Patent Description:
A pressure sensor commonly includes a sensor diaphragm and piezoresistors disposed on the sensor diaphragm. An applied force or pressure deflects the sensor diaphragm, which changes the resistance of the piezoresistors on the diaphragm, correspondingly changing a measured output of the pressure sensor that reflects the force or pressure.

A full-bridge pressure sensor is used to increase the accuracy and reliability of the sensor measurements. The full-bridge sensor, however, requires a sensor diaphragm sized to accommodate four piezoresistors to form the full Wheatstone bridge, which increases the necessary size of the pressure sensor. Current solutions cannot provide the accuracy and performance of a full-bridge sensor in applications, such as medical applications, that have significant size restrictions.

<CIT> discloses a sensor assembly element having a substrate. First and second dies are attached to respective first and second outer surfaces of the substrate and each die comprises a diaphragm. The sensor assembly has a full-bridge pressure sensor including a plurality of piezoresistive elements disposed into the first diaphragm of the first die.

<CIT> discloses a pseudo differential pressure sensor having a Wheatstone bridge comprising a first subset of piezoresistors arranged on a first diaphragm of a first absolute pressure sensor and a second subset of piezoresistors arranged on a second diaphragm of a second absolute pressure sensor.

<CIT> discloses a pressure sensing element mounted on a substrate wherein the pressure sensing element has a diaphragm on a pair of supports.

<CIT> discloses a pressure sensor having a substrate and a diaphragm wherein the diaphragm has pressure-sensitive elements. An integrated circuit is electrically connected to the pressure sensor.

According to the present invention, there is provided a sensor assembly as claimed in claim <NUM>.

The invention will now be described by way of example with reference to the accompanying Figures, of which:.

Arrangements and exemplary embodiments of the present disclosure will be described hereinafter in detail with reference to the attached drawings, wherein like reference numerals refer to like elements. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the arrangements and embodiments set forth herein; rather, these arrangements and embodiments are provided so that the present disclosure will convey the concept of the disclosure to those skilled in the art. In addition, in the following detailed description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the disclosed arrangements and embodiments. However, it is apparent that one or more embodiments may also be implemented without these specific details.

Throughout the drawings, only one of a plurality of identical elements may be labeled in a figure for clarity of the drawings, but the detailed description of the element herein applies equally to each of the identically appearing elements in the figure. Directional descriptors used in the specification are merely for clarity of the description and for differentiation of the various directions. These directional descriptors do not imply or require any particular orientation of the disclosed elements.

A sensor assembly <NUM> according to an arrangement is shown in <FIG>. The sensor assembly <NUM> includes a substrate <NUM>, a first die <NUM> attached to the substrate <NUM>, a second die <NUM> attached to the substrate <NUM>, a full-bridge pressure sensor <NUM> disposed on the first die <NUM> and the second die <NUM>, and an integrated circuit <NUM> connected to the full-bridge pressure sensor <NUM>.

The substrate <NUM> has a first outer surface <NUM> and a second outer surface <NUM> opposite the first outer surface <NUM> in a first direction D1, shown in <FIG>. The substrate <NUM> may be a silicon material, a glass material, a sapphire material, or any other type of material used in piezoresistive sensor substrates.

In the arrangement shown in <FIG>, the substrate <NUM> includes a first portion <NUM> and a second portion <NUM> formed separately from one another and bonded together at a bond <NUM>. The first portion <NUM> and the second portion <NUM> are each formed of the material of the substrate <NUM>. The first portion <NUM> has the first outer surface <NUM> and a first inner surface <NUM> opposite the first outer surface <NUM> in the first direction D1. The second portion <NUM> has the second outer surface <NUM> and a second inner surface <NUM> opposite the second outer surface <NUM> in the first direction D1. The first inner surface <NUM> is bonded to the second inner surface <NUM> by the bond <NUM>, which may be a fusion bond, an epoxy bond, an anodic bond, a eutectic bond, or any other type of bond that can attach the first portion <NUM> to the second portion <NUM>. In some embodiments, the bond <NUM> may be electrically conductive and form an electrical connection. In another embodiment, the substrate <NUM> can be formed monolithically in a single piece with the first outer surface <NUM> and the second outer surface <NUM>.

As shown in the arangement of <FIG>, the substrate <NUM> has a first contact <NUM> on the first outer surface <NUM> and a second contact <NUM> on the second outer surface <NUM>. The first contact <NUM> and the second contact <NUM> may be formed of any conductive material, such as gold or copper, that permits an external electrical connection.

