the package, the same pressure sensor device <NUM>).

In particular, as shown in step <NUM>, a controller of this testing equipment 49b (for example a PID - Proportional Integral Derivative - controller) adjusts the heating/cooling of the pressure sensor device <NUM> (for example, using the information provided as a feedback by the temperature sensor <NUM> internal to the same pressure sensor device <NUM>).

Then, at step <NUM>, a verification is made by the same controller whether the established temperature set point has been reached within a third temperature range, for example of ±<NUM> around the aforementioned set point (note that this third temperature range is intermediate between the aforementioned first and second temperature ranges).

Following a positive verification, the same controller proceeds to a new verification, at step <NUM>, to verify that the temperature is stable within the aforementioned second temperature range, for example of ±<NUM>, around the established set point.

In case the verification is positive, at step <NUM>, it is determined that the set point has been reached and the calibration procedure is implemented, for example by acquiring and storing a corresponding value for the pressure signal provided at the output of the pressure sensor device <NUM>.

In this case, in parallel to the temperature adjustment action implemented by the testing equipment 49b, as soon as it is verified, at step <NUM>, that the established temperature set point has been reached within the aforementioned first temperature range, for example of ±<NUM>, the internal heating of the same pressure sensor device <NUM> is also enabled, at step <NUM>, by enabling the corresponding heating structure <NUM> with the supply of the heating current.

Note that this internal heating therefore operates in conjunction with the heating from the outside implemented by testing equipment 49b, thus speeding up reaching of the established temperature set point.

In particular, as shown in step <NUM>, the feedback control of the heating current supplied to the heating structure <NUM> is implemented, for example by the aforementioned temperature adjustment module <NUM> internal to the processing circuit <NUM>, in order to reach the stable temperature of the same heating structure <NUM>.

As soon as it is verified, at step <NUM>, that the temperature is stable within the second temperature range around the established set point, it is determined that the set point has been reached and the acquisition of the calibration signal is implemented (as previously described at step <NUM>).

The procedure may then proceed iteratively with the establishment of a new temperature set point (at step <NUM>), for example having a value higher than the previous one, until the calibration of the pressure sensor device <NUM> ends.

The advantages that the present solution affords are clear from the preceding description.

In any case, it is highlighted that integration of the heating structure <NUM> within the pressure sensor device <NUM> allows a considerable reduction of the times required by the electrical test procedure of the same pressure sensor device <NUM> and also a reduction of the complexity of the testing equipment 49b.

The presence of this heating structure <NUM> allows the temperature of each pressure sensor device <NUM> to be finely adjusted, possibly also during its normal operation (even outside the aforementioned electrical test procedure).

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

In particular, it is highlighted that the number and arrangement of the resistive elements <NUM> of the aforementioned heating structure <NUM> may vary with respect to what has been previously illustrated by way of example. For example, these resistive elements <NUM> may be arranged around the entire perimeter of the membrane <NUM> of the pressure detection structure <NUM> in the horizontal plane xy, or be arranged side by side to only one or even more of the sides of the same membrane <NUM>. The same resistive elements <NUM> may also be made with a material other than polysilicon.

Claim 1:
An electrical testing system (<NUM>), comprising:
a pressure sensor device (<NUM>);
a test chamber (49a), accommodating the pressure sensor device (<NUM>); and
a testing equipment (49b), arranged in the test chamber (49a) and configured to acquire, at different temperature reference values, output signals from the pressure detection structure (<NUM>) of the pressure sensor device (<NUM>),
wherein the pressure sensor device (<NUM>) comprises:
a pressure detection structure (<NUM>) provided in a first die (<NUM>) of semiconductor material;
a package (<NUM>), configured to internally accommodate said pressure detection structure (<NUM>) in an impermeable manner, said package (<NUM>) comprising a base structure (<NUM>) and a body structure (<NUM>), arranged on the base structure (<NUM>), having an access opening (<NUM>) in contact with an external environment and internally defining a housing cavity (<NUM>), in which said first die (<NUM>) is arranged covered with a coating material (<NUM>); and
a heating structure (<NUM>), accommodated in said housing cavity (<NUM>) and configured to implement heating of said pressure detection structure (<NUM>) from the inside of said package (<NUM>),
wherein the testing equipment (49b) is configured to adjust the temperature of said pressure detection structure (<NUM>) from outside of said package (<NUM>), in cooperation and in conjunction with said heating structure (<NUM>);
said testing equipment (49b) being further operable to heat from the outside, by heat conduction, the pressure detection structure (<NUM>) of the pressure sensor device (<NUM>).