The first die <NUM>, as shown in <FIG>, has a pair of first supports <NUM> and a first diaphragm <NUM> extending between the first supports <NUM>. The first diaphragm <NUM> is deflectable with respect to the first supports <NUM>. The first die <NUM> is formed of a silicon material. In an embodiment, the first die <NUM> is monolithically formed in a single piece with the first supports <NUM> and the first diaphragm <NUM>, and the silicon material of the first die <NUM> is etched to form the first diaphragm <NUM>. In another embodiment, the first diaphragm <NUM> is formed separately from the first supports <NUM> and is attached to the first supports <NUM>.

The second die <NUM>, as shown in <FIG>, has a pair of second supports <NUM> and a second diaphragm <NUM> extending between the second supports <NUM>. The second diaphragm <NUM> is deflectable with respect to the second supports <NUM>. The second die <NUM> is formed of a silicon material. In an embodiment, the second die <NUM> is monolithically formed in a single piece with the second supports <NUM> and the second diaphragm <NUM>, and the silicon material of the second die <NUM> is etched to form the second diaphragm <NUM>. In another embodiment, the second diaphragm <NUM> is formed separately from the second supports <NUM> and is attached to the second supports <NUM>. In an embodiment, the first die <NUM> and the second die <NUM> are identical.

The full-bridge pressure sensor <NUM>, as shown in <FIG>, includes a plurality of piezoresistive elements <NUM> disposed on the first die <NUM> and the second die <NUM>. The piezoresistive elements <NUM> include a first subset <NUM> of at least two of the piezoresistive elements <NUM> disposed on the first diaphragm <NUM> and a second subset <NUM> of at least two of the piezoresistive elements <NUM> disposed on the second diaphragm <NUM>. The piezoresistive elements <NUM> are an elemental material that is patterned over or embedded into the silicon material of the first die <NUM> and the second die <NUM>; the piezoresistive elements <NUM> can be positioned on a surface of or within the diaphragms <NUM>, <NUM>. In an embodiment, the elemental material is a positive dopant, such as p-type boron, but could be any type of material used to create a piezoresistor in a silicon material.

The full-bridge pressure sensor <NUM> includes four piezoresistive elements <NUM> in the shown embodiment that form a full Wheatstone bridge. In this embodiment, the first subset <NUM> is a first half-bridge that includes two piezoresistive elements <NUM> on the first diaphragm <NUM> and the second subset <NUM> is a second half-bridge that includes another two piezoresistive elements <NUM> on the second diaphragm <NUM>, as shown in <FIG>.

As shown in <FIG>, the integrated circuit <NUM> has a processor <NUM> and a memory <NUM> connected to the processor <NUM>. The memory <NUM> is a non-transitory computer-readable medium storing algorithms that, when executed by the processor <NUM>, perform the functions of the integrated circuit <NUM> described herein. The integrated circuit <NUM> can be any kind of application-specific integrated circuit (ASIC) or application-specific standard product (ASSP) chip that is capable of being used in piezoresitive sensor applications as described herein.

In the sensor assembly <NUM> shown in <FIG>, the first die <NUM> is attached to the first outer surface <NUM> and the second die <NUM> is attached to the second outer surface <NUM>. The first supports <NUM> of the first die <NUM> are bonded to the first outer surface <NUM>, for example by fusion bonding, anodic bonding, thermal compression, or solder, and separate the first diaphragm <NUM> from the first outer surface <NUM> in the first direction D1. The first diaphragm <NUM> with the first subset <NUM> of the piezoresistive elements <NUM> is deflectable toward the first outer surface <NUM> in the first direction D1. The second supports <NUM> of the second die <NUM> are bonded to the second outer surface <NUM>, for example by fusion bonding, anodic bonding, thermal compression, or solder, and separate the second diaphragm <NUM> from the second outer surface <NUM> in the first direction D1. The second diaphragm <NUM> with the second subset <NUM> of piezoresistive elements <NUM> is deflectable toward the second outer surface <NUM> in the first direction D1.

In the shown arrangement, the first subset <NUM> of piezoresistive elements <NUM> are disposed on a side of the first diaphragm <NUM> facing away from the first outer surface <NUM> in the first direction D1 and the second subset <NUM> of piezoresistive elements <NUM> are disposed on a side of the second diaphragm <NUM> facing away from the second outer surface <NUM> in the first direction D1. In another embodiment, the first subset <NUM> may be disposed on a side of the first diaphragm <NUM> facing the first outer surface <NUM> and/or the second subset <NUM> may be disposed on a side of the second diaphragm <NUM> facing the second outer surface <NUM>. In another embodiment, the first subset <NUM> can be embedded within the first diaphragm <NUM> and/or the second subset <NUM> can be embedded within the second diaphragm <NUM>. In another embodiment, the first contact <NUM> can alternatively be positioned on the first diaphragm <NUM> and the second contact <NUM> can be positioned on the second diaphragm <NUM>.

The first subset <NUM> on the first diaphragm <NUM> lies in a first plane P1 normal to the first direction D1 and parallel to the first outer surface <NUM>, and the second subset <NUM> on the second diaphragm <NUM> lies in a second plane P2 normal to the first direction D1 and parallel to the second outer surface <NUM>. As shown in <FIG>, the first plane P1 is separated from the second plane P2 in the first direction D1. In the arrangement of the sensor assembly <NUM> shown in <FIG>, the first die <NUM> with the first subset <NUM> and the second die <NUM> with the second subset <NUM> are mirror symmetrical about the substrate <NUM>.

The integrated circuit <NUM>, as shown in <FIG>, has a pair of electrical leads <NUM> connected to the first contact <NUM> and the second contact <NUM>. The integrated circuit <NUM> is electrically connected to the piezoresistive elements <NUM> of the first subset <NUM> and the second subset <NUM> through the contacts <NUM>, <NUM>. In the arrangement shown in <FIG>, the integrated circuit <NUM> is external to and spaced apart from the substrate <NUM>, the first die <NUM>, and the second die <NUM>.

In use of the sensor assembly <NUM> to measure a force or pressure, the pressure causes deflection of the first diaphragm <NUM> and the second diaphragm <NUM>, which changes a resistance of the first subset <NUM> and the second subset <NUM> of the piezoresistive elements <NUM> forming the full-bridge pressure sensor <NUM>. The first subset <NUM> or first half-bridge is electrically connected to the first contact <NUM> and a first signal <NUM> representing the change in resistance of the first subset <NUM> that corresponds to the pressure measured by the first subset <NUM> is transmitted to the integrated circuit <NUM> through the first contact <NUM> and one of the electrical leads <NUM>. The second subset <NUM> or second half-bridge is electrically connected to the second contact <NUM> and a second signal <NUM> representing the same applied pressure is transmitted to the integrated circuit <NUM> through the second contact <NUM> and one of the electrical leads <NUM>.

Even though the first subset <NUM> and the second subset <NUM> act as a full-bridge sensor <NUM> to measure the same pressure applied to the sensor assembly <NUM>, because the first subset <NUM> and the second subset <NUM> are positioned in the planes P1, P2 spaced apart from one another, the first signal <NUM> and the second signal <NUM> may have some difference due to positional variations in the applied pressure. The integrated circuit <NUM> has a calibration algorithm stored on the memory <NUM> that, when executed by the processor <NUM>, corrects a signal error between the first signal <NUM> and the second signal <NUM>. The processor <NUM> retrieves a calibrated value stored in the memory <NUM> based on known temperature and pressure and compares it to the signals <NUM>, <NUM> to generate the correct compensation for the signal error. The integrated circuit <NUM> combines the first signal <NUM> and the second signal <NUM> to output a measured pressure <NUM> applied to the sensor assembly <NUM> and measured by the full bridge pressure sensor <NUM>.

Another arrangement and exemplary embodiments of the sensor assembly <NUM> are shown in <FIG>. Like reference numbers refer to like elements with respect to the embodiment of the sensor assembly <NUM> shown in <FIG>, and primarily the differences of the arrangements and embodiments in <FIG> will be described in detail.

In the sensor assembly <NUM> shown in <FIG>, the integrated circuit <NUM> is positioned or interposed between the first portion <NUM> and the second portion <NUM> of the substrate <NUM>. The first inner surface <NUM> of the first portion <NUM> is attached or bonded to a first side of the integrated circuit <NUM> and the second inner surface <NUM> is attached or bonded to a second side of the integrated circuit <NUM> opposite the first side in the first direction D1.

In the arrangement shown in <FIG>, instead of the contacts <NUM>, <NUM> in the embodiment of <FIG>, the integrated circuit <NUM> disposed between the portions <NUM>, <NUM> of the substrate <NUM> is electrically connected to the first subset <NUM> and the second subset <NUM> of the full-bridge pressure sensor <NUM> by a via <NUM>. The via <NUM> extends from the first outer surface <NUM> to the second outer surface <NUM> of the substrate <NUM>, through the first portion <NUM>, the integrated circuit <NUM>, and the second portion <NUM>. In an embodiment, the via <NUM> is a passageway through the portions <NUM>, <NUM> and the integrated circuit <NUM> that is plated with an electrically conductive material, such as copper.

In the embodiments shown in <FIG>, the sensor assembly <NUM> includes a first integrated circuit <NUM> and a second integrated circuit <NUM> that each include the components of the integrated circuit <NUM> described above. The first integrated circuit <NUM> is disposed on the first outer surface <NUM> adjacent to the first die <NUM> and the second integrated circuit <NUM> is disposed on the second outer surface <NUM> adjacent to the second die <NUM>. The first integrated circuit <NUM> is connected to the first subset <NUM> and processes the signal from the first subset <NUM> while the second integrated circuit <NUM> is connected to the second subset <NUM> and processes the signal from the second subset <NUM>. The integrated circuits <NUM>, <NUM> are further connected to one another, with either or both of the integrated circuits <NUM>, <NUM> capable of performing the aforementioned correction of signal error and outputting of the measured pressure <NUM> sensed by the full-bridge pressure sensor <NUM>. In another embodiment, the sensor assembly <NUM> can include one of the first integrated circuit <NUM> disposed on the first outer surface <NUM> or the second integrated circuit <NUM> disposed on the second outer surface <NUM>.

In the embodiments shown in <FIG> and <FIG>, the dies <NUM>, <NUM> and the integrated circuits <NUM>, <NUM> are positioned mirror symmetrical about the substrate <NUM>. In another embodiment shown in <FIG>, the dies <NUM>, <NUM> and the integrated circuits <NUM>, <NUM> are offset from one another in a second direction D2 perpendicular to the first direction D1 and parallel to the first outer surface <NUM> and the second outer surface <NUM>.

In the embodiments of <FIG> and <FIG>, the piezoresistive elements <NUM> of the full-bridge pressure sensor <NUM> and the integrated circuits <NUM>, <NUM> are electrically connected by the via <NUM>. The via <NUM> can extend straight through the portions <NUM>, <NUM> of the substrate <NUM> in the first direction D1, as shown in <FIG>, or can have different sections in the portions <NUM>, <NUM> that are electrically connected and offset from one another in the second direction D2, as shown in <FIG>. In the embodiment of <FIG>, the piezoresistive elements <NUM> of the full-bridge pressure sensor <NUM> and the integrated circuits <NUM>, <NUM> are electrically connected by external electrical leads <NUM> connecting contacts <NUM>, <NUM> on the outer surfaces <NUM>, <NUM> of the substrate <NUM>, as similarly described with respect to <FIG> above.

In the embodiment of <FIG>, at least one of the first supports <NUM> is sufficiently wide in the second direction D2 that the first integrated circuit <NUM> and the first contact <NUM> are disposed on a surface of the first die <NUM>. The first integrated circuit <NUM> and the first contact <NUM> are aligned with the first support <NUM> in the first direction D1 and spaced apart from the first diaphragm <NUM> in the second direction D2. Likewise, at least one of the second supports <NUM> is sufficiently wide in the second direction D2 that the second integrated circuit <NUM> and the second contact <NUM> are disposed on a surface of the second die <NUM>. The second integrated circuit <NUM> and the second contact <NUM> are aligned with the second support <NUM> in the first direction D1 and spaced apart from the second diaphragm <NUM> in the second direction D2.

Claim 1:
A sensor assembly (<NUM>), comprising:
a substrate (<NUM>) having a first outer surface (<NUM>) and a second outer surface (<NUM>) opposite the first outer surface (<NUM>);
a first die (<NUM>) attached to the first outer surface (<NUM>) and having a first diaphragm (<NUM>);
a second die (<NUM>) attached to the second outer surface (<NUM>) and having a second diaphragm (<NUM>);
a full-bridge pressure sensor (<NUM>) including a plurality of piezoresistive elements (<NUM>), a first subset (<NUM>) of at least two of the plurality of piezoresistive elements (<NUM>) is disposed on or in the first diaphragm (<NUM>); and
an integrated circuit (<NUM>);
characterized in that
the full-bridge pressure sensor (<NUM>) includes a second subset (<NUM>) of at least two of the plurality of piezoresistive elements (<NUM>) disposed on or in the second diaphragm (<NUM>), the first subset (<NUM>) and the second subset (<NUM>) of the piezoresistive elements (<NUM>) are connected to the integrated circuit (<NUM>), the integrated circuit (<NUM>) is configured to receive a first signal (<NUM>) from the first subset (<NUM>) and a second signal (<NUM>) from the second subset (<NUM>), the integrated circuit (<NUM>) is configured to correct a signal error between the first signal (<NUM>) and the second signal (<NUM>) and to measure a pressure around the sensor assembly (<NUM>); and
the integrated circuit (<NUM>) is a first integrated circuit (<NUM>) disposed on the first outer surface (<NUM>) and further comprising a second integrated circuit (<NUM>) disposed on the second outer surface (<NUM>